PLANT NUTRIENT EFFICIENCY - A COMPARISON OF DEFINITIONS AND SUGGESTED IMPROVEMENT

Selection of plant cultivars tolerant of low nutrient supply may increase productivity on low fertility soils and reduce fertilizer requirements. Considerable effort has been directed towards identifying 'nutrient efficient' species and germplasms, but the many different definitions for efficiency make the use of the term ambiguous. The concept of nutrient efficiency was evaluated using data from a study of differences in germplasm response to phosphorus (P) availability in white clover (Trifolium repens L.) and alfalfa (Medicago sativa L.) grown in a sand-alumina culture. Application of various criteria identified in the literature as measures of nutrient efficiency did not clarify differences between purportedly P efficient and inefficient germplasms. Germplasms differed in maximum shoot and total dry mass and in solution P concentration required to achieve 80% maximum yield, but not in tissue P concentration, internal P utilization, or P uptake per unit of fine root dry mass. Differences may have resulted from factors other than efficient use of available P. To reduce the confounding effects that other factors have on nutrient efficiency, we propose that equivalent yields of germplasms be demonstrated where nutrients are not limiting. Mechanisms that enable enhanced nutrient efficiency can be identified less ambiguously using this improved approach.