Brassica Cultivars: P Response and Fertilizer Efficient Cropping

The responses of 12 genotypes of Brassica oleracea to a range of levels of fertilizer-P were studied in glasshouse and field experiments, as part of a program to characterise the genetics of P responses. This paper describes some of the results and how they may lead to improvements in the efficiency of P fertilizer use and pollution control. Good fits to the data for each genotype and each experiment were obtained by the equation 1/W = 1/A + 1/(B·Px), where A and B are fitted coefficients, W is the measured plant dry weight, and Px is a measure of plant available P in the rooting medium. B for the different genotypes was approximately proportional to A. In consequence, as the ratio of A/B defines the fractional increase in W with increase in Px, it follows that inter-genotype differences in P-response were small. A near proportional relationship also covered the edible weights of 8 other Brassicaceae. All genotypes grew well on a sandy loam soil containing only about 20 mg kg-1 of Olsen extractable soil-P. Other work suggests that at this low soil P-level the conversion of P into soil forms that are virtually unavailable to crops is small in two contrasting UK arable soils but at higher levels conversion can be considerable. It is argued that high yielding rotations of Brassicaceae and cereals (which can also yield well on low P soils) may be sustained indefinitely on some soils, with about 20 mg kg-1 Olsen extractable soil-P, by annual applications of only slightly more P than is removed by harvest of the crop.