Each August we audit our green maintenance program by taking undisturbed core samples off of 5 of our greens which represent five different eras of green construction on our course and BenchMarking them against samples taken in previous years, our testing is done by ISTRC (International Sports Turf Research Center). We test the infiltration rate, air porosity, water holding capacity, bulk density and organic matter accumulation in the top 4" of the green and the results dictate our management program for the next 8, growing season, months. Last year, because of 23" of rain in 8 weeks and the resulting weak turf it left behind we were unable to perform routine minor management practices throughout the summer so our ISTRC test result indicated we were in need of a more aggressive program which started with a DryJect late last August followed by aggressive core aeration the last week of October and finally the DryJecting last week. Had we been able to perform our summer program there is a good chance the aggressive coring last October would not have been needed.
OK, so what does all this mumbo, jumbo me to me the GOLFER?? Smooth, fast, firm, healthy, consistent greens are a result of having the right balance of drainage and dead and living grass roots in the surface 4" of the green and that balance, inturn, renders the correct balance of oxygen to water that grass roots thrive on. Let me also say, grass root growth, itself, depletes oxygen pore space by pushing it out with new root growth and old roots die off naturally all season long leaving behind a mussy residue that plugs the soil reducing water infiltration rates. Well, this is a simple explanation of the dynamic world of grass root growth on a green and is the reason why we sand topdress, spike, knife, dryject, hydroject, solid tine and sometimes have to core aerate to maintain a prescribed soil balance that renders a fast, firm and smooth putting surface.
Pictured; DryJect sand injection. Profile of injected sand. Sweeping surface sand. Finished. 
