Harvest Timing and Height

It’s almost go time! Be ready for 1st cut to maximize quality.

The snow has finally left the fields and while the ground is still wet, the first cut will be upon us within a few weeks. While there is always so much to do, take the time to make sure you’re ready to head to the field when the time is right. Timing is everything and as we experienced last year, you just never know when that dry warm stretch is going to arrive.

With the first cut we are really trying to balance dry matter yield with forage quality, namely fiber digestibility. As cool season grasses mature, they move from leafy vegetative growth to reproductive growth. As they start to elongate, woodier stems grow to support seed heads. These stems contain more fiber, and a higher proportion of that fiber is less digestible. Figure 1 shows this transition in orchardgrass that was harvested weekly starting on 12-May and through 23-May when it began showing seed heads. At the early harvest when the plants were still vegetative, fiber content is low and fiber digestibility is high. As harvest is delayed a week, fiber content increases, in this case by about 2.5%, and fiber digestibility decreased by about 5%. As we reach heading, fiber content is now another 3% higher and fiber digestibility reduced by another 5%. Some research has shown a 0.5 lb milk increase for every 1% increase in fiber digestibility. That means delaying harvest too long can really impact milk production.                                                                 

Figure 1. Weekly changes in quality of orchardgrass.

The timing of this transition from vegetative to reproductive stages is going to largely depend on the species and varieties out in the field. Table 1 shows average heading dates we’ve noted in our perennial cool season grass variety trials over the last three years.

Even if you are running short on feed this spring, resist the temptation to go out and scalp the fields down to the ground! Mowing to the ground removes all the plant leaves but can also remove the plant crown and new side shoots (tillers).  Grasses store energy and new growth potential in their crown and the crown is found in the first 2 to 3 inches of the plant. When this is removed, instead of the plant collecting the sun’s rays to regrow the plant must draw on root energy reserves to elongate those leaves to restart photosynthesis. This takes longer and over time diminishes plant vigor and resilience to drought or other adverse conditions. Repeated low mowing will cause your stands to weaken and thin leading to overall reduced yield, quality, and persistence. While that crown holds energy for the plant, it is actually the least nutritious and digestible portion of the plant. Therefore, while you may be getting a little more tonnage, it is of low quality and increases the risk of soil contamination. This tradeoff is demonstrated in Figure 2 which shows yield and fiber digestibility at three cutting heights. We observed a 7% reduction in yield when cutting at 3.0” vs 1.5” but fiber digestibility increased by 5%.

Figure 2. Yield vs quality of forage cut at three heights.

Leaving more stubble in the field has some additional benefits too. Higher stubble can help lift the forage off the ground, allow for better air flow, and faster drying. Faster drying means more plant sugars available to encourage proper fermentation of the feed. More residual protects the soil and helps to maintain cooler ground temperatures. This can help retain moisture and keep the soil microorganisms cool. If the soil gets too hot, these microorganisms slow down or go dormant, limiting the soil’s ability to cycle nutrients and provide other critical functions.

For all these reasons, take the time to get ready for the first cut and be ready to roll by mid-May. Check over your equipment, install some high skid shoes, and go make some high-quality 1st cut! For more information from our trials, visit our website https://www.uvm.edu/extension/nwcrops/research.

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