CROP RESPONSES TO DIFFERENTIAL GYPSUM APPLICATIONS IN A HIGHLY SODIC SOIL AND THE TOLERANCE OF SEVERAL CROPS TO EXCHANGEABLE SODIUM UNDER FIELD CONDITIONS

Effect of five levels of gypsum, 0, 7.5, 15.0, 22.5, and 30 t/ha, on soil properties and yields of several crops in a highly sodic soil was studied in a field experiment. The soils are representative of nearly 2.5 million ha of sodic soils in the Indo-Gangetic plains in north India. Results showed that reduction in soil ESP was quicker and extended to deeper depths when rice (Oryza sativa) was grown. Rice was also found to be a highly tolerant crop to exchangeable sodium, while wheat (Triticum aestivum) was only moderately so. These results are contrary to those of the U.S. Salinity Laboratory, which rated rice as an only moderately tolerant crop and wheat as tolerant to excess exchangeable sodium. Differences in growing conditions in their pot culture studies and our field plots are possible reasons for these contrasting results. Crops like mash (Phaeseolus mungo), lentil (lens esculentum), and gram (Cicer arietinum) were found to be sensitive and to fail to yield satisfactorily in the presence of the high sodicity of subsoil layers. Dhaincha (Sesbania aculeata), a green manure crop, was found to be tolerant, and bajra (Pennisetum typhoideum) was found to be a semitolerant crop.