Spatio-temporal Windows Of PAR On The Cotton Canopy In Intercropping Alley Of Jujube

Drought and little rain, the per capita arable land is scarce in south Xinjiang, in order to make full use of land resources, jujube(Ziziphus jujuba)-cotton(Gossypium hirsutum)intercropping is one of the main way in south Xinjiang. But the intercropping is unreasonable,it will be cause of a fierce competition between fruit trees and crops, especially in the competition of light. Light is the basis of crop yield formation, but in agroforestry system the upper canopy shading could affect the crops absorption of light utilization,so that crops stunted in growth slow,resulting in a decrease in crop yield. In this paper, the jujube-cotton intercropping system were considered as the object,and photosynthetic active radiation(PAR)of cotton normal growth and development as the foothold, combined the method of field sampling with indoor analysis, the cotton photosynthetic parameters, the variation of light environments in jujube intercropping roadway, spatio-temporal windpws of PAR on the cotton canopy and its influencing factors were studied. The main results were as follows:In the same light intensity, the net photosynthetic rate(Pn) of cotton was maximum at five euphylla period, and the minimum at boll opening period. In the whole growth period of cotton of the light saturation point(LSP) as follows: five euphylla period> squaring period>three euphylla period> bloming period> boll opening period, the change trend presents unimodal inverted “U” type. The light compensation point(LCP) of cotton in the same as the change trend presents unimodal, as follows: five euphylla period> three euphylla period>squaring period> bloming period? boll opening period.In jujube-cotton intercropping system, the PAR diurnal variation in each site of intercropping alley was similar to that of monoculture cotton, and the trend of them were all parabola. Under the same plant spacing, the older the age, the bigger the shading degree of canopy to intercropping alley in each site, and the weaker the PAR received by cotton canopy.While under the same age, the greater the plant spacing, the smaller the shading degree of canopy to intercropping alley in each site, and the stronger the PAR received by cotton canopy.At the same planting spacing mode, the greater the saturation PAR spatio-temporal window, the higher the cotton yield. The five euphylla period was an important period of nutrition growth of cotton. In this period, the saturation spatio-temporal window of cotton was the smallest, so five euphylla period was the key period of cotton yield formation.The LSP level of cotton in each growth period directly determined the size of the cotton canopy saturation PAR spatio-temporal window. And the main factors effecting saturation PAR spatio-temporal window of cotton at different growth stages were crown diameter and planting spacing. Besides, the relationships between saturation PAR spatio-temporal window of cotton at different growth stages, and crown diameter(X2) and row spacing + line spacing(X5) wasY =-4.181-1.352 X2 +2.027 X5.