Luckily, most complex chemicals needed by plants are already present in the soil, but they're usually deficient when it comes to producing a super-successful yield. Quite often, food plots result in poor yields for a variety of reasons, from over-browsing, poor pH balance, weed competition, moisture irregularity and nutrient deficiencies. Wildlife managers need to control these factors to produce a mature, lush food plot attractive to targeted wildlife.
While all these factors are important, two of them - over-browsing and weed competition - will never become a problem if the plants don't get the required nutrients as fertilizers when needed. Deer cannot over-browse something that isn't there.
Fertilizers originate directly from a variety of sources, from rock to animal by-products. Some are organic, and others are inorganic and completely manufactured in a super-sized industrial laboratory. Typical fertilizers contain the various concentrations of six macro-nutrients: nitrogen [N], phosphorus (phosphate) [P], potassium (or potash) [K], calcium [C], magnesium [Mg], and sulfur [S]. Eight micro-nutrients are also present: copper [Cu], manganese [Mn], iron [Fe], zinc [Zn], nickel [Ni], boron [B], chlorine [Cl], and molybdenum [Mo]. All plants require these nutrients for proper growth and reproduction. Specifically, the macro-nutrients provide benefits to plants as listed below:
Nitrogen: required for plant development and green leafy growth (greatest importance);
Phosphorus: increases blooms, seed formation, and a strong root system;
Potassium: regulates water, encourages vigorous growth and disease resistance;
Calcium: promotes new growth of shoots and roots;
Magnesium: promotes seed formation, greening, absorption of plant foods;Sulfur: promotes vigorous growth and deep greening.
The numbers printed on a bag of fertilizer indicate the composition of nitrogen, phosphorus, and potassium by weight. So, a 50-pound bag of 10-10-10 general fertilizer contains 10-percent of each of these macro-nutrients (10 percent N, 10 percent P, and 10 percent K) or five pounds each of N, P, and K per 50-pound bag. When a site requires 50 pounds of P per acre, 10 bags of 10-10-10 are needed. While not always listed in bold print, fertilizers contain other concentrations of macro and micro-nutrients that plants require. Examine the guaranteed analysis for these other nutrients.
Depending on the fertilizer requirement for the site, fertilizers can be mixed to obtain the desired application recommendation. Fertilizers are sold in various concentrations, from completely balanced fertilizers of equal concentrations of NPK to incomplete fertilizers missing one or two components; such as, extreme concentrations of NPK: 82-percent anhydrous ammonia gas (82-0-0), triple super-phosphate (0-46-0), and Potassium sulfate (0-0-60).
Granular fertilizers should be broadcast across the plot and worked into the soil with the seeds simultaneously or just before distributing and covering the seed. Drag harrows will adequately work fertilizers into the soil. Granular fertilizers should be distributed under dry conditions for maximum effectiveness, followed by a light rain. While precipitation begins dissolving fertilizer into the soil, too much rainfall will wash away the fertilizer. Fertilizer treatments should wait until more satisfactory conditions if severe rain events are planned within the forecast.
Many of these fertilizers will become active as soon as contact is made with the soil. Nitrogen is the heavy hitter here, and the water soluble forms are the best to use; such as, urea, ammonium nitrate, ammonium sulfate, calcium nitrate, and potassium nitrate. Nitrogen fertilizers are unstable and will convert to usable or non-usable compounds very quickly after application depending on the level of oxygen and moisture in the soil. Typically, nitrogen should always be applied under dry conditions and worked into the soil. If nitrogen sits too long on the surface, it will convert to a gaseous form and be lost.
Ammonium-based fertilizers are better to use for most applications as well. The ammonium-based fertilizers will stick to soil particles due to opposite electron charges and will be converted to nitrite more slowly, giving the plants the ability to absorb the nitrogen before denitrification or loss into the atmosphere.
Nitrite forms of nitrogen are not recommended in well-drained, sandy soils. The nitrite will repel soil particles and can leach through the soil quickly after a heavy rainfall. Fertilizers are expensive, and farmers need to apply to offer the crops the best chance for utilization.
Sometimes, nitrogen fertilizers will come coated with sulfur that allows the nitrogen to be emitted in more of a slow-release format. Farmers should consider these slow-release types for crops that need a season-long nitrogen application.
When applying fertilizers at layback or after plants have emerged, applications should never be made when the plants are wet. The nitrogen will burn the leaves and potentially kill the plants on contact. Granular fertilizers should be distributed under dry conditions for maximum effectiveness, followed by a light rain. Fertilizing before planting and throughout the growing season are beneficial to get the nutrients to the plants effectively.