indigenous soil and water conservation techniques: effects on runoff, erosion, and crop yields under...

P u b l i s h i n g

Australian Journal of Soil ResearchCSIRO PublishingPO Box 1139 (150 Oxford St)Collingwood, Vic. 3066, Australia

Telephone: +61 3 9662 7628Fax: +61 3 9662 7611Email: [email protected]

Published by CSIRO Publishing for CSIRO and the Australian Academy of Science

w w w . p u b l i s h . c s i r o . a u / j o u r n a l s / a j s r

All enquiries and manuscripts should be directed to:

Volume 40, 2002© CSIRO 2002

Australian Journalof Soil Research

An international journal for the publication oforiginal research into all aspects of soil science

Aust. J. Soil Res., 2002, 40, 367–379

© CSIRO 2002 0004-9573/02/03036710.1071/SR01037

Indigenous soil and water conservation techniques: effects on runoff, erosion, and crop yields under semi-arid conditions

I. I. C. WakindikiA and M. Ben-HurBC

ADepartment of Soil Science, Egerton University, PO Box 536, Njoro, Kenya.BInstitute of Soil, Water and Environmental Sciences, The Volcani Center,

Agricultural Research Organization, PO Box 6, Bet Dagan, 50250, Israel.CCorresponding author; email: [email protected]

A joint contribution from the Department of Soil Science, Egerton University, PO Box 536, Njoro, Kenya, and the Agricultural Research Organization, the Volcani Center, Israel, No. 603/01, 2001 series.

Abstract

Smallholder farmers in arid and semi-arid regions use indigenous soil and water conservation (ISWC)techniques, such as trash lines and stone lines spaced about 15 m apart across the slope. This work evaluatedthe effects of size of trash lines and decreasing the space between trash or stone lines to 2 m on runoff,erosion, and corn and cowpea yields. Big trash line (BTL), small trash line (STL), and stone line (SL)techniques, and a control (no ISWC technique) were evaluated in 12 runoff plots (2 by 6 m each) with 10%slope in a semi-arid area in Kenya, during 5 consecutive rainy seasons. The ISWC techniques significantly(P ≤ 0.05) decreased runoff and soil loss, and increased corn and cowpea yields, compared with the controltreatment in most of the rainy seasons. The BTL was, in general, the most effective technique; no consistentdifferences were found between the STL and SL techniques. In BTL, STL, SL, and control, the seasonalaverage runoff for each treatment was 25, 31, 29, and 51 mm, respectively; the seasonal average soil losswas 0.23, 0.33, 0.3, and 0.67 Mg/ha, respectively; and the seasonal average biomass (grain and stover ofcorn and cowpea) was 4.8, 4.0, 4.0, and 2.5 Mg/ha, respectively. The seasonal biomass increased linearlyand significantly (P ≤ 0.01) with increasing water infiltration. As more water infiltrated, more water wasavailable for crop production, and the yield was higher.

Additional keywords: trash lines, stone lines, steep land, seal formation.

SR01037Soil and water conservati on ef fects on r unoffI . I. C W aki ndi kiandM Ben- HurI . I. C Waki ndikiand M. Ben- Hur

Introduction

Runoff and soil erosion are serious and widespread land degradation problems in manyparts of the world (Hudson 1992). In Kenya, runoff and soil erosion have been identified asmajor factors in low crop yields since the 1930s, through loss of water (Maher 1937, 1946;Tiffen et al. 1994) and plant nutrients (Gachene et al. 1997), and reduction in effectiverooting depth (Gachene 1995). The problems are severe in semi-arid regions because erraticrainfall, long dry periods, and poor vegetation cover (Thomas et al. 1997) expose the soilsurface to water erosion.

To combat the massive problems of runoff and erosion, poor smallholder farmers in aridand semi-arid regions often use inexpensive, indigenous soil and water conservation(ISWC) techniques (Hallsworth 1987; Ostberg 1988). Critchley et al. (1994) observed thatISWC techniques aim to conserve soil and water in situ and allocated them to 6 categories,based on the type of technology: grass strips, trash lines, pits, earth bunds, stone lines, andprotection ditches.

Inventories of ISWC techniques abound in the literature (Hallsworth 1987; InternationalFund for Agricultural Development 1992; Kerr and Sanghi 1992; Roose 1992; Reij et al.1996). Many of these studies recognised the usefulness of ISWC techniques to the poor

368 I. I. C. Wakindiki and M. Ben-Hur

smallholder farmers and lamented the scarcity of quantitative investigations (Chambers1983; Richards 1985; Willcocks and Twomlow 1993; Wakindiki et al. 1998). A few isolatedstudies that focused on soil moisture conservation by the pitting technique indicated thatcrop yields increased in treated plots compared with the controls. For example, in a semi-arid region in Kenya, Gichangi et al. (1992) harvested 0.81 Mg/ha of cowpea grain intreated plots and 0.31 Mg/ha in untreated plots, under seasonal rainfall of 330 mm. In Niger,Hassan (1996) obtained 0.4 Mg/ha of millet grain from untreated plots and 1 Mg/ha fromtreated plots. In Mali, where the seasonal rainfall of 538 mm fell in 35 days, Wedumet al. (1996) obtained 1.49 Mg/ha of sorghum grain from treated land compared with0.39 Mg/ha from untreated land.

