|KAWAKAMI, E - University Of Arkansas|
|OOSEERHUIS, D - University Of Arkansas|
Submitted to: Arkansas Experiment Station Research Series
Publication Type: Experiment Station
Publication Acceptance Date: 3/31/2011
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, reports of yield improvements 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. A field study was conducted at the University of Arkansas Cotton Branch Station at Marianna and a growth chamber study was conducted in Fayetteville. 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. Seedcotton yield improvements were observed with addition of NBPT to foliar urea in 2009 but not in 2010. The growth chamber study showed that the addition of NBPT to foliar urea application decreased urease activity and it showed a trend for increasing leaf urea content. It is hypothesized that addition of NBTP improved yield through increased uptake and assimilation of foliar applied urea by altering the physiology of cotton plants.