Vulnerability and adaptation to climate variability and change in smallholder farming systems in Zimbabwe

Keywords: Climate change; Increased climate variability; Vulnerability; Smallholder farmers; Adaptation Climate change and increased climate variability are currently seen as the major constraints to the already stressed smallholder farming livelihood system in southern Africa. The main objectives of this study were first to understand the nature and sources of vulnerability of smallholder farmers to climate variability and change, and second to use this knowledge to evaluate possible farm-level management options that can enhance the adaptive capacity of smallholder farmers in the face of increased climate variability and long-term change in climate. The study was conducted in Makoni and Hwedza districts in eastern Zimbabwe. Local famers’ and expert empirical knowledge were combined using research tools that mainly included detailed field observations and surveys, systems analysis and field experimentation, and simulation modelling (the Agricultural Production Systems Simulator (APSIM)). To understand the nature and sources of vulnerability, long term climate data were analysed and farmers were interviewed individually and in groups. On-farm experimentation and simulation modelling were conducted to evaluate the impacts and interactions of adaptation options namely maize cultivar choice, staggered planting dates, and variable fertilizer rates, on maize yield under both short-term climate variability and long-term climate change. Another on-farm experiment was conducted to assess whether small grains (finger millet and sorghum) perform as well as maize under variable soil and rainfall conditions. The long-term rainfall and temperature analyses closely supports farmers’ perceptions that the total annual rainfall has so far not changed, but variability in the rainfall distribution within seasons has increased. The number of rain days has decreased, and the frequency of dry spells within season increased. The mean daily minimum temperature increased by 0.2°C per decade in Makoni, and by 0.5°C per decade in Hwedza, over the period from 1962 to 2000. The surface air temperature is further projected to increase significantly in Makoni and Hwedza, by 2100. The impacts of rising temperatures and increased rainfall variability among smallholder households were highly differentiated because different households depend on varied farming livelihood sub-systems, which were exposed uniquely to aspects of climatic risk. For example, livestock production was sensitive to drought due to lack of feed, affecting resource-endowed farmers, who often own relatively large herds of cattle. Crop production was more sensitive to increased rainfall variability, affecting especially farmers with intermediate resource endowment. Availability of wild fruits and social safety nets were affected directly and indirectly by extreme temperatures and increased rainfall variability, impacting the livelihoods of poorer farmers. Farmers have also access to different biophysical and socioeconomic resources such as fertilizer and farm labour inputs, and as a result they respond variedly to impacts of a changing climate. Thus, alongside climate variability and change, farmers also faced biophysical and socioeconomic challenges, and these challenges had strong interactions with adaptation options to climate change. Experimentation in this studydemonstrated that the maize cultivars currently on the market in Zimbabwe, and in many parts of southern Africa, exhibit narrow differences in maturity time such that they do not respond differently to prolonged dry spells. The yield performance for all three cultivars is projected to be similar in future change in climates, consistent with results from the experiments.In the current cropping system farmers can select any cultivar available on the market without a yield penalty. However, with climate change none of the available cultivars will be able to compensate for the decline in yield. Greater maize grain yields were obtained with both the early (25 October – 20 November) and normal (21 November – 15 December) plantings, with no significant differences between these planting windows(e.g. on average 5 t ha-1 in Makoni, and 3 t ha-1 in Hwedza for the high fertilization rate).Contrary to previous research findings, there is a reasonably wide planting window in which good yields can be obtained if the rains start on time, but if the start of the rains is delayed until after the beginning of December planting should be done as soon as possible. Regardless of the amount of fertilizer applied, yields were reduced strongly when planting was substantially delayed by four weeks after the start of the rainy season. Maize yielded more than finger millet and sorghum even when rainfall was poor in the 2010/2011 season. For example, maize yielded 2.4 t ha-1 compared with 1.6 t ha-1 for finger millet and 0.4 t ha-1 for sorghum in the 2010/2011 rainfall season in Makoni. Finger millet and sorghum failed to emerge unless fertilizer was applied. Application of manure alone failed to address this challenge of poor emergence until fertilizer was added. Sorghum suffered critical yield losses due to bird damage. The better performance of maize over finger millet and sorghum suggested that the recommendation to substitute small grains for maize as a viable adaptation option to a changing climate, will neither be the best option for robust adaptation nor attractive for farmers in southern Africa. Alternatively spreading crops across the farm and in time can be a viable strategy to spread climatic risk as well as improve human nutrition. Poor soil fertility constrained yield more strongly than rainfall and late planting, as demonstrated by the large yield gap (> 1.2 t ha-1) between the unfertilized and fertilized cultivars even in the poor rainfall season (2010/2011). Fertilization increased yield significantly under both the baseline and future climates particularly when planting before mid-December.The maize response to mineral nitrogen is, however, projected to decline as climate changes, although effects only become substantial towards the end of the 21st Century. Soil fertility management is therefore likely to be a major entry point for increasing the adaptive capacity of smallholder farmers to climate change and increased climate variability. However, management of factors related to both nutrient resource access and farmers decisions to enhance resource use efficiencies are critical if agriculture is to be used as robust adaptation options to climate change by smallholder in Southern Africa.</p

