Abstract
Calcareous soils are highly deficient in boron (B) due to having high levels of free CaCO3 and low organic matter. This has become one of the most important deficient micronutrients in Indian soil after zinc (Zn). For various rice (Oryza sativa L.)-based cropping systems, B fertilization is essential for increasing crop productivity and the biofortification of the crop, thus a suitable soil application protocol for B fertilization is required for B-deficient soils. In a six-year experiment, different rates of B application, namely, 0.5, 1.0, 1.5, and 2.0 kg ha(-1) y(-1), were evaluated to determine the effects of three different modes of B fertilization, i.e., applied only in the first year, applied in alternating years, and applied every year, in a rice (Oryza sativa L.)-Indian mustard (Brassica juncea L.) cropping system. It was observed that the application of B at 1.5 kg ha(-1) every year or 2 kg ha(-1) in alternate years resulted in the highest yield of rice and mustard, as well as the maximum system productivity of the rice-mustard cropping system. Application of 2 kg ha(-1) of B in the initial year showed the maximum B uptake by rice, while application of 1.5-2.0 kg ha(-1) of B every year resulted in the maximum B uptake by the mustard crop. Application of B at 2 kg ha(-1) in alternate years or 1.5 kg ha(-1) every year was the best B-application protocol in B-deficient calcareous soils for ensuring the highest productivity of the rice-mustard cropping system and B availability in the soil.