Emerging Boron Deficiency in Soils and Crops in India and Its Management.
M. V. Singh, Indian Institute of Soil Science, Bhopal, India
Boron deficiency has emerged as an important micronutrient problem in Indian soils and crops next to zinc. Attempts were therefore, made to evaluate the extent of boron deficiency in different agroecological zones of India and assess the relative efficiency of different sources for its correction in different crops. Survey studies revealed that deficiency of boron ranges from 1-84% with a mean of 33% being maximum in Teesta alluvial soils. Its deficiency has been widely found in highly calcareous of Bihar, Tamil Nadu, eastern Uttar Pradesh and Saurashtra, sandy soils of Haryana and Rajasthan, hill and sub mountaneous soils of north Himalayan and north eastern states and in red and lateritic soils of Orissa, Karnataka, Andhra Pradesh and Kokan region. Extent of boron deficiencies varied widely with soil types, cropping systems and agro ecological situations. Intensive cropping of high yielding crop varieties have aggravated the emergence of boron deficiency in several soils which were earlier not testing low in available boron. Map showing boron deficiency has been prepared and relationship with various soil properties has been established. Efficiency of different amelioration techniques and response of crops to boron fertilization involving various boron sources, micronutrient mixtures and organic manures, their application mode, rate and frequency, residual effect on succeeding crops, screening of tolerant crops or genotypes have been evaluated in more than 100 field experiments under different agro-ecological situations to suggest cost efficient technological options suited to specific location, soil type, crop and management situations. Field studies conducted under Borax Penta hydrate Granular (Granubor II) All India Research Network revealed that boron deficiency could be corrected more efficiently in cauliflower, onion, tomato, groundnut, mustard, sunflower, chickpea, lentil, soybean, maize, wheat and cotton crops by soil or foliar application of boron. Basal application of boron through broadcast on surface soil was found significantly superior than top dressing in boron deficient soils. However, foliar sprays of 0.2 per cent borax solution were found more efficient in several horticultural crops like mango, citrus, litchi, cauliflower, tomato compared to field crops. When basal application of boron was missed, top dressing of boron before first or second irrigation also effectively corrected its deficiency. Among sources, efficiency of borax decahydrate and borax pentahydrate granular (Granobor II) was found equal and both the sources did not differ significantly in increasing maize, cauliflower, soybean and, sunflower yields. Basal soil application of 0.5-1.5 kg B ha-1 to alternate crop was found optimum and better than foliar sprays on cereals, oilseeds and pulse based cropping systems. Application of 1.5-2.0 kg B ha-1 left significant residual effect on two to four succeeding crops. But application of more than 2 kg B ha-1 showed detrimental effect on yield of soybean, gram, maize, chickpea, and groundnut and cauliflower crops. Paddy crop did not respond to either of soil or foliar application irrespective of boron sources due to much of boron supply from irrigation water. Foliar sprays of multi micronutrient mixture containing boron were found beneficial in correcting its deficiency in grapes, mango, litchi and citrus crops in boron deficient soils. Balanced and integrated supply of 0.25-0.50 kg B ha-1 with organic manures 8-10 t ha-1 FYM annually was found more efficient than borax alone in increasing crop yields. Critical levels of boron in soils and its characteristic deficiency symptoms have been established in different field crops for better diagnosis. Also ready recknor for combined application of granubor and phosphatic fertilizers have been developed for suggesting suitable strategies for amelioration of born deficiency in divergent soils and crops.