Appy nitrogen now, keep cows off

I know we have had a wet year and, have a lot of hay stored.  For those of you who do not like to feed hay any more then you need to, you might want to put some nitrogen on some grass fields now and keep the cows off until first frost.  Remember, it costs 37 cents per head per day to graze a cow, and $2.50 per head per day to feed one cow hay.

Agronomic Basics for Stockpiling Pastures:

Stockpiling can be defined as growing pasture for later use. In Kentucky this typically means applying nitrogen (N) to tall fescue pastures in August, letting them grow through the fall, and then grazing during the late fall and early winter. Kentucky bluegrass and other cool-season grasses will also respond to nitrogen applications in the fall, but this publication focuses on tall fescue since it shows a higher N response and stockpiles better for winter grazing.

The best pastures to target are those with the thickest stands of fescue. Fescue responds extremely well to N applications in late summer and has an amazing ability to retain its nutrient value through the winter. Targeted pastures should have low concentrations of weeds and low amounts of clover since legumes do not stockpile well after frost and the yield benefit of added N is less than in pure fescue stands. Moreover, N has the potential to reduce the clover component of the sward as the additional fescue growth will compete with the legumes. A good rule of thumb is that where clover makes up more than 20 percent of the stand, the short-term yield increase from nitrogen will not typically outweigh the long-term forage quality and nitrogen fixation benefit of the lost clover.

Pastures should be grazed or mowed to reduce fescue height to 2 to 3 inches during early to mid-August. Remove animals before overgrazing occurs or initial regrowth will be slow. Grazing or mowing removes low quality summer growth and allows the plant to produce high quality leaves. Assuming that there is adequate soil moisture, a considerable amount of growth will occur within four to six weeks, but waiting 8 to 12 weeks before grazing is preferable.

The optimal time to apply N is in early to mid-August. Prior applications may encourage the growth of weedy grasses like crabgrass. Waiting until September will reduce the efficiency of N conversion into plant growth. For example, one Kentucky study showed that N conversion efficiency (lbs dry matter fescue growth per unit N) was 27:1 on Aug 1, 26:1 on Aug 15, 19:1 on Sept 1, and 11:1 on Oct 1. Therefore, when N application is delayed until September or beyond, optimal N application rate will decrease, and you should carefully consider the benefit of increased fescue growth compared to the cost of purchased hay. N response efficiency also depends on soil moisture. Without rain and/or adequate soil moisture, N response will be low, but even with small amounts of rain tall fescue has an amazing potential for fall growth. In areas that are exceptionally dry, applying N can be somewhat of a gamble in terms of the response.

Traditional “stockpiling” involves keeping cattle off the pasture until late fall, but this practice may be difficult wen pasture production is low. If forage is needed, N fertilized pastures can be grazed in the early fall, but it is recommended that cattle be kept off these pastures for at least a month. An alternative strategy is to feed hay during the stockpiling period to supplement the pastures that cattle are on.

Tall fescue growth will occur without added N, but University of Kentucky Cooperative Extension emphasizes the importance of adding N for maximum growth and forage quality. In Kentucky, nitrogen (90 units or actual lbs N) increased forage production by over a ton and protein by 5 percentage points. In Ohio, nitrogen (90 units or actual lbs. N) increased protein by 9 percentage points and improved overall digestibility. Another reason to stockpile fescue is that it retains its quality extremely well through the winter months. In an Arkansas research study, stockpiled fescue was higher quality (12 percent CP and 55 percent TDN) even in early March than average quality hay. This attribute can be particularly beneficial for a late winter or spring calving cow-herd.

There are several forms of N available for pasture use, but the two main types are ammonium nitrate and urea. Ammonium nitrate is an excellent form to use in late summer because it is not subject to surface volatilization. Urea is generally a cheaper source of N, but a significant amount of N can be completely lost under hot, humid conditions favoring volatilization. Typical urea losses in late summer range from 15-30 percent, but can approach 40-50 percent when there is no rainfall for several days after application. Fortunately, urease inhibitors (e.g. Agrotain) have been recently developed to reduce volatilization losses with urea (see AGR-185 referenced on last page). Even though they add to the overall cost, urease inhibitors are recommended in the summer for urea due to the unpredictable rainfall in August. Be aware that all urease inhibitors are not equally effective.

Besides the application of N, it is important that stockpiled fields be limed and fertilized with P and K to acceptable levels (see AGR-1 referenced on last page). Where possible, stockpiled tall fescue fields should be strip grazed and stocked heavily enough to graze down each paddock in 7 to 10 days or less. This allows the forage to be efficiently utilized without excessive trampling and waste. Since tall fescue does not re-grow in the winter, a back fence is not needed when strip grazing stockpiled growth.

Greater detail of the stockpiling process can be found in the UK extension publication AGR-162 “Stockpiling for Fall and Winter Pasture” which can be found at: http://www.ca.uky.edu/agc/pubs/agr/agr162/agr162.pdf or your county extension office.