PROGNOSIS OF BORON DEFICIENCY IN OILSEED RAPE (BRASSICA-NAPUS) BY PLANT ANALYSIS

In areas where soils are low in boron (B), the ability to predict B de ficiency by plant analysis depends on the development of calibrated st andards and offers the potential of preventing or minimising losses in seed yield. The present study aimed at establishing relationships bet ween seed yield in winter oilseed rape (Brassica napus) and B concentr ations in defined leaves during growth before flowering and from them to determine critical values for the prognosis of B deficiency. Oilsee d rape cv. Zheyouyou 2 was grown in 10 field experiments in Zhejiang p rovince, south-east China, with B rates from 0 to 3.3 kg/ha. At 4 of t he sites, oilseed rape was resown in the following year to assess seas onal effects on critical concentrations. Experiments were conducted on the 3 main soil groups on which oilseed rape is grown in southeast Ch ina. The youngest open leaf (YOL) was selected as the sampling part be cause its B concentrations were strongly responsive to increasing B su pply and well correlated with seed yield response. In this study, the best model of the relationship between YOL B concentration and yield w as the Mitscherlich equation, which explained 68-89% of the variation in the data. The calculated critical range in the YOL at seedling stag e was 20-25 mg B/kg and appeared to be valid in 2 seasons and on 3 soi l types. The critical B range for prognosis of B deficiency was found to predict consistently those crops in farmers' fields that had low se ed yield and low soil B, but needs to be evaluated in other growing en vironments especially those for spring rape.