Legumes and livestock in no-till crop rotations: Effects on nitrous oxide emissions, carbon sequestration, yield, and wheat protein content

Abstract

Context

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 (N₂O) from cropland soils in South Africa.

Objective

Assess the production performance, soil greenhouse gas emissions, and soil carbon sequestration of different crop rotations.

Methods

Continuous measurement over one year of direct soil N₂O and methane fluxes and analysis of 20 years of historical data on soil carbon sequestration, yields, fertiliser applications, and wheat (Triticum aestivum) protein content.

Results and conclusions

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 N₂O production, where systems which integrated legumes and livestock vs. cash crops only had 0.31–0.42 vs. 0.14 kg N₂O-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.

Significance

Legumes and livestock incorporation in crop rotations interact with nitrogen management. Most N₂O 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 N₂O mitigation strategies is the lack of existing N₂O flux datasets needed to develop specific, regional emission factors.