Fertilizer: What You Need to Know

By William Cousins

 Whether you’re a first-time food plotter or an old hand, you probably know that the planting instructions aren’t the same for all Whitetail Institute products, but they all contain at least one step calling for the addition of fertilizer to the seedbed. Have you ever stopped to consider why?

More specifically, what exactly does fertilizer do? The quick, general answer is that it adds nutrients to the seedbed. Just like humans, plants need access to nutrients to survive, grow and be healthy. Humans get most of the nutrients they need from food. Plants get them from the air, water and soil. Fertilizers don’t address the nutrients plants get from the air and water because they’re readily available. As for nutrients plants get from the soil, most soils hold some of the essential nutrients plants need, but more often than not, the level of one or more essential soil nutrients is lower than optimum. Fertilizer is used to add nutrients to the soil to bring any existing nutrient levels that are low into optimum range. Most of us know the basic roles nutrients play in our bodies. For example, we know protein is needed for muscle growth, and Vitamin C can help ward off the common cold. Surprisingly few, though, know the specific roles nutrients play in the plant world. Obviously, there isn’t enough room here to provide a fully detailed explanation. Thankfully, only a few soil nutrients are of real concern to most food-plotters, and there’s plenty of room to hit the high points of those. In this article, we’ll limit this discussion to the major roles of nutrients in fertilizer.

Preliminary Matters Soil pH and Lime. Even though soil pH and lime are neither nutrients nor fertilizers, no discussion of what fertilizers do would be complete without at least mentioning them. That’s because fertilizer does nothing unless the plants can access it, and unless soil pH is within the neutral range (about 6.5 to 7.5), soil nutrients are bound up in a way that keeps most forage plants from fully accessing them. For example, if you fertilize and plant in soil with a soil pH of 5.0 without raising soil pH by adding lime to the seedbed first, the forage you just planted will almost always be able to access only about half of the fertilizer you put out. In other words, if you spend $100 on fertilizer and plant in 5.0 pH soil, you’ll be flushing about $50 down the toilet. That’s why soil pH is the most important factor you can control to assure food plot success, and why the existing soil pH of your soil is the first reading you should look at when you receive your soil-test report back from the lab.

Test Your Soil With a Laboratory Soil- Test Kit. Only a soil test performed by a qualified soil-testing laboratory can provide the precision to make sure you know exactly what the pH of your soil is, what the existing levels of soil nutrients are, and how much lime and what fertilizer you should add to the seedbed to correct deficiencies. The benefits offered by precision laboratory soil testing are real. It can mean the difference that makes your forage stand really flourish, and save you money at the same time. Often, you can save hundreds of dollars by eliminating wasted lime and fertilizer expenses. High-quality laboratory soil-test kits are available from the Whitetail Institute, agricultural universities, county agents and many farm supply stores. In this article, we’ll be referring to the report generated by the Whitetail Institute’s soil-testing laboratory because it is specifically designed for food plotters instead of farmers. It cuts right to the chase, providing only the information most food-plotters really need in an easy-to-read format.

Soil Test “Readings” and “Recommendations.” The Whitetail Institute soil-test report provides readings of existing soil pH levels and soil nutrients, and includes recommendations of what to add to the soil to bring any low levels into optimum range. This distinction is important for understanding the report. One reason is that a reading for nitrogen isn’t provided, but a recommendation for nitrogen fertilizer is. That’s because nitrogen in the air, while plentiful, is not a form of nitrogen that plants can use directly, so in most cases, you’ll need to add a standard amount of nitrogen based on the needs of the forage you’ll be planting or maintaining. Another reason is that terminology can differ a bit between a soil-test report’s readings and recommendations. For example, the readings of the phosphorus and potassium levels in the soil sample are stated as “phosphorous” and “potassium,” and the fertilizer recommendations for correcting low levels are respectively stated as “phosphate” and “potash.” In other words, phosphorous and potassium are the nutrients, and if those levels are less than optimum, phosphate and potash, respectively, are the fertilizers used to correct them. When you receive your soil test report back from the Whitetail Institute soil-testing laboratory, the first thing to check is the lab’s reading of the “Actual Soil pH” of the sample you sent in. This is clearly shown at the top right of Page One. If this number is lower than 6.5, you will find a lime recommendation in Table 1 on page one of the Whitetail Institute report. For best results, you should try to add the amount of recommended lime as early as possible. Be sure to incorporate the lime into the seedbed by disking or tilling so that it can work as quickly and fully as possible.

