The potential contribution of growing rapeseed in winter fallow fields across Yangtze River Basin to energy and food security in China

Highlights

• Precise winter fallow periods in the Yangtze River basin are identified at the grid level using remote sensing and a unique dataset of rapeseeds growing records at 84 observation stations over 1981-2011.

• Considering adaptations on sowing dates and cultivars, the total potential of rapeseed production on winter fallow land could reach 15.17 million tons, on average 1,950 kg/ha.

• By coupling the AEZ and CHINAGRO-II models, we estimate economic benefit of rapeseed production and its impact on edible oil security of China.

• A 60% realization of the production potential would reduce China's rapeseed import to zero and further reduce soybean import by 8.1 million tons in 2020.

Abstract

To solve the energy crisis and protect the ecological environment has been the central concern of the sustainable development debate. The reproducibility and lower environmental impacts of bioenergy have attracted increasing attention in the debate. This research investigates the potentials of growing rapeseed in winter fallow fields across the Yangtze River Basin (YRB) to serve the goal of boosting bioenergy production and improving edible oil security in China. It first quantifies the extent of winter fallow fields in the Basin and identifies the accurate starting and ending dates of the fallowing at the grid-cell level. It then matches the fallowing periods with the growing period grid-by-grid and assesses the current and future potentials of rapeseed production across the matched grid-cells in the region. The assessments take into consideration of climate change adaptations on sowing dates and on the choice of varieties with suitable growth cycle length. Finally, by coupling the Agro-Ecological Zones (AEZ) model and CHINAGRO-II economic model, this research simulates economically meaningful levels of rapeseeds production and trade for 2020 and 2030. A 60% realization of the production potential would increase total rapeseed supply by 9.1 million tons, reduce China's rapeseed import to zero and further reduce soybean import by 8.1 million tons in 2020. In 2030, the import of rapeseed would be reduced from 15 million tons under baseline to 7.3 million tons.

Introduction

Energy is the lifeblood of the world's economy and the driving force for social development. The ever-increasing global energy demand has become a significant challenge for the development of human society in the 21st century. Fossil fuels based on petroleum, coal, and natural gas have provided approximately 90% of the world's energy since the 19th century. However, the sustainability of the fossil fuel supply is highly questionable, primarily due to its no renewability and high level of CO₂ emission (Ajanovic and Haas, 2010; Arvidsson et al., 2011; Baka and Roland-Holst, 2009; Batchelor et al., 1995; Rockwell, 2011). To address the unsustainability concern over conventional fossil fuel, renewable energy has become promoted worldwide. Compared to fossil fuels, biofuels are regarded as being more beneficial in terms of promoting energy security, internalizing socioeconomic externalities, and mitigating environmental impact (Bomba et al., 2007; Cherubini et al., 2009). As a consequence, bioenergy has become an important renewable energy source in recent years. Bioenergy used for electricity and biofuels for transportation have increased significantly. Global biofuel production in 2018 reached 154 billion liters, an increase of 10 billion liters (6.5%) in comparison to the level in 2017. The growth rate is almost twice of that in 2017. Due to the improved market prospects in China, Brazil, and the US, the global bioenergy production is expected to increase by 25% between 2019 and 2024 (IEA, 2019).

However, biofuel crop production may also harm the environment by changing land use and by deforestation (Rulli et al., 2016). Biofuel production needs water and land resources, which could have been used to produce food. Driven by the recent food crises and the consequent increase in food prices, food and biofuel production is at the forefront of the energy-food debate, leading to the trade-off issues across the nexus of food, energy, and water (Smith et al., 2010; Rulli et al., 2016).

