By Nathan Stacey and Andy Bary, Washington State University-Puyallup Research & Extension Center
Golf course turfgrasses are managed as highly manicured playing fields, maintained to optimize turfgrass health and aesthetic value and, approximately 16,000 golf courses are operated for public or private use in the United States. Frequent fertilization and supplemental irrigation are often used to promote turfgrass health and create an acceptable playing field, yet organic sources of nitrogen (N) are utilized sparingly.
Eagle’s Pride golf course and the Earthworks composting facility are both located at Joint Base Lewis-McChord (JBLM), about an hours’ drive south of Seattle, WA. Beginning in 2014, Washington State University (WSU) researchers partnered with Eagle’s Pride and Earthworks staff to evaluate whether composted biosolids (Earthworks produced) could be utilized as a nutrient source on Eagle’s Pride fairways. The composted biosolid was screened to 3/8 of an inch and then top-dressed onto select fairways (Fig. 1). Over a two-year period (three seasons), researchers gathered samples in one, two, and three week intervals, and then tested those samples for chemical (soil-based plant nutrients) and physical (ability to hold water) changes that resulted from composted biosolids applications.
Turgrass plants require N for growth and maintenance, this inorganic N is typically found in the soil as either nitrate (NO3- ) or ammonium (NH4+) and results from natural soil processes which is partly governed by soil moisture. When additional quantities of N are needed, supplemental fertilization is often used to meet those demands. Composted biosolids can provide N to the soil, but the majority of that N is organic, which must be transformed into the plant available inorganic forms (NO3- and NH4+). Because turfgrass plants utilize N from the soil, samples from both soil and turfgrass tissue were analyzed for N concentrations following the composted biosolids top-dressing, and then compared to plots that received no amendment (control) or a synthetic N fertilizer. When analyzed, the amount of tissue N reflected the amount of N applied, rather than the source of N (composted biosolid versus synthetic fertilizer) suggesting that composted biosolid N is available to turfgrass plants in quantities and forms sufficient for uptake. Not surprisingly, soil samples reflected similar results where plant available N (think nitrate) was readily available following applications of the composted biosolid. Lower N concentrations in both tissue and soil were observed during the spring collection, likely due to cooler soil temperatures, as most of these soil processes are dependent upon soil temperature. In addition, applications of a composted biosolid can affect soil water and, in each of three seasons, the amount of available soil water was increased by an average of 8 % when compared to soil from unamended control plots.
Adding to the evidence that composted biosolids can act as an effective nutrient substitute by improving plant aesthetics and growth (Fig. 2) paralleled the tissue and soil data. The study did not investigate the effects of rate, nor did it address the frequency of application. In practice, owing to the amount of organic matter in composted biosolids, both frequency and rate of application would need to be monitored. In addition, the immediacy of both tissue and soil N responses would be governed by soil temperature and moisture and reasonable expectations with regards to turfgrass growth responses should be considered if a composted biosolid is incorporated into a nutrient management program.