Investigation of the effect of different leguminous cover crops on the nitrogen use efficiency of spring barley

Abstract

The research focus was to investigate the effect of different Nitrogen Fixing Crops (NFC) used as green manure (GM) on the Nitrogen Use Efficiency (NUE) of spring barley (SB) (Hordeum Vulgare var Westminster), with different N-fertiliser treatments, in Scotland coldtemperate climatic conditions. Different GM’s treatments were grown during a year, then, SB was sown in it. A low rate of N-fertiliser was applied to half of the SB plots to study the effect of mixed N sources (NFC used as GM and mineral N-fertiliser) on NUE. The N fluctuation in soil, the soil fauna activity and the crop biomass production according to the different treatments were assessed. The analysis of the decomposition rate, the N content of the SB crops and, thus, the calculation of the NUE could not be carried out due to technical and time issues. To replace temporarily the NUE, the amount of biomass created per unit of N available was calculated (BNU=BiomassGS60/(SMN GS0 ±Nfertiliser) ) and called Biomass N Use (BNU), with BiomassGS60 being the SB biomass at anthesis, SMN GS0 being the soil mineral N content at SB sowing and N-fertiliser being the N applied as fertiliser. The NFC treatments enhanced the soil mineral N content and triggered the soil fauna activity in comparison with the controls but had no noticeable effect on the SB biomass production. The addition of N-fertiliser has shown to increase the soil mineral N content, the biomass of the SB, and supposedly will improve the grain yield. The BNU of SB varied accordingly to the previous NFC and N-fertiliser treatments. The addition of N-fertiliser drastically decreased the BNU while it improved of 15% the crop biomass production. While the BNU of the NFC treatments with addition of N-fertiliser seemed all similar, without N-fertiliser they have shown interesting differences; with control (ryegrass) being one of the highest BNU, alongside with lupin, peas, mixture B and white clover, which could mean that some legumes could be as effective as grass at removing N from the soil while fixing N from the atmosphere. However, the relevance of BNU calculation is questionable because there is no evidence that it might represent reliably the NUE.