TA 44 Results
Annual Forbs
The interaction Treatment*Time is highly significant at 0.001. During the second year, the 90 cy/ac rate indicates a significantly higher annual forb cover and showed a steep increasing trend compared to any of the other application rates. The 60, 30, and 15 cy/ac rates had decreasing trends in annual forb cover class during the second year. Under normal circumstances, annual forbs would not be considered desirable ground cover in efforts to minimize soil erosion; however, in severe situations (immediately post-training), this growth form may be the only plant cover suited to the situation. Over a two year period, the high rate of compost can have a substantial effect in the maintenance of an annual forb crop while more desirable species are reestablished; however, at the high rates, compost would pose potential water quality problems that would minimize any vegetation gain.
Figure 1. Results of multivariate analysis for compost rate impacts on annual forbs.
Annual Grasses
The effects of time and treatment are significant at levels 0.001 and 0.078 respectively. The time is significant due to seasonal variation. The 60 cy/ac rate had significantly higher annual grass ground cover at the end of the first year and beginning of the second, but the ground cover dropped to zero by the end of the second year. For this site, annual grasses do not play a significant role in the plant community.
Figure 2. of multivariate analysis for compost rate impacts on annual grasses.
Perennial Forbs
The Treatment*Time interaction was significant at 0.023 level. This suggests that the five rates have different time patterns. The 90 cy/ac compost rate shows a significantly higher perennial forb cover class than any other compost rate in the second year. The residual effect of compost with the retention of nutrients in the soil provides the time required to establish a healthy perennial forb component within the community. The 30 cy/ac compost rate also presented a significantly higher perennial forb cover class than the control by the second year of data collection. Only the 90 cy/ac had a perennial forb component with an upward trend during the two years; however, recommending 90 cy/ac as a compost rate for revegetation will elevate water quality issues.
Figure 3. Results of multivariate analysis for compost rate impacts on perennial forbs.
Perennial Grasses
The Treatment*Time effect was significant at 0.014 level which means that all five compost rates present a seasonal pattern, but that pattern is not the same for all treatments. All the rates, including the control, have shown an increasing trend of perennial grasses over the two years of data collection. After two years, the 15 and 30 yd3/acre present significantly higher perennial grass cover compared to the 60 and 90 yd3/acre treatments, but are not significantly different from the control plot. The data do not show evidence of compost application benefiting perennial grasses since the control exhibited the same trend as the treatments.
Figure 4. Results of multivariate analysis for compost rate impacts on perennial grasses.
Bareground
The interaction Treatment*Time is highly significant at 0.001 which indicates that the time pattern is different for most of the compost rates. The 90 cy/ac had the steepest decrease in bareground cover as well as the lowest percentage of bare ground cover by the second year of the experiment. These results reveal the revegetation benefits of using 90 cy/ac; however, this high treatment rate could result in water quality problems.
Figure 5. Results of multivariate analysis for compost rate impacts on bareground.
Experimental Conclusions
Based upon this experiment, we conclude that there is not enough evidence to justify high rates of compost, greater than 30 yd3/acre. There is no evidence that erosion control growth forms, perennial grasses or forbs, are significantly influenced by the higher rates of compost application. Furthermore, the use of such high rates per acre would significantly increase the cost of treatment for large scale land application as well as increase the potential of effecting water quality.