This Is AuburnElectronic Theses and Dissertations

Evaluation of Manufactured Organic Soil Amendments for Consumer Use




Thaxton, Blake

Type of Degree





Commercial substrate blending companies and fertilizer companies are now producing manufactured substrates and fertilizers that are marketed as “organic.” Homeowners care about the aesthetics of their landscape, thus the consumers buy fertilizers to achieve a greener lawn. However, most current products are market driven with little research to document product effectiveness. Physical properties play a major role in the character and effectiveness of a fertilizer. Properties that have agronomic consequences are particle size distribution and the rate of disintegration in water of a fertilizer, which is the first step towards solubility. Particle size distribution also plays a factor in the ability to spread effectively and ease of coverage of a specific area. In experiment one, a set of test sieves where used to determine the particle size distribution of two manufactured organic fertilizers, Secret Garden pelletized (SGP) and Secret Garden Granular (SGG) products, and also Scott’s Organic Choice Lawn Fertilizer (SOC). SGP had the largest portion of large particles of the three fertilizers evaluated with ~50% being caught in a No. 6 (3.36 mm) sieve, SOC had a more heterogeneous mixture, and SGG had the smallest particles of the three fertilizers. In the 60-second disintegration in water test experiment, SOC had significantly heavier un-disintegrated dry weights than the other two fertilizers suggesting that SOC dissolves less rapidly. For the second part of the experiment, the 300-second portion, there were different results. SGG (14.14g) and SOC (10.85g) had the heaviest un-disintegrated dry weight remaining of the three fertilizers. There were no differences in the 480 second test using an altered procedure to obtain comparable rates. A second study evaluated the effects on the aesthetics of Meyer Zoysia turf following applications of four commercially available fertilizers. At 2 weeks after application (WAA), SGG (8.25 lbs N/ 5000 ft2), SGP (8.25 lbs N/ 5000 ft2), SGP (6.6 lbs N/5000 ft2), Sodium Nitrate (3.26 lbs N/ 5000 ft2), and Urea-ammonium nitrate (3.12 lbs N/ 5000 ft2) had the highest visual ratings. Still at 4 WAA, the same treatments had the highest visual ratings (VR). At 6 WAA SGP (8.25 lbs N/ 5000 ft2) outperformed SGP (3.3 lbs N/ 5000 ft2), Urea-ammonium nitrate (3.12 lbs N/ 5000 ft2), and SGG treatments 3.3 lbs N/ 5000 ft2 and 4.125 lbs N/ 5000 ft2. All of the remaining treatments were similar to SGP (8.25 lbs N/ 5000 ft2). At 10 WAA no VR differences were observed among treatments. Initial readings on leaf chlorophyll content (LCC) were taken at 4 WAA. The following treatments were rated the highest at the initial readings: SGG (4.125 lbs N/5000 ft2), SGG (6.6 lbs N/5000 ft2), SGG (8.25 lbs N/5000 ft2), SGP (3.3 lbs N/5000 ft2), SGP (6.6 lbs N/5000 ft2), SGP (8.25 lbs N/5000 ft2), SOC (4.001 lbs N/ 5000 ft2), SOC (8.002 lbs N/ 5000 ft2), and ammonium nitrate. At 6 WAA there was little difference among the treatments. The only difference was SGP (4.25 lbs N/ 5000 ft2) outperforming and SOC (4.001 lbs N/ 5000 ft2). By 10 WAA all treatments were statistical similar in LCC. Warm season grasses have a dormant period during winter and when cold enough there is no green tissue visible. In the spring when temperatures begin to rise the turfgrass begins to put out new shoots, stolons and rhizomes. This time period has become to be known as spring green-up and is very important in landscape and turfgrass management. Fertilizer and other lawn amendments are commonly applied to promote the new growth once the temperatures rise. The demand for organic products has caused manufacturers to begin producing “green” amendment products for spring green-up use. In a third study, effects on the spring green-up of turf following applications of four commercially available fertilizers were evaluated. At 2 WAA SGG (8.25 lbs N/ 5000 ft2) VR was significantly higher than several treatments including the non-fertilized control, however SGP (6.6 lbs N/ 5000 ft2), SGP (4.125 lbs N/5000 ft2), SGG (6.6 lbs N/ 5000 ft2), SGP (4.125 lbs N/5000 ft2), and SOC (8.002 lbs N/ 5000 ft2), VR were statistically similar. By 10 and 11 WAA all fertilized treatments were similar. An additional study evaluated the growth of two vegetables, squash and cabbage, grown in different depths of manufactured organic compost. Home vegetable gardening has begun to regain popularity over the last few years. With the “green” movement in full swing home gardeners are always looking for new ideas to become “organic” or sustainable in the way they produce vegetables. Organic soilless substrates in raised beds may be a way for homeowners to achieve their vision of sustainability. There were no significant differences in yield among the treatments of different depths of compost and the non-amended earthen bed control for the entirety of the study.