ALBERT

Description: Crop uptake of the major cations from the soil solution depends not only on their absolute amounts but also on their quantitative relationships. The risk of accentuating nutrient deficiencies through unbalanced cation ratios arising from injudicious fertilization practices is particularly high in the poorly buffered, continuously cropped/fertilized savannah soils of Nigeria. This paper evaluates the preliminary results of a long-term investigation of the effects of continuous fertilization on soil cation ratios, crop nutrition and yield in northern Nigeria. The effects of nine factorial combinations of three levels (0, 25 and 50 kg∙ha−1) each of K and Mg (applied in 1976) are being monitored on two soils — Dystric Nitosol or Oxisol (at Mokwa) and Ferric Luvisol or Ultisol (at Yandev) using maize (Zea mays L.) as a test crop. Soil and index leaf K, Ca and Mg concentrations were related to yield by means of correlation and regression analyses. Maize yields were strongly and negatively related to soil exchangeable K, and percent in plant tissue, and highly significantly and positively correlated with percent Ca in plant tissue, soil Ca:K and (Ca + Mg):K ratios. It is thus evident that K depressed yields by creating unfavorable soil Ca:K, (Ca + Mg):K ratios, and to a lesser degree, Mg:K ratios through its repressive action on these two other cations. The results have demonstrated the practical significance of the inverse Ca-K relationship in crop nutrition with respect to the Nigerian savannah soils and have also shown the fragile nature of the balance between the major cations and how easily the balance can be upset by injudicious fertilizer use and management. This calls for caution in the development of fertilizer programs for the area. Use of fertilizers containing a high Ca concentration is suggested.