evaluating horticultural practices for sustainable tomato

Graduate Theses and Dissertations Iowa State University Capstones, Theses andDissertations

2014

Evaluating horticultural practices for sustainabletomato production in Kamuli, UgandaSharon Mbabazi TusiimeIowa State University

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Evaluating horticultural practices for sustainable tomato production in Kamuli, Uganda

by

Sharon M. Tusiime

A thesis submitted to the graduate faculty

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Major: Horticulture

Program of Study Committee:

Gail R. Nonnecke, Major Professor

Mark Gleason

Helen Jensen

Dorothy Masinde

Ajay Nair

Iowa State University

Ames, Iowa

2014

Copyright © Sharon. M. Tusiime, 2014. All rights reserved.

ii

DEDICATION

This is dedicated to my family and friends.

iii

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS .................................................................................... iv

ABSTRACT………………………………. ........................................................... v

CHAPTER 1 GENERAL INTRODUCTION ....................................................... 1

Thesis Organization ............................................................................................. 1

Introduction. …..................................................................................................... 1

Literature Cited .................................................................................................... 10

CHAPTER 2 EVALUATION OF HORTICULTURAL PRACTICES FOR

SUSTAINABLE TOMATO PRODUCTION IN KAMULI DISTRICT,

UGANDA………………………………………………………………………… 17

Abstract…… ........................................................................................................ 17

Introduction ......................................................................................................... 18

Materials and Methods ......................................................................................... 19

Results……. ......................................................................................................... 23

Discussion………… ............................................................................................ 28

Study Limitations………………………………………………………………. 31

Summary and Conclusions……. ......................................................................... 31

Literature Cited… ................................................................................................ 32

Tables…………………………………………………………………………... 35

CHAPTER 3 GENERAL CONCLUSIONS ......................................................... 43

Future Research…………………………………………… ............................... 43

Literature Cited………………………………………………………………... . 44

APPENDIX ….. ...................................................................................................... 45

iv

ACKNOWLEDGEMENTS

I extend my sincere gratitude to my major professor Dr. Gail Nonnecke, and my

committee members, Dr. Mark Gleason, Dr. Helen Jensen, Dr. Dorothy Masinde and Dr. Ajay

Nair, for their continued support during my master’s degree.

In addition, I also thank the faculty, staff, and students of the Department of Horticulture and

the Global Resource Systems major for making my time at Iowa State University a wonderful

experience. I sincerely appreciate the College of Agriculture and Life Sciences for their

financial support for my training and research.

I offer my appreciation to Nakanyonyi Primary School for providing a research site for

the field experiments. Special thanks to research assistance in the Kamuli District from

Micheal Nabugere, Juliet Kukundakwe, and Dennis Lutwama. Finally, thanks to my family for

their encouragement and support during my graduate studies.

v

ABSTRACT

Tomatoes are a source of income and food security for small-landholder farmers across

Uganda, including the Kamuli District. Studies regarding sustainable practices are needed to

increase production of the crop and improve farmers’ livelihoods. This study investigated three

tomato cultivars, Heinz 1370, Nuru F1, and MT 56, pesticide application, staking, and

mulching for their effect on yield, disease severity and gross margin of tomato production in

the Kamuli District of Uganda. The treatments were tested in a randomized complete block

design with a factorial and split-plot arrangement during two growing seasons in 2013. Total

and marketable fruit number, marketable fruit weight, gross margin, and disease severity

(assessed using the area under disease progress curve) were measured.

Results indicated that disease-resistant cultivar, MT 56, in combination with pesticide

application and soil mulch provided the highest marketable fruit number and marketable fruit

weight and all treatments had a positive gross margin in the first season. A combination of MT

56, no pesticide application and no mulch resulted in the only positive gross margin in season

two. Application of pesticides reduced disease severity (early blight, Alternaria solani) for all

cultivars in season one, and in season two for Heinz 1370 and Nuru F1, but did not affect

disease severity for MT 56 in the second season. Using soil mulch reduced the severity of early

blight disease, but decreased the gross margin when purchased. Staking did not affect yield or

disease severity of plants and decreased the gross margin.

1

CHAPTER 1: GENERAL INTRODUCTION

Written in the format of HortScience, a journal of the American Society for Horticultural

Science

Thesis Organization

This thesis includes three chapters. Chapter one is a general introduction to the research.

The second chapter is a manuscript that presents research results from experiments to

determine sustainable horticultural practices for producing tomatoes in the Kamuli District of

Uganda. The third chapter includes general conclusions of the studies and recommendations

for further research.

Introduction

Research designed to provide new information for extension agents working with

small- landholder tomato growers in the Kamuli District of Uganda was completed for this

thesis. Experiments evaluated methods of producing tomatoes using sustainable horticultural

practices.

Tomato (Lycopersicon esculentum Mill.) is a high-value vegetable crop that is widely

consumed fresh or processed and grown in almost every country of the world (Naika et al.,

2005). The increase in area of production and value has increased the economic significance of

the crop worldwide (Bodunde et al., 1993). Recently, tomato production has been emphasized

as a source of food security and income in Uganda (Ssekyewa, 2006).

Rao et al. (1998) found that tomatoes and tomato products have numerous health benefits and

also contribute to a well-balanced diet. They are a key source of essential nutrients including

2

vitamin A, C and E (Beecher, 1998), providing approximately 20 mg of vitamin C per 100

grams of edible product (Wilcox et al., 2003). One medium ripe tomato (~145 grams) can

provide up to 40% of the Recommended Daily Allowance of vitamin C and 20% of vitamin A

(Kelly and Boyhan, 2010). Tomatoes also contain lycopene, a red pigment serving as a natural

anti-oxidant (Shi and Manguer, 2000; Sies et al., 1992), calcium, water, and niacin, which are

essential for metabolism (Olaniyi et al., 2010).

In Uganda, tomatoes are among the most important and prominent horticultural crops

grown for both home consumption and the domestic market (Kennedy, 2008). Production of

tomatoes in rural areas of the country has increased employment and improved farmers’

livelihoods (Kennedy, 2008). The tomato is considered to be a top priority for production, is

viewed as the main income crop compared to other vegetables (Goldman and Kathleen, 2002;

NARO, 1999; Valera, 1995), and is grown and consumed in every district of Uganda (Mukiibi,

2001; Mwaule, 1995). The districts of Kasese, Kabale, Mbale, Kapchorwa, Mubende, Masaka,

Mpigi, Wakiso and Mbarara (Kennedy, 2008) have the largest area of production. In African

meals, tomatoes are consumed in sauces, soup, domestic meat or fish dishes, and fresh in

salads. They can also be processed into purées, juices, and ketchup (Kelly and Boyhan, 2010).

Canned and dried tomatoes are additional important processed products (Naika et al., 2005).

Uganda has dry seasons (Jan. to Feb. and June to Aug.) and wet seasons (Mar. to mid-June and

mid-Aug. to Dec.); with dry and wet seasons alternating in a year (Mukiibi, 2001). Tomato

cultivation is continuous throughout the year, with planting occurring at the beginning of each

wet season (Tumwine, 1999). Tomatoes are seeded, transplants established and set in fields,

and fruits mature within a period of 90-120 days after sowing seeds for transplants. In Uganda,

tomato plantings are harvested over a time period of 3-4 weeks (Naika et al., 2005). The most

3

commonly grown cultivars in Uganda are Moneymaker, Marglobe, Heinz 1370, and Roma

(Kalibballa, 2011; Ssejjemba, 2008; Tumwine, 1999).

Although tomatoes serve as a source of livelihood for many rural farmers in Uganda,

pests hinder their production. Insects such as aphids (Myzus persicae), thrips (Frankliniella

spp.), fruit worms (Helicoverpa armigera), mites (Tetranychus evansi), and diseases, including

bacterial wilt (Ralstonia solanacearum), early blight (Alternaria solani) and late blight

(Phytophthora infestans), lead to yield losses (Akemn et al., 2000; Anastacia et al., 2011;

Ssekyewa, 2006; Tumwine et al., 2002a). Farmers typically use chemical pesticides to control

the pests. Economic concerns arise from the over-reliance and use of pesticides, which increase

the costs of production (Mukiibi, 2001; Mwaule, 1995), and pesticide agrochemicals have a

potential negative impact on the environment. Farmers often apply pesticides without

protective clothing and use faulty equipment (personal observation), which could lead to health

problems. Research conducted in Uganda identified a potential disease-resistant tomato

cultivar MT 56 to provide control of bacterial wilt (Akemn et al., 2000; Fayad et al., 2013).

