Keywords: potassium, genotypic differences. uptake efficiency, utilisation efficiency, harvest index, nutrient cycling.
Cultivars with increased efficiency of uptake and utilisation of soil nutrients are likely to have positive environmental effects through reduced usage of chemicals in agriculture. This review assesses the available literature on differential uptake and utilisation efficiency of potassium (K) in farming systems. Large areas of agricultural land in the world are deficient in K (e.g. 3/4 of paddy soils in China, 2/3 of the wheatbelt in southern Australia), with export in agricultural produce (especially hay) and leaching (especially in sandy soils) contributing to lowering of K content in the soil. The capacity of a genotype to grow and yield well in soils low in available K is K efficiency. Genotypic differences in efficiency of K uptake and utilisation have been reported for all major economically important plants. The K-efficient phenotype is a complex one comprising a mixture of uptake and utilisation efficiency mechanisms. Differential exudation of organic compounds to facilitate release of non-exchangeable K is one of the mechanisms of differential K uptake efficiency. Genotypes efficient in K uptake may have a larger surface area of contact between roots and soil and increased uptake at the root-soil interface to maintain a larger diffusive gradient toward roots. Better translocation of K into different organs, greater capacity to maintain cytosolic K+ concentration within optimal ranges, and increased capacity to substitute Na+ for K+ are the main mechanisms underlying K utilisation efficiency. Further breeding for increased K efficiency will be dependent on identification of suitable markers and compounding of efficiency mechanisms into locally adapted germplasm.
Zed Rengel and P M Damon, Soil Science and Plant Nutrition M087, School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia.
27 pages, 3 figures, 1 table, 108 references.