/AnMtgsAbsts2009.54993 The Influence of Nitrogen Application Time and a Urease Inhibitor On Winter Wheat Yield.

Tuesday, November 3, 2009: 3:00 PM
Convention Center, Room 319, Third Floor

Nathan Slaton1, Richard Norman1, Russell DeLong2, Bobby Golden2, Trenton Roberts2 and Jason Kelley3, (1)Crop, Soil, and Environmental Sciences Department, Univ. of Arkansas, Fayetteville, AR
(2)Univ. of Arkansas, Fayetteville, AR
(3)Cooperative Extension Service, Univ. of Arkansas, Little Rock, AR
Abstract:
Nitrogen (N) is generally the most-limiting nutrient for soft red winter wheat (Triticum aestivum L.) production in Arkansas. Late winter environmental conditions vary annually and may influence N loss from surface-applied urea. Our objectives were to evaluate how N application time influences wheat yield and whether wheat yields benefit from urea treated with the urease inhibitor N-(n-Butyl)-thiophosphoric triamide (NBPT). A preliminary study was conducted in 2007 with four N application times (10 February - 25 March) comparing 84 kg N ha-1 from urea and urea+NBPT. In 2008, tests were established at two sites and three N-fertilizers sources (urea, urea+NBPT, and urea+NBPT+dicyandiamide) were applied at 84 kg N ha-1 and compared to 140 kg N ha-1 as urea+NBPT and a no N control. In 2007, wheat yields, averaged across N application times, were 243 kg ha-1 greater for urea+NBPT than urea (P = 0.0417). However, the non-significant interaction suggested that wheat yields were greater for urea+NBPT only when N was applied 25 March. In 2008, wheat yield was affected (P <0.05) by the N application time × N source interaction. Wheat receiving 140 kg N ha-1 as urea+NBPT produced greater yields than all N sources applied at 84 kg N ha-1 when N was applied 15 February or 1 March. Wheat yields were uniform among all N sources, regardless of N rate, when N was applied 15 March and 1 April. Comparing N application dates within each N source applied at 84 kg N ha-1 showed that wheat yields were generally equal when N was applied from 15 February through 15 March, but occasionally declined when N was delayed until 1 April. When 140 kg N ha-1 was applied yields were greatest for the 15 February application date, intermediate for the 1 and 15 March application dates, and lowest for N applied on 1 April. Results suggest that loss of fertilizer N via NH3 volatilization, leaching, and denitrification were low and urease and/or nitrification inhibitors provide little benefit for wheat grown in Arkansas. A sufficient rate of N should be applied beginning in mid-February to maximize wheat yield potential.