Effect of Improved Plant Nutrition on Maize ( Zea mays ) and Rice ( Oriza sativa ) Grain Chemical Nutrient Content Under Smallholder Farming Systems in Tanzania

Maize and rice are the primary cereal crops constituting more than 50 % of the dietary energy for the population of Tanzania. The current increased demand for food to feed an increasing population in the country has called either for an expansion of cultivated land or intensification of these two crops. Expansion of cultivated land is limited by high land use pressure and the concern over natural resources conservation. The only way to grow more food is then through agricultural intensification by improving plant nutrition and protection. Smallholder farmers, however, lack information on appropriate use of agro-inputs and the effect of inorganic fertilizers on these cereals’ grain quality. This has led to either improper or disproportionate use of inorganic fertilizers resulting in disappointing low yield and frequent household food insecurity. To address this matter, a public–private partnership comprising two public universities and multinational companies dealing with fertilizer and crop protection was initiated in December 2010, aiming at demonstrating the effect of appropriate inorganic fertilizer use on the yield and chemical composition of maize and rice grains. In total, four farms of maize and three of rice crops in different villages and districts were selected for the demonstration that was carried out from 2011 to 2014. The demonstrated treatments were farmers’ practice (FP) and appropriate use of inorganic fertilizers (YSS). Maize and rice grains were harvested, oven dried and analyzed for Nitrogen (N), Phosphorus (P), Potassium (K), Magnesium (Mg), Sulphur (S), Calcium (Ca), Boron (Bo), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) and Zinc (Zn). The concentrations of N, P, K, Mg and S were not significantly (P > 0.05) different between the farmers’ and appropriate inorganic fertilizers use practices and ranged from 1.21 to 1.69, 0.18 to 0.34, 0.24 to 41, 0.08 to 0.13 and 0.09 to 0.12 % for maize grain and from 0.97 to 1.19, 0.26 to 0.31, 0.28 to 0.41, 0.09 to 0.12 and 0.07 to 0.10 % for rice grain, respectively. Comparable nutrients in the two agronomic practices are related to nutrient dilution under YSS due to high biomass production since grain yields under YSS were significantly (P 0.0.5) from those from farmers’ practice in terms of nutrient concentration, it can be concluded that farmers’ practice grains obtained nutrients mainly from soil reserve and thus soil fertility mining with crop harvest. There is an urgent need, therefore, to train farmers on the appropriate improvement of plant nutrition to reduce depletion of soil fertility. The calcium concentration in maize grain regardless of farming practice was very low; thus, maize diets should include Ca-rich foods.