Field Crops Research 166 (2014) 128–136

Zinc fertilization influence on maize productivity and grain nutritionalquality under integrated soil fertility management in Zimbabwe

Grace M. Manzeke a,b, Florence Mtambanengwe a,b, Hatirarami Nezomba a,b,Paul Mapfumo a,b,*aDepartment of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabweb Soil Fertility Consortium for Southern Africa (SOFECSA), University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe

A R T I C L E I N F O

Article history:Received 11 March 2014Received in revised form 28 May 2014Accepted 29 May 2014Available online 2 July 2014

Keywords:Added zinc benefitsMaize grain qualityOrganic nutrient resourcesP–Zn interactionSmallholder farmers

A B S T R A C T

Current efforts to promote integrated soil fertility management (ISFM) for improved productivity ofstaple cereal crops in sub-Saharan Africa have paid little attention to soil micronutrient deficienciesunder smallholder farming. This has not only compromised yields, but also undermined the nutritionalquality of harvested grains. To address this knowledge gap, a study was carried out over two croppingseasons in Hwedza district in eastern Zimbabwe to assess the added grain yield and nutritional benefits ofzinc (Zn) fertilizer application to maize (Zea mays L.) under different ISFM options. In all cases, Znapplication resulted in added maize grain and quality benefits. Application of Zn (11 kg ha�1) incombination with organic nutrient resources (5 t ha�1), and mineral fertilizers (90 kg N ha�1 and 26 kgP ha�1) gave the highest maize grain yields of up to 3.9 t ha�1; which translated to 1.3 times more yieldthan under sole mineral NPK fertilizers. In the subsequent season, there were significantly higher residualeffects (2 t ha�1) from organic xZn combinations compared with sole mineral fertilizer treatments.Organic nutrient resources and Zn application significantly (P < 0.05) influenced maize grain P and Znconcentration, with cattle manure consistently producing the highest grain P concentrations of 0.44%.Maize grain under combinations of mineral NPK, Zn and leaf litter gave the highest grain Znconcentration of up to 35 mg kg�1. The Zn-based treatments increased grain Zn concentration and yieldby 67 and 29%, respectively, indicating that there was much more benefit in grain quality than just yieldafter external Zn application. Combined organic resource and Zn fertilization also resulted in a significantbuild up of plant available soil P and ethylenediaminetetraacetic acid (EDTA) extractable Zn.Concentrations of 7.4 mg P kg�1 and 5.5 mg Zn kg�1 were measured after application of organics,compared with initial values of 5.2 mg kg�1 and 1.15 mg kg�1, respectively. It was concluded that benefitsof ISFM options currently promoted in smallholder farming systems in Zimbabwe are constrained by soilZn deficiencies. Combining these ISFM options with Zn fertilizer formulations increased yields and grainquality of the staple maize, enhancing scope for agronomic fortification of maize to enhance humannutrition.

ã 2014 Elsevier B.V. All rights reserved.

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1. Introduction

Apart from inadequate soil N and P, soil zinc (Zn) deficienciesalso pose a serious threat to global crop production andfood nutrition (Cakmak, 2002; Nube and Voortman, 2006), with50% of cereal grown areas exhibiting deficiencies (Graham and

* Corresponding author at: University of Zimbabwe, Soil Science & AgriculturalEngineering, Soil Fertility Consortium for Southern Africa, University of Zimbabwe,Harare, Zimbabwe. Tel.: +263 712 803 971; fax: +263 4 307 304.

E-mail addresses: gmanzeke@agric.uz.ac.zw (G.M. Manzeke),fmtamba@agri.uz.ac.zw (F. Mtambanengwe), hatienez@yahoo.co.uk (H. Nezomba),pmapfumo@agric.uz.ac.zw, paulmapfumo@gmail.com (P. Mapfumo).

http://dx.doi.org/10.1016/j.fcr.2014.05.0190378-4290/ã 2014 Elsevier B.V. All rights reserved.

Welch, 1996; Grant, 1981). This results in insufficient amounts ofZn in cereal grains to meet human nutritional needs, particularlyfor the majority of poor people in developing countries whose dietsare dominated by maize, rice and wheat (Cakmak, 2008;World Bank, 2008). Globally, 162 million children under the ageof five years are stunted due to malnutrition with 36% of thispopulation found in Africa (WHO, 2012). Grain Zn concentrationsas low as 5–12 mg Zn kg�1 in wheat (Erdal et al., 2002) and13–23 mg Zn kg�1 in maize (Manzeke et al., 2012) have beenmeasured in cereal crops produced in Zn-deficient soils. This isagainst the recommended 40–60 mg Zn kg�1 necessary to meethuman requirements (Pfeiffer and McClafferty, 2007). For example,during early 2000s, 6.4% of the children in Zimbabwe were said to

G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136 129

be undernourished with a significant proportion of the ruralpopulation experiencing acute malnutrition (FAO/WFP, 2002).

More than 300 enzymes involved in the key metabolicprocesses (e.g. carbohydrate and protein metabolism) in humanscontain Zn (FAO/WHO, 1996; Cakmak et al., 1999). This emphasisesthe need for adequate grain Zn in cereal-based human diets.Recommended intake of dietary Zn ranges from 1.1 to 11.2 mgday�1 in children and 3.0–19.0 mg day�1 in adults (FAO/WHO,1996; Imtiaz et al., 2010). However, in poor communities, intake infood is often inadequate (Nube and Voortman, 2006). About two-thirds of all global deaths in children are associated withmicronutrient nutritional deficiencies, and sub-optimal growthand mortality are some of the severe symptoms associated with Zndeficiency (Welch, 2002). In pregnant women, Zn deficiencysymptoms may include high rates of infectious diseases andcomplications during pregnancy or at birth (Ruel and Bouis, 1998;Welch, 2002).

