Pushing the limits of fertilizer N recovery in a semiarid climate with improved N management

A common goal of N fertility programs should be to provide for the highest recovery of applied fertilizer N in the targeted crop species consistent with maximum yield and/or economic returns.

IPNI-2016-USA-MT19

22 May 2017

2016 Annual Interpretive Summary


A common goal of nitrogen (N) fertility programs should be to provide the highest recovery of applied fertilizer N in the targeted crop species, consistent with maximum yield and/or economic returns. Previous research in Montana’s semiarid climate has shown that fertilizer N recovery (FNR) can be improved by inclusion of nitrate fertilizer sources, and/or addition of urease inhibitors (such as NBPT) to regular urea (46-0-0). The goal of this research project was to evaluate the impact of fertilizer N management strategies that included a number of different fertilizer N sources in addition to urea on FNR, and yield and grain protein of wheat. In the fall of 2015, winter wheat field trials were established on a dryland field site at the MSU-Central Agricultural Research Center (CARC) near Moccasin, MT. A second location was established on a private farm near Coffee Creek, MT but was lost due to a severe hail storm in 2016. Field trials at CARC consisted of an unfertilized control plus five N application strategies including spring urea, spring urea+NBPT+Instinct II (respectively urease and nitrification inhibitors), spring CAN27TM (27-0-0-10 Ca a mixture of ammonium nitrate and calcium/magnesium carbonate) and spring TropicoteTM (15.5 -0-0-19 Ca), and spring-stem elongation (50%:50% split) TropicoteTM. All fertilizer N sources were applied at three rates (45, 90, and 135 lb N/A), except the split TropicoteTM application (90 lb N/A only).

Fertilizer N recovery was quantified with 15N-enriched fertilizer microplots (24 ft2) embedded inside of larger macroplots (190 ft2). Fertilizer 15N recovery (% applied) at maturity was significantly affected by N management and equivalent to 35%, 47%, 40%, 45%, and 51% for urea, urea+NBPT+Instinct II, CAN27TM, TropicoteTM, and the split TropicoteTM applications, respectively. Winter wheat grain yield was responsive to all fertilizer N application strategies, increasing yield by an average of 39 bu/A over the unfertilized control (19 bu/A). Spring urea applications resulted in modestly lower yields (2.5 to 5.3 bu/A) than the other N fertilizer sources. Grain protein was significantly improved with N fertilization, an average 3.1% over all N sources x rates, relative to the unfertilized control at 8.0% protein. In general, wheat grain protein was more sensitive to N fertilizer sources than yield. The highest grain protein was achieved by applying TropicoteTM as a 50:50 split spring and stem elongation applications. Results from this first year of study demonstrated that NH3 volatilization of urea represents a significant pathway of N loss, and that N fertility programs should consider other N sources/products (including NBPT), and split-applications in order to improve FNR, yield or protein of wheat.

This research project is planned to be conducted for two more field seasons.