Abstract: As a kind of main material for biogas plants, industrial biogas crop plays an important role in energy and ecology area, in which ecological factors should be considered during the screening and planting of industrial biogas crop.Among those ecological factors, net ecosystem production(NEP) and water use efficiency(WUE) are the most important ones.NEP can indicate the status of carbon sinks or sources, and WUE can reflect the coupling of carbon and water cycles at ecosystem level.Screening those crops with high NEP and WUE will be beneficial to the decreasing of greenhouse gas emissions and the increasing of water using effect, which also can promote the development of biogas industry.To provide theoretical basis for the screening and scale planting of industrial biogas crop, the NEP and WUE of 4 crops in central Yunnan, including 2 types of maize (Zea mays L.) Quchen 9 and Yunrui 88, hybrid pennisetum (Penniseturm americanum × P.purpureum) and alfalfa (Medicago sativa), were analyzed under normal planting conditions.The measurements were taken on the pilot farm(25°18′N and 102°45′E, with an elevation of 1978 m) of Yunnan Agriculture University, Kunming, China.The climate was classified as subtropical plateau monsoon climate, with a mean annual temperature of 15.3 ℃ and a mean annual precipitation of 979.3 mm.The soil was upland red soil.The experiment was arranged in a randomized block design with 3 replicates, and there were a total of 15 experimental plots with an area of 30 m2 for each plot.All plots were surrounded and separated by concrete ridges.The ridges were 100 cm underground and 20 cm aboveground.The 2 breeds of maize were transplanted on May 20th and harvested on September 29th, 2013.Hybrid pennisetum and alfalfa were planted on March 20th, 2012 by cuttage propagation and seed reproduction separately, and both were reaped 3 times on May 20th, July 12th and September 29th, 2013, respectively.The NEP and WUE were investigated during the growing period of maize, from May 20th to September 29th, 2013.For hybrid pennisetum and alfalfa, the total amount of the last 2 harvests was the aboveground biomass.Soil core method (Luoyang shovel) was used to obtain the root samples of hybrid pennisetum and alfalfa in 0-90 cm soil layer.The underground biomass of 2 crops was determined on May 20th and September 29th, 2013 respectively, and the difference for the 2 times was the increasing amount of the underground biomass.The roots were obtained when the corn was harvested, and the underground biomass was determined by drying the roots.Soil water content was observed with a PR2 soil moisture meter.Soil respiration was measured by the soda lime absorption method and corrected by the static closed chamber.The water evaporation was detected by the no-weighting-lysimeter.The meteorological indices, including temperature and rainfall, were recorded with a weather station.The NEP was calculated by subtracting the quantity of soil respiration from net primary productivity.The evapotranspiration, the population water use efficiency(WUEp), and the ecosystem water use efficiency (WUEe) were estimated by water balance equation.The results showed that: 1) The NEP decreased in this order: hybrid pennisetum (17 533.1 kg/hm²) > maize Quchen 9(9 172.9 kg/hm²) > maize Yunrui 88(8 462.7 kg/hm²)>alfalfa(273.6 kg/hm²)>bare land(-2 377.0 kg/hm²).The data showed that the 4 industrial biogas crops acted as a CO₂ sink.No significant difference in NEP could be observed between the 2 breeds of maize, while significant difference at the 0.01 level was showed between any 2 crops of maize, hybrid pennisetum and alfalfa.2) The WUEp of the crops decreased as follows: hybrid pennisetum (10.89 kg/m3)>maize Quchen 9 (7.23 kg/m3)>maize Yunrui 88 (6.79 kg/m3)>alfalfa(3.46 kg/m3).And the WUEe decreased in the same order: hybrid pennisetum(4.19 kg/m3)>maize Quchen 9(2.38 kg/m3)>maize Yunrui 88(2.20 kg/m3)>alfalfa(0.06 kg/m3).No significant difference could be observed in WUEp and WUEe between the 2 breeds of maize, while significant difference at the 0.01 level was showed between any 2 crops of maize, hybrid pennisetum and alfalfa.Comprehensively considering biomass, NEP, WUEp and WUEe, the bybrid pennisetum demonstrates obvious advantage over other 3 crops under normal planting conditions and is more preferential to be popularized and cultivated.