In plants, the physiological functions of Zn include carbohydrateand protein metabolism, membrane integrity, auxin metabolismand reproduction (Alloway, 2008). Concentrations in soil rangefrom 10 to 300 mg kg�1 (Kiekens, 1995) depending on parentrock responsible for soil formation. Low concentrations of�48 mg kg�1 have often been measured in granitic parent rocks(Krauskopf, 1967; Wedepohl, 1978), which account for �70% ofcropped lands by smallholders in Zimbabwe (Thompson andPurves, 1978). Maize grown on such soils is therefore oftendeficient in Zn and other essential micronutrients. This papertherefore focuses on how application of Zn-containing mineralfertilizers to staple cereal crops may contribute towards improvedyields and grain quality as a pathway to enhancing nutrition ofsmallholder communities in maize-based farming systems.Agronomic fortification could be a cost-effective strategy toenhance nutrition in these communities given that the majorityof farmers often do not have the financial capacity to purchaseother Zn-rich foods including meat (FAO/WHO, 1996).

In Zimbabwe and other parts of sub-Saharan Africa, there arewidespread deficiencies of common macro- and micronutrients ongranite derived sandy soils (Tagwira, 1991). This has prompted asearch for deeper understanding of the roles of different nutrientresources in soil fertility management (Mapfumo et al., 2013). Useof external mineral fertilizers by most farmers has often beenconstrained by their high costs. Consequently, most resource-constrained farmers have often resorted to combined use of locallyavailable organic nutrient resources and the limited mineralfertilizer they can afford (World Bank, 1995; Mapfumo and Giller,2001). Several studies have evaluated the importance of suchorganic nutrient resources including woodland litter, livestockmanure and green manure crops in improving crop productivity ona sustainable basis (Zingore, 2006; Mtambanengwe and Mapfumo,2009). However, few studies have explicitly examined the value ofthese local organics as sources of micronutrients such as Zn, andtheir potential interactions with Zn-containing mineral fertilizers.The limited empirical studies available suggest that, Zn supplied inlocally-available organic nutrient resources in Zimbabwe isinsufficient to sustain the required levels of cereal grain yieldsand nutrient concentrations without external mineral fertilization(Manzeke et al., 2012). This paper therefore aims to investigate andquantify the added benefits of Zn fertilization as a pathway toagronomic fortification of staple maize under combined use oforganic and mineral NPK fertilizers as currently promoted amongsmallholder farmers in the context of ISFM. The specific objectivesof the study were to: (i) evaluate the potential role of cattle manureand woodland litter, as sources of Zn and P in maize production,(ii) assess the added grain yield and quality benefits of Znfollowing combined use of organic nutrient resources and mineralNPK fertilizers.

2. Materials and methods

2.1. Study site

The study was conducted between 2009 and 2011 in Goto wardin Hwedza smallholder farming area (18�410S, 31�420E) in easternZimbabwe, under the auspices of the Soil Fertility Consortium forSouthern Africa (SOFECSA). The SOFECSA work focused onpromoting co-learning approaches with farmers and diverseservice providers in eastern Zimbabwe. Hwedza is �150 kmsouth-east of Harare, and in agro-ecological region (NR) II whichreceives about 750 mm of annual rainfall (Vincent and Thomas,1961; Department of Surveyor-General, 1984). According to theWorld Reference Base (2006), soils dominant in Hwedza can beclassified as Arenosols and Lixisols. The major limiting nutrientsfor crop production for these soils are N, P, S and Zn (Grant, 1981;Mapfumo and Giller, 2001).

Hwedza has been under smallholder settlement for over 80years with farm holdings ranging from 1 ha to 5 ha. Farming inHwedza is predominantly based on mixed crop-livestock systems,with maize (Zea mays L.) production dominating. Legumes such asgroundnut (Arachis hypogaea L.), cowpea (Vigna unguiculata L.) andcommon beans (Phaseolus vulgaris L.) are also grown but on arelatively small scale. Cattle are the dominant livestock andimportant for provision of manure, draught power and meat butare owned by a few farmers.

2.2. Preliminary assessment of soil Zn status in farmers’ fields

A preliminary field study was conducted during the dry monthsof August–September 2009, to investigate soil Zn status of differentsmallholder farms. Working with farmers and local nationalagricultural extension workers (AEWs), 15 farms were randomlyselected and soil samples collected at 10 random points within eachfarmer’s field from a depth of 0 to 20 cm using an auger. Sampleswere then placed in well-labelled polythene bags, air-dried andsieved through a 2 mm sieve. A sub-sample from each of theprepared soil sample was used to analyse for extractable Zn usingthe ethylenediaminetetraacetic acid (EDTA) method (IITA Manual,1981; Norvell, 1989). Soil extractable Zn was then measured byatomic absorption spectroscopy using a Varian SpectrAA 50spectrophotometer. Soil texture was determined using the hy-drometer method (Gee and Bauder, 1986). Results from thisdiagnostic exercise were used to inform selection of the field sitefor experimentation. Consequently, a field at Nhika farm that had aZn concentration of 1.15 mg kg�1 was selected for experimentation.Field soils with values below 1.5 mg Zn kg�1 are normallyconsidered as indicating deficiencies in cropping systems(Dobermann and Fairhurst, 2000; Zare et al., 2009). The selectedfield had a loamy sand soil with a pH of 4.9 (0.01 M CaCl2). AvailableN and P, organic carbon (C) and exchangeable base values arepresented in Table 1.

