Yield and Nitrogen Uptake in Organic Potato Production with Green Manures as Pre-Crop and the Effect of Supplementary Fertilization with Fermented Slurry

Abstract

ABSTRACT Differences in yield and N uptake in cultivation systems using autumn or full-season green manures as a pre-crop in organic potato (Solanum tuberosum L.) production were studied in five trials carried out on two sites, one on a poor soil and the other on a more fertile soil, in southern Sweden in 2000–2002. The effects of supplementary fertilization with fermented slurry after the autumn green manure were also studied. Using a one-year green manure as the pre-crop did not increase yields cornpared with the autumn green manure, probably due to poor growth. The cut biomass contained 36–44 kg N ha−1. However, a two-year green manure (107 kg N ha−1) as the pre-crop increased yields. Yields were not affected by how the full-season green manures were managed; the cut biomass was either removed or left on the soil surface. The fermented slurry contained between 37 and 94 kg NH4-N ha−1. On the site with the poorer soil, supplementary fertilization with fermented slurry increased N uptake by approximately 50% and, in one season, yields by approximately 40%. On the site with the more fertile soil, fertilization with fermented slurry had no effect on N uptake or yield. On both sites, there was a positive correlation between potato yield and total N uptake, and on the site with the poor soil also with the amount of N in the soil one week after emergence. In November, residual mineral N in the soil at 0–0.9 m depth was lower in the poor soil (25–60 kg N ha−1) than in the more fertile soil (50–90 kg N ha−1). There were no indications of N leaching between harvest in September and the last soil sampling occasion in November for any of the fertilization regimes studied, but high N-min values in two of the experiments posed a risk of leaching later in the crop rotation.