Soil nutrient deficiency assessment under soybean cropping systems using the DRIS system in northern and central Benin

Abstract

Soybean is one of the promising crops in the Benin agro-industrial sector, but its production is carried out at the expense of the inherent soil fertility. The present study aims to apply the DRIS (Diagnosis and Recommendation Integrated System) for nutrient status assessment in farmers’ soybean fields in northern and central Benin. Sixty-two plant leaf samples were collected during a survey carried out in 2019 in farmers’ fields. Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and zinc (Zn) concentrations in the leaf samples were analysed. DRIS norms were used to calculate the various paired nutrient ratios in the high-yielding population. Nutrient balance indices (NBI) were also determined. Nutrient requirements based on NBI were ranked according Zn > N > P > Ca > K > Mg, highlighting the importance of Zn and N in soybean nutrition. Paired nutrient ratios (N/P, N/K, Mg/N, N/Ca, Ca/P, K/Ca, Mg/Ca, Zn/Mg) were either significantly (p = 0.0001) higher or lower than those in the literature, excluding Mg/P, Mg/K, P/Zn, Ca/Zn, N/Zn K/Zn and P/K paired ratios. This observation indicates the necessity of calibrating DRIS norms taking into account local conditions and cropping systems. The DRIS model could be an important tool for refining soybean nutrient needs in a cropping system. Zinc and N levels limited soybean cultivation in farmers’ fields and must be included in the soybean fertiliser formulations to ensure optimal yield of soybean in Benin.