Farming Magazine - June, 2009


Forages: Hay Harvest Tips

By Everett D. Thomas

Making recommendations to farmers is more rewarding when you discover that some of what you’ve been suggesting is being validated “down on the farm,” which, of course, is the only place that counts. That’s why I was pleased when a farmer approached me after I gave a talk about managing hay crops to a group of Pennsylvania dairy farmers. I had explained why they should leave 3 to 4 inches of stubble when mowing cool-season forage grasses, even though field conditions may permit a shorter stubble height. In the “old days” (before the rapid adoption of disk mowers), farmers were more careful about mowing height because hitting a stone or scalping the soil surface with a sicklebar mower often meant stopping to repair a broken knife section. But, it takes a serious stone to stop a disk mower, so some farmers started using it as a dual-purpose tool: combination mower and land leveler.

University agronomists are encouraging lower mowing heights for alfalfa because of significant yield increases with only a modest affect on forage quality. But, there’s a big difference between alfalfa and forage grasses in how they store nutrients. Alfalfa stores the nutrients for the next crop in its taproot, regrowing from crown buds while the cut stems die soon after harvest, but grass regrows from the cut stems and has little ability to store nutrients in its root system. Nutrients for the next crop are stored in the bottom few inches of the plant, and mowing to a 1 to 2-inch stubble height robs grass of much of its food supply. A few inches of stubble also leaves some green forage for photosynthesis. After hearing this explanation, the farmer said, “So that’s why my neighbor’s orchardgrass comes back so much faster after cutting than mine does. He leaves a higher stubble than I do.” This farmer wasn’t alone in having problems due to close mowing: Enough farmers in Pennsylvania and Maryland were experiencing reduced orchardgrass regrowth, and in some cases stand depletion, that University of Maryland Extension Forage Crops Specialist Les Vough—retired but still quite active—emphasizes the importance of leaving at least 3 inches of stubble on orchardgrass.

Forage ash concentrations are increasing

Another way we know that the “close mowing syndrome” is widespread is by the increasing ash levels in the forage analyses of hay crop silages. Scalping the soil with a diskbine can result in soil being deposited onto the mowed forage. Some of the soil falls off during chopping, but enough remains that we’re increasingly seeing ash concentrations of over 10 percent. Since “internal” ash—crop minerals including calcium, potassium, phosphorus and chloride—total about 6 percent of hay crop dry matter, the difference between 6 percent and 10 percent ash is mostly soil. I’ve seen as much as a 10 percent “dirt difference” between total and internal ash content. That means that for every 9 pounds of forage the farmer is feeding, he’s feeding 1 pound of soil, and soil has very poor digestibility! Farmers who scalp the soil surface and then make narrow windrows will probably have higher ash contents in their silage than farmers who make wide windrows. That’s because stretching windrows to at least two-thirds of cutterbar width allows the crop to dry more uniformly and less soil is therefore likely to be trapped in the wet forage in the bottom of the windrow.

Challenging an old recommendation

Not only are we having to make changes in mowing height to prevent high ash levels and reduced grass regrowth problems, but agronomists are now taking a new look at whether we should condition hay crops harvested for silage. Two recent New York State trials found no significant difference in hay crop silage drying time due to conditioning. (The research was with wide windrows, almost certainly a necessity in any decision to eliminate hay crop conditioning.) In one 2008 trial, alfalfa mowed at 9:30 a.m. and not conditioned was about 2 percentage points lower in moisture by 3:00 p.m. than alfalfa from the same field that was mowed and conditioned, also at 9:30 a.m. There are physiological reasons for this, but what’s more important is what happens, not why. If a farmer is thinking about eliminating conditioning, it would be prudent to do so on a trial basis: Mow and condition 90 percent of a field, then relax the rolls on the conditioner so the crop “flows” through the rolls with little crimping or crushing. Then, when the farmer starts chopping, he should check to see if the part of the field he didn’t condition is at least as dry as the part he conditioned.

That’s what happened with two Amish brothers farming in Lancaster County, Pa., though they didn’t attempt the “no conditioning” practice intentionally. They mowed an alfalfa field and got half the field conditioned—mowing and conditioning involves separate trips for most Amish farmers— before their conditioner broke. When they chopped the field for silage, they were amazed to discover that the half they didn’t condition was lower in moisture!

Relative Forage Quality

Farm milk prices have been terrible, and while it’s tempting to cut every input cost possible, one place not to scrimp is on forage analysis. A fairly new test, Relative Forage Quality (RFQ), is available from an increasing number of forage analysis labs. It requires digestibility analysis of the forage, but this is available from most testing labs, usually at a modest cost. This is one expense you should incur, because it will predict the milk-producing ability of your forage. Relative Feed Value (RFV) has been around a lot longer than RFQ, and while it’s useful for evaluating pure alfalfa, it’s of much less use for mixed forages such as alfalfagrass. RFV is most useful for buying and selling alfalfa hay, while RFQ rates the forage for dairy cow rations. An RFQ of 160 means that the forage is of “milk cow” quality.

Ev Thomas has worked as an agronomist in New York for 42 years, first with Cornell University Cooperative Extension, then with the William H. Miner Agricultural Research Institute in Chazy, N.Y., including managing its 680-acre crop operation. He continues to work part-time for Miner Institute and is now an agronomist at Oak Point Agronomics. He has a written our Forage column for over 10 years and has been an expert contributor on a number of other topics.