SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: http://read.dmtmag.com/i/448298
www.stma.org February 2015 | SportsTurf 23 you probably have between 20 and 30 percent sand in there now, maybe less. What happens if you add just a little bit of sand and move the percent sand from say 22 to 25%? If you were trying to amend the top 3 inches that would translate into about 30 tons of straight sand per acre. You've now moved your soil texture from Point A in Figure 2 to Point B Do you think this helps? The answer is no and it may even hurt, here's why. Look at Figure 3. Imagine that the rect- angle represents a soup can filled with flour. There have been some holes poked in the bottom to allow water to drain. Imagine that the marbles aren't there yet. Let's percolate the flour in the soup can. It has some percolation rate, I don't know what it is but it percolates at some rate. Now let's add those marbles. After we added the marbles, did the percola- tion rate go up or go down? Think about it for a second. If you said no change, you are, for all practical purposes correct. Likely we wouldn't be able to measure much change, but if we could, we would find that the percolation rate would go down. The reason is that before water would move through the areas where the marbles were, now the water much move around those areas. As you add more and more marbles the percolation rate keeps going down until you have enough marbles, so that they are all touching each other, and there isn't quite enough flour to fill in all the gaps. At that point the percolation rate, and thus macroporosity, increases. The textbooks tell us that this hap- pens at around 60% sand and I believe if you have the perfect sand and only the perfect sand, then this may be true. My experience is that it typically hap- pens around 75% sand. If a 3% increase equals 30 tons per acre, what does a 50% increase mean? It means 500 ton per acre to amend the top 3 inches. And this is the minimum that is likely to be required. So if you are topdressing a native soil field, use straight compost. Could you cut that compost with a little bit of topsoil? I guess, but why? You have all the sand silt and clay you need, all you need for good quality topsoil is the addition of organic matter. Remember, adding a little bit of sand is sometimes worse than adding no sand at all. Bricks have a lot of sand in them. Typically they are about 60% sand. Now if you have a native soil field and want to change to managing a sand field or at least a sand cap field that is a different story. Now you want to follow what the golf courses typically do to their push-up greens, that is, build a layer of almost pure sand on the surface. You're not mixing in the sand; you are layering it on the surface (Figure 4). Here is a really good guide on one method to accomplish building a 'push-up' sports field, or as it is typically referred to: a sand cap system. http:// turf.msu.edu/assets/ArticlePDFs/Built- Up-Sand-Capped-System.pdf Several words of caution: For a sand Figure 3. Saturated flow through a soup can filled with flour. The colored round objects represent marbles. Figure 2. Textural triangle; points A and B are both silt loam soil with point B having 3% more sand than Point A. Figure 4. Sand Cap.