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Highlights • Soil moisture and yield were observed for 6-year grain, forage and bioenergy crops. • Potential bioethanol production and groundwater decline were calculated. • Sorghum rotation produced more bioethanol per unit of groundwater decline. • Net groundwater withdrawal for perennial switchgrass was the smallest. Abstract Managing the complex demands on available energy, food and water is a fundamental challenge for a world with increasingly tenuous resource pools. The North China Plain's groundwater crisis has become increasingly serious due to decades-long over-exploitation for irrigation to pursue high grain yield. This combined challenge motivated investigation of ways to mitigate the groundwater table decline while fostering the use of renewable bioenergy resources. To provide insights about tradeoffs among water, food and energy, we performed a six-year experiment from 2010 to 2015 in the North China Plain where groundwater use, biomass and biofuel production and water use efficiency were compared for four cropping systems. They are winter wheat-summer maize (WM, grains, 1-year cycle), ryegrass–sweet sorghum (RS, forage plus bioenergy crops, 1-year cycle), winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS, forage, bioenergy plus grain crops, 2-year cycle), and perennial switchgrass (SG, bioenergy crop). Actual evapotranspiration (ET a) and recharge to groundwater were calculated and validated using observed soil moisture contents. Results showed ET a of the cropping systems were statistically similar ranging from 694 to 730 mm yr−1 with the exception of switchgrass which was significantly less at 504 mm yr-1. The water table was projected to decline by about 1.3 m yr-1 for all three multi-crop rotations and 0.4 m yr-1 for switchgrass. In terms of bioethanol production per unit land and per unit ET a , the ryegrass-sweet sorghum (RS) rotation performed best with 25.0 m3 ha-1 and 5.7 L m-3 outperforming the yearly winter wheat–summer maize (WM) rotation (11.7 m3 ha-1 and 3.3 L m-3) and switchgrass (11.4 m3 ha-1 and 2.6 L m-3). The multiple year rotation of winter wheat–summer maize→ ryegrass–sweet sorghum (WMRS) yielded 16.9 m3 bioethanol per hectare and 4.3 L m-3 bioethanol per m3 ET a. When optimizing bioethanol against net groundwater depletion, RS and switchgrass outperformed the two grain-based rotations with 15.5 L and 14.4 L of bioethanol per m3 of depleted groundwater, ahead of WMRS at 10.9 L m-3 and WM at 9.1 L m-3. These results are significant for setting governmental policies on sustainable use of groundwater by various crop mixes. [ABSTRACT FROM AUTHOR]

Intensive double cropping in the North China Plain has been challenged by serious environmental problems. Crop rotation is one of the important strategies for sustainable agriculture, which can reduce production risk and environmental impact. Yet, few studies have assessed enhanced crop rotation diversity on GHG emissions in the North China Plain. Carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2 O) emissions and yields were measured from four cropping systems: (1) wheat (Triticum aestivum L.)-maize (Zea mays L.) double cropping (WM); (2) peanut (Arachis hypogaea L.) and WM rotation (PWM); (3) ryegrass (Lolium perenne L.)-cotton (Gossypium hirsutum L.), peanut and WM rotation (RCPWM); and (4) continuous cotton (C), to determine if enhanced crop rotation diversity can reduce greenhouse gas (GHG) emissions and improve yields. The RCPWM, PWM and WM cropping system produced 11.9%, 15.7% and 32.4% higher net greenhouse gas emissions (GHGE), respectively, than the C cropping system each year by the soil-based method assessing the field productive process. From 2017 to 2018, in the same crop planting seasons, RCPWM had lower cumulative N 2 O and CO 2 emissions, and produced similar peanut, wheat, and maize yields when compared to PWM. In 2018, PWM had higher cumulative N 2 O than WM during the wheat period, and they had similar seasonal cumulative N 2 O emissions during the maize period. Meanwhile, PWM produced lower cumulative CO 2 emissions and higher wheat and maize yields. In 2019, RCPWM did not have significantly different seasonal cumulative N 2 O emissions and yield, but slightly higher soil CO 2 emissions than C during the cotton season. The GHG emission intensity (GHGI) of the same crops was lower in RCPWM than in PWM during the peanut, wheat, and maize period or slightly higher than in the C treatment during cotton period. The results demonstrate that RCPWM could reduce soil N 2 O emissions when the same crops in PWM were compared due to less soil CO 2 emissions that the previous cotton brought about. The RCPWM system did not show a lower soil organic carbon (SOC) sequestration rate than the PWM and C systems. Therefore, increasing cotton into the peanut and wheat-maize rotation system (RCPWM) for more diversified system can help reduce soil GHG emissions without sacrificing yields. • PWM, RCPWM and C cropping systems reduced indirect GWP compared to WM. • PWM did not decrease soil N 2 O emissions but improved wheat and maize yield. • The previous cotton lowered soil CO 2 and N 2 O emissions for next crop growing season. • Increasing crop species in rotation could reduce soil GHG emissions without sacrificing yields. [ABSTRACT FROM AUTHOR]