The trash line technique uses lines made of crop material that remains after harvestingthe grains or pulses. The material is formed into ridges across the slope, and these ridgesare sometimes modified by the inclusion of logs or pegs (Gichuki 1992; Silitoe 1993). Thestone line technique, in which stones are arranged in lines across the slope, is used wherestones are abundant on the soil surface. Trash lines allow water to infiltrate into the soil inthe area directly beneath them, and the trash rots after a few seasons, thus adding organicmatter to the soil.

The trash and stone line techniques both form semi-permeable barriers across the slopethat decrease the surface runoff velocity and increase the infiltration duration of theimpounded water, but allow passage of excess runoff. As a result, the amount of infiltratedwater increases and the runoff volume and its erosive power decrease. Likewise, retentionof sediment in the trash and stone lines results in reduced soil and nutrient losses (Gacheneet al. 1997).

Gichuki (1992) observed that farmers in Kenya placed the trash or stone lines about15 m apart in the field. However, in semi-arid regions, seal formation is common(Kemper and Miller 1974), decreasing the infiltration rate and increasing runoff andsoil erosion (Ben-Hur et al. 1985a). The raindrop impact energy causes the soil surfacestructure to break down and consequent seal formation. This seal is thin (few millimeters)and is characterised by greater density, higher strength, finer pores, and lowersaturated conductivity than the underlying soil (McIntyre 1958; Evans and Buol 1968).Under seal-formation conditions, the 15-m spacing between the trash or stone lines isprobably too large to prevent surface runoff and soil erosion in the cultivated field duringrainstorms.

In a semi-arid region in eastern Kenya, Okoba et al. (1998) observedsignificant reductions in runoff and soil erosion in Luvisols protected by trash andstone line techniques when the spacing between the lines was reduced to 7.5 m.Furthermore, when the trash line technique was applied under seal-formationconditions, it limited seal formation under the line, so that surface runoff flowing across thearea between the trash lines could infiltrate beneath the trash, thus decreasing the totalrunoff.

It was hypothesised that decreasing the spacing between the trash and stone lines to 2 mwould significantly increase the efficiency of these ISWC techniques in reducing runoffand erosion and in increasing crop yield under seal formation conditions. Moreover, in thiscase, 2 rows of plants are sown between the trash lines to attempt to optimise any benefitsfrom the water that infiltrates in the trash-covered area. The objective of the present workwas to study the effects of decreasing the space between the trash and stone lines to 2 m andof the size of the trash lines on runoff, erosion, and crop yield during consecutive rainyseasons under semi-arid conditions.

Soil and water conservation effects on runoff 369

Materials and methods

Site description

The experiment was conducted at Tunyai, Kenya. The site is located at approximately 37°50´E and 0°2´S.The long-term average annual rainfall in this region is 600 mm, which is distributed almost equally between2 rainy seasons: March–May and second October–December, referred to below as Seasons 1 and 2,respectively. The annual average precipitation in this region is 40–50% of the potential evaporation. Rain-fed smallholder subsistence agriculture is the dominant land use in this region.

A soil profile was opened in the experimental site, and was described according to soil taxonomyguidelines (Food and Agricultural Organisation 1977) and soil color charts (Munsell Color Company1971). Soil samples were collected from each main horizon and their physical and chemical properties(Table 1) were determined. The soils at the site are classified as Rhodic Ferralsols (Food and AgriculturalOrganisation 1990) or Rhodic Eutrustox (Soil Survey Staff 1998) and the soil profile was deep and welldrained. The dominant clay in the studied soil was kaolinite with small amount of gibbsite. This soilmineralogy was determined by X-ray diffraction method (Whittig 1965). Soil texture was determined bymeans of the hydrometer method (Day 1965) after pretreating the samples with 30% hydrogen peroxide andshaking them in calgon solution overnight. The soil chemical properties were determined according toHinga et al. (1980). The pH was measured at a soil : water ratio of 1 : 2.5.

The land at the experimental site had previously lain fallow for about 5 years, being used for cattlegrazing. In February 1997, this land was cleared and cultivated with hand tools. A cutoff drain was dugabove the experimental site to prevent surface runoff from higher ground from entering the experimentalarea. Twelve runoff plots measuring 2 m by 6 m each were constructed along a contour on a 10% slope;they were separated from each other by buffer zones about 2 m wide. Each plot was enclosed by galvanisediron sheets embedded 0.2 m into the ground and projecting 0.2 m above it, and an end plate was installedat the end of each plot to block the runoff and direct it into a trough. Each trough was covered with a lid toprevent direct entry of rainfall. The trough delivered the runoff into a 1-m3 tank via a conveyor pipe. Thisdesign was similar to that used by Gachene et al. (1997). The tanks containing runoff were emptied eachmorning. The runoff in each tank was mixed thoroughly and 3 subsamples were taken to determine theamount of soil loss by weighing the sediment after oven drying at 105°C. The daily rainfall was recordedwith a rain gauge at the nearby Tunyai meteorological station.

