Soil and cotton responses to tillage and ameliorant treatments in a brown clay soil. 2. Growth, yield and quality of cotton

Abstract

Furrow irrigated cotton was grown in 1965-66 and 1966-67 on previously uncultivated dense clay soil to which the following treatments were applied before sowing in 1965 ; normal ploughing (18 cm), precision ripping (30 cm), deep ploughing (40 cm), deep ripping (60 cm), and deep ploughing and deep ripping combined, with and without application of gypsum at 10 tons an acre or organic matter at 2 1/2 tons an acre. Each of the three deep tillages increased lint yield by about 12 per cent in the first season, but in the second season the combined deep ripping and deep ploughing alone gave a significant increase of 17 per cent. Precision ripping had no influence on yield. The gypsum treatment gave increases in both seasons (16 per cent in 1966 and 34 per cent in 1967) whereas organic matter had no effect. The higher yields were produced from a greater number of larger bolls, on taller, more vigorous plants with more main stem nodes. These effects on plant growth and yield were interpreted as resulting from the changes in subsoil porosity and water entry at irrigation (reported previously). As with the soil properties, the tillage and ameliorant treatments did not interact significantly on plant growth and yield. Changes in the quality of the lint accompanied the yield increases. Deep tillage and particularly gypsum application produced finer (lower Micronaire values), but longer and more elastic fibres than the control. However, differences between seasons were generally greater than those due to treatments, and the lowering of Micronaire values by gypsum or deep tillage could be regarded as either beneficial or deleterious depending on the seasonal conditions during lint development. By improving soil tilth, gypsum application increased seedling establishment and hence yield potential, and this could be of considerable practical significance in commercial crops grown on soils responsive to gypsum.