Microclimatic responses to shelterbelt structural configuration in an arid cotton agroforestry system

Introduction: Farmland shelterbelts serve as important ecological barriers that protect agricultural systems. Investigating the effects of shelterbelts with different structural configurations on farmland microclimate is of great significance for optimizing shelterbelt structure and improving farmland ecological stability. Methods: In this study, structural characteristics including the number of rows, length, spacing, and porosity were comprehensively considered. Three types of shelterbelt configurations (Grade I, II, and III) were selected using a typical sampling method in the 12th Regiment of Alar City, Xinjiang, with open farmland serving as the control (CK). Microclimate factors, including wind speed (WS), air temperature (TA), air humidity (RH), light intensity (LI), and soil temperature (ST), were measured at different horizontal distances from the shelterbelt during four cotton growth stages (Seedling Stage, Budding Stage, Flowering Stage, Boll Opening Stage). Results: The results showed that the microclimate-regulating effect of shelterbelts increased with the improvement of shelterbelt grade, generally following the order Grade I > Grade II > Grade III. Among them, Grade I shelterbelts showed the most pronounced wind-speed reduction and hydrothermal regulation effects throughout the whole cotton growth period. The relative wind-speed reduction rate ranged from 72.50% to 97.78%, while the relative interaction index (RII) ranged from -0.164 to 0.010 for LI, from -0.063 to 0.166 for RH, from -0.055 to 0.005 for ST, and from -0.066 to 0.012 for TA. Spatially, wind speed under all three shelterbelt grades reached its minimum at 0.5H and then gradually increased with distance from the shelterbelt. TA was relatively low at 0.5H, and the cooling effect was more pronounced at noon. RH was higher at 1H and gradually approached the control level with increasing distance. LI increased with height in the vertical direction, while its horizontal distribution was relatively stable, with only a slight decrease near the shelterbelt. ST at the 10-15 cm soil layer was lower than that at the 0-10 cm layer, and a low-temperature center occurred horizontally at 2H-3H, with ST generally decreasing as the cotton growth period progressed. Discussion: This study indicates that shelterbelt structures with more rows, better belt continuity, richer tree species composition, and moderate porosity are more conducive to improving the farmland microclimate. These findings provide a theoretical basis for optimizing farmland shelterbelt structure and regulating microclimate in agroforestry systems in arid regions.