Root Length Density in Maize/Cowpea Intercropping under a Basin Tillage System in a Semi-Arid Area of Zimbabwe

A study to assess the effect of intercropping maize (Zea mays L.) and cowpea (Vigna unguiculata L.) within the same basin or outside the basin on root length density (RLD) was conducted at the International Crop Research Institute for Semi-Arid Tropics (ICRISAT) Matopos Research Station from December 2009 to April 2010. The experiment was laid out in a Randomised Complete Block Design (RCBD) with four treatments replicated four times namely; sole maize, sole cowpea, maizecowpea intercrop with cowpea and maize planted within the same basin and maize-cowpea intercrop with cowpea planted 20 cm outside the maize basin. There was significant difference (P < 0.001) in RLD, grain yield and stover yield. Maize-cowpea intercropped within the same basin achieved higher RLD, grain yield and stover yield than cowpea that was intercropped outside the basin and the sole crops. The land equivalent ratio (LER) in both intercrop designs showed that intercropping had better grain yield performance when compared to sole cropping. It can be concluded that intercropping maize and cowpeas within the same basin can result in an environment around the crop achieving higher RLD which translates to better grain yield compared to the sole cropping and intercropping cowpeas outside the basin

Is maize-cowpea intercropping a viable option for smallholder farms in the risky environments of semi-arid southern Africa?

Intercropping cereals with legumes can potentially enhance productivity and soil fertility. There is limited experimental evidence on the mechanisms underlying benefits or risks in intercropping systems and below-ground interactions in intercrops remain largely unstudied. Such understanding can inform strategies towards maximising returns to investments, particularly in poor fertility soils on smallholder farms in semi-arid areas of sub-Saharan Africa. Additive intercropping experiments were established covering several seasons (2010/11–2014/15) and different conditions (on-station and on-farm) to determine effects on soil chemical variables, root dynamics and yield of intercrops. Maize was planted with the first effective rains and received either no fertiliser or 40 kg N ha−1. Cowpea was planted on the same date as maize or three weeks after planting maize in intercrops or sole stands and received no fertiliser. End-of-season available N was highest (P 1. Intercropping, however, resulted in compromised cowpea yields especially under the relay intercrop compared with the sole cowpea stands whilst maize yield was either not affected or improved. We attributed this to the lack of below-ground niche differentiation in root distribution between maize and cowpea. Maize–cowpea intercropping with low doses of N fertiliser resulted in over-yielding compared with monocropping. Intercropping proved to be a robust option across seasons and soil types, confirming that it is a promising option for resource-poor smallholders

Tillage, mulch and fertiliser impacts on soil nitrogen availability and maize production in semi-arid Zimbabwe

Conservation agriculture has been promoted widely in sub-Saharan African to cushion smallholder farmers against the adverse effects of soil fertility decline, stabilize crop yields and increase resilience to climate change and variability. Our study aimed to determine if aspects of CA, namely tillage and mulching with manure and fertiliser application, improved soil mineral N release, plant N uptake and maize yields in cropping systems on poor soils in semi-arid Matobo, Zimbabwe. The experiment, run for three seasons (2012/13–2014/15), was a split-split plot design with three replicates. Tillage (animal-drawn ploughing and ripping) was the main plot treatment and residue application was the sub plot treatment with two levels (100% residues removed or retained after harvest). Five fertility amendments (mineral fertiliser at 0, 20 and 40 kg N ha-1, 5 t ha-1 manure only and 5 t ha-1 manure + 20 kg N ha-1) were sub-sub plot treatments. Plough tillage stimulated N mineralisation by 4–19 kg N ha-1 and maize N uptake 13–23% more than the ripper tillage. When mulch was added to the plough tillage, mineralisation was slowed resulting in less crop N uptake (by 5–19%) compared with no mulch application. N uptake was highest in the manure treatments. N recovery and agronomic N efficiency by maize were highly variable over the three seasons, reflecting the uncertainty complicating farmers’ decision making. Nitrogen recovery in the manure treatments was generally poor in the first season resulting in low grain yields in the range 100–260 kg ha-1 regardless of tillage, though higher in subsequent seasons. In the second season manure application gave the largest grain yields under the ripper tillage, both with and without mulch averaging 1850 and 2228 kg ha-1 respectively. Under the plough tillage, the 40 kg N ha-1 treatment gave the highest grain yields of 1985 kg ha-1. In the third season yields were generally poor under all treatments due to low and poorly-distributed rainfall. The CA principles of minimum soil disturbance and maintenance of a permanent mulch cover resulted in reduced soil mineral N availability for crop uptake and poor maize yields. Nutrient inputs through mineral fertilisers and manure are key to ensuring production in such infertile, sandy soils which predominate in semi-arid regions of southern Africa

