Ranching practices interactively affect soil nutrients in subtropical wetlands
Ho, Janet, Elizabeth H. Boughton, David G. Jenkins, Grgory Sonnier, Patrick J. Bohlen, and Lisa G. Chambers. Ranching Practices Interactively Affect Soil Nutrients in Subtropical Wetlands. Agriculture, Ecosystems & Environment 254 (2018): 13037.
Growing demand for food from ﬁnite agricultural lands requires the optimization of agricultural management, including the potential interactive eﬀects of these practices on ecosystems. We experimentally examined the interactive and temporal eﬀects of three ranching practices (pasture management intensity, livestock grazing, and prescribed ﬁre) on soil nutrients in 40 geographically-isolated seasonal wetlands. Wetlands were embedded in a subtropical ranch, and the long-term experiment used a factorial design with wetlands as experimental units. Soils (0–15 cm) were collected three times over 9 years; at experiment start (2007), one year after prescribed burns started (2009), and seven years later (2016). Samples were analyzed for soil bulk density, organic matter (OM), total nitrogen (N), carbon (C), and phosphorous (P). A lag eﬀect was observed in response to ﬁre; differences were not observed in 2009, but were detected in 2016 after multiple ﬁre cycles had occurred. Rangeland practices showed 2- and 3-way interactive eﬀects, especially for total P and N stocks. Total P increased most in the wetlands embedded within highly managed, grazed, and burned pastures (2.31 ± 0.76 g m−2 yr−1), consistent with legacy eﬀects of historical fertilizer application, cattle activity, and ash deposit due to ﬁre. Wetlands in semi-natural and burned pastures had the lowest rates of soil N storage (5.13 ± 7.33 g m−2 yr−1) compared to all other treatments (24.5 ± 10.8 g m−2 yr−1). Total C stocks were not signiﬁcantly impacted by ranching practices throughout the study. In summary, ranching practices can additively and interactively alter soil nutrient stocks after a time lag, and legacy eﬀects of P application still impact wetlands decades later. Our study is one of few focused on ranchland wetlands and shows that wetlands in highly managed, grazed, and/or burned pastures can sequester soil P and N, playing an important role in nutrient processing for agricultural landscapes and watersheds.