Diagnosing boron deficiency in rapeseed and mustard by plant analysis and soil testing

Abstract

Boron (B) deficiency is a widespread nutritional disorder in crop plants, including rapeseed and mustard. However, plant analysis and soil testing diagnostic criteria for B are inadequately reported in the literature. Therefore, greenhouse and incubation studies were carried out using a B‐deficient alkaline calcareous soil (hot water extractable B, 0.11 mg/kg) of Pakistan to determine the internal and soil test B requirement of rapeseed and mustard. Boron fertilization substantially enhanced the growth of both species; the maximum increase in grain yield was 43% for rapeseed and 36% for mustard over the yield of respective control plants. Fertilizer requirement for near‐maximum (95%) grain yield was 0.7 mg B/kg for rapeseed and 0.9 mg B/kg for mustard. Critical plant tissue B concentration in rapeseed was 32 mg/kg in whole shoots and 38 mg/kg in most recently matured leaves. However, internal B requirement of mustard was relatively greater: i.e. 41 mg/kg in whole shoots and 49 mg/kg in leaves. The three soil tests studied, hot water, hydrochloric acid (HCl), and mannitol, were almost equally effective in determining soil B status. Because of simplicity and low cost, however, the HCl method appears superior than the other two for routine B analysis. Critical soil B levels (mg/kg) for rapeseed were: hot water, 0.5; HCl, 0.45; and mannitol, 0.4. Similar to internal B requirements, soil test critical B levels (mg/kg) were also greater for mustard, i.e. hot water, 0.6; HCl, 0.55; and mannitol, 0.48.