Effects of irrigation, fertilization and crop straw management on nitrous oxide and nitric oxide emissions from a wheat–maize rotation field in northern China

Abstract

One-year winter wheat–summer maize rotation is the most popular double cropping system in north-central China, and this highly productive system is an important source of nitrous oxide (N₂O) and nitric oxide (NO) emissions due to the high fertilizer N and irrigation water inputs. To sustain the high crop production and mitigate the detrimental impacts of N₂O and NO emissions, improved management practices are extensively applied. The aim of this study is therefore to evaluate the effects of an improved management practice of irrigation, fertilization and crop straw on grain yield and N₂O and NO emissions for a wheat–maize rotation field in northern China. Using automated and manual chamber measuring systems, we monitored N₂O and NO fluxes for the conventional (CT, 2007–2008), improved (IT, 2007–2008), straw-amended (WS, 2008–2009), straw-not-amended (NS, 2008–2009), and no N-fertilizer treatments (WS–NN, 2008–2009), respectively, for one rotation-year. The grain yields were determined for CT and IT for three rotation-years (2005–2008) and for WS, NS and WS–NN for one rotation-year (2008–2009). The improved management of irrigation and fertilization reduced the annual N fertilization rate and irrigation amount by 17% and 30%, respectively; increased the maize yield by 7–14%; and significantly decreased the N₂O and NO emissions by 7% (p < 0.05) and 29% (p < 0.01), respectively. The incorporation of wheat straw increased the cumulative N₂O and NO emissions in the following maize season by 58% (p < 0.01) and 13%, respectively, whereas the effects of maize straw application were not remarkable. The N₂O and NO emission factors of applied N were 2.32 ± 2.32% and 0.42 ± 1.69% for wheat straw and 0.67 ± 0.23% and 0.54 ± 0.15% for chemical N-fertilizers, respectively. Compared to conventional management practices using high application rates of irrigation water and chemical N-fertilizer as well as the field burning of crop straw, the improved management strategy presented here has obvious environmentally positive effects on grain yield and mitigation of N₂O and NO emissions.

Introduction

Nitrous oxide (N₂O) plays an important role in the recent global warming trend and participates in the destruction of stratospheric ozone (O₃) (IPCC, 2007). In contrast, nitric oxide (NO) is a precursor of tropospheric O₃, which contributes to global warming (IPCC, 2007). Fertilized agricultural fields are important sources of atmospheric N₂O and NO (Bouwman et al., 2002). In most agricultural soils, both gases are formed biologically via nitrification and denitrification, and these microbial processes are strongly affected by natural conditions and agricultural management (Ludwig et al., 2001, Snyder et al., 2009).

China is one of the major agricultural countries in the world. To increase grain yield and soil fertility, many new management practices, including fertilization, irrigation, crop straw application, and double- and triple-cropping are applied in intensive cropland areas of China. The 1-year winter wheat–summer maize rotation is the most popular double-cropping system and has been adopted across a wide range of climate zones in north-central China. The highly productive double-cropping system relies on inputs of irrigation water (90–690 mm year⁻¹, Wang et al., 2008) and chemical fertilizer (500–700 kg N ha⁻¹ year⁻¹, Zhen et al., 2006, Ju et al., 2009) that far exceed the optimum or recommended water and fertilizer inputs (127–350 kg N ha⁻¹ year⁻¹, Liu et al., 2003, Zhao et al., 2006, He et al., 2009, Wang et al., 2010). The overuse of irrigation water and chemical N-fertilizer has been ubiquitous and triggered many environmental problems, such as water pollution, drawdown of groundwater table, soil salination, soil acidification and emission of gaseous N (Zhen et al., 2006, Ju et al., 2009). To mitigate the detrimental effects, improved management practices need to be fully evaluated and popularized. Many studies have been carried out to estimate the impacts of improved irrigation and fertilization management on crop yield, nutrient use efficiency, N leaching, soil organic matter and N accumulation in deeper soil layers in the wheat–maize rotation fields of China (Liu et al., 2003, Mack et al., 2005, Xu et al., 2006, He et al., 2009, Wang et al., 2010). However, to date, no study has been carried out to clarify the role of these improved management practices in the mitigation of N₂O and NO emissions. Furthermore, the application of wheat and maize straws has become popular because the Chinese government has banned the field burning of crop straws. The combined application of chemical fertilizer and crop straw is thought to be beneficial for improving soil fertility and nutrient utilization. On the other hand, it may increase or decrease soil N₂O and NO emissions depending on the type, mode, timing and quantity of the chemical fertilizer application and the quantity and quality of the incorporated straws (Baggs et al., 2003, Garcia-Ruiz and Baggs, 2007). The complex interactive influences of chemical fertilizer and wheat/maize straw on soil N₂O and NO emissions have not been adequately surveyed. Therefore, we investigated the N₂O and NO fluxes as well as the crop yields for conventional, improved, straw-amended, straw-not-amended, and no N-fertilizer treatments in a typical irrigated wheat–maize rotation field in northern China. The objectives of this study were (a) to quantify the effects of improved irrigation and fertilization management on crop yield and N₂O and NO emissions; (b) to characterize the combined effects of wheat/maize straw and chemical N-fertilizer applications on the cumulative emissions of both gases; and, (c) to calculate the emission factors of both gases for applied N in the form of crop straw and chemical N-fertilizer.