2.3. Field experimentation

The field experiment was established with the first effectiverains in November 2009. The selected field was prepared byconventional ploughing and following treatments were effected onexperimental plots measuring 4.5 m� 5 m in gross area:

1. 90 kg N ha�1 + 26 kg P ha�1.2. 90 kg N ha�1 + 26 kg P ha�1 + Zn.3. 30 kg N ha�1 + 14 kg P ha�1.4. 30 kg N ha�1 + 14 kg P ha�1 + Zn.5. 90 kg N ha�1 + 14 kg P ha�1.6. 90 kg N ha�1 + 14 kg P ha�1 + Zn.

Table 1Initial physical and chemical characteristics of the soil at Nhikafarm, Hwedza, Zimbabwe.

Parameter Value

Clay (%) 12 (0.3)Sand (%) 82 (1)Textural class Loamy sandMineral N (mg kg�1)a 25.0 (1.2)Total N (%) 0.06 (0.002)Available P (mg kg�1)b 5.2 (1)Organic carbon (%)c 0.45 (0.04)pH (CaCl2) 4.9 (0.15)EDTA extractable Zn (mg kg�1) 1.15 (0.2)Ca (cmolc kg�1) 0.8 (0.06)Mg (cmolc kg�1) 0.4 (0.01)K (cmolc kg�1) 0.1 (0.005)

a Mineralizable N after 2 weeks of anaerobic incubation.b Olsen method.c Walkley–Black method. Figures in parentheses denote standard

error.

0 50 100 15 0 2000

20

40

60

80

Rai

nfal

l (m

m)

a) 2009 /10

Tot al = 745 mm

130 G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136

7. 30 kg N ha�1 + 26 kg P ha�1.8. 30 kg N ha�1 + 26 kg P ha�1 + Zn.9. Cattle manure + 90 kg N ha�1 + 26 kg P ha�1.

10. Cattle manure + 90 kg N ha�1 + 26 kg P ha�1 + Zn.11. Leaf litter + 90 kg N ha�1 + 26 kg P ha�1.12. Leaf litter + 90 kg N ha�1 + 26 kg P ha�1 + Zn.13. Absolute control (no amendment applied).

The treatments fell into three broad categories: (1) high rates ofN and P � Zn; (2) low rates of N and P � Zn and (3) organic andinorganic fertilizer combinations. Nitrogen and P were applied attwo different rates that respond to different farmer resourcegroups in the area (Mtambanengwe and Mapfumo, 2008).Phosphorus and Zn were broadcast as PKS blend(0N:32P2O5:16K2O:5S) and ZnSO4�7H2O, respectively, beforeplanting. Zinc sulphate was applied at a rate of 50 kg ha�1 tosupply 11 kg Zn ha�1, and had a water solubility of 95% which isabove the least acceptable range of 40–50% required for a granularfertilizer to be effective for the immediate crop (Mortvedt, 1992).Cattle manure and woodland litter were sampled and analysed(Table 2) before they were broadcast and hand-incorporated to adepth of 0.15 m using hand hoes. All plots were planted to an earlyto medium maturing maize cultivar, SC513, at an inter-row spacingof 0.9 m and within-row spacing of 0.3 m. The experimental designwas a randomized complete block design (RCBD), with 3 replicates

Table 2Quality of organic resources used under a loamy sand soil type at Hwedza fieldexperiment in Zimbabwe.

Parameter Organic amendment

Cattle manure Leaf litter

Sand (%) 52 43Ash (%) 14.5 19.5Organic C (%) 15.5 31.4N (%) 0.81 0.98Pa (%) 0.08 0.11C:N 19 32C:P 194 285Ligninb (%) 2.9 6.5Polyphenolc (%) 0.2 3.2Zincd (mg kg�1) 22 60Ca (%) 1.37 1.63Mg (%) 0.57 0.91K (%) 0.99 0.87

a Molybdate–vanadophosphoric acid method.b Acid detergent fibre method.c Modified Folin–Ciocalteau.d Aqua Regia.

per treatment. Nitrogen was applied as top dressing in the form ofammonium nitrate (34.5% N) in 3 splits, 30% at 2 weeks afteremergence (WAE); 40% at 6 WAE and 30% at silking. The cropwas kept weed-free through hand weeding. Maize stalk borer(Busseola fusca) was controlled with thionex (2.5% carbaryl)granules applied at a rate of 3–4 kg ha�1 at 6 WAE.

During the second cropping season (2010/11), all plots wereplanted to maize with no Zn fertilization. Zinc fertilizers are knownto have residual effects which last up to 4 years (Martens andWestermann, 1991). However, N and P fertilizer application ratesand general agronomic practices were similar to those in the firstseason. The study site received a total of 840 mm, approximately100 mm more than the rainfall received in the first cropping season(Fig. 1).

2.4. Assessment of maize grain yield and nutrient uptake patterns

At the end of each cropping season, maize grain yields weredetermined at physiological maturity from net plots measuring2.7 m�3 m, and quantified at 12.5% grain moisture content. Maizegrain sub-samples were ground in a stainless steel Thomas–WileyModel 4 Laboratory mill (Thomas Scientific, USA) and analysed fortotal Zn. To investigate the influence of Zn and organic nutrientresource fertilization on maize P uptake, grain samples were alsoanalysed for P following digestion with nitric acid (HNO3) and 50%

Day (starting 1 Oc tober)

0 50 100 15 0 200

Rai

nfal

l (m

m)

0

20

40

60

80b) 201 0/1 1

Total = 84 0 mm

Fig. 1. Rainfall distribution and amount received throughout the experimentalperiod during evaluation of Zn fertilization for added grain yield and qualitybenefits in Zimbabwe.

