Net greenhouse gas balance with cover crops in semi-arid irrigated cropping systems
2022
Climate-smart agriculture has been increasingly emphasized to mitigate anthropogenic greenhouse gases (GHG) emissions, yet the mitigation potential of individual management practices is largely unknown. This study evaluated CO2 and N2O emissions, net CO2 equivalent GHG balance (GHGnet), greenhouse gas intensity (GHGI), yield-scaled GHG emissions, and soil properties in an irrigated forage corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench] rotation. Both corn and sorghum were present each year, and four different winter cover crops treatments were established in a randomized complete block design and replicated four times. Treatments were mixtures of 1) grasses, brassicas, and legumes (GBL), 2) grasses and brassicas (GB), 3) grasses and legumes (GL), and 4) a no-cover crop (NCC) control. Grass cover crops were annual ryegrass (Lolium multiflorum) and winter triticale (Triticale hexaploid Lart.), whereas brassicas were turnip (Brassica rapa subsp. rapa) and daikon radish (Raphanus sativus var. Longipinnatus), and legumes were pea (Pisum sativum subsp. arvense L.) and berseem clover (Trifolium alexandrinum L.). Our results show 5–10 times higher soil respiration with cover crop mixtures than NCC during the cover crop phase. Greater C inputs with cover cropping balanced the higher CO2 flux, and no effects were observed during the cash crop phase. The NCC released 44% less N2O-N (10.2 g N2O-N ha-1 day-1) than GL (18.3 g N2O-N ha-1 day-1), but similar to GBL and GB in the corn phase of the rotation. During the sorghum phase, NCC released 77% less (7.7 g N2O-N ha-1 day-1) N2O-N than GBL (34.4 g N2O-N ha-1 day-1), but similar to GB and GL. Cover crops did not affect GHG intensity, yield-scaled emissions, and net GHG balance. Instead, cover cropping increased the subsequent forage crop yield and soil carbon input. Integrating cover crops could be a climate-smart strategy for sustainable forage production in irrigated arid and semi-arid cropping systems.
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