Rapeseed has the advantage of serving as the source of both biodiesel and edible oil. In the diesel sector, production of biodiesel from rapeseed has been appreciated for its high energy efficiency and low environmental impact (Zhang et al., 2011). More attractively, rapeseed is sowed in late autumn or early spring and harvested in early summer, thus does not compete for land and water with major summer crops, such as rice and maize in the Yangtze River Basin (YRB) region. This research is motivated by this observation and the fact that winter fallow fields have existed in the YRB region and the extent of winter fallowing has increased significantly in recent years due to migration of rural labor forces to non-agricultural sectors (Yan et al., 2016; Liu et al., 2018). If we can accurately map the areas suitable for rapeseed growth on fallowed land and quantify the potential and also economically feasible production gains from planting rapeseed in these areas, the results will provide science-informed information and incentive to both policy makers and local farmers. A better utilization of these resources via policy stimulation and farmers’ responses can effectively increase bioenergy production and ease China's energy pressure.

On the other hand, it is worth noting that China has become the world's largest producer and consumer of rapeseed oil (Tian et al., 2018). The CHINAGRO-II economic model, which was established by a team at the International Institute of Applied Systems Analysis (IIASA) and its collaborators (Fischer et al., 2007; Keyzer et al., 2010; Sun, 2014), predicted that China would need to import more than 15 million tons of edible oil to meet domestic consumption demand by 2030 (Tian et al., 2018). This plausible heavy dependence on edible oil imports is likely to undermine China's food security in the future. This foreseen pressure further strengthens our motivation to develop instruments for the purpose of accurately measuring the starting and ending dates of fallowing on each grid-cell of the fallowed land, matching the fallowing periods with the growing period requirements of rapeseeds on the grid, and assessing the current and future potentials of rapeseed production across the matched grid-cells in the region. The results will facilitate effective use of the winter fallow land in the Basin and thus promoting China's energy and food security.

An emerging body of literature focuses on exploring the potential productivity of winter fallow fields. The first challenge in such exploration is how to accurately identify the starting and ending dates of fallow periods at the grid-cell level. The existing method is to extract the time nodes of fallow periods based on remote sensing data only (Zhai et al., 2012), without paying attention to local records of crop calendars and farmer's adaptations on sowing dates and variety choices under historical and future climate changes. For example, Liu et al. (2018) extracted the last harvest dates in previous year and the earliest sowing dates in the current year using remote sensing data only. They then simulated the potential production of rapeseed in their identified winter fallow fields using the agro-ecological zone (AEZ) model of the IIASA and FAO (IIASA/FAO, 2012, 2018). However, they did not validate the starting and ending dates of winter fallow fields using the local records of crop growing calendars which are available at the local agro-meteorological observation stations. This lack of validation in Liu et al. (2018) led to an overestimation or underestimation of suitable fallow land areas for winter rapeseed production in different parts of the YRB region. Their AEZ simulation has the following three limitations. First, they employed the default cultivar parameters of rapeseed varieties in the original AEZ model, without updating and enrichment based on the available records of the local agro-meteorological observation stations. Second, they used 140 days as the uniformed available time for winter fallow fields without considering the significant variation in agro-climate conditions across this huge region. Third, they ignored the adaptation on sowing dates and on the choice of varieties with growth cycle length suitable to local climate conditions.

The present research aims to address all of the above limitations. First, we identify the accurate starting and ending dates of winter fallowing by employing remote sensing discrimination methods and a unique dataset that records detailed crop growing calendars at 84 agro-meteorological observation stations in the YRB over 1981-2011. Second, we enrich and update the rapeseed cultivar parameter of the AEZ model according to the detailed observation data and historical climate data based on our previous work, and then match the fallowing periods with the growing period requirements of the suitable rapeseed variety at the grid-cell level. In this way, we can extract accurate location and extent of winter fallow fields. The updated and enriched AEZ model indicates that the shortest growth period for winter rapeseed is 150 days rather than 140 days. Third, we run the updated AEZ model to assess the production potential of growing rapeseeds in the winter fallow fields we have identified. The AEZ runs take account of the adaptations on planting dates and on the choice of varieties with suitable growth cycle length. The AEZ model is capable of allocating most suitable planting dates and cultivars to match the agro-climatic conditions at the grid-cell level (Fischer et al., 2002, 2012). Forth, we simulate economically meaningful levels of rapeseeds production and trade for 2020 and 2030 by coupling the AEZ model and the CHINAGRO-II economic model.