Effects of planting pattern on canopy light utilization and yield formation in machine-harvested cotton field

Abstract: Light radiation transmission inside the canopy is an important determinant to optimize planting patterns for deep integration of agricultural machinery and techniques, thereby realizing standardized planting and mechanized operation. However, it is still unclear about the regulation mechanism of machine-harvested cotton planting mode on canopy light radiation transmission and yield formation. In this study, a two-year field experiment was carried out under the same density in Xinjiang cotton areas of western China, in order to clarify the effects of planting patterns on canopy light utilization and yield in mechanically harvested cotton. Three kinds of machine-harvested cotton were set. An investigation was also made on the evolution characteristics of canopy structure, canopy effective radiation, and yield formation under different configurations. The correlation analysis was carried out between planting pattern, canopy light interception, and yield composition factors. The results demonstrated that there was an obvious spatial and temporal heterogeneity in the canopy structure of cotton under different planting patterns and the characteristics of light radiation transmission inside. The canopy transmittance of S1（Each film planting three rows） changed in the horizontal direction of "V" in the early stage of growth, compared with the treatment of S3. Meanwhile, the expansion of row spacing increased the distribution of PAR（Photosynthetically active radiation） between the rows in the cotton fields, but there was no significant influence on the transmittance near the rows of cotton. In the later stage of growth, the transmittance of the cotton field in each horizontal direction changed slightly, but the transmittance of the lower layer under the treatment of S1 was significantly higher than that of S2（Each film planting four rows） and S3（Each film planting six rows）. The average row spacing significantly enhanced the boll number and weight at the lower part of cotton, finally promoting the yield. The two-year seed cotton yields of S1 cotton were 6 507.50 and 6 161.08 kg/hm2, which were 10.66%, 23.10%（2017） and 10.29%, 15.32%（2018）higher than that of S2 and S3 cotton, respectively. There was a significant positive correlation between the average row spacing, the yield composition, and the light interception rate of the lower layer, whereas, a negative correlation was found between the middle layer, the upper layer, and the total light interception rate. This indicated that the average row spacing reduced the optical interception rate in the middle and upper layers, while increased the optical interception rate in the lower layer for higher yield, although the total optical interception rate in the canopy tended to decrease. The "each film planting three rows" machine-harvested cotton planting mode can increase the PAR transmittance in the middle and lower parts of the upper canopy in the vertical direction, where the utilization efficiency of light energy was improved as a whole, compared with the arrow row treatment. The number of bolls increased by 16.7%, the quality of cotton bolls increased by 6.6%, and the final yield increased by 19.21%, compared with the traditional one. The planting mode mainly determined the light transmission in the vertical direction, thereby dominating the PAR transmittance and interception in the canopy. The light transmittance of the middle and lower canopy gradually increased, with the increase of average row spacing. The varying degrees alleviated the excessive concentration of interleaved leaves between the wide and narrow rows, resulting in the canopy closure and the supply of photosynthetic products in the middle and lower canopy. Therefore, the "each film planting three rows" machine-picked cotton planting mode can be expected to concurrently improve the cotton yield and light energy utilization. Consequently, the quality of mechanical picking can greatly promote the deep integration of mechanical harvesting and agricultural machinery