Long‐term 4R nitrogen management in dryland wheat–fallow systems

Abstract Several short‐term studies have investigated 4R (right source, rate, time, and place) N management for dryland wheat ( Triticum aestivum L.) production and profitability, but few long‐term studies exist in the United States or abroad. This study evaluated long‐term impacts of several aspects of 4R N management on dryland hard red wheat yield, protein, and return to N. Experiments were conducted at Nephi and Blue Creek, UT, during 1995–2007. Fourteen N treatments evaluated performance of starter fertilizer, fall applications of anhydrous ammonia (AA) with and without nitrapyrin (AA‐Nitrapyrin and AA, respectively), and several split applications in the fall and spring. Across years, winter wheat required N to increase yield, protein, and returns at both sites. Applying 56 kg N ha −1 as AA in the fall usually produced the best return to N compared to other N treatments. Starter N (6 kg N ha −1 ) at fall planting rarely increased yield, protein, or returns at either site. Across both sites, nitrapyrin increased mean annual yield by 0.6 Mg ha −1 and mean return to N by $150 ha −1 . Spring application of N was rarely required and only increased yield in 13% of the years. Results indicate that nitrapryin is often needed with fall AA applications to optimize yield and returns and that starter N or extra N in the spring are rarely economical in dryland wheat in Utah and possibly the greater Intermountain West. Further, N rate had the most influence among 4Rs on wheat production and should be the focus of future efforts to improve 4R stewardship.