Fluid fertilizers are packaged and sold either as clear liquids (solutions) or as liquids that have suspended solid particles (suspensions). Fertilizer solutions can also be made from dry milled products intended to be dissolved in water. Fertilizer solutions are sprayed onto the turf, delivering a source of water soluble nitrogen (WSN) and other desired nutrients, such as iron (Fe). The nutrients are either watered down into the soil for root uptake, or foliar absorbed. The reason for applying WSN to turf this way is to achieve a short-term, rapid response - particularly turf green-up. Sports turf managers considering liquid applications should be aware of the following:
(1) There is a higher risk of burn potential, so smaller amounts of fertilizer are used (1-tenth to 2-tenths of a pound N/1000 sq.ft.) at more frequent intervals. This is often referred to as "spoon feeding".
(2) Applying too much WSN at any one time will produce growth surges. Growth surges produce turf tissue with large, thin-walled leaf cells. It is reasonable to assert therefore that high N fertilizer inputs could increase the risk of disease. For example, research suggests that quick-release sources of N and subsequent growth surges increases the risk of grey leaf spot incidence.
(3) Some nutrients such as calcium and iron are immobile in plants. If these nutrients are foliar absorbed they will not be translocated to the turf roots.
(4) If liquids are applied to the turf, allowed to dry and not washed into the rootzone they can be mowed off. This is particularly important if mowing is frequent and clippings are removed. Nutrient loss from foliar applications with clipping removal can be significant and may therefore negatively affect the anticipated fertilizer response.
(5) There is little/no research on how much of these products are absorbed, how they affect turf recovery from wear, and, most importantly, if they are supplying enough N for healthy turf growth in high-wear situations such as athletic fields. It is highly unlikely that nutrients from foliar applications contribute significantly to the reserve bank of soil nutrients, especially if clippings are removed. More research is needed to clarify these interactions.
Granular fertilizers with a portion of nitrogen as a slow-release source are recommended for sports turf situations for several reasons:
* A portion of the fertilizer is not immediately available, so there is less likelihood for burn. Larger amounts can be applied at less frequent intervals, saving labour costs.
* There is less likelihood of growth surges because the slow-release nutrients are metered out over several weeks. For example, our research this year with a 21-4-11 PCSCU mini prill with 28% WSN and 72% slow-release N has provided the turf with a constant source of N (0.1 - 0.3lbs N/1000 sq.ft per week) for 6-8 weeks - see picture top left of the turf response.
* Think of it as a bank! Granular slow-release fertilizers offer a sound base for healthy turf growth on athletic fields - they are the "savings" account for the turf. Additional applications of liquids may offer some benefits if a quick green-up response is desired for a sporting event - think of it as the "checking" account.
Thanks to Dr. Chuck Darrah for his editorial review.Author's: Dr. John Street & Pam Sherratt