Potential use of biosolids to reforest degraded areas with New Zealand native vegetation

Biosolids could potentially be used for reforestation of degraded soils in New Zealand with native vegetation. Many native plant species of New Zealand thrive in low-fertility soils, and there is scant knowledge about their nutrient requirements. Therefore, it is unclear whether they will respond positively to the addition of biosolids. We used a pot trial to determine the responses of 11 native plant species to biosolids addition (10% w/w, similar to 90 Mg hm(-2)) on two distinct degraded soils, Lismore stony silt loam and a Kaikoura sand. We also intended to prove that the soil microbial activity improves with the addition of biosolids, depending on the plant species. All species grew better in Lismore stony silt loam than the Kaikoura sand. All species in the Lismore stony silt loam responded positively to biosolids. The response to biosolids addition in the Kaikoura sand was variable, with four species showing no improvement in growth when biosolids were added. The nutrient status (N, P, S, Cu, and Zn) of all species improved when the two soils were amended with biosolids. However, some plant species, especially Pittosporum tenuifolium Sol. ex Gaertn. and Coprosma robusta Raoul, showed concerning concentrations of Cd (up to 2.4 mg kg(-1)). Dehydrogenase activity of soils (indicator of soil microbial activity) increased in biosolids-amended soils, with a strong species effect. Future work should involve field trials to determine the effect of biosolids addition on the establishment of native plant communities.