Spatial-temporal dynamics of grain yield and the potential driving factors at the county level in China

© 2020 Elsevier Ltd Understanding the spatial-temporal dynamics of grain production and the influencing factors at the county level in China may promote the knowledge of land-use management and local policymaking, which are conducive to food security and the sustainable development of society. This study aims to evaluate China's grain yield (GY) from 2000 to 2014 and investigate the potential driving factors (PDFs) that affect the spatial-temporal dynamics of GY, including land, labor force, capital, and macro-background. Specifically, the locational Gini coefficient and exploratory spatial data analysis (ESDA) were used to characterize the spatial patterns of GY and its correlations with PDFs. Spatial regression models (SRMs) were employed to investigate the spatial dependence of GY on each PDF in 2000, 2005, 2010 and 2014. Results reveal that China's grain production has been on the rise with high-yield regions distributed mainly within the northeastern agricultural regions. Moreover, the proportion of counties in the northeastern agricultural regions with high grain yield has increased, while the number of low-yielding counties has increased in other agricultural regions. This finding highlights the increasing trend of spatial polarization in grain production. The significant bivariate Moran's I (p < 0.05) further revealed a global spatial spillover effect in the spatial correlation of GY and four PDFs. The spatial correlations could be categorized into four types: high GY and high PDFs, high GY and low PDFs, low GY and high PDFs, and low GY and low PDFs. SRMs were capable of quantifying the spatial dependence of GY on various PDFs, thereby revealing that land factors had a substantial effect on the grain production dynamics nationwide. The exploration of the spatial relationships between GY and PDFs provide a reference for formulating scientific and reasonable agricultural policies

On the interactions between land and water use in Brazilian rainfed agriculture

In the coming decades, one of humankind’s main challenges will be to guarantee food supply for a growing population while managing ever more scarce resources, and safeguarding the availability of water and land for natural ecosystems. Brazil is a country with abundance of water and land resources, and has recently become one of the world’s main exporters of agricultural commodities. The Brazilian agricultural sector recently went through unprecedented intensification and extensification processes, which include the expansion of cropland and pasture areas into vulnerable ecosystems. This PhD thesis advances the research field on water and land resources assessment by investigating the following processes: i) changes in green water use by major rainfed crops in Brazil during recent decades ii) potential improvements of land and green water productivity for Brazilian rainfed crops, with and without implementation of supplemental irrigation, iii) influences of intensification and expansion of soybean production in Brazil on green water use, and iv) impacts of double-cropping on water use intensity. The process-based biogeophysical crop model EPIC was chosen and applied to simulate water use and crop growth for Brazilian rainfed crops, under diverse management conditions. In Chapter 2, I simulated yields, water use and water productivity for soybeans, maize, cotton and wheat under different scenarios of agricultural management, for rainfed and irrigated conditions. Chapter 3 focuses on soybean and maize, and analyzes water use for the production of these crops under single and double-cropping conditions. The results show an increase in green water use for the production of maize, cotton, soybeans and wheat from 145 to 263 km3 per year between 1990 and 2013. This increase is in large part due to the expansion of harvested area for soybean production. The analysis of management scenarios shows that improving nutrient management has a larger potential to improve land and water productivity compared to supplemental irrigation. Furthermore, supplemental irrigation would lead to a reduction in water productivity despite marginal improvements in land productivity. The analysis of double-cropping practices for soybean and maize production systems finds a greater water appropriation of these systems avoiding cropland expansion and improving overall water productivity. This thesis improves the understanding of current and future use of land and water, the role of intensification and expansion processes, and interactions between land and water use. The results lead to the main conclusion that harvested area expansion has been a major driving force in the increase of green water appropriation in Brazil in the last decades, but that different intensification processes have led to a more productive use of water and land over time. More importantly, the growth of double-cropping has allowed a decoupling between the appropriation of water and land, allowing a great increase of agricultural water use without further expansion of cropland