Legumes and livestock in no-till crop rotations: Effects on nitrous oxide emissions, carbon sequestration, yield, and wheat protein content
Lisa Matthews, Johann Strauss, Thorsten Reinsch, Hendrik P. J. Smit, F. Taube, Christof Kluss, Pieter A. Swanepoel
Abstract
Crop rotation is seen as a ‘Climate-Smart Agriculture’ practice, but there are knowledge gaps around their climate impacts. This is the first direct measurement of nitrous oxide emissions (N 2 O) from cropland soils in South Africa. Assess the production performance, soil greenhouse gas emissions, and soil carbon sequestration of different crop rotations. Continuous measurement over one year of direct soil N 2 O and methane fluxes and analysis of 20 years of historical data on soil carbon sequestration, yields, fertiliser applications, and wheat ( Triticum aestivum ) protein content. Rotations that contained legumes and livestock produced higher wheat (3.5–3.6 vs 3.1 t ha −1 year −1 ) and canola yields (1.5–1.8 vs 1.3 t ha −1 year −1 ) with superior wheat protein contents, while the cash crop only system's protein content decreased by 0.085 absolute % points annually (compared to 0.01–0.05 %). The results suggest a strong crop rotation legacy effect on the accumulation and availability of nitrogen in the soil profile, for both crop growth and N 2 O production, where systems which integrated legumes and livestock vs. cash crops only had 0.31–0.42 vs. 0.14 kg N 2 O-N ha −1 year −1 . All systems showed a significant increase of soil organic carbon of 0.24–0.30 Mg C ha −1 year −1 over the 20-year period. Legumes and livestock incorporation in crop rotations interact with nitrogen management. Most N 2 O emissions occurred after precipitation in the otherwise dry summer, making reduction difficult as minimal management activities occur over this fallow period. A significant challenge in designing N 2 O mitigation strategies is the lack of existing N 2 O flux datasets needed to develop specific, regional emission factors. • Crop rotation strategies have legacy effects on production and climate impact. • Rotations without livestock: low N 2 O emissions, but low yield, high fertiliser need. • Dropping wheat protein of cash crop-only rotations over 20 years were unsustainable. • Crop rotations with legumes/livestock had better wheat yields and grain quality. • Emission hotspots are off-season, making reduction hard.