Hay Crop Harvest Considerations

By Everett D. Thomas

The term "hay crop" instead of "hay" is used in the title because much of the legumes and grasses on dairy farms are harvested as medium-moisture silage, typically at 35 to 40 percent dry matter. Theoretically there shouldn't be much difference in harvest schedules regardless of how the crop is managed, but harvest for silage doesn't require as long a "weather window," and it gets the crop off the field and into storage at least one day sooner. The result, whether intentional or not, is that a lot more hay fields managed for silage wind up getting harvested one more time than if the fields were managed for dry hay. We often hear of farmers in the northeastern U.S. discussing fourth-cut alfalfa silage, but seldom do they say much about fourth-cut hay.

Mowing height

This issue of Farming will catch some farmers in the midst of first-cut harvest, while others will have already finished the first cutting. We've discussed mowing height before, but it's timely to note again: Mowing height is something you need to pay attention to, especially if you're mowing fields with a significant amount of improved grasses. Grass mowing height is critical since the nutrients for the next crop are in the bottom few inches of the aboveground portion of the plants. Mowing forage grasses at 2 percent or less stubble height will maximize first-cut yield, but will minimize regrowth. Continued close mowing may harm or even kill the plants. Mow grasses at about 4-inch stubble height; if you doubt this, mow part of one field at your normal mowing height (if it's much less than 4 inches), and then mow the rest of it at 4 inches. Farmers have told me that they can see an obvious difference in regrowth.

Alfalfa mowing height is also worth mentioning, but for a different reason. Alfalfa regrows from crown buds; therefore, as long as you don't mow low enough to damage the crowns, mowing height has no impact on regrowth. Comparing low versus high mowing height, the increased yield should outweigh the slight decrease in forage quality. Research at Miner Institute found a 10 percent yield increase and only a 4 percent decrease in fiber digestibility when mowing at 2-inch versus 4-inch stubble height. However, mowing at a short stubble height isn't recommended if part of what you're harvesting is Mother Earth. Forage analysis summaries showed a marked increase in forage ash levels as disc mowers became popular. (Thankfully, recent ash analyses have shown a slight decline, suggesting that at least some farmers have listened to these warnings.) Pay attention to ash concentrations in hay crop silages, and if they're higher than about 10 percent (about half of which is "internal" ash from crop nutrients such as calcium and potassium) do some troubleshooting to determine the reason. A high ash level could be due to mowing height, but it also could be overly aggressive raking. "A cloud of dust and a hearty 'Hi-yo Silver'" is fine for the Lone Ranger, but it shouldn't describe your hay raking process.

Second-cut timing

During a barn meeting a farmer showed me a sample of his second-cut orchardgrass hay that looked OK - good color and no visible heads - but his cows were milking poorly. I asked about his harvest interval between first and second cutting, and while he didn't know exactly he said it was over six weeks. At my suggestion he had the hay tested for quality, and not surprisingly fiber levels were very high. High forage NDF leads to reduced intake, and reduced intake leads to ... well, you know what that leads to. In this situation there wasn't much he could do except to replace some of this hay with better quality forage.

We have a better idea of the "correct" harvest interval between first and second cuttings for alfalfa and alfalfa-grass, where alfalfa is the main component of yield. The harvest interval between these cuttings depends somewhat on weather conditions, but generally is in the 30 to 35-day range. We can rely on the stage of growth to guide harvest timing, with mid to late bud stages usually providing the best combination of yield and quality. Second-cut grass, on the other hand, often will continue to mature, losing quality every day, without the appearance of heads. Therefore, timing of second (and subsequent) grass harvests is a bit of by guess and by gosh. As soon as there's enough yield to justify harvest, mow. Not very scientific is it, because "enough yield" is in the eye of the beholder. For those who insist on a numerical guide: If it's been much over 30 days since first cut and there's enough regrowth to justify mowing, you'd better have a good reason not to mow.

The decision of when to mow second and subsequent harvests of grass is influenced by weather and growing conditions, but it is also influenced by grass species. Some cool-season grasses such as timothy don't grow nearly as well after the soil warms up compared to other species such as orchardgrass and tall fescue. For instance, in a 2011 Cornell University trial seeded in summer 2009, third-cut orchardgrass harvested in mid-August yielded 64 percent more than did timothy harvested on the same date. We often find that the harvest interval between first and second-cut grasses needs to be somewhat shorter than for later harvests. For instance, in the previously mentioned trial the harvest interval Cornell used between first and second cut was 32 days, while between second and third harvests it was 51 days, and between third and fourth harvests it was 61 days.

Stem to silo the same day

The goal is to get forages from stem to silo as quickly as possible, of course at an appropriate dry matter content. "Stem to silo the same day" is a lot easier to accomplish with second and third harvests than it is with first for two reasons: First, forage aftermath yields are almost never as high, so the forage dries faster following mowing; second, the soil surface isn't usually as moist during these later harvests, and forages dry faster when sitting over a dry soil surface than over a moist one. Remember to spread windrows as wide as possible, raking or merging into windrows just before chopping. Once windrowed, forages dry much more slowly, giving you more time to chop them before they get too dry.

Ev Thomas has worked as an agronomist in New York for 45 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 13 years and has been an expert contributor on a number of other topics.