Root Turnover Increases With Fertilizer Rates in Pecan Seedlings.

Pecan is an important nut crop native to the United States. In the last decade, increased global demand for pecans as both a health food and a desirable import to China has led to more pecan orchards being planted. Increased production has led to an increase in the overall amount of nitrogen (N) fertilizer applied in the orchards. Nitrogen, when not applied in the correct amount, can have undesired consequences on tree physiology as well as on the environment. Nitrogen fertilizer is mainly taken up by fine roots, and a healthy root system upon establishment usually leads to greater yields in the future. However, an over-application of N fertilizer may reduce root production and/or accelerate root death. The objective of the study was to observe seasonal root production and root turnover of pecan seedlings exposed to five N-application rates: 0N, 0.25N, 0.5N, 1N, and 2N, where N = 229.5 kg/ha of (NH₄)₂SO₄, the recommended application rate for pecan in Texas. The minirhizotron method was used to non-destructively observe roots through time to determine what effects, if any, fertilizer treatments have on root production and lifespan in pecan seedlings. Preliminary data showed that, at a depth of 14-28 cm, root lifespan decreased with increased N-application rates, while standing root length remained similar among lower fertilizer treatments and decreased in the 2N treatment. The lack of a reduction in standing root length concomitant with decreases in root lifespan suggests that up until the recommended application rate an increase in new root production counteracted the reduced root lifespan, however, when the trees were over-fertilized (2N) new root production could not compensate for the decrease in root lifespan, thus leading to an overall reduced amount of standing root length.