The impact of modern farming practices on soil fertility and quality in England and Wales

Abstract

Data are presented on the effects of modern farming practices on soil as an agricultural resource in England and Wales (E&W), namely: nutrient status, pH, soil organic carbon (SOC), heavy metal concentrations, and on soil erosion risk. Fertilizer-N inputs to tillage (arable) and grassland soils increased from 84 and 65 kg/ha N in 1969 to 151 and 120 kg/ha N, respectively, in 1997. The estimated N surplus (inputs less outputs) increased from 84 and 96 kg/ha N to 102 and 154 kg/ha N, respectively, over the same time. Phosphorus inputs to tillage (mean 37 kg/ha P) and grassland (mean 21 kg/ha P) changed little over the period. However, P surpluses decreased from 25 kg/ha P in 1969 to 15 kg/ha P in 1997 on tillage land (largely as a result of greater P offtakes), and from 20 to 17 kg/ha P in 1997 on grassland (largely because of a small decrease in fertilizer P). The cumulative tillage land soil P surplus was c. 580 kg/ha P, and was estimated to increase topsoil total P concentrations by c. 170 mg/kg P and Olsen-extractable soil P by c. 26 mg/l P. The mean annual P surplus for grassland was 18 kg/ha P which, over the study period, added c. 427 kg/ha P to the soil, an increase in topsoil total P of c. 214 mg/kg P, and in Olsen-extractable P of 19 mg/l P.

Concentrations of SOC in some soils have decreased between 1980 and 1995, especially where soils have been ploughed out of grassland and on lowland organic and peaty soils in tillage. The mean SOC of soils in arable/ley cultivation in 1980 was 3·4% and 2·8% in 1995.

The proportion of arable soils with pH < 6·0 decreased from 10% in 1969–73 to 4% in 1990–93, reflecting the better targeting of lime inputs. In contrast, the proportion of grassland soils with pH < 6·0 increased from 39% in 1969–73 to 56% in 1990–93.

Although there were statistically significant changes in the mean soil concentrations of Cd, Cu, Ni, Pb and Zn between 1980 and 1995, many of the changes were small in absolute terms. Hence, there was little evidence of marked or systematic changes in topsoil total heavy metal concentrations that could not be explained by factors other than increased pollutant loadings.

Over the next 50 years or so, the threat from soil erosion to crop productivity will be greatest on shallow soils ([les ] c. 0·3 m depth), mostly over chalk and sandstone as further removal of soil will lead to increased drought stress. Provided that nutrient supplies are maintained, the evidence is that losses in arable crops on eroded soils would range between 2% and 8% of current yields.

Thus, within the limitations of the data available, both in time and space, we found little evidence that most soils in E&W cannot continue to support modern farming practices, and the associated crop and animal outputs, given appropriate inputs of nutrients and an adequate degree of crop protection.