Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 17, 1996
Publication Date: N/A
Interpretive Summary: Conservation production systems continue to increase as an effective alternative system for reducing soil erosion and increasing soil water storage. However, these systems sometimes exhibit suppressed yield because of increased N-losses through leaching, denitrification and immobilization. Nitrification inhibitors have shown to be effective in reducing these losses. Field studies were conducted to determine the effectiveness of tw nitrification inhibitors (nitrapyrin and DCD) and their placement with urea on the mineral nitrogen status and their effect on grain yield and grain nitrogen under no-till winter wheat production in the Southern Great Plains. Experimental results indicated that fall applied urea treated with DCD reduced nitrogen losses and retained most of the applied nitrogen in the top 4 inches of the soil surface. However, urea treated with DCD and placed 3 to 4 inches below soil surface in the fall increased soil nitrogen nto that of broadcast of urea. Increased availability of nitrogen with DCD-urea and placed below the surface resulted in a 31% increase in grain yield when compared with urea broadcast. Nitrogen is a sizable portion of production cost and losses of nitrogen may result in reduced yield. Addition of nitrification inhibitors to urea not only increase nitrogen availability to crop but also minimizes losses to groundwater and to the atmosphere.
Technical Abstract: Fall applied urea treated with nitrification inhibitors (NIs) for winter wheat may reduce N losses in soils from denitrification and leaching by maintaining applied urea in ammoniacal form. A field study was conducted from 1990 to 1994 on Renfrow silt loam near El Reno, OK, to evaluate dicyandiamide (DCD) and nitrapyrin (NP) compounds and their placement effect in reducing nitrification of urea-N in soils. Urea at the rate of 60 kg N ha-1 treated with or without NIs (NP 0.56 kg ha-1 or DCD 10% N) was placed 3 to 4 cm below the seed at seeding (BL) or broadcast (BR) same day after seeding. Soil samples were collected from 0 to 30 cm in the fall and spring. In the 0 to 10 cm zone DCD or NP treatments significantly reduced nitrification in BL plots in the fall as compared to BR plots. Soil mineral N concentration below 10 cm were higher in all N treatments than the control. Ammonium concentration in the top 10 cm at spring sampling was ssignificantly lower than fall. However, the spring differences among urea with NIs with either placement were similar and higher than BR urea without NI. Ammonium % of the total inorganic-N was greater in both fall and spring when urea treated with NIs. Urea treated with NIs increased grain yield from 7% to 31% when compared with BR without NI. Grain yield was highest with DCBL (31%) followed by DCBR (26%), and NPBR (24%) to that of BR without NI. These results suggest that deep placement of urea treated with DCD or NP under conservation tillage in the Southern Great Plains has the potential to reduce nitrification and increase N availability, and improve grain yield as compared with surface broadcast urea without NIs.