Loss of trace elements from agricultural soil.

Soil erosion is a world-wide issue driven by land management and climate change. Research has focussed on soil loss rates from agricultural land. However, the loss of trace elements essential for soil and plant health, or potentially toxic elements that occur as impurities in fertilisers and manures, is poorly understood. This study reports on the loads and forms of copper, cadmium, manganese, nickel, selenium and zinc lost from three types of agricultural systems at Rothamsted Research's North Wyke Farm Platform over five individual storm events. Loads reflected a combination of concentrations in the soil, annual additions from fertilisers, the ability to leach from the soil and rainfall intensity. Arable fields demonstrated an order of magnitude greater loss of soil compared to pasture. Consequently, particulate-bound losses were higher, and the proportion of losses in solution were 29% lower on average, compared with pasture. Overall losses for each element were statistically similar for pastures. In comparison, arable fields showed greater average losses for five essential elements (15.3%) compared to pasture (9.7%). Nickel exhibited the greatest average loss (27% overall; 39% for arable) and zinc the lowest (2% overall; 3% for arable). The predominant loss of cadmium was in the dissolved phase (96% overall; 92% arable), followed by selenium (81%/63%), nickel (64%/35%) and copper (61%/34%). Conversely, dissolved losses of manganese (38%/21%) and zinc (28%/8%) were lower than particulate losses. We conclude that overall loss, and form of the loss, varies significantly between arable and pastoral systems, and the physico-chemical properties of the element itself.