Physics of a Green 7/1/2012



Physics of a Green

Healthy white roots persist in an aerification hole from this springs aerification. Filling the hole all the way to the top with sand keeps the surface from being sealed off by organic matter and allows the plant to roots to occupy increased air poe space.

 

 Over the past few months we have been exploring the agronomic and physical properties of our greens. These test include standard fertility test, saturated soil test, physical analysis of the top four inches verses the bottom four and irrigation water quality.  It is important to be able to quantify the current conditions for a couple of reasons.  First, this information helps us to develop specific programs and procedures to maximize our results and seasonal performance.  Second, it gives us the ability to measure and quantify our results moving forward.

            The physical analysis test revealed the original material (4-8 inch sample) used to construct the greens as tested is a good quality sand.  It falls out of USGA specifications slightly, on the fine end of the spectrum. It appears that the sand was blended with an organic component, most likely peat moss.  The water infiltration rate is still at 8.1 inches per hour, which exceeds the 6 inch minimum suggested by the USGA. The cap and air pore space sits at 42.8% with 24.2% being air filled pore space and 18.5% capillary space. Moisture retention at 30 cm. is 12.2%.   Overall, it is a reasonable greens mix from a physical standpoint that is still exhibiting good qualities for a USGA putting green.

 

           The impacted or modified region of the greens mix (0-4 inch sample) shows the results of the historic greens maintenance programs over time.  The upper sand profile is within USGA specifications. The organic matter content has increased significantly with corresponding reductions in water infiltration and air filled pore space.  Air porosity represents the larger non-capillary porosity of the sample. This figure will greatly affect the percolation rate. It is this pore space that the plant occupies, and is therefore one of the major factors that dictate the success of a rootzone to support the plant.  The capillary space has increased dramatically as a result of the organic matter.  Moisture retention at 30cm is 23.1%. The elevated organic matter in the upper profile is retaining more water which is having a negative impact on on root development and moisture management. This also shifts the playing field in favor of poa annua.

            This data has revealed several opportunities for improvement.  The organic matter development in the upper profile has exceeded the cultural practices on the putting greens.  The need to increase the aerification, needle tining, venting, and topdressing is evident. Spring and fall aerification with ½-5/8” tines is warranted. Venting should occur every three weeks throughout the growing season. We also need to reduce nitrogen inputs into the 1.5-2.5 pound per thousand square feet region on the greens. We also need to find topdressing sand that is several degrees coarser than the material we are currently using. These efforts are intended to increase the air pore space and reduce the organic matter content in the upper profile of the greens.  It will take a full 2 seasons to bend the organic matter curve that we are currently on.