If you’ve heard it once, you’ve heard it a dozen times: Get a soil test before you plant your food plots. It’s true. Nothing will improve the health of a food plot more than properly amended soil. A soil test will tell you exactly what your plants need in order to thrive and they will tell you the pH level of your soil, a vital factor in the plant health equation.
Don’t cut corners, though. Do-it-yourself soil test kits are available at most garden stores, but they aren’t worth the expense. They might indicate a high pH, a lack of nitrogen or an abundance of potassium, but that’s all they’ll tell you. The results are vague and you won’t be able to determine how much fertilizer or lime your plots need to thrive.
Instead, get a professional soil test from your local county extension agent or from a reputable company that sells food plot products. They will tell you everything you need to know. They’ll provide pinpoint recommendations of the basic nutrient needs of the exact plants you are putting in your food plots. Whitetail Institute’s soil test kits, for example, are tailored for each of the company’s products.
“Every plant has different nutrient needs,” says Whitetail Institute Vice President Steve Scott. “You are doing yourself and your food plots a favor if you use a test kit that is tailored for a specific seed.”
Soil test kits don’t just help your plots reach their full potential. They’ll actually save you money, adds Scott. What’s the point of spending money on seed, gas and fertilizer if your plots don’t thrive?
“A soil test might tell you that you don’t need as much lime or fertilizer as you think you need,” says Scott.
What Does It All Mean?
The better test results list the current nutrient levels in your soil along with the recommended rates for the specific plant you want to grow. Some also offer a glimpse into the various micro-nutrients in your soil. Magnesium, copper, iron and other nutrients are just as vital to a healthy food plot as nitrogen, potassium and phosphorous. The good news is those micro-nutrient levels are usually adequate already.
“It’s very rare that the micro-nutrients need to be amended,” says Virginia Tech soil testing lab director Steve Heckendorn. “In many cases, an application of lime can bring the micro-nutrients to healthy levels if they are not already.”
However, any or all the primary soil nutrients — nitrogen (N), phosphorous (P) and potassium (K) — may be lacking. Those numbers correspond to the letters of a bag of fertilizer. A sack of 10-10-10, for instance, has 10 percent nitrogen, 10 percent phosphorous and 10 percent potassium. (The remaining 70 percent of the ingredients is filler.)
Generally, nitrogen is what makes plants green. The leaves of plants with healthy levels of nitrogen will be a deep, vibrant green, while plants with low nitrogen levels tend to be yellow or dull green. Phosphorous helps boost a plant’s flower and seed productivity, which is why flowering plants like sunflowers thrive in phosphorous-rich soil. Potassium builds strong roots and stems.
All three are the critical links to healthy plants, but the amount you need varies by the soil as well as the plant itself. Some plants, grasses, for instance, need higher levels of nitrogen to thrive. That’s why soil tests for oats, wheat and other grasses typically recommend fertilizers with a higher amount of nitrogen. Legumes like clover and soybeans actually add, or “fix,” nitrogen into the soil. They usually don’t need as much nitrogen, but they might need higher levels of potassium and phosphorous.
Your soil test results will tell you what you need, usually in terms of pounds per acre. Some break down the application rate for each 1,000 square feet. Whatever your test results show, you’ll have to do some calculating. If, for example, your test results recommend 500 pounds of 10-20-10 per acre, but your plot is only 100 feet by 50 feet, you’ll have to figure out the application rate on your own. An acre is 43,560 square feet, but your plot is 5,000 square feet, or about a ninth of an acre. That means you’ll need just 55 pounds or so of fertilizer.
The Lime Factor
Fertilizer feeds plants, but they won’t get the full benefit from the nutrients if the soil’s pH level is off. That’s why every good soil test will provide a pH number, which indicates the soil’s acidity or alkalinity. Generally, most plants thrive in soil with a pH level of between 6.0 and 7.0. A pH level of 7.0 is considered neutral. Levels below that are acid; those above are considered alkaline. Lime raises the pH level, but not all soil needs lime.
