Nitrate Leaching as Affected by Introduction or Discontinuation of Cover Crop Use

Abstract

AbstractA 24‐yr‐old permanent field trial with spring‐sown crops was used in a nitrate N leaching study to determine (i) the effect of long‐term cover crop use compared with the introduction of perennial ryegrass (Lolium perenne L.) as a cover crop on plots with a history of no previous cover crop use and (ii) the effect of discontinuing long‐term use of ryegrass as a cover crop compared with no previous cover crop use. The cover crop (seed rate 8–10 kg ha−1) was undersown in spring wheat (Triticum aestivum L.). The field trial was conducted on a coarse sand (Orthic Haplohumod) under temperate coastal climate conditions in Denmark. From 1993 to 1997, nitrate leaching was estimated by use of soil water samples from ceramic cups in four treatments: cover crop since 1968, cover crop since 1993, no cover crop, and cover crop until 1993. Each treatment was carried out at two N rates: 60 and 120 kg N ha−1 yr−1. As an average of 4 yr and two N rates, leaching was 14 kg N ha−1 yr−1 or 29% higher in plots with long‐term previous cover crop use than in plots without. The effect of previous long‐term use of ryegrass as a cover crop lasted at least 4 yr. Thus, if the higher N mineralization due to long‐term use of cover crop is not taken into consideration by adjusting the cropping system, the reduction in nitrate leaching caused by the cover crop may not be as significant in the long‐term.