Tomato cultivars

Ugandan farmers grow different commercial tomato cultivars in the different regions of

the country. Cultivars include, Marglobe, Pakmor, Tropic, VF 6203, Peto-C-8100159, Heinz

1370, Moneymaker, Roma and Tengeru-97 (Kalibballa, 2011; Mwaule, 1995; Ssejjemba,

2008; Tumwine, 1999). According to Mwaule (1995), cultivars suitable for both fresh

consumption and processing include Marglobe, Parkmor, Tropic VF 6203 and Peto-C-

8100159, which is resistant to Verticillium spp. and Fusarium spp. Some cultivars have been

found to be tolerant/resistant to the most common diseases that affect tomatoes in Uganda. For

example, MT 56 has shown resistance to bacterial wilt (Karungi et.al., 2012; Mwaule, 1995),

4

and the hybrid tomato Assila, from Monsanto, was found to be resistant to Tomato Yellow

Leaf Curl Virus (TYLCV) (Matete and Ndung’u, 2011).

Tomato yield is dependent on the cultivars grown throughout the temperate and tropical

regions (Ashrafuzzaman et al., 2010; Erinle and Quinn, 1980; Peet et al., 2004; Watten and

Busch, 1984). In this research, the three cultivars used in field experiments included Heinz

1370, MT 56, and Nuru F1.

Heinz 1370 is a determinate tomato cultivar (Jensen and Mingochi, 1988), originally

from the United States of America, but currently grown in most of the world including

developing countries. It is the primary cultivar grown in the Kamuli District of Uganda and

farmers may save seed for future crops. It is a late midseason cultivar with an erect medium

large-sized vine that spreads to 42-48 inches, is resistant to cracking and Fusarium wilt disease,

and has a thick foliage cover. Fruits have a deep globe shape and are red, smooth and medium-

sized (100-125 fruits per 25 lbs). It can be used in fresh and processed products (Brown and

Gould, 1964). ‘Heinz 1370’ is susceptible to diseases including late blight, early blight,

bacterial wilt and worms like nematodes (Akemn et al., 2000; Baliyan and Madhava, 2013).

MT 56 is a determinate tomato cultivar that was bred and developed by Makerere University,

Uganda, and is resistant to tomato bacterial wilt (Karungi et al., 2011). This cultivar’s adoption

is constrained by limited availability because the seed has not yet been released widely to the

Ugandan farmers. Thus, its adoption among farmers of different regions has been slow

(Montgomery, 2011).

Nuru F1 is a determinate, early maturing F1 hybrid with excellent vigor (East African

Seed Company, 2014). The fruits are oval, glossy, have an attractive red color, are firm, have a

long shelf life (over 3 weeks) and can tolerate long-distance transportation. The yield potential

5

is 25 tons/acre (56 MT/ha). Currently, no studies have been completed to determine Nuru F1’s

susceptibility to common tomato diseases.

Soil mulch

Mulching is defined as a process of covering/spreading a layer of material on at least

30% of the soil surface (Erenstein, 2003). This practice has been used in conservation farming

and sustainable agriculture to improve crop yields through water retention, soil ecology

improvement, and general environmental maintenance (Erenstein, 2003). Mulch can be of

organic origin, such as straw, grass, leaves, composted yard waste, newspaper, sawdust, wood

bark, cedar chips, pine needles and recycled ground wood pallets (Skroch et al.,1992; Tiquia et

al., 2002) or composed of inorganic materials, such as polyethylene, woven polypropylene,

rocks, and rock chips (Skroch et al., 1992). Mulch can be either produced off site or produced

on site before the crop is grown (Erenstein, 2003).

As a horticultural practice, soil mulch contributes to plant growth by improving water

infiltration, retention, and reducing runoff (Erenstein, 2002, 2003; Skroch et al., 1992). It

reduces and controls soil erosion by providing a cover on the soil surface (Erenstein, 2002,

2003; Lal, 1994). In the tropics, organic matter and nutrients were found in the largest

concentrations in the top soil; mulch helps to keep top soil in place (Erenstein, 2002) and

increases crop yields (Erenstein, 1999).

Soil mulch also helps to control weeds, retain moisture in the soil, and reduce crop

diseases (Arin and Ankara, 2001; Hoitink and Boehm, 1999). It protects the soil surface from

direct and harsh sunlight and therefore shields it against temperature fluctuations (Lal et al.,

1990). Mulching helps control soil borne diseases, especially when used in combination with

solarization (Katan, 1980). It also reduces rain splash that could potentially transfer soil

6

inoculum to the tomato plant (Kennelly, 2009; Thurston, 1992). Mulching of tomatoes involves

inputs of labor, time, transportation of off-site mulch, and any insecticides needed to treat

mulch, such as those used to prevent termite damage (personal observation).

Staking

Staking supports plants with strong and durable materials, like wooden sticks or metal

poles, to reduce contact between fruits, stems, leaves and the ground (Saunyama and Knapp,

2004). Staking of plants lessens decay of the fruit and plant parts from soil borne diseases,

thereby improving on fruit quality (Chen and Lal, 1999). Additional studies have shown that

staking also contributes to improved vegetative growth and marketable and total yield

(Adelena, 1976; Jensen 1957; Mangal et al., 1981; Muhammed and Singh, 2007; Olasantan,

1985; Quinn, 1973, 1975; Wurster and Nganga, 1970). However, other studies have contrasted

the benefits and found that staking reduces total yield (Huxley, 1962; Voinea and Bunescu,

1957).

Staking contributes to increased air flow around tomato plants and fruits, which in turn

helps in the control of early blight (Kennelly, 2009). Emmons and Scott (1997) stated that

staking tomatoes can reduce the incidence of cuticle cracking by as much as four times. In

tomato production, it is common to stake or trellis indeterminate cultivars to provide support,

but is not as common a practice in the determinate cultivars (Saunyama and Knapp, 2004;

Taber et al., 2008).

Staking may involve costs such as stakes, labor, machinery, time, and transportation of

the stakes. In some areas of the world, staking may not be practiced because of the high labor

requirements involved in the activity (Wurster and Nganga, 1970). Although staking helps to

reduce lodging caused by rain and wind, Ozminkowsk et al. (1990) found that it is a costly

7

practice in terms of materials, time, and labor. Chen and Lal (1999) further reported that these

costs can be offset by higher returns.

Use of pesticides

According to the United States Federal Insecticide, Fungicide, and Rodenticide Act

(FIFRA), a pesticide is "any substance or mixture of substances intended for avoiding,

terminating, repelling, or mitigating any insects, rodents, nematodes, fungi, or weeds, or any

other form of life declared to be pests, and any substance or mixture of substances intended for

use as a plant regulator, defoliant, or desiccant" (Lang, 1993). In tomato production, the

pesticides used include fungicides (contact and systemic) to protect against fungal infections,

insecticides to protect against insects, and herbicides to protect against weeds (Akemo et al.,

2001). In Uganda, tomato growers may use all or some of the above mentioned pesticides

depending on the availability of capital, knowledge about their existence, and expertise

required to properly use the chemicals (Akemo et al., 2001).

A survey (Tumwine et al., 2002b) on current practices for disease management in

Uganda revealed that >90% of tomato growers in several districts use a contact fungicide,

Dithane M-45 (Mancozeb). Ugandan tomato growers do not commonly use systemic

fungicides as control measures, either due to unavailability of the products or lack of farmers’

awareness of these fungicides (Ssemwogere et al., 2013). Bacterial wilt is a major problem,

especially among farmers who do not have access to the resistant cultivar MT 56

(Montgomery, 2011), since this is the most effective way to control the disease.

The use of fungicides, such as Mancozeb, increases tomato yields by increasing retention

of flowers and fruit on plants (Tumwine et al., 2002a). Pesticides used in tomato production are

expensive in Uganda. As a result, they greatly increase the cost of production especially among

8

small-landholder farmers who do not possess sufficient financial capital for these inputs

(Akemo et al., 2001; Frontem, 2003; Karungi et al., 2011). In some cases, farmers use pesticide

rates that are below the recommended rates, leading to resistance of diseases to the pesticides

(Bommarco and Ekbom, 1995; ICIPE, 2009; Sherf and Macnab, 1986; Ssemwogerere et al.,

2013; Tumwine et al., 2002b).

Rationale

In the Kamuli district, the number of hectares in tomato production is low; such that

tomatoes are not featured among crops listed in a district baseline survey’s data (Sseguya and

Masinde, 2005). Yet, tomatoes are very important to small-landholder farmers because they

ensure food security as well as income generation (Ssejjemba, 2008). Farmers are faced with a

number of challenges which hinder them from successfully producing and economically

benefiting from tomato production. Kasenge et al. (2002), Ssekyewa (2006), and Tumwine

(1999) noted that problems associated with tomato production included lack of improved

cultivars, pests, including insects and diseases, and inadequate information about sustainable

horticultural practices.

Farmers use pesticides to control disease and insect pests in tomatoes in Uganda.