Treatmen t

Mai

ze g

rain

yie

ld (t

ha-1

)

0 kg N + 0 kg P

30 kg N + 14 kg P

30 kg N + 14 kg P + Zn

30 kg N + 26 kg P

30 kg N + 26 kg P + Zn

90 kg N + 14 kg P

90 kg N + 14 kg P + Zn

90 kg N + 26 kg P

90 kg N + 26 kg P + Zn

Cattlemanure + 90 kg N + 26 kg P

Cattlemanure + 90 kg N + 26 kg P + Zn

Leaf litter + 90 kg N + 26 kg P

Leaf litter + 90 kg N + 26 kg P + Zn

0

1

2

3

4

5

6

Fig. 2. Maize grain yields after application of Zn in combination with organic andinorganic fertilizers in Hwedza, eastern Zimbabwe during the 2009/10 croppingseason (bars represent SEM).

Treatmen t

Mai

ze g

rain

yie

ld (t

ha-1

)

0 kg N + 0 kg P

30 kg N + 14 kg P

30 kg N + 14 kg P + *Zn

30 kg N + 26 kg P

30 kg N + 26 kg P + *Zn

90 kg N + 14 kg P

90 kg N + 14 kg P + *Zn

90 kg N + 26 kg P

90 kg N + 26 kg P + *Zn

*Cattlemanure + 90 kg N + 26 kg P

*Cattlemanure + 90 kg N + 26 kg P + *Zn

*Leaf litter + 90 kg N + 26 kg P

*Leaf litter + 90 kg N + 26 kg P + *Zn

0

1

2

3

4

5

6

Fig. 3. Residual organic and Zn fertility effects on maize grain yields followingapplication of inorganic NPK in the 2010/11 cropping season in Hwedza, Zimbabwe.Asterisks indicate residual fertility (bars represent SEM).

G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136 131

hydrogen peroxide (H2O2) (Anderson and Ingram, 1993). Nutrientuptake was quantified on a dry weight basis using the formula:

Grain nutrient uptake ðKg ha�1Þ¼ grain nutrient concentration ðmg kg�1Þ � grain yieldðt ha�1Þ

2.5. Determining changes in soil chemical properties after 2 years ofmaize mono-cropping

At the end of the second cropping season in May 2011, soilsamples were collected from five randomly selected points ineach plot. Samples were prepared and analysed for extractableZn, available P, total N, organic carbon (C) and exchangeablebases (calcium (Ca2+), magnesium (Mg2+) and potassium (K+)).Plant-available Zn was measured on the basis of EDTA-extractable soil Zn (Manzeke et al., 2012). Total N wasdetermined using the micro-Kjeldahl digestion method whilethe acidified ammonium acetate method was used forexchangeable bases (Anderson and Ingram, 1993). Organic Cwas determined using the Walkley–Black method. Concentra-tions of EDTA extractable Zn, Ca and Mg were then determinedby atomic absorption spectrophotometry while C, N and P weredetermined colorimetrically (Anderson and Ingram, 1993). Theconcentration of K+ was determined by flame emissionspectroscopy on a Corning 400 flame photometer.

2.6. Data analyses

Data were analysed using analysis of variance (ANOVA) withGENSTAT for Windows, Discovery Edition 13 (GENSTAT, 2010) todetermine treatment differences with respect to maize grain yield,grain nutrient uptake and soil chemical properties. Meanseparations were done using the honestly significant difference(HSD)/Tukey’s test (Steel and Torrie, 1980) at P < 0.05.

3. Results

3.1. Effects of combined organic and inorganic fertilizer and Znaddition on maize grain yield

Highest grain yields of 3.9 t ha�1 were recorded after combinedapplication of leaf litter and mineral NPK and Zn fertilizer,significantly (P < 0.05) out-yielding the non-fertilized controland the 30 kg N ha�1 + 14 kg P ha�1 + Zn treatment by 387% and248%, respectively (Fig. 2). However, maize yield under theleaf litter treatment did not differ significantly (P > 0.05) from acorresponding cattle manure treatment, which produced3.5 t ha�1. Application of high rates of N and P and Zn produced2.5 t ha�1 of maize grain compared with 1.6 t ha�1 under thecorresponding low fertilizer rates.

Zinc fertilization gave an added yield benefit to both soleorganic and mineral fertilizer as well as their combinations. Yieldsincreased by 0.5 t ha�1 in sole mineral fertilizer treatments and by0.7 t ha�1 when the fertilizers were used in combination withorganic nutrient resources, translating to about 22% increase forboth treatments (Fig. 2). The results also showed higher Zn residualfertility effects where organic nutrient resources were applied thanin other treatments. This was reflected by a significantly higheryield increase of 21% with organic and mineral fertilizercombinations compared with a 5% increase when sole mineralfertilizers were used (Fig. 3). A significant reduction in grain yieldranging from 51 to 100% was measured when NPK with/without Znwas applied at low rates compared to high NPK rates. This suggeststhat with Zn fertilization, farmers still need to apply therecommended rates of macronutrients.

3.2. Fertilizer effects on maize grain Zn concentration and uptake

Maize grain Zn concentration was significantly (P < 0.01)influenced by different types of fertilizers and rates, and rangedfrom 15.4 to 35.0 mg kg�1 (Table 3). Application of Zn to bothorganic and mineral fertilizer treatments yielded significantlysuperior grain Zn concentrations of up to 35 mg kg�1 comparedwith 15.4 mg kg�1 for the absolute control treatment. With respectto the absolute control, grain Zn concentration increased bybetween 42–88% in sole mineral fertilizer treatments and

Table 3Total Zn uptake and concentration of the nutrient in grain for maize following application of Zn and combinations of organic and inorganic fertilizer in Hwedza, easternZimbabwe.

