A SURVEY OF TREE SIZE IN A PECAN ORCHARD AS A PROXY OF CARBON FLUX, SOIL SALINITY AND TEXTURE

Flood irrigation is contributing to salt accumulations in soils and affecting the growth and development of pecan trees in a 40-year-old orchard in Tornillo, Texas. Our group has worked on the links among irrigation, soil salinity, calcite formation and CO₂ release. This project investigated the direct impacts of irrigation, soil texture and salt buildup on tree health and crop yields. Using satellite images, we selected a small region of the orchard for our study area where a large variation in tree growth was observed. A total of 510 trees were measured for their diameter at breast height (DBH), ranging from 28cm - 55cm. Using allometric formulas for pecan trees, we determined biomass from diameter at breast height. Results showed that trees with greater diameters are most likely to have deeper and heavier root mass, produce more leaves, and pertain the highest mass in above-and-below-ground perennial parts. Additionally, tree size data were plotted against conductivity data from the same coverage, that are over 0.5m, 1m, 3m and 6m soils from EM-38 and EM31. Comparison showed that higher conductivity levels, proxy of clay-dominant soils, correlated with smaller tree diameters. The strongest correlation between conductivity and tree size is observed at 1m. In soils pertaining higher clay concentrations, water infiltration is reduced, thus increasing evaporation rates and resulting in excess salt accumulations that stunt tree growth. It is also possible that clay soils limit root growths and thus primary productivity.