Zinc fertilization increases productivity and grain nutritional quality of cowpea (Vigna unguiculata [L.] Walp.) under integrated soil fertility management

Cowpea (Vigna unguiculata [L.] Walp.) is an important but under-studied grain legume which can potentially contribute to improved dietary zinc (Zn) intake in sub-Saharan Africa. In this study, surveys were conducted on smallholder farms in Zimbabwe during 2014/15 to determine the influence of diverse soil fertility management options on cowpea grain productivity and nutrition quality. Guided by the surveys, field experiments were conducted to investigate the influence of Zn fertilizer on the productivity and quality of cowpea under integrated soil fertility management (ISFM). Experiments were conducted on two soil-types, namely, sandy (6% clay) and red clay (57% clay) in 2014/15 and 2015/16 where cowpea was grown in rotation with staple maize (Zea mays L.) and fertilized with combinations of Zn, nitrogen (N), phosphorus (P) and two organic nutrient resources, cattle manure and woodland leaf litter. Cowpea grain yields on surveyed farms ranged from 0.3 to 0.9 t ha−1, with grain Zn concentration ranging from 23.9 to 30.1 mg kg−1. The highest grain Zn concentration was on fields where organic nutrient resources were applied in combination with mineral N and P fertilizers. Within the field experiments, mean grain yields of cowpea increased by between 12 and 18% on both soil types when Zn fertilizer was applied, from a baseline of 1.6 and 1.1 t ha−1 on red clay and sandy soils, respectively. When Zn fertilizer was co-applied with organic nutrient resources, grain Zn concentrations of cowpea reached 42.1 mg kg−1 (red clay) and 44.7 mg kg−1 (sandy) against grain Zn concentrations of 35.9 mg kg−1 and 31.1 mg kg−1 measured in cowpea grown with no Zn fertilizer on red clay and sandy soils, respectively. Agronomic biofortification of legumes is feasible and has the potential to contribute significantly towards increasing dietary Zn intake by humans. A greater increase in grain Zn of cowpea grown on sandy than red clay soils under Zn fertilization illustrates the influence of soil type on Zn uptake, which should be explored further in agronomic biofortification programs

Can nitrogen fertilizer management improve grain iron concentration of agro-biofortified crops in Zimbabwe?

Improving iron (Fe) concentration in staple grain crops could help reduce Fe-deficiency anaemia in communities dependent on plant-based diets. Co-application of nitrogen (N) and zinc (Zn) fertilizers has been reported to improve both yield and grain Zn concentration of crops in smallholder farming systems. This study was conducted to determine if similar effects are observed for grain Fe concentration. Field experiments were conducted in two years, in two contrasting agro-ecologies in Zimbabwe, on maize (Zea mays L.), cowpea (Vigna unguiculata [L.] Walp) and two finger millet (Eleusine coracana (L.) Gaertn.) “seed pools”. The two finger millet “seed pools” were collected during previous farmer surveys to represent “high” and “low” Fe concentrations. All plots received foliar Fe-ethylene diamine tetra-acetic acid (EDTA) fertilizer and one of seven N treatments, representing mineral or organic N sources, and combinations thereof. Higher grain yields were observed in larger N treatments. Grain Fe concentration increased according to species: maize < finger millet < cowpea but varied widely according to treatment. Significant effects of N-form on grain Fe concentration were observed in the low finger millet “seed pool”, for which mineral N fertilizer application increased grain Fe concentration to a greater extent than other N forms, but not for the other species. Whilst good soil fertility management is essential for yield and grain quality, effects on grain Fe concentration are less consistent than reported previously for Zn

Fertilizer management and soil type influence grain zinc and iron concentration under contrasting smallholder cropping systems in Zimbabwe