However, pesticide use is low due to the fact that Uganda is a land-locked country (United

Nations Development Program, 2008) and pesticides are imported and transported to Uganda

via truck. Transportation costs increase the price of pesticides, often making them an

unaffordable input by the rural small-landholder farmers. The cost of pesticides increases the

production cost for farmers who are able to buy pesticides. In Uganda, pesticide markets are

unregulated, resulting in unscrupulous practices including sale of expired, adulterated or

banned products. Excessive pesticide use due to calendar applications without environmental

9

and pest monitoring and inappropriate chemical handling practices may increase risks to

human health (Karungi et al., 2011; Tumwine, 1999). While Integrated Pest Management

(IPM) can be very important in tomato production, weather monitoring (for disease), scouting

and economic thresholds (for insects) are not used in the Kamuli district.

Fresh and perishable crops, like tomatoes, are at a production disadvantage in Uganda

compared to dry non-perishable crops. Poor infrastructure, including roads in the Kamuli

District, lack of proper packaging for transport, and a lack of temperature control expose the

produce to spoilage, increasing postharvest losses and reducing farmers’ returns.

Area-specific studies are needed to provide farmers and extension specialists information that

is relevant to their situation, enabling them to make appropriate production choices or

recommendations that result in the most economically feasible decisions given their limited

resources. The proposed research examines sustainable horticultural practices that rural small-

landholder farmers in the Kamuli District of Uganda can adopt.

Objective

The overall goal of this study is to determine horticultural practices for sustainable

tomato production in Kamuli District of Uganda. The study aims to evaluate sustainable

horticultural practices of resistant cultivars, pesticide application, staking of plants, and use of

a soil mulch for producing tomatoes in Kamuli district of Uganda.

Hypothesis

The hypothesis of the study is that the use of tolerant/resistant cultivars, pesticides,

staking and using a soil mulch will increase yield and gross margin obtained in the tomato

plots.

10

Significance

New information will enable small-landholder farmers to make appropriate production

decisions given their limited resources in the Kamuli District of Uganda, and extension

workers can provide appropriate recommendations about tomato production and its potential

gross margin for small-landholder farmers in Uganda.

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17

CHAPTER 2. EVALUATION OF HORTICULTURAL PRACTICES FOR

SUSTAINABLE TOMATO PRODUCTION IN KAMULI DISTRICT, UGANDA.

A paper to be submitted to HortScience

Sharon M. Tusiime1, Gail Nonnecke2,*, Dorothy Masinde3 and Helen Jensen4

1Graduate Student, 2Morrill Professor, University Professor, 3Lecturer, Department of

Horticulture, 4Professor, Department of Economics, Iowa State University, Ames, Iowa 50011.

*Corresponding author G.R. Nonnecke (Email address: [email protected])

Additional index words. Lycopersicon esculentum, pesticide application, stake, mulch, disease

severity, gross margin

Abstract.

Tomato cultivars (Heinz 1370, Nuru F1, and MT 56), pesticide application (±), staking

(±), and mulching (±) were tested for their effect on yield, disease severity, and gross margin in

tomato production in the Kamuli District of Uganda. Treatments were tested in a randomized

complete block design with a factorial and split-plot arrangement in two growing seasons

during 2013. Total and marketable fruit number, marketable fruit weight, gross margin, and

disease severity (assessed using the area under disease progress curve) were measured.

Results indicated that disease-resistant cultivar, MT 56, in combination with pesticide

application and soil mulch provided the highest marketable fruit number and marketable fruit

weight and all treatments had a positive gross margin in the first season. A combination of MT

56, no pesticide application and no mulch resulted in the only positive gross margin in season

two. Application of pesticides reduced disease severity (early blight, Alternaria solani) for all

cultivars in season one, and in season two for Heinz 1370 and Nuru F1, but did not affect

disease severity for MT 56 in the second season. Using soil mulch reduced the severity of early

blight disease, but decreased the gross margin when purchased. Staking did not affect yield or

disease severity of plants and decreased the gross margin.

18

Introduction

Tomato (Lycopersicon esculentum Mill.) is the most widely grown vegetable crop in

Uganda and is popular in the diets of its citizens. Most cultivation of tomato is by farmers who

own 2 ha or less of land (Karungi et al., 2011). Tomatoes contribute to a farm income in

Uganda of about $104 per annum (World Bank, 1993), but their production is challenged by

various factors. Pests include insects such as fruit worms (Helicoverpa armigera), thrips

(Frankliniella spp.), aphids (Myzus persicae) and mites (Tetranychus evansi), and diseases

include early blight (Alternaria solani), late blight (Phytophthora infestans), and bacterial wilt

(Ralstonia solanacearum). Additional limitations include lack of improved cultivars and

inadequate information on sustainable horticultural practices (Akemn et al., 2000; Anastacia et

al., 2011; Kasenge et al., 2002; Sekyewa, 2006; Tumwine, 1999 and Tumwine et al., 2002a).

In an effort to manage the pest problems, fungicides and insecticides have been used (Akemo

et al., 2001; Tumwine, 2002b). Potential disease-resistant or tolerant cultivars (Akemn et al.,

2000; Fayad et al., 2013) and cultural practices such as mulching and staking have been

identified to assist in disease management (Akemo et al., 2001). However, the sustainability of

cultural practices for tomato production among rural small-landholder farmers has not been

studied extensively in Uganda.

The objective of this work was to determine sustainable practices for producing tomatoes

in the Kamuli District of Uganda by evaluating tolerant/resistant cultivars, pesticide use,

staking, and mulching and their impact on yield, disease severity and gross margin. Evaluating

horticultural practices for sustainable tomato production will enable farmers to benefit through

increased personal consumption and farm income. Appropriate production choices that result

in the most economical and sustainable practices for farmers with limited resources are needed.

19

Materials and Methods

Production of seedlings. On 22 April 2013, tomato seeds of Heinz 1370, MT 56 and Nuru

F1 were planted and seedlings raised in transplant boxes (0.6m long×0.4m wide×0.1m deep),

which contained steam sterilized soil. Dried elephant grass (Pennisetum purpureum Schmach.)

was placed on top of the boxes to maintain soil moisture and hand watering was done as often

as required to enable germination. On 4 May, the elephant grass was removed from the top of

the box and a shade structure with elephant grass on its roof was built directly over the boxes.

Victory (Mancozeb and metalaxyl) fungicide was applied (by spraying) to the seedlings once

per week at recommended label rates. After approximately four weeks (4 May through 1 June),

the shade was removed from above the boxes to allow the transplants to harden off, and on 10

June the seedlings were transplanted into the research plots.

Research plots. A field plot experiment was established and maintained in 2013 in season

one, Apr. to Aug., and in season two, Sept. to Dec., in the Kamuli District of Uganda on land

of the Nakanyonyi Primary School (00 56’ 34.4” N 330 02’ 19.6” E). In each growing season the

plots were on different but similar sites at the primary school. The Kamuli District receives a

bi-modal rainfall that ranges between 900-1500 mm annually, with two growing seasons. In

Mar. to May/June, is when most of the rains are received in the first growing season, and in

Aug. to Oct. is when rains are received in the second season but are less than the first season

(Kamuli District Local Government, 2011). Supplemental hand watering was used in each

season during transplant establishment, and weekly thereafter if rainfall of 2.5 cm was

received.

The experiment was laid out in a randomized complete block design with a factorial and

split-plot arrangement of treatments. Raised bed plots measuring 9.8 m long, 0.91 m wide and

20

0.30 m high were prepared using manual tillage and tomato seedlings transplanted into plots.

The treatments used were cultivar, pesticide application, staking (main plots) and mulching

(split plots). Treatments included three cultivars (Heinz 1370, Nuru F1 and MT 56), two levels

of pesticide application (pesticide and no pesticide), two methods of plant training (staked and

not staked) and two levels of soil mulching (mulched and without mulch). The 9.8-m long

raised beds had 16 plants spaced 0.60 m apart with the split plot having eight plants mulched

and eight plants not mulched. A distance of 0.60m was between the raised beds.

Soil fertility. Seven random samples were taken from the different locations of the field,

gravel removed by hand, and samples ground into finer particles. Equal quantities from each

sample were mixed together thoroughly to make one representative sample per field, which

was submitted to the Soil, Water and Plant Analytical Laboratory, College of Agriculture and

Environmental Sciences, Makerere University, Kampala, Uganda, for analysis. Fertilizer was

added to achieve uniform and optimal fertility across plots prior to treatment application using

amounts based on Iowa State University soil test result interpretations (Nair, Personal

Communications). Calcium Carbonate (lime) was applied at16.99 kg/plot in season one and

9.99 kg/plot in season two. In addition, 0.236kg and 0.249kg of Calcium ammonium nitrate

(nitrogen/N), applied in season one and two, respectively, were added at planting and fruiting,

0.332 kg of Muriate of Potash (potassium/K2O), and 0.433 kg of Triple Super Phosphate

(phosphorous/P2O5) were applied in each season to maintain tomato growth and development.

