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The inclusion of cover crops during fallow (i.e., green fallow) may mitigate greenhouse gas (GHG) emissions from dryland cropping systems. An investigation was conducted to quantify the effects of chemical and green fallow on soil organic C (SOC) and C[O.sub.2], C[H.sub.4], and [N.sub.2]O flux within spring wheat (Triticum aestivum L.)--fallow (chemical fallow) and spring wheat--safflower (Carthamus tinctorius L.)--rye (Secale cereale L.) (green fallow) under no-till management in west-central North Dakota. Using static chamber methodology, flux measurements were made during 19 mo of the fallow period of each cropping system. Soil samples collected before initiation of flux measurements indicated no difference in SOC in the surface 10 cm between cropping systems. Additionally, differences in gas flux between cropping systems were few. Emission of C[O.sub.2] was greater under green fallow than chemical fallow during spring thaw until the termination of rye (P = 0.0071). Uptake of atmospheric C[H.sub.4] was the dominant exchange process during the evaluation period, and was significantly (P = 0.0124) greater under chemical fallow (-2.7 g C[H.sub.4]-C [ha.sup.-1] [d.sup.-1]) than green fallow (-1.5 g C[H.sub.4]-C [ha.sup.-1] [d.sup.-1]) following the termination of rye. Cumulative fluxes of C[O.sub.2], C[H.sub.4], and [N.sub.2]O did not differ between the chemical- and green-fallow phases during the 19-mo period (P = 0.1293, 0.2629, and 0.9979, respectively). The results from this evaluation suggest there was no net GHG benefit from incorporating a rye cover crop during the fallow phase of a dryland cropping system under no-till management. Abbreviations: GHG, greenhouse gas; POM, particulate organic matter; SOC, soil organic carbon; WFPS, water-filled pore space. doi:10.2136/sssaj2008.0368

The Soil Management Assessment Framework (SMAF) was developed to assess conservation effects on soil, and uses multiple soil quality indicator measurements to compare soil functioning. Our objective was to develop a SMAF- compatible scoring equation for soil [beta]-glucosidase (BG) activity using published data sets representing different soils and management. The resulting equation was an S-shaped curve: y = a/[1 + bexp(-cx)], where x is the measured BG activity (mg p-nitrophenol [PNP] released [kg.sup.-1] soil [h.sup.-1]), a and b are constants, and c is a factor modified by soil classification, texture, and climate. Data from a study conducted near Mandan, ND were used to test the model for sensitivity to crop management systems. Soil organic C (SOC) content at the site measured 247 to 687 g [kg.sup.-1], while BG activity ranged from 33 to 675 mg [kg.sup.-1] [h.sup.-1]. Using SMAF, SOC indicator scores ranged from 0.25 to 0.73, while BG activity scores varied from 0.17 to 0.93. As the work progressed, it became apparent that when BG activity values were normalized to the SOC content, the resulting ratio could indicate C sequestration trends, with ratios of 10 to 17 g PNP [kg.sup.-1] SOC [h.sup.-1] reflective of systems in equilibrium. Ratios > 17 were mostly from recently altered management systems with SOC contents trending upward, while ratios < 10 were generally from soils that were expected to continue to lose soil C. The application of a sensitive C cycling enzyme activity such as BG should improve the SMAF soil quality assessments for soil functions where soil metabolic activity or C-cycle enzyme activity play a role. Abbreviations: BG, [beta]-glucosidase; CEAP, Conservation Effects Assessment Project; CRP, Conservation Reserve Program; MBC, microbial biomass carbon; PNP, p-nitrophenol; SMAF, Soil Management Assessment Framework; SOC, soil organic carbon; SOM, soil organic matter. doi:10.2136/sssaj2009.0029

Grasslands have an underground biomass component that serves as a carbon (C) storage sink. Switchgrass (Panicum virgatum L.) has potential as a biofuel crop. Our objectives were to determine biomass and C partitioning in aboveground and belowground plant components and changes in soil organic C in switchgrass. Cultivars Sunburst and Dacotah were field grown over 3 yr at Mandan, ND. Aboveground biomass was sampled and separated into leaves, stems, senesced, and litter biomass. Root biomass to 1.1-m depth and soil organic C to 0.9-m depth was determined. Soil C loss from respiratory processes was determined by measuring C[O.sub.2] flux from early May to late October. At seed ripe harvest, stem biomass accounted for 46% of total aboveground biomass, leaves 7%, senesced plant parts 43%, and fitter 4%. Excluding crowns, root biomass averaged 27% of the total plant biomass and 84% when crown tissue was included with root biomass. Carbon partitioning among aboveground, crown, and root biomass showed that crown tissue contained approximately 50% of the total biomass C. Regression analysis indicated that soil organic C to 0.9-m depth increased at the rate of 1.01 kg C [m.sup.-1] [yr.sup.-1]. Carbon lost through soil respiration processes was equal to 44% of the C content of the total plant biomass. Although an amount equal to nearly half of the C captured in plant biomass during a year is lost through soil respiration, these results suggest that northern Great Plains switchgrass plantings have potential for storing a significant quantity of soil C., THE RAPID RATE of increase in atmospheric C[O.sub.2] levels has placed emphasis on better understanding the role of agriculture in mitigating this increase. The vast area of perennial grasslands and [...]

Understanding long-term management effects on soil properties is necessary to determine the relative sustainability of cropping systems. Soil physical, chemical, and biological properties were measured in a long-term cropping system study in the Western Corn Belt. Properties were evaluated after 16 yr in four crop sequences [continuous corn (zea mays L.) (CC), corn-soybean [Glycine max. (L.)] (C-SB), corn-oat (Avena sativa L.) + clover (80% sweet clover [Melilotus officinalis L.] and 20% red clover [Trifolium pratense L.])-grain sorghum [(Sorghum bicolor (L.) Moench)-soybean (C-OCL-SG-SB), and corn-soybean-grain sorghum-oat + clover (C-SB-SG-OCL)] each at three N fertilization rates (ZERO, LOW, and HIGH) to a soil depth of 30.5 cm on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudolls). Nitrogen fertilization had a greater impact on soil properties than crop sequence, with management effects most pronounced at 0 to 7.6 cm. Increased N rate resulted in greater organic C, total N, and particulate organic matter (POM), but lower soil pH. Increased N rate also reduced microbial biomass by ~20% between the HIGH and ZERO N-rate treatments. The C-SB-SG-OCL sequence possessed more potentially mineralizable N (PMN) (57 vs. 46 kg [ha.sup.-1] for average of CC and C-SB) and a higher percentage of POM present as soil organic matter (17.1% for the C-SB-SG-OCL sequence vs. 13.9% for other sequences). Within the context of soil functions and cropping system performance, results from this study indicate the