Spatial distribution characteristics of photosynthetic active radiation in cotton canopy based on geo-statistics

Photosynthetic active radiation (PAR) using efficiency is an important factor affecting crop yield and quality. Precisely and accurately quantifying PAR spatial distribution within crop canopy is of great significance for reasonable plant density arrangement，plant architecture molding，and variety selection for high yield. In this study, Geo-statistical theory and methods were applied to study the PAR spatial distribution in 6 different cotton plant densities. Spatial correlations of PAR and spatial distribution characteristics of transmittance in different cotton communities were studied. The results showed that: 1) During the early growth stage, PAR spatial distribution had a moderate spatial correlation, with most of the structural component variance proportions below 0.75. However, during the mid-late growth stage, PAR spatial distribution had a high degree of spatial correlation, with almost all the structural component variance proportions above 0.9; 2) At the early cotton growth stage, PAR transmittance exhibited a long and narrow "V" shape and were gradually reduced from the middle toward the rows. At the mid-late growth stage, PAR transmittance exhibited a short and shallow "V" shape in the upper canopy and that in the lower part showed gradually linear decrease; 3)The variations of mean PAR transmittance over the whole growth period in 6 cotton communities presented quadratic trends. PAR interception rates were increased over the plant density, and cotton community biomass were increased gradually, but the economic production began to decline in the plant density of 69,000 plants/hm2.