Micronutrient deficiencies remain prevalent in food systems of southern Africa, although advances in biofortification through crop breeding and agronomy provide opportunities to address these. We determined baseline soil availability of zinc (Zn) and iron (Fe) and the effects of soil type and farmer management on extractable soil Zn and Fe and subsequent concentration in cereal and legume grains under two contrasting agro-ecologies in Zimbabwe. Soil and crop surveys were conducted in Hwedza and Mutasa Districts of Zimbabwe in 2015–16 on 350 locations over different soil types. Fields with different levels of productivity (designated as “most” and “least” productive fields) were sampled using an inherited hierarchical randomized sampling design. Grain Zn and Fe concentration in maize (Zea mays), sorghum (Sorghum bicolor), finger millet (Eleusine coracana) and cowpea (Vigna unguiculata) were generally insufficient for adequate human nutrition. A Linear Mixed Effects (LME) model revealed that diethylene triamine penta-acetic acid- (DTPA) extractable soil Zn concentration and grain Zn concentration were affected primarily by field productivity level. DTPA-extractable soil Zn concentration was more than two-fold greater on the most productive fields (mean 0.8 mg kg−1) than on the least productive fields, with mean grain Zn concentration of 25.2 mg grain Zn kg−1 which was 13% greater than seen on the least productive fields. An interaction effect of field productivity level and total soil Zn concentration on DTPA-extractable soil Zn concentration suggests potential contribution of organic matter management to unlocking unavailable forms of soil Zn. DTPA-extractable soil Fe and grain Fe concentration were primarily affected by soil type and crop type, respectively. The LME modelling approach revealed additional soil geochemical covariates affected DTPA-extractable soil Zn and Fe concentration and grain Zn and Fe concentration within Districts. Future studies can therefore be powered to detect their roles at wider spatial scales for sustainable management of crop Zn and Fe nutrition

Good soil management can reduce dietary zinc deficiency in Zimbabwe

Dietary zinc (Zn) deficiency is widespread in sub-Saharan Africa (SSA) with adverse impacts on human health. Agronomic biofortification with Zn fertilizers and improved soil fertility management, using mineral and organic nutrient resources, has previously been shown to increase Zn concentration of staple grain crops, including maize. Here, we show the potential of different soil fertility management options on maize crops to reduce dietary Zn deficiency in Zimbabwe using secondary data from a set of survey and field experiments. An ex-ante approach was used, informed by published evidence from studies in three contrasting smallholder production systems in Zimbabwe. To estimate current Zn deficiency in Zimbabwe, data on dietary Zn supply from non-maize sources from the Global Expanded Nutrient Supply (GENuS) data set were linked to maize grain Zn composition observed under typical current soil fertility management scenarios. A baseline dietary Zn deficiency prevalence of 68% was estimated from a reference maize grain Zn composition value of 16.6 mg kg-1 and an estimated dietary Zn intake of 9.3 mg capita-1 day-1 from all food sources. The potential health benefits of reducing Zn deficiency using different soil fertility management scenarios were quantified within a Disability Adjusted Life Years (DALYs) framework. A scenario using optimal mineral NPK fertilizers and locally available organic nutrient resources (i.e. cattle manure and leaf litter), but without additional soil Zn fertilizer applications, is estimated to increase maize grain Zn concentration to 19.3 mg kg-1. This would reduce the estimated prevalence of dietary Zn deficiency to 55%, potentially saving 2,238 DALYs year-1. Universal adoption of optimal fertilizers, to include soil Zn applications and locally available organic leaf litter, is estimated to increase maize grain Zn concentration to 32.4 mg kg-1 and reduce dietary Zn deficiency to 16.7%, potentially saving 9,119 DALYs year-1. Potential monetized yield gains from adopting improved soil fertility management range from 49-to 158-fold larger than the potential reduction in DALYs, if the latter are monetized using standard methods. Farmers should be incentivized to adopt improved soil fertility management to improve both crop yield and quality

Soil organic matter dynamics and crop productivity as affected by organic resource quality and management practices on smallholder farms

