Focus on fertilizer
23 Jan, 2008 By: Fred Hume Athletic Turf NewsSelecting the correct fertilizers for sports fields and on an ongoing basis can be confusing. There are a multitude of products to choose and some may be labeled for specific crops or uses. To avoid improperly selecting and using fertilizers, it is best to understand the make-up of a product beyond the N-P-K analysis or the name on the bag.
The first step should be to conduct a comprehensive soil test. Mineral soil has a tremendous influence on plant nutrition. It can store, transform and supply nutrients to plants, as well as affect the availability of applied fertilizers. A measurement of soil pH and nutrient status is essential. If pH is too high or low, added nutrients such as iron may be ineffective. If a soil already contains a high level of a specific nutrient (e.g. phosphorus), there is little need or advantage to plants in adding more in the form of fertilizer. The goal in deterring a fertilizer program should be to add only those nutrients that are lacking in order to optimize plant growth during the establishment and maintenance phases. A soil test should identify the nutrients you need to add and guide you on the correct rate to add them. Supplying unneeded nutrients can have adverse environmental impact that should be avoided.
When you are ready to select fertilizers with the correct nutrient ratios, there are other fertilizer product properties that you should keep in mind. Cost per bag may be a factor, but landscapers should examine the value they are getting and consider the entire seasonal cost, including labor, when comparing product costs. Some may be lower cost but more labor intensive, while others may cost more per bag but are easier to apply and provide longer-term benefits. Another key factor is how soluble the fertilizer is. Fertilizers can be classified into various types: soluble and slow-release/controlled release.
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Soluable solution
Soluble fertilizers are designed to be mixed with water and then sprayed or drenched into the soil. They also may be broadcast on top of the soil in a granular form. Solubles provide a quick response in terms of plant growth, but their impact is rather limited over time (Fig. 1). After a soluble fertilizer is applied, it has a residual effect of only two to three weeks. During this time plants can quickly go from lush growth to deficiency after a single application due to the "feast or famine" cycle. Although these products may cost less per bag, they may need to be applied a number of times during the growing season, leading to more labor and a higher total fertilizer cost per season. Since these products have a highly soluble nature, they may be more prone to run-off with excess water. Additionally, solubles have a higher potential to burn plants especially in the heat of summer, and the best strategy when employing solubles is to apply lower rates/more frequently for optimal plant growth.
Sustain the gain
Slow-release fertilizers (SRF) and controlled-release fertilizers (CRF) supply sustained nutrient feeding with a single application. Some SRFs may require some soil microbial action to convert nutrients into a plant available form. Controlled-release fertilizers are typically coated with technologies that tie nutrient release with soil temperature.
While these fertilizers typically have a higher cost per bag compared to solubles, they can supply a much longer nutrient residual response (12-16 weeks) with a single application. CRFs provide the greatest degree of plant safety and have a much lower potential to burn plants. CRFs also ensure a consistent and predictable supply of nutrients over the period of time as defined by the label, and they don't generally produce the excessive initial surge growth that solubles can.
SRFs and CRFs can be applied at higher rates and much less frequently than solubles. Full-season feeding can actually be achieved with a single application of CRF.
The right nutrients
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