Treatment 2009/10 2010/11

Grain Zn (mg kg�1) Zn uptake (g ha�1) Grain Zn (mg kg�1) Zn uptake (g ha�1)

90 kg N ha�1 + 26 kg P ha�1 19.2b 46.5bc 20.7b 18.0ab

90 kg N ha�1 + 26 kg P ha�1 + Zn 22.6cd 65.5c 28.9cd 34.5b

30 kg N ha�1 + 14 kg P ha�1 18.1ab 20.3a 17.5ab 11.8ab

30 kg N ha�1 + 14 kg P ha�1 + Zn 20.4bc 39.2b 21.9bc 19.0ab

90 kg N ha�1 + 14 kg P ha�1 18.9b 40.8bc 19.8b 19.0ab

90 kg N ha�1 + 14 kg P ha�1 + Zn 20.8bc 53.5bc 23.0bc 22.9ab

30 kg N ha�1 + 26 kg P ha�1 21.7c 41.2bc 23.1bc 21.9ab

30 kg N ha�1 + 26 kg P ha�1 + Zn 21.9c 32.9ab 25.8c 27.0b

Cattle manure + 26 kg P ha�1 + 90 N ha�1 23.1cd 67.0c 25.4c 53.0c

Cattle manure + 26 kg P ha�1 + 90 N ha�1 + Zn 24.9d 87.2c 31.0d 81.5d

Leaf litter + 26 kg P ha�1 + 90 N ha�1 23.9cd 76.0c 29.1cd 72.2d

Leaf litter + 26 kg P ha�1 + 90 N ha�1 + Zn 29.7e 115.3d 35.0e 105.4e

Absolute control (0 kg N ha�1 + 0 kg P ha�1) 16.1a 9.7a 15.4a 7.7a

Mean 21.3 52.2 24.2 37.6SED 1.2** 12.5** 1.9* 7.7*

CV (%) 11.7 18.0 12.4 16.3

Homogeneous groups are denoted by the same letter. Zinc was applied at a uniform rate of 11 kg ha�1.* Treatment effect significant at P < 0.05.** Treatment effect significant at P < 0.01.

132 G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136

103–130% when combinations were used (Table 3). Addition of Znto the combination of leaf litter and NPK fertilizer producedbetween 29.7 and 35.0 mg kg�1 of grain Zn and was significantlydifferent from those obtained when manure was used.These significant differences in the proportional increase inconcentrations between sole inorganic fertilizer treatments andcombinations of different organic and inorganic fertilizers can bepartly attributed to inherent differences in Zn stocks contained inthe nutrient sources. Cattle manure and leaf litter most likelycontributed to the Zn available for plant uptake.

There were contrasting Zn uptake patterns in maize betweenthe first and second season for the organic and mineral fertilizer-based treatments. Application of Zn increased grain Zn concen-trations by 18% in sole mineral fertilizer treatments and by up to24% in combinations of organic and inorganic fertilizer treatmentsduring the first cropping season (2009–2010). However, in thesecond season (2010–2011), there was a small difference in uptakebetween treatments with and without Zn. For example, organicand inorganic fertilizer treatments with Zn had an increase of 22%compared to a 39% difference in uptake in sole mineral fertilizertreatments (Table 3). Although sole mineral fertilized treatmentshad a huge percentage increase in grain Zn concentrationsfollowing application, average concentrations of 22.6 mg kg�1

were, however, lower than those measured with combinations(30.1 mg kg�1) implying a greater need for Zn fertilization byfarmers who use sole mineral fertilizers. Application of solemineral NPK resulted in a significant increase in grain Zn

Table 4Added benefits in grain yield and total Zn uptake following co-application of Zn fertiliz

Zinc treatment Zn fertilization grain yieldadvantage (%)

Yield advcontrol (

30 kg N ha�1 + 14 kg P ha�1 + Zn 49.5 147

30 kg N ha�1 + 26 kg P ha�1 + Zn 19.0 162

90 kg N ha�1 + 14 kg P ha�1 + Zn 11.0 217

90 kg N ha�1 + 26 kg P ha�1 + Zn 28.5 262

Cattle manure + 26 kg P ha�1 + 90N ha�1 + Zn

23.5 452

Leaf litter + 26 kg P ha�1 + 90 N ha�1 +Zn

22.0 525

Zinc was applied at a uniform rate of 11 kg ha�1.

concentration of 20.7 mg kg�1, amounting to a 34% increase overthe absolute control treatment. This suggests increased Zn miningwhere macronutrients are continuously applied.

Overall, maize grain Zn uptake ranged from 9.7–115.3 g Zn ha�1

during the 2009/10 and 7.7–105.4 g Zn ha�1 in the 2010/11croppingseason (Table 3). The benefits of Zn fertilization were significantlyexpressed in increased maize grain Zn uptake compared withincreased grain yields. For example, there was a 50% increase ingrain yield after application of Zn but an increase of up to 77% grainZn uptake was measured under the low N and P treatment(Table 4).

3.3. Grain P concentration and uptake as affected by organic resourcequality and Zn fertilization

Significant differences (P < 0.05) in P concentration and uptakewere exhibited among treatments, with concentration ranges of0.19–0.44% measured during the two cropping seasons (Table 5).Combined application of cattle manure and inorganic NPK resultedin 47% higher P concentrations than those attained in the solemineral fertilizer treatments and almost double the amount in theabsolute control. In the first season (2009–10) of application,organic resource quality had no influence on grain P concen-trations. However, during the second season of cropping, cattlemanure gave significantly higher grain P concentrations comparedwith leaf litter, possibly due to improved mineralization duringthis season.

er with combinations of regular NPK formulations and organic nutrient resources.

antage over the%)

Zinc uptake over non-Zntreatment(%)

Zinc uptake over thecontrol(%)

77.0 22523.5 28826.0 32466.5 46242.5 884

48.0 1168

Table 5Grain P concentration and uptake following fertilization with different macronutrient and Zn fertilizers in combination with organic nutrient resources in Hwedza,Zimbabwe.

