Fertilizer responses of groundnuts (Arachis hypogae L.) under continuous intensive cultivation in the Nigerian savannah

Up until now, potash fertilization has not been part of the recommended practices for groundnut production in Nigeria and only low levels of P are recommended in line with the level of agricultural technology available to the farmer. The change from the traditional non-intensive farming practice to continuous intensive cultivation coupled with the introduction of better yielding/more-nutrient demanding crop varieties have led to a deficiency of a number of nutrients.Field experiments were carried out for 5 years (repeated on the same sites) at 8 locations in northern Nigeria to evaluate the effect of four levels of phosphorus (0, 8, 16 and 24 kg P ha^–1) and three levels of potassium (0, 20, and 40 kg K ha^–1) on yield and related parameters in groundnut. Soils at the various sites were essentially loamy sands with low levels of organic carbon and cation exchange capacity.The yield levels in the Guinea savannah were generally higher than those in the Sudan savannah but the response pattern was the same. There was significant response to applied P up to 24 kg P ha^–1. Potash applied at 20 kg K ha^–1 produced significantly higher pod yields than the control plots, but higher rates of applied K did not result in any further significant yield increase, although there was a clear consistent trend towards higher yields as the K rates increased. Phosphate X potash interaction had no significant effect on yield.Except for K, the uptake of all nutrients were significantly increased by P levels. However, only the K content of haulms and the N content of kernels were significantly increased by K application. On the average, about 58% of N, 68% of P, 19% of K, 5% of Ca and 22% of Mg were contained in the kernels while 27% of N, 23% of P, 64% of K, 83% of Ca and 69% of Mg were contained in the haulms. The implication of this is that the complete removal of groundnut residue will deplete the soil cation reverves rapidly unless these losses are compensated through fertilizer use.