– Dwane Miller, Penn State Extension Educator, Agronomy
Whether you’re taking the crop as haylage or dry hay, it’s important to pay attention to forage cutting height. One of our goals as farmers is to maximize our yield; however, cutting a crop too low can lead to several negative issues. The introduction of the disk-type mowers (discbines) allows for cutting very close to the ground. I’ve seen many fields that have been “scalped” right to ground level. This differs considerably from the older sickle bar mowers (haybines), whose technology required that some level of stubble height remain. Stand longevity can be compromised when the crop is cut too low. As a general rule, alfalfa can be cut closer to the ground than our grass crops. We need to think about where energy reserves are stored in the crop. For alfalfa, carbohydrates are stored below the ground in the taproot. Grasses store their energy above ground in the stem base or tillers. Frequent mowing at a close height will continue to deplete these energy reserves, resulting in stand longevity issues.
The second consequence for mowing too close to the ground is increased ash content of the forage. All forage has a natural ash content of approximately 6%. However, mowing too closely with disk mowers can add soil to the crop, and increase the ash content by as much as 10-12% (18% ash content in total analysis). If we all had table-top smooth fields, it would also be much easier to make a closer cut across all fields. However, things such as groundhog holes and the unevenness of fields can add to increased ash content of our harvested forage.
So, the million-dollar question is how low can you go? The best answer is…it depends! The first question I always ask is — is it a solid stand or a mixed stand? If you have grasses involved, you must keep cutting height higher than a pure stand of legume, if you want to keep the grass in the stand. Keep in mind these are minimum recommendations; it’s OK to mow higher than the numbers below.
Here are my Minimum cutting height recommendations:
Alfalfa or Clover
- 2” minimum. Some literature shows a cutting height of 1” will not reduce stand longevity but remember the increased ash content issue. Also, keep in mind that frequent cutting at early maturity will continue to deplete carbohydrate reserves. One cutting of alfalfa should be allowed to reach the bloom stage each year.
Cool Season Grasses (Orchardgrass, Timothy)
- 4” during the establishment year
- 3” minimum during production years. This is where we see most of our stand longevity issues. Frequent cutting of cool season grasses at a low height will continue to deplete energy reserves.
- You must manage for the predominant species. Do you have a grass stand with some alfalfa, or an alfalfa stand with some grass?
- Alfalfa with some grass: 2.5” minimum
- Grass with some alfalfa: 3” minimum (if you want to keep the grass stand!)