Energy/water budgets and productivity of the typical croplands irrigated with groundwater and surface water in the North China Plain

Although irrigation has markedly increased agricultural productivity in the North China Plain, it has reduced groundwater levels by up to 0.8 m yr−1 and dried up the Yellow River for extended times since the 1970s. The objective of this study was to compare water, energy, and carbon fluxes in regions irrigated with groundwater and surface water (Yellow River) using almost four years of eddy covariance data from agricultural stations in Luancheng (water table depth: ∼42 m) and Weishan (near Yellow River, water table depth: 1–3 m). Irrigation is mostly restricted to winter wheat as summer maize grows during the rainy season. Mean annual ET was 693 mm yr−1 for Luancheng site, which is higher than Weishan site (648 mm, ignore partial years). About ∼390–480 mm of ET occurred during the wheat season (from early October to next early June, about 247 days), 230–300 mm in the maize season (from early June to late September, about 107 days). Annual crop yields were ∼6864 kg/ha in the two regions. Annual water use efficiencies ranged from 4 to 6 g CO2 kg−1 H2O. Water use efficiencies were higher for maize than for wheat. Annual cropland carbon budget (CCB) was 230–280 g C m−2 yr−1 at the two sites and suggested a weak carbon sink. Irrigation compensated for seasonal and inter-annual variability in precipitation. Shifting the cropping pattern from wheat–maize double crops to a single crop of maize could significantly reduce water withdrawal and lead to a more sustainable use of water resource in this region.