Efficient use of nutrients: an art of balancing

Nutrient-use efficiency is conceived as the product of uptake efficiency, i.e., the ratio of actual uptake to potential supply, and utilization efficiency, i.e., the ratio of yield to actual uptake. Both depend on the availability of the nutrient in relation to other growth factors, and require N, P and K perfectly in balance to reach their maximum values. Hence, the cause of a low recovery of fertilizer nutrients may be wastage due to unbalanced supplies of nutrients, apart from fixation in the soil or loss from the soil. The ratios of the supplies of N, P and K for nutritional balance were established and used for the calculation of 'nutrient supply equivalent', defined as the supply of a nutrient that has the same effect on yield as a supply of 1 kg N. A triangular diagram is proposed with supply equivalents of N, P and K along the sides. At each point in the diagram, the sum of supply equivalents is 100%, and maximum nutrient efficiency is found in the centre. In the field, the influence of other growth factors on nutrient-use efficiency usually consisted of a direct effect on nutrient utilization efficiency, and an indirect effect on nutrient uptake efficiency. The latter was partly driven by utilization efficiency. Sunny weather and soil biological activity acted positively in this way, and soil acidification and moisture stress negatively. (C) 1998 Elsevier Science B.V.