Cutting carbon footprints of vegetable production with integrated soil - crop system management: A case study of greenhouse pepper production

Highlights

• Integrated soil-crop system management (ISSM) increased fruit yield by 17% compared to farmers’ practice (FP).

• ISSM reduced the nitrogen (N) inputs by 46%, compared to FP.

• ISSM reduced greenhouse gas emission by 19% and the carbon (C) footprint by 30%, compared to FP.

• ISSM increased the fruit yield by 10% with a similar C footprint, compared to soil remediation alone.

• Reducing excessive N inputs and improving yields were critical measures to reduce the C footprint.

Abstract

In China there is an urgent need to improve the sustainability of vegetable production by increasing yields and reducing the environmental losses. However, whilst various single nutrient management measures have proved successful at reducing environmental losses, they have not simultaneously increased yield. Here, we report on a three-year field experiment that used an integrated soil - crop system management (ISSM) approach, to improve crop (pepper) yield and to cut carbon (C) and nitrogen (N) footprints of greenhouse vegetable production in the Yangtze River Basin, China. Treatments included farmers’ practice (FP) for nutrient inputs, soil and crop management; soil remediation (SR), as a single factor approach to optimize soil management, including control of soil borne pathogens and reduced nutrient input by organic resources; and ISSM, as a systematic integrated approach, which includes the combined optimization of factors, including soil remediation, reduced planting density, and improved timing of inorganic fertilizer applications (rate and form). Measurements of pepper yield and N concentrations were used to calculate N offtake, and the C and N footprints were then calculated using life cycle assessment. The three-year continuous field experiment indicated that the mean pepper yield (fresh weight) from the ISSM treatments were 48 t ha⁻¹, 17% and 10% greater than that of the FP and SR treatments (p < 0.05), respectively. The reactive nitrogen (Nr) losses from the FP, SR, and ISSM treatments were 82, 52 and 59 kg N ha⁻¹, respectively. The greenhouse gas emissions of FP, SR, and ISSM treatments were 7061, 5279 and 5728 kg CO₂-eq ha⁻¹, respectively. The N and C footprints of the ISSM treatment were significantly lower than the FP treatment by 39% and 30%, respectively, as a result of both a 46% reduction in N inputs (especially an 80% reduction in organic N inputs) and a greater yield. The yield increase contributed to 26% and 37% the reduction of N and C footprints in ISSM treatment, respectively. Meanwhile, there were no significant difference in the N and C footprints between SR and ISSM. This study highlights that the ISSM strategy can produce greater pepper yields with lower environmental costs, and can contribute to sustainable greenhouse vegetable production, and that SR, whilst being a single factor strategy, is a useful first step towards ISSM.

Introduction

Vegetables are extremely important in human nutrition as sources of nutrients and non-nutritive food constituents as well as for the reduction in disease risks (Boeing et al., 2012). During the last two decades, global vegetable production has increased by 186% (FAO, 2016). However, intensive vegetable production is associated with high inputs of nutrients, resulting in relatively high losses to the environment, including reactive nitrogen (N), which contribute to eutrophication (Muñoz et al., 2008; Perrin et al., 2014), acidification (Perrin et al., 2014), and greenhouse gas (GHG) emissions (Perrin et al., 2014; Wang et al., 2018a, Wang et al., 2018b) that result in climate change. With further population growth, changes in dietary preferences, limited agricultural land and increased environment pressure, there is need to greatly improve yield whilst minimizing the environmental impacts of vegetable production.

Recently, the GHG emission and reactive nitrogen (Nr) loss have been paid more attention in intensive vegetable production system associated with high inputs, especially N fertilizer input (Perrin et al., 2014; Liang et al., 2019). In addition, carbon (C) footprint and N footprint are useful evaluation indicators to denote the GHG emission or Nr loss (nitrous oxide [N₂O] emissions, ammonia [NH₃] volatilization and nitrate leaching) to the environment during the production of per ton of products (Gan et al., 2011; Leach et al., 2012), and life cycle assessment (LCA) is widely accepted for C footprint and N footprint (Xue et al., 2016; Zhou et al., 2019). Various single nutrient management measures have been shown to significantly mitigate the environmental impacts of vegetable production, e.g. optimizing the fertilizer rate (Khoshnevisan et al., 2014), using enhanced-efficiency fertilizers (Li et al., 2018; Kanter and Searchinger, 2018), use of fertigation, and substituting inorganic fertilisers with organic fertilisers and manures (Zhou et al., 2019). However, most of those management measures have been shown to only maintain vegetable yields or marginally increase yields. For example, Min et al. (2012) indicated that decreasing excessive traditional N rate of inorganic fertilizer by 40% based on crop nutrient recommendation, could reduce the N leaching by 40% with no effect on vegetable yield in intensive greenhouse systems of southern China. Kanter and Searchinger (2018) used a meta-analysis to show that enhanced-efficiency fertilizers (both nitrification inhibitors and polymer-coated fertilizers) could reduce the nitrous oxide (N₂O) emission and N leaching from crop production by 25–60%, with an average yield increase of only 7.5% in global crop systems. However, sustainable intensification of agriculture systems is needed to support the growing population in China over the next few decades, so not only do improved management practices need to reduce environmental losses, but at the same time, crop yield must grow substantially (Foley et al., 2011; Tilman et al., 2011). Therefore, a new integrated strategy needs to be adopted.

A systematic approach has been developed to mitigate environmental impacts whilst improving crop yield for global crop sustainability (Liu et al., 2015; Ladha et al., 2016). The integrated soil-crop system management (ISSM) approach, which includes the optimization of crop, soil, nutrient and water management, has been developed to significantly increase crop yields, improve fertilizer use efficiency, and to reduce GHG emissions in cereal production systems (Chen et al., 2011, 2014). For example, adoption of the ISSM strategy reduced the C footprints by 31–47%, with 21–87% greater yield and lower N fertilizer use for cereal crop systems in China (Chen et al., 2014). However, there is a lack of empirical evidence to support the adoption of ISSM in vegetable production systems.

Pepper (Capsicum annuum L) is an important vegetable in China. The total area of vegetable production in plastic greenhouses has increased rapidly in China (from 1.8 M ha in 2000 to 3.4 M ha in 2010, Chang et al., 2013) because it extends the growing season and results in a high-quality product (Chang et al., 2011, 2013). Our previous data from farmers’ surveys in the Yangtze River Basin has indicated that the best farmers (top 25%)’ practice has resulted in 25% lower environmental losses coupled with a 27% increase in the yield of pepper (Wang et al., 2018c), and indicated the potential of using an integrated systematic approach. It is important to note that the integrated systematic approach needs to be designed to address practices of soil, crop, nutrient and water management for specific crops and biophysical conditions (Wezel et al., 2014; Lu et al., 2015). Hence, the aim of this study was to examine the impacts of integrated soil-crop system management practices on yield and N and C footprints of a greenhouse pepper production system in the Yangtze River Basin in south-east China.