Lab 5. Soil Water This week’s lab will take place at the Cornell University Turfgrass Field Research Laboratory and Robert Trent Jones Golf Course. At the Turfgrass Research Laboratory, we will conduct one percolation test as a group. Then we will take infiltration measurements at the turf plots. These plots have different soil textures, which will affect their infiltration rates. In the second part of the lab, we will take infiltration and surface runoff measurements on the golf course. Your task will be to access the suitability of a site for a septic system and to access whether soil management has maintained good infiltration rates. Objectives • Examine the effects of soil texture, structure and compaction on water infiltration • Measure the impact of soil compaction on surface runoff • Distinguish between soil infiltration and percolation and identify important soil properties that impact these processes • Perform a percolation test for septic systems Reading • 5.6 Infiltration and Percolation • 6.8 Percolation and Groundwater • 6.9 Enhancing Soil Drainage • 6.10 Septic System Drain Fields Site Background The Turfgrass Field Research Laboratory is comprised of twenty-eight acres of turfgrass field research and borders the No. 8 fairway of the Robert Trent Jones Golf Course at Cornell University. This site established in 1973 and has seen consistent growth and development. Researchers are investigating environmental, soil, and turfgrass management issues on 120 mini-greens that represent a portion of the Turfgrass Field Research Laboratory. Additional facilities include an equipment repair shop, storage barn, and a state-of-the-art pesticide management facility, which is shared jointly by the Turfgrass Field Research Laboratory and the Robert Trent Jones Golf Course. An in-ground irrigation system, controlled by a new Toro LTC central/satellite system, irrigates one-third of the field research laboratory. The remaining land area can beirrigated by means of temporary above ground solid-set system supplied by strategically located hydrants. Irrigation water, which is supplied by a nearby creek, is pumped into a quarter-acre holding pond at the research laboratory and then pumped put to the irrigation system. Native soil types range from sandy loams to silty clay loams. The 18-hole University Golf Course, the front nine of which was completed in 1954 with funds contributed by alumni, is a championship course designed by the noted golf architect Robert Trent Jones (Cornell ’30). The back nine layout (between Warren Road and Pleasant Grove Road) was the university’s first nine holes and has been in use since 1941. Urban Soils Until now the labs have focused on soils as a natural component of the rural environment. We also need to consider high-use urban and suburban landscapes. The soils will have many similar characteristics to agricultural and forested lands. However, they also have unique management needs, in large part due to their greater exposure to human influences. Even more than agricultural lands, the physical and chemical alteration of urban soils results in degradation of structure, resulting in loss of macropores, surface crusting, and restricted aeration and drainage, as well as contamination from toxins. While these problems tend to be associated with urban/suburban environments, they can be found in any area that receives a high degree of human traffic, such as camping and picnic areas, hiking trails, and parks. The maintenance of soil structure is particularly important in the management of urban and high-use soils. Conditions in urban setting that contribute to soil structural degradation include transportation or displacement of soil, lack of vegetative cover, low organic matter, altered wet-dry and freeze-thaw cycles, and unremitting traffic. Infiltration and Percolation A well-structure “healthy” soil, containing earthworm castings and root channels, will have more continuous macropores connected to the surface, contributing to rapid infiltration of water, than a compacted soil with scarce vegetation. Soil compaction crushes macropores, which in turn reduces infiltration. A slower infiltration rates increases the probability of surface runoff. In addition, the force of runoff water accelerates erosion during intense rainfallevents. Water infiltration into soil is also influenced by soil texture and surface characteristics. A heavy textured with few large pores such as clay would have a slower infiltration rate that a sandy soil. Soils that have no vegetative cover are vulnerable to forming surface crust. The lack of surface pores in a crusted soil diminishes vertical infiltration of water, resulting in surface water runoff. When water does infiltrate the surface, macropores fill and water begins to move downward and laterally through the profile in a process called percolation. Percolation involves both saturated and unsaturated flow. An abrupt change in pore size, such as from a fine-textured soil to an underlying coarse textured soil, will influence the percolation process by altering the rate of water movement. Examples of abrupt changes in soil structure and texture include natural horizons such as fragipans or man-made modifications resulting from grading. Under unsaturated conditions, macropores are filled with air and water movement occurs through finer micropores. Under saturated conditions, water movement occurs by gravity flow through macropores. Sandy soils generally have higher macropore space compared to clayey soils and thus have a higher rate of saturated flow. The importance of saturated and unsaturated flow rates in soil is not confined to managing soils to optimize plant growth. Water movement through soil is also an important consideration for waste disposal. For instance, rural homeowners who are not served by a city’s sewage system have to install a septic system to dispose of household wastewater. Before installing a septic system, a soil scientist has to assess the suitability of the residence’s soil for handling wastewater. This assessment is done with a percolation or perc test. A perc test measures the permeability of the soil. The test requires digging a hole of approximately 12 inches by 12 inches, which is then pre-soaked from several hours up to a day. After the soil is sufficiently saturated, water is added to the hole to