Efficient Management Of Water And Nitrogen For Alfalfa And Irrigation Decision Support System With Center-Pivot System

Shortage of water resource has been one of the major limiting factors for alfalfa production in the commercial grass zones of China.In recent years,with the promotion of rural land transfer and adjustment of agricultural structure,use of center-pivot irrigation systems has gradually increased in alfalfa irrigation areas.Using field experiments and model simulation,a systematic analysis of water and nitrogen management of alfalfa was conducted to address the issues ofimproper water and nitrogen management and low intelligence with center-pivot irrigation systems in alfalfa irrigation areas.For quantification of the demand for water and nitrogen of alfalfa,the effects of water-fertilizer coupling on alfalfa yield and quality were evaluated.The effects of methods and rates of urea application on NH3 volatilization and alfalfa growth were also investigated.Meanwhile,the interception of water by alfalfa canopy with center-pivot irrigation was estimated.Moreover,APSIM-Lucerne model was calibrated and validated in semi-arid areas of Inner Mongolia Autonomous Region to evaluate the water and nitrogen management on the alfalfa growth.Furthermore,an irrigation decision support model was constructed and the corresponding software was developed.Main results and conclusions of this study are as follows:(1)In 2014 and 2015,a field study was conducted in Inner Mongolia.Three irrigation levels(100%,80%,60%ET)and three nitrogen application rates(69.0,48.3,27.6 kg hm-2)used to evaluate the effects of water-fertilizer coupling on alfalfa growth,yield and quality.The results showed yield was significantly affected by the irrigation rather than the urea application rates.The partial factor productivity(PFP)of nitrogen and water use effiency(WUE)significantly increased(P ≤ 0.05)with the decline of urea applications rates and irrigation,respectively.No significant(P>0.05)difference existed in annual yield between 100%and 80%ET irrigation levels.Compared to the irrigation at 100%and 80%ET level,the irrigation at 60%ET level caused significant(P ≤ 0.05)reduction of yield by 10%and 11%,respectively.Neither fertilizer application nor water-fertilizer coupling had no significant(P>0.05)effect on alfalfa yield and quality in the whole growing season.The annual water requirement is about 508 mm for alfalfa with three harvests in southwest of Inner Mongolia.The water production functions of alfalfa were parabolic in each harvest.The proportions of seasonal total actual water applied in each cutting were approximately 25%,32%and 43%,with contributions to annual yield accounting for 54%,30%and 16%,respectively,indicating that the third harvest of alfalfa had a great potential to improve WUE and save more water.Over-irrigation caused by end gun slightly increased alfalfa annual yield,but it reduced the quality and WUE.Therefore,an end gun in the center pivot irrigation system should be carefully selected for improving uniformity of the water application.A management of 27.6 kg hm-2 of nitrogen application rates after harvest in each cutting were recommended for high PFP of nitrogen.We also recommended 80%ET of Irrigation level in the first two cuttings and 60%ET irrigation level in the third cutting to improve and WUE in semi-arid region such as western Inner Mongolia in China.(2)In 2016 and 2017,a study was conducted at an experimental station of China Agricultural University in Zhuozhou,Hebei Province,China,to quantify NH3 volatilization by banding,surface broadcasting and center-pivot fertigation methods at three nitrogen application rates(69.0,48.3,27.6 kg hm-2).The effects of application methods on the yields and fine root biomass of alfalfa were also investigated in this study.The results showed that cumulative NH3 volatilization losses were significantly affected(P<0.05)by N application methods.The losses of banding,broadcasting,and fertigation were 1.08%,1.34%,and 3.80%of total urea application rates,respectively.The nitrogen application rates of 69.0 kg hm-2 significantly increased cumulative NH3 volatilization losses.Comparing to banding and broadcasting methods,fertigation caused a higher cumulative NH3 losses,but led to much higher yields,fine root biomass and nitrogen agronomic efficiency.Therefore,the fertigation method could be economically beneficial and environmentally sound in the North China Plain,where intensive cropping system is widely adopted.(3)In 2016,a field experiment was simultaneously conducted at an experimental station of China Agricultural University in Zhuozhou,to quantify water interception by alfalfa canopy under center-pivot irrigation.In the experiment,three levels of water application depth(5.9,11.8,17.7 mm)were tested.Canopy interception for three growth stages of alfalfa(S1-growth stage,S2-branching stage,S3-early flowering stage)was measured under R3000 sprinklers with three nozzles(15#,25#and35#)using the weighing method in this study.The results showed that the canopy interception ratio of alfalfa significantly(P ≤ 0.05)decreased with the increase of water application depth rather than the nozzles.The canopy interception ratio increased with the growth of alfalfa,with the values of 10.38%(S1),13.39%(S2)and 15.18%(S3),respectively.(4)Parameterization and validation of APSIM-Lucerne model for center-pivot irrigated alfalfa were conducted using the data in 2014～2015.The results indicated that the modified model accurately simulated the growth day and annual yields,with NRMSE of 1.00%-5.82%and 6.69%～10.86%.The model simulated the dynamic of alfalfa height and soil water with acceptable accuracy,with NRMSE of 7.9%～29.06%and 23.63%～33.38%.(5)A fuzzy decision support system(FDSS)of alfalfa was built based on the APSIM-Lucerne model and field experiments.The system combined a predictive model of soil water,alfalfa growth,water consumption of alfalfa and an inference system computing.The fuzzy logic inference system calculated irrigation amounts based on the soil water and plant height using the mamdani algorithm.The soil water and plant height were calculated based on the deviation comparison between measured and predicted values and weight assignments.Further,we developed an online software which could generate an updated e-mail for users.