Mary Ann Rose
Hao Wang
Mary Ann Rose,Ohio Agricultural Research and Development Center/Ohio State University Extension/Horticulture and Crop Science; Hao Wang, Horticulture and Crop Science
This study evaluated the suitability of four types of composted waste materials as soil amendments for bedding plants and examined the effect of these amendments with or without sulfur (3 lbs. per 100 sq. ft) on the soil pH. Two sources of composted municipal sludge (CMS), composted yardwaste, composted leaves, and peat were applied in two-inch layers and incorporated into field soil. The four annual species chosen varied in response to the soil amendments; overall, the amendments improved growth or appearance in at least some annual species compared to unamended field soil. The ranking of treatments, in terms of their benefit to plant growth, was peat > CMS (both sources) > composted yardwaste > composted leaves > unamended soil. Amending soil with composted leaves, composted yardwaste, and CMS significantly increased soil pH in some of the samples; however, soluble salt levels in soil were not affected. Sulfur addition effectively lowered soil pH 0.6 units two months after application and increased soluble salts.
There are potential benefits from using composted organic waste materials as soil amendments in the landscape. These materials are produced throughout the country as a solution to waste disposal problems and are economically attractive compared to traditional soil amendments such as peat.
Several types of compost are available, depending on the locality. Most recently, composted yardwaste has been produced in response to curbside yardwaste bans (Glenn, 1991). Relatively little is known about the suitability of this product as a landscape soil amendment. Other products, such as composted leaves, have been available for years. Composted municipal sludge (CMS) has been investigated extensively for over a decade, and many studies have demonstrated growth enhancement of ornamental species with its use (Smith and Treaster, 1985, 1991b; Ticknor et al., 1985; Devitt et al., 1991; Purman and Gouin, 1992).
In a two-year study at The Ohio State University, Smith and Treaster (1991a, 1992) found that CMS improved growth in nine of 12 annual bedding plant species. Growth of aster, geranium, and dusty miller was decreased or inconsistent in CMS treatments. Some problems associated with CMS use as a soil amendment include high soluble salts and high pH; soluble salts may have contributed to poor growth in the Ohio State study.
The objectives in this study were to evaluate four composted waste materials that are available in Ohio and to compare their effects on the soil and bedding plant growth compared to peat and unamended field soil. The four compost products used were:
A second objective of the study was to examine the effect of the high-pH composts, with and without sulfur addition, on soil pH over the course of the growing season.
Research plots were located at the Ohio State University, on a Crosby silty-clay-loam soil. Soil tests indicated a relatively high level of fertility in the soil (soil analysis in lbs/A: 156 phosphorus, 663 potassium, 5310 calcium, and 826 magnesium). Five soil amendments were used -- composted yardwaste, composted municipal sewage sludge from two Ohio cities (CMS-Akron and CMS-Columbus), composted leaves, and peat.
In June 1995, a two-inch layer of each amendment was applied to field soil plots and rototilled six inches deep. A sixth treatment (control) consisted of rototilled field soil with no amendment. Sulfur was incorporated at two rates, 0 and 3 pounds per 100 square feet. Each four- by 10-foot plot was planted on July 3, 1995, with four bedding plant species -- 'Orbit' geranium, 'State Fair' zinnia, 'Scarlet Sophia' marigold, and 'Dream Red' petunia. Each treatment was replicated three times. All plots were fertilized on July 10 with 18-6-12 slow release fertilizer at 60 lbs. N per acre.
Soil from each plot was sampled July 7, August 10, and October 2. Soil samples were tested for soluble salts (electrical conductivity, EC) and pH. On September 15, visual ratings of all plots were taken before plants were harvested for fresh and dry weights.
Soil Amendment Effect on Growth The spring and early summer of 1995 were extremely wet, and soil amendments in most cases appeared to improve growth and ameliorate water-logging in the heavy field soil. With the exception of composted leaves, all soil amendments significantly improved the growth and increased fresh or dry weights in some of the annual species compared to unamended soil (Tables 1, 2, 3). Petunias were most responsive to soil amendments and exhibited the widest range in growth responses. Petunias in the control plots were poor in appearance, while control plots of the other three species were acceptable in appearance. Zinnia was the least responsive of the species to the soil amendments. Only peat improved visual ratings in zinnia, while no treatment improved their fresh or dry weights relative to the control.
