Abstract Soil can act as a source or sink for methane (CH 4 ), a potent greenhouse gas and key component of atmospheric carbon cycling. We monitored CH 4 fluxes over 4 years in a semiarid, sprinkler‐irrigated crop rotation spring wheat ( Triticum aestivum L.), potato ( Solanum tuberosum L.), barley ( Hordeum vulgare L.), and sugar beet ( Beta vulgaris L.) in southern Idaho to evaluate the effects of dairy manure and synthetic fertilizer. Treatments included an unfertilized control, synthetic fertilizer, and three manure rates (18, 36, and 52 Mg ha − 1 ). Fluxes were measured using static closed chambers. Across all treatments and years, soils acted as a net CH 4 sink, where negative flux values indicate net uptake. Fluxes ranged from −1.5 ± 1.0 g CH 4 ha − 1 day − 1 (control) to −1.3 ± 1.0 g CH 4 ha − 1 day − 1 (high manure). Manure weakened uptake in proportion to rate, while synthetic fertilizer and low manure maintained control‐like fluxes. Uptake peaked in October (2.3 ± 0.6 g CH 4 ha − 1 day − 1 ) and December (2.1 ± 0.7 g CH 4 ha − 1 day − 1 ), was lowest in June (0.9 ± 0.6 g CH 4 ha − 1 day − 1 ), and was moderate during freeze–thaw transitions. Uptake was highest in 2014 (2.0 ± 0.7 g CH 4 ha − 1 day − 1 ) during a potato year with extensive tillage and lowest in 2016 (0.8 ± 0.3 g CH 4 ha − 1 day − 1 ) when monitoring ended earlier. Cumulative uptake was weakest in high manure (1.72 kg CH 4 ha − 1 ) and strongest in low manure (2.04 kg CH 4 ha − 1 ) and control (2.01 kg CH 4 ha − 1 ). Overall, organic amendments reduced uptake but did not shift soils to a net source.
Miito et al. (2026) studied this question.