Crop productivity in low-input agricultural systems is largely a function of the soil’s capacity to hold and release nutrients in soil organic matter (SOM). Although sandy soils on most Zimbabwean smallholder farms inherently contain a small amount of SOM, large variability in soil productivity (fertility gradients) exists between adjacent fields or field sections within the same farm. Farmer management of such variability remains a challenge and sustainable option for soil productivity are required. This study was based on the hypothesis that SOM, a renewable resource, is the driving force behind sustainable crop productivity on depleted sandy soils. Relationships between maize yields and SOM contents, nitrogen (N) release patterns, and their links with organic matter management practices by farmers differing in resource endowment were evaluated under different Natural Regions (NR) in the smallholder farming areas of Chikwaka (NR II: >750 mm yr-1), Chinyika (NR III: 650-750 mm yr-1) and Zimuto (NR IV: 450-650 mm yr-1). The cumulative effect of applying known quantities of different quality organic resources on SOM formation and maize productivity was also evaluated on-station at Domboshawa (NR II) and Makoholi (NR IV) Experimental Stations following incorporation of sunnhemp (Crotalaria juncea) green manure, calliandra (Calliandra calothyrsus) prunings, cattle manure, maize (Zea mays) stover and pine (Pinus patula) sawdust into soil. Farmers’ perception of soil productivity was consistent with laboratory indices across the different rainfall zones. Criteria for ranking the most productive ‘rich’ and least productive ‘poor’ fields ranged from colour through elements of soil structure to crop response following external nutrient inputs. Laboratory analysis showed that rich fields contained significantly more soil organic carbon (SOC) ranging between 5 - 8 g kg-1, compared with between 3 - 6 g kg-1 for designated poor fields. Differences in SOC contents between rich and poor fields were wider in the old communal areas of Chikwaka and Zimuto with >70 years of smallholder farming than in Chinyika (<25 years), suggesting that the observed fertility gradients are a cumulative effect of years of differential management practices by the different farmer classes. Overall, rich fields received between 0.3 - 13 t C ha-1 compared to 0.1 - 6 t C ha-1 for poor fields with resource endowment apparently dictating the intensity of use. Organic inputs with a C:N ratio >25 (the bulk of available resources on-farm) contributed significantly to overall particulate organic matter (POM) size in sandy soils. The intensity of C management was reflected more in meso- POM (53-250 μm diameter) compared to the macro-POM (250-2000 μm diameter) fraction suggesting that the larger POM fraction has a high turnover and is not protected from degradation. However, early season (within five weeks of incorporation) N availability from these materials was low (<5% of added N) resulting in poor maize performance during the vegetative phase. This may justify the high organic matter loading strategy of up to 50 t ha-1 employed by those farmers who often achieve yields of >3 t ha-1 on coarse sands. Practical management options for smallholder farmers who usually access low quality resources may include pre-application treatments such as composting or organic/mineral N fertilizer combinations to enhance N availability. The overall size of the organo-mineral fraction (<53 μm diameter) in these soils was small (<250 g kg-1 soil) and stable, and was not influenced by quality and quantity of C inputs and time over which they had been applied. High quality organic materials (e.g. sunnhemp) apparently enhanced the N-supply capacity of the organo-mineral fraction without necessarily increasing its size. However, such materials (C:N <25) released between 15-25% of added N within five weeks of incorporation, suggesting that a significant proportion of N is lost before uptake. The challenge is to enhance the efficiency with which N release from high quality materials can be managed. Maize productivity, and most likely that of other cereals, on depleted sandy soils was related to within-season mineral N fluxes and labile POM fraction. Both factors were ii primarily a function of differential capacity to manage organic matter by different farmer classes. Sustenance of optimal maize yields on sandy soils may only be possible through regular supply of both high and low quality materials in combination with mineral fertilizers, particularly N. High quality C inputs are likely to enhance short-term nutrient supply capacity of a small organo-mineral fraction present, while slow decomposing materials would contribute towards the long-term maintenance of critical SOM pools.,Nutrient Use Efficiency and Soil Organic Matter (NUESOM)project (Grant 2002 FS 189)funded by Rockefeller Foundation (RF), RF’s African Careers Award Grant,TSBFCIAT’s African Network (AfNet)and International Foundation for Scienc

