Fate of Tagged Fertilizer Nitrogen Applied to Winter Wheat

Abstract

A field experiment using ammonium sulfate tagged with 7.65 A% 15N was conducted to assess how rates and times fertilizer is applied influence the fate of N applied to winter wheat (Triticum aestivum L.). Bottomless metal boxes were pressed 142 cm into the soil to confine the tagged fertilizer. Treatments, replicated four times, consisted of two rates (50 and 100 kg N/ha) and two application times (fall and spring). Fertilizer N used by the crop and that remaining in the upper 180‐cm of the soil after harvest were measured. Amounts of ammonium‐N and nitrate‐N from the fertilizer in the 0 to 10‐cm layer also were determined.The N balance indicated 9.7 – 10.3 kg N/ha were unaccounted for at the 50‐kg N rate and 19.7 · 23.4 kg, at the 100‐kg rate. Losses did not differ significantly between application times. With 100 kg/ha the crop removed significantly more fertilizer N, and significantly less remained in the soil with spring than with fall applications. The crop used similar amounts of total N in each case, but with the spring applications more fertilizer N but less soil N was taken up. Fertilizer applications caused no priming effect on mineralization of indigenous soil N. Most of the fertilizer remaining in the soil was in the 0 to 10‐cm layer, with no evidence of N moving deeper than 50 cm, so losses were from gaseous loss rather than leaching.Most of the fertilizer N in the 0 to 10‐cm layer of soil after harvest was immobilized, with only 9.6 – 11.5% remaining in inorganic forms. Immobilization was the principal reason for differences in spring and fall applications and for limited leaching. The percentages of NH4+‐N and NO3‐‐N, which originated from the fertilizer were 4 – 8 times the percentages of total N from the fertilizer, so more fertilizer N was in inorganic forms than was the case with indigenous soil N. Since there was a direct relationship between amounts of NO3‐‐N in the surface soil from fertilizer and amounts of N unaccounted for, it was concluded that gaseous losses resulted from denitrification processes.

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

“…The rather small fraction of residual fertilizer found in the soil may be compared with values obtained by other investigators which were either slightly more elevated (Van Cleemput and Baert, 1984;Olson et al, 1979;Strebel et a1.,1980) or markedly higher (Van Cleemput et al, 1981;Leitch and Vaidyanathan, 1983;Olson, 1982;Olson and Swallow, 1984) than our own results.…”

“…The application of fertilizer N did not lead to any increase in soil N uptake by the crop, ruling out the possibility of added nitrogen interaction (ANI) (Jenkinson et al, 1985). Moreover, recent field experiments have shown that the amount of soil-derived N taken up by the wheat crop is not influenced by the time of split application, by the splitting pattern and by the amount of the applied fertilizer (Leitch and Vaidyanathan, 1983;Olson et al, 1979;RecousPeuch Lestrade, 1983;Remy, 1985). Table 5 shows the percent nitrogen derived from the fertilizer (%NDFF) for each split application calculated for the different plants parts, namely, the grain, straw, and crown, the latter including I cm stubble and the larger roots as indicated above.…”

Increased plant nitrogen loss with increasing nitrogen applied in winter wheat observed with15nitrogen

“…Harris et al ( 1994) found more applied fertilizer N loss during a drought year than during a normal one. Olson et al (1979) found 100 kg N ha 1 rate plots had twice as much fertilizer N that was unaccounted for as did the 50 kg N ha' 1 rate plots. They also found most of the fertilizer remaining in the soil was in the top 0-10 cm layer of soil, with no sign of N below 50 cm.…”

“…Webster et al (1986) found 22% of the fertilizer applied in the first year remained in the soil at the end of the growing season; slightly more than half of which was found in the upper 15 cm. Olson et al ( 1979) found 70-75% of the total fertilizer N was in the top 10 cm of the soil profile, while 70-91% was in the top 20 cm. Reddy and Reddy(1993)foundthatthe first 15 cm of the soil profile contained one-half of the residual N. Harris et al (1994) noted that the microbial biomass recovered up to 6% of the applied fertilizer N, while the nonbiomass organic fraction contained 14% of the applied N.…”

“…They also found most of the fertilizer remaining in the soil was in the top 0-10 cm layer of soil, with no sign of N below 50 cm. Olson et al ( 1979) concluded that unaccounted N losses were not due to leaching, but to gaseous losses. Carter et al (1967) concluded N was lost in the gaseous form throughout the year, but was more intense in the warmer months.…”