Responses Of Yield And Quality To Low-P Stress And Fertilizer Application In A Double-Low Oilseed Rape

Oilseed rape is one of the most important oil crops in China. Low yield and inferior quality in oilseed rape can affect people's daily life and limit the use of rapeseed cake. Field experiment was conducted in 2004-2006 in Dapu, Wuxi, Jiangshu Province. Soil available-P was relatively low in experimental site. With"Yangyou 6", a very popular double-low cultivar in this area, as material, the experiment was a split-plot design with three replicates in which N and P treatment was arranged in subplot and mainplot, respectively. The main purpose of this study was to investigate the responses of growth, nutrient uptake, yield and quality of double-low rape to low-P stress and application of N and P fertilizer. Results showed as follows:(1) N application significantly increased NH4+-N and NO3--N in soil, especially in early development stage of double-low oilseed rape while P application decreased NH4+-N and NO3--N due to the enhanced uptake by rape plant under P treatment. Alkali-hydrolyzable N and available K was not affected N, P application. Soil available P slightly increased in N treatment and significantly increased in P treatment.(2) N recovery (%) in rape plant was limited under low-P stress and moderate P application significantly increased N recovery. N application also enhanced P recovery in rape plant, but N application had little effect on P recovery when P fertilizer was over-rated.(3) Both N and P application enhanced the accumulation of N, P and K in rapeseed plant, but over-rated P application inhibited nutrient accumulation while amount of N applied had little influence on nutrient accumulation.(4) Low-P stress significantly depressed dry matter (DM) accumulation. Moderate P application obviously enhanced DM while DM was reduced in over-rated P treatment. N application also improved DM but no difference was found between N application rates.(5) Both N and P application could significantly increased plant height, the number of leaves and branches. P application increased the number of leaves at recovering stage due to enhanced tolerance to low temperature during winter. The weight of seeds and pod shells increased in N and P treatment, but the former increased more which led to the increase of the ratio of seed to shell.(6) N application significantly increased seed yield of double-low rape, but the effect was dependent on P application level. The yield effect of N application was relatively low under low-P stress and significantly increased when moderate P was applied.(7) The effect of N and P application on yield components was year-dependent, although N and P application increased rapeseed yield in both 2005 and 2006. In 2005 yield increase was mainly due to the increased number of seeds per pod under N and P treatment, while in 2006 yield increase was achieved by increased number of branches per plant.(8) N application decreased the content of oil and protein in rapeseed and had no obvious effect on glucosinolate in the seeds. Oil content was not affected by P application and protein content tended to increase in P treatment. P application could significantly increased glucosinolate content. N application could decrease the content of palmitic acid, linoleic acid and erucic acid and had little effect on oleic acid and linolenic acid in the oil. The content of oleic acid decreased and erucic acid increased in P treatment. Other fatty acids were not affected by P application...