Cultivars. Tomato cultivars included the following: Heinz 1370, a locally grown

determinate cultivar, that was bred for processing; MT 56, an improved selection that was bred

and developed at Makerere University, Uganda and is resistant to tomato bacterial wilt

21

(Ralstonia solanacearum) (Karungi et al., 2011); and Nuru F1, a determinate early maturing F1

hybrid (East African Seed Company, 2014).

Pesticides. All pesticides were applied with a plastic backpack sprayer to the plots

receiving the pesticide treatment. Pesticides used in both growing seasons included two

products containing systemic fungicides, Ridomil (metalaxyl) and Victory (Mancozeb and

metalaxyl), one contact fungicide of Dithane M-45 (Mancozeb), and two insecticides (not part

of treatments), Thionex (endosulfan 35% EC, emulsifiable concentrate) and Methomex

(methomyl 90% SP, soluble powder). Products containing systemic fungicides were applied

once every two weeks; the products were alternated in successive applications. The contact

fungicide and the insecticides were each applied once per week. The spray regime followed the

label recommendations.

Staking. Tomato plants were tied to a trellis between stakes on 11 July and 5 Aug. during

the first season and 22 Oct. and 12 Nov. in season two, 2013. Sisal twine was used to support

plants between the wooden, 1.5m-long stakes. Pruning of tomato plants was not used in the

experiment.

Mulching. Dried elephant grass (Pennisetum purpureum Schmach.) was applied to the

soil surface of mulched plots at a depth of 0.1 m. To prevent termite damage to the mulch,

Pyrinex (chlorpyrifos) was applied at label rates over the top of the mulch as soon as mulch

was placed on treatment plots.

Weeding. Hand weeding was completed every three weeks, and all the weeds were

removed from the plots.

Harvesting. Fruits were harvested twice a week starting 29 July through 10 Aug. in

season one and 25 Nov. through 16 Dec. in the second season, 2013. Yield data were collected

22

from all the eight plants in each sub-plot. Marketable (suitable for the market) fruits were

counted and weighed. Since there is no standard grade of tomatoes in Uganda, we classified

and counted non-marketable fruits as those with splitted surfaces and/or insect and disease

damage.

Labor. Hand labor was used for all activities. The time in minutes for pesticide

application, staking, and mulching was recorded across all cultivars and was included in the

calculation of the gross margin.

Disease severity. Disease severity data were collected by observing the leaves of all eight

plants per sub-plot for early and late blight and bacterial wilt symptoms every week after all

treatments had been applied to the plots. The percentage of leaves attributed to disease was

recorded for each sub-plot. These values were then used to calculate the area under the disease

progress curve (AUDPC). The formula used to calculate the AUDPC was =Σ [(Xi+1

+ Xi )

/2][ti+1

- ti]; where X

i = the percentage of the leaves damaged at i

thweek, t

i = the time in days

after appearance of the disease at ith

week, n = the total number of observations (Madden et al.,

2007). These values were then subjected to analysis of variance to determine whether the

treatments had an effect on disease severity.

Gross margin. The variable costs of tomato production included labor and all the inputs

directly related to the treatments, including, seeds, pesticides, stakes, and mulch. The total

production costs are the sum of the fixed costs and variable costs (Engindeniz, 2007); for this

experiment, however, we did not include the fixed costs because the goal was to determine the

costs incurred for each particular treatment, which were calculated using the current input

prices and labor costs (Engindeniz, 2006). Costs of practices that were assumed to be equal for

all plots were not included in the calculation of gross margin, such as labor and inputs of

Ni - 1

i=1

i=1

23

transplant boxes, land preparation, transplanting, fertilizer application and watering.

Transportation of inputs to research sites, such as mulch and stakes, were also not included in

the gross margin because they were locally available. The costs that accrued from using the

different treatments were calculated by dividing the overall cost of the treatment by the number

of plots that received the treatment. To determine the gross production (revenue) for the

different treatments, the average price of fresh tomatoes in the town of Kamuli at the time of

harvest was multiplied by the fruit weight (kg per plot). The gross margin that accrued from

use of the different treatments was determined by the difference between the gross production

value and the cost incurred (Engindeniz, 2007). The gross margin data were subjected to

analysis of variance to determine the most viable practice.

Data analysis. Results for yield variables, AUDPC values, and gross margin were

analyzed as a randomized complete block and a split plot design using PROC MIXED routine

of the SAS program (Version 9.3; SAS institute, Cary, NC, 2011). Differences between least

square (LS) MEANS of treatments were determined using LS MEANS statements and defining

custom orthogonal contrasts between LS MEANS across cultivars. Significance of these

differences was determined based on Turkey’s adjustment for multiple comparisons.

Results

Interactions occurred among the main effects of cultivar, pesticide application, mulching

and growing season (Table 1). Therefore, data were analyzed and are presented within cultivar

and growing seasons for pesticide application and mulch. There was no interaction of the main

effect of staking.

24

Cultivar

In the first season, cultivar MT 56 yielded 42 and 73 more fruits than Nuru F1 and Heinz

1370 respectively, while Nuru F1 yielded 31 more fruits than Heinz 1370. In season two, ‘MT

56’ produced 23 more fruits than ‘Heinz 1370’ while ‘Nuru F1’ produced 57 and 34 more

fruits than Heinz 1370 and MT 56 respectively (Table 2). For marketable fruit number, in

season one, cultivar MT 56 yielded 21 and 43 more marketable fruit than Nuru F1 and Heinz

1370 respectively, while Nuru F1 produced 22 more marketable fruit than Heinz 1370. In the

second season, ‘MT 56’ produced 14 more marketable fruit than ‘Heinz 1370’ while ‘Nuru F1’

produced 29 and 14 more marketable fruit than ‘Heinz 1370’ and ‘MT 56’, respectively (Table

2).

In season one, ‘MT 56’ yielded 1.91kg and 2.30 kg more fruit weight than ‘Nuru F1’ and

Heinz 1370, respectively (Table 2). ‘MT 56’ produced 1.98kg more fruit weight than ‘Heinz

1370’, while ‘Nuru F1’ produced 1.33kg more fruit weight than ‘Heinz 1370’ in the second

season. ‘MT 56’ had a positive gross margin (profit) of 0.67(USD) while ‘Nuru F1’ (-1.64

USD) and ‘Heinz 1370’ (-1.19 USD) produced negative gross margins (loss) in the first

season. This pattern was consistent in season two, with ‘MT 56’ producing a positive gross

margin of 0.18 USD, while ‘Nuru F1’ and ‘Heinz 1370’ produced a negative gross margin of -

1.11 USD and -1.35 USD respectively (Table 2).

Cultivar Nuru F1’s AUDPC was 101 and 270 higher than that of Heinz 1370 and MT 56

respectively, while the AUDPC of Heinz 1370 was 168.79 higher than that of MT 56 in season

one. In season two, the AUDPC of ‘MT 56’, was 546 and 444 lower than that of ‘Heinz 1370’

and ‘Nuru F1’ respectively (Table 2).

25

Horticultural practices within cultivars

‘Heinz 1370’. Total and marketable fruit number and marketable fruit weight did not

differ for treatments in each season. The highest gross margin was from sub-plots that did not

receive pesticide and soil mulch but it did not differ from those receiving pesticide and without

mulch in both seasons. All gross margins were negative (loss) and in season one and two, the

lowest gross margins were from sub-plots receiving pesticides and mulch but did not differ

from sub-plots with pesticide and without mulch, and sub-plots with no pesticide and mulch

(Table 3).

‘Nuru F1’. In season one, there were no differences among treatments for total and

marketable fruit number, marketable fruit weight and gross margin. However, in season two,

application of pesticides and soil mulch yielded the highest total fruit number (136),

marketable fruit number (72) and marketable fruit weight (4.25 kg). Sub-plots that did not

receive pesticides and mulch yielded the least total and marketable fruit number and fruit

weight, but did not differ from pesticide and no mulch, no pesticide and mulch for marketable

fruit weight, no pesticide and mulch for total and marketable fruit number. This however

differed from pesticide and no mulch for total fruit number. For the marketable fruit number,

sub-plots receiving pesticide but without mulch did not differ from sub-plots of no pesticide

and with mulch (Table 3).

Although all gross margins were negative in season one and two, sub-plots that did not

receive pesticide and mulch had the best gross margins but did not differ than pesticide and

mulch and pesticide and no mulch. The least gross margin came from sub-plots that did not

receive pesticide but had mulch and they did not differ from pesticide and mulch and pesticide

and no mulch (Table 3).