Effect of hand-hoe based conservation agriculture on soil fertility and maize yield in selected smallholder areas in Zimbabwe

Conservation agriculture (CA) based on hand-hoe prepared planting basins is being widely promoted in southern Africa, targeting resource-constrained farmers with limited access to draft power. This study was conducted across 15 districts covering four agro-ecological zones in Zimbabwe where paired CA and conventional animal drawn tillage (CADT) plots had been established on 450 farms as part of CA promotion. The aim of the study was to assess the effect of CA on soil pH, organic C, total P and maize (Zea mays L.) grain yield compared with CADT, and also to evaluate the yield benefits of mulching and crop rotation in CA with or without mineral fertilizer use. It was hypothesized that CA improved the pH, organic C, total P of the soils (Arenosols) and grain yield compared with CADT and that mulching and crop rotation in CA increased maize grain yield. A total of 1014 soil samples (0–0.2 m depth) were taken at the end of the 2009/10 cropping season and analyzed for pH, organic C and total P. Grain yield was determined in 2009/10 and 2010/11 from 0.01 ha net plots. There was no significant difference in average soil pH, total P and organic C between CA and CADT plots and therefore the hypothesis that CA improves these soil properties was rejected. Average concentration for organic C for both CA and CADT plots was less than 10 g kg−1, a minimum threshold for well managed soils. When combined with mineral fertilizer: mulching, crop rotation, and mulching + crop rotation in CA increased maize grain yield by 20–33%, 7–9% and 58–69%, respectively. With no mineral fertilizer application, mulching, crop rotation, and mulching + crop rotation depressed maize grain yield by 48%, 28% and 36%, respectively. Therefore the hypothesis that mulching and crop rotation increase maize grain yield was accepted when mineral fertilizer was added and rejected when the fertilizer was not added. It was concluded that the yield benefits of CA can only be realized when mineral fertilizer is also applied. All the three CA principles in combination with mineral fertilizer results in highest yield benefits compared with one or two principles as currently done by most smallholder farmers in Zimbabwe. Access to mineral fertilizer is an important factor in the targeting of CA promotion in smallholder areas of Zimbabwe and similar socio-ecological zones in sub-Saharan Africa

Effect of soil fertility management strategies and resource-endowment on spatial soil fertility gradients, plant nutrient uptake and maize growth at two smallholder areas, north-western Zimbabwe

We investigate the effects of smallholder farmer resource-endowment and soil nutrient management strategies on plant nutrient uptake and growth across soil fertility gradients under semi-arid conditions. Soil fertility gradients as influenced by farmers’ resource availability may affect the response of crops to fertilizer addition and therefore productivity. The study was conducted in Njelele and Nemangwe smallholder areas (450-800 mm per annum, unimodal) in north-western Zimbabwe. Soil and maize cobleaf samples were collected from fields of farmers (varying resource endowment) located near to (homefields) and far away (outfields) from the farmers’ homesteads during the 2005-6 season. The samples were analysed for selected soil fertility indicators and soil samples were further used to test maize growth response to various nutrient applications under greenhouse conditions. Soil fertility (organic C, total N and available P) significantly (P<0.05) decreased from resourceendowed to resource-constrained farmers, and from outfields to homefields, but the latter differences were only significant for available P. Besides resource-endowment and field type, response to nutrient applications also depended on soil texture. In sandy soil, both N and P were limiting to MAIZE growth in outfields while N was most limiting in the homefield. It was concluded that resource-endowment and nutrient resource management strategies employed by farmers result in soil fertility gradients which affect response of crops to fertilisation and therefore need to be factored in the development of fertiliser recommendations

