FERTILITY
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manager to apply the essential nutrients at the proper time and amount to meet the needs of the field ( s ) without causing damage to the environment . With this in mind , it ’ s important to know ( 1 ) how each fertilizer carrier releases nutrients , ( 2 ) where to place your applications for best effect and ( 3 ) when to apply nutrients for greatest efficiency .
Figure 1 provides specifics on the various release characteristics of fertilizer carriers found in common products on the market today . Most commonly , the nutrient in question is nitrogen . There are two general types of release rates for fertilizers : quick-release and slow- or controlled-release .
Quick-release fertilizers are primarily water-soluble nitrogen ( WSN ), and when applied to the soil and irrigated , will begin to release nutrients to the plant almost immediately . Slow-release fertilizers have a more complex make-up and a wider variety of formulations . The most common forms are slowly available water-soluble nitrogen ( SAWSN ). Of the SAWSN , sulfur coated urea ( SCU ), polymer coated urea ( PCU ), polymer coated sulfur coated urea ( PCSCU ) and methylene urea ( MU ) are most common . Other formulations are given the name water-insoluble nitrogen sources ( WIN ) and include urea-formaldehyde ( UF ) and a variety of organic sources . These sources are extremely stable and require ideal conditions to release nutrients .
Because ammonium sulfate and urea are completely water soluble , they can be applied while conditions are cool / cold and unsuitable for microbial activity . WSN are the best choices during early spring and late fall . SCU , PCU and PCSCU are prills of quick-release urea coated with layers of sulfur and / or polymer to slow the breakdown of the fertilizer and the subsequent release of the nutrient . The rate of release depends on the thickness of the coating , soil temperature and moisture content . Stabilized N sources ( i . e ., LSN or UFLEXX ) rely on nitrification inhibitors to delay the N conversion to nitrate , helping it stay attached to the soil as ammonium for a longer period of time . They are water soluble , but can be moderately applied throughout the season . MU and UF are homogenous fertilizers made up of chains of urea and formaldehyde reacted together to control the release of nitrogen . Generally , the longer the chains , the longer the
release . Reacted fertilizers require water and microbes to break down the fertilizer , and are most effective when temperatures are consistently above 55 ° F .
Figure 2 illustrates the best times of year for applying the various types of nutrient carriers . Fortunately , many fertilizers are formulated with multiple carriers . This allows a sports field manager to reduce the number of applications that may be required during the season . For example , a fertilizer formulated with 25 % urea and 75 % methylene urea could potentially be used to apply 2 pounds of N per 1,000 sq . ft . in the spring and provide 0.5 pounds of N immediately and 1.5 pounds of N throughout the summer – all with one single application . This approach would provide an opportunity to reduce the need for several applications .
A big benefit from fertilizing in fall is to bolster turfgrass recovery from the numerous stresses of summer . Other benefits include increased winter stress tolerance , potential to expand the root system without a corresponding surge in foliar growth commonly seen in spring or early summer ( that may occur at the expense of increased rooting ), and reduced leaf succulence . Slow-release forms of nitrogen such as SCU , PCU and PCSCU that are activated via soil moisture are appropriate for early fall applications , as well as the microbially dependent MU , UF and organic sources . In late fall , soil temperatures are too cold for these sources to be of benefit ; in this timeframe , a shift to quickly available soluble sources – such as urea , ammonium nitrate and ammonium sulfate – is best .
Figure 3 illustrates the incorrect application of a quality fertilizer carrier . This photo , taken Novem- sportsfieldmanagementonline . com January 2022 | SportsField Management
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