Comparison of crop yields and soil conditions during 30 years under annual tillage or grazed pasture

Abstract

SUMMARYCrop 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 subseque8tly 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 0·17%. 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 depth.