Risk management options in maize cropping systems in semi-arid areas of Southern Africa

Although rainfed cropping in semi-arid areas is risky due to frequent droughts and dry spells, planting early with the first rains is often expected to result in yield benefits. We hypothesised that planting early leads to yield benefits if the planting coincides with a mineral N flush at the start of the season but leads to crop failure if there is a false start to the cropping season. The effects of different management options, including tillage (ploughing and ripping), mulch (two levels 0 and 2 t ha−1) and fertility amendments (five levels: 0; 20 and 40 kg N ha−1; 5 t manure ha−1 and 5 t ha−1 manure + 20 kg N ha−1) on grain yields were simulated using the calibrated and tested APSIM model over a 30-year period (1984–2015). Yields were simulated and compared across seven planting date scenarios (1 November, 15 November, 30 November, 15 December, 31 December, 15 January and planting when cumulative rainfall of 20 mm was received in three consecutive days). Planting with the first rains with manure + 20 kg N ha−1 resulted in the best average yield of 2271 kg ha−1 whilst the poorest average yields of 22 kg ha−1 were observed with planting on 15 January with no fertility amendment (0 kg N ha−1). Planting early (1 Nov to 15 Nov) and with the first rains resulted in exceeding the food self-sufficiency threshold of 1080 kg ha-1 in 40–83 % of the cases if fertility amendments are applied, as well as a low probability of complete crop failure, ranging from 0 to 40%. Grain yield penalties due to a false start followed the trend: ripper + mulch > plough + mulch > ripper (no mulch) averaging 256, 190 and 182 kg ha-1 respectively across all the fertility treatments. The model was able to simulate the occurrence of the mineral N flush with the first rains. Its coincidence with planting resulted in average yield benefits of 712, 452, 382 and 210 kg ha-1 for the following respective planting dates: 1 Nov, 15 Nov, 30 Nov, variable date when >20 mm rainfall was received. Early planting, in combination with reduced tillage, mulch and N containing fertility amendments is critical to reduce risk of crop failure in the smallholder cropping systems of semi-arid areas of southern Africa and achieve the best possible yields

Grain Yield Responses of Selected Crop Varieties at Two Pairs of Temperature Analogue Sites in Sub-humid and Semi-arid Areas of Zimbabwe

Climate analogues, based on 30 years meteorological data, were identified in smallholder areas of Zimbabwe. The sites were Kadoma (722 mm annual mean rainfall; 21.8 °C annual mean temperature) which was the higher temperature analogue site for Mazowe (842 mm annual mean rainfall; 18.2 °C annual mean temperature) for wetter areas, and Chiredzi (541 mm annual mean rainfall; 21.3 °C annual mean temperature) which was the higher temperature analogue site for Matobo (567 mm annual mean rainfall: 18.4 °C annual mean temperature) for drier areas. At each site and for each crop, three varieties were laid out in a randomized complete block design with three replications. The trials were conducted for two seasons (2011/2012 and 2012/2013). Maize and groundnut yields were higher at the cooler and wet sites and decreased significantly at the warmer and dry sites. In case of sorghum and cowpea, yields at the hotter site remained high implying that these crops are more tolerant to warmer temperatures predicted for 2050. At the drier sites, yields for all crops were significantly lower at the hotter site implying that crop production in the 2050s climate of the cooler site will be more difficult. The hypothesis that with increasing surface temperatures in a climate change scenario short duration genotypes can perform better compared with long duration was not confirmed