26

‘MT 56’. Total fruit number and gross margin in season one, total and marketable fruit

number, and marketable fruit weight in season two, were not different among treatments. In the

first season, sub-plots with application of pesticides and mulch had the highest fruit weight

(6.21 kg) and marketable fruit (91.8), but did not differ than pesticide and no mulch, and no

pesticide and mulch. Sub-plots that did not receive pesticides and mulch produced the lowest

fruit weights (1.28 kg), but were not different than sub-plots without pesticide and mulch, and

plots with pesticide and no mulch. The same trend was seen in the marketable fruit number

where no pesticide and no mulch sub-plots yielded the least fruit, but did not differ from no

pesticide and mulch (Table 3). The sub-plots in which pesticides and mulch were not applied

produced a positive gross margin (profit) of 1.61 USD and did not differ from pesticide and no

mulch sub-plots (0.40 USD). Application of pesticide and soil mulch produced the least gross

margin, but did not differ than no pesticide and mulch, and pesticide and no mulch (Table 3).

Positive gross margins (profits) were received for all treatments when the mulch was locally

available (not purchased) but labor for its application included in the calculation of the gross

margin (Table 4).

In season one, the break-even price for ‘MT 56’ (0.55USD) was below the Kamuli

average price (0.8USD), and the break-even yield (4.34kg) was below the actual yield received

from experiments (marketable fruit weight) (6.21kg). This explains the positive gross margins

received by cultivar MT 56 (Table 5).

Because there were no significant interactions between staking and growing season, both

seasons were combined for total and marketable fruit number, marketable fruit weight, and

gross margin (Table 6). Although staking did not impact total and marketable fruit number, and

marketable fruit weight, all gross margins were negative (losses) and a better gross margin was

27

obtained from the plots that were not staked (-0.51 USD) compared to those that were staked (-

0.96 USD) (Table 6).

AUDPC

Interactions occurred among the main effects of cultivar, pesticide application, and

growing season for AUDPC. Therefore, data were analyzed and are presented within cultivar

and growing seasons for pesticide application (Table 7). There was no interaction for the main

effects of staking and mulching.

Application of pesticides to ‘Heinz 1370’ sub-plots had a lower AUDPC in the first

(3141) and second (1083) seasons respectively compared to sub-plots that did not receive

pesticides (Table 7). For cultivar Nuru F1, sub-plots that received pesticides had a lower

AUDPC in season one (3210) than non-pesticide sub-plots (3638) and a similar trend was

observed in the second season, where pesticide sub-plots had (1007) and non-pesticide sub-

plots (1341). In ‘MT 56’, the AUDPC for pesticide sub-plots (2904) was lower than non-

pesticide sub-plots (3404) in season one. However, in the second season, sub-plots that

received pesticide had an AUDPC of 634 but did not differ from the sub-plots that did not

receive pesticide (825) (Table 7).

Since, there were no significant interactions between growing seasons, staking and

mulching for AUDPC, values are presented as a combination of both seasons. Although the

AUDPC was not different for staked and unstaked sub-plots, mulching reduced AUDPC in

both seasons (Table 8).

28

Discussion

Tomato production is important for small-landholder farmers in rural Uganda because

tomatoes are a source of income and are widely consumed by Ugandans. Challenges of

inadequate information on the horticultural practices formed the basis for this investigation.

Cultivars, pesticide application, staking, and mulching were tested for their impact on tomato

yield, disease severity and gross margin.

We expected to see interactions between growing season and cultivar because the Kamuli

District has two growing seasons and receives a bi-modal rainfall that ranges between 900-

1500mm annually. The months of Mar. through May/June characterize the main season, in

which most of the rains are received, and Aug. through Oct. include the second season in

which less rains are received (Kamuli District Local Government, 2011). Also, the cultivars

used in this study were different genetically.

‘MT 56’ yielded better than ‘Nuru F1’ and ‘Heinz 1370’ and had a higher gross margin in

season one due to the least early blight disease (lowest AUDPC) and more marketable fruit

number, resulting into a higher marketable fruit weight. The higher marketable fruit weight

together with a lower cost of seed compared to ‘Nuru F1’ increased the gross margin for ‘MT

56’. This is in agreement with Nonnecke (Unpublished 2012), who observed yield differences

in various tomato cultivars in the Kamuli district and where MT 56 was among the highest-

yielding cultivars. On the other hand, cultivar Nuru F1 out yielded MT 56 in the second season

probably because Nuru F1 performs better in a season that does not receive a lot of rainfall.

‘Heinz 1370’ produced the least total and marketable fruit number due to more early

blight disease that reduced fruit production. Baliyan and Madhava (2013) reported Heinz 1370

29

as a low yielding cultivar which is similar to our results but Heinz 1370 did not differ from

Nuru F1 in marketable fruit weight and gross margin.

A high AUDPC value is associated with more disease, and in both seasons ‘MT 56’ had

the least AUDPC and early blight disease. Some genetic tolerance to early blight might exist

although it was bred for resistance against bacterial wilt (Karungi et al., 2011). ‘Nuru F1’ had

the highest disease in season one but was not different than ‘Heinz 1370’ in the second season.

‘Nuru F1’ may have been selected for yield components and not disease tolerance. Our data

agree with Maršić et al. (2005) who reported Heinz 1370 to be more susceptible to disease

compared to the other cultivars and Baliyan and Madhava (2013) who found Heinz 1370 was

susceptible to various pests including diseases of early blight and late blight.

Because Heinz 1370 is not a high-yielding cultivar (Baliyan and Madhava., 2013;

Tudzarov, 1996), all gross margins were negative (a loss) in both season when pesticides and

mulch were used, and the lower yields could not offset the input costs incurred. The yield

obtained from ‘Heinz 1370’ was below the break-even yield. Application of pesticides and use

of soil mulch in the second season produced the highest total and marketable fruit number and

marketable fruit weight in ‘Nuru F1’ (Table 2), agreeing with Akemn et al., (2000), who found

an increase in tomato yields with the use of Dithane M45. The overall gross margins were

negative (loss) because the higher cost of ‘Nuru F1’ seeds increased the total cost and the yield

obtained was below the break-even yield; therefore, the revenues obtained could not offset the

high costs.

For ‘MT 56’, sub-plots that received pesticide and mulch yielded the highest marketable

fruit weight and marketable fruit in season one primarily because pesticides were able to

decrease disease, reducing the number of non-marketable fruits and increasing the marketable

30

fruit. These results are consistent with Frontem (2003), who found more tomato yield in plots

that received pesticides compared to those that did not receive any pesticides due to a reduction

in early blight disease. Keinath et al. (1996) reported a 38% increase in tomato fruit weight

when pesticides were applied. In addition, mulching could have lessened the problems

associated with tomato growth, such as soil erosion (Erenstein, 2002), weeds (Campiglia et al.,

2010), leaching of nutrients (Olasantan, 1999), and improved the soil’s physical environment

(soil moisture, temperature) (Erenstein, 1999; Hapaala et al., 2014). Higher gross margin was

achieved in plots without pesticides. No costs were incurred when pesticides, stakes, and

mulch were not used in the treatment plots and ‘MT 56’ seeds did not cost as much as the

‘Nuru F1’ hybrid seed.

The application of pesticides reduced early blight disease for ‘Heinz 1370’, ‘Nuru F1’ in

the first and second seasons and for ‘MT 56’ in the first season. Earlier studies by Frontem,

(2003) and Sood and Sharma (2004) found low early blight severity with the use of pesticides

compared to no pesticide use. However, in season two, when less rainfall typically occurs, the

‘MT 56’ sub-plots that received pesticide did not differ from the no pesticide sub-plots in terms

of early blight disease.

In both seasons, the staked and unstaked plots did not differ in terms of total and

marketable fruit number and marketable fruit weight, agreeing with Tewari and Vishunavat

(2012) who reported no difference in tomato yield as a result of staking. In contrast, earlier

studies by Huxley (1962) Wurster and Nganga (1970), and Strijdom (1955) found that staking

reduced tomato yields, while Karungi et al., (2011) indicated that the staking increased yields.

Mulching reduced disease possibly because it lessened soil splash onto the lower leaves of the

plant since the soil particles may contain early blight fungus spores. Mulching acts as a barrier

31

and prevents the soil fungal spores moving to the plants from the soil surface. Mills et al.

(2002) reported similar results in which mulching using hairy vetch residue decreased soil

particle dispersal by raindrops and reduced early blight disease.

