Boron availability in soils and its nutrition of crops under long-term fertility experiments in India

Using 12 long-term (of 15 to 42 years duration) experiments with different cropping systems under various soils and agro-climatic conditions, we studied how different (inorganic and integrated) nutrient management practices influenced boron (B) availability in soils, and its nutrition of nine crops. To this end, four nutrient management practices viz., NPK (recommended dose of N, P and K), NPK + FYM (farmyard manure), control and fallow, which were common in all the experiments, were selected and their effects on B availability in soils were tested using four commonly used methods viz., hot-CaCl2 (HCC), KH2PO4 (PDP), mannitol-CaCl2 (MCC) and hydrochloric acid (HCl) in relation to B nutrition of wheat, rice, cowpea, sorghum, sesame, mustard, groundnut, soybean and lentil. Amounts of B extracted by the four different methods followed the order HCC = HCl > MCC > PDP across the tested soils. Averaged over the extractants, long-term nutrient management practices with NPK + FYM resulted in 15% increases in available B in soil over the control, which produced 20% increase in plant tissue B concentration. Such increases with integrated (NPK + FYM) nutrient management practices maintained available B in soils and plant tissues above its critical limits that supplied adequate amounts of B for nutrition of all the tested crops grown intensively for so many years. A B balance study in six experimental sites showed a net B accumulation over time as irrigation water contained and supplied (130-296 g B ha(-1) year(-1)) more B than removed by harvested crops. Of the four methods used, HCC was the best for assessment of availability of B in soils under long-term cultivation.