Back to Basics:
Grass hay meadow fertilization: Yes or no?

by Brad Schultz, Humboldt County Extension Educator;
Jason C. Davison, Northeast/Central Area Forage and Alternative Crops Specialist;
Ron Torell, Northeast/Central Area Livestock Specialist; and
Dave Bohnert, Oregon State University

Sharpen your shovels and your pencils. Many producers question whether they should purchase expensive hay this fall or expensive fertilizer this spring. This month, we discuss how irrigation and fertilizer management determine which plants are most common in a hay field and their effect on the quality, quantity and long-term production of forage from grass-hay meadows.

Quality factors
Hay quality depends on the type of forage plants in the field, fertilization practices, irrigation management, and the growth stage at harvest. Proper management can increase the biomass of desired plant species and improve their nutritional quality.

Continuous irrigation occurs on most meadow hay lands in the Intermountain West. Meadows remain saturated during much of the growing season and dry out in mid- to late summer. Prolonged saturation increases sedges and rushes — both low-quality forage plants. Intermittent irrigation allows the soil to periodically dry out, become warmer and have more soil oxygen. These factors increase desirable grass species, which improves hay quality. The specific soil type (e.g., clay, loam or sand) determines the frequency and duration of irrigation.

Soil fertility, particularly, available nitrogen, also influences a meadow's plant composition. Unfertilized meadows, with few desirable grasses and mostly sedges and rushes, can become mostly desired grasses with annual fertilization. The conversion to grasses may take three to five years, but can be reversed if fertilization stops. Applying higher rates of fertilizer will speed up the process.

It's elemental
Nitrogen (N) is the most important element for plant growth. The amount applied affects production more than the type applied. Usually 80 to 100 pounds (lb.) of actual nitrogen per acre results in optimum forage production. Higher rates can result in more hay production and quicker conversion to desired grasses, but higher rates usually are not economical.

Nitrogen should be applied in the fall unless the fields remain saturated from a high water table or flooding. For fields grazed in the spring, nitrogen should be applied after livestock are removed. Nitrogen concentrates in the forages' leaves. When livestock graze the leaves, nitrogen is lost. If fertilization occurs after livestock are moved from meadows, there must be enough irrigation water to move the fertilizer into the root zone and provide for full plant growth.

Phosphorus (P) often has low levels in western hay meadows, and high soil pH further limits its availability. Phosphorus, particularly in combination with nitrogen, can dramatically increase forage production and forage quality. When phosphorous is deficient, producers should apply three parts nitrogen to one part phosphorus (i.e. 30-10-0). All other nutrients required for plant growth are normally not deficient in the West.
Percent crude protein (CP) and total digestible nutrients (TDN) are useful indicators of hay quality. As their percentages increase, hay quality improves. Crude protein is the nitrogen compound in forage, and all are lumped together when computing rations for livestock. TDN is a calculated figure representing the sum of all the digestible organic nutrients in the feed.

Sixty years of forage testing in northeastern Nevada show that fertilizing meadows usually improves forage quality. Additional research in Colorado, Oregon and Idaho had similar results. At nitrogen application rates greater than 80 lb. per acre, the additional nitrogen increased CP levels. When nitrogen application rates were less than 80 lb. per acre, CP levels decreased. The amount of nitrogen applied was enough to increase forage production, but the nitrogen became diluted across the increased biomass, reducing the protein content.

An analysis of more than 300 hay samples from northeastern Nevada found that CP was 2.6% higher on fertilized meadows. Fertilized, early cut hay (before July 15) averaged 5.0% more CP than non-fertilized, late-cut hay (after July 15).
Table 1 summarizes the average chemical analysis for fertilized and non-fertilized hay samples, across a wide variety of treatments. The fertilized hays received varying amounts and types of nutrients. The figures shown in Table 1 represent a combination of hays cut early and late. The quality differences become important when they are compared with the nutrient requirements of a pregnant, 1,000-lb. cow in the second and third trimesters (see Table 2). Non-fertilized hay clearly does not meet a cow's nutrient requirements, except for calcium (Ca). Fertilized hay, however, is adequate in every category.

Hay yields are usually expressed as tons of hay harvested per acre. Pounds of CP harvested per acre may be a more meaningful production figure. Fertilized hay has about 2.6% more CP than non-fertilized hay; therefore, one ton of fertilized hay has 52 lb. more CP than a ton of non-fertilized hay. Also, the fertilized hay will produce significantly more forage from the same acreage.

Several factors determine the economic returns from a fertilization program. Typically, fields with deep, loamy soil and abundant, manageable water supplies will have the best economic return. However, low-quality hay fields can produce economic returns if fertilizer prices are not too high. Producers are advised to follow recommended irrigation practices and test fertilization on a small scale. Production increases should then be compared with the cost of the fertilizer. Producers should remember that changing plant species with fertilizer and water management takes time. A two- to three-year trial may be necessary.

Summary
Nitrogen fertilization often more than doubles grass hay yield and increases the hay's nutritional quality. High prices for purchased hay and soaring feed costs suggest that better yields of high-quality grass hay are an important consideration — probably more important than high fertilizer prices. Grass hay producers in the Intermountain West can produce high-quality hay with proper management, which should include intermittent irrigation, proper fertilization and harvesting hay at the proper growth stage. Each individual practice helps, but application of all three practices yields the highest quantity and quality of hay at the lowest price.

As always, if you would like to discuss this article or simply would like to talk cows, do not hesitate to contact Brad Schultz at 775-623-6304 or schultzb@unce.unr.edu; Jason (Jay) Davison at 775-423-5121 or davisonj@unce.unr.edu; Ron at 775-738-1721 or torellr@unce.unr.edu; or Dave Bohnert at 541-573-8910 or dave.bohnert@oregonstate.edu.