DRY-MATTER YIELD AND NITROGEN RECOVERY FROM BROMEGRASS IN SOUTH-CENTRAL ALBERTA AS AFFECTED BY RATE OF LONG-TERM NITROGEN APPLICATIONS

A field experiment was conducted on a Thin Black Chernozemic soil at Crossfield in south-central Alberta to determine the effect of long-term application of ammonium nitrate on dry matter yield (DMY), protein yield (PY), protein concentration, N use efficiency and recovery of N applied to bromegrass (Bromus inermis Leyss.) grown for hay. The N fertilizer was applied at 0, 56, 112, 168, 224, 280, and 336 kg N/ha in early spring of every year from 1968 to 1986. The DMY increased with applied N achieving a maximum at 224 kg N/ha, though the rate of increase in DMY from N fertilization was greatest with the first two increments applied (i.e. 56 and 112 kg N/ha). Protein yield and protein concentration maximized at 336 kg N/ha. The DMY was greater with a single-cut system than with a double-cut system. The DMY varied from year to year, but it was not closely related to precipitation received during the April to August period (R2 = 0.37). However, in some years low DMYs were associated with low precipitation, or a lack of timeliness of rainfall, or a combination of both. The N use efficiency and % N recovery in bromegrass decreased with increasing N rate. The maximum DMY calculated from quadratic regressions ranged from 3.16 t/ha to 7.91 t/ha, and maximum N Tate ranged from 205 to 258 kg N/ha. In summary, DMY, PY, and protein concentration increased, and N use efficiency and % N recovery decreased with increasing N rate in this 19-year study.