Agriculture intensifies soil moisture decline in Northern China

Abstract

Northern China is one of the most densely populated regions in the world. Agricultural activities have intensified since the 1980s to provide food security to the country. However, this intensification has likely contributed to an increasing scarcity in water resources, which may in turn be endangering food security. Based on in-situ measurements of soil moisture collected in agricultural plots during 1983-2012, we find that topsoil (0-50 cm) volumetric water content during the growing season has declined significantly (p < 0.01), with a trend of -0.011 to -0.015 m(3) m(-3) per decade. Observed discharge declines for the three large river basins are consistent with the effects of agricultural intensification, although other factors (e.g. dam constructions) likely have contributed to these trends. Practices like fertilizer application have favoured biomass growth and increased transpiration rates, thus reducing available soil water. In addition, the rapid proliferation of water-expensive crops (e.g., maize) and the expansion of the area dedicated to food production have also contributed to soil drying. Adoption of alternative agricultural practices that can meet the immediate food demand without compromising future water resources seem critical for the sustainability of the food production system.

Figure 1. Growing season trends in Northern China (NC)

: a) Volumetric soil moisture (θ_v) trend during 1983–2010 across NC and at the 40 agricultural meteorological stations (circles on the map) during 1983–2012. The former is derived from CCI-WACMOS soil moisture product and the latter is from in-situ measurements of the top 0–10 cm soil. The red polygons delineate the boundaries of the Yellow, Haihe and Liaohe river basins from west to east, respectively. Note that the boundary of Liaohe river basin is only extended to Tieling gauge station. b) Terrestrial water storage (TWS) trend during 2003–2013. c) Discharge (Q) trends in the three basins during 1980–2012. d) Average θ_v trends in 0–10 cm, 10–20 cm and 20–50 cm soil across the 40 agricultural meteorological stations during 1983–2012. e) Fraction coverage of cropland in 2010. f–h) Palmer Drought Severity Index (PDSI), air temperature (T) and Precipitation (P) trend during 1984–2007. The black dots in f–h) represent the locations of 307 weather stations. All maps are generated via ArcMap10.2, and their projected coordinate systems are Asia North Albers Equal Area Conical.

Figure 2. Fertilizer use experiment and fertilizer use trend in Northern China

: a) water consumption in N0P0-N4P4 fertilizer use treatments between 2008–2010, which is derived from fertilizer use experiment in Wuchuan Field Experiment Station, where N0P0–N4P4 stand for increasing fertilizer use treatments that correspond to Table S1; and b) fertilizer use (F) trend during 1983–2006 across the region. Note that area without fertilizer use data is left vacant. The map in b) is generated via ArcMap10.2, and the projected coordinate system is Asia North Albers Equal Area Conical.

Figure 3. Changes in crop area and yield per unit area in Northern China during 1980–2011

: a) total crop area in the region; b) planting area for each major crop; and c) yield per unit area for each major crop.

Figure 4. Variation of volumetric soil moisture (θ_v) in topsoil (0–50 cm) of pristine pasture and different crop fields in Wuchuan Agricultural Meteorology Observation Station during 1983–2009.