Residual effectiveness of boron fertilizer for oilseed rape in intensivelycropped rice-based rotations

Long-term field experiments (3-4 years) were conducted to evaluate the resi dual effect of boron (B) fertilizer for oilseed rape (Brassica napus L.) in an intensive crop rotation including two rice (Oryza sativa) crops per yea r. Experiments were conducted on four sites where the soil types were sandy , silty and clayey Inceptisols, and an Ultisol, located in the Zhejiang Pro vince, Southeast China. Application of B fertilizer at rates of 1.1, 1.65 a nd 3.3 kg B/ha in the first year showed a different residual effect on oils eed yield in successive years, but had only small positive effects on the r ice grain yield at two sites. The residual effect of 1.1 kg B/ha remained f ully effective in correcting B deficiency in oilseed rape for 2 years in th e Inceptisols, whereas the residual effect of 1.65 kg B/ha continued to cor rect B deficiency for at least 3 years in both the Inceptisols and the Ulti sol. Foliar application of B fertilizer generally corrected B deficiency fo r oilseed rape but showed limited residual effect in the following years af ter application. The decline in residual values of B from a single fertiliz er addition was closely related to the soil and leaf B concentration. Soil available B also decreased dramatically with the advance of rotation, but a larger decrease was found at a depth of 20-40-cm for the Inceptisols and t he Ultisol. Thus, a more detailed understanding of the B cycling in the sys tem is now needed to optimize management of B fertilizer.