COMPARISON OF CROP YIELDS AND SOIL-CONDITIONS DURING 30 YEARS UNDER ANNUAL TILLAGE OR GRAZED PASTURE

Crop yields and soil properties of grazed grass-clover pasture and arable plots at the Grasslands Research Institute, Hurley, UK were measured over 30 years (1955–84). Yields of herbage declined from 9.6 t DM/ha in the first harvest year to 4–6 t in years 5 to 8 but subsequently increased (after liming) to give a mean yield of 8.2 t for 1963–84. Yields of barley in plots receiving a seed-bed application of 45 kg N/ha averaged (1962–80) 3.1 t/ha and, in plots top dressed with an additional 100 kg N/ha, 4.1 t/ha but after 1969, response to additional N and yield under both N treatments showed a marked decline. Soil carbon increased during the first 10 years under pasture from 1.2 to 1.8% and soil N from 0.13 to 0.7%. These increases, equivalent to 1 t C and 75 kg N/ha per year, occurred at the same time as the initial decline in herbage yield noted above. During the subsequent 20 years, C and N remained relatively constant and herbage yields increased. Soil C and N decreased under 30 years’ arable management to 0.8% C and 0.1 % N, equivalent to a loss of 290 kg C and 25 kg N/ha per year. Major factors that appear to have influenced herbage yields were (i) soil moisture, (ii) accumulation of N in the soil organic matter during the first 8 years and the subsequent increase in the rate of mineralization, and (iii) the action of the earthworm population in creating a stone-free, fertile layer of top soil. As for barley, it was concluded that yields could not be maintained indefinitely on this soil series, as a result of the loss of soil structure and the development of a compact layer of soil at plough dejtlh. © 1990, Cambridge University Press. All rights reserved.