Urea Nitrogen Budget for a Subarctic Agricultural Soil

Abstract

Urea is the predominant form of fertilizer N used in Alaska. However, little information is available on the N‐recovery efficiency (NRE) or the ultimate fate of urea‐N in subarctic soils. This study was conducted to determine the NRE and the ultimate fate of urea‐N applied in the spring for barley (Hordeum vulgare L.) production in interior Alaska. Urea and Ca(NO3)2 were applied at 100 kg N ha−1 and either incorporated into or left on the soil surface in each of three cropping years. Also, 15N‐labeled urea was applied to small plots. Ammonia traps and soil and plant samples were used to track the form and movement of the applied N. Ammonia volatilization losses were negligible. Deep soil samplings indicated negligible leaching of N. The NRE, as determined by the difference method, was estimated to be about 60% for urea and 73% for Ca(NO3)2. By the isotope dilution method, NRE for urea was calculated to be about 41%. An apparent added nitrogen interaction (ANI) accounted for an additional 16.5%. Approximately 43% of the applied urea‐N was recovered in the soil organic matter at the end of the season, 1% remained in the soil as inorganic N, and 15% was unaccounted for and assumed lost through denitrification. Grain yields did not differ due to N source or placement, but total plant N uptake was greater from the Ca(NO3)2 than from the urea source. Nitrogen placement did not affect N uptake. Fertilizer N cycling in this subarctic soil did not differ greatly from fertilizer N cycling in more temperate regions.

Effects of nitrogen fertilizer on dry matter and nitrogen yields of herbaceous legumes in interior Alaska

“…Despite the dry conditions, winter vetch, flatpea., and faba6ean each produced more than 3 t ha-t when weeds were controlled, so these species should be studied further despite the apparent lack of yield stability. Sparrow et al (1993) reported markedly higher herbage yields for fababean and field pea at Delta Junction. In that study, early season rainfall (May to June) was 132-179% higher than average.…”

“…En plus des espdces prometteuses ddjir observ6es auparavant, le trifle dAlexandrie, le trdfle sagittifoli6, la vesce d'hiver et le pois de (Sparrow et d. 1993). All species studied performed well on the neutral soil (avg.…”

Impact of Agricultural Land‐use Change on Carbon Storage in Boreal Alaska

“…Soil textural classes ranged from loamy sand to silt loam, with most soils being classified as sandy loams (Table 2). Clay content averaged 8.7%, and did not exceed 20%, which is typical for interior Alaska (Knight & Sparrow, 1993; Van Cleve et al , 1993). A weakly acidic to neutral pH was measured in the top 20 cm of the mineral soils, with no significant differences among sites.…”

Dissipation of Bromide and Metribuzin Affected by Tillage and Crop Residue Management in Subarctic Alaska

“…In addition, leaching is minimal at this time of year in interior Alaska. Knight and Sparrow (1993) found negligible leaching of fertilizer N in a barley cropping system over the course of three growing seasons. Leaching may also be minimal because evapotranspiration exceeds precipitation between May and July, so soil water reserves are rapidly depleted (Braley, 1980;Sharratt, 1998).…”

“…In interior Alaska, Knight and Sparrow (1993) found that fertilizer N is vulnerable to movement within a soil that is subjected to conventional tillage. Leaching of N, however, was negligible as NO 3 and NH 4 were not detected below a depth of 0.45 m in the soil profile over the course of three growing seasons.…”