Having a keen sense of anticipation is perhaps one of the most desirable human qualities. When given a set of circumstances, being able to accurately predict outcomes puts you at an advantage in nearly all facets of life, including farming. It’s this anticipatory sense that should at least help guide you when the initial cutting of hay needs to be made.
Although plant maturity is the primary driver of forage quality for any cutting, there are several other factors that can significantly impact the final harvested forage quality. One of these factors is environmental conditions, especially temperature and moisture. We generally know what those are or have been, so use this information to your advantage.
A unique set of circumstances sets up first cutting for harvesting what is typically the most digestible fiber of the season. Top on the list is the cool weather that usually persists as legumes and grasses mature in the spring. This slows lignin deposition and generally keeps fiber digestibility at peak levels compared to subsequent summer cuttings.
A typical year has a wide degree of environmental conditions that occur during the initial growth cycle of alfalfa and grasses. Most springs are characterized by wide fluctuations in temperature. We also see differences from year to year as one may be mostly cool while others tend toward above average warmth.
These temperature swings have an impact on forage growth and quality, so monitoring these factors needs to become a passion during late spring.
Heating up
Temperature is the driving force behind most physiological processes that occur in a plant. Photosynthesis, respiration, translocation of nutrients, carbon partitioning, and cell wall formation all are driven by the digital thermometer reading.
The relationship of temperature to plant physiology should come as no surprise. We see these effects every year when comparing forage regrowth and quality during summer to that of regrowth and quality in the fall. Forage quality can improve over time in the fall because of cooler growing temperatures. This is as true for alfalfa as it is for fall-seeded oats.
In a past Utah research trial, alfalfa acid detergent fiber (ADF) and neutral detergent fiber (NDF) were compared from an intermountain area where night temperatures averaged 45°F to that of a lowland where night temperatures were 70°F. Daytime temperatures were similar in both areas.
The ADF concentration for the alfalfa grown at the higher elevation was 28% compared to 32% for the alfalfa grown in the lowland. Similarly, NDF values for the high-elevation alfalfa was 35% compared to 39% for the lowland. Although digestibility wasn’t measured, it’s easy to guess which one held an advantage.
As the temperature of the growing environment rises, it has the following overall effects on plant growth and forage quality:
• Reduces the stem diameter
• Accelerates the rate of maturity
• Enhances lignification
• Lowers the plant height
• Lowers the leaf-to-stem ratio
• Lowers the fiber digestibility
Moisture matters, too
Although somewhat secondary to temperature, soil moisture status can also have an impact on forage growth and nutritional value. Mature alfalfa, for example, is about 75% to 80% water. In a 2-ton (dry matter) per acre standing crop, this translates to 8 tons of water.
Water is essential for forage growth, and any moisture deficit situation will have physiological ramifications. A drought condition tends to delay plant maturity if it occurs early in the growth cycle, lowers plant height, raises the leaf-to-stem ratio, and generally drops the NDF content.
Interactions exist
Environmental factors like temperature and soil moisture status cannot be disregarded when trying to explain or anticipate forage quality characteristics, especially for the initial spring cutting.
Making a prediction of forage quality based solely on morphological stage often is erroneous when confounding environmental conditions exist.
The ideal growing conditions from the standpoint of forage quality would be a cool drought, which is rare. However, the positive forage quality impact of dry conditions would be negated by high temperatures during a hot drought when forage quality drops fast and maturity accelerates.
Environmental conditions are often the reason why forage quality is not what is expected based on calendar date or stage of maturity. For this reason, knowing how these factors interact and impact forage quality can be of value and put to good use when anticipating the right time to cut.
Although anticipating the status of forage quality based on your knowledge of environmental conditions is an asset, there are also tools to take some of the “guesswork” out of the optimum first-cut harvest date. These include accessing local alfalfa scissors-cut information, estimating forage quality based on growing degree units (GDUs), or using the predictive equations for alfalfa quality (PEAQ) to determine forage quality in your own fields.
Although none of these approaches may be perfect, they will usually help you to avoid a major forage quality train wreck.
