THE RESIDUAL EFFECT OF LIME ON CROP YIELDS, pH, AND OTHER CHEMICAL CHARACTERISTICS OF A GREY WOODED SOIL BROKEN TO DIFFERENT DEPTHS

Abstract

A virgin Grey Wooded soil in which soil pH increased with depth of profile was ploughed to different depths on first breaking the land. It was observed that irrespective of depth of ploughing, calcitic limestone applied at 2 and 4 tons per acre respectively still exerted an effect on crop yields 7 years after application. The predominant effect of increases in soil pH and crop yields were attributable to lime, though with 6-in. ploughing nitrogen had a significant effect in increasing soil pH but no significant effect on crop yields. Phosphorus did not significantly affect soil pH with any of the ploughing treatments imposed, but had some effect on crop yields with 6-in. ploughing and 24-in. ploughing. In the absence of lime application, soil pH decreased substantially in the first year of cropping and then remained fairly constant. An application of 2 tons of lime per acre was just sufficient to maintain the natural pH of the different soil layers and yet caused substantial increases in crop yields. With 4 tons of lime per acre, the increase in soil pH was at a maximum in the first year after application, and with 6-in. ploughing was maintained at this level. However with 12-in. ploughing and 24-in. ploughing the maximum pH attained was not maintained.Lime applied to the surface soil affected soil pH in the subsurface soil.Irrespective of initial ploughing treatment on breaking the land, lime decreased organic matter and increased Bray 'acid-soluble' phosphorus in the surface soil. With 6-in. and 12-in. ploughing, lime increased Bray 'adsorbed' phosphorus, but caused a decrease with 24-in. ploughing. On the application of lime, increases in Bray 'acid-soluble' phosphorus were in general more pronounced than increases in Bray 'adsorbed' phosphorus.