Experimental design

Four treatments, each with 3 replicates, were randomly assigned to the runoff plots. The treatments were:(1) big trash lines (BTL)—trash lines 0.6 m wide and 0.3 m high, with total trash content of 2.5 Mg/ha;(2) small trash lines (STL)—trash lines 0.3 m wide and 0.15 m high, with total trash content of 1.5 Mg/ha;(3) stone lines (SL)—stone lines 0.3 m wide and 0.15 m high; and (4) control—no ISWC technique applied.All the trash and stone lines constructed in the respective runoff plots in these treatments were alignedacross the slope at a 2-m spacing.

Agronomic aspects (e.g. time of planting, plant population, seed varieties, etc.) at the experimentalsite were in accordance with the local practices and conditions. No inorganic fertilisers were added, but5 Mg/ha of farmyard manure was added at the beginning of each season. Seeds were planted just before orafter the first rainstorm in each rainy season. Katumani composite, a drought-escaping corn (Zea mays L.)variety, was planted as a sole crop during the first season of each year of the study. The spacing betweenthe corn plants was 0.25 m within the rows and 0.75 m between the rows. Two rows were planted betweenthe trash or stone lines, in the plots where these techniques were applied. In the second season in each yearof the study, corn was intercropped with cowpea (Vigna unguiculata) variety M66 in all the treatment plots.A single row of this crop was planted between the 2 rows of corn at a spacing of 0.25 m within the row. Theplant rows and spacing between the plants in the control treatment were the same as in the trash and stoneline treatments. All plots were kept free of weeds by hand hoeing during the rainy seasons. At the end ofeach season, the crop was harvested by hand and the dry weights of crop grains and stover from each plotwere determined.

Statistic analyses

Data were analysed as a complete randomised design using procedures described by Steel and Torrie (1981)for analysis of variance. Separation of means was tested using Turkey’s honestly significant difference witha P = 0.05 significant level.


Tab

le 1

.S

ome

ph

ysic

al a

nd

ch

emic

al p

rop

erti

es o

f th

e so

il p

rofi

leC

EC

, cat

ion

exch

ange

cap

acit

y; O

C, o

rgan

ic c

arbo

n

Hor

izon

Dep

th (

m)

Bou

ndar

yC

olou

rTe

xtur

eC

utan

sS

truc

ture

Pore

sC

onsi

sten

cyO

ther

s

Ap

0–0

.25

Cle

ar w

avy

2.5

YR

¾,

redd

ish

brow

nC

lay

Nil

Mod

erat

e fi

ne

crum

byM

any

very

fin

e, f

ine,

m

ediu

m, a

nd c

oars

eS

ligh

tly h

ard;

ver

y fr

iabl

e; s

ligh

tly s

tick

y,

slig

htly

pla

stic

Man

y ro

ots

B1

0.25

–0.5

5G

radu

al

smoo

th2.

5 Y

R ¾

, dar

k re

ddis

h br

own

Cla

yN

ilM

oder

ate

med

ium

sub-

angu

lar

bloc

kyM

any

very

fin

e an

d fi

ne,

few

med

ium

and

coa

rse

Har

d; f

riab

le; s

ligh

tly

stic

ky, s

ligh

tly p

last

icS

ligh

tly

com

pact

B2

0.55

–1.2

10 Y

R ¾

, dus

ky

red

Cla

yV

ery

fine

pa

tchy

and

th

in c

lay

Wea

k m

ediu

m

sub-

angu

lar

bloc

kyM

any

very

fin

e, f

ine,

and

m

ediu

m, f

ew c

oars

eS

ligh

tly h

ard;

ver

y fr

iabl

e; s

ligh

tly s

tick

y,

slig

htly

pla

stic

Non

e

Dep

thS

and

Sil

tC

lay

CE

CpH

OC

NP

KC

aM

gN

a(m

)(g

/kg)

cmol

(+)/

kg(H

2O)

(g/k

g)(m

g/kg

)(c

mol

(+

)/kg

)

0–0.

2516

024

060

018

5.7

9.0

0.9

0.8

0.19

2.62

1.52

0.05

0.25

–0.5

510

022

068

020

6.1

8.5

0.5

0.9

0.28

3.0

1.88

0.09

0.55

–1.2

120

180

700

155.

95.

90.

40.

90.

222.

92.

080.

1


Results and discussion

Seasonal distribution of rain and runoff

The distribution of daily rainfall for 5 consecutive rainy seasons is presented in Fig. 1. Thepattern of rainfall distributions over the 5 seasons showed marked variations in bothfrequency of storms and amount of rainfall. The 2 rainy seasons in 1997 showed a normaldistribution pattern of daily rainfall. In Season 1, a peak of 78 mm rainfall was reached on12 April; the total rainfall in this season was 507 mm, which was 44% higher than the long-term average (Fig. 1). In Season 2 of 1997, daily rainstorms increased in magnitude as theseason progressed and a peak of 91 mm rainfall was reached on 13 November. The totalrainfall in this season was 1334 mm, which was 4.3 times greater than the long-termaverage.