Lack of resilience in African smallholder farming : exploring measures to enhance the adaptive capacity of local communities to pressure climate change : final technical report - Zimbabwe (October 2010)

The table of contents for this item can be shared with the requester. The requester may then choose one chapter, up to 10% of the item, as per the Fair Dealing provision of the Canadian Copyright ActThe project worked with smallholder farming communities to identify opportunities for enhancing the capacity of different households to meet their staple food requirements and livelihood options in the wake of climate change and variability. The project supported smallholder farmers in identifying and using appropriate integrated soil fertility management (ISFM) innovations and other improved farming technologies to enhance the capacity of participating institutions and individual researchers to conduct and manage research and development at various levels. Integrated soil fertility management (ISFM) and livelihoods were used as entry points. Detailed accounts of project activities in Zambia, Zimbabwe, Mozambique, Tanzania, Uganda, Mali, and Ghana are provided

Point of no return? Rehabilitating desgraded soils for increased crop productivity on samllholder farmas in eastern Zimbabwe

Soil degradation is a major threat to Southern Africa's agricultural production. Crops show generally weak responses to mineral fertilizers on degraded soils. A three-year study was conducted between 2009 and 2012 on smallholder farms in eastern Zimbabwe to explore entry points for rehabilitating degraded croplands using principles of integrated soil fertility management (ISFM) supported through farmers' local knowledge of soils. Participatory research approaches were first used to investigate farmers' understanding of soil degradation and the commonly used local diagnostic indicators. Farmers' determinants of degraded soils centered on crop performance, indicator weed species and soil physical attributes, and matched laboratory parameters. Overall, physical and chemical properties of the degraded soils were significantly lower than reported values for productive sandy soils in Zimbabwe. Evaluated on ten degraded field sites of corresponding catenary positions and similar slope, the main ISFM options involved nitrogen-fixing herbaceous legumes planted in the first year, with subsequent addition of cattle manure in the second year. In the third year, the influence of the ISFM options on maize productivity and changes in soil biological activity were then evaluated. Phosphorus was applied every year under each sequence. The controls were natural fallow and continuous maize. The treatments were randomly assigned to plots at each of the experimental sites and replicated across farms. Above-ground biomass carbon (C) and nitrogen (N) accumulation was 3038 kg ha− 1 and 203 kg ha− 1, respectively, under 1-year indigenous legume fallow (indifallow) against 518 kg C ha− 1 and 14 kg N ha− 1 under 1-year natural fallow. Two-year indifallow produced approximately three times the biomass N attained under the 2-year natural fallow. When all the treatments were planted to a maize test crop in the third year, herbaceous legume-based sequences showed the highest response to mineral fertilizer N compared with natural fallow-based sequences and continuous fertilized maize. A regression of maize yields against mineral N fertilizer showed a maximum yield of 2.5 t ha− 1 under the herbaceous legume-based sequences against 1 t ha− 1 under continuous fertilized maize and natural fallow-based options following addition of 120 kg ha− 1 of mineral N fertilizer. ‘Green-start’, a Crotalaria juncea L. (sunnhemp)-based sequence, and ‘Indifallow-start 1’, an indigenous legume-based sequence, gave the highest microbial biomass C (MBC) of 243 mg kg− 1 soil compared with 187 mg kg− 1 soil under continuous maize. Microbial biomass N showed a similar trend. Under ‘Green-start’ and ‘Indifallow-start 1’, MBC to organic C ratio averaged 7; about one and half times more than under natural fallow-based sequences and continuous fertilized maize. Consistent with microbial biomass, soil carbon dioxide (CO2) emission under ‘Green-start’ and ‘Indifallow-start 1’ was 22% higher than under natural fallow-based sequences. Continuous maize treatments gave higher metabolic quotients (qCO2) than legume-based sequences, indicating a lower microbial efficiency under the former. We concluded that short-term restoration of productivity of degraded sandy soils should focus on high quality organic resource application and P fertilization to stimulate microbial activity and induce responses to mineral fertilizers. When coupled to P fertilization, herbaceous legume-based ISFM sequences provide a potential entry point for reversing soil degradation and offer opportunities for increasing crop productivity in dominant smallholder farming systems of Zimbabwe and other parts of Southern Africa.Fil: Nezomba, Hatirarami. University of Zimbabwe. Department of Soil Science and Agricultural Engineering; Zimbabwe. University of Zimbabwe. Soil Fertility Consortium for Southern; ZimbabweFil: Mtambanengwe, Florence. University of Zimbabwe. Department of Soil Science and Agricultural Engineering; Zimbabwe. University of Zimbabwe. Soil Fertility Consortium for Southern; ZimbabweFil: Tittonell, Pablo Adrian. Wageningen University and Research Centre; Holanda. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; ArgentinaFil: Mapfumo, Paul. University of Zimbabwe. Department of Soil Science and Agricultural Engineering; Zimbabwe. University of Zimbabwe. Soil Fertility Consortium for Southern; Zimbabw

