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Abstract: Switchgrass (Panicum virgatum L.) is being evaluated as a bioenergy crop for the northern Great Plains. Field measurements of CO2, CH4, and N2O flux are needed to estimate the net greenhouse gas (GHG) balance of this biofeedstock. The study objective was to determine effects of recommended Nitrogen (N) fertilization (67 kg ha−1 of N applied) and unfertilized switchgrass on growing season soil-atmosphere CO2, CH4, and N2O flux using static chamber methodology. Mean hourly CO2 flux was greatest during periods of active switchgrass growth and was similar between N fertilizer treatments (P = 0.09). Mean hourly N2O flux was consistently greater under N fertilization than without N throughout the growing season. Overall, N fertilization of switchgrass affected cumulative growing-season N2O flux (27.6 kg ha−1 ± 4.0 kg ha−1 vs. 86.3 kg ha−1 ± 14.3 kg ha−1 as CO2 equivalents (CO2eq) for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P < 0.01), but not cumulative CO2 or CH4 flux (P = 0.08 and 0.51, respectively). Aboveground biomass production was greater with N application (6.8 Mg ha−1 ± 0.5 Mg ha−1 dry matter) than without N (3.2 Mg ha−1 ± 0.5 Mg ha−1) (P < 0.05). Net greenhouse gas intensity (GHGI; kg GHG flux kg− 1 harvest yield as CO2eq) for switchgrass production was similar between N treatments (0.71 vs. 0.44 for 0 kg ha−1 and 67 kg ha−1 of N applied, respectively; P = 0.18). [Copyright &y& Elsevier]

Abstract: Soil respiration is a process influenced by land use, management practices, and environmental conditions. Our objectives were to evaluate relationships between management-induced differences in soil organic carbon (SOC) and soil CO2 efflux from continuous no-till spring wheat (Triticum aestivum L.), spring wheat-fallow under no-till, and a native mixed-grass prairie with grazing near Mandan, ND. A Werner–Sen–Chama soil complex (Entic Haplustoll, Typic Haplustoll, and Typic Calciustoll) was present at the grassland site and a Wilton silt loam (Pachic Haplustoll) at the cropping sites. Soil chambers were used to measure soil CO2 effluxes about every 21 days starting 14 May 2001 to 1 April 2003. Soil water and soil temperature were measured at time of CO2 efflux measurements. Soil organic carbon, microbial biomass carbon (MBC), and above and belowground plant biomass were measured in mid-July each year. Root biomass to 0.3m depth of the undisturbed grassland was significantly greater (12.3Mgha−1) than under continuous wheat (1.3Mgha−1) and wheat-fallow (0.3Mgha−1). Grassland SOC content of 84Mgha−1 to 0.3m soil depth was 1.2 times greater than continuous wheat and 1.3 times greater than wheat-fallow. The MBC of the grassland was 2.2Mgha−1, or 3.6 times greater than continuous wheat and 7.2 times greater than wheat-fallow treatments. Soil CO2 efflux averaged 2.8gCO2–Cm−2 day−1 for grassland, compared to 1.9gCO2–Cm−2 day−1 for wheat fallow and 1.6gCO2–Cm−2 day−1 for continuous wheat treatments. Although these CO2 efflux rates were based on measurements made at intervals of about 21 days, the differences among treatments with time were rather consistent. Differences in soil CO2 efflux among treatments could be attributed to differences in SOC and MBC, suggesting that land use plays a significant role in soil CO2 efflux from respiration. [Copyright &y& Elsevier]

Abstract: Switchgrass (Panicum virgatum L.) is considered to be a valuable bioenergy crop with significant potential to sequester soil organic carbon (SOC). A study was conducted to evaluate soil carbon stocks within established switchgrass stands and nearby cultivated cropland on farms throughout the northern Great Plains and northern Cornbelt. Soil from 42 paired switchgrass/cropland sites throughout MN, ND, and SD was sampled to a depth of 120cm and analyzed for soil carbon in depth increments of 0–5, 5–10, 10–20, 20–30, 30–60, 60–90, and 90–120cm. SOC was greater () in switchgrass stands than cultivated cropland at 0–5, 30–60, and 60–90cm. Differences in SOC between switchgrass stands and cultivated cropland were especially pronounced at deeper soil depths, where treatment differences were 7.74 and 4.35Mgha−1 for the 30–60 and 60–90cm depths, respectively. Greater root biomass below 30cm in switchgrass likely contributed to trends in SOC between switchgrass stands and cultivated cropland. Switchgrass appears to be effective at storing SOC not just near the soil surface, but also at depths below 30cm where carbon is less susceptible to mineralization and loss. [Copyright &y& Elsevier]

The high indigenous soil organic carbon content, root biomass, and microbial populations in prairie soils provide a source of carbon dioxide (CO2) that is important in the carbon budget of grasslands. Soil chambers were used to measure soil CO2 flux from a grazed mixed-grass prairie (GP), nongrazed mixed-grass prairie (NGP), and grazed western wheatgrass (WWG) [Pascopyrum smithii (Rybd) Lo¨ve] grasslands in the Northern Great Plains, USA. Objectives were to quantify soil CO2 fluxes for each site and to determine the contribution of soil temperature, soil water content, and air temperature to soil CO2 flux. Soil CO2 fluxes were measured on each site about every 21 d at 13:00 h during the 25 April–27 October growing period from 1996 to 2000 for NGP and GP and from 1996 to 1998 for WWG. Dormant period fluxes were measured on the GP from 28 October to 26 April from 1999 to 2001. In addition, five sequential daytime measurements were made on each site for 3 days each year. Fluxes were low in the spring and autumn and peaked concurrent with biomass in late June to mid-July. Maximum fluxes for these dissimilar managed grasslands averaged 5.8 g CO2-C m−2 d−1 for NGP, 6.9 g CO2-C m−2 d−1 for GP, and 6.1 g CO2-C m−2 d−1 for WWG. Soil fluxes measured during the dormant period decreased to near zero during the months of December, January, and February and then increased rapidly in March as soil temperatures increased. Daily soil flux during the growing period averaged 3.5 g CO2-C m−2 d−1 for NGP, 4.3 g CO2-C m−2 d−1 for GP, and 4.0 g CO2-C m−2 d−1 for WWG. Dormant period fluxes for the GP averaged 0.5 g CO2-C m−2 d−1. Regression analysis indicated that soil temperature accounted for 65%, soil water content 5%, and air temperature 3% of flux variability. Growing period soil CO2 flux over years averaged 728 g CO2-C m−2 and dormant period CO2 flux averaged 86 g CO2-C m−2. A predictive relationship describing the response of soil CO2 flux to changes in soil temperature was developed using the minimum, maximum, and optimum soil temperatures for soil CO2 flux. The model provides an estimate of the important dormant period soil flux component in annual ecosystem carbon budgets. [Copyright &y& Elsevier]

Abstract: Dynamic cropping systems, which involve a long-term strategy of annual crop sequencing, require detailed information on management components known to influence crop performance. Considering that proper sequencing of crops is an important component for successful dynamic cropping systems, a research project was undertaken to determine the advantages and/or disadvantages of previous crop and crop residues for numerous crop sequences. A multi-disciplinary team of scientists evaluated crop sequence effects of 10 crops (barley, canola, crambe, dry bean, dry pea, flax, safflower, soybean, spring wheat, and sunflower) on seed yield, soil coverage by residue, soil water use, surface soil properties, and plant diseases in central North Dakota. Two years were required to establish a crop by crop residue matrix (crop matrix). During the second year (site 1, 1999; site 2, 2000) 10 crops were evaluated with a crop matrix. During the third and fourth year spring wheat (site 1, 2000; site 2, 2001) and sunflower (site 1, 2001; site 2, 2002), respectively, were seeded over the crop matrix. The seed yield of four crops (crambe, flax, safflower, and soybean) of the 10 crops evaluated in the crop matrix was influenced by the preceding crop at site 1 in 1999 an above average moisture year. The seed yield of eight crops (canola, crambe, dry bean, flax, safflower, soybean, spring wheat, and barley) was influenced by the preceding crop at site 2 in 2000 a more average precipitation year. Some of the lowest seed yields were obtained when a crop was seeded on its own residue. A synthesis of seed yield data from a given year provided overall values for positive and negative effects of crops and crop residue on subsequent crops. In general, the three legume crops had positive effects in contrast to non-leguminous crops, which usually had negative effects. However, sunflower was an exception among the non-leguminous crops; at site 2 in 2000, sunflower was positive for subsequent crops compared with canola or crambe, which had negative effects. Crop sequences composed of small cereal grains had the highest soil coverage by residue while sequences of two dicotyledonous species had considerably lower coverage. Soil water use among crops varied, ranging from sunflower with the numerically highest soil water use to dry pea with the least. Significant changes in surface soil properties due to crops were generally not detected in this short-term project. Given the variation in Sclerotinia disease incidence for canola, crambe, safflower, and sunflower within the crop matrix, it was difficult to detect significant differences based on the previous crop. Differences were evident two years later when the highest incidence of Sclerotinia basal stalk rot for sunflower was detected in plots where crambe was grown two years earlier. During the third year, when spring wheat was seeded over a crop matrix, spring wheat yields increased following 23 and 19 crop sequence treatments out of a possible 100 at site 1 and site 2, respectively, compared to the continuous wheat treatment. All crop sequence treatments that yielded better than the continuous wheat treatment were comprised of mostly non-cereal crops, demonstrating the positive impact of crop diversity on cereal crop production. The severity of leaf spot diseases on spring wheat were affected by crop sequence and fungal spore production was greatest on the continuous wheat treatment. Even though decreases in leaf spot disease severity and modest yield increases were obtained with some crop sequence treatments, significant yield increases due to reduced leaf spot disease severity were not obtained under our conditions. [Copyright &y& Elsevier]