All four species of bedding plants amended with peat were rated significantly higher than the controls. In general, the peat plots produced the greatest number of superior plants and greater fresh and dry weights. The two CMS amendments increased the visual ratings and dry weights in two of the four species (geranium and petunia). Composted yardwaste increased visual ratings and fresh and dry weights of petunia only.
Although composted leaves did not statistically increase weight or visual ratings in any bedding plant species, these trends were apparent in the data (Tables 1, 2, 3).
Soil Amendment Effect on Soil EC and pH Soil amendments did not significantly increase soil soluble salts in any of the three sample dates (Table 4). However, soil pH was significantly increased by most of the composted waste materials. Soil pH was increased by as much as 1.1 unit. In general, the pH of the treatment plots was ranked in the following order -- composted leaves > yardwaste > CMS-Columbus > CMS-Akron > control >> peat. Soil pH was decreased by at least a full unit in the peat-amended plots compared to unamended field soil. The effects of the amendments on soil pH were stable throughout all sample dates.
Sulfur Effect on Soil Soluble Salts and pH Sulfur significantly increased soluble salts and decreased soil pH in all sample dates (Table 5). Elemental sulfur is oxidized to sulfuric acid by microorganisms in the soil. Sulfuric acid releases sulfate ions in the soil, which contribute to soluble salts. While the effect of sulfur on soil EC was highly significant, no detrimental effect on growth was observed. The highest soluble salt level attained was 1.0 mmhos.cm, which should not injure plants.
Sulfur significantly reduced the pH in all sampling dates. In July, the average pH of the sulfur treatments was 0.2 units lower than the minus-sulfur treatments. The pH of the sulfur treatments continued to decrease with time, and by August, the average pH was 0.6 units lower than minus-sulfur treatments. The gradual reduction in soil pH with sulfur addition was expected, because the chemical reaction that takes place is temperature- and time-dependent.
Sulfur addition had no significant effect on the visual ratings and weights of bedding plants (data not shown); however, these species are not known for soil pH preferences.
Conclusions Bedding plant species varied in their response to the soil amendments, but in general, there was a clear trend that all soil amendments improved growth in at least some annual species. The ranking of treatments, in terms of their benefit to plant growth, was peat > CMS (both sources) > composted yardwaste > composted leaves > unamended soil. Since the CMS products have considerably more nutritive value than peat or the other materials, the results suggest that in this experiment, the improvement of soil physical characteristics was more critical than improvement of soil fertility. This is not surprising, given the very wet year in Columbus and the naturally high level of fertility present in the research field soil.
While the soluble salt and pH effect of the composts were not critical factors in this experiment, the evidence that composts may significantly increase soil pH and EC may be important with plants such as azaleas and rhododendrons. This group of plants prefers a lower pH and is sensitive to soluble salts. Attempting to lower soil pH with elemental sulfur could be detrimental if soluble salts were greatly increased as a result. Fortunately, soluble salts are subject to leaching by rainfall; thus, the soluble salts that accompany the sulfur reaction should not persist. A second year of work is planned to study the long-term effects of sulfur and composted waste materials on soil pH and EC.
| Table 1. The effect of composted soil amendments on visual ratings of bedding plants. Averages of visual observations made September 15, 1995. | ||||
|---|---|---|---|---|
| Amendment | Geranium | Marigold | Petunia | Zinnia |
| Peat | 3.9a | 3.9a | 3.7a | 4.0a |
| CMS-Akron1 | 3.9a | 3.5ab | 3.0bc | 3.2ab |
| CMS-Columbus | 3.2ab | 4.2a | 3.5ab | 3.4ab |
| Composted Yardwaste | 3.1ab | 3.8ab | 3.3abc | 3.6ab |
