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Diversifying cropping sequence reduces nitrogen leaching risks

Beillouin D., Pelzer E., Baranger E., Carrouée B., Gernay C., de Chezelles E., Schneider A., Jeuffroy M.H.. 2021. Field Crops Research, 272 : 8 p..

DOI: 10.1016/j.fcr.2021.108268

Overuse of chemical fertiliser in cereal cropping systems has resulted in severe degradation of air and water quality. Diversifying cropping sequence with legumes provides a natural source of nitrogen (N), but also increases N leaching risks after their growing period. Here, we hypothesize that legumes and other break crops, i.e., crops grown to diversify the cropping sequence, reduce N leaching at the rotation scale due to their contribution to increasing nutrient use efficiency and crop N recovery of the following cereal crops. In two 4-year experiments conducted in northern France, we monitored agronomic performance and the changes in the soil mineral N content at field scale in six preceding crop-current crop combinations including winter wheat (Triticum aestivum), pea (Pisum sativum L.) and oilseed rape (Brassica napus L.). We quantified N leaching after each crop as a function of the preceding crop with a water-fluxes model based on soil mineral N content, climate data and soil characteristics. We then simulated N leaching at the rotation scale, for 20 years of climate conditions and various cropping management systems. We show that growing pea or oilseed rape reduced soil mineral N content at harvest of the following cereals (up to mean values of -28 and -19¿kg N ha-1 respectively), and N leaching risks during winter of the following cereals compared to the wheat-wheat cropping sequence. Although N leaching was higher during the winter after pea was cultivated, the cumulative losses over four experimental years of the pea cropping sequences were not significantly higher than the no-break cropping sequences. Over the 20 climate years, sequences including pea, oilseed rape, volunteers or catch crops reduced simulated N leaching by up to 40 % compared to wheat monoculture. Our study confirms that N leaching not only depends on the current crop but is also affected by the preceding crop. A large potential reduction in nitrogen leaching could be achieved in many intensive cereal-growing regions with very limited cropping sequence diversity.

Mots-clés : rotation culturale; diversification; azote; fixation de l'azote; lessivage du sol; légumineuse; triticum aestivum; pisum sativum; brassica napus; teneur en azote; france

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