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

Date

Date

First season Second season

1997 1997

1998 1998

1999

Rai

nfal

l (m

m)

01.iii 31.iii 30.iv 30.v

01.x 31.x 30.xi 30.xii

Fig. 1. Distribution of daily rainfall for five consecutive rainy seasons.


The daily rainfall distribution in Season 1 of 1998 exhibited an ‘M’ pattern (Fig. 1). The2 daily rainfall peaks were 94 mm on 20 March and 80 mm on 9 May; the total rainfall inthis season was 611 mm, which was 73% higher than the long-term average. The totalrainfall in season 2 of 1998 was 253 mm, which was similar to the long-term average value;in this rainy season, 79% of the rainfall fell in 14 out of the 18 rainy days in November, and2 daily rainstorms occurred in December. The rainfall distribution in this season did notshow a clear peak.

Rainfall distribution during Season 1 of 1999 was skewed towards the end of the season(Fig. 1). The total rainfall in this season was 243 mm, which was similar to the long-termaverage. These significant variations in rainfall distribution among the various rainyseasons are typical of a semi-arid region.

Daily runoff during the 5 rainy seasons and for the various treatments is presentedin Fig. 2, as percentages of daily rainfall. In general, the changes in runoff percentagewith time showed similar patterns in all the treatments, and the runoff percentage inthe control treatment was higher, in most cases, than those in the ISWC treatments(Fig. 2). These differences between the control and the ISWC treatments are discussedbelow.

Runoff was generated by 5, 6, 5, 2, and 2 storms during the 5 consecutive rainy seasons(Fig. 2). Generally, daily runoff was associated with rainfall >30 mm on that day (Figs 1 and2), but on some days rainfall >30 mm did not generate runoff. For example, during Season2 in 1997, rainfall generated runoff on only 6 of the 16 days on which it exceeded 30 mm.Subjecting the soil from the experimental site to simulated rainfall revealed that theinfiltration rate of this soil decreased as cumulative rainfall increased, until a finalinfiltration rate of 20.5 mm/h was reached (Wakindiki and Ben-Hur 2002). This decreaseof the infiltration rate was a result of seal formation. In the rainstorms that did not generaterunoff, it is likely that the low rainfall intensity of these rainstorms was below theinfiltration rate and/or that the water storage capacity of the soil surface could acceptenough water to prevent runoff.

In Season 1 of 1997, the runoff started in the second rainstorm of 43 mm (Figs 1 and 2).The next rainstorm that generated runoff was on 4 April; the rainfall depth of this rainstormwas the greatest of the season, 78 mm (Fig. 1). After that date, the runoff percentagedecreased, in general, with time. The rainstorms that generated runoff after 4 Aprilprecipitated 44, 34, and 42 mm and the runoff percentages that were obtained from theserainstorms in the control treatment were 30, 16, and 19%, respectively.

In the Season 2 of 1997, the runoff started on 4 October, when the day’s rainfall was55 mm (Figs 1 and 2). After this date, the runoff percentage increased with time up tohighest value (54% in the control treatment) in the day’s rainfall of 91 mm, which was thegreatest rainfall depth of that season. After that day’s rainfall, the runoff percentages in thecontrol treatment decreased to 22, 18, and 17%, from rainstorms of 61, 57, and 59 mm,respectively.

In Season 1 of 1998, the highest runoff percentage (32% in the control treatment) wasobtained from a day’s rainfall of 94 mm, which was the second rainstorm of that season(Figs 1 and 2). One day later, a day’s rainfall of 45 mm generated 9% runoff in the controltreatment. After this rainstorm, no runoff was obtained during a long period until April 28;during this time 184 mm of rainfall fell within 17 days (Figs 1 and 2). Of the remainingrainstorms of that season, runoff was generated only by rainstorms of 47, 36, and 80 mm,and the runoff percentages in these rainstorms for the control treatment were 9.3, 6.6, and16.4%, respectively.


During the last 2 rainy seasons, rainstorms on only 2 days in each season generatedrunoff (Fig. 2). In season 2 of 1998, these rainstorms were fairly near the beginning of thecrop-growing season (4 and 17 November) (Fig. 1). In contrast, the 2 rainstorms thatgenerated runoff in Season 1 of 1999 fell towards the end of the crop-growing seasons, on7 and 12 May.

