Leek production in conventional and organic arable-vegetable rotations in the Netherlands

Leek production, one of the most important vegetables grown on the sandy soils in the South East of the Netherlands, is known to have a high rate of nitrogen leaching. Nitrogen leaching from leek cultivation depends not only on the cropping strategy but also on the whole farming system. The objective of this study was to evaluate nitrogen losses and crop yield of leek cultivation and the total farming system with different fertilization strategies. A farming systems experiment with two conventional and one organic farming system with arable and vegetable crops on sandy soils was evaluated. One conventional farming system (LOW) had a low organic matter input consisting of crop residues and green manure crops only. The other conventional farming system (STANDARD) had a regular organic matter input including cattle and pig slurry. The organic system had a high organic matter input because of the use of farm yard manure and cow slurry. Data of crop yield, nutrient balances and nitrate leaching for the period 2011-2016 are discussed. In the LOW system, crop production was on average 5% lower than in STANDARD. Nitrogen surplus was lower in LOW than in STANDARD. Phosphorus surplus was about equal between the systems and potassium surplus was higher in LOW than in STANDARD. Nitrate leaching was comparable in LOW and STANDARD, but both above the limit set in the EU nitrates directive of 50 mg L-1. Other indicators of nitrogen leaching as soil mineral nitrogen content and nitrogen surplus indicate that leaching risk in LOW is lower than in STANDARD. Leek yield in the organic system was low because of incidences of pests and diseases. However, in years with low disease pressure yields were only a few percent lower compared to the conventional yields. Nutrient surpluses of N, P and K were high in the organic system. Nitrogen leaching was below 50 mg L-1 in the organic system. A dilemma still exists between crop yield and nitrate leaching in the conventional systems: lower nitrate leaching is coupled with lower crop yields. The organic system gives relatively low yield however with good results regarding nitrate leaching.