Study Limitations

At the time of this study, the cultivar MT 56 had not been officially released in the

Ugandan horticulture industry. Preparations for the release of this cultivar are underway, but

availability of MT 56 seeds may be a challenge for tomato growers in Uganda. Also, because

this experiment was controlled, the results are dependent on the prices used. Different prices

may lead to different results. Other factors limiting tomato yield in the Kamuli District include

low soil quality, unreliable rainfall affecting seasonal distribution, and limited extension

services in horticultural crops to help farmers.

Summary and Conclusions

Disease-resistant cultivar, MT 56, in combination with pesticide application and soil

mulch provided the highest marketable fruit number and marketable fruit weight and all

treatments had a positive gross margin in the first season. A combination of ‘MT 56’, no

pesticide application and no mulch resulted in the only positive gross margin in season two.

Application of pesticides reduced disease severity (early blight, Alternaria solani) for all

cultivars in season one, and season two for Heinz 1370 and Nuru F1, but did not affect disease

severity for MT 56 in the second season. Using soil mulch reduced the severity of early blight

disease, but decreased the gross margin when purchased. Staking did not affect yield or disease

severity of plants and decreased the gross margin.

32

There is need for a reputable and certified seed industry in Uganda to distribute improved

cultivars to benefit small-landholder farmers. Because there are few disease-tolerant cultivars,

further research to develop additional disease-tolerant cultivars will help farmers increase

production and profitability.

In Uganda, reliable soil quality and climate data of all districts are not available. Efforts

should be made to provide accurate weather information and site-specific soil maps for the

Kamuli District. These data are needed to help small-landholder farmers and extension agents

plan their agricultural activities, determine integrated pest management strategies, and make

informed production decisions to sustainably produce tomatoes.

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35

Table 1. Four-way analysis of variance of main effects for total and marketable fruit number, marketable fruit weight, gross margin,

and early blight severity assessed by area under the disease progress curve (AUDPC) of tomatoes in Kamuli District, Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9 m; data represent all harvests across two seasons in 2013.

y AUDPC- Area under the disease progress curve was calculated using = Σ [(X

i+1 + X

i ) / 2][t

i+1 - t

i]; where X

i = the percentage of the

leaves damaged at ith

week, ti = the time in days after appearance of the disease at i

thweek, n = the total number of observations.

x P-value of interaction effect between main effects as determined by Tukey’s adjustment for multiple comparisons. w GS- growing season 1= May to Aug. and 2= Sept. to Dec.

Treatment Total Fruit

Number

(No./sub-plotz)

Marketable Fruit

Number

(No./sub-plot)

Marketable Fruit

Weight

(Kg/sub-plot)

Gross Margin

(USD/sub-

plot)

AUDPC

(per sub-plot y)

Cultivar

Cultivar* Pesticide 0.0143x 0.0271 0.1798 0.1798 0.8613

Cultivar* Stake 0.7680 0.6925 0.3724 0.3724 0.1113

Cultivar* Mulch 0.2798 0.2258 0.1273 0.1273 0.8077

Cultivar* GSw <.0001 <.0001 0.0300 0.0392 <.0001

Pesticide Application

Pesticide* Stake 0.1291 0.6665 0.6436 0.6436 0.0602

Pesticide* Mulch 0.9705 0.5977 0.2886 0.2886 0.8531

Pesticide* GS 0.8908 0.3874 0.3568 0.0516 0.0278

Staking

Stake* Mulch 0.2363 0.4309 0.0759 0.0759 0.0766

Stake* GS 0.8443 0.9232 0.8322 0.2364 0.2631

Mulching

Mulch* GS 0.1597 0.0502 0.0973 <.0001 0.1509

i=1

Ni - 1

36

Table 2. Comparisons of cultivar for total and marketable fruit number, marketable fruit weight, gross margin, and early blight

severity assessed by area under the disease progress curve (AUDPC) of tomatoes in Kamuli District, Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9 m; data represent all harvests across two seasons in 2013. y Data obtained in Uganda Shillings and converted to US dollars (I USD = 2500 UGX, Uganda Shillings).

x AUDPC- Area under the disease progress curve was calculated using = Σ [(X

i+1 + X

i ) / 2][t

i+1 - t

i]; where X

i = the percentage of the

leaves damaged at ith

week, ti = the time in days after appearance of the disease at i

thweek, n = the total number of observations.

w Growing season 1= May to Aug. and 2 = Sept. to Dec. v Orthogonal comparison value within a column is the difference of all treatment combination means among cultivars within a

growing season at P ≤ 0.05; NS= not significant

Cultivar

Total Fruit

Number (No./sub-plotz)

Marketable

Fruit

Number

(No./sub-plot)

Marketable

Fruit

Weight

(Kg/sub-plot)

Gross Margin

(USD/sub-ploty)

AUDPC

(per sub-plotx)

Growing seasonw Growing season Growing season Growing season Growing season

1 2 1 2 1 2 1 2 1 2

Heinz 1370 50 21 16 9 1.21 0.77 -1.19 -1.35 3323 1275

MT 56 123 44 60 24 3.60 2.76 0.67 0.18 3154 729

Nuru F1 81 78 39 38 1.68 2.10 -1.64 -1.11 3424 1174

Comparisonsv

Heinz 1370 vs Nuru F1 -31 -57 -22 -29 NS -1.33 NS NS -101 NS

Heinz 1370 vs MT 56 -73 -23 -43 -14 -2.30 -1.98 -1.86 -1.53 169 546

Nuru F1 vs MT 56 -42 34 -21 14 -1.91 NS -2.31 -1.30 270 444

i=1

Ni - 1

37

Table 3. Total and marketable fruit number, marketable fruit weight, and gross margin of three tomato cultivars grown with or

without pesticide application and soil mulch in the Kamuli District, Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9 m. y The gross margin was calculated by subtracting the costs of applying pesticides and mulch from the revenue accrued. Data

obtained in Uganda Shillings and converted to US dollars (I USD = 2500 UGX, Uganda Shillings). x Growing season 1 = May to Aug. and 2 = Sept. to Dec. w Mean separation within a column and cultivar by Tukey-Kramer (P ≤ 0.05); Means followed by the same letter within columns are

not different from one another. v Total fruit number represents the quantity of fruits harvested per plot. Marketable fruit is the number of fruits suitable for the

market. Marketable fruit weight is the kilograms of the marketable fruit per plot.

Treatment

Total Fruit

Number

(No./sub-plotz)

Marketable Fruit

Number

(No./sub-plot)

Marketable Fruit

Weight

(Kg/sub-plot)

Gross Margin

(USD/sub-ploty)

Growing seasonx Growing season Growing season Growing season

Heinz

Pesticide and Mulch

1 2 1 2 1 2 1 2

60 aw, v

30 a

24 a

16 a

1.70 a

1.18 a

-2.42 b

-2.62 b

Pesticide and No mulch 65 a 20 a 17 a 10 a 1.43 a 0.86 a -1.46 ab -0.82 ab

No Pesticide and Mulch 50 a 20 a 19 a 8 a 1.36 a 0.67 a -0.61 ab -1.88 b

No pesticide and No mulch 25 a 15 a 5 a 5 a 0.33 a 0.37 a -0.26 a -0.07 a

Nuru F1

Pesticide and Mulch

104 a

136 a

57 a

72 a

2.71 a

4.25 a

-2.44 a

-0.99 ab

Pesticide and No mulch 74 a 91 b 35 a 41 b 1.41 a 2.20 b -2.30 a -0.58 ab

No Pesticide and Mulch 87 a 44 c 37 a 24 bc 1.60 a 1.16 b -1.26 a -2.32 b

No pesticide and No mulch 57 a 43 c 26 a 15 c 1.01 a 0.80 b -0.54 a -0.56 a

MT 56

Pesticide and Mulch

151 a

41 a

92 a

24 a

6.21 a

3.13 a

1.13 a

-1.11 b

Pesticide and No mulch 118 a 37 a 63 a 24 a 3.46 b 2.46 a 0.11 a 0.40 ab

No Pesticide and Mulch 136 a 55 a 60 ab 26 a 3.46 b 2.89 a 1.01 a -0.16 b

No pesticide and No mulch 88 a 43 a 24 b 21 a 1.28 b 2.54 a 0.45 a 1.61 a

38

Table 4. Gross margin of tomato cultivars grown with and without pesticide application and soil mulch

Gross Margin

(USD/sub-plotz)

With labor and cost of mulch

Gross Margin

(USD/sub-ploty)

With labor and without cost of mulch

Treatment Growing seasonx Growing season

MT 56

Pesticide and Mulch

1 2 1 2

1.13 aw

-1.11 b

2.10 a

0.61 a

Pesticide and No mulch 0.11 a 0.40 ab 0.11 a 0.40 a

No Pesticide and Mulch 1.01 a -0.16 b 1.99 a 1.56 a

No Pesticide and No mulch 0.45 a 1.61 a 0.45 a 1.61 a z The gross margin was calculated by subtracting the costs of applying pesticides and mulch from the revenue accrued. y The gross margin was calculated by subtracting the costs of applying pesticides and labor for mulch from the revenue accrued.

