Foliar Fertilization of Cotton

Transcription

1 Foliar Fertilization of Cotton Bill Robertson, Leo Espinoza, and Brian Weatherford 1 RESEARCH PROBLEM Yield responses from supplemental soil or foliar nitrogen (N) applications are often erratic. The boll load or lack thereof can be an important factor in determining the positive outcome from foliar feeding (Oosterhuis and Bondada, 2001). Petiole sampling can give an accurate indication of the nutritional status of the plant. However, petiole sampling does not give the user any indication of the boll load or the impact of the boll load on plant development. The success rate of increasing yields and obtaining a return on investment would likely improve if greater efforts were made to evaluate boll load as well as the nutritional status in making supplemental foliar-n applications. BACKGROUND INFORMATION The Cotton Nutrient Monitoring (CNM) program in Arkansas was established to provide a tool producers could utilize to avoid over-fertilization of cotton. As prices of fertilizer have increased and producers better understand the role of N fertilization, the occurrence of over-fertilization is much more rare. With the onset of boll weevil eradication and the increased use of Bollgard technology, fruit retention rates often are very high at first flower. This situation presents a challenge to the producer to meet the enormous demands for water and nutrients after flowering begins to avoid significant shed of fruit. Utilizing the COTMAN program in conjunction with the CNM program, producers can better evaluate and predict the demand of the boll load on the plant in relation to the N status in making decisions on the need for supplemental N fertilization. 1 Extension agronomist - cotton, extension agronomist - soils, and agronomy technician, respectively, Cooperative Extension Service, Little Rock. 94

2 Summaries of Arkansas Cotton Research 2002 RESEARCH DESCRIPTION The study was conducted in producer fields with treatments being replicated four times over a period of five years. Petiole samples and COTMAN data were collected on a weekly basis beginning near match-head square (MHS). Foliar products were applied by ground beginning the second week of flowering and continued on a set schedule. Treatments included an untreated control (UTC), CoRoN (25-0-0), and a 23% urea solution (Table 1). Plots were harvested with the producer s picker or a plot picker and samples were taken for determining fiber quality. Lint fraction was determined from ginning hand harvested grab samples on a laboratory gin RESULTS In 1999, boll load resulted in NAWF values tracking parallel to the Target Development Curve (TDC) (Fig. 1). Trend lines from the CNM indicated deficient N status was impending prior to or at the third week of flower or sample period 5. A significant yield response was observed with foliar feeding. The CNM program recommended foliar N one week after treatment was initiated. The following year the boll load and growing conditions did not result in NAWF values tracking parallel to the TDC (Fig. 2). Trend lines from the CNM did not predict a deficient N situation until near sample period 7. Foliar feeding did not result in a yield response although a recommendation was made to apply foliar N by the CNM program. During the course of this study with foliar N treatments being applied regardless of boll load and nutritional status, CoRoN numerically out-yielded the untreated control in four of the five years by an average of 32 pounds. The 23% urea treatment contained extra application expenses and was numerically better than the untreated control in three of the five years by an average of only 17 lb/acre (Table 2). PRACTICAL APPLICATION Numerical yield responses (averaging lb lint/a) were obtained with foliar N fertilization without regard to boll load or petiole N status but may not be cost effective. Utilizing COTMAN to evaluate the demands placed on the plant during boll fill, coupled with knowledge of the nutritional status of the plant, can result in significant yield improvements. When boll retention is high and NAWF tracks parallel to that of the TDC, significant yield responses to foliar feeding are often observed. LITERATURE CITED Oosterhuis, D.M. and Bondada, B.R Yield responses of cotton to foliar nitrogen as influenced by sink strength, petiole, and soil nitrogen. Journal Plant Nutrition 24:

3 AAES Research Series 507 Table 1. Rates and timings of foliar feed products. Week of flowering Treatment UTC CoRoN 1 gal/acre -- 1 gal/acre 23% urea solution 3 gal/acre 3 gal/acre 3 gal/acre Table 2. Lint yield means from foliar feeding treatments, 1998 to 2002, regardless of boll load. Lint yield Treatment year avg (lb/acre) UTC CoRoN % urea solution LSD (0.05) NS 83 NS NS NS NS 96

4 Summaries of Arkansas Cotton Research 2002 Fig. 1. COTMAN growth curves (top) and Cotton Nutrient Monitoring program output (bottom) in

5 AAES Research Series 507 Fig. 2. COTMAN growth curves (top) and Cotton Nutrient Monitoring program output (bottom) in