| Many countries in the world are facing the contradiction of the increasing population and the limiting cultivated land area,therefore,how to use the limited cultivated land to produce enough food is facing big challenges.The light resource for farmland is limited,and how to improve the output of the farming system by increasing the light interception and light use efficiency is an urgent problem to be solved.Based on above,we therefore conducted experiments in 2013-2015 located at Heze city,Shandong province.The maize and-soybean strip intercropping was researched as compared to traditional maize and soybean intercropping,sole maize and sole soybean.The ILTM(instantaneous light transmission model)model,HHLA(horizontally homogeneous leaf area)model and ERCRT(extended row crop radiation transmission)model were used to analyze the light distribution,light interception and light use efficiency in different maize and soybean strip intercropping configurations.In additional,the growth of intercropped soybean was studied using the Beta model based on accumulated temperature,and the relationships between crop growth and light environment,light interception were analyzed.The main results were followings:(1)The growth of intercrops were regulated by the temporal and spatial distribution of the light in intercropping.Our research applied the instantaneous light transmission model(ILTM)to estimate of the light intensity of each point in intercropping systems.The simulated value was compared to measured value to improve the credibility of results.How light environment at top of soybean canopy regulated the growth of soybean was researched.Compared to monoculture,the photosynthetically active radiation(PAR)at top of soybean canopy for strip intercropping decreased by 48%,which affects 50%up-regulation of plant height.20%down-regulation of stem diameter,30%up-regulation of specific leaf area,30%down-regulation of leaf area,25%down-regulation of the dry weight.30%down-regulation of yield;the photosynthetically active radiation(PAR)at top of soybean canopy for row intercropping decreased by 67%.which affects 50%up-regulation of plant height,30%down-regulation of stem diameter.40%up-regulation of specific leaf area,45%down-regulation of leaf area,48%down-regulation of the dry weight,52%down-regulation of yield.In addition,the weak light environment increased the heat demand for appearance of soybean phytomers,and prolonged the growth time of the soybean organs.The instantaneous light transmission model used in this research can provide supports to the development of structural-functional plant model,and then it will be contributed to the study of the crop response to light and temperature.(2)The light interception(LI)for different intercropping systems were varied significantly.The HHLA(horizontally homogeneous leaf area)and ERCRT(extended row crop radiation transmission)models were used to calculate the LI for intercrops.We tested different strip intercropping configurations(based on ERCRT model)and a row intercropping(based on HHLA model)to calculate LI for intercrop species.The results show that,for strip intercropping,light interception amount of intercropped soybean was 35%of that of monoculture,and light interception amount of intercropped maize was 75%of that of monoculture;for row intercropping,light interception amount of intercropped soybean was 25%of that of monoculture,and light interception amount of intercropped maize was 85%of that of monoculture.With the distance of maize strip increased by 0.2 m,the light interception amount for soybean increased by 32 MJ m-2,that for maize decreased by 36 MJ m-2.In addition,soybean morphological plasticity is not benefit to the accumulation of light interception amount of soybean.The soybean varieties with smaller morphological plasticity should be considered in production.(3)After crop intercepted the light,light use efficiency(LUE)determined the dry matter accumulation,and then the harvest index(HI)determined the yield.The results showed that the LUE of intercropped maize was 1.16 times that of monoculture,and the LUE of intercropped soybean was 1.5 times that of monoculture.It can be used to simulate the crop dry matter accumulation by using light interception and light use efficiency.This method can also be applied to the production for the selection of reasonable configuration.Harvest index(HI)represented how much dry matter transferred to grain.The HI of intercropped soybean was equivalent to 90%of monoculture.The number of grains per plant was the limited factor of soybean yield.(4)The interspecific light competition differed in different maize and soybean intercropping configurations,and led to the difference of yield and LER.With the distance between maize strip increased by 10 cm,the light interception of maize decreased by 1.5%,and the light interception of soybean increased by 1.5%.With the distance between maize strip expanded from 1.3 m to 1.8 m,the competition disadvantage of soybean quickly relieved,thus resulting in the competitive ratio(CR)of soybean increased from 0.28 to 0.81,and LERs increased from 0.39 to 0.53.However,with the maize row reduced from 0.4 m to 0.2 m,the competitive ratio(CR)of soybean decreased from 1.94 to 1.25,and the partial LERm decreased from 0.93 to 0.81.A maize row width of 0.4 m with the distance between maize strips of 1.6 m(A3)was the optimal configuration for farmers that could achieve the highest LER and MAI up to 1.42(1.40,1.43 and 1.42 for 2013,2014 and 2015)and 1338(1232,1500 and 1282 dollar ha-1 for 2013,2014 and 2015),respectively.Above all,considering the light interception,light distribution,light use efficiency,interspecific competition and land use efficiency,the configuration with maize row of 0.4 m(distance between maize strip:1.6 m;the distance between maize row and soybean row:0.6 m)was the recommended configuration for farmers. |
