Abstract
We compared wheat yield, losses of nitrogen (N) in leaching, and gaseous losses as nitrous oxide (N2O) in silt and sand soil lysimeters. The studied cultivation systems were based on mineral fertilizer or mineral fertilizer together with clover green manure mulched at three different time points (August, October or May) before sowing of the main crop (either winter or spring wheat). Replacing 50–60% of mineral fertilizer N with green manure from a mixture of three clover species did not compromise the crop yield of winter or spring wheat. The results suggest that mulching of the green manure in the spring succeeding its sowing is the most beneficial practice with respect to environmental impacts. Total N leaching was higher from sandy soil than from silt loam whereas emissions of N2O were higher from the silt soil. Residual N from the clover biomass did not lead to an increase in leaching losses of N during the growing season or one year from the harvest. However, the residual N can be a source of high N2O emissions during the winter period in boreal climatic conditions.
Highlights
Agricultural soils are a significant source of the greenhouse gas nitrous oxide (N2O) and eutrophication of watercourses
A total of 36 lysimeters (4 replicates per treatment) arranged in two blocks were included in a split-plot design for studying the effects of green manure based cultivation on crop yield, gaseous emissions and nutrient leaching in silt and sandy soil
Winter wheat was sown in August 2013 in treatments GM1 and MF1 while spring wheat was sown in May 2014 in the other treatments
Summary
Agricultural soils are a significant source of the greenhouse gas nitrous oxide (N2O) and eutrophication of watercourses. Half of the greenhouse gas emissions from agriculture and half of the nitrogen (N) load to surface waters originate from agricultural soils (Statistics Finland 2020, Uusitalo et al 2007). Improving nutrient management in crop production is a key factor in reducing these losses since all N not bound to living organisms is available for the processes causing gaseous or leaching losses. Mineral fertilizers are the most common and readily available source of N for crops. Mineral fertilizers add greenhouse gas emission load to the carbon footprint of products (Heusala et al 2020) and they do not maintain soil carbon stocks like organic fertilizers (Sanden et al 2018). An option to replace part or all mineral fertilizer is to use green manure, i.e. plant material additional to the main crop, that releases nutrients for the main crop while its biomass decomposes. Additional benefits of the extra biomass are the carbon input it brings to the soil (Poeplau and Don 2015) and multiple other ecosystem services like reduction of erosion and improved soil structure and microbial activity (BlancoCanqui et al 2015)
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