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Addressing the problem of low crop productivity and food insecurity can be accelerated through community-centered implementation of good agricultural management practices. This study was conducted in Babati, Northern Tanzania. The objective of the study was to determine nitrogen (N) and phosphorus (P) application requirements for maize, and demonstrate economically viable best bet yield-improving management technologies under three ecozones namely; 'low elevation low rainfall', 'medium elevation high rainfall' and 'medium elevation low rainfall' ecozone. Two sets of trials were conducted: N (0, 45, 90, 120 and 150 kg [ha.sup.-1]) and P (0, 15, 30, 40 kg [ha.sup.-1]) response trials in 16 representative fields in three seasons of 2013/14, 2014/205 and 2015/16 and; demonstrations trials in 8 farmer-selected fields in 2015/16 season. Combined N and P application increased maize yields by 32 to 62% over single nutrient applications. In the medium elevation low rainfall ecozone, 60-86% yield response to nitrogen was observed. Largely, modest applications of 50 kg N [ha.sup.-1] and 20 kg P [ha.sup.-1] resulted in profitable (marginal rate of return (MRR) of 2.4 to 3.0) yield increases of up to 214% over the farmers practice (unfertilized), varying with variety and ecozone. The source of P (DAP or Minjingu Mazao) had little influence on maize productivity except under low altitude low rainfall where Minjingu Mazao is unprofitable. Farmer rankings and agronomic indices showed new maize hybrids namely Meru H513, Meru H515 and SC627 as priority across the ecozones; Mams H913 is suitable mainly in medium elevation low rainfall ecozone. The conclusion is that use of new maize hybrids and appropriate rates of locally available N and P nutrient sources can bridge existing yield gaps and reduce food insecurity. Technologies from community-driven research in development are easily adopted by a large number of farmers and could result in a quick, yet lasting productivity gains. Key words: Phosphorus sources, ecozones, profitability, farmer preferences, innovation, INTRODUCTION To achieve food security, increasing crop yield per unit area, production intensification through soil fertility management and appropriate varieties under good agronomic practices is needed [1, 2]. Current production [...]

Summary: Increasing yields in farmer fields is a priority to address increasing food demands. The study was conducted within four wheat-growing areas in Ethiopia: Debre Birhan, Hosaina, Sinana and Maychew. The objectives were to identify (1) best-bet soil fertility management options based on agronomic performance and economic evaluation and (2) key yield-reducing factors in farmer fields based on an agronomic survey among 55 participating farmers. Two types of on-farm experiments were conducted: researcher-managed trials that tested combinations of nutrients, including micronutrients, organic resources or both over two cropping seasons and farmer-managed trials comparing ' improved practice ' against 'farmer's practice'. Fertilizer treatment affected wheat productivity in Debre Birhan (p < 0.01), a site limited in sulphur. Here, full NPK increased yields over the control (p < 0.05), whereas a combination of NPK and manure was better than the application of manure as the only source of added nutrients (p < 0.05). Applying half the recommended NPK with micronutrients and manure achieved similar yields as the full fertilizer treatment. In Hosaina, treatment had no significant effect on wheat productivity, although a combination of NPK and zinc resulted in an additional 26–57% yield relative to the other treatments. In Maychew, a significant treatment effect (p < 0.05) was observed. Here, the treatment with lower rates of nitrogen and phosphorous had lower yields than the full NPK treatment. A significant effect of plant densities on on-farm productivity was also observed. We conclude that although nutrient management including use of micronutrients is important in specific cases, investments to optimize plant densities have a huge potential to increase food productivity. [ABSTRACT FROM AUTHOR]