Farmyard manure application and associated root proliferation improve the net greenhouse gas balance of Italian ryegrass - Maize double-cropping field in Nasu, Japan.

In Japan, most cows are fed indoors, so cow manure must be carefully treated and used to manage soil fertility. The objective of this study was to compare the net greenhouse gas (GHG) balance (NGHGB) of Italian ryegrass - corn (maize) double-cropping fields receiving farmyard manure (FYM), slurry, or methane fermentation digestion liquid (MFDL). FYM, Slurry, MFDL, mineral fertilizer only (Fert.), and no-N control (Cont.) plots were set up in a randomized block design (n = 3). FYM, slurry, or MFDL was applied to meet the K requirement for forage production, and then mineral fertilizers were supplemented to meet the N and P requirements. From September 2017 to September 2020, C inputs as manure and crop residue, heterotrophic respiration (R _H ), and emissions of methane (CH ₄ ) and nitrous oxide (N ₂ O) from soil were determined. The similarity of the total yields in FYM, Slurry, MFDL, and Fert. plots reflected judicious fertility management. However, the residue-C input of Italian ryegrass was 38% greater in FYM plots than in the other plots. Manure-C input decreased in the order of FYM > Slurry > MFDL plots. R _H was greater in FYM and Slurry plots than in MFDL plots. Net ecosystem C balance (NECB) ([residue-C + manure-C] - [R _H -C + CH ₄ -C]) decreased in the order of FYM > Slurry > MFDL plots. N ₂ O emission was greater in Slurry and MFDL plots than in FYM plots. Consequently, NGHGB ([CH ₄ and N ₂ O emissions] - NECB) in terms of CO ₂ equivalent decreased in the order of MFDL > Slurry > FYM plots, so FYM application contributed most to GHG mitigation. Yield-scaled NGHGB was smallest in FYM plots owing to the synergy of the greatest residue-C and manure-C inputs, less N ₂ O emission, and the achievement of a high enough yield, reflecting judicious fertility management based on manure and mineral fertilizer.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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