|The four ‘R’s|
|Thursday, November 29, 2012 1:16 PM|
Using the right fertilizer rate starts with knowing your crop nutrient requirements. The right rate should be based on soil and tissue tests taken from an accredited laboratory and should be based on Tri-state agronomic fertilizer guidelines. Soil tests should be taken a minimum of every 3-5 years. A study of agricultural testing laboratories found that while a majority were testing and reporting nutrient levels correctly; their guidelines for the amount of fertilizer to apply were vastly different. So in many cases, fertilizer was being recommended when it was not needed (Mullen and Dayton, 2011). Farmers need to keep good fertilizer records to see how their soil tests change over time.
The right fertilizer source means adjusting for the purity and the solubility of the product. Many companies are using products like Avail or Jumpstart with P fertilizer. These products increase the solubility, making them more plant-available but also easier to lose. With fewer impurities, the fertilizer nutrient content increases. Plants take up soluble nutrients but unfortunately that increases the chance of surface water runoff.
Applying fertilizer at the right time means not applying fertilizer or manure to frozen or snow-covered soil. The recommendation is to apply fertilizer or manure to growing crops or when the crops will need the nutrients to minimize losses. Incorporating or banding fertilizer at planting time is the preferred method. Do not apply before a projected heavy rainfall or precipitation event like melting snow. Frozen and snow- covered applications have the greatest risk of off-site movement whether manure or commercial fertilizer (LaBarge, 2012). About 90 percent of the nutrients are lost each year during major rainfall events (2 inch rains or greater) or during snow melt (Sharpley, 2012).
What other practices can farmers do to minimize P losses? Farmers should continue to utilize proper best management practices like soil conservation. Avoid plowing and tilling the soil and utilize no-till or minimum till with at least 30-percent residue cover. Protecting the soil with residue increases water infiltration and allows the nutrients to contact the soil particles where it may be absorbed and available for plant uptake. Using cover crops will improve soil health and nutrient retention and recycling. Most major and minor soil nutrients are tied up in an organic form and are less susceptible to runoff. Filter strips, grass waterways, buffers, and wetlands are encouraged to treat and filter out nutrients before it reaches our rivers and lakes.
Other practices that farmers can adopt include repairing and fixing broken tile lines quickly before the soil erodes and nutrients are lost. Surface inlets should be protected with a plastic cover to prevent surface runoff. A majority of the nutrients are in the top 1-2 inches of topsoil. When the soil erodes, the sediment that is lost is composed of the richest soil, the soil organic matter which tends to float and to be easily transported to surface water. Concentrated surface runoff should be treated if possible before entering a stream. Nitrogen and phosphorus bioreactors situated in tile outlets have been shown to reduce nutrient losses by 70-90 percent (Brown, 2011). Controlled drainage structures which hold back the water during the winter have shown similar results (Brown, 2011).