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Occurrence of poorly responsive soils in western Kenya and associated nutrient imbalances in maize (Zea mays L.)

Njoroge, Ruth, Otinga, Abigael N., Okalebo, John R., Pepela, Mary, Merckx, Roel
Field crops research 2017 v.210 pp. 162-174
NPK fertilizers, Zea mays, bioavailability, copper, corn, crop yield, fertilizer application, magnesium, nutrient content, nutrient deficiencies, nutrients, potassium, soil, Kenya
A poor response to fertilizer application is one of the persisting constraints preventing closure of the maize yield gaps in Sub-Saharan Africa (SSA). It is speculated that nutrient imbalances derived from deficient and/or excessive concentrations could be one of the causes of this limited response of maize to fertilizer. This is however not confirmed and the extent of such poor response is ill-documented. To investigate this, we conducted 44 on-farm trials with a two treatment structure (with and without NPK fertilizer) in two subsequent seasons, the 2014 long rains (LR) and short rains (SR) distributed across two sites: Bungoma-Southwest and Busia-North in western Kenya. As a discriminating criterion between responsive and poorly responsive soils, we used a Value Cost Ratio (VCR) of 2 of NPK fertilizer use. Nutrient sufficiency ranges were developed using compositional nutrient diagnosis (CND method) and then used to identify both deficient and/or excessive nutrient concentrations occurring in maize grown in the poorly responsive soils.Results show that 48% of all fields from both sites could be classified as ‘poorly responsive’, with small VCR values ranging between 0.1 and 1.99. Nutrient deficiencies were more prevalent than situations of excessive concentrations in such fields. N-deficiency was the most common in the unfertilized (control) plots occurring in between 80 and 89% of the poorly responsive plots. Zn-deficiency became apparent in the fertilized plots and was observed at similar frequencies in this treatment. The next most widespread nutrient deficiencies in poorly responsive soils were those of P and Cu affecting between 70 and 79% of both control and fertilized plots. K and Mg deficiencies were rare in both treatments. This study indicates that the occurrence of poorly responsive soils in Bungoma-southwest and Busia-North is likely related to micronutrient deficiencies. These findings necessitate further investigation on the bioavailability of these micronutrients nutrients in such soils and a validation trial to evaluate the extent of crop responses.