The complexity of measuring cropland use intensity: An empirical study

Qiangyi Yu,Mingtao Xiang,Zhanli Sun,Wenbin Wu

doi:10.1016/j.agsy.2021.103180

Abstract

CONTEXTCropland intensification promises additional food supply without further expanding croplands into natural ecosystems. Cropland use intensity measures the degree of intensification by various indicators, both from input and output perspectives; all of these indicators are however not always coherent—which may cause confusion and send contradicting signals to policymakers. Few empirical studies have been conducted to relate and compare various intensity indicators. OBJECTIVEIn this study, we start with a hypothesis that cropland use intensity measured by different indicators may differ. We then test such a hypothesis based on empirical evidence in a typical multi-cropped region (i.e., Jinxian County) in Jiangxi Province—a major breadbasket in Southern China. METHODSWe focus on two widely used indicators, i.e., multi-cropping frequency (MCF) and crop growth duration (GDa), measured by a hybrid time-series remote sensing dataset which fuses MODIS and Gaofen-1 images for the year 2015. We map these two indicators independently at a 16 m spatial resolution. For each pixel, MCF takes value from 1 to 3 corresponding to single-, double- and triple- cropping; while GDa is quantified by the accumulative crop growth days within the study year. We relate the values of two indicators, summarize the descriptive statistics of GDa grouped by MCF categories, and compare MCF and GDa values by using a box-whisker chart, a bivariate map, and a set of statistical tests. RESULTS AND CONCLUSIONSWe find that a significant overlap of GDa exists between single cropping and double cropping both visually and statistically. In other words, the different cropland intensity levels measured by MCF appear to be the same if measured by GDa. The box-whisker chart shows that the GDa of single cropping in the upper quarter is substantially longer than the GDa of double cropping in the lower quarter. The non-parametric tests show that the overlapped GDa between single cropping and double cropping exists substantially, which may cause confusion. Moreover, the bivariate map shows that single cropping with shorter growth duration (i.e., consistent low intensity) and double cropping with longer growth duration (i.e., consistent high intensity) account for 44% and 28%, respectively, while the rest manifested as inconsistent which accounts for another 28% of the total cropland area. SIGNIFICANCEThese results confirm our hypothesis—the inconsistency among intensification indicators. Different measurements may convey contradicting messages for policymakers in pursuing the sustainable intensification goals, which suggests more efforts are required to understand the multidimensionality of the process of cropland intensification for distinct policy measurements.

Highlights

Global food production has increased dramatically in the past few decades, there are still about 821 million people suffering from hunger (FAO, 2018)
multi-cropping frequency (MCF) mapping In Xiang et al (2019), we developed a GF-MODIS dataset by fusing MODIS Terra data product (MOD09Q1) and Gaofen-1 (GF-1, Chinese high-resolution remote sensing satellite) Wide Field of View (WFV) images, and obtained the smoothed NDVI curve by using the Harmonic Analysis of Time Series method (HANTS)
The results show that the means, medians, and distri bution of growth duration (GDa) are significantly different between single cropping and double cropping

Summary

Introduction

Global food production has increased dramatically in the past few decades, there are still about 821 million people suffering from hunger (FAO, 2018). More food still needs to be produced to increase global food security, especially under the current COVID pandemic (Laborde et al, 2020; Stephens et al, 2020). This undoubtedly brings more pressure on agriculture to further increase production, which re quires either expanding cropland into nature areas or intensifying the existing use of cropland (Wu et al, 2014). Even the reclamation of abandoned cropland, e.g., in the former Soviet Union countries, could provide extra food It will release the sequestrated carbon as well (Meyfroidt et al, 2016; Schier horn et al, 2014). Most of the additional food production will have to come from cropland intensification, i.e., more food pro duction per unit of land (Charles et al, 2014; Stephens et al, 2018; Wu et al, 2014)

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