Grain yield of selected crops at four climate analogue locations in Zimbabwe

Predicted warmer climates are likely to negatively affect production systems and expose smallholder farmers in sub-Saharan Africa, whose adaptive capacity is limited mainly due to poverty, to food insecurity. We studied the performance of selected varieties representing short, medium and long duration growth periods of four crops (maize (Zea mays L.), sorghum (Sorghum bicolor L.), groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata L.) at two pairs (wet and dry) of 2050s climate analogue sites. Climate analogues, based on 30 years metereological data, were identified in smallholder areas of Zimbabwe. The sites were Kadoma (722 mm annual mean rainfall; 21.8oC annual mean temperature) which was the higher-temperature analogue site for Mazowe (842 mm annual mean rainfall; 18.2oC annual mean temperature) for wetter areas, and Chiredzi (541 mm annual mean rainfall; 21.3oC annual mean temperature) which was the higher-temperature analogue site for Matobo (567 mm annual mean rainfall: 18.4oC annual mean temperature) for drier areas. First season (2011/12) results showed that for the wetter pair, maize and groundnut grain yields were significantly higher at the cooler site (Mazowe). Sorghum yields were not significantly different between the sites and there was no grain yield for cowpea at the cooler site due to a fungal disease. Varietal yield differences were only significantly higher (P<0.05) at the cooler site for groundnut where the short duration variety had the highest yield (3809 kg/ha) and the medium duration variety the lowest yield (1420 kg/ha), compared with 140-355 kg/ha at the hotter site where growth was poor for all varieties. For the drier sites, maize, sorghum and cowpea grain yields were higher at the cooler site (Matobo) compared with the hotter sites (Chiredzi) but varietal differences were not significant. Results for the second season (2012/13) will be presented

Micro Doses, Mega Benefits Promoting Fertilizer Use in Semi-Arid Zimbabwe

The contents of this document are (1) soil fertility and crop production in the smallholder systems, (2) current knowledge about fertilizer use in the dry areas of Zimbabwe, (3) low Input Options – microdosing, (4) what is microdosing? (5) types of N fertilizer available in Zimbabwe, (6) evidence of success from the drier areas of Zimbabwe, (7) how much fertilizer should a farmer buy? (8) where and how can farmers get fertilizer? (9) how sustainable is microdosing? (10) how can farmers maximize returns on their investment in fertility amendments? (11) introducing and Promoting Microdosing to Smallholder farmers, (12) training farmers in microdosing and (13) setting up demonstrations on microdosing

Weed growth and labor demand under hand-hoe based reduced tillage in smallholder farmers’ fields in Zimbabwe

Conservation agriculture based on hand hoe dug planting basins has been widely promoted for the last decade or two in the smallholder farming sector of southern Africa targeting resource constrained households without access to draft power. In Zimbabwe planting basins are used by about one hundred thousand households but on small plots (<0.5 ha) although most are unable to adopt soil surface mulching and crop rotation due to competing uses for crop residues as livestock feed and poorly developed markets for other crops, respectively. We report on the effects of reduced tillage based on hand-hoe dug planting basins (PB) on weed growth (20 farms), and labor demand and returns to investment (50 farms) compared with animal-drawn mouldboard plough based conventional tillage (CONV) in maize (Zea mays L.) fields, across selected districts located in contrasting agro-ecological zones in Zimbabwe. Weed growth was assessed through a survey conducted at the end of the 2009/10 and 2010/11 cropping seasons. Labor demand and returns to investment were measured on 50 farms across five districts using direct observations during the 2011/12 cropping season. The survey showed that farmers on average weeded their PB plots 2.7 times per season compared to 1.7–1.9 times in CONV plots (P < 0.001), and timing was often delayed in the former. Reduced tillage plots had 17% (P < 0.001) more weed ground cover and 9% (P < 0.05) more weed dry matter compared with CONV plots in the 2009/10 season, and differences in 2010/11 were not significant. Weed growth was highest in semi-arid areas (natural regions III and IV) compared with wetter sub-humid areas (natural region II) and arid areas (natural region V). Farmers planted their PB plots 12–23 days earlier, weeding frequency was 42.1–58.9% higher in PB plots, compared with CONV. Labor demand was more than double under PB (84.7 man days ha−1, weeding 48.1 man days ha−1) compared to CONV (38.6 man days ha−1). However, returns to investment were 42.7% higher under PB (U$1.77) compared with CONV (U$1.24). Weed growth and labor demand remained high under PB tillage even after several years, interventions such as the use of alternative weed control methods need to be introduced to farmers to reduce labor demand and consequently increase its adoption both in terms of number of farmers and cultivated area in southern Africa