Assessment of the impacts of climate variability and change on rainfed cereal crop productivity in central Tanzania

Abstract

Though production of cereal crops in Tanzania could succumb to the projected climate change, research has mainly focused on maize (Zea mays L), the main staple crop for the country, and just little work has been done to analyse climate change impacts specifically on sorghum [Sorghum bicolor (L) Moench]. This study analysed the nature and sources of vulnerability on sorghum production by smallholder farmers due to climate variability and change and evaluated possible farm-level adaptation 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 Dodoma and Singida regions in central Tanzania. Local famers‟ management practices from databases and surveys were combined with field experimentation and simulation modelling. The Agricultural Production Systems SIMulator (APSIM) and Decision Support System for Agro-technological Transfer (DSSAT) models were calibrated and validated to predict growth and yield of sorghum under rainfed conditions in the case study regions. Three sorghum varieties: Macia, Pato and Tegemeo were used. The models were parameterized using different agronomic parameters (phenological development, dry matter accumulation and grain yield) and climatic data. Efficiency of the models were tested using model validation skill scores including d-stat, root mean square error (RMSE) and regression coefficient (R 2 ). To understand the nature of vulnerability, long term historical rainfall data were analysed. Simulations were conducted to evaluate the impacts and interactions of adaptation options, namely: staggered planting dates, recommended planting density, and variable fertilizer rates on sorghum and maize yields under long-term climate change towards the mid-century. The long-term rainfall analysis shows that total annual rainfall has so far notiii changed, but variability in the rainfall distribution within seasons has increased. Experimentation in this study demonstrated that the tested sorghum varieties had variable maturity dates and different responses to prolonged dry spells. Thus, the early maturing variety Macia (102 days) was able to avoid terminal drought versus Pato (118 days) and Tegemeo (114). Statistical analysis show a significant (at 0.05 level) inter-seasonal effect on grain yield and total biomass of the sorghum varieties. Agricultural production systems in semi-arid central Tanzania are projected to be affected by expected changes in climatic conditions over the next decades and century. Simulation results show that Macia will not be affected by climate change. In contrast, early maturing maize variety Situka was not able to compensate for the decline in yield under climate change. However, fertilizer application increased Situka yield significantly under future climates particularly when early planting was adopted. Coupled with increasing population pressure and declining soil fertility, climate variability and change are relentless driving forces to reduce agricultural productivity in the near future. Because agriculture causes a variety of benefits and challenges, impacts of climate change on agricultural systems are of importance from an economic but also from a social and environmental point of view. Assessment of impacts and potential adaptation supports the decision making processes of farmers, governments, and other stakeholders. Adaptation options such as changes in sowing dates, changes in planting density and fertilizer application were evaluated. To adapt to the changing climate, early sowing and increasing plant density per hectare and fertilizer application would be feasible options. The selection of an earlier sowing date for maize, for instance, would be the appropriate response to offset the negative effect of increased temperature. This change in planting date would allow for the crop to develop during a period of the year with loweriv temperatures, thereby decreasing developmental rates and increasing the growth duration, especially the grain filling period. The study also found that site specific agro-ecological conditions such as soil type characterize farmers‟ responses to decisions on the type of crop and/or crop variety to grow in a given season. This is partly due to their perceptions on soil fertility status among soil types taking spatial variability across the fields into account. Other socio-economic factors ranging from food tastes and preferences to markets and prices, variably but strongly influence decisions on continued adoption of drought tolerant crops (sorghum and millets) versus the susceptible maize. The results show that these factors and associated challenges have the potential to bring negative externalities, therefore, efforts to minimize the impacts from climate variability and change should go alongside with addressing the reported perception and preference challenges. 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 other factors related to improved varieties, nutrient resource access and socio-economic factors is critical for rainfed cereal production under changing climate. This dissertation addresses impacts and adaptation to climate change on sorghum production (with some comparison with maize) in the central zone of Tanzania. An overview over different approaches of modelling climate change impacts on crop production as well as a review of studies that analyse climate change impacts on agriculture in sub-Saharan Africa and Tanzania in particular are given in the introductory Chapter 1. Chapter 2 describes the evaluation of the performance of three sorghum varieties at the field level and assessment of their performance over a long-term period using biophysical modelling. In Chapter 3, an approach that integrates the biophysical modelsv DSSAT and APSIM model with GCMs is used to analyse the impact of climate change on sorghum and maize production. Chapter 4 investigates the influence of driving factors separate from impacts of climate change on the production of sorghum relative to other cereals important in the zone. General discussion and conclusions are given in Chapter 5.