Conventional and reduced tillage, and set-aside land – Effects on nitrogen, phosphorus and potassium subsurface leaching from a clay soil during 9 years

Abstract

This study investigated the effect of two different autumn tillage intensities, and a permanent green fallow, on subsurface nutrient leaching losses during nine years, with the overall aim to evaluate strategies for reduced nutrient load from arable land. The main hypotheses were that crop production results in larger leaching losses of nitrogen (N), phosphorus (P) and potassium (K) than a green fallow, and that reduced tillage (RT) is a measure for reduced N leaching without reduction of grain yields compared to conventional tillage (CT). The field site was a clay soil (47 % clay, Uderic Haploboroll) in south-west Sweden and the field experiment was equipped with separately tile-drained plots to record the subsurface drainage water flow. The water was analyzed for total N, nitrate-N, total P, phosphate-P and K. Grain yields of main crops and contents of soil mineral N were also determined. Long-term average and most annual means show no significant impact of tillage system, concerning N, P and K leaching losses or yields of main crops. There were indications of higher N leaching using CT compared to RT. Average leaching losses were 3.9 kg N ha⁻¹ yr⁻¹, 0.4 kg P ha⁻¹ yr⁻¹ and 6.5 kg K ha⁻¹ yr⁻¹ from the tilled plots. In 9-year average, the permanent green fallow reduced the soil mineral N content in autumn and decreased the transport of nitrate-N in drainage water compared to both tillage systems. However, green fallow could not be considered a mitigation option for P and K leaching losses.