Treatment 2009/10 2010/11

Grain P (%) P uptake (kg ha�1) Grain P (%) P uptake(kg ha�1)

90 kg N ha�1 + 26 kg P ha�1 0.28cd 6.8c 0.30c 2.6ab

90 kg N ha�1 + 26 kg P ha�1 + Zn 0.26c 7.5cd 0.30c 3.6b

30 kg N ha�1 + 14 kg P ha�1 0.23b 2.6ab 0.25b 1.7ab

26 kg P ha�1 + Zn 0.21ab 4.0b 0.23ab 2.0ab

90 kg N ha�1 + 14 kg P ha�1 0.21ab 4.5b 0.23ab 2.2ab

90 kg N ha�1 + 14 kg P ha�1 + Zn 0.23b 5.9bc 0.21a 2.1ab

30 kg N ha�1 + 26 kg P ha�1 0.26c 3.9b 0.29c 2.8b

30 kg N ha�1 + 14 kg P ha�1 + Zn 0.27c 5.1bc 0.28c 2.9b

Cattle manure + 26 kg P ha�1 + 90 N ha�1 0.32d 9.3d 0.44g 9.2c

Cattle manure + 26 kg P ha�1 + 90 N ha�1 + Zn 0.25bc 8.8cd 0.39f 10.3c

Leaf litter + 26 kg P ha�1 + 90 N ha�1 0.19a 9.5d 0.36e 8.9c

Leaf litter + 26 kg P ha�1 + 90 N ha�1 + Zn 0.25 9.8d 0.32d 9.6c

Absolute control (0 kg N ha�1 + 0 kg P ha�1) 0.19a 1.1a 0.21a 1.1a

Mean 0.25 6.1 0.30 4.7SED 0.01* 1.1* 0.01* 0.8*

CV (%) 13.1 12.6 14.3 14.9

Within a column, means followed by the same letter are not significantly different.* Treatment effect significant at P < 0.05. Within a column, means followed by the same letter are not significantly different.

G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136 133

In sole mineral fertilized treatments, Zn had no significanteffect on grain P concentration (P > 0.05). In contrast, there was asignificant decrease in grain P when Zn was co-applied withorganic and inorganic fertilizer combinations, with Zn applicationapparently reducing P uptake by 13% (Table 5). High P fertilizerrates evidently resulted in correspondingly high maize grain P. Forexample, application of P at 14 kg P ha�1 gave concentrationsaveraging 0.22% and this was significantly lower than 0.28%P measured in maize grain, which received 26 kg P ha�1. GrainP uptake ranged between 8.8 and 10.3 kg P ha�1 in organic nutrientresource-based treatments, superceding uptake in sole mineralfertilized treatments by about three times (Table 5). This suggeststhat organic nutrient resources also improved plant P nutrition.Estimating that 65% of P is available as phytic acid (PA), results fromthe study consistently showed significantly (P < 0.05) reduced PA:Zn molar ratios under co-application of organic and mineralfertilizers with Zn compared to non-Zn treatments. Phytic acid:Znmolar ratios ranged from 57 to 107 and the ratios were reduced bybetween 6 and 42%, with the highest reduction attained afterfertilization of maize with leaf litter and Zn (data not shown).

Table 6Effects of maize cropping and management of different fertilizers on soil chemical pro

Treatment Parameter

Available Zn Available P

(mg kg�1) (mg kg�1)

Initial nutrient concentration 1.15 5.2

90 kg N ha�1 + 26 kg P ha�1 1.27a 5.4ab

90 kg N ha�1 + 26 kg P ha�1 + Zn 2.75b 5.6b

30 kg N ha�1 + 14 kg P ha�1 1.19a 5.4ab

30 kg N ha�1 + 14 kg P ha�1 + Zn 2.32b 5.2ab

90 kg N ha�1 + 14 kg P ha�1 + Zn 2.57b 5.3ab

90 kg N ha�1 + 14 kg P ha�1 1.21a 5.1ab

30 kg N ha�1 + 26 kg P ha�1 + Zn 1.75ab 5.5b

30 kg N ha�1 + 26 kg P ha�1 1.12a 5.3ab

Cattle manure + 26 kg P ha�1 + 90 N ha�1 2.33b 7.2d

Cattle manure + 26 kg P ha�1 + 90 N ha�1 + Zn 4.02c 7.4d

Leaf litter + 26 kg P ha�1 + 90 N ha�1 2.60b 6.2c

Leaf litter + 26 kg P ha�1 + 90 N ha�1 + Zn 5.48d 6.5c

Absolute control (0 kg N ha�1 + 0 kg P ha�1) 0.97a 5.0a

SED 0.51* 0.2*

ns: no treatment differences recorded at P < 0.05. Zinc was applied at a uniform rate o* Significant differences measured at P < 0.05.

