Calcium and magnesium

Soybean calcium and magnesium needs can be met if dolomitic limestone is used to increase soil pH to ameliorate acid soils.

Micronutrients

Zinc and sometimes manganese, molybdenum or copper are most frequently required for soybean. Zinc, manganese and copper deficiencies have been effectively treated with the sulphate forms of these elements. Care must be taken to achieve uniform distribution; even spreading prevents adverse effects. Iron chlorosis or iron deficiency on high-pH soils is by no means rare. This can be prevented by dusting 100-160 g ha-1 iron chelate (DTPA or EDDHA) onto the soil along the rows. Spraying the foliage in early growth with iron sulphate, nitrate or chelate can also give good results (Fauconnier, 1986). In India, field studies have shown that the application of 5 kg Zn ha-1 as zinc sulphate to soybean was found adequate to meet the zinc requirement of both soybean and wheat crops in soybean-wheat rotation on black soils of central India (Sammi Reddy et al., 2007). If deficiency is severe, the rate of zinc application may be increased to 10 kg ha-1, which increases the yield benefits significantly. Zinc chelates are added to soils at 10-15 kg ha-1 to correct zinc deficiency, but chelates are very expensive compared to zinc sulphate. A basal application of zinc through broadcast is preferred. If soil application is missed, a spray of 0.5% zinc sulphate solution neutralized with 0.25% lime or 0.20% zinc chelate solution two to three times in 300-500 l ha-1 at 7- to 10-day intervals between 20 and 45 days after germination also corrects the zinc deficiency. In total, about 3-4 kg zinc chelate or 7-10 kg zinc sulphate ha-1 is required for 3-4 foliar sprays (M.V. Singh, Bhopal, 2008, personal communication).

On boron-deficient black soils of central India, an application of 4 kg borax ha-1 has been found to be effective for correcting boron deficiency (Acharya et al., 2003). Boronated superphosphate was found to be the best source for soybean-wheat systems as it also supplies phosphorus and sulphur (Shinde et al., 1990).

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