Changes in a Doveton clay loam after 12 years of direct-drill maize production

Abstract

After 8 years of direct-drill maize production at Cedara on a Hutton/Doveton clay loam (Typic Plinthustult) it was found that the top 120-mm layer had become somewhat denser and that organic carbon levels in the top 20 mm were higher than in conventionally tilled plots. Direct-drill plots also displayed superior soil water conservation properties and this was reflected in better maize grain yields during seasons of below average rainfall. After a further 4 years the plots were again the subject of a detailed investigation and it was found that soil dry bulk densities had stabilized while surface organic carbon levels had increased in the interim from 3,8 to 4,7% in the direct-drill plots but had remained unchanged in the conventionally tilled plots at around 3,3%. Surface pH levels in the direct-drill plots had dropped further while P, K and Al levels were higher in the direct-drill than conventionally tilled plots. Earthworm counts were significantly higher in the direct-drill plots.