In Seasons 1 and 2 of 1997 and Season 1 of 1998, in which runoff was generated both atthe beginning and the end of the growing season, the runoff percentages in the control

0

15

30

45

0

20

40

60

0

10

20

30

40

0

2

4

6

8

Run

off (

%)

Date

First season

1999

1998

Second season

0

2

4

6

8

10

Control

Big trash lines

Small trash lines

Stone lines

Date

1997 1997

1998

26.iii 31.iii 5.iv 10.iv 15.iv 20.iv 25.iv 7.x 17.x 27.x 6.xi 16.xi 26.xi 6.xii

3.xi 5.xi 7.xi 9.xi 11.xi 13.xi 15.xi 17.xi16.iii 26.iii 5.iv 15.iv 25.iv 5.v 15.v

6.v 7.v 8.v 9.v 10.v 11.v 12.v

Fig. 2. Daily runoff as percentages of daily rainfall during the five rainy seasons and for thevarious treatments.


treatment early in the growing seasons were significantly higher than those towards theirends (Fig. 2). This was in spite of the fact that the rainfall amounts late in the growingseason were similar to or greater than those at the beginning (Fig. 1). These differences inrunoff percentages between the beginning and end of the growing season could be due tothe effect of the crop canopy on seal formation. At the beginning of the growing season, thecrop canopy was sparse and most of the soil surface was exposed. Under these conditions,the raindrop impact probably broke down the aggregates at the soil surface, so forming aseal, which, in turn, decreased the infiltration rate and increased the runoff (Fig. 2).However, the drying of the seal between consecutive rainstorms breaks down the crust,resulting in an increase in the soil infiltration rate (Ben-Hur et al. 1985b). In contrast,towards the end of the growing season, the crop canopy was extensive and most of the soilsurface was covered and protected against the raindrop impact. In this case, the renewal ofthe seal and the resulting decrease in the infiltration rate were probably limited. This couldexplain the relatively low runoff percentages towards the end of the growing season (Fig. 2).

The seasonal rainfall depths, and the cumulative depths and percentages of the runoff inthe various treatments during the 5 rainy seasons, are presented in Table 2. The runoff depthin the control treatment ranged from 6 mm in Season 2 of 1998 to 115 mm in Season 2 of1997, and the runoff percentage in this treatment was highest (14.5%) in Season 1 of 1997and lowest (2.5%) in Season 2 of 1998. This wide variation among the rainy seasons in therunoff percentages was most likely caused by the wide variation in the rainfallcharacteristics, such as rainstorm depth, intensity, and frequency.

Effects of ISWC techniques

The BTL, STL, and SL techniques significantly decreased the runoff compared with thecontrol treatment in all the rainy seasons (Table 2). In most of the seasons the plots treatedwith the BTL technique had significantly less seasonal runoff than the rest of the ISWCtechniques that were studied. Likewise, the SL technique was, in general more efficient indecreasing the runoff than the STL technique (Table 2).

The mechanism that could account for the reduction in the runoff by the studied ISWCtechniques is that both the trash and stone lines decreased the runoff velocity along theslope, thus, in turn, increasing the duration of infiltration and the amount of infiltratedwater. Also, with the BTL and STL techniques, the trash that covered the soil surfacereduced seal formation and increased the infiltration rate in the area beneath the trash; inthese cases, the high infiltration rate in the area beneath the trash decreased the total runofffrom the treated plot. The lower runoff that was obtained with the SL technique than withthe STL technique (Table 2) indicated that the small lines of trash in the latter techniquewere not efficient in decreasing the runoff velocity or in increasing the infiltration rate in

Table 2. Seasonal rainfall and runoff in five rainy seasons and various treatmentsWithin rows, values followed by the same letters are not significantly different at P = 0.05

Season Rainfall Control Big trash lines Small trash lines Stone lines(mm) (mm) (%) (mm) (%) (mm) (%) (mm) (%)

1, 1997 507 73a 14.5 51c 10 48c 9.4 64b 12.62, 1997 1334 115a 8.6 46d 3.7 71b 5.3 57c 4.21, 1998 611 54a 8.9 27c 4.3 31b 5.0 21d 3.52, 1998 253 6a 2.5 2b 0.6 2b 0.9 1d 0.31, 1999 243 7a 2.9 1b 0.5 2b 0.8 1b 0.5


the area below the trash. However, the larger size of the trash line in the BTL techniqueincreased these efficiencies.

Seasonal soil losses in the various rainy seasons and under the various treatments arepresented in Table 3. The soil losses in the control treatment were relatively high, rangingfrom 0.47 Mg/ha in Season 1 of 1999 to 0.84 Mg/ha in Season 2 of 1997 (Table 3). All theISWC techniques significantly (P ≤ 0.05) decreased the soil loss compared with the controltreatment during all the rainy seasons. The lowest soil losses in all the rainy seasonsoccurred with the BTL technique; however, no significant differences in soil losses betweenthe STL and SL techniques were found except during Season 2 of 1997 (Table 3). Theaverage soil loss over the 5 rainy seasons was greater in the control treatment than in theBTL, STL, and SL treatments by factors of 2.8, 2.1, and 2.2, respectively (Table 3).However, the average runoff over the 5 rainy seasons was greater in the control treatmentthan in the BTL, STL, and SL treatments by factors of 2.0, 1.7, and 1.8, respectively(Table 2). These results indicate that the effect of the ISWC techniques in decreasing soilloss was not only by reduction of the surface runoff. Trapping of the sediments as the excessrunoff passed through the trash and stone lines used in the ISWC techniques was probablyanother mechanism that decreased the soil loss.

