GREEN MANURING WITH CLOVER AND RYEGRASS CATCH CROPS UNDERSOWN IN SPRING WHEAT - EFFECTS ON SOIL-STRUCTURE

The objective of the present study was to investigate the potential of undersown catch crops to counteract soil degradation after autumn plo ughing. Italian ryegrass (Lolium multiflorum Lam.) and white clover (T rifolium repens L.) were undersown in spring wheat on a loam soil in s outhern Norway, allowed to grow as cover crops after grain harvest and ploughed in to 20 cm depth as green manure in late October. Ryegrass prevented a collapse of the ridged plough furrow profile during winter , which occurred on gain monoculture and white-clover plots. Also, it tended to improve the water stability of aggregates, aggregate size di stribution, bulk density, and pore volume in soil sampled in May. The preservation of the plough furrow profile was mainly attributed to enm eshment by an extensive system of fine roots and less to rhizosphere a nd microbial effects on aggregate stability. The results showed that r yegrass catch crops may give rapid structure improvements that are lik ely to contribute appreciably to easier seedbed preparation and less s oil degradation in arable farming systems, even if the soil is ploughe d in autumn.