N AND P FERTILIZATION OF BROMEGRASS IN THE DARK BROWN SOIL ZONE OF SASKATCHEWAN

Abstract

A 5–yr study was conducted on a Dark Brown loam at Scott, Saskatchewan to determine the effect of rate of ammonium nitrate-N (34–0–0) and urea-N (46–0–0) on bromegrass (Bromus inermis Leyss.) production and quality, N recovery and N use efficiency when the N was applied either annually or as a single application at the start of the experiment. The effect of phosphorus (P) on the above listed parameters was also assessed. Each N source was applied at once-only rates of 0, 100, 200, 400, and 800 kg ha−1 and annual rates were 0, 50, 100 and 200 kg ha−1. Phosphorus was applied in 1976, 1979 and 1981 at 100 kg ha−1 P2O5. Forage dry matter was positively related to precipitation received in April–June (r = 0.91**) and in April of the crop year plus the previous September (r = 0.80**). Dry matter response to N rates generally increased at a decreasing rate in early years but linearly in later years. Over the first 4 yr, annual applications of N resulted in up to 37% more dry matter than the single applications. Dry matter production was generally greater when ammonium nitrate was applied than when urea was used; these differences were more consistent at medium N rates. Dry matter was increased by P only when N was applied. Nitrogen concentration in forage was directly related to N rate in years of good precipitation, was greater in dry than wet years, and when N was applied annually, but was unaffected by N source. Phosphorus fertilization increased P concentration of forage but heavy dry matter production reduced P concentration. Annual N applications increased P concentration in forage only in the first year and N source had no effect. Toxic concentrations of NO3–N in the forage occurred in the first year only at N rates [Formula: see text] and were directly related to the amount of N applied. Except for the 800 kg ha−1 N rate in the second year, there were no further indications of NO3–N toxicity. Accumulated N use efficiency decreased linearly with increasing N rate and was greater for ammonium nitrate than for urea except at very high N rates. Accumulated N recovery was inversely related to N rate for the single method of application but unaffected by N rate applied annually. Over the first 4 yr, accumulated N recovery was greater for the single application at low N rates, but was greater for annual applications of N at high N rates. P fertilization increased N recovery.Key words: N source, bromegrass, N recovery, yield, quality, application method