Nitrogen Fertilization Methods for No-till Cropping of Winter Wheat in Central Montana

Earlier research in Alberta and North Dakota showed that using larger granules of urea compared to regular sized ag-grade urea was a means of increasing crop yield and reducing the potential for denitrification losses by slowing down nitrification of urea nitrogen (N). It is thought that a larger granule urea (up to 10 mm in diameter) that is used in helicopter applications to forestry replanting stands, and in agro-forestry plantations could be used as a broadcast application in no-till cropping systems in the Northern Great Plains (NGP). Recent developments of technology now allow the treatment of different sized granules of urea with both a urease and a nitrification inhibitor (i.e. Agrotain and DCD). This study will investigate the following factors in a factorial field experiment.


16 Apr 2014

2013 Annual Interpretive Summary

The primary way to apply N fertilizer to winter wheat in Montana is to broadcast urea onto the soil surface in the late fall, or early spring. Because urea can quickly convert to ammonia, there can be some initial losses due to volatilization. Once urea moves into soil with precipitation, it is eventually converted to nitrate by soil microbes. The nitrate form of N is readily available for crop uptake, but can be subject to either leaching or denitrification losses if very wet conditions occur during the early spring portion of the crop year. This project was conducted to assess the potential benefits of using various additives or enhanced sources of urea fertilizer compared with regular broadcast applications of urea. These include a urease inhibitor with urea by itself or in conjunction with a nitrification inhibitor. A controlled-release or polymer coated urea (ESN) was also compared with untreated urea. The three years of experiments were conducted on different no-till fields at the Central Agriculture Research Center, Moccasin, Montana. The precipitation received was 21.6, 11 and 13.3 in. in 2011, 2012 and 2013 crop years, respectively. These years were categorized as wet, very dry and dry year, respectively. There were some at-planting (late September) applications of urea. A second treatment received seed-furrow-applied fertilizer as regular urea or as ESN. The third treatment was a mid-row band application of regular urea.

There was a significant effect of precipitation amount and precipitation timing on the relative wheat yields of the various N fertilizer treatments. For example, grain yields in the very dry year were higher from fall-broadcast compared to spring-broadcast urea. Conditions experienced during the three years were not conducive to large volatile losses of ammonia, so significant yield differences were not observed between untreated urea and urea treated with a urease inhibitor. ESN fertilization resulted in a greater yield (32.5 bu/A) than fall-broadcast urea (27.7 bu/A) in the wet year, probably due to reduced denitrification and or leaching losses. However, wheat yields in the very dry year were 25.5 and 31.9 bu/A for ESN and fall-broadcast urea, respectively. The very dry growing conditions likely restricted N release and availability from ESN, compared to urea. There was a benefit of adding a nitrification inhibitor only during the wet year, compared to untreated urea. In summary, the use of ESN or an added nitrification inhibitor are potentially more beneficial in higher moisture years compared to drier years.