Comparative short-term performance of soil water management options for increased productivity of maize-cowpea intercropping in semi-arid Zimbabwe

Rainfall variability poses a great challenge to rainfed cropping in sub-Saharan Africa. We evaluated, over three cropping seasons, conservation agriculture (reduced tillage and mulching) and farmer prioritized conventional tillage- and mulching-based options on seasonal soil water retention, and subsequent productivity of maize (Zea mays L.) and cowpea (Vigna unguiculata Walp L.) in mono- and inter-crops in Eastern Zimbabwe. The experiments were established on sand and clay soils. The first cropping season (2014/15) received evenly distributed rainfall (hereinafter referred to as ‘wetter’), while the two succeeding seasons (2015/16 and 2016/17) had high incidences of intra-seasonal dry spells (hereinafter referred to as ‘drier’). Overall, conventional tillage had 10–31% and 27–40% more moisture than conservation agriculture treatments on sand and clay soils, respectively. Soil moisture was most retained in intercrop under mulch-based conventional tillage. Maize grain yield during the ‘wetter’ season on sand soil was highest and least (P > 0.05) in intercrop under conservation agriculture (2.3 Mg ha−1) and mulch-based conventional tillage (1 Mg ha−1), respectively. On clay soil, intercrop under mulch-based conventional tillage (2.4 Mg ha−1) yielded the best. During the ‘drier’ seasons, intercrop under mulch-based conventional tillage achieved the best maize grain yield on both sand (1.5 Mg ha−1) and clay (1.4 Mg ha−1) soils. Mulching increased maize grain yield by 55–90% during the ‘drier’ seasons, but reduced water use efficiency (WUE) by approximately 15% during the ‘wetter’ season. Over the three seasons, cowpea grain yield did not exceed 1 Mg ha−1 in both mono- and inter-crops. The study revealed contrasting short-term effects of soil water management options on soil moisture retention and intercropping productivity as dictated by seasonal rainfall variability and soil type. These findings point to the need for tillage and mulching typologies across soil types to minimize negative effects of rainfall variability on crop productivity

Increasing phosphorus rate alters microbial dynamics and soil available P in a Lixisol of Zimbabwe.