3.4. Organic and inorganic fertilization effect on plant available soil Pand Zn status

Application of Zn in combination with organic and inorganicfertilizers contributed significantly (P < 0.05) to build-up ofavailable soil Zn and P. However, none of other measured soilchemical parameters appeared to have been altered by themanagement practice (Table 6). Available soil P ranged from5.0 mg kg�1 in the absolute control treatment to 7.4 mg kg�1 intreatments receiving combinations of cattle manure and mineralfertilizer. Available soil Zn of 5.5 mg kg�1 was attained after co-application of leaf litter with mineral NPK and Zn. This wassignificantly different (P < 0.05) from concentrations of <1.0 mgkg�1 measured in the non-fertilized treatment. On the other hand,soils under cattle manure treatment recorded an availableZn concentration of 4.0 mg kg�1 (Table 6) but this was significantlylower than for leaf litter by 37%. This may be attributed to higheravailable Zn concentrations, of 60 mg kg�1, in leaf litter comparedto concentrations of 22 mg kg�1 measured in cattle manuresamples. Consistently, soils receiving sole mineral NPK had an

perties at the end of the experimental period.

N O.C Ca Mg K(%) (%) cmolc kg�1 cmolc kg�1

0.06 0.45 2.89 1.91 0.300.07 0.45 2.41 1.97 0.290.06 0.47 2.55 1.34 0.270.05 0.43 2.33 1.27 0.280.06 0.43 2.33 1.94 0.270.07 0.40 2.45 1.88 0.290.05 0.46 2.57 1.61 0.260.06 0.42 2.52 1.92 0.260.04 0.43 2.69 1.25 0.300.07 0.49 2.41 1.48 0.310.06 0.51 2.52 1.21 0.290.08 0.50 2.87 1.56 0.290.09 0.48 2.92 1.01 0.300.05 0.45 2.83 1.45 0.280.05ns 0.25ns 0.60ns 0.45ns 0.05ns

f 11 kg ha�1.

134 G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136

average soil Zn concentration of 1.2 mg kg�1, a value about 67% lessthan that attained under combinations of mineral fertilizers andorganic nutrient resources and 54% less than the NPK + Zntreatments (Table 6).

4. Discussion

4.1. Zinc as a missing component in current ISFM options available tofarmers

Application of Zn as either a sole mineral fertilizer or incombination with organic nutrient resources improved maizegrain yields. Zinc deficiency compromised yield by 20% in solemineral fertilized treatments and by 23% when combinations wereapplied. Although there was a greater decrease in yield incombination treatments, yields attained under sole mineralfertilized treatments were also comparatively low. In wheat andrice systems, Zn fertilization has also been reported to increaseyield (Yilmaz et al., 1997; Slaton et al., 2001). Zinc deficiency hasoften been associated with poor seed germination and seedlingdevelopment (Alloway, 2008). The results suggest that Zndeficiency is one of reasons why the maize yield potential of>5 t ha�1 (Mapfumo et al., 2013) is not attained under smallholderfarming systems in otherwise high potential regions in Zimbabwe.Integrated soil fertility management practices primarily based onuse of combinations of NPK fertilizers and locally available organicnutrient resources and legume-cereal rotations have largely beenpromoted to increase soil productivity in smallholder croppingareas in Zimbabwe (e.g. Manzeke et al., 2012; Mapfumo andMtambanengwe, 2004; Mapfumo et al., 2013; Nezomba et al.,2014). Findings from the current study show that an additional1 t ha�1 of maize grain is attainable after co-application of Zn withorganic and inorganic NPK fertilizers. This suggests that farmerscould benefit more if such ISFM options were supplemented withZn. Positive yield benefits have also been reported with othermicronutrients such as copper (Cu), boron (Bo) and iron (Fe)(Mukurumbira and Nemasasi, 1997). It is well known that Znkick-starts growth through improved seedling vigour, root growthand chlorophyll concentration, which results in enhanced nutrientuptake and crop productivity (Cakmak et al., 1999; Alloway, 2008).Adequate Zn fertilization can also alleviate biotic and abiotic stressevents in crops grown on farmers’ fields due to benefits on severalphysiological processes including bio-synthesis of growthhormones essential for photosynthesis (Sharma et al., 1982;Oosterhuis et al., 1991; Cakmak, 2000).

Significantly higher yields attained under application of 90 kgN ha�1 + 26 kg P ha�1 + Zn compared to lower NPK treatmentssuggest that application of adequate levels of nutrients isimportant to maintain high soil N, P and Zn fluxes throughoutthe crop life cycle for improved yields (Mtambanengwe, 2006).Findings from this study clearly show that yields attained undercurrent farmer soil fertility management practises were limited bylow soil micronutrient contents. Blending to include Zn and otheressential micronutrients in current fertilizer formulations coupledwith sensitization and co-learning with farmers to evaluate thesewould be a possible entry point to increase crop yields and grainquality under ISFM.

4.2. Added value of Zn and organic nutrient resource application onmaize grain nutrient concentration and uptake

Studies on ISFM have mainly focused on improving soil fertilityand grain yields through application of farm available organicnutrient resources and mineral NPK fertilizers (Mapfumo andGiller, 2001; Mtambanengwe and Mapfumo, 2006; Adjei-Nsiahet al., 2008) with seldom attention being given to improving the

nutritional composition of these grains. Results from the presentstudy showed that use of farmers’ current fertilization options incombination with Zn improved maize grain Zn concentration.Combinations of organic and inorganic fertilizer treatments hadhigher Zn concentrations compared to the sole mineral treatmentspossibly due to their capacity to supply inherent Zn and increasemicronutrient mass fractions in staple cereals (Grusak et al., 1999;Rupa et al., 2003). Attainment of the highest grain Znconcentrations of 35 mg kg�1 in leaf litter treatments wasattributable to its superior concentration of the micronutrientwhich averaged 60 mg Zn kg�1 compared with say 22 mg Zn kg�1 incattle manure. The tropical savanna woodland of Southern Africadominated by miombo tree species of the genera Brachystegia,Combretum and Julbernadia have the capacity to extract nutrientsfrom deeper soil horizons and deposit in leaves (Müller-Sämannand Kotschi, 1994; Ryan et al., 2011). A study conducted undersimilar climatic conditions and soils indicated higher Zn concen-trations in the sub-soil than in top soil (Shoko and Moyo, 2011).

