Critical phosphate (P) and inorganic phosphate (Pi) concentrations for the growth of winter oilseed rape (Brassica napus)

Abstract

Oilseed rape (Brassica napus) (OSR) has a high phosphorus (P) requirement for growth. Plant testing procedures give a measure of the actual physiological P status of OSR and indicate whether the plants requirements are being met by soil P supplies. This paper considers the effect of soil P supply on the amount of P and inorganic Pi (H2PO4 −) within tissues of OSR and relates these results to effects on growth. OSR (cv. Apex) was grown in a field experiment, consisting of plots with soil Olsen-P values ranging between 4–69 ppm P-PO4. The crop was sampled at the rosette growth stage and tissue analysed for Pi mM concentration and total %P content in dry matter. The dry weight of the shoot was measured and related to soil Olsen-P, tissue Pi mM and %P concentration by fitting Mitscherlich curves to the data. Shoot dry weight varied from 144–306 g m−2,with a critical soil Olsen-P of 21 ppm PO4-P (R2=0.58) giving 95% of the maximum shoot dry weight. A critical shoot Pi of 13.8 mM Pi (R2=0.77) or 0.67% P, and a critical largest-leaf blade Pi of 5.9 mM (R2=0.78) or 0.53% P and a lar gest-leaf petiole Pi of 1.8 mM (R2=0.72) or 0.48% P were calculated for 95% maximum shoot dry weight. Preliminary plant diagnostic values for assessing whether OSR plants are sufficient in Pi for growth have been established.