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Low risks of toxicity from boron fertiliser in oilseed rape-rice rotations in southeast China
- Wang, K., Yang, Y., Bell, R.W., Xue, J.M., Ye, Z.O., Wei, Y.Z.
- Nutrient cycling in agroecosystems 1999 v.54 no.2 pp. 189-197
- Oryza sativa, Brassica napus, boron fertilizers, crop rotation, phytotoxicity, crop yield, soil fertility, nutrient availability, field experimentation, stems, shoots, biomass, nutrient content, nutrient deficiencies, application rate, China
- Yields in intensive rice (Oryza sativa L.)-based rotations in Asia are stagnating or declining because of decreasing nutrient availability and depletion of soil nutrient reserves. In the rape (Brassica napus L.)-rice-rice cropping rotation of southeast China, where boron (B) deficiency is widespread and B fertiliser is needed to correct it, our objective was to evaluate the risks of fertiliser-induced B toxicity in oilseed rape and in rice. Response of oilseed rape to B fertiliser application at rates up to 6.6 kg B ha(-1) was studied in seven field experiments on three contrasting soils of Zhejiang province, alluvial, red and blue-purple soils. The effects of up to 3.3 kg B ha(-1) in year, 6.6 kg B ha(-1) in 2 years or 9.9 kg B ha(-1) in 3 years were studied on oilseed rape and the one or two rice crops grown immediately after rape in each annual crop rotation. Soils varied in initial hot CaCl(2)-extractable B in the 0-15-cm layer from 0.24 to 0.99 mg kg(-1). At the stem elongation stage of oilseed rape, 3.3 kg B ha(-1) depressed shoot dry matter on soils with low clay and organic matter content. However, the subsequent effects of high fertiliser B on seed yield were minimal even at 6.6 kg B ha(-1). Moreover, the application of a total of 6.6 or 9.9 kg B ha(-1) as successive annual applications of 3.3 kg B ha(-1) to oilseed rape generally had no negative effect on seed yield of oilseed rape. The single exception was on a sandy alluvial soil where a total of 6.6 kg B ha(-1) in 2 years slightly depressed seed yield of oilseed rape. Grain yields of rice crops grown in rotation after oilseed rape were unaffected by B applications up to 6.17 kg ha(-1). The minimal effects of a total of 6.6 kg B ha(-1) applied over 2 years on seed yield were consistent with the modest increase in hot CaCl(2)-extractable B levels. It is concluded that there is limited risk of B toxicity from the use of borax fertiliser at up to 4-8 times recommended rates in rape-rice cropping rotations in southeast China. The low risk of B toxicity, can be attributed to the relatively high B removal in harvested seed, grain and stubble, the redistribution of fertiliser B by leaching in the 0-60 cm layer and to B sorption.