Winter legume-rice rotations can reduce nitrogen pollution and carbon footprint while maintaining net ecosystem economic benefits
Graphical abstract
Introduction
Farmland is a major contributor to global climate change, accounting for 52% and 84% of global anthropogenic emissions of methane (CH4), and nitrous oxide (N2O), respectively, with losses in reactive N via waterborne and airborne nitrogen (N) flows that amount to 32–45 and 26–60 Tg N yr−1, respectively (Smil, 1999; Smith et al., 2008). Rice is a staple food in many regions providing 50% of dietary caloric intake and representing 22% of global cereal harvested area (FAO, 2015). To meet the food demands of an expanding world population, rice yields have increased over the last three decades, due in part to the intensive use of synthetic fertilizers (Hossain and Singh, 2000). The overuse of N fertilizer in rice paddy fields has led to greenhouse gas (GHG) emissions and non-point source pollution (Choudhury and Kennedy, 2005; Linquist et al., 2012). Minimizing GHG emissions in rice is difficult due to a trade-off between CH4 and N2O emissions (Hou et al., 2000), where emissions of one GHG tend to increase with the implementation of management practices designed to reduce emissions of the other.
In Asia, conventional rice-wheat cropping system dominates agricultural land, occupying 24 million ha in South Asia and China (Ladha et al., 2003) and providing food security for more than 400 million people. Under this cropping system, rice is generally grown in the rainy season of the summer months, followed by wheat cultivation in the winter months. However, wheat yields are significantly lower in many rice-based cropping regions than in wheat-based systems (Ladha et al., 2000). For example, wheat yields in the Taihu Lake Plain, a typical rice-wheat cropping region in China, are usually below 5.0 t ha−1, far lower than that in the main wheat producing area of the North China Plain (commonly above 6.0 t ha−1) (Zhu and Zhang, 2010). Lower yields are possibly due to soil compaction caused by land preparation; flooding of the preceding rice crop and waterlogging resulting from disproportional winter rainfall in the subtropical monsoon climate (Dickin and Wright, 2008; Sharma et al., 2003). The efficiency and environmental sustainability of wheat production in the rice-wheat system is further compromised by the impact of intensive inputs of chemical N fertilizer during wheat cultivation, where losses of NH3, denitrification, and N runoff and leaching of total N input have been estimated at 12%, 21% and 23%, respectively (Zhao et al., 2012).
Efforts to reduce the environmental impacts of rice-based cropping systems include improved tillage practices, development of crop genotypes with higher nutrient use efficiency, more effective water management, and diversified crop rotations (Smith et al., 2008). Farming systems that reduce reliance on external inputs like synthetic fertilizers have been suggested by IPCC (2007) to mitigate GHG emissions. Historically, leguminous crops were an integral component of arable systems, including rice rotations, but their use during the 20th century declined with the adoption of synthetic N fertilizers (Crews and Peoples, 2004) despite their value in biological N-fixation (Vance et al., 2000). A lack of improvement in legume yields compared with cereals has also limited legume cultivation (Graham and Vance, 2003). However, current challenges of agricultural practices are not only to fulfill food supply but also to increase the sustainability of agriculture (Tilman et al., 2002), thus highlighting the potential environmental benefits of integrating legumes into cereal crop rotations.
Previous work indicates the use of leguminous crops with associated reductions in N fertilizer use within rice crop rotations could lower reactive N losses and GHG emissions. Xia et al. (2016) found that legumes substituted for winter wheat reduced greenhouse gas intensity by 11–41%, while Zhao et al. (2015a) showed that legume-rice rotations decreased reactive N losses by roughly half compared with a rice-wheat rotation. However a better understanding of the effects of legumes in a rice rotation on the mitigation of C emissions and N losses is needed to develop strategies for minimizing potential tradeoffs between environmental and economic outcomes. Indeed, despite the potential environmental benefits, encouraging farmers to increase the cultivation of legumes also requires economic evidence. Economic assessments that are based not only on grain yield revenues and costs of production, but assign an economic value to the environmental and social benefits of agricultural practices are increasingly valuable tools (Ness et al., 2007). However, few economic assessments on legume-rice rotations have taken into consideration environmental benefits (Mucheru-Muna et al., 2010; Pimentel et al., 2005), for instance, the potential for reductions in reactive N losses and C footprint.
The sustainability of a production system and field management activities may be assessed using LCA where GHG emissions are quantified as CO2 equivalents (CO2-eq) to determine a total C footprint (IPCC, 2006). At the same time, the estimation of NEEB allows calculating the balance of economic benefits of grain yield revenue with input costs and carbon and environmental costs related to C emissions and N losses, respectively (Li et al., 2015). Here, we combined the approaches of 1) long-term field measurements of cropping systems N and C dynamics with LCA to quantify the C footprint and 2) NEEB to quantify the holistic economic benefits of rice-legume rotations in comparison to conventional rice-wheat or rice-rape rotations in the Taihu Lake Region in southeastern China. Our objectives were to 1) investigate the long-term effects of growing winter legumes on crop yields, GHG emissions, NH3 volatilization, and N leaching and runoff; 2) evaluate C footprint using LCA and reactive N losses by long-term field measurements; and 3) assess the environmental economic benefits of rice-legume rotations using NEEB. The data from this study provide important insights into the economic feasibility of replacing conventional rotations with rice-legume rotations while also considering potential environmental benefits.
