Reed Canarygrass Yield, Crude Protein, and Nitrate N Response to Fertilizer N

Reed canarygrass (Phalaris arundinacea L.) is a high-yielding, cool-season forage that responds to high rates of N. Forage growers need additional information on N management strategies for improving production without inducing negative consequences. Three, 1-yr studies were conducted from 1992 to 1994 on a Webster clay loam (fine-loamy, mixed, superactive, mesic Typic Endoaquolls) in southern Minnesota to determine the optimum rate of N and the effect of split applications of N on forage yield, crude protein (CP), forage nitrate N concentration, and residual soil nitrate (RSN). Ammonium nitrate was topdressed to established stands of reed canarygrass at rates from 0 to 600 lb N/acre. Single, early-season (April or May) applications were compared with split applications (early-season + after first cutting). Total dry matter (DM) production was optimized by N rates totaling 250 to 300 lb/acre in 1992 and 1993 and by only 150 to 200 lb/acre in the lower yielding year, 1994. Split applications of N did not further improve DM yields above those obtained with the optimum N rate applied as a single, early-season treatment. Forage nitrate N concentrations ranged from 40 to 7230 ppm (>3000 is considered dangerous) and were greatly influenced by rate and time of N application and growing season conditions. Residual soil nitrate did not accumulate until the agronomic optimum N rate was exceeded by 100 lb/acre. Results from this study indicate that DM yield and CP percentage of reed canarygrass can be optimized with high rates of N applied early in the season, but undesirably high concentrations of nitrate N in the forage should be expected when optimum rates of fertilizer N are exceeded. Research QuestionReed canarygrass is a high-yielding cool-season forage that responds to high rates of N. Some forage growers and livestock producers have questioned the effect that high N rates have on crude protein levels and nitrate N concentrations in the forage. Studies were conducted to determine the optimum rate of N and the effect of split applications of N on forage yield, crude protein (CP) percentage, forage Nitrate N concentration, and residual soil nitrate (RSN). Literature SummaryPrevious research has shown very high yields of reed canarygrass with annual N rates up to 300 lb/acre. Although some studies have investigated the effect of N rates and timing on dry matter (DM) yield, few studies have compared their effect on CP percentage, nitrate N concentrations of the forage, and RSN. Nitrate N can accumulate in the forage when high rates of N are used. Concentrations of nitrate N greater than 0.30% (3000 ppm) can be considered hazardous for livestock while concentrations less than 0.15% (1500 ppm) are generally considered safe. Study DescriptionThree 1-yr studies were conducted from 1992 through 1994 on established stands of reed canarygrass grown on a Webster clay loam in south-central Minnesota. Nitrogen was applied as ammonium nitrate at annual rates ranging from 0 to 600 lb N/acre. A single, early-season (April) application was compared with applications split between April and after the first cutting (June). Three cuttings were taken each year and were analyzed for total Kjeldahl N and nitrate N. Soil samples were taken in 1-ft increments from the 5-ft profile in November and were analyzed for nitrate N. Applied QuestionsHow were total DM yield and yield distribution affected by rate and time of N application? Total DM yield was optimized with N rates totaling 250 to 300 lb/acre in 1992 and 1993 and by only 150 to 200 lb N/acre in the lower yielding year, 1994. When the optimum total N rate was applied as a single treatment in April, yields were not improved further with split applications equaling the same total rate of N. Based on these data and recognizing weather variability, a realistic N recommendation to optimize reed canarygrass DM yield on fine-textured soils of the region would be to apply no more than 200 lb N/acre in April. If ideal weather resulted in very high first cutting yields, supplemental applications of 50 to 100 lb N/acre would be warranted. The single, early season application, however, did skew the distribution of annual yield toward the first cutting (52%) compared with 31% for the second cutting. Split-applying N at an optimum rate resulted in equal yield distribution between the first cutting (39%) and the second cutting (38%) for the 3 yr. Thus, split application of N may be desirable for producers desiring greater summer production to support livestock grazing operations. How was crude protein affected by N application? Averaged across cuttings, CP was increased over the control by 4.4, 5.1, and 3.3 percentage points by the optimum N treatment in 1992, 1993, and 1994, respectively. Crude protein concentration in the fertilized forage peaked at 23.4% for the second cutting in 1993, but when averaged across years was 18.0, 18.1, and 13.0% for the first, second, and third cuttings, respectively. These high CP concentrations demonstrate the ability of fertilized reed canarygrass to take up N and serve as a high protein forage for cattle. Were forage nitrate N concentrations affected by the rate and time of N fertilization? Nitrate N concentrations were greatly affected by the rate and time of N application, especially in the second cutting where concentrations ranged from 50 to 7230 ppm. Total N rates greater thanl50 lb/acre gave hazardous nitrate N concentrations greater than 3000 ppm in one year, while more than 300 lb N/acre was required in another year. Nitrate N concentrations in the third cutting were less than 3000 ppm unless 400 lb or more N/acre had been applied. Livestock farmers have the choice of (i) fertilizing for maximum yields and then blending the high-nitrate forage with a low-nitrate forage so that the critical total nitrate intake is not exceeded, or (ii) using reduced rates of N fertilizer to produce lower yields of forage with acceptable concentrations of nitrate, which would allow the forage to be used as a sole feedstock for cattle. At what annual N rate did elevated levels of RSN begin to accumulate? RSN did not begin to accumulate in the soil profile until the total N application rate exceeded the rate needed for optimum yield by 100 lb N/acre. Our results indicate that the root system of reed canarygrass apparently has the ability to assimilate a modest over-application of N for 1 yr without allowing excess nitrates to accumulate for potential movement to ground and surface water.