How to Handle Drought-Stressed Alfalfa

The 2006 growing season is experiencing a swing in growing conditions. From a perfect spring to excessively dry conditions. Many hay producers have completely dry soils and there is no rain in the forecast. Alfalfa growth is slow and under stress. Under these conditions, the alfalfa is unlikely to re-grow much after harvest, at least until the rains return. And even though alfalfa is a unique crop in its ability to go dormant during extended dry periods, it requires an inch or several inches of rain to recover depending on its state of dormancy and the current soil conditions. To maximize the yield from the current stand, alfalfa should be managed to ensure survival. The cutting management, fertilization and insect control methods should be examined.

Alfalfa Quality

When alfalfa is subjected to drought conditions, the feed quality often increases. This is because plant responds by decreasing the stem number and their elongation, inadvertently increasing the leaf to stem ratio. This results in an increase in forage quality (higher crude protein and digestibility, especially ADF). Additionally, photosynthetic activity continues during the early phase of drought, allowing nutrients to accumulate while growth slows. It should be noted, that although quality is increasing, dry conditions also reduce nodule formation and nitrogen fixation, therefore extended dry conditions will eventually reduce plant metabolism.

Established Alfalfa

Only harvest your alfalfa if there is sufficient yield to justify harvesting costs. It is also important to maintain enough leaf material for the stressed plant to continue photosynthesis and root growth. Some experts recommend using a threshold of 10 inches in height and mid to full flower to trigger harvesting. Full bloom is when virtually every stem has one or more flowers open. At this point yield has reached its maximum yield, and quality will begin to decrease, even if rain occurs. Harvesting at this stage will also allow the plant to build root reserves and fully recover from dry weather and cutting stresses, providing the best yield scenario for the subsequent harvest. If areas of the field vary in development, base cuttings on the slowest developing plants in the field.

Cutting height should be as short as possible to maximize yield and quality. However, one should also raise the cutting height if plants have been cut early and frequently in previous seasons and to avoid contaminating the hay with dirt and foreign material.

If the alfalfa is less than 10 inches tall, cutting it will reduce stand longevity. Therefore, it is recommended to leave the stand and harvest it at the next harvesting interval, or until sufficient precipitation occurs. At that point you may either,

1. harvest the old growth for a low quality feed, exposing the newly initiated crown buds to sun, allowing them to produce a high quality subsequent harvest, or
2. delay cutting the old growth until the new stems have reach their optimum stage and harvest both the old and new growth for a medium quality feed.

Both options will not affect the overwintering ability of the stand as long as the final harvest is 6 weeks before the killing frost.

Seedling Alfalfa Stands

If the stand was seeded this spring it may be harvested this fall without detrimental effects to the plant. However, similar to established stands, only harvest if enough biomass exists to justify harvesting costs and if the stand is at least 10 inches in height, and no later than six weeks prior to the killing frost. Cutting height should be as short as possible to maximize yield and quality, but high enough to avoid contaminating the hay with dirt and foreign material. It is also important to maintain enough leaf material for the stressed plant to continue photosynthesis and root growth.

Grass Stands

Similar to alfalfa, grass yields are reduced under dry conditions, therefore only harvest your grass if there is sufficient yield to justify harvesting costs. Unlike alfalfa, dry conditions reduce feed quality as fiber levels increase and protein and energy levels decrease. To maximize yield and quality, grass stands should be harvested at heading; at this stage little gains in yield are obtained but quality decreases rapidly. Grass stands less than 10 inches tall may be left unharvested without harming plant health. However, excess growth should be removed prior to winter to reduce the risk of stand loss to snow mould, especially for those grasses known not to stand up well from snow fall (ex, orchard grass). If moisture levels improve, adding approximately 30 to 40 lbs of inorganic nitrogen fertilizer (not manure) is a good tool to stimulate fall growth, and potentially provide some additional feeding. Moisture-stress pastures should also be mowed to control weeds and small brush.

Fertility

It is of utmost importance to ensure that all fertility levels both alfalfa and grasses are optimum in order for it to regain lost yield when moisture levels return to normal.

Insect Control

After a stand is harvested, new shoots emerging will be susceptible to insect feeding, and in particular to the 2006 growing season, alfalfa weevils may reduce subsequent yields. A solution as simple as cutting the alfalfa is often most effective in controlling the weevil feeding; however, be aware that weevils may feed on regrowth. This is only a concern under dry conditions where the slow re-growth is not able to keep up to the weevil feeding.

Feeding

Since forage quality is significantly affected by extended dry conditions, be sure to test all your feed before feeding and adjust your rations accordingly.

For more information please contact your local Farm Extension Specialist or visit the following links:

• Forage Resources - University of Wisconsin Extension
• Effects of Drought Conditions on Commonly Fed Forages - West Virginia University Extension Service