Soil chemical properties after long‐term nitrogen fertilization of bromegrass: Source and time of nitrogen application

Abstract

Abstract Two field experiments were conducted on a Thin Black Chernozemic soil in south‐central Alberta to determine the effect of source and time of application of N to bromegrass on soil chemical properties. In the first experiment, the effects of four times of application (early fall, late fall, early spring and late spring) and two N sources (urea and ammonium nitrate) applied at 112 kg N/ha for 11 years were determined. In the second experiment, four N sources (ammonium sulphate ‐ A.S., urea, ammonium nitrate ‐ A.N. and calcium nitrate ‐C.N.) and two N rates (168 and 336 kg N/ha) were applied annually in early spring for 5 years. In the first experiment there was more accumulation of NO3‐N in soil with A.N. than urea with fall and late spring applications, but there was little or no accumulation of NO3‐N below 60 cm. Considering the 60‐cm depth, only 0.9 to 13.8 % of the cumulative N applications (1232 kg N/ha) was found as NO3‐N. The accumulation of NH4‐N was small and was generally greater with A.N. than urea in the surface layer. Extractable P in the 0–30 cm depth was approximately one‐half in the N‐treated plots as compared to the control plots. Extractable Ca, Mg, and K concentration was decreased in the shallow depths by N applications, but none of the selected parameters indicated substantial differences among time of application or between A.N. and urea. The total C concentration was greater in the 0–5 cm layer on the N‐fertilized plots than the control plots. In the second experiment, the 168 kg N/ha rate gave results much like those obtained in the foregoing experiment but the 336 kg N/ha rate exhibited greater influence due to N source. Of the 1680 kg N/ha applied during a 5‐year period the apparent residual fertilizer N as NO3‐N in the 0–60 cm of soil was 386, 515, 797, and 1252 kg N/ha for A.S., urea, A.N. and C.N., respectively. It was noteworthy that the NO3‐N accumulation did not extend below the 60 cm depth. The A.S. treatment produced the highest concentrations of NH4‐N, extractable P and total C and N and lowest concentrations of extractable Ca, Mg, and K in the 0–5 cm layer and in some cases this influence extended into lower layers as well. For both experiments, the changes in the extractable NH4‐N, P, Ca, Mg, and K were in most instances correlated with soil pH changes which occurred after the N applications. In summary, time, source and rate of N application influenced soil contents of NO3‐N, NH4‐N, extractable P, Ca, Mg, and K, and total C and N.