| Composted Leaves | 3.5ab | 3.5ab | 2.8cd | 3.4ab |
| Control (No Amendment) | 2.7b | 2.9b | 2.2d | 2.7b |
| Minimum significant difference | 1.1 | 1.0 | 0.6 | 1.2 |
| Growth and quality were rated on a 1 to 5 scale. 5 = excellent, 4 = good, 3 = acceptable, 2 = poor, 1 = very poor. | ||||
| Treatments followed by the same letter are not significantly different. | ||||
| Table 2. The effect of composted soil amendments on fresh weights (grams) of bedding plants, September 15, 1995. | ||||
|---|---|---|---|---|
| Amendment | Geranium | Marigold | Petunia | Zinnia |
| Peat | 166ab | 866 | 185a | 379 |
| CMS-Akron | 218a | 767 | 128b | 360 |
| CMS-Columbus | 177ab | 865 | 136b | 350 |
| Composted Yardwaste | 199ab | 808 | 135b | 384 |
| Composted Leaves | 158ab | 831 | 98bc | 342 |
| Control (No Amendment) | 134b | 636 | 82c | 279 |
| Minimum significant difference | 81 | ns | 39 | ns |
| Treatments followed by the same letter are not significantly different. | ||||
| ns = no statistical differences among treatments. | ||||
| Table 3. The effect of composted soil amendments on average dry weights (grams) of bedding plants, September 15, 1995. | ||||
|---|---|---|---|---|
| Amendment | Geranium | Marigold | Petunia | Zinnia |
| Peat | 25 | 132ab | 26a | 77 |
| CMS-Akron | 30 | 109ab | 18bc | 72 |
| CMS-Columbus | 27 | 127ab | 22ab | 64 |
| Composted Yardwaste | 30 | 133a | 20b | 70 |
| Composted Leaves | 27 | 120ab | 14c | 65 |
| Control (No Amendment) | 25 | 95b | 14c | 53 |
| Minimum significant difference | ns | 37 | 5 | ns |
| Treatments followed by the same letter are not significantly different. | ||||
| ns = no statistical differences among treatments. | ||||
| Table 4. The effect of compost addition on soil soluble salts (EC, mmhos.cm) and pH. | ||||||
|---|---|---|---|---|---|---|
| July | Aug. | Oct. | ||||
| EC | pH | EC | pH | EC | pH | |
| Composted leaves | 0.44 | 7.7a | 0.47 | 7.5a | 0.75 | 7.4a |
| Composted yardwaste | 0.48 | 7.3b | 0.47 | 7.1ab | 0.78 | 7.2a |
| CMS-Columbus | 0.45 | 7.0bc | 0.38 | 7.0b | 0.71 | 7.0ab |
| CMS -Akron | 0.52 | 6.8cd | 0.42 | 6.8bc | 0.80 | 6.9ab |
| Control (no amendment) | 0.50 | 6.7d | 0.49 | 6.4c | 0.70 | 6.7b |
| Peat | 0.54 | 5.2e | 0.43 | 5.3d | 0.68 | 5.6c |
| Minimum significant difference | ns | 0.3 | ns | 0.5 | ns | 0.5 |
| Treatments followed by the same letter are not significantly different. | ||||||
| ns = no differences among treatments. | ||||||
| Table 5. The effect of sulfur addition on soil soluble salts (EC, mmhos.cm) and pH. | ||||||
|---|---|---|---|---|---|---|
| July | Aug. | Oct. | ||||
| EC | pH | EC | pH | EC | pH | |
| minus S | 0.37 | 6.9 | 0.23 | 7.0 | 0.44 | 7.1 |
| plus S | 0.61 | 6.7 | 0.65 | 6.4 | 1.00 | 6.5 |
| Compost treatments are averaged. | ||||||
| All differences are statistically significant. | ||||||
Devitt, D. A., R. L. Morris, and D. C. Bowman. 1991. Response of periwinkle to composted sewage sludge used as a soil amendment. J. Envir. Hort 9(4):176-181.
Glenn, J. 1991. Yard waste as a mandated resource. Biocycle 32(9):30-31.
Purman, J. R. and F. R. Gouin. 1992. Influence of compost aging and fertilizer regimes on the growth of bedding plants, transplants, and poinsettia. J. Environ. Hort. 10(1):52-54.
Smith, E. and S. A. Treaster. 1985. Growth of container grown nursery stock produced in composted municipal sludge amended media. Ohio State University Research Circular 284:8-11.
Smith, E. and S. A. Treaster. 1991a. Application of composted municipal sludge in the landscape. Ohio State University Research Circular 140:19-21.
Smith, E. and S. A. Treaster. 1991b. Composted municipal sludge from two Ohio cities for container-grown woody ornamentals. Ohio State University Research Circular 137:22-24.
Smith, E. and S. A. Treaster. 1992. A two-year evaluation of composted municipal sludge in the landscape. Ohio State University Research Circular 140:1-4.
Ticknor, R. L., D. D. Hemphill, and D. J. Flower. 1985. Growth response of Photinia and Thuja and nutrient concentration in tissues and potting medium as influenced by composted sewage sludge, peat, bark, and sawdust in potting media. J. Environ. Hort. 3(4):176-180.