Boron

Boron (B) is an essential micronutrient for plants, and plant requirements for this nutrient are lower than the requirements for all other nutrients except molybdenum and copper. It is the only nonmetal among the micronutrients and also the only micronutrient present over a wide pH range as a neutral molecule rather than an ion (Epstein and Bloom, 2005). Although B uptake of crop plants is not higher than the uptake of other nutrients, its deficiency has been reported in many parts of the world. Sillanpaa’s (1990) analysis of 190 soil samples from 15 countries revealed that 31% of these soils were low in B. Similarly, Asad et al. (2003) reported that B fertilizers increased sunflower yield in Australia. Xu et al. (2001) reported that more than 33 million ha cultivated land in China are B deficient. Mahler and Shafii (2007) reported that the Pacific Northwest is considered a B-deficient region in the United States. White and Zasoski (1999) reported that modern crop cultivars are highly sensitive to low micronutrient levels, including B. Shorrocks (1997) and Fageria et al. (2002) reported that B deficiency has been reported in at least 80 countries in 132 crop species. It is estimated that worldwide about 15 million ha of agricultural land are annually treated with B fertilizers (Shorrocks, 1997). Fageria (2000) reported responses of B application to dry bean, corn, soybean, and wheat grown on Brazilian Oxisols under greenhouse conditions. Similarly, Fageria et al. (2007) reported dry bean response to B fertilization in a Brazilian Oxisol in a field experiment. Figure 12.1 shows response of dry bean to B fertilization applied to a Brazilian Oxisol. Similarly, root growth of soybean and corn were also improved with B fertilization applied to a Brazilian Oxisol (Figure 12.2 and Figure 12.3). Mortvedt (1994) reported that B sorption on aluminum and iron oxide minerals plays a significant role in soils and helps explain the need for B fertilization in many tropical soils. Oplinger et al. (1993) reported that 0.28 kg B ha-1 applied foliarly increased soybean yields by 3% when averaged across 29 trials conducted on B-sufficient soils in the midwestern United States. Slaton et al. (2002) and Ross et al. (2006) reported that B deficiency in soybean in many counties of northeast Arkansas has been observed. Al-Molla (1985) reported a 15% yield increase from application of granular B at the R1 soybean stage (Fehr and Caviness, 1977) in Poinsett and Craighead counties of Arkansas, United States.