Correlation of Soil Tests with Response of Wheat to Applied Copper

The values for available copper in ten soils of Kanpur district obtained by the five extractants viz., N neutral NH₄OAc, 0.1 N HCl, 0.02 M EDTA, 1% citric acid and water were correlated with per cent yield of grain and straw of wheat var. Kalyansona as well as with the per cent uptake of Cu from applied CuSO₄. N neutral NH₄OAc showed the highest correlation coefficient followed by 0.2 M EDTA significant at 1% level, while 0.1 N HCl extractable Cu was significant at 5% level. The values did not approach the level of significance in case of citric acid and water. Highest response was recorded with the application of 5 kg CuSO₄/ha in those soils containing less than 0.5 ppm N neutral NH₄OAc extractable Cu. Extractants may be placed in the following order with regard to their suitability: N neutral NH₄OAc > 0.02 M EDTA > 0.1 N HCl.