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Fertilization (Timing of N application , Manure application, Alfalfa-grass, Low potassium grass)

Timing of N application
A study using reed canarygrass in southern Minnesota concluded that optimum dry matter (DM) yield and crude protein (CP) content occurred with a single spring application of N fertilizer (Vetsch and Russelle, 1999). One application of N fertilizer in the spring produced maximum yields, compared to split applications. This differs from past recommendations in most regions.

We set up an experiment to investigate split N application on perennial grasses in 2000. Reed canarygrass, orchardgrass and tall fescue were established in replicated small plots at two locations in central New York State, Ithaca, and Mt. Pleasant, a high elevation site. In 2001-2003 the following treatments were applied: 1) 200 lbs/a actual N in the spring; 2) 100 lbs N in the spring and 100 lbs after 1st harvest; 3) 100 lbs N in the spring, 50 lbs N after 1st harvest and 50 lbs N after 2nd harvest; and 4) No nitrogen fertilizer applied.

Figure 2.     Yield of grass with or without split application of nitrogen fertilizer. 0.0.0 refers to the pounds of actual N applied at spring green-up, after first harvest, and after second harvest. (Averages of two locations, three years, and four replicates.)

Over 3 years and 3 species there were no differences in forage yield between 200 lbs of N split applied twice (100+100) or split applied three times (100+50+50) (Fig. 2). One application of N in the spring was consistently lower yielding than split applications of N, however, and averaged 8% lower yield. The response to split application of N was smallest with reed canarygrass. Tall fescue produced the highest yields. Fertilized grasses yielded 124% more forage than unfertilized grass.

Manure application on grass
Intensively managed perennial grasses have the potential to absorb large quantities of N from manure. We applied dairy manure to orchardgrass and tall fescue, on land that had not received any manure application for several decades (Cherney et al., 2002c). Dry matter yield of grass receiving 30 wet tons/acre of manure was similar to that of N-fertilized grass after two years of manure application. Residual effects of manure on grass yield were large for at least three years following manure application.

Alfalfa-grass mixtures
If a mixed stand is 50% or more grass, use N management like it was 100% grass. Either manure or commercial N application will favor grass over alfalfa and hasten the decline of alfalfa in a mixed stand. If a mixed stand is 30% or more grass, apply harvest management as if it were 100% grass. Grass-legume forage is as good or better than either pure alfalfa or pure grass for lactating dairy cows.

Low potassium grass for non-lactating cows
Relatively low K concentration in non-lactating dairy cow diets is critical to animal health. Species selection, fertilization, harvest management, and time of season can all impact the K concentration of grass forage. Perennial grasses are luxury consumers of K, resulting in high K forages grown on fields with excess soil K due to repeated animal manure applications (Cherney et al., 1998).

The goal of a K management program for perennial cool-season grasses for non-lactating dairy cow forage is to provide sufficient K for plant functions without accumulating excess plant K. Potassium fertilization did not have a large effect on DM yield of cool-season perennial grasses under a low intensity harvest management regime (Cherney and Cherney, 2005b). Potassium deficiency symptoms were not observed on any of the grass species, although K concentration in fall harvested forage dropped below 0.8% in timothy. In another study, K concentration in reed canarygrass dropped below 0.8% (Cherney et al., 2003b). Forage quality also was not greatly affected by K fertilization, although it did affect forage K concentration and concentrations of some other elements. Timothy forage tended to be low in elemental concentrations in general, with lowest forage K concentrations among the five grass species studied. It is possible to achieve sufficiently low forage K concentrations for non-lactating dairy cow forage in cool-season grasses and maintain stand persistence.