LAUSR

Abstract The management of soil fertility under yam crop production is limited by the problem of adequacy between soil characteristics and the manure proposed for crop intensification. In practice, the recommended manure concentration is very often dominated by nitrogen (N) and potassium (K). We have studied the response of Dioscorea alata var Bete-bete to the NK fertilization of two different types of soil commonly utilized for yam crop production. First, we evaluated the production capacity of these soils based on the mineral balances within the soil and the rate of nutrient absorption by yam. The equivalent of 156 kg ha−1 N + 384 kg ha−1 K2O (potassium oxide) was applied and compared to a control without fertilizer on brown soil (Site 1 or S1) and two red soils (Sites 2 and 3 or S2 and S3). S1 was the most balanced, with the best production capacity (20.1 t ha−1). NK manure supply on S1 was statistically not perceptible (16.7 t ha−1). On the other hand, the production capacity of S2 (13.1 t ha−1) and S3 (15.3 t ha−1) was reduced by manuring (9.6 and 8.3 t ha−1, respectively). The imbalance between soil N and exchangeable calcium (Ca2+) has been identified as the cause of the decline in yam yields under soil NK fertilization condition. In soil fertility management, fertilizer inputs must be adequate in terms of the individual physical and chemical characteristics of soils.