The yields, of grain and stover, of corn and cowpea in the various rainy seasons andunder various treatments are presented in Table 4. Cowpea was grown as an intercrop onlyin Seasons 2 of 1997 and 1998; therefore, Table 4 presents the cowpea yields only for thoseseasons. The grain yield of corn in the control treatment ranged from 0.16 Mg/ha in Season

Table 3. Seasonal soil loss (Mg/ha) for the various rainy seasons and treatmentsWithin rows, values followed by the same letters are not significantly different at P = 0.05

Season Control Big trash lines Small trash lines Stone lines

1, 1997 0.69a 0.26c 0.44b 0.42b2, 1997 0.84a 0.43c 0.53b 0.36d1, 1998 0.56a 0.15c 0.21b 0.22b2, 1998 0.79a 0.24c 0.35b 0.35b1, 1999 0.47a 0.09c 0.10b 0.14b

Table 4. Seasonal yields (Mg/ha) of corn and cowpea in the five rainy seasons and under the various treatments

Within rows, values followed by the same letters for grain or stover are not significantly different at P = 0.05

Season Control Big trash lines Small trash lines Stone linesGrain Stover Grain Stover Grain Stover Grain Stover

Corn

1, 1997 0.42b 1.25b 0.74a 2.1a 0.54b 2.02a 0.48b 1.92a2, 1997 0.56c 1.42c 1.22a 4.2a 0.84b 3.82b 0.89b 3.65b1, 1998 0.54c 1.49c 1.47a 3.2a 0.86b 2.52b 1.28a 2.63b2, 1998 0.25d 0.65c 1.11a 2.84a 0.66c 1.51b 1.0b 1.65b1, 1999 0.16b 0.67b 0.42a 0.86a 0.46a 0.84a 0.41a 0.9a

Cowpea

2, 1997 0.44b 2.09a 0.56a 2.05a 0.41b 2.16a 0.42b 2.0a2, 1998 0.56c 1.94d 0.94a 2.39b 0.84b 2.55a 0.84b 2.2c


1 of 1999, with seasonal rainfall of 243 mm, to 0.56 Mg/ha in Season 2 of 1997, withseasonal rainfall of 1334 mm (Tables 2 and 4). The same general trend was found in thestover yield of the corn in this treatment. The grain yields of cowpea in the control treatmentwere 0.44 and 0.59 Mg/ha in Season 2 of 1997 and 1998, respectively, and their stoveryields were 2.09 and 1.94 Mg/ha, respectively (Table 4).

The total crop biomass (grain plus stover of corn and cowpea) in the consecutive rainyseasons was 1.67, 4.51, 2.03, 3.43, 0.83 Mg/ha, respectively, in the control treatment(Table 4). The rainfall efficiency, with respect to water use, could be defined as the ratiobetween the crop biomass and the rainfall depth during the growing season. In the controltreatment, the rainfall efficiencies in the consecutive rainy seasons were 3.3, 3.4, 3.3, 13.5,and 3.4 Mg/mm, respectively. These results indicate that the rainfall efficiencies in thevarious rainy seasons were similar, except that in Season 2 of 1998, which was much higher.This high rainfall efficiency in Season 2 of 1998 was probably a result of the low seasonalrainfall (253 mm) and the highly uniform distribution of the rainstorms, particularly in theearly part of this growing season (Fig. 1). This apparently ensured the presence of enoughavailable water for the establishment and growth of plants in critical stages.

All the ISWC techniques significantly increased the corn yield in all the rainyseasons except for the STL and SL techniques in Season 1 of 1997. The highest yield inall the rainy seasons, except Season 1 of 1999, was obtained with the BTL technique.However, no consistent differences in corn yield between the STL and SL techniques werefound.

In contrast, for the cowpea, the BTL treatment significantly increased the grain yield inthe 2 growing seasons, but it increased the stover yield significantly only in Season 2 of1998. Likewise, the STL and SL techniques significantly increased the grain and stoveryields of the cowpea in Season 2 of 1998, but had no significant effect on the cowpea yieldin Season 2 of 1997.

The total biomass yields with the BTL technique in the consecutive rainy seasons were1.7, 1.8, 2.3, 2.1, and 1.5 times higher than those in the control treatment (Table 4). Thesame trend in the increase of the biomass yield relative to the control was found in the STLand SL treatments. These results indicate that the ISWC techniques were most effective inincreasing the yields in Seasons 1 and 2 of 1998. This high effectiveness of the ISWtechniques was probably a result of the rainfall distribution, i.e. rainfall depth and intervalsbetween the rainstorms, in Seasons 1 and 2 of 1998.

