Integrative effects of soil tillage and straw management on crop yields and greenhouse gas emissions in a rice–wheat cropping system
Introduction
Soil tillage and straw management can alter carbon (C) and nitrogen (N) dynamics and consequently induce considerable changes in greenhouse gas (GHG) emissions and crop productivity (Paustian et al., 1997, Lal, 2004, Smith et al., 2008, Liu et al., 2014). For example, straw incorporation can stimulate GHG emissions through increasing C availability for methanogenics in paddy soils (Yan et al., 2005) and denitrifiers in dry-land soils (Luo et al., 1999). Also, in comparison to conventional tillage, no-tillage, and reduced tillage can enhance soil C sequestration by decreasing soil C decomposition and/or C turnover, thereby mitigating GHG emissions (Six et al., 2000, Al-Kaisi and Yin, 2005, Van Grogenigen et al., 2011, Ruan and Philip Robertson, 2013). Furthermore, reduced tillage and straw incorporation alone or in concert can improve crop yields through improving soil fertility (Malhi and Lemke, 2007, Küstermann et al., 2013).
Rice–wheat rotation system is the most popular cropping system in East Asia, covering ca. 13 million hectares each year in China (Frolking et al., 2002). Because this system consists of both irrigated rice and dry-land wheat, it raises unique challenges for quantifying the total GHG emissions. Agricultural practices, such as soil tillage and straw incorporation management, play an important role on crop productivity and/or GHG emissions (Ma et al., 2009, Pandey et al., 2012, Yao et al., 2013, Brennan et al., 2014). Therefore, it is imperative to assess the impact of agricultural practices on crop yields and GHG emissions and determine the mitigation potential management practices for agronomic innovations.
There are an increasing number of studies assessing soil tillage and straw management effects on GHG emissions and/or crop productivity in rice–wheat cropping areas. However, most of them have only considered single cropping season (Zou et al., 2005, Gangwar et al., 2006, Yao et al., 2009) and few have quantified the impact across a whole rotation cycle where multiple cropping is involved. For example, Zou et al. (2005) reported that straw incorporation increased CH4 emission and reduced N2O emission in the rice season. But Yao et al. (2009) showed that straw incorporation decreased N2O emission in the non-rice season. Also, reduced tillage perturbations were found to reduce CH4 and N2O emissions and grain yield (Pandey et al., 2012). To date, there are still many uncertainties about the effects of soil tillage and straw management practices on crop yields and GHG emissions. One of the main reasons might be due to the experimental duration, as most of existing studies were based on very short-term experiments (Ma et al., 2009, Yao et al., 2013). Yet effects of soil tillage and straw management practices on soil C storage and GHG mitigation are complex and may vary with practice duration (Duiker and Lal, 1999, Six et al., 2004, Smith et al., 2008). Also, it is worthy to mention that soil tillage and straw management practices are often intermingled together in field. However, existing field studies have mainly determined the effects of either tillage or straw management practices and the interactions of these two practices are not well documented (Bayer et al., 2014). Therefore, it is essential to further quantify the long-term effects of soil tillage and straw management on crop yields and GHG emissions across a whole rotation cycle in multiple cropping systems.
The objective of this study was to assess the effects of soil tillage and straw management on CH4 and N2O emissions and crop yields in the rice–wheat rotation system. Year-round measurements of CH4 and N2O emissions were conducted in an existing long-term field experiment to assess the net effect across the whole rotation cycle. Also, field soils were obtained from these long-term plots and incubated to estimate soil C and N mineralization under simulated soil tillage and straw management practices.
Section snippets
Experimental site description
Our field measurements of CH4 and N2O fluxes were conducted with the long-term tillage experiment located at the Institute of Agricultural Sciences in Taihu Lake District, Wuxi city (31°27′N, 120°25′E), Jiangsu Province, China. The Taihu region represents a northern subtropical monsoon climate with an annual temperature of about 15.7 °C, an average annual precipitation of 1094 mm, and the effective accumulated temperature (above 10 °C) of 4947 °C. The soil has a clayey loam, developed from loessial
CH4 fluxes and seasonal/annual cumulative emissions
During both rice seasons, CH4 fluxes were the highest right after transplanting (7 days) across all treatments and remained relatively high for another 3–4 weeks (Fig. 1a). CH4 fluxes decreased quickly after week 5 and remained at a low level since. The highest CH4 fluxes ranged from 391 to 1667 mg CH4C m−2 d−1, and from 314 to 1933 mg CH4C m−2 d−1 in 2011 and 2012, respectively. Averaged cumulative CH4 emissions were 3457 and 6872 kg CO2eq ha−1 for the non-straw and straw incorporated treatments,
Effects of soil tillage and straw incorporation on CH4 emission
Our results showed that straw incorporation can have significantly different effects on CH4 emissions between rice and wheat growing seasons (Fig. 1; Table 2). These differences likely stem from the resulting impacts of different management regimes on soil C and O2 for methanogens. Two pathways of CH4 production contribute to CH4 emissions in rice paddies. Acetotrophy process (C6H12O6 3CO2 + 3CH4) is considered to be the dominant process, contributing about 2/3 of the CH4 produced (Segers, 1998,
Conclusions
Our assessment of GHG emissions and crop yields across the whole rotation cycle showed different a picture from results either from the rice or wheat season alone. Also, trade-off occurred between crop yield and CH4 emissions as influenced by soil tillage and straw incorporation management practices. Based on annual GWP and crop yield analyses, tillage regimes of rotary tillage in the wheat season followed by plowing in the rice season, irrespective of straw management was an optimum practice
Acknowledgements
This work was supported by the National Key Technology Support Program of China (2011BAD16B14), the Program for New Century Excellent Talents in University (NCET-05-0492), the GEF Project of Climate Smart Staple Crop Production in China (P144531), the Innovation Program of CAAS and the grant of China Scholarship Council (CSC).
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