“Soils tend to be more acid east of the Mississippi, but the levels will vary by soil types,” says Heckendorn. “Generally, sandy soils like those near the coastal plain have a higher pH level and heavy, clay soils have a lower pH.”
Simply put, the addition of lime in acidic soils helps dissolve the nutrients in the ground, making them more available to the plant’s roots. Phosphorous in particular needs the proper pH level so it can fully benefit the plants.
The key to getting the full benefit of a lime application, says Heckendorf, is to get the lime down to the plant’s roots. That means you’ll need to till it in after it is spread on the surface. Even when it is disked in, lime can take months to alter the soil’s pH level.
“There is no quick fix for changing the pH level of your soil, but it will take much longer if you just put lime on the soil’s surface. You are only altering the pH level of the very top layer of soil, because it can take a very long time for the lime to work its way down to the plant’s roots if it isn’t disked in,” says Heckendorf. “It can take a year and a half to fully react.”
Pelleted lime, the type found in bags at garden stores, can take even longer to alter the pH level. It’s also considerably more expensive than pulverized, powdered agricultural lime sold in bulk at farmer’s cooperatives and supply stores. Pelleted lime is easier to spread, though. It’s a good choice for small plots, and it might be the only option for plots that can’t be reached by a large spreader truck. Ag lime is a better choice if you need a large amount, but instead of spreading it yourself, have your local farm supply store spread it for you. They’ll charge you for the labor, of course, but if you need a ton or more, it will certainly be worth it. Their trucks can spread a couple of tons in just a matter of minutes.
What ever you do, don’t scrimp on the lime. It’s much less expensive than fertilizer, which will only benefit your plants if the soil’s pH level is correct.
“It can take some time to get the pH to the right level, but once you do, you’ll see very good results,” adds Heckendorn. “Once you get it right, you should take a soil sample every couple of years to make sure it doesn’t need another lime application.”
Implementing A Soil Test
Soil test results include recommended amounts of each type of fertilizer and the proper amount of lime to grow a healthy food plot. Knowing what to use is one thing. Knowing how and when to implement the recommendations is entirely different. Timing also matters.
“We recommend putting your fertilizer down and then disking it in right before you put your seed down,” says Scott. “By incorporating the fertilizer into the soil instead of spreading it on top of the soil, you encourage the plant roots to go down and not out as they grow towards the nutrients.”
Lime should also be disked into the soil for the same reasons. It will help speed up the soil amendment process and it will also prevent the lime from running off the surface of your plots during a heavy rain.
“Put your lime down as far in advance as possible. Although it will start to change the pH level of your soil pretty quickly, it can take a very long time to fully alter the pH level to where it needs to be,” adds Scott.
The recommended lime application rate is pretty straightforward on any soil test, so stick to it. Don’t cut corners. Be warned, though. If soil needs lime, it often needs lots of it.
The recommended fertilizer levels aren’t quite as simple. Some soil tests will recommend an even blend like 10-10-10 or 13-13-13, both of which are readily available at garden and hardware stores. However, many soil types lack a specific nutrient and require an uneven blend, something like 17-10-10. That means you’ll need a fertilizer that might not be readily available at your local hardware or garden store. Don’t panic. Scott says it’s relatively easy to find different bagged fertilizers that can be combined to achieve the desired recommended rates.
“We include a chart on our soil tests that show several combinations of common bagged fertilizers so you can use different rates of each one to get the right combination,” he says.
Farm supply stores that cater to professional farmers can make custom blends tailored to your exact needs. Of course, they might have a minimum load requirement, but if you are fertilizing a few acres, you might meet their minimum. They simply pour different amounts of each type of fertilizer into the bed of your truck at the same time. All you have to do is spread it.
If neither of those options is possible, get as close as you can to the recommended application rates, even if it means putting down a bit more of one or more nutrient than is recommended. Putting some fertilizer down is better than putting none down, but if you have a choice, follow the rates recommended in your soil test results.