Reduction of Nitrogen Fertilizer Requirements and Nitrous Oxide Emissions Using Legume Cover Crops in a No-Tillage Sorghum Production System

• Main Authors: G. Y. Mahama, P. V. V. Prasad, K. L. Roozeboom, J. B. Nippert, C. W. Rice
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Sustainability
• Subjects: crop rotation; cover crops; greenhouse gas emissions; legumes; nitrogen management; nitrous oxide
• Online Access: https://www.mdpi.com/2071-1050/12/11/4403

Nitrous oxide (N₂O) emission from denitrification in agricultural soils often increases with nitrogen (N) fertilizer and soil nitrate (NO₃⁻) concentrations. Our hypothesis is that legume cover crops can improve efficiency of N fertilizer and can decrease N₂O emissions compared to non–cover crop systems. The objectives of this study were to (a) evaluate the performance of summer leguminous cover crops in terms of N uptake and carbon (C) accumulation following winter wheat and (b) to quantify the effects of summer leguminous cover crops and N fertilizer rates on N₂O emissions and grain yield of the subsequent grain sorghum crop. Field experiments were conducted in the context of a wheatsorghum rotation for two seasons in Kansas. Treatments consisted of doublecropped leguminous cover crops following winter wheat harvest with no fertilizer applied to the following grain sorghum or no cover crop after wheat harvest and N fertilizer rates applied to the grain sorghum. The cover crops were cowpea (<i>Vigna unguiculata</i> L. Walp.), pigeon pea (<i>Cajanus cajan</i> L. Millsp.), and sunn hemp (<i>Crotalaria juncea</i> L.). The three N treatments (were 0, 90, and 180 kg·N·ha⁻¹). Fallow systems with 90 and 180 kg·N·ha⁻¹ produced significantly greater N₂O emissions compared with cropping systems that received no N fertilizer. Emissions of N₂O were similar for various cover crops and fallow systems with 0 kg·N·ha⁻¹. Among cover crops, pigeon pea and cowpea had greater C accumulation and N uptake than sunn hemp. Grain yield of sorghum following different cover crops was similar and significantly higher than fallow systems with 0 kg·N·ha⁻¹. Although fallow systems with 90 and 180 kg·N·ha⁻¹ produced maximum sorghum grain yields, N₂O emissions per unit of grain yield decreased as the amount of N fertilizer was reduced. We conclude that including leguminous cover crops can decrease N fertilizer requirements for a subsequent sorghum crop, potentially reducing N₂O emissions per unit grain yield and providing options for adaptation to and mitigation of climate change.