Light And Water Use Of Forage Maize/Alfalfa Intercropping System In Loess Plateau

The Loess Plateau is the one of main forage producing area in China.However,due to uneven rainfall distribution,limited cultivated land and insufficient forage supply,it is essential to choose a scientific and reasonable plating mode to increase forage production and maximize resource utilization.The research on the productivity,light interception and utilization,water use of different intercropping systems has important theoretical and practical significance for optimizing intercropping mode,improving ecological environment and promoting ecological sustainable development.This study was conducted from 2018 to 2020 at the Qingyang Experimental Station of Lanzhou University.Forage maize and alfalfa were selected as the research objects.Five planting patterns were set up,which were sole maize（SM）,sole alfalfa（SA）,one row of maize intercropped with two rows of alfalfa（I12）,two rows of maize intercropped with two rows of alfalfa（I22）and two rows of maize intercropped with four rows of alfalfa（I24）.Field experiment and mathematical simulation were used in this study.The yield,protein yield,light interception and water use of maize/alfalfa intercropping population were studied,and the following research results were initially obtained:（1）Sole maize had the highest yield,with 27.5,28.6 and 24.5 t ha^-1 in 2018-2020.The crude protein yields of I24,I12,and SA treatments were the highest in 2018,2019,and 2020,with 2.39,2.74,and 3.11 t ha^-1,respectively.In 2018,only land equivalent ratio（LER）of I24 treatment was greater than 1,and LER of maize in all intercropping treatments was greater than its planting ratio,showing the advantage of intercropping.In 2019 and 2020,the LER of the I12 and I24 intercropping populations was 1.01-1.11,respectively.However,but the partial LER of alfalfa and maize in the I24 intercropping population was greater than their planting ratio,and both crops show the advantage of intercropping.（2）The soil water content of intercropping was between that of sole maize and sole alfalfa,and a crop that had competitive advantage would use the soil water of another crop strip.By measuring the soil water content at a depth of 5 m,the average soil water content of I12,I12 and I24 intercropping below 180 cm was 7.8%,13.7%and 9.8%higher than that of sole alfalfa,and 14.7%,10.0%and 13.0%lower than that of sole maize.Compared with the water consumption of monocropping,intercropping increased by 0-1%in 2018,1-5%in 2019,and the water use of every planting mode was close in2020.In terms of yield-based water use efficiency（WUE_B）,I12 and I24 intercropping were 2%-5%and 2%-26%higher than sole cropping,while the I22 was lower than sole cropping,with values of 2%-4%.In terms of water use efficiency(WUE_CP)based on crude protein production,WUE_CP of the I12 was higher 11%and 13%than that of the monocropping in 2019 and 2020,the I22 was 5%higher than the monocropping WUE_CPin 2020,and WUE_CP of the I24 intercropping was 6%,7%and 5%higher than the sole cropping in the three years.（3）An ERCRT（Extended row crop radiation transmission）model and a light instantaneous transmission model for simulating crop strip intercropping were established in this study,and the measured values in field experiments were used to validate the light model.Simulated the photosynthetically active radiation（PAR）at the bottom of the crop canopy,and it was found that the correlation coefficients between the simulated and measured values of maize and alfalfa were 0.87 and 0.84,and the root mean square error（RMSE）and the mean absolute error（MAE）of the simulated values were 0.40,0.55 MJ m^-2 d^-1 and 0.33,0.44 MJ m^-2 d^-1,respectively.The correlation coefficient of the instantaneous transmission model for the simulated and measured values of maize and alfalfa was 0.71,and MAE and RMSE were 7.4-130.8μmol m^-2 s^-1 and 8.8-166.5μmol m^-2 s^-1,respectively.The results showed that both models could better simulate the radiation interception of maize/alfalfa intercropping.（4）The light interception in sole alfalfa was the lowest in 2018,while sole alfalfa had the highest light interception with 1006.6 and 1184.8 MJ m^-2,respectively,followed by I12 in 2019 and 2020.In 2018,PAR interceptions of I12,I22 and I24 populations were 11%,4%and 9%higher than those of monoculture,11%,5%and 9%higher in2019,and 2%,0%and 2%higher in 2020.The three-year average yield-based light use efficiency（LUE_B）of maize in I12,I22,and I24 intercropping populations were 4.35,4.13 and 4.74 g MJ^-1,respectively,which were 9.9%,14.5%and 1.9%lower than that of sole maize.Only LUE_B of alfalfa in I22 intercropping was higher than sole alfalfa.The three-year average light use efficiency based on crude protein yield(LUE_CP)of maize in I12,I22,and I24 intercropping populations were 0.35,0.32 and 0.38 g MJ^-1,respectively,which were 9.1%,18.6%and 2.9%lower than that of monocropping maize.only The LUE_CP of alfalfa in I22 intercropping was higher than that of sole alfalfa.In summary,reasonable forage maize/alfalfa intercropping can effectively alleviate the problem of deep soil desiccation caused by long-term alfalfa planting,improve the light environment of the intercropping population,and increase its water and light energy use efficiency.Forage maize showed the advantage of intercropping in the first year.In the second and third years,the growth of forage maize was restricted during the first and second crops of alfalfa.but maize recovered and became the dominant species during the third cutting of alfalfa.In particular,the yield,crude protein yield,and light and water use efficiency of the intercropping population of 2rows maize and 4 rows of alfalfa were more stable during the three years.