The following article contains some interesting ideas... http://aggie-horticulture.tamu.edu/archives/parsons/turf/publications/fertiliz.html "The "peaks" and "valleys" in growth rate observed between applications of soluble nitrogen fertilizers may not be obvious on frequently mowed turf areas, but they can have a detrimental effect on the grass. Short bursts of growth after fertilizer application followed by a period of slow growth can deplete carbohydrate reserves in the grass, reduce root development and eventually thin a turf. These effects are not readily apparent by observing growth rate and color responses to fertilization. Long term observations and responses to stress would more accurately establish the effect of soluble nitrogen sources on turf." The interestting thing about this statement that it kind of explains how/why carb reserves get used up with early Spring N apps, among other things...
Same article: "Slow-release nitrogen sources build up "residual" soil nitrogen that is made available to the grass at varying rates. The rate at which "residual" nitrogen is made available (released) may vary with nitrogen source, temperature, moisture, pH, particle size and time of application. Knowledge of a particular nitrogen source and of conditions favorable for nitrogen release is necessary for a turf manager to determine the timing and rates of application of slow-release fertilizers."
Residual build up of N in the soil that is released when adequate water is present and extreme temps are avoided would be a great plus for even tempered healthy growth... Would this be an adequate reason to use organic fertilizers during the summer? ...In that an additional expense would be justified at the beginning of summer, but may possibly be compensated by 'skipping' the next app and holding off until Fall, as the 'residuals' from slow release and organic ferts get used up??
Nice article but it also states that organic sources should not be concerted a slow release fert and not a good winter fert. lNevertheless, organic nitrogen sources can be effectively used in most turf maintenance programs. Nitrogen release from organic sources is dependent on microorganisms; thus, factors that favor microbial activity increase the rate of nitrogen release from these materials. Organic materials are not considered good nitrogen sources for winter months because of the low activity of microbes. During other seasons organic sources are very effective. Charles Cue
And that does make sense to me... Where I'm looking for a healthier turf is in the heat of summer when the color fades and growth sometimes stops and some plant go into dormancy. With Orgferts being reliant on microbes for N release, it would makes sense that the only time N was released would be when conditions are correct for both roots and microbes. Whereas synferts would more easily volitize or leach during short infrequent events of heavy downpours, and therest of the time is hot and dry... If we follow the following bit of logic, it would seem that our winterizer, below 50 degree soil temp almost always have to be synthetic... ... "Fertilizer applications should be timed to coincide with favorable temperatures for growth of turfgrasses. Also, nitrogen sources should be selected based on their availability to grasses under expected temperature conditions. For example, organic nitrogen sources and ureaformaldehyde do not release nitrogen at sufficient rates for turf growth when soil temperatures are below 50ºF. ..." The other point with organic fertilizers for the summer is that they'll help build a structure that is conducive to healthy root growth and provide CE sites that ferts can hang onto longer... Does that seem worth it?
"Potassium is often present in large quantities in soils, but very small amounts may be in the available form (K+). Potassium is a constituent of many soil minerals and is held very strongly by clay particles. For potassium to be taken up by the grass it must be in the solution in the potassium ion (K+) form. An equilibrium exists between the K+ in solution and that held by clay particles (see illustration). As the grass root takes up the K+ from the soil solution, additional K+ is released from the soil solution to the clay particles. Clay particles, thus, serve as a reservoir for K+ and help to reduce the amount of K+ lost by leaching." This brings up an iteresting point that is never discussed as a possible issue in fert programs. Just like P it appears that K is likely to be available in a 'fertile' soil... In this case a fertile soil would likely just have clay particles in... Can soil tests measure how much K is being held by the clay particles? or do they only measure how much K is available at any given time w/out regard to the 'K resevoir'?
P and K are not comparable, and soils tests give you semi-quanitative numbers on the labile K pool (exchangeable & solution K). Some testing methodologies will only give you numbers on exchangeable K.
I only meant that the idea of "Available" P changes on an 'as neede' basis with the presence of AMF, as this article claimed that "Available" K changes as on an 'as needed' basis with the presence of clay particles... The question now becomes: How do we know if there is enough 'reserve K' in the clay for there to be a healthy amount available to the turf as needed?
You mean by this statement? "...semi-quanitative numbers on the labile K pool (exchangeable & solution K). ..." If I take a soil sample down to the testing lab, Which test would I ask for? (by name) and how would I know that the K is being release at an adequate pace to provide the necessary amounts on a timely basis? (is the amount adequate to assume the rate?) It would be good to be able to take a soil test to a client and show that he needn't apply any K for his winterizer...
