Sustainability of intensification of smallholder maize production in Tanzania

Abstract

Tanzania’s fast growing population will increase the demand for food crops, particularly maize. Sustainable intensification is needed to meet this demand while, at the same time, preserving the environment and climate. A joint project of Yara, Syngenta, Sokoine University of Agriculture, and the Norwegian University of Life Sciences demonstrated that a balanced supply of crop nutrients together with other improved practices has the potential to increase maize yields and farm profitability. A framework was developed and applied to assess the potential impacts of different cropping intensities on climate, soil, water, and biodiversity in order to evaluate the environmental sustainability of the measures. Maize yields increased by 49-163 % compared to prevailing farmer practice (FP). This in turn may reduce the need for arable land expansion and thus potentially avoid GHG emissions. If GHG emissions from potential arable land expansion into tropical scrubland are considered, GHG emissions from the low-yielding treatments would be 3.6-12 times greater than the CFP of the improved protocol. Low positive soil nutrient balances with the improved cropping protocol indicate sustainable fertilizer use, which can replenish the soil with sufficient nutrients. In contrast, FP often showed negative nutrient balances, signifying unsustainable nutrient mining even at low yield levels. The increased nitrogen rates and crop productivity lead to increased soil acidification, which needs compensation from liming. The improved maize protocol doubled maize stover biomass, which can be used to improve the organic matter and fertility of the soil either through direct incorporation into the soil or through feeding livestock and producing and applying manure. A water footprint calculation at one site revealed that the maize produced according to FP consumed 50 % more water per ton of grain compared to the improved protocol. Biodiversity was assessed in different ways. In-field biodiversity was reduced with the suggested protocol, while on-farm biodiversity was enhanced through the planting of additional trees instead of expanding cropland. About 50 % less land was needed to produce one ton of maize grain, reducing pressure for land expansion that would have potential negative effects on biodiversity on a larger scale.