Improved agronomic management is important to reduce yield gaps and enhance food security in sub-Saharan Africa. This study was undertaken to understand contributing factors to observed yield gaps for maize in farmer fields and to demonstrate appropriate agronomic survey methods. The study aimed to (1) demonstrate an approach for farmlevel agronomic survey, (2) identify key crop production constraints and (3) define the nutrient input and output balances of different fields. Agronomic survey was conducted in 117 farmer fields randomly distributed in a 10 km by 10 km block in Babati, northern Tanzania. A semi-structured questionnaire and production measurements were used to collect data which were analyzed with regression classification and mixed effect models. The exploitable maize yield gap at farm-level reaches up to 7.4 t ha -1 , and only \5 % of fields achieve maize grain yield of 5 t ha -1 . Slope, plant density, distance from homestead, crop variety, timing of planting and period since conversion significantly influenced maize yields. For example, fields on flat land had up to 1.6 t ha -1 more maize grain yield than those on steep slopes while fields with plant density [24,000 plants ha -1 had 900 kg ha -1 more yield than those with less density. At least 52 % of the fields had negative nutrient balances. We conclude that cropping systems used in Babati should be preferentially supplemented with mineral fertilizers while optimizing plant density, increasing manure application and appropriate varietal choice in order to reduce the yield gaps.

Declining crops yield in the smallholder farmers cropping systems of sub-Saharan African (SSA) present the need to develop more sustainable production systems. Depletion of essential plant nutrients from the soils have been cited as the main contributing factors due to continues cultivation of cereal crops without application of organic/ inorganic fertilizers. Of all the plant nutrients, reports showed that nitrogen is among the most limiting plant nutrient as it plays crucial roles in the plant growth and physiological processes. The most efficient way of adding nitrogen to the soils is through inorganic amendments. However, this is an expensive method and creates bottleneck to smallholder farmers in most countries of sub-Saharan Africa. Legumes are potential sources of plant nutrients that complement/supplement inorganic fertilizers for cereal crops because of their ability to fix biological nitrogen (N) when included to the cropping systems. By fixing atmospheric N2, legumes offer the most effective way of increasing the productivity of poor soils either in monoculture, intercropping, crop rotations, or mixed cropping systems. This review paper discuses the role of cereal legume intercropping systems on soil fertility improvement, its impact on weeds, pests, diseases and water use efficiency, the biological nitrogen fixation, the amounts of N transferred to associated cereal crops, nutrients uptake and partition, legume biomass decomposition and mineralization, grain yields, land equivalent ratio and economic benefits.

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The study to investigate the effect of Rhizobium inoculation and cropping systems on the uptake of macronutrients in shoot, root and whole plant of Phaseolus vulgaris and Lablab purpureus was conducted at Selian Agricultural Research Institute (SARI) for two cropping seasons. A randomized complete block design was used in a 3-factorial arrangement with two levels of Rhizobium (with and without rhizobia), two legumes (P. vulgaris and L. purpureus) and five cropping systems (sole maize or sole legumes, 1 row maize to 1 row legumes (1:1) i.e. 0 m or 0.45 m of legume from maize row, 1 row maize to 2 rows of legumes (1:2) i.e. 0.1 m or 0.2 m of legumes from maize rows). The result showed that Rhizobium inoculation significantly (P0.001) increased the uptake of N, P, K, Ca and Mg in the plant parts and whole plant. Similarly, cropping systems significantly (P0.001) increased the uptake of N, K and Mg in shoots and whole plant of P. vulgaris and L. purpureus but decreased the P and Ca content in roots. Legumes significantly increased the uptake of the macronutrients in shoots and roots but more nutrients concentration in shoots than roots for both cropping seasons. There were significant (P0.001) interaction between; Rhizobium x legumes x cropping systems on whole plant uptake of N in cropping season 1 and 2. Regardless of the type of interaction, inoculated legumes maximized the uptake of macronutrients in shoots, roots and whole plant.

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