Effect of Nitrogen Application on Pecan Above Ground Physiology and Root Traits

The United States pecan industry is experiencing a rapid acreage increase. Many growers believe high rates of nitrogen (N) accelerate tree development and increase yields; however, a high rate of N application may not be cost-effective and can be harmful to the environment. The aim of this project was to evaluate the effect of N application rate on young pecan seedling performance as measured through photosynthesis, water use efficiency (WUE, defined as the ratio between net assimilation rate and transpiration rate), growth, and to determine if and when N application rates had an effect on root system, especially specific root length (SRL) and root length density (RLD) following five N application rates (0x, 1/4x, 1/2x, 1x, and 2x, where x corresponded to the recommended rate, as reported by Texas AgriLife Extension). Soil sampling was performed five days after N application and continued throughout two growing seasons for evaluation of soil nitrate and SRL and RLD. Diameter of the seedlings was measured at two locations on each tree throughout both years of the experiment. Gas exchange was measured every 3-4 weeks using an infrared gas analyzer. Results showed that soil N was higher in the 1x and 2x treatments than in the other treatments. However, N treatment did not affect amount of WUE, net photosynthesis rate, trunk growth, SRL, or RLD. Therefore, it is possible that the most effective rate of N application for young pecan seedlings is likely much lower than recommended rates.