Recovery of Nitrogen and Phosphorus after 17 Years from Various Fertilizer Materials Applied to Crested Wheatgrass

Information is limited regarding duration of residual effects from different N fertilizer sources upon herbage production and N and P recovery. A field experiment was conducted for 17 years on a Temvik silt loam (fine-silty, mixed Typic Haploborolls) at Mandan, N.D., to study the effects of 5 years of N and P fertilization upon the production of crested wheatgrass [Agropyron desertorum (Fisch. ex Link), Schult.) and upon N and P recovery during and after fertilization. Fertilizer rates were 0, 90, and 180 kg N/ha from ammonium nitrate, ammonium sulfate, calcium nitrate, or urea, and 19 or 39 kg P/ha. Dry matter production and fertilizer N recovery in aboveground herbage production were least for urea, especially at 180 kg N/ha with P, but there was little difference between the other N sources. Cumulative 17-year dry matter production was increased about 15 Mg/ha with 90 kg N/ha, and 20 to 25 Mg/ha with 180 kg N/ha. Residual effects from calcium nitrate persisted a few years longer than from other N sources and averaged 58 % recovery of N compared to 48 % for urea. Fertilizer P recovery varied from 26.8 % when P was applied with calcium nitrate to 18.2 % with ammonium sulfate. Cumulative dry matter production was increased 4 to 5 Mg/ha in 17 years by P fertilization. Fertilization with N doubled recovery of fertilizer P. Soil pH in the surface 150 mm of soil, 5 years after fertilization ceased, varied from 6.5 with calcium nitrate to 5.5 with ammonium sulfate. Fertilizer N recovered after fertilization ceased could largely be accounted for by depletion of inorganic soil N pools that had accumulated during the fertilization period. While ammonium sulfate was being applied, inorganic N accumulated primarily as exchangeable ammonium in the surface 0.3 m. Little inorganic soil N accumulated from urea application, suggesting that much N was lost by volatilization. From all sources, 70 to 160 kg fertilizer N/ha was still immobilized in the root biomass, 5 years after fertilization ceased.