Sulfur Availability on Lodgepole Pine Sites in British Columbia

Abstract

Growth response of lodgepole pine (Pinus contorta Dougl.ex. Loud var. latifolia Engelm.ex S. wats.) to N fertilization is limited by insufficient S on certain sites in British Columbia. This study was conducted to document differences in soil and foliar S fractions between sites with either adequate or insufficient S as determined by foliar nutrient data and growth response information obtained from previously established fertilization research trials with N and N + S application, and to examine relationships among soil S fractions, foliar S status, and growth response to N fertilization. Mineral soil total S concentrations were very low (∼65 mg kg−1) at both S‐sufficient and S‐deficient sites, and were not different between the sites. Soluble inorganic SO4 concentration was significantly greater in B horizon soil at the S‐sufficient sites than at the S‐deficient sites. Soluble inorganic SO4 was significantly and positively correlated with organic SO4 (r2 = 0.24; P = 0.03) and organic C (r2 = 0.76; P < 0.001). Foliar SO4‐S was significantly greater at the S‐sufficient sites, and was significantly and positively correlated with B‐horizon soluble inorganic SO4 (r2 = 0.84; P < 0.001), organic SO4 (r2 = 0.46; P = 0.032), and organic C (r2 = 0.72; P = 0.002). The highest R2 for a regression model between soil or foliar properties and response to N fertilization was for a model containing foliar N, foliar SO4‐S, and B horizon organic C (R2 = 0.81; P = 0.004). Cycling of soluble inorganic SO4 through organic SO4 in mineral soil appears to be the process limiting S availability on S‐deficient sites. Organic SO4 and soluble inorganic SO4 concentrations at the S‐sufficient sites are maintaining foliar SO4‐S at levels required for response to N fertilization.