Soil aggregate dynamics and plant community response after biosolids application in a semiarid grassland
Wallace, B.M., Krzic, M., Newman, R.F., Forge, T.A., Broersma, K., Neilsen, G. (2016). Soil aggregate dynamics and plant community response after biosolids application in a semiarid grassland. Journal of Environmental Quality, [online] 45(5), 1663-1671. http://dx.doi.org/10.2134/jeq2016.01.0030
Plain language summary
Biosolids are organic wastewater solids that have been treated, usually through anaerobic digestion, to make them microbiologically suitable for land application. Biosolids are rich sources of plant nutrients and research has demonstrated that they can improve the productivity of forage grasses in semiarid grasslands in the short term. However, longer-term effects of biosolids on soil structure and shifts in the composition of plant communities are not well known. An experiment was established in 2001 to determine the effects of a single application of biosolids, at two different rates (20 and 60 tonne dry biosolids per hectare), on soil aggregate stability, an indicator of soil health, and composition of the plant community in a semiarid grassland in the southern interior of British Columbia. Soil aggregate stability was measured in 2005, 2006 and 2009; and the plant community was assessed in 2009. There were significant increases in soil aggregate stability with the low and high biosolids applications, respectively. The low biosolids application rate had no effect on plant community composition, but the high rate reduced the abundance of perennial forage plant species while increasing the abundance of forbs that are less valuable as forage. These results indicate that while biosolids may improve some aspects of soil health, application to native grasslands in semiarid environments should be done cautiously and consider the potential for longer-term changes in plant species composition.
Biosolids may improve the ecological function of degraded semiarid grasslands, but an understanding of the plant community is essential. An experiment was established in 2001 to determine the effects of a single surface application of biosolids on soil aggregate stability and the composition of the plant community in a semiarid grassland in British Columbia, Canada. Four treatments were evaluated: (i) surface biosolids application at 20 (Bio-20) and (ii) 60 Mg ha-1 (Bio-60), (iii) mineral fertilizer, and (iv) a control. All treatments were replicated in four blocks. Soil was sampled during the spring (May), summer (June-July), and fall (October) in 2005, 2006, and 2009; the plant community was assessed in 2009. The greatest increases in size of stable aggregates relative to the control were in the spring and summer, which coincided with a 1.6-to 2.1-fold increase in the spring concentration of N within stable aggregates when biosolids were applied at 20 and 60 Mg ha-1, respectively. Nitrogen concentrations from the Bio-60 treatment were not different from the control, but the Bio-20 treatment had 42% greater N than all other treatments during summer. Biosolids application in this ecosystem did not increase perennial forage grass species relative to the control, and when biosolids were applied at a rate of 60 Mg ha-1 there was a 75% reduction in the perennial forage plant species. The application of biosolids to native grasslands in semiarid environments should be done cautiously, especially when winter annual plant species (e.g., cheatgrass [Bromus tectorum L.]) are present before application.