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Soil Moisture—The Most Important Ingredient for Successful Food Plots

By: Dr. Grant R. Woods and Bryan Kinkel

Being responsible for establishing food plots throughout the whitetail’s range, we have been frustrated by the weather during the summer and fall of 2000. Rainfall and temperatures have varied greatly across the eastern U.S. Drought conditions continued in the Southeast for the third consecutive year, and the extreme lack of rainfall this past summer and fall caused widespread food plot failures. On the other hand, many of the northeastern states were significantly wetter and cooler than normal. For example, New York experienced the tenth coldest summer on record. The bright spot were the central states. After a cooler than normal spring, Pennsylvania experienced ideal growing conditions. The early–season deer harvest data collected from this area already reflect the good growing conditions.

Clearly, nothing is more beneficial to food plots than receiving the appropriate amount of rainfall at the right time. In past issues of Quality Whitetails, we have written about lime and the major components of fertilizer. These additives are certainly important elements of establishing and maintaining successful food plots. If fact, no plant species can express full growth potential without the correct soil pH and soil fertility. However, recent experiences with food plot establishment pointed out our neglect in writing about the most important factor for food plot production—soil moisture. Without appropriate and timely amounts of rain, planted seeds have about as much chance of surviving and maturing as a yearling 8–pointer on a property operating under traditional deer management.

Most sportsmen realize that water is the key to survival for both plants and animals. For example, in an emergency situation, humans can survive for weeks without food, but just a few days without water. This is true for most other living organisms. Most plant species can maintain life for several days, even weeks, on existing food reserves. However, once the available moisture is consumed, all growth stops and death soon occurs.

Most southern states experienced severe drought conditions during the summer and fall of 2000. In fact, October was the driest month on record in several states with some areas receiving no rainfall during the entire month and numerous others receiving 1/4–inch or less. Although these recent dry conditions have been record setting, the fall months are typically the driest months of the year in much of the Southeast.

This fact is of great importance since cool season foods plots are traditionally planted in September and October in this region. This tradition often results in seeds being sown during extended dry periods. When seeds are planted during extremely dry periods with no rain predicted, it is termed “dusting in.” Using this planting technique is risky—it is a gamble whether seeds will receive adequate soil moisture to germinate and grow before they desiccate (dry out) and die. This year, dusting in was a poor gamble across the South as many food plots established by this technique resulted in total failures. That is to say that there was almost no germination more than 30 days after planting.

Soil moisture at the time of planting, or just after planting, is the key to ensuring successful germination even during dry periods. For example, this fall we planted several new test cultivars (plant varieties) in northwestern South Carolina. They were planted in late September, which was the last time the area received any measurable precipitation. Prior to planting, the plot had been sprayed with a non–selective herbicide to kill all existing vegetation, and had been limed and fertilized according to soil test recommendations. Although these steps had been completed for several weeks, we waited until it rained to plant. When the rain finally arrived, the seed was planted during the rain with a hand–held broadcast seeder.

Many hunters/managers do not realize the value of broadcasting seed during the rain. This practice achieves three goals: covering the seed to the appropriate depth, compacting the soil, and ensuring adequate soil moisture for germination.

Most sportsmen realize that seed should be covered with soil after planting. However, covering the seed too deep can be just as detrimental as not covering it at all. In essence, seeds must have enough energy stored to germinate, grow to the surface, and develop a leaf before they can create additional energy through photosynthesis. Therefore, seed buried too deep (more than 1/4–inch for small seed and 1–inch for large seed) frequently use all of their stored energy and die before they can develop a leaf and “refuel.” For these reasons, when hunters say they used a disk to “bury” their seed, we ask them if they sang a funeral hymn, because they were literally burying their seed!

However, when seed is broadcast during a rain (flash floods excluded), the force of the raindrops pushes the seed slightly into the soil. In addition, the resulting splash causes additional soil to settle on top of the seed. Simply put, rain typically covers seed placed on top of a relatively soft seedbed approximately 1/4–inch deep—just the right depth for small seeds.

Rain also serves to pack the soil by collapsing some of the air pockets in the soil column. This is important for seedling growth because roots will not grow through air pockets. For example, you have probably noticed that roots of houseplants rarely grow out of the holes in the bottom of the pots. This is because air prevents root growth. Therefore, because seeds that have just geminated have very few roots, the death of even one root due to air pockets in the soil can kill the seedling.

In contrast, using the broadcast method just after a rain can result in poor germination. After a rain, the soil surface naturally dries more quickly than the subsurface, creating a crust. Hence, the developing roots of broadcast seed would have difficulty penetrating this crust. In addition, there is no “splash” to push the seed into the soil or to cover it. The bottom line is if broadcasting is the planting method used, much greater success can be achieved if the seeds are sown before a rain.

The two photographs illustrate the difference between planting before versus after a rain. The growing plot is one of our test plots that were planted during the rain. The plot without much vegetation was established less than one mile away, but several days after the last rain.

Planting just before or during a rain ensures that there is adequate soil moisture available within the root zone for seeds to geminate. Seeds of many plant species require specific temperature and moisture conditions to germinate. If the moisture content is below a certain threshold, the seeds will desiccate and die. This is the primary reason most seed companies suggest that seed be stored in a dry environment until planting. When seed is dusted in, especially during the fall, the temperature is usually adequate to cause germination. However, without adequate soil moisture, a large percentage of the seed will not germinate.

It is important to understand that when all the elements are correct for the seeds to germinate, except moisture, the seeds are forced to consume their stored energy at a high rate to stay alive. As a result, when seeds are dusted in, a high percentage of seeds will literally starve to death before they receive enough moisture to germinate and begin creating more food through photosynthesis.

In hindsight, we made a mistake with my series of food plot articles. We should have prioritized the articles, writing about the importance of soil moisture before writing the articles on lime and fertilizer. Looking back at the 2000 spring and fall planting season, most food plot planters would agree that adequate soil moisture is more important than any other aspect of their food plot preparation. Without adequate soil moisture, disking, liming, fertilizing, and planting are just like throwing money down a rat hole. Thinking ahead to the 2001 planting season, we strongly suggest considering soil moisture as the primary determining factor when determining the best date to plant your food plots.

Dr. Grant Woods and Bryan Kinkel are research biologists with Woods and Associates, Inc. Both are involved in research concerning deer population dynamics, deer behavior, and advancements in forage production. Grant and Bryan also assist hunting clubs and private landowners throughout the U.S. to improve the quality of their deer herds through site–specific management techniques. Members of Woods and Associates are regular contributors to Quality Whitetails.