Science-based decision support for formulating crop fertilizer recommendations in sub-Saharan Africa

Open Access Article; Published online: 31 Jan 2020In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha−1 in Nigeria, 2.3, 0.9 and 0.2 t ha−1 in Ethiopia, and 1.5, 0.8 and 0.2 t ha−1 in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg−1 N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha−1 and K by 24 and 38 kg ha−1 than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha−1) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg−1, respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg−1). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha−1 than the blanket recommendations, but maize yield (6 t ha−1) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers

Long-term nitrate and phosphate loading of river water in the Upper Manyame Catchment, Zimbabwe

Urbanisation and agriculture represent a dramatic example of human interference in catchment hydrology. The impact of agricultural, domestic, industrial and municipal activities on river flow and water quality within the Upper Manyame Catchment Area (UMCA) was assessed using 7-year nitrate, phosphate and water flow rate data, collected by the Environmental Management Agency (EMA). Water samples for nitrate and phosphate analysis were collected at 8 points along the Manyame (2 points), Marimba (2 points) and Mukuvisi (4 points) rivers, and runoff volume was recorded at the mouth of each river. Annual runoff of each river was closely related to rainfall amount, with the lowest runoff being recorded during drought years. High nitrate and phosphate concentrations were recorded directly downstream of residential, municipal and industrial areas suggesting that these were the major sources of the pollutants found in the river water. For example, phosphate concentration at 2 sites along Mukuvisi River (downstream of domestic and industrial areas) exceeded the statutory limit (0.5 mg/ℓ) for ‘safe’ or good quality water (‘blue’ category) according to the Zimbabwe Water (Waste and Effluent Disposal) Regulations, and ranged from 0.78 mg/ℓ during the dry season to 2.23 mg/ℓ during the wet season. In the Marimba River phosphate concentration at Site 4 (downstream of domestic, industrial and sewage processing plant) also exceeded the safe water quality standard by 4–6 times. Although Marimba River contributes the lowest proportion of runoff (relative to the other two rivers sampled) entering Lake Chivero, it contributed the highest nitrate (114 840 kg/yr) and phosphate (84 324 kg/yr) loading. It was concluded that anthropogenic activities within the UMCA were the major sources of nitrate and phosphate pollution in the three rivers and pose a serious threat to the ecological sustainability of the rivers and lakes downstream, and to the economic wellbeing of nearby cities which rely on the water for potable use

Quantifying variability in maize yield response to nutrient applications in the northern Nigeria Savanna

Open Access JournalDiagnostic on-farm nutrient omission trials were conducted over two cropping seasons (2015 and 2016) to assess soil nutrients related constraints to maize yield in the northern Nigerian savanna agro-ecological zone and to quantify their variability. Two sets of trials were conducted side by side, one with an open pollinated maize variety (OPV) and the other one with a hybrid maize variety and each set had six equal treatments laid out in 198 farmers’ fields. The treatments comprised (i) a control, (ii) a PK (‘−N,’ without N), (iii) an NK (‘−P,’ without P), (iv) an NP (‘−K,’ without K), (v) an NPK and (vi) an NPK + S + Ca + Mg + Zn + B (‘+SMM,’ NPK plus secondary macro- and micro-nutrients). Moderate to a large variability in most soil characteristics was observed in the studied fields. Consequently, cluster analysis revealed three distinct yield-nutrient response classes common for the two types of maize varieties. These define classes were fields that have (i) no-response to any nutrient, (ii) a large response to N and P and (iii) a large response to N alone. Although overall yield performance of OPV and hybrid varieties was similar, a distinct fourth class was identified for the hybrid variety, (iv) fields with a large response to N and secondary macro- and micro-nutrients. The results indicate that the large variability in soil nutrients related constraints need to be accounted for to optimize maize yield in the northern Nigerian savanna. The development of field- and area-specific fertilizer recommendations is highly needed, using simple decision support tools that consider variable soil fertility conditions and yield responses as obtained from this study

Improved nutrient use and manure management in Africa

Scaling up agronomic technologies and practices for African farming systems has the potential to benefit low-input systems in becoming more productive while reducing greenhouse gas (GHG) emissions. This policy brief provides an overview of soil management and fertility enhancement using organic fertilizers including manure. Strengthening technical capacity of agricultural extension should be prioritized, parallel to coordinated research on soil information systems. Reducing GHG while increasing productivity requires a combination of organic and mineral fertilizers; climate-smart technologies; legume-cereal rotations; agroforestry, and applying the right source of fertilizer, the right amount, at the right time, in the right place (www. ipni.net/4R)