A possible reason for the increased crop yields in the ISWC treatments is the lowerrunoff in the plots where the ISWC techniques were applied, which in turn, increased thewater infiltration in these plots (Table 2). Seasonal biomass yields as functions of theseasonal infiltrated water in the various treatments and rainy seasons, and the regressionline between these variables are presented in Fig. 3. This Figure indicates that the seasonalbiomass increased linearly and significantly (P ≤ 0.01) with increasing water infiltration:the more the water infiltration, the more the water available for crop production and higherthe yield. However, the scatter of the points around the regression line, especially for thelow values of water infiltration, was relatively high (Fig. 3). This wide scatter of the pointswas a result of the effect of the rainfall distribution on the rainfall efficiency and of theeffectiveness of the ISWC techniques in increasing the yield.

Conclusions

(1) Runoff, in general, was associated with daily rainstorms >30 mm. This runoff wasprobably associated with seal formation that decreased the infiltration rate of the soil.


(2) The runoff percentages in the control treatment were, in general, significantly(P ≤ 0.05) higher in the early part of the growing seasons than towards the end. Thiswas apparently because early in the growing season, most of the soil surface was bareand exposed to the raindrops that formed a seal and led to a low infiltration rate. Incontrast, towards the end of the growing season, the crop canopy was dense, and soprotected the soil surface from impacts and limited the renewal of the seal andincreased runoff.

(3) The BTL, STL and SL techniques, with 2-m space between the lines, significantly(P ≤ 0.05) decreased the runoff and soil loss compared with the control treatment inall the rainy seasons studied. These treatments probably decreased the runoff velocityalong the slope, which in turn, increased the duration of infiltration and the amount ofinfiltrated water. Also, the trash lines limited the seal formation in the area beneaththem, which led to increased infiltration and decreased runoff. The decrease in soilloss was due to the action of the trash and stone lines in reducing runoff and in trap-ping the sediments.

(4) The BTL, STL, and SL techniques increased the crop yield significantly (P ≤ 0.05).The seasonal biomass yield in all the treatments increased linearly and significantlywith an increasing water infiltration. This indicated that the main reason for theincreased crop yield in the ISWC treatments was the lower runoff in theses treatmentsthat increased the available water for crop production.

Acknowledgments

The authors thank E. Njeru for assisting in fieldwork and Dr A. P. Gonzalez from thefaculty of Sciences, University of La Coruna, Spain for the mineralogy analysis. TheGerman Academic Exchange Service (DAAD) and the International Foundation forScience (IFS) provided financial supports which are gratefully acknowledged.

References

Ben-Hur M, Shainberg I, Bakker D, Keren R (1985a) Effect of soil texture and CaCO3 content on waterinfiltration in crusted soils as related to water salinity. Irrigation Science 6, 281–284.

Ben-Hur M, Shainberg I, Keren R, Gal M (1985b) Effect of water quality and drying on soil crustproperties. Soil Science Society of America Journal 49, 191–196.

y = 0.004x + 1.71

r 2 = 0.37

0

2

4

6

8

10

0 200 400 600 800 1000 1200 1400

Seasonal infiltrated water (mm)

Bio

mas

s yi

eld

(Mg/

ha)

Fig. 3. Seasonal biomass yield as functions of the seasonal infiltrated water and the regression line for the various treatments and rainy seasons.


Chambers R (1983) ‘Rural development: Putting the last first.’ (Longman: London)Critchley WRS, Reij C, Willcocks TJ (1994) Indigenous soil and water conservation: A review of the

state of knowledge and prospects for building on traditions. Land Degradation and Rehabilitation 5,293–314.

Day PR (1965) Particle fractionation and particle size analysis. In ‘Methods of soil analysis. Part 1’. (Ed.CA Black) pp. 545–567. Agronomy Monograph No. 9. (American Society of Agronomy: Madison, WI)

Evans DD, Buol SW (1968) Micromorphological study of soil crusts. Soil Science Society of AmericaProceedings 32, 19–22.

Food and Agricultural Organization (1977) ‘Guidelines for soil profile description.’ (FAO: Rome)Food and Agricultural Organization (1990) ‘Soil map of the world. Revised legend.’ World Resources

Report 60. (FAO: Rome)Gachene CKK (1995) Effect of soil erosion on soil properties and crop response in central Kenya. PhD

dissertation, Reports and Dissertations 22, Swedish University of Agricultural Sciences, Uppsala.Gachene CKK, Jarvis NJ, Linner H, Mbuvi JP (1997) Soil erosion effects on soil properties in a highland

area of central Kenya. Soil Science Society of America Journal 61, 559–564.Gichangi EM, Jones RK, Njarui DM, Simpson JR, Mututho JMN, Kitheka SK (1992) Pitting practices for

rehabilitating eroded grazing land in the semi arid tropics of eastern Kenya. In ‘Erosion, conservationand small-scale farming’. (Eds H Hurni, K Tato) pp. 439–452. (Geographica Bernensia: Bern)

Gichuki FN (1992) Indigenous land husbandry practices. Report OD/92/9. Silsoe Research Institute,Silsoe.