On the other hand, application of Zn to sole mineral fertilizedtreatments did not differ significantly from organic nutrientresource treatments without Zn, supporting the idea that organicssupply multiple nutrients and enhance nutrient interactions(Palm et al., 1997; Mtambanengwe and Mapfumo, 2009;Manzeke et al., 2012). This suggests that farmers who apply solemineral NPK fertilizers have a greater demand for Zn than thosewho use combinations of organic and inorganic fertilizers and aretherefore possibly at a higher risk of malnutrition. Effects of Znwere more pronounced when measured in uptake than in yield,showing the importance of Zn in improving grain quality (Cakmak,2008). Considering most smallholder farmers are financiallyconstrained and often use retained seed (CIMMYT, 2007; www.n2africa.org), it is important to fortify maize through combinedapplication of organic nutrient resources with Zn fertilizers. Cropseeds containing high Zn concentrations at harvest often exhibitsuperior establishment potential under stressful environments(Rengel and Graham, 1995; Yilmaz et al., 1997).

Superior P concentrations were measured in grain producedunder combined use of organic and inorganic fertilizers, revealingthe capacity of leaf litter and cattle manure to enhance P supply.Zinc fertilization, on the other hand, significantly reduced grainP concentrations only when applied in combination with organicand NPK fertilizer treatments. Most cereals contain anti-nutrition-al factors that include phytic acid, a form in which up to 85% P isstored, mostly in the aleurone and embryo parts of the grain(Mazzolini et al., 1985; Graham et al., 2001). In this regard, it isimportant to practice soil fertility management practices thatreduce concentrations of such inhibitors. Phytic acid significantlyreduces bioavailability of Zn to humans through binding with theelement, rendering it unavailable for significant biological impactson human health (Alloway, 2008; Cakmak, 2008). Fertilizationoptions that include use of Zn and organic nutrient resources is apotential strategy for alleviating high phytate levels associatedwith P fertilization. High levels of soil Zn are known to suppressP uptake and vice-versa (Adriano et al., 1971; Loneragan and Webb,1993; Impa and Johnson-Beebout, 2012). A recent review ofseveral studies analysing P and Zn interactions in cereals hasrevealed the value of agronomic fortification in reducing PA:Znmolar ratio to within the known critical levels of between 15 and20 (Joy et al., 2014).

Nitrogen application resulted in significantly higher grain Znconcentrations compared to the non-N treatment suggesting N is amajor factor driving uptake of Zn in maize-based croppingsystems. Nitrogen is known to possibly influence rhizospherepH and synthesis of organic acids which act as chelators forimproved plant Zn uptake (Alloway, 2008; Marschner, 2012).During senescence, cereals are known to re-translocate cationic

G.M. Manzeke et al. / Field Crops Research 166 (2014) 128–136 135

nutrients such as potassium (K) and Zn to grain and N is known tobe the main factor stimulating the translocation of Zn (Shi et al.,2010; Kutman et al., 2011; Barunawati et al., 2013).

4.3. Fertilizer induced mining of micronutrients in current farmingpractices

The fertilization regimes used in the experiment had significanteffects on soil P and Zn availability but not on other soil chemicalparameters. Several studies demonstrated the capacity of organicsto supply significant amounts of Zn to crops (Prasad and Sinha,1982; Tagwira, 1991; Lupwayi et al., 2000). However, relatedstudies have revealed that the Zn released from the various organicnutrient resources available to farmers is insufficient to supportmaize production requirements (Manzeke et al., 2012). Treatmentsreceiving NPK nutrient alone in this study evidently inducedhigher Zn uptake, suggesting that current fertilizer managementpractices by farmers in Zimbabwe promote Zn mining, and arelikely to result in long-term severe deficiencies in soils. Zincfertilization in smallholder farms is therefore important to offsetnegative nutrient balances resulting from inherent deficienciesand low levels of nutrient inputs.

5. Conclusions

Integrated soil fertility management (ISFM) practices currentlypromoted in smallholder farms mainly include application of solemineral fertilizers and combinations of locally available organicnutrient resources and inorganic NPK fertilizers. These fertilizationstrategies, however, lack Zn, which on the other hand, is inherentlydeficient in sandy soils. In this regard, external Zn fertilization isrequired to curb accelerated Zn mining associated with the currentpromotion of NPK mineral fertilizer use. Application of organic andmineral NPK and Zn fertilizers significantly improved grain qualitywith potential benefits of supplying residual Zn and P to thesubsequent maize crop. Farmers who apply sole mineral fertilizershave an even greater demand for external Zn fertilization thanthose who co-apply mineral fertilizers with locally availableorganic nutrient resources such as cattle manure and woodlandlitter. Overall, the study reveals a need for greater scientificunderstanding of nutrient interactions for sustainable cropproductivity under the ISFM framework and related approachestargeted for smallholder farmers in Africa.

Acknowledgements

The study was funded by The Harvest Plus Zinc Project entitled“Use of zinc containing fertilizers for enriching cereal grains withzinc and improving yield in different countries” through acollaborative grant to Sabanci University of Turkey and theUniversity of Zimbabwe’s Faculty of Agriculture. The role of theSoil Fertility Consortium for Southern Africa (SOFECSA) innovationplatforms (IPs) which promoted different integrated soil fertilitymanagement options and conservation agriculture in the study sitewith additional funding from the ABACO project funded by the EUthrough the African Conservation Tillage Network (ACT) enabledcompletion of this paper.

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