Manure application in managed grasslands can contribute to soil organic carbon sequestration: evidence from field experiments across Japan

We conducted field experiments in nine managed grassland sites spanning annual temperatures of 5.8–16.3 °C for 5 years to investigate the effects of farmyard manure (FYM) application and environmental conditions on soil organic carbon (SOC) stock changes. Experimental plots were established with three (zero, low, and high) levels of continuous FYM application at each site, and soil samples down to 30 cm depths were annually collected to determine SOC stocks. Annual changes in SOC stocks were analyzed by fitting a linear mixed-effect model, including the sites as random-effects. Based on the model, low and high level FYM application lead to 1.9–10.4 (4.8 on average) and 3.4–15.1 (8.4 on average) Mg C ha −1 year −1 of SOC increase across the sites, respectively. The random-effects for annual changes in SOC stocks were not correlated with soil type (andic vs. non-andic) but positively correlated with the duration, implying that the grassland maintenance without renovation contributed more to SOC sequestration than soil type. Simple simulations using the model showed that SOC stocks increased at all nine sites with recommended (low) level of FYM application. The simulation also revealed that SOC sequestration with the recommended level FYM application can be maintained even under a global change scenario with temperature rise of up to 2.8 °C above the current level. These results indicated that managed grasslands in Japan with the recommended level FYM application can contribute to climate change mitigation via SOC sequestration even under future climate change.