THE EFFECT OF MECHANICAL IMPEDANCE AND SOIL AERATION AS AFFECTED BY SURFACE LOADING ON THE GROWTH OF PEAS

In a 2 year field experiment on a marine sandy loam soil, a typic fluvaquent, a roller was used to simulate current and possible future running gear. Loading the soil with variable weight on the roller was used to obtain a well defined treatment and should result in better control of the soil conditions created than in usual field studies. This improves the possibility for understanding and modelling the effects of changes in soil structure on crop performance for a variety of traffic treatments. Soil physical properties and subsequent growth of peas in a simulated wet season were affected significantly by the load on the roller. Wetness of the topsoil at loading had a significant effect only when the topsoil was heavily loaded. Crack formation in the 10-15 cm layer, especially after heavy loading of wet soil, to some extent disturbed the uniformity of soil conditions produced. Negative crop responses to compaction could be explained by the occurrence of restricted aeration and mechanical impedance to root growth after this soil structural heterogeneity had been taken into account.