Soil phosphorus (P) deficiency is a major challenge to food security in most parts of sub-Saharan Africa, including Zimbabwe, where farmers largely depend on local organic nutrient resources as fertilizer in the production of crops. Soil microorganisms can contribute to synchronous availability of soil P to plants through regulating immobilization and mineralization cycles of soil P pools but their activity may be influenced by antecedent soil P, P fertilizer application regimes and P uptake by plants. Using soils collected from plots where Crotalaria juncea (high quality), Calliandra calothyrsus (medium quality), cattle manure (variable quality), maize stover and Pinus patula sawdust (both low quality) were applied at the rate of 4 t C ha-1 with 16 kg P ha-1 at the start of every season over 16 seasons. A pot study was conducted to evaluate the influence of increasing inorganic P fertilizer rates (26 and 36 kg P ha-1) on soil microbial dynamics, soil P pools, and maize P uptake. Results indicated that nineteen (19) fungal and forty-two (42) bacterial colonies were identified over the study period. Fungi dominated bacteria on day one, with Aspergillus niger showing a 30-98% abundance that depends on organic resource quality. Overall, microbial diversity peaked activity characterized succession on day 29, which coincided with a significant (P<0.05) increase in P availability. Increasing P rate to 26 kg P ha-1 amplified the microbial diverse peak activity under medium-high quality resources while under the control the peak emerged earlier on day 15. Mucor and Bacillus had peak abundances on day 43 and 57, respectively, across treatments regardless of P rates. Treatment and P rate had a significant (P<0.01) effect on microbial P. Bacteria were more responsive to added P than fungi. Increasing P to 36 kg P ha-1 also stimulated an earlier microbial diverse peak activity under maize stover on day 15. Addition of P alone, without supplying complementary nutrients such as N, did not have a positive effect on maize P uptake. Farmers need to co-apply medium-high quality organic resources with high fertilizer P rates to increase microbial diversity, plant available P and maize growth on sandy soils (Lixisols). Our results suggest that there is a need to reconsider existing P fertilizer recommendations, currently pegged at between 26 and 30 kg P ha-1, for maize production on sandy soils as well as develop new fertilizer formulations to intensify crop production in Zimbabwe

Combinations of in-field moisture conservation and soil fertility management reduce effect of intra-seasonal dry spells on maize under semi-arid conditions

The high frequency of prolonged intra-season dry spells since the turn of the 21st century continues to heighten risk of crop failure in rainfed cropping systems of Southern Africa including Zimbabwe. This study explored the effects of combining in-field moisture conservation techniques and soil fertility management on maize (Zea mays L.) productivity under rainfed conditions in semi-arid eastern Zimbabwe. Treatment combinations were co-designed with farmers through participatory approaches, and tested on-farm on sandy and clayey soils over three consecutive seasons (2015/16–2017/18). Two tillage practices namely conventional (CT) and reduced tillage (RT), with 30 % mulch cover of dried thatching grass (Hyparrhenia filipendula (L.) Stapf) applied either at planting or tasseling or at both stages, were combined with low (35 kg N ha−1, 14 kg P ha−1and 3 t ha−1 of manure) and high (90 kg N ha−1, 26 kg P ha−1 and 7 t ha−1 of manure) fertilizer application rates in a split-split plot design. Intra-seasonal dry spells were more frequent during the first two seasons (i.e. 2015/16 and 2016/17), while the 2017/18 season was rather wet with well-distributed rains. Soil water content varied significantly (p -1 during the 2015/16 and 2016/17, respectively. However, during the wet 2017/18 season, the combination of RT + mulching at planting + high fertilizer rate yielded the best (3.5 t ha-1). On clayey soil, CT + mulching (at both stages) + high fertilizer rate gave the highest yields of 2.4, 2.9 and 3.4 t ha-1 in 2015/16, 2016/17 and 2017/18, respectively. Water use efficiency (WUE) was greatest under CT + mulching (at both stages) + high fertilizer rate especially during seasons that had high occurrence of intra-seasonal dry spells. Overall, the combination CT + mulching (at both stages) + high fertilizer rate increased maize yield by over 200 % and 300 % compared to the non-mulched treatments on sandy and clay soil, respectively, particularly during seasons with high incidences of intra-seasonal dry spells. Consequently, the treatment combination achieved the best economic returns during the drier seasons although income returns were reduced during the wetter season because of considerable yield loss due to waterlogging, particularly on the sandy soil. We thus conclude that mulching at strategic crop growth stages in combination with tillage and judicious addition of organic and inorganic fertilizers is a promising agronomic technique for reducing effects of intra-seasonal dry spells on maize productivity in rainfed smallholder cropping systems. Increasing farmer access to organic and inorganic fertilizers is, however, key to accelerated adoption of such agronomic techniques.</p