Compositional nutrient diagnosis (CND) and associated yield predictions in maize: a case study in the northern Guinea savanna of Nigeria

Open Access Article; Published online: 17 Aug 2022Developing optimal strategies for nutrient management of soils and crops at a larger scale requires an understanding of nutrient limitations and imbalances. The availability of extensive data (n = 1,781) from 2-yr nutrient omission trials in the most suitable agroecological zone for maize (Zea mays L.) in Nigeria (i.e., the northern Guinea savanna) provides an opportunity to assess nutrient limitations and imbalances using the concept of multi-ratio compositional nutrient diagnosis (CND). We also compared and contrasted the use of linear regression models and bootstrap forest machine learning to predict maize yield based on nutrient concentration in ear leaves. The results showed that 35% of the experimental plots had low yields due to nutrient imbalances (hereafter referred to as low yield imbalanced [LYI]). These experimental plots were dominated by control plots (without any nutrients applied), plots without N fertilization, and plots without P fertilization. Using the control plot as the ultimate indicator of nutrient imbalance, the significantly limiting nutrients in order of decreasing frequency of deficiency were N, P, S, Ca > Cu, and B. Both linear regression and bootstrap forest machine learning models fairly predicted maize grain yield based on nutrient concentration in ear leaves only in the LYI group and when examining all data with an independent validation dataset. These results suggest that nutrient management strategies, especially through the site-specific management approach, should consider S, Ca, Cu, and B in addition to the existing nutrients N, P, and K to improve nutrient balance and maize yield in the study area

Climate change and maize yield in southern Africa: what can farm management do?

There is concern that food insecurity will increase in southern Africa due to climate change. We quantified the response of maize yield to projected climate change and to three key management options – planting date, fertilizer use and cultivar choice – using the crop simulation model, agricultural production systems simulator (APSIM), at two contrasting sites in Zimbabwe. Three climate periods up to 2100 were selected to cover both near- and long-term climates. Future climate data under two radiative forcing scenarios were generated from five global circulation models. The temperature is projected to increase significantly in Zimbabwe by 2100 with no significant change in mean annual total rainfall. When planting before mid-December with a high fertilizer rate, the simulated average grain yield for all three maize cultivars declined by 13% for the periods 2010–2039 and 2040–2069 and by 20% for 2070–2099 compared with the baseline climate, under low radiative forcing. Larger declines in yield of up to 32% were predicted for 2070–2099 with high radiative forcing. Despite differences in annual rainfall, similar trends in yield changes were observed for the two sites studied, Hwedza and Makoni. The yield response to delay in planting was nonlinear. Fertilizer increased yield significantly under both baseline and future climates. The response of maize to mineral nitrogen decreased with progressing climate change, implying a decrease in the optimal fertilizer rate in the future. Our results suggest that in the near future, improved crop and soil fertility management will remain important for enhanced maize yield. Towards the end of the 21st century, however, none of the farm management options tested in the study can avoid large yield losses in southern Africa due to climate change. There is a need to transform the current cropping systems of southern Africa to offset the negative impacts of climate change

Waste to resource: use of water treatment residual for increased maize productivity and micronutrient content

Soil degradation, which is linked to poor nutrient management, remains a major constraint to sustained crop production in smallholder urban agriculture (UA) in sub-Saharan Africa (SSA). While organic nutrient resources are often used in UA to complement mineral fertilizers in soil fertility management, they are usually scarce and of poor quality to provide optimum nutrients for crop uptake. Alternative soil nutrient management options are required. This study, therefore, evaluates the short-term benefits of applying an aluminium-based water treatment residual (Al-WTR), in combination with compost and inorganic P fertilizer, on soil chemical properties, and maize (Zea mays L.) productivity and nutrient uptake. An eight-week greenhouse experiment was established with 12 treatments consisting of soil, Al-WTR and compost (with or without P fertilizer). The co-amendment (10% Al-WTR + 10% compost) produced maize shoot biomass of 3.92 ± 0.16 g at 5 weeks after emergence, significantly (p < 0.05) out-yielding the unamended control which yielded 1.33 ± 0.17 g. The addition of P fertilizer to the co-amendment further increased maize shoot yield by about twofold (7.23 ± 0.07 g). The co-amendment (10% Al-WTR + 10% C) with P increased maize uptake of zinc (Zn), copper (Cu) and manganese (Mn), compared with 10% C + P. Overall, the results demonstrate that combining Al-WTR, compost and P fertilizer increases maize productivity and micronutrient uptake in comparison with single amendments of compost and fertilizer. The enhanced micronutrient uptake can potentially improve maize grain quality, and subsequently human nutrition for the urban population of SSA, partly addressing the UN’s Sustainable Development Goal number 3 of improving diets