Extractants and Critical Limits of Available Soil Sulphur for Maize (Zea mays L.)

摘要

Pot experiments were conducted for two years using twenty-four soils, representing major soil orders of India to assess the suitability of fourteen extractants for establishing critical limits of deficiency of available soil sulphur for maize (Zea mays L.). The soils were extracted with 0.15% CaCl_2.2H_2O, 500 mg P L~(-1) Ca (H_2PO_4)_2.H_2O, Wolf, Mehlich-2, Mehlich-3, Mehlich-3 + charcoal, modified calcium chloride (0.15% CaCl_2.2H_2O + 0.5MCH_3COONH_4+ 0.5MCH_3COOH), 0.25MKC1 at 40 deg C, 0.25M KC1 at 50 deg C, 0.25MKC1 at 50 deg C + charcoal, 0.25MKC1 at 60 deg C, 0.25MKC1 at 60 deg C + charcoal, 500 mg P L~(-1) KH_2PO_4 and 0.125MKC1 + 0. 075% CaCl_2.2H_2O at 50 deg C extractants. The extractable/available soil sulphur content of soils studiedvaried widely by different extraction methods. The results showed that soil sulphur contents extracted by 0.15% CaCl_2.2H_2O, 0.25MKC13hr 40 deg C, 0.25M KC13hr 50 deg C and 0.25MKC1 3hr 50 deg C + charcoal was correlated significantly with most of the plant parameters of maize. The soil sulphur content extracted by 500 mg P L~(-1) Ca(H_2PO_4)_2.H_2O, Wolf, Mehlich-2, Mehlich-3, Mehlich-3 + cliarcoal, modified CaCl_2.2H_2O,500 mg P L~(-1) KH_2PO_4 and 0.125M KC1 + 0.075% CaCl_2. 2H_2O 3hr 50 deg C provided non-significant correlation with most of the biological indices of maize, indicating that these extractants are not suitable for the prediction of sulphur availability to maize. The critical limits of extractable/available soil sulphur for maize by promising extractants namely, 0.15% CaCl_2.2H_20,0.25M KC1 at 50 deg C, 0.25 M KC1 at 50 deg C + charcoal and 0.25MKC1 at 40 deg C, were found to be 8.33, 9.14, 7.73 and 13.30 mg S kg~(-1) soil, respectively. The critical tissue sulphur concentration in maize plant was found to be 1120 mg kg~(-1) (0.112%) on dry weight basis. For the maize 0.15% CaCl_2.2H_20, 0.25MKC1 at 50 deg C and 0.25M KC1 at 50 deg C + charcoal could be recommended as more suitable soil sulphur extractants followed by 0.25% KC1 at 40 deg C.