The Rothamsted Long Term Experiments: Still Providing New Understanding of Organic Matter and Soil Quality after 170 Years.

Experiments on winter wheat, spring barley and pasture were started at Rothamsted between 1843 and 1856 and still continue. The original aim was to measure effects of manures and fertilizers on crop yields but they rapidly took on wider significance and currently contribute to our understanding of agricultural sustainability. Subtle interactions between soil organic matter content and crop yields continue to emerge. The founders had the foresight to archive samples of crops and soils; these have been analysed using modern techniques and used for many unforeseen purposes including pollutant dynamics. Further experiments were initiated later to study land-use change and management practices including crop rotations, tillage, fallowing and straw retention/removal. Nitrogen dynamics have been studied using ¹⁵N micro-plots established within the experiments.

Archived samples have been used for measuring changes in soil organic carbon (SOC) content in response to management. Results clearly show gradual changes in SOC between equilibrium values. The data contributed to the development of the Rothamsted Carbon Model, RothC, and the understanding that SOC comprises fractions differing widely in their decomposability. Soils from the experiments were used in the development of chloroform fumigation methods for measuring C, N and P held in the soil microbial biomass. More recently molecular methods have been used to assess the influence of management practices on soil biological populations and biodiversity.

The impacts of changes in SOC on soil physical properties have been studied at a range of scales including field measurements of plough draught (energy required to pull a plough through the soil) and laboratory studies on aggregate stability and soil compressability using tri-axial testing. A key finding is that small changes in total SOC can have disproportionately large effects on soil physical properties.

Additional understanding of processes is gained by comparing results from long-term experiments in diverse environments.