Data obtained in Uganda Shillings and converted to US dollars (I USD = 2500 UGX, Uganda Shillings). x Growing season 1= May to Aug. and 2 = Sept. to Dec. w Mean separation within a column and cultivar by Tukey-Kramer (P ≤ 0.05); Means followed by the same letter within

columns are not different from one another.

39

Table 5. Marketable fruit weight, cost of seed, mulch, and pesticide application, and break-even analysis for three tomato cultivars

grown in two seasons in the Kamuli District, Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9m. y Costs were calculated by dividing the overall cost of the treatment by the number of plots that received the treatment. Data

obtained in Uganda Shillings and converted to US dollars (I USD = 2500 UGX, Uganda Shillings). x Break-even price = variable cost ÷ fruit weight. w Break-even yield = marketable fruit weight = variable cost ÷ price (Kamuli average price = 0.8 USD/kg). v GS = growing season 1= May to Aug. and 2 = Sept. to Dec.

Cultivar

Marketable

Fruit Weight

(Kg/sub-plotz)

Costsy (USD/sub-plot) Variable Cost

(USD/sub-plot)

Break-even

Pricex

(USD/sub-plot)

Break-even

Yieldw

(Kg/sub-plot) Seed Mulching Pesticide

Application

GSv GS GS GS GS GS GS

1 2 1 2 1 2 1 2 1 2 1 2 1 2

Heinz 1370 1.70 1.18 0.16 0.16 1.17 2.05 2.07 1.14 3.42 3.36 2.01 2.85 4.28 4.2

Nuru F1 2.71 4.25 1.00 1.00 1.17 2.05 2.07 1.14 4.25 4.19 1.57 0.98 5.32 5.2

MT 56 6.21 3.13 0.21 0.21 1.17 2.05 2.07 1.14 3.47 3.41 0.55 1.09 4.34 4.2

40

Table 6. Total and marketable fruit number, marketable fruit weight, and gross margin of tomatoes with or without staking in the

Kamuli District, Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9m; data represent all harvests across two seasons in 2013. y The gross margin was calculated by subtracting the costs of staking from the revenue accrued. Data obtained in Uganda Shillings

and converted to US dollars (I USD = 2500 UGX, Uganda Shillings). x Total fruit number represents the quantity of fruits harvested per plot. Marketable fruit is the number of fruits suitable for the

market. Marketable fruit weight is the kilograms of the marketable fruit per plot. w Mean separation by Tukey-Kramer (P ≤ 0.05); means followed by the same letter within columns are not different from one

another.

Treatment

Total Fruit

Number

(No./ sub-plotz)

Marketable Fruit

Number

(No./sub-plot)

Marketable Fruit

Weight

(Kg/sub-plot)

Gross Margin

(USD/sub-ploty)

Staking

Stake

68 ax, w

31 a

2.09 a

-0.96 a

No stake 64 a 31 a 1.95 a -0.51 b

NS NS NS 0.006

41

Table 7. Early blight severity assessed by area under disease progress curve (AUDPC) of three

tomato cultivars grown with or without pesticide application and in the Kamuli District,

Uganda, 2013.

z Sub-plots included 8 plants and a row length of 4.9m; data represent all area under disease

progress curve values across two seasons in 2013. y Growing season 1= May to Aug. and 2= Sept. to Dec. x Mean separation by Tukey-Kramer (P ≤ 0.05); means followed by the same letter within

columns are not different from one another. w AUDPC- Area under the disease progress curve was calculated using = Σ [(X

i+1 + X

i ) /

2][ti+1

- ti]; where X


thweek, t



week, n = the total number of observations.

Treatment

AUDPC (per sub-plotz)

Growing seasony

Heinz

Pesticide

1 2

3141 b x, w

1083 b

No Pesticide 3505 a 1468 a

Nuru

Pesticide

3210 b

1007 b


MT 56

Pesticide

2904 b

634 a


Ni - 1

i=1

42

Table 8. Early blight severity assessed by area under disease progress curve (AUDPC) of

tomatoes grown with or without staking or soil mulch in the Kamuli District, Uganda, 2013 in

in two growing seasonsz.

z Growing season 1= May to Aug. and 2= Sept. to Dec. y Sub-plots included 8 plants and a row length of 4.9m; data represent all area under disease

progress curve values across two growing seasons in 2013. x Mean separation by Tukey-Kramer (P ≤ 0.05); means followed by the same letter within

columns are not different from one another. w AUDPC- Area under the disease progress curve was calculated using = Σ [(X

i+1 + X

i ) /

2][ti+1

- ti]; where X


thweek, t



week, n = the total number of observations.

Treatment AUDPC (per ploty)

Staking

Stake 2172 ax, w

No stake 2188 a

P ≤ 0.05 NS

Mulching

Mulch 2167 b

No mulch 2192 a

P ≤ 0.05 0.0002

i=1

Ni - 1

43

CHAPTER 3. GENERAL CONCLUSIONS

Although challenged by plant and environmental factors, tomato production can diversify

the agricultural enterprises of small-landholder farmers in rural Uganda, especially in the

Kamuli District. The results of this study evaluated the horticultural practices of cultivars,

application of pesticides, staking, and mulching. Data from the experiment showed that the

application of pesticides reduced disease severity (early blight) in both seasons. The disease

resistant cultivar MT 56 had higher yield and gross margin than the susceptible, widely grown,

Heinz 1370. The difference in performance between these cultivars was expected because of

their genetic differences. ‘MT 56’ was bred for resistance against bacterial wilt, but also may

have exhibited tolerance to early blight disease. ‘Heinz 1370’ is susceptible to early blight, late

blight and bacterial wilt (Akemn et al., 2000; Maršić et al., 2005).

Staking did not affect the yield and disease severity of the tomato cultivars in both

seasons but using soil mulch increased yield, and reduced disease severity of early blight.

These results were expected because soil mulch acts as a barrier between the plant and fungal

spores (Hapaala et al., 2014).

Future Research

Due to limited access to quality seed, there is need for a reputable and certified seed

industry. An assessment of the current seed industry is needed with improvements to benefit

commercial horticultural vegetable production. Due to limited disease-tolerant cultivars,

further research should select more disease-tolerant cultivars to help farmers increase

production and profits in tomatoes. Because this study was completed under controlled

44

experiments, conditions might be different with farmer fields. Farmers also may not have

access to soil analysis and fertilizers to optimize soil fertility or to fungicides to control

diseases. Further studies could be done on small-landholder farmer fields so that it is more

pertinent to their situation.

Soil quality and climate data of all districts are not available in Uganda. Public efforts

should be made to gather and share accurate weather information and site-specific soil maps

for the Kamuli District. These data are needed to help small-landholder farmers and extension

agents plan their agricultural activities, determine integrated pest management strategies, and

make informed production decisions to sustainably produce tomatoes.

Literature Cited

Akemn, M.C., S.Kyamanywa, G. Luther, C. Ssekyewa, J.M. Erbaugh, and H. Warren. 2000.



2000/eam0106.pdf [26 Nov 2013].

Hapaala, T., P. Palonene, A. Korpela, and J. Ahorkus. 2014. Feasibility of paper mulches in

crop production: A review. Agri. Food Science. 23:60-79.

Maršić, K.N, J. Osvald, and M. Jakše. 2005. Evaluation of ten cultivars of determinate tomato

(Lycopersicum esculentum Mill.), grown under different climatic conditions. Acta Agri.

Slovenica. 85: 321-328.



45

APPENDIX

A. Assumptions for calculating the gross margin of treatments

B. Costs of production

Table 1. Costs of treatments, input and labor used in tomato production, Kamuli District,

Uganda, 2013.

Table 2. Additional variable costs of inputs and labor used in tomato production, Kamuli

District, Uganda, 2013.

C. Soil test results

i) Season one

ii) Season two

iii) Recommendations

46

Assumptions

1. All fixed costs, for example rent for land, were assumed to be equal for all treatments and

were not used in the calculation of the gross margin.

2. Costs of labor and inputs of transplant boxes, land preparation, transplanting, fertilizer

application, watering and were assumed to be equal for all treatments and were not included in

the calculation of gross margin.

47

Appendix Table 1. Costs of treatments, input and labor used in tomato production, Kamuli

District, Uganda, 2013.

z Costs were calculated using current input and labor costs in Butansi sub-county, Kamuli

District, Uganda, 2013, and were obtained in Uganda Shillings. Uganda Shillings were

converted to US dollars at the exchange rate of 1 USD = 2500 UGX. y Growing season 1= May to Aug. and 2 = Sept. to Dec. x Value is calculated by dividing the overall cost of the treatment by the number of plots that

received the treatment.

