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The objective of this study was to quantify soil methane (CH4) and nitrous oxide (N2O) emissions when converting from minimum and no-tillage systems to subsoiling (tilled soil to a depth of 40 cm to 45 cm) in the North China Plain. The relationships between CH4 and N2O flux and soil temperature, moisture, NH4 +-N, organic carbon (SOC) and pH were investigated over 18 months using a split-plot design. The soil absorption of CH4 appeared to increase after conversion from no-tillage (NT) to subsoiling (NTS), from harrow tillage (HT) to subsoiling (HTS) and from rotary tillage (RT) to subsoiling (RTS). N2O emissions also increased after conversion. Furthermore, after conversion to subsoiling, the combined global warming potential (GWP) of CH4 and N2O increased by approximately 0.05 kg CO2 ha−1 for HTS, 0.02 kg CO2 ha−1 for RTS and 0.23 kg CO2 ha−1 for NTS. Soil temperature, moisture, SOC, NH4 +-N and pH also changed after conversion to subsoiling. These changes were correlated with CH4 uptake and N2O emissions. However, there was no significant correlation between N2O emissions and soil temperature in this study. The grain yields of wheat improved after conversion to subsoiling. Under HTS, RTS and NTS, the average grain yield was elevated by approximately 42.5%, 27.8% and 60.3% respectively. Our findings indicate that RTS and HTS would be ideal rotation tillage systems to balance GWP decreases and grain yield improvements in the North China Plain region.

A study was conducted on the effect of two single practices, including soil tillage and returning straw to soil, and their interaction on soil porosity of maize-wheat cropping system. Field experiments involved four tillage practices, including conventional tillage (C), zero-tillage (Z), harrow-tillage (H) and subsoil-tillage (S), with straw absent (A) or straw present (P). Total porosity, capillary porosity and non-capillary porosity of soil were investigated. The results showed that the soil total porosity of 0-10 soil layer was mostly affected; conventional tillage can increase the capillary porosity of soil, but the non-capillary porosity of S was the highest. Returning of straw can increase the porosity of soil. Through the analysis of affecting force, it can be concluded that interaction of soil tillage and straw is the most important factor to soil porosity, while the controlling factor to non-capillary porosity was soil tillage treatment.

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Long-term tillage and straw incorporation significantly affect soil organic carbon (SOC) sequestration and crop yield. However, the studies on the SOC sources under multicropping system are relatively few. The objective of this study was to evaluate the effects of conservation tillage on SOC and crop yields and distinguish the SOC sources from wheat (C3) and maize (C4). Therefore, the dynamics of SOC, SOC sequestration, and crop yield were evaluated during 15 years of conservation agriculture under conventional tillage (CT), subsoiling (ST), rotary tillage (RT), and zero tillage (ZT) without or with straw incorporation (CTS, STS, RTS, and ZTS, respectively). The results indicated that the highest mean SOC concentration in the 0-to 30-cm soil was found under STS (11.80 g kg −1 ), which increased by 2.29 g kg −1 than that under CT, whereas RT had the lowest mean SOC concentration (8.10 g kg −1 ). The increases in annual yield ranged from 0.58 (ZT) to 4.93 (ST) Mg ha −1 during 2005-2017. In comparison with the annual yield of CT, that of STS increased by 2 Mg ha −1 and was significantly higher than other treatments (p < .05) except ZTS and CTS. In comparison with CT, the SOC stock and carbon sequestration rate of STS were the highest and increased by 15.64 Mg ha −1 and 1.05 Mg ha −1 yr −1 , respectively, in the 0-to 30-cm soil. Moreover, the relative contribution of wheat residues to SOC was higher than maize residues under all treatments. Thus, subsoiling combined with C3 straw incorporation was more suitable for restoring degraded land and increasing yields. K E Y W O R D S 13 C, carbon sequestration, crop yield, soil carbon source, soil degradation

Tillage and crop residue inputs are important factors that impact soil aggregation and soil organic C (SOC) decomposition. is study evaluated the impacts of tillage and 10 yr of crop residue removal on aggregate stability, distribution, and associated C. e research was conducted in North China between 2002 and 2011. e treatments were ve tillage systems that included conventional tillage (CT), subsoiling (ST), harrow tillage (HT), rotary tillage (RT), and no-till (NT) in combination with crop residue retention (P) or residue removal (A). e results indicate that 74 to 82% of aggregates were macroaggregates (0.25-5 mm) and that these aggregates contained from 53 to 87% of the SOC in the 0-to 30-cm depth. Tillage and residue removal reduced macroaggregates and SOC levels, especially under the RT treatment, but residue inputs slowed down the rate of SOC depletion in the soil. e treatments of no-till with residue retention (NTP) and subsoiling with residue retention (STP), accumulated more C in stable macroaggregates and signi cantly increased SOC levels, which increased 13.37 and 9.59 Mg C ha -1 , respectively, in 10 yr. Crop residue input combined with an appropriate tillage system is an e ective method for maintaining and improving low-quality soil and SOC levels in the widespread wheat (Triticum aestivum L.)-maize (Zea mays L.) cropping system of North China.

Appropriate tillage plays an important role in mitigating the emissions of greenhouse gases (GHG) in regions with higher crop yields, but the emission situations of some reduced tillage systems such as subsoiling, harrow tillage and rotary tillage are not comprehensively studied. The objective of this study was to evaluate the emission characteristics of GHG (CH4 and N2O) under four reduced tillage systems from October 2007 to August 2009 based on a 10-yr tillage experiment in the North China Plain, which included no-tillage (NT) and three reduced tillage systems of subsoil tillage (ST), harrow tillage (HT) and rotary tillage (RT), with the conventional tillage (CT) as the control. The soil under the five tillage systems was an absorption sink for CH4 and an emission source for N2O. The soil temperature positive impacted on the CH4 absorption by the soils of different tillage systems, while a significant negative correlation was observed between the absorption and soil moisture. The main driving factor for increased N2O emission was not the soil temperature but the soil moisture and the content of nitrate. In the two rotation cycle of wheat-maize system (10/2007–10/2008 and 10/2008–10/2009), averaged cumulative uptake fluxes of CH4 under CT, ST, HT, RT and NT systems were approximately 1.67, 1.72, 1.63, 1.77 and 1.17 t ha−1 year−1, respectively, and meanwhile, approximately 4.43, 4.38, 4.47, 4.30 and 4.61 t ha−1 year−1 of N2O were emitted from soil of these systems, respectively. Moreover, they also gained 33.73, 34.63, 32.62, 34.56 and 27.54 t ha−1 yields during two crop-rotation periods, respectively. Based on these comparisons, the rotary tillage and subsoiling mitigated the emissions of CH4 and N2O as well as improving crop productivity of a wheat-maize cropping system.

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