Soil Aggregate Dynamics and Plant Community Response after Biosolids Application in a Semiarid Grassland
2016
Wallace, Brian M. | Krzic, Maja | Newman, Reg F. | Forge, Tom A. | Broersma, Klaas | Neilsen, G. H.
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.
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