Apparent Nitrogen Recovery from Fall‐Applied Ammoniated Phosphates and Ammonium Sulfate Fertilizers

Abstract

Phosphorus fertilizer is frequently fall-applied for corn (Zea mays L.). Diammonium-(DAP) or monoammonium-phosphates (MAP) are the preferred P fertilizers and the N in MAP and DAP is assumed to be available for corn. Our objective was to evaluate the eff ect of application time on availability of ammoniated-phosphate N to the crop in two diff erent environments. In a laboratory study, MAP and DAP at rates of 70 and 140 mg N kg −1 soil were incubated at either 80 or 120% fi eld capacity (FC). Nitrifi cation proceeded rapidly in all treatments, but nitrate levels fell to near zero by 8 wk at 120% FC while remaining above 50% aft er 16 wk at 80% FC. In a 3-yr study at Waseca, MN and Urbana, IL with a factorial combination of three N sources [DAP, MAP, ammonium-sulfate (AMS)], two application times (fall, spring), and two N rates (45, 90 kg N ha −1 ), N rate and application time, but not N source, aff ected grain yield and inorganic soil-N concentrations. Yields were 0.71 and 0.37 Mg ha −1 greater for spring than fall applications at Urbana and Waseca, respectively. Late May soil-N recovery ranged from 31 to 35 and 90 to 100% for fall and spring applications, respectively. It thus appears that only about one-third of N applied in the fall as ammoniated phosphates at typical rates is available to the next year's corn crop in Corn Belt mollisols. Colder, drier fall to spring conditions may increase this proportion, while warmer, wetter conditions would be expected to lower availability.

Managing Phosphorus Loss from Agroecosystems of the Midwestern United States: A Review

“…The consensus among studies was that a yield response of corn or soybean was observed when STP values were very low to low (9-16 mg kg −1 ) and a yield increase to deep placement of P was seldom observed, with a few exceptions [22,24,25,33]. Phosphorus fertilizer application timing and source studies in Illinois have investigated diammonium-phosphate (DAP) or monoammonium-phosphate (MAP) sources and the interaction with application timing (fall or spring) [34]. Spring applications of P resulted in a greater yield response for corn (0.37 to 0.71 Mg ha −1 ) than fall applications [34].…”

“…Phosphorus fertilizer application timing and source studies in Illinois have investigated diammonium-phosphate (DAP) or monoammonium-phosphate (MAP) sources and the interaction with application timing (fall or spring) [34]. Spring applications of P resulted in a greater yield response for corn (0.37 to 0.71 Mg ha −1 ) than fall applications [34]. In Iowa, P application for no-till corn and soybean was evaluated at 20 sites in three years for a fall and spring broadcast application of triple superphosphate (TSP) on soils with STP values ranging between 6 to 29 mg P kg −1 [35].…”

“…Research studies have been reported on 4R's of P management and the impact of tillage systems on crop production and runoff P loss in the central U.S. [28,29,31,32,34,41,[59][60][61]. Many researchers have reported dissolved reactive phosphorus (DRP) to be greater in surface water runoff under no-till systems compared to other tillage systems [41,59,62].…”

The fate of nitrogen of ammonium phosphate fertilizers: A blind spot

“…To overcome this, unrealistically high rates of ammonium phosphate fertilizers are sometimes used in studies. For example, Fernández et al (2010) applied MAP at an order of magnitude greater than typical rates to quantify soil recovery of N of up to 90 kg N ha −1 , equivalent to 172 kg P ha −1 . Yang et al (2023) applied magnesium ammonium phosphate (i.e., struvite) on an N basis in order to compare N losses relative to urea, of up to 150 kg N ha −1 , equivalent to 360 kg P ha −1 .…”

“…For example, the USDA classifies ammonium phosphate fertilizers as a P fertilizer, and thus N from MAP, DAP, and APP is not included in national fertilizer N budgets (Decock, 2014). In the U.S. Corn Belt, a proportion or in some cases all of the ammonium phosphate N is often excluded from agronomic N budgets (e.g., McGrath, 2022; Nafziger, 2018) based on assumptions or limited evidence that there is variable (i.e., weather‐dependent) availability of ammonium phosphate N to the crop (Fernández et al., 2010). As a result, the magnitude and fate of N co‐applied with P of ammonium phosphates are overlooked, constituting an appreciable blind spot in the anthropogenic N cycle.…”