Treatments Costs USD/Sub-plotz

Growing seasony (1) Growing season (2)

Input Labor Input Labor

Cultivar (seed)

Heinz 0.16 x - 0.16 -

MT 56 0.21 - 0.21 -

Nuru F1 1.00 - 1.00 -

Pesticide application 1.26 0.81 0.69 0.44

Staking 0.56 0.16 0.07 0.33

Mulching 0.97 0.2 1.72 0.33

48

Appendix Table 2. Additional variable costs of inputs and labor used in tomato production,

Kamuli District, Uganda, 2013.

z Costs were calculated using current input and labor costs in Butansi sub-county, Kamuli

District, Uganda, 2013, and were obtained in Uganda Shillings. Uganda Shillings were

converted to US dollars at the exchange rate of 1 USD = 2500 UGX. y Growing season 1= May to Aug. and 2 = Sept. to Dec.

x Overall cost; not calculated per plot. w Value is calculated per plot, by dividing the overall cost of the treatment by the number of

plots that received the treatment.

Additional variable cost Costs USDz

Growing seasony (1) Growing season (2)

Input Labor Input Labor

Transplant boxesx 24.00 - - -

Raising transplants - 7.20 - 7.60

Land preparationw - 0.33 - 0.92

Transplanting - 0.12 - 0.18

Fertilizer application 1.85 0.31 2.07 0.12

Watering - 0.09 - 0.16

Harvesting - 0.03 - 0.01

49

Soil test results: season one

COLLEGE OF AGRICULTURAL AND ENVIROMENTAL SCIENCES

SCHOOL OF AGRICULTURAL SCIENCES

Department of Agricultural Production

The soil sample was first air dried, pounded in a mortar with pestle and screened

through a 2.00 mm sieve to remove any debris then subjected to analysis for a

spectrum of parameters.

Cu Zn Fe Mn

ppm(mg/kg)

1.3 2.35 186.2 52.6

Bonny Balikuddembe

Senior Laboratory Technician

Soil, Water and Plant Analytical Laboratory

pH

OM N P K Na Ca Mg %Sand Clay Silt

%age ppm cmoles/kg Texture

4.8 1.21 0.10 2.23 0.20 0.10 2.2 1.22 52.0 42.0 6.0

MAKERERE UNIVERSITY P. O .Box 7062 Kampala- Uganda

Cables: “MAKUNIKA”

E-mail:[email protected]

Fax: +256-414-531641

Phone: +256-414-533580

50

Soil test results: season two

COLLEGE OF AGRICULTURAL AND ENVIROMENTAL SCIENCES

SCHOOL OF AGRICULTURAL SCIENCES

Department of Agricultural Production

The soil sample was first air dried, pounded in a mortar with pestle and screened

through a 2.00mm sieve to remove any debris then subjected to analysis for a spectrum

of parameters.

pH OM N Av.P Ca Mg Na K %Sand %Clay %Silt

%age ppm cmoles/kg Texture

5.6 1.13 0.11 4.7 6.0 2.96 0.07 0.16 58.0 34.0 8.0

Cu Zn Fe Mn

ppm(mg/kg)

1.23 1.54 125.3 56.2

Bonny Balikuddembe

Senior Laboratory Technician

Soil, Water and Plant Analytical Laboratory

UNIVERSITY MAKERERE

P. O .Box 7062 Kampala- Uganda

Cables: “MAKUNIKA”

E-mail:[email protected]

Fax: +256-414-531641

Phone: +256-414-533580

51

Soil fertility recommendations:

PH: Preferred soil pH for production of most vegetables is in the range of 6.0-6.8. Your

soil needs liming to increase the pH and aid in the availability of nutrients such as calcium,

magnesium, and even N, P, and K. We need to bring the pH to around 6.5 for that this soil will

need 10,000 lb/A of CaCO3.

This recommendation is expressed in terms of 100% pure Calcium carbonate (CaCO3)

equivalent (CCE). It is assumed that the lime is fine (lime fineness of 50% - 70% through a 60

mesh screen) and will be incorporated to 6.75 inch tillage depth. If local lime does not meet

these criteria, use the following steps to adjust final recommendations:

Step 1: Select most appropriate lime type or purity and multiply the recommended rate

by the factor

(Lime Type, Purity)

Calcium Carbonate Multiplying Factor

90% to 110% (CCE or TNP) 1.00

80% to 89% 1.17

70% to 79% 1.33

60% to 69% 1.54

50% to 59% 1.81

100% pure CaCO3 (40% Ca) 1.00

52

Dolomitic Lime Multiplying Factor

50% CaCO3 + 50% MgCO3 (22%Ca + 15%Mg) 0.92

75% CaCO3 + 25% MgCO3 (31%Ca + 7% Mg) 0.96

Other Materials Multiplying Factor

*Calcium oxide (burnt lime) 0.56

*Calcium hydroxide (hydrated lime) 0.74

Granulated slag 1.00

*These materials may achieve the target soil pH in 1 to 12 days after application.

You also have to account for the screen size for lime:

Select the multiplying factor from the table below and multiply

the results from step 1 by this factor

% lime Passing Through

Screen Size

Multiplying Factor

100 Mesh 60 Mesh

80-100 95-100 0.80

60-79 70-94 0.85

40-59 50-69 1.00

30-39 50-69 1.25

20-29 30-39 1.45

10-19 20-29 1.70

0-9 0-19 2.00

This will get you the final lime application rate for your plot.

53

Organic matter and Nitrogen: Organic matter is low (1.1%). Generally 1% of organic

matter is expected to release up to 20 pounds of nitrogen per acre starting mid to late summer.

One should credit this nitrogen to the soil and adjust nitrogen application rate accordingly. In

this case with 1.1% organic matter you can expect 22 lbs/A of nitrogen release. One thing to

keep in mind is that this nitrogen is not available at once. It would depend upon factors such as

soil temperature, drainage, and soil microbial activity. The nitrogen requirement for tomato

crop is 130lb nitrogen/A in low organic matter soil (1/2 broadcast, 1/2 sidedress when fruit

appears). Some of the sources that you can use: Urea (46% N), Liquid nitrogen (UAN; 30%

N), Ammonium sulfate (21% N), or Ammonium nitrate (33.5% N). I believe urea would be the

cheapest and easily available N source for you. If using urea then: Broadcast 141 lb/A urea at

planting followed by side-dressing of 141 lb urea when fruit appears.

I would recommend supplementing fertilizer with compost, if it is available. Typically

vegetable growers would apply 2-5 tons of compost per acre. In case you use compos, then

determine the N content in compost and then assume that 25% of that N will be available the

first year. Adjust your fertilizer rate accordingly.

Phosphorous (P): Soil P is low. For tomato production you would need to apply around

200lb/A of P2O5 (note it is P2O5 not P; this makes it easy as fertilizers formulations are N-

P2O5-K2O). Sources of P2O5 could be MAP (Monoammonium phosphate) or DAP

(Diammonium phosphate). DAP is usually 18-46-0. In case you are using DAP apply 435 lb/A

of DAP at planting.

Potassium (K): Soil K was expressed in cmoles/kg and I multiplied it by 10 to make it

mmoles/kg and then its molar mass (39) to convert it to mg/kg, which is ppm. In this soil I

would recommend applying 200lb/A of K2O: Commonly available formulations are 0-0-50

54

(Potassium sulfate) and 0-0-60 (Muriate of Potash). If using 0-0-50, apply 400 lb of that

fertilizer.

Zinc (Zn): Optimum level of Zinc for vegetable production is ‘more than 0.7 ppm’.

Usually Zinc deficiencies are not common in acid soils. Your soil levels for Zinc are optimum.

Calcium (6.0 cmoles/kg): I converted cmoles/kg to ppm and it came to 2400 ppm.

These levels are normal.

Magnesium (2.96 cmoles/kg): I converted cmoles/kg to ppm and it came to 710 ppm.

This level is high but fine.

Iron (125.23 ppm). It is in the high range (basically due to low soil pH), but ok.

Copper: Responses to copper by crops on mineral soils (loams, clay loams, etc.) have not

been demonstrated; therefore, copper fertilizer is not recommended for crops grown on mineral

soils.

I hope this information assists you in optimizing soil nutrient levels. Please feel free to

contact me if you have additional questions/queries/or suggestions. You can also call me on my

cell phone 517-898-5349.

Sincerely,

Ajay Nair

Assistant Professor & Vegetable Extension Specialist Department of Horticulture, Iowa State

University Phone: 515-294-7080 Email: [email protected]

http://www.extension.iastate.edu/vegetablelab http://iowavegetables.blogspot.com/

evaluating horticultural practices for sustainable tomato

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