Soil changes in ley-arable experiments

Abstract

The effects of four five-course and six four-course rotations on some physical and chemical properties of a sandy loam overlying London Clay are reported. Periods under ley increased the water stability of the air-dry soil aggregates, the resistance of moist soil aggregates to simulated raindrops, the rate of drainage under 60 cm. of water tension as measured in the laboratory, decreased the draw-bar pull during ploughing and the force required to crush air-dry aggregates. These effects increased with the number of years under grass. After 2 years of arable cultivation the effect of a 3-year ley on water-stable aggregation was still apparent whereas the effect of a 2-year ley had largely disappeared, and those of a 1-year ley had completely disappeared. A 2-year ley in a five-course ley-arable rotation was sufficient to maintain the total soil nitrogen at about 0·16%. With one year of ley in a four-course rotation a slow decline in nitrogen was found when the initial level was about 0·21%. The rate of CO 2 formation in soils of the arable break was proportional to the number of years they had been under ley; the longer the period the greater the volume of CO 2 produced. Evidence is presented that fertilizer nitrogen is used most efficiently by cereals growing in soil in good physical condition. This is usually best following a period under grass.