Forage crops boost the productivity and environmental sustainability of dairy farmers in southern Tanzania

Abstract

The adoption of cultivated forages is critical for enhancing biomass production, milk yield, and soil health in mixed smallholder dairy farming systems in the Southern Highlands of Tanzania. Yet most farmers continue to rely on traditional forage varieties such as Guatemala, Rhodes grass, and Napier grass for fodder. This study combines biophysical data from on-farm forage trials with simple environmental calculations to assess biomass production. Using data from six trials across three districts (Mufindi, Njombe, and Rungwe), we conducted a comprehensive analysis, comparing dry matter and crude protein yields of 14 different forage treatments and quantifying changes in SOC over a three-year period. These empirical data were then incorporated in an ex-ante environmental assessment of typical dairy farming. Key findings highlight significant variability in forages’ performance across districts—Rungwe district, with the highest rainfall, exhibiting the highest dry matter yields. Forage grass-legume intercrops outperformed the pure grasses in crude protein yields. Despite minimal changes in SOC over the three-year monitoring period, Mufindi district showed measurable SOC increases. This can be attributed to the initially low SOC content at the two study sitesand slower decomposition due to the colder temperatures in one of the sites compared to Njombe and Rungwe. The environmental analysis reveals large land, soil, and greenhouse gas (GHG) emissions footprints associated with current feeding practices across intensive dairy farms. However, replacing crop residues with high-quality forages such as Brachiaria hybrid Cayman and Rhodes grasses could improve milk productivity and result in neutral or positive environmental outcomes. At scale, improved forages increased milk yield by 15 %, reduced water and land footprints by 17 %, and enhanced soil-erosion resistance by 63 %, although GHGs emissions increased by 2 %. Our findings underscore the potential of cultivated forages for enhancing dairy production, improving soil health, and alleviating land- and water-use pressures in the Southern Highlands of Tanzania. Future long-term experimental studies, complemented by biophysical modeling, would be valuable in identifying the context-specific forage and management options for the dairy sector’s sustainability.