Project Summaries

08-451  Project Manager: P. F. O'Leary


Megha N. Parajulee, Texas AgriLife Research

The relationship between nitrogen fertilizer application in cotton and subsequent changes in lint and seed yield is well-understood. However, little research has been done to evaluate the role of nitrogen fertility in arthropod population abundance in cotton, particularly in a high yield potential subsurface drip irrigation production system. Previous work suggests that there exists a non-linear relationship between soil nitrogen availability and cotton aphid abundance in cotton. However, interaction between plant-available soil nitrogen and moisture ultimately determines arthropod population dynamics, at least for the cotton aphid. Also, there is a lack of information on plant parameter values with respect to varying rates of available soil nitrogen in cotton production. A multi-year comprehensive field study has been ongoing to examine the effect of soil nitrogen (residual nitrogen plus applied nitrogen) on cotton agronomic growth parameters and arthropod abundances under a drip irrigation production system. Fixed-rate nitrogen application experimental plots, previously established and fixed for five years prior to the initiation of this project in 2008, consisted of five augmented nitrogen fertility levels (0, 50, 100, 150, and 200 lb/acre) with five replications. Each year, soil in each experimental plot was sampled for residual nitrogen analysis immediately prior to planting or before treatment deployment. Rates of applied N exceeding 100 lb/acre resulted in higher residual nitrogen detection during the following season. However, variation in residual nitrogen did not significantly affect early plant growth (plant height, root length, or leaf area). Increased N levels corresponded to increased leaf chlorophyll content, but leaf chlorophyll content was generally consistent across nitrogen levels exceeding 100 lb/acre. Aphid abundance was significantly lower in zero N plots versus other plots every year when cotton aphids were present. In 2010, aphid populations surpassed economic threshold in all N-augmented plots, whereas aphids remained below 50/per leaf, except for 1 week, in zero-N plots. Higher rates of applied N (>100 lbs/A) resulted in significantly higher leaf chlorophyll content compared to that in lower or zero N plots. No arthropod populations develop in 2011 due to extreme temperature and drought. A strong correlation was found between leaf chlorophyll content and lint yield. Nitrogen fertility level influenced fruiting profile and boll maturity. Plants ceased setting additional squares in zero and 50-lb N plots 2 wk into flowering while higher N plots were actively producing squares. Averaged over four years (2008-2011), the zero-N treatment produced the lowest yield (912 lb/acre) and yield increased curvilinearly with each additional 50 lb N added, with highest average lint yield occurring in 150 lb N/acre treatment (1,288 lb/acre). Although two synthetic pyrethroid applications were applied to all treatment plots during August 2012 to encourage a cotton aphid buildup, observed aphid numbers remained low for 2012. This year's arthropod sampling then focused on community composition and relative numbers of other cotton pest and beneficial species among the five nitrogen treatments. Nitrogen augmentation rates significantly influenced all agronomic parameters evaluated in this study, most with curvilinear relationships. These relationships observed in 2012 are similar to what have been observed in previous years.


Project Year: 2012

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