Forage production from Rocky Mountain meadows is characteristically low, averaging 1.3 ton/acre. Research has shown that lack of N fertilization is a major factor limiting yield. Little research has compared N fertilizer sources, rates, and application time for meadow pastures. Experiments were conducted on a less productive Edlin sandy loam soil (coarse‐loamy, mixed Borollic Camborthids) located near Saratoga, WY, and on a more productive Mayoworth sandy clay loam soil (fine, montmorillinitic Argic Cryoborolls) near Granby, CO, over 3 yr. Treatments consisted of factorial combinations of two application times (fall and spring), five N rates (0, 50, 100, 150, and 200 lb N/acre), and two N sources (ammonium nitrate [AN] and urea). Forage production increased from 1.1 ton/acre with no N fertilizer to 3.4 ton/acre on the Edlin soil and from 2.7 ton/acre to 4.9 ton/acre on the Mayoworth soil with 150 lb N/acre as AN. Optimum economic N rate varied with source, time of application, and most importantly, with yield potential of the soil. Ammonium nitrate consistently produced more forage and higher fertilizer recovery efficiency than urea at equal N rates. Spring N application produced higher yields and higher fertilizer recovery efficiency than fall application on the more productive Mayoworth soil. On the Edlin soil, time of application did not affect forage production. Fall application may be necessary, however, where mountain meadows are wet during the spring fertilization period, preventing access to fertilizer application equipment. For fall application, AN should be used as the N source, since AN provided the highest yield and fertilizer recovery efficiency. On the Edlin soil, 150 lb N/acre spring‐applied increased protein from 7.1% to 8.7% and 9.2% for urea and AN, respectively. On the more productive Mayoworth soil, forage protein concentration increased less dramatically with similar N application rates. If producers are interested in producing quality forage, adequate N fertilization is vital. Research Question Mountain meadow forage production plays a vital role in livestock management in the Rocky Mountain region. The average forage yield of mountain meadows is about 1.3 ton/acre. Fertilization is an economical way to increase forage production on irrigated meadows. The objectives of this study were to determine the forage yield and quality responses of mountain meadows to N fertilization and to compare the effectiveness of both spring and fall application of ammonium nitrate (AN) and urea fertilizer and the economics of N fertilization of mountain meadows. Literature Summary Most studies that have been conducted in Colorado and Wyoming have demonstrated that forage production can be increased by N fertilization. There are very few studies comparing fall vs. spring application or urea vs. AN as N sources on mountain meadow soils of varying productivity. Nitrogen fertilizer use efficiency has been reported to be low (20 to 28%) for mountain meadows, primarily because of poor irrigation water management. Study Description The study was conducted on two soils, a less productive Edlin sandy loam near Saratoga, WY (7200 ft elevation) and a more productive Mayoworth sandy clay loam near Granby, CO (8,125 ft elevation), for 3 yr. Experimental Design The experimental design at each site consisted of a factorial combination of two application times (fall and spring), five N rates (0, 50, 100, 150, and 200 lb N/acre), and two N sources (AN and urea) with a split plot treatment arrangement in randomized complete blocks with four replications. Application time was the main plot, rate the split‐plot, and N source the split‐split‐plot. The fall application was applied in September and the spring application in May when spring growth resumed. Applied Question Will the application of N fertilizer increase yields and protein? The application of N resulted in an average increase in yield from 1.1 ton/acre with no N fertilizer to 3.4 ton/acre on the less productive Edlin soil and from 2.7 ton/acre to 4.9 ton/acre on the more productive Mayoworth soil with the application of 150 lb N/acre (Fig. ). On the Edlin soil, 150 lb N/acre spring‐applied increased protein from 7.1% to 8.7% and 9.5% for urea and AN, respectively. On the more productive Mayoworth soil, forage protein concentrations increased less dramatically with similar N application rates. If producers are interested in producing quality forage, adequate N fertilization is vital. The effect of N rate, N source and time of application on a forage yield from a less productive soil (Edlin) and more productive soil (Mayoworth). image Is there a difference in N source? Ammonium nitrate produced up to 0.5 ton/acre more hay than urea at equal N rates, averaging 0.2 to 0.3 ton/acre more forage over all N rates. Can ammonium nitrate or urea fertilizer be applied in the fall and still be cost effective? Yield response and fertilizer recovery efficiency were lower with fall‐applied urea. The optimum economic rate varied with source, time of application, and most importantly with site yield potential. If the meadows are wet in the spring, fall fertilization may be the only alternative for many producers. If fall applications are required, AN should be used as the N source, since our data show this source would provide the highest economic response and fertilizer recovery efficiency.
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Follett et al. (1995) studied this question.