Assessment of the Nutrient Status and Limiting Nutrients for Maize Production in Smallholder Farm Fields in Kenya

Abstract

Low crop yields in Sub Saharan Africa (SSA) are as a result of declining soil fertility. Most farmers rely on nutrient recycling in their farms which is not sustainable as it leaves the soils depleted of nutrients. Consequently, this study was conducted to assess the limiting nutrients in soils of major farming regions in Kenya and to assess the effect of applied nutrients on the growth and development of maize. Thirteen counties in Kenya were selected whereby a total of 23 soil samples at a soil depth of 0 to 30 cm were collected for soil analysis of total nitrogen, total organic carbon, phosphorus, potassium, calcium, magnesium, manganese, copper, iron, zinc, sodium, electrical conductivity, cation exchange capacity (CEC), base saturation and soil pH had mean values were of 0.12%, 1.12, 19.09, 220.43, 1397.39, 163.98, 120, 52, 3.95, 52.78, 1.86, 92.80 mg kg-1, 0.11mS/c, 11.98 Cmol (+)/kg, 83.13% and, 5.96, respectively. A nutrient omission trial was set up in the greenhouse at the Kenya Agricultural and Livestock Research Organization (KALRO) Kabete using a completely randomized design. This study had a total of 12 treatments as follows; complete (all macro and micro nutrients added), complete plus lime added, five treatments in which one macro nutrient was removed from the solution of nutrients, another treatment in which micro-nutrient mixture was eliminated from the solution of nutrients, a similar treatment with each of the micro nutrients except zinc, the other with all micronutrients except boron, one treatment with all the micro nutrients except molybdenum and one control (distilled water only). In majority of the soils, significantly (P<0.05) higher shoot dry weights were observed in the complete treatment than in the treatments with fewer nutrient elements. The results showed that poor maize growth was mainly due to deficiencies of nitrogen, phosphorus and zinc. Potassium was mainly deficient in western Kenya. Addition of these nutrients improved the yield in majority of the soils. The inherent low soil fertility was correlated with low dry matter yields implying that farmers in areas with declining soil fertility will continue to obtain low crop yields unless organic or inorganic fertilizers are included in management. Rapid assessment of soil fertility is necessary for tailored soil fertility interventions in most regions of Kenya, to achieve household food security. Meaningful maize yields can only be obtained with soil fertility interventions incorporating all the limiting nutrients in a specific region. Further research is needed to correlate and calibrate the plant availability of macronutrients and micronutrients in laboratory, greenhouse, and field trials for site specific smart fertilizer recommendations in Kenya.