摘要：Switchgrass is an introduced C4 grass in the semi-arid Loess Plateau of China, but there is a lack of information to assess its ecological invasive risk. In this study, Old World bluestems (native C4 grass) and switchgrass were sowed at five mixture ratios (8:0, 6:2, 4:4, 2:6 and 0:8) under two soil water levels (80% field capacity (FC) and 40% FC) and two nitrogen (N) treatments (0 and 100 mg N/kg dry soil, termed N0-unfertilized and N1-fertilized treatments, respectively) in a pot experiment in 2012. Biomass, root morphological traits and relative competitive abilities of these two species were analyzed. Results showed that biomass of both species was significantly greater under 80% FC or N fertilization, and switchgrass had a relatively larger root: shoot ratio (RSR). Total root length (TRL) and root surface area (RSA) of switchgrass were significantly higher under 80% FC irrespective of N treatment, while those of Old World bluestems were only significantly higher under N fertilization. N had no significant effect on TRL and RSA of switchgrass, while RSA of Old World bluestems significantly increased under 80% FC and N fertilization. Under 40% FC and N0-unfertilized treatment, the aggressivity of Old World bluestems was larger than zero at 2:6 and 4:4 mixture ratios of two species, whereas it was close to zero at 6:2 mixture ratio. Root competitive ability of switchgrass significantly increased under 80% FC or N fertilization. The aggressivity of Old World bluestems was negative at 6:2 mixture ratio under 80% FC and N fertilization, while it was positive at 2:6 mixture ratio. Switchgrass may become more aggressive when N deposition or rainfall increases, while a proper mixture ratio with appropriate water and N management could help with grassland management in the semi-arid Loess Plateau.
摘要：Plastic mulched ridge-furrow irrigation is a useful method to improve crop productivity and decrease salt accumulation in arid saline areas. However, inappropriate irrigation and fertilizer practices may result in ecological and environmental problems. In order to improve the resource use efficiency in these areas, we investigated the effects of different irrigation amounts (400 (I1), 300 (I2) and 200 (I3) mm) and nitrogen application rates (300 (F1) and 150 (F2) kg N/hm2) on water consumption, salt variation and resource use efficiency of spring maize (Zea mays L.) in the Hetao Irrigation District (HID) of Northwest China in 2017 and 2018. Result showed that soil water contents were 0.2%–8.9% and 13.9%–18.1% lower for I2 and I3 than for I1, respectively, but that was slightly higher for F2 than for F1. Soil salt contents were 7.8%–23.5% and 48.5%–48.9% lower for I2 than for I1 and I3, but that was 1.6%–5.5% higher for F1 than for F2. Less salt leaching at the early growth stage (from sowing to six-leaf stage) and higher salt accumulation at the peak growth stage (from six-leaf to tasseling stage and from grain-filling to maturity stage) resulted in a higher soil salt content for I3 than for I1 and I2. Grain yields for I1 and I2 were significantly higher than that for I3 and irrigation water use efficiency for I2 was 14.7%–34.0% higher than that for I1. Compared with F1, F2 increased the partial factor productivity (PFP) of nitrogen fertilizer by more than 80%. PFP was not significantly different between I1F2 and I2F2, but significantly higher than those of other treatments. Considering the goal of saving water and nitrogen resources, and ensuring food security, we recommended the combination of I2F2 to ensure the sustainable development of agriculture in the HID and other similar arid saline areas.