Soil Nutrients and Fertilizers Most food plotters need only be concerned with five soil nutrients: nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), and magnesium (Mg). And what’s even better, three of these (N,P and K) can be easily addressed with commonly available bagged fertilizer blends, and the other two (Ca and Mg) can be supplied by the lime you add to raise soil pH. It isn’t beneficial, though, (and in some cases it can be detrimental to forage growth) to add way too much of any one element to the seedbed. And again, that’s where the accuracy of laboratory soil testing is such a great benefit.

Nitrogen. Nitrogen is needed for just about every process a plant goes through, but for lack of a better word, the biggest role nitrogen plays is to promote leafy growth. You can sometimes tell if nitrogen is lacking by the yellowing of the plant’s leaves, especially if the leaves that are yellowing are older.

Phosphorous. Phosphorus is especially important for early plant growth, root growth and energy storage, and it helps plants mature. Low phosphorous levels can be the reason for slow plant growth, leaf curling or die-back, weak stems and roots, a purple appearance in older leaves and stems, and reduced cold tolerance. And here’s yet another example of how having a laboratory test your soil can really save you money. As part of the planting instructions for all its forage products, the Whitetail Institute provides alternative fertilizer recommendations for situations in which a laboratory soil test isn’t available. Since these alternative recommendations are designed to apply to the broadest range of situations, rarely will they be precise in an individual case, and if they are, then it will be by chance. The soil-test report that accompanies this article shows that the customer is planning to plant Imperial Whitetail PowerPlant. The alternative (if a laboratory soil test isn’t available) fertilizer recommendations the Whitetail Institute provides in its planting instructions for PowerPlant call for the addition of “400 pounds of 13-13-13” to the seedbed just before planting, and that includes 52 pounds of phosphate. The bar chart at the top of page one of the soil test report, though, shows that this particular customer’s soil already has a phosphorous level that is higher than adequate, and consequently, Tables 1 and 2 recommend that no phosphate be added to the seedbed. The Whitetail Institute soil-test report costs about $13. Fifty pounds of phosphate currently costs about $20 to 25. By spending $13 on a laboratory soil test, the customer in this case will save the money he would have otherwise spent on excess phosphorous fertilizer.

Potassium. Potassium is also important for root development, and it aids in water uptake by the plant, improving its tolerance of heat and drought. Potassium also helps the plant’s winter hardiness and increases its overall health and vigor.

Calcium and Magnesium. Just as calcium is important for helping build strong bones and teeth in humans, it’s also essential for building strong cell walls in plants so that they’re healthier and better able to withstand stress. Magnesium plays an important role in photosynthesis, the process by which plants use energy from the sun to synthesize their food from the nutrients they get from air and water. The Whitetail Institute soil-test report provides readings as to what your soil’s existing levels of calcium and magnesium are. From the food-plotter’s perspective, calcium and magnesium usually don’t require amendment, because they’re otherwise available and any shortfalls are corrected with other soil additives, such as limestone added to correct low soil pH.

The Importance of Nutrient Balance. It’s very important for the level of one soil nutrient to be in balance with the others. This, again, highlights the preference for testing your soil with a laboratory soil test kit. Only a qualified soil-testing laboratory can take into account all the relevant soil and forage-specific factors needed to make precise fertilizer recommendations. And that’s another way the Whitetail Institute’s soil-test report makes it especially easy for food plotters to determine what fertilizer to buy. Table 2 on Page Two is a chart showing alternative combinations of commonly available fertilizer blends that can be used to meet the report’s fertilizer recommendations. You need to clearly understand that everything in one block is one alternative, and everything in the next block is another alternative. In other words, whichever block you decide to go with, apply everything in that block. If you’d like additional information, please call the Whitetail Institute’s in-house consultants at (800) 688-3030. The call and the service are free.