Effect of margin strips on soil mineral nitrogen and plant biodiversity

Abstract

We studied the effects of two- to three-year-old unfertilized field margin strips, installed between the pre-existing field boundary and the field crop, on soil ammonium N and nitrate N, and on the botanical composition of the adjacent semi-natural vegetation in the field boundary. Margin plots were regenerated spontaneously or were sown to grass/forb mixtures and were managed under a cutting regime with removal of cuttings. In general, soil nitrate N, soil ammonium N and soil mineral N losses were significantly affected by distance from the field crop edge and not by plant community type. The further away from the crop edge, the lower soil nitrate (up to fivefold lower than in the crop) was found in the margin strip, but soil ammonium N was approximately 50% higher close to nearby trees and shrubs. Inside the margin strip, total soil mineral N as well as N loss during winter was minimal at a distance of 5 m from the crop edge. The reduction of soil nitrate N near the boundary by the presence of a margin strip was responsible for the increase in abundance of less competitive species and for an up to 20% higher species-richness within the field boundaries. In summary, our results show clearly that margin strips both decrease N pollution of groundwater and increase botanical diversity. A minimal margin width of 5 m is recommended.