|KAWAKAMI, E - University Of Arkansas|
|OOSTERHUIS, D - University Of Arkansas|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/18/2011
Publication Date: N/A
Interpretive Summary: Urea is the most recommended foliar nitrogen source, due to its relatively low toxicity, quick absorption, and low cost; however, reports of yield improvement with foliar application of urea are inconsistent. Because some portion of the urea sold to farmers contains additives to limit nitrogen losses in the soil, the objectives of this research were to study the effect of foliar urea application, with and without an additive, on the yield of field-grown cotton. Various soil urea application rates were utilized, and 11.2 kg of foliar urea nitrogen was applied per hectare (with and without additives). There was a clear advantage of including an additive in foliar applied urea, where two applications of foliar urea with NBPT can supply 25% of the full recommended soil rate. This would mean that farmers could reduce input costs by applying substantially less urea to the soil and still obtain optimal yields with a small input of foliar applied urea with N loss inhibitors later in the season.
Technical Abstract: Urea is the most recommended foliar N source, due to its relatively low toxicity, quick absorption, and low cost. However, in the literature reports of yield increments with foliar urea application are not consistent. The objectives of this research were to study foliar urea assimilation in cotton and to test the effect of the urease inhibitor N-butyl thiophosphoric triamide (NBPT) in cotton foliar urea application. The study was conducted at the University of Arkansas Cotton Branch Station at Marianna. Treatments consisted of: (T1) full recommended N soil rate with no foliar N application; (T2) 75% of recommended N soil rate with no foliar application; (T3) 75% of recommended N soil rate with two foliar urea applications; (T4) 75% of recommended N soil rate with two foliar urea plus NBPT applications. Each foliar urea application was calculated to supply 11.2 kg of N per hectare. The results showed that treatment T4 had a significantly higher seedcotton yield compared to T3, indicating a positive effect of adding NBPT to foliar urea application. No yield differences were observed between treatments T3 and T2; thus application of foliar urea had no effect on seedcotton yield. Yields of the treatments T4 and T1 were not statistically different, showing that two applications of foliar urea with NBPT can supply 25% of the full recommended N soil rate. Three distinct hypotheses could explain these results: (1) addition of NBTP improved the uptake and assimilation of foliar applied urea; (2) NBPT itself improved the physiology of cotton plants; (3) application of foliar urea with NBPT helped the uptake of the portion of urea that was drift to the soil surface. Currently, these hypotheses are being tested in a growth room study at the Arkansas Agricultural Research and Extension Center.