Hallsworth EG (1987) ‘Anatomy, physiology and psychology of erosion.’ (Wiley: London)Hassan A (1996) Improved traditional planting pits in the Tahoua department Niger: an example of rapid

adoption by farmers. In ‘Sustaining the soil: Indigenous soil and water conservation in Africa’. (EdsC Reij, I Scoones, C Toulmin) pp. 56–61. (International Institute for Environment and Development:London)

Hinga G, Muchena FN, Njihia CM (Eds) (1980) ‘Physical and chemical methods of soil analysis.’ (NationalAgricultural Laboratories: Nairobi)

Hudson NW (1992) ‘Soil conservation.’ (Batsford: London)International Fund for Agricultural Development (1992) ‘Soil and water conservation in sub-Saharan

Africa. Towards sustainable production by the rural poor.’ (IFAD: Rome)Kemper WD, Miller DE (1974) Management of crusting soils: Some practical possibilities. In ‘Soil crusts.’

Technical Bulletin Number 214. (Eds JW Carry, DD Evans) pp. 1–6. (Agricultural ExperimentalStation, University of Arizona: Arizona)

Kerr J, Sanghi NK (1992) ‘Indigenous soil and water conservation in India’s semi-arid tropics.’ GatekeeperSeries Number 34. (International Institute for Environment and Development: London)

McIntyre DS (1958) Permeability measurements of soil crusts formed by raindrop impact. Soil Science 85,185–189.

Maher C (1937) ‘Soil erosion and land utilisation in Ukambani reserve.’ (Department of Agriculture:Nairobi)

Maher C (1946) Goats, fire and blowing sands. East African Agricultural Journal 11, 173–180.Munsell Color Company (1971) ‘Munsell color charts.’ (Munsell Color Company: Baltimore, MD)Okoba B, Twomlow S, Mugo C (1998) Evaluation of indigenous soil and water conservation technologies

for runoff and soil loss control in semi-arid Mbeere district, Kenya. In ‘Proceedings of LandManagement Workshop’. Kabale, Uganda. (Eds SR Briggs, J Ellis-Jones, SJ Twomlow) pp. 25–41.(Silsoe Research Institute: Silsoe)

Ostberg W (1988) ‘We eat trees.’ Working Paper No. 82. (Swedish University of Agricultural Sciences:Uppsala)

Reij C, Scoones I, Toulmin C (Eds) (1996) ‘Sustaining the Soil: Indigenous soil and water conservation inAfrica.’ (Earthscan: London)

Richards P (1985) ‘Indigenous agricultural revolution.’ (Hutchison: London)Roose E (1992) Traditional and modern strategies for soil and water conservation in the Sudano–Sahelian

areas of West Africa. In ‘Erosion, conservation and small-scale farming’. (Eds H Hurni, K Tato)pp. 349–365. (Geographica Bernensia: Bern)

Silitoe P (1993) Losing ground? Soil loss and erosion in the highlands of Papua New Guinea. LandDegradation and Rehabilitation 4, 143–166.

Soil Survey Staff (1998) ‘Keys to soil taxonomy.’ 8th edn. SMSS Technical Monograph No. 19. (USDA-NRCS: Washington, DC)


http://www.publish.csiro.au/journals/ajsr

Steel RGD Torrie JH (1981) ‘Principles and procedures of statistics: a biometrical approach.’ (McGraw-Hill: London)

Thomas DB, Eriksson A, Grunder M, Mburu JK (Eds) (1997) ‘Soil and Water Conservation Manual forKenya.’ (Ministry of Agriculture, Livestock Development and Marketing: Nairobi)

Tiffen M, Mortimore M, Gichuki F (1994) ‘More people less erosion. Environmental recovery in Kenya.’(Wiley: Chichester, London)

Wakindiki IIC, Ben-Hur M (2002) Soil mineralogy effects on crust micromorphology, infiltration anderosion. Soil Science Society of America Journal 66, (in press).

Wakindiki IIC, Mochoge BE, Ben-Hur M, Runguma D (1998) Socio-cultural and economic aspects ofindigenous soil and water conservation in the semi-arid Tharaka, eastern Kenya. In ‘Proceedings ofInternational Symposium on Arid Region Soil’. pp. 426–431. (International Union of Soil Science:Menemen-Izmir)

Wedum J, Doumbia Y, Sonogo B, Dicko G, Oussoumana C (1996) Rehabilitating degraded land: Zai in theDjenne Circle of Mali. In ‘Sustaining the soil: Indigenous soil and water conservation’. (Eds C Reij,I Scoones, C Toulmin) pp. 62–68. (Earthscan: London)

Whittig LD (1965) X-ray diffraction techniques for mineral identification and mineralogical composition.In ‘Methods of soil analysis’. Agronomy No. 9, Part 1. pp. 671–698. (American Society of Agronomy:Madison, WI)

Willcocks TH, Twomlow SJ (1993) A review of tillage methods and soil and water conservation in SouthernAfrica. Soil and Tillage Research 27, 73–94.

Manuscript received 1 May 2001, accepted 15 October 2001

indigenous soil and water conservation techniques: effects on runoff, erosion, and crop yields under...

Documents