Section snippets
Site description
The study was conducted between 2011 and 2016 at the Yixing Base for Non-point Source Pollution Control, Changshu National Agro-Ecosystem Observation and Research Station, Chinese Academy of Sciences (Fig. 1a). The climate is humid subtropical monsoon with an average temperature of 15.7 °C and annual rainfall of 1226 mm, with 886 mm of rainfall occurring during the summer rice growth period. The predominant soil type is a Gleyi-Stagnic Anthrosols derived from lacustrine deposits. Soil
Crops yields and chemical N input
Rice crop yields did not vary among the four rotations (Fig. 3a). Yields ranged from 6.23 to 8.50 Mg ha−1 in R-W, 6.30–8.92 Mg ha−1 in R-Ra, 6.42–9.83 Mg ha−1 in R-F and 6.70–8.57 Mg ha−1 in R-M, averaging 7.59–7.88 Mg ha−1 among rotations. Yields of the winter crops varied among the rotations, where yields were 3.03–6.27 Mg ha−1 for wheat, 0.87–1.69 Mg ha−1 for rape, <1.00–1.84 Mg ha−1 for fava bean, and 1.09–4.63 Mg ha−1 dry matter of milk vetch as green manure (Fig. 3b). Grain yields of
Effects of legumes on N losses and C footprint
Rice-wheat cropping systems are characterized by high rates of reactive N losses and CO2 emissions due to the “high input-high loss-high pollution” management approach (Zhao et al., 2012). Comprehensive comparisons of the environmental performance of alternative rotations which also account for impacts on yield and economic outcomes are needed to guide the development of sustainable rice production systems in southeastern China. Our results provide strong evidence that introducing legumes
Conclusion
Our study showed rice-legume rotations offer great potential to mitigate C footprint and reactive N losses compared with conventional rice rotations including wheat or rape as a winter crop. We found FCF and reactive N losses were 46–50% and 50–57% lower, respectively, when legumes were substituted for wheat. A key reason for these mitigation effects is the >63% reduction in annual application of synthetic N fertilizer, with no N fertilizer applied to legumes and a reduced rate applied to rice.
Acknowledgements
The authors gratefully acknowledge the participating technicians and farmers at Yixing Base of Changshu National Agro-Ecosystem Observation and Research Station, Chinese Academy of Sciences (CAS) for their help with the field trial management. We thank Mrs. Yang Li, Mrs. Chunyan Wang and Mr. Qingqian Wang for their assistance with data collection and analysis. We also thank anonymous reviewers and editors for their valuable comments. This work was supported by the National Key R&D Program of
References (53)
- et al.
Does growing grain legumes or applying lime cost effectively lower greenhouse gas emissions from wheat production in a semi-arid climate?
J. Clean. Prod.
(2014) - et al.
Intra- and inter-year variability of agricultural carbon footprints – a case study on field-grown tomatoes
J. Clean. Prod.
(2017) - et al.
Legume versus fertilizer sources of nitrogen: ecological tradeoffs and human needs
Agric. Ecosyst. Environ.
(2004) - et al.
The effects of winter waterlogging and summer drought on the growth and yield of winter wheat (triticum aestivum l.)
Eur. J. Agron.
(2008) - et al.
Research progress and strategies for multifunctional rapeseed: a case study of China
J. of Integr. Agri
(2016) - et al.
Combined effects of nitrogen fertilization and biochar on the net global warming potential, greenhouse gas intensity and net ecosystem economic budget in intensive vegetable agriculture in southeastern China
Atmos. Environ.
(2015) - et al.
Effect of local conditions and machinery characteristics on the environmental impacts of primary soil tillage
J. Clean. Prod.
(2017) - et al.
Estimating the value of carbon sequestration ecosystem services in the mediterranean sea: an ecological economics approach
Global Environ. Change
(2015) - et al.
A staggered maize–legume intercrop arrangement robustly increases crop yields and economic returns in the highlands of central Kenya
Field Crop. Res.
(2010) - et al.
Categorising tools for sustainability assessment
Ecol. Econ.
(2007)
Approaches and uncertainties in nutrient budgets: implications for nutrient management and environmental policies
Eur. J. Agron.
Integrating agronomic practices to reduce greenhouse gas emissions while increasing the economic return in a rice-based cropping system
Agric. Ecosyst. Environ.
Spatial and temporal patterns of carbon footprints of grain crops in China
J. Clean. Prod.
Managing nitrogen for sustainable wheat production
J. Clean. Prod.
Effects of tillage practices and straw returning methods on greenhouse gas emissions and net ecosystem economic budget in rice–wheat cropping systems in Central China
Atmos. Environ.
Tillage effects on carbon footprint and ecosystem services of climate regulation in a winter wheat–summer maize cropping system of the North China Plain
Ecol. Indicat.
Maintaining rice yield and reducing n pollution by substituting winter legume for wheat in a heavily-fertilized rice-based cropping system of Southeast China
Agric. Ecosyst. Environ.
Nonlinear response of nitric oxide emissions to a nitrogen application gradient: a case study during the wheat season in a Chinese rice-wheat rotation system
Atmos. Environ.
Studies on the anaerobic decomposition of plant materials: comparison of the course of decomposition of rice straw under anaerobic, aerobic and partially aerobic conditions
Biochem. J.
Nitrous oxide emission from soils after incorporating crop residues
Soil Use Manag.
Nitrogen fertilizer losses from rice soils and control of environmental pollution problems
Commun. Soil Sci. Plant Anal.
Magnitude and biophysical regulators of methane emission and consumption in the australian agricultural, forest, and submerged landscapes: a review
Plant Soil
FAOSTAT Online Database
Legumes: importance and constraints to greater use
Plant Physiol
The carbon footprints of food crop production
Int. J. Agric. Sustain.
Fertilizer use in asian agriculture: implications for sustaining food security and the environment
Nutr. Cycl. in Agroecol
Cited by (84)
The storm runoff management strategy based on agricultural ditch nutrient loss characteristics in Erhai Lake, China
2024, Journal of Contaminant Hydrology