Effect of rate and source of N fertilizer on yield, quality and N recovery of bromegrass grown for hay

Abstract

Field experiments were conducted at two locations in north-central Alberta to determine the effect of N rate and source on dry matter and protein yield, concentration of protein and NO₃—N, recovery of applied N and N use efficiency of smooth bromegrass (Bromus inermis L.) grown as hay. Ammonium nitrate was applied annually for 3 years at 0, 50, 100, 150, 200 and 300 kg N ha⁻¹, and once initially in the first year only at 150 and 300 kg N ha⁻¹. Urea was applied annually at 50 and 100 kg N ha⁻¹. The N fertilizers were broadcast in early spring. At both locations, total dry matter yield (TDY = cut 1 + cut 2) increased with increasing N rate up to the highest rate (300 kg N ha⁻¹) applied. Maximum yield of the first cut was achieved with 150 kg N ha⁻¹ in four of the six site years. The effect of initial single applications of N lasted for only 2 years and was greatest in the first year. Over the 3-year period, annual applications of N generally produced higher forage yields than the equivalent amounts of N applied in single applications. Protein concentrations and protein yield increased with increasing N rate at both locations, but at one site protein concentration decreased with the first increment of applied N before increasing with additional N increments. Concentration of NO₃—N potentially toxic to livestock (>2.3 g kg⁻¹) occurred with rates of 200 and 300 kg N ha⁻¹ in the first year and with 300 kg N ha⁻¹ in the following years at both locations. Ammonium nitrate was slightly more effective than urea in increasing TDY, protein yield, N use efficiency and recovery of applied N in forage.