No abstract

Litter decomposition, particularly from belowground pools, is a key process controlling the flow of nutrients and the sustainability of native and cultivated grazinglands. This study evaluated in situ belowground decomposition of sawpalmetto (Serenoa repens [W. Bartram] Small) and bahiagrass (Paspalum notatum Flügge; BG), which corresponded to the predominant plant species in native and cultivated pastures in the southeastern United States. Belowground biomass decomposition (180 d) was estimated using the litterbag technique during the summer and winter. Season showed no effect on belowground decomposition. Decomposition followed a double exponential model (P ≤ .01) and was greater for BG than for native rangeland (NR) (−0.0008 and −0.0001 g g −1 d −1 , respectively; P = .0035), resulting in less remaining material at the end of incubation for BG (74% compared with 93% for NR; P ≤ .002). Greater decomposition in BG occurred due to more favorable chemical composition than NR, namely greater initial N concentration (17 and 8 g kg −1 organic matter for BG and NR, respectively) and lower initial C/N ratio (29 and 65 for BG and NR, respectively), lignin/N ratio (13 and 54 for BG and NR, respectively), and C/P ratio (407 and 1,327 for BG and NR, respectively). Despite the differences in initial C/N ratios, remaining N was similar between BG and NR at end of incubation (96 and 84%, respectively; P = .3711). Land use intensification in grazinglands, in particular conversion of native rangelands to cultivated pastures, can have major impacts on belowground decomposition and on the biogeochemical cycle of nutrients in these ecosystems.

Integrated crop-livestock (ICL) systems have shown potential to provide a variety of environmental benefits including soil carbon (C) increases relative to conventional row cropping systems. However, studies documenting C dynamics of ICL systems in the northern Great Plains are lacking relative to other agroecosystems. Soil carbon dioxide (CO 2 ) efflux, crop biomass, and soil organic matter (SOM) pools were monitored over 3 years in an ICL rotation (corn [Zea mays L.]/soybean [Glycine max L.]-spring wheat [Triticum aestivum L.] + cover crop-cover crop) with fall grazing, a conventional cropping system rotation (corn-spring wheat-soybean) and fall grazed and ungrazed mixed-grass pasture near Mandan, ND. Cropped treatments were under no-till management. Annual aboveground crop residue biomass C was similar in the ICL and conventional systems, while less in the grazed pasture (4.18, 3.83, and 1.21 Mg C ha −1 year −1 respectively; p = 0.039). Annual soil CO 2 efflux was greater in the ICL, grazed, and ungrazed pasture systems than the conventional system (8. 05, 8.73, 8.25, and 5.81 Mg C ha −1 year −1 , respectively; p < 0.001). Among crop phases in the ICL and conventional cropping systems, cover crops contributed to greater CO 2 efflux in the spring and fall. SOM and C mineralization were greater at 0-5 cm in the ICL system compared to the conventional cropping system (6.6% vs. 6.3%, p = 0.028 and 248 vs. 184 mg CO 2 -C kg −1 , p < 0.001, respectively). Interseeded cover crops in ICL systems can contribute increased root respiration and enhanced SOM pools relative to conventional cropping systems under semiarid conditions.