Stability and organic matter content of surface soil aggregates under different methods of cultivation and in grassland

The effects of direct drilling, shallow and deep tine cultivation, ploughing, and of growing and permanent grass sward on the stability and organic matter content of surface soil aggregates were studied on a range of soils in Southern England. Cultivation treatments were applied continuously for 4 to 6 years. Generally, relative aggregate stability, assessed by turbidimetric and wet-sieving techniques, was enhanced by direct drilling and other forms of simplified cultivation compared with ploughing. Increased stability was associated with increased organic matter status and was not pronounced under grass. In the case of a soil which was previously under permanent grass stability and organic matter content declined after direct drilling but significantly less so than after mouldboard ploughing. Differences in aggregate stability were detected in some soils only after modifying the test procedure and it appeared likely that the magnitude of differences were variable within a season and were related possibly to the tilth forming properties of the soils.