The effects of nitrogen fertilizer rates in a long-term reduced tillage cropping system on dry matter and nitrogen accumulation in an oil radish (Raphanus sativus L.) cover crop

Abstract: This study was undertaken to evaluate the effects of long-term N fertilizer application rates on dry matter (DM) production and nitrogen (N) accumulation in an oil radish (Raphanus sativus L.) cover crop. The N fertilizer application was done to the main crop winter wheat (Triticum spp.) before oil radish. The experiment was carried out at the research station (Lönnstorp) at SLU, Alnarp in a long-term experiment with (conventional and reduced tillage systems) different N fertilizer application rates in a crop rotation including cover crops. The autumn cover crop DM production and N accumulation were significantly increased with the increased amount of N fertilizer applications to the main crop. According to the hypothesis, the observations of DM production and N accumulation were expected to be in a linear trend with the N levels but they were highly significant with the N levels without any linear increasing tendency. A socio-economic evaluation of cover crops was estimated by comparing the establishment costs of cover crop and the economic value of N conserved in the cover crop, assuming its value to be similar to the value of synthetic N fertilizer. The results showed that the cost of establishing oil radish as cover crop was not completely compensated by the economic value of N conserved in the system. However, several other beneficial aspects of cover crops are discussed to have positive effects in agrosystems, but their economic valuations are complex. Incorporation of cover crop in cropping system has shown to improve biodiversity, suppress of pests and weeds, reduce soil erosion, improve soil organic matter (SOM) and soil texture and structure. Finally, considering the beneficial environmental aspects of cover crops, introducing more subsidies from national and international levels will increase the interest of farmers to grow more cover crops to improve sustainability of cropping system.