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SOIL & WATER MANAGEMENT & CONSERVATION

Reclamation of Abandoned Natural Gas Wellsites with Organic Amendments: Effects on Soil Carbon, Nitrogen, and Phosphorus

Lethbridge Research Centre, Agriculture and Agri-Food Canada, 5403 1st Ave. S., Lethbridge, AB T1J 4B1, Canada

^* Corresponding author (larneyf{at}agr.gc.ca).

Organic amendments have been used to restore productivity to disturbed soils such as those on abandoned oil and natural gas wellsites. A study was conducted on three abandoned wellsites in southern Alberta, Canada to examine the effects of one-time applications of alfalfa (Medicago sativa L.) hay or beef cattle (Bos taurus) feedlot manure compost on soil properties under continuous wheat (Triticum aestivum L.). The base amendment rate (1x) [dry wt.] was 5.3 Mg ha^–1 for compost and 3.1 Mg ha^–1 for alfalfa. The five amendment rates of 0, 1x, 2x, 4x, and 8x were soil-incorporated at the wellsites. Although approximately twice as much C was applied with alfalfa than with compost, final SOC content was similar for the two amendment treatments, indicating the greater stability of compost-derived C. Nitrate N content in the 0- to 60-cm depth was not affected by compost rate (mean 213 kg ha^–1) but increased by 7.78 kg ha^–1 for each Mg ha^–1 increase in alfalfa rate. This result reflects the greater stability of compost-N compared with alfalfa-N and suggests a lower risk of NO₃–N leaching with compost application. Compost rates >20 Mg ha^–1 resulted in excessive extractable P build-up in the topsoil (up to 95.7 mg kg^–1), which may pose environmental risk to surface water. We recommend amending wellsites with up to 12 Mg ha^–1 of alfalfa or <20 Mg ha^–1 of compost during reclamation to improve C storage and nutrient cycling while minimizing nutrient loss to water systems.

Abbreviations: MKP, modified Kelowna-extractable P • SOC, soil organic carbon