Soil sampling and chemical analysis
Soil (400g) was collected from a representative spot in each DKO field. For clover field trials 6 representative samples of 400g soil were collected in the clover-free aisles between the plots. Each plot was then assigned the values of the nearest soil sampling site. Soil chemical analysis was performed by AGROLAB Agrar und Umwelt GmbH (Germany). Traits measured were: pH, phosphorus (mg/100g), potassium (mg/100g), magnesium (mg/100g), copper (mg/kg), humus, coarse sand (0.2-2mm), fine sand (0.02-0.2mm), silt (0.002-0.02mm), and clay (<0.002mm).