Micronutrient deficiencies in rainfed calcareous soils of Pakistan. II. Boron nutrition of the peanut plant

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Abstract
The rainfed soils of peanut (Arachis hypogaea L.) growing fields in the Potohar plateau of Pakistan are alkaline (pH=8.0±0.2) and calcareous (CaCO3=7.1±3.3%) with low organic matter contents (0.65±0.29%) and the crop is grown without adequate fertilization. The peanut crop grown on such soils was suspected to suffer from boron (B) deficiency. Therefore, a nutrient indexing of B was carried out by sampling 100 random fields representing 20 soil series. The surface soil HWE B ranged from 0.10 to 1.08 mg/kg and averaged 0.47 mg/kg. Boron content of subsoils was slightly lower than the surface soils. Fifteen soil series out of 20 and 60% of the total field locations exhibited extractable B levels ≤0.5 mg/kg, therefore, may have less than adequate available B for crop production. The rest of the fields were marginally fertile in B, 0.51 to 0.59 mg B/kg soil. Boron content of peanut plants (∼4‐cm shoot terminals) ranged from 12.0 to 97.9 mg/kg and averaged 34.6 mg/kg. About one‐half of the plant samples contained 50 mg B/kg. Thus, plant analysis as well as soil testing revealed widespread B deficiency in peanut crop. In a field experiment on an alkaline calcareous Typic Hapludalfs, B fertilization at 0.5 to 1.0 kg B/ha increased pod yield of rainfed peanut (cv. BARD‐699) by 10% over control. However, ≥2.0 kg B/ha proved toxic and 4.0 kg B/ha resulted in 18% yield reduction. Fertilizer B requirement for near‐maximum (95%) pod yield was estimated to be 0.5 kg B/ha and critical B concentration in shoot terminals was 29 mg B/kg. Extreme care is suggested to avoid overdose and/or uneven field distribution of B fertilizer as peanut is highly sensitive to B toxicity. Suggested corrective measures for B deficiency are B fertilization or cultivation of peanut varieties tolerant to B deficiency.

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