Analyzing plant nutrient uptake and utilization efficiencies: comparison between crops and approaches

Various indices are applied to evaluate the nutrient (mostly nitrogen, N) use efficiency of plants, but those indices have rarely been compared across different crops, and the co-limitation of growth by nutrients other than N is usually not considered. To conceptually and quantitatively compare the indices of a plant-level, a plant-soil-level and a field-level (difference) method for the assessment of N use across a set of different annual and perennial crops; and to use some plant-level indices for exploring the co-limitation of growth by nutrients other than N in wheat. Data sets from previously published studies on wheat (grain), maize (feed), potato (starch), grassland ley (feed) and Salix (bio-energy) field-grown in Sweden were re-analyzed. This study is first in conceptually and quantitatively comparing various popular N use indices across a wide range of annual and perennial crops; and also proposes a methodology for exploring the co-limitation of growth by nutrients other than N. When comparing the plant-level and plant-soil-level methods, the indices relating crop yields to the amounts of plant-internal N were correlated, while the N-uptake indices were not. Only few of the field-level (difference-method) indices were correlated with indices of the two other methods.