Phosphorus response components of different Brassica oleracea genotypes are reproducible in different environments

Better criteria for selecting cultivars for their ability to grow well on low-P soils could reduce waste of fertilizer P. The objective of this study was to quantify and determine the reproducibility of two crop parameters (A and Km) responsible for differences in the response of 12 Brassica oleracea L. genotypes to P supply. Modified Michaelis-Menten equations were fitted to shoot dry weight responses to P supply for each genotype In each of three glasshouse and three field experiments. One of the fitted parameters (A) defined the maximum shoot dry weight that could be obtained with ample P, and the other (Km) defined the efficiency of root P-nptake as the concentration of extractable soil P in the rooting medium at which growth was half the maximum. The equations fitted the data well. Ranking and regression analyses showed that intergenotypic differences in A were considerable, and reproducible, but that differences in Km, were small. Thus, B. oleracea genotypes yielding most on a P-sufficient soil will also yield most on a P-deficient soil. However, both the maximum yield (A) and the efficiency of root-P uptake (Km) vary considerably between different vegetable crops. Thus, a graphical procedure to select crops for highest yields on low-P soils, on the basis of a comparison of A and Km values, is described. © Crop Science Society of America.