Nitrogen (N) over-application is a serious problem in intensive agricultural production areas with consequent large N losses and environmental pollution. In contrast to N, potassium (K) application has been neglected in many developing countries and this has resulted in soil K depletion in agricultural ecosystems and prevented increases in crop yields. Nitrogenpotassium interaction is currently a topic of interest in many studies and the focus of this review is K nutrition under varied N regimes. Nitrogen form and application rate and time influence soil K fixation and release, as well as K uptake, transport, cycling and reutilization within crops. High yielding quality crops can be obtained by optimal N: K nutritional ratios. High rates of applications of N and K do not necessarily lead to increased yield increments and may even reduce yield. Yield response to K uptake depends on N nutritional status and the interaction is usually positive when NO 3 − -N is supplied. Antagonism between NH 4 + and K + in uptake was mostly attributed to simple competitive effects in the past while evidence showing mixednoncompetitive interactions existed. Two components of membrane transport systems for K uptake by plants are a high-affinity K + transport system which is inhibited by NH 4 + and a low-affinity K + transport system which is relatively NH 4 + insensitive. Potassium is highly mobile within plants but its flow and partitioning can change depending on the forms of N supply. NH 4 + nutrition in comparison to NO 3 − -supply results in more K translocation to leaves. A better understanding of the mechanism of N-K interaction can be a useful guide to best nutrient management in agricultural practice in order to achieve high yields with high nutrient use efficiency.

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