March 10, 2007 Article
by David Rodriguez
Big dogs and beautiful lawns are not compatible. If you want a beautiful backyard, don’t think that you can turn a dog or even rambunctious children loose to romp and stomp.
The pitter-patter of little feet signals devastation to lawn grasses. Not only do grasses suffer, but all plants, even the majestic redwoods of California, cannot endure the consequences of foot steps. Giant Sequoia trees, over 2,000 years old, began to decline for no known reason. Finally it was discovered that hundreds of people walking around and around at the base of the trees and looking up-fascinated by the size and height of the trees-were trampling to death these natural monuments. The problem? Soil compaction!
Compaction destroys soil structure, thus increasing density, carbon dioxide concentrations (plant roots need oxygen to live and grow) and heat build-up. Additionally, it creates surface runoff rather than allowing water to penetrate the roots. Compaction subsequently decreases the amount of large pore space available, as well as oxygen in the soil, water penetration, and nutrient influx.
When compaction increases soil density, root elongation is inhibited, causing poor development of root systems essential for summer survival. This damage is more severe in drier, heavier soils.
Plant roots need oxygen to survive, and as the density of a compacted soil increases, carbon dioxide and other toxic gasses do not readily move from the root system. Their concentration can build up to the point that they actually become toxic to the root.
Compaction is very much a surface phenomenon affecting mainly the top four inches of soil. Compacted soils do not allow rapid water penetration, causing increased runoff. This means that more irrigation is necessary to adequately soak compacted areas to get water to the root-feeding zone during times of drought stress.
Compacted soils are hotter in the summer and colder in the winter because of the conductivity of tight soil particles. Lower temperatures in the spring could result in less root growth, delayed green-up and even winter-kill.
Porosity of compacted soil is less. Both the numbers of pores and their size are decreased. Small pores in soil are usually filled with water, so water begins to replace air in a compacted soil. In the absence of air, plant root cannot actively absorb nutrients, causing plant decline. Pathogenic fungus organisms thrive in higher soil temperatures in the presence of a lack of oxygen. Thus, the probability of summer disease problems is increased in a compacted soil. Weeds that can persist in low oxygen soils can gain the competitive edge over desirable grasses and take over.
Managing turf to minimize the negative effects of compaction is important. Management considerations that are helpful in this regard include aerification, traffic control, water management, soil modification, efforts to both improve drainage and irrigation design, and turf grass selection.
Core aerification is extremely beneficial in increasing air exchange, water infiltration rates, water retention, nutrient penetration and thatch decomposition. It also decreases surface runoff, therefore increasing water- use efficiency while reducing total irrigation requirements. Warm-season grasses such as St. Augustine and Bermuda can be beneficially aerified from the time they green-up until the time they go dormant in the fall. Once-a-month aerification on heavily trafficked Bermuda grass would not be detrimental. Total number of aerifications per year needs to be linked to fertility levels and amount of traffic. Two to five aerifications per year should be considered average for heavily-trafficked turf.
Minimizing traffic whenever possible is important. Minimizing traffic when soil is wet is critical because compaction damage is greater on a wet soil than on a dry soil. Timing irrigation to allow adequate time for drainage prior to traffic can be a critical factor in reducing compaction damage.
For more information about dog and animal compaction control, see:
David Rodriguez is the County Extension Agent-Horticulture for Bexar County. For more information, call the Master Gardener ‘Hotline’ at (210) 467-6575 or visit our County Extension website at: http://bexar-tx.tamu.edu and click on Horticulture and Gardening.