Distribution patterns of available P and K in rape rhizosphere in relation to genotypic difference

Plant genotypic differences in available K and P distribution at root-soil interface were studied with five rape varieties, which were 890206 (Brassica. campestris), Indian Mustard (Brassica juncea), Luzhoujinhuang (Brassica juncea), K-100 (Brassica juncea) and Xinongchangjiao (Brassica napus). The significant depletion of P and K was observed in the rhizosphere of all five rape varieties. The depletion rate of available P was in the range of 28-44% and the order followed: 890206 > Indian Mustard > K-100 > Xinongchangjiao > Luzhoujinhuang. The depletion area of available P occurred within 3-5 mm from root surface; and a wider depletion range was observed in the rhizosphere of the variety tolerant to low nutrient supply as compared to that of sensitive varieties. The depletion range of available K within the 10 mm from the root surface with the rate ranging from 31% to 48% and was wider than that of available P. The variety 890206 showed the highest absorption capability. Xinongchangjiao and Luzhoujinhuang showed higher depletion rate than that of K-100 and Indian Mustard, indicating that high-yield varieties of 890206 and Xinongchangjiao had higher absorption capacity of K than that of low-yield variety K-100. The results indicated that K depletion rate in the rhizosphere of rape was higher than that of cotton and was similar to that of two K enrichment plant-tobacco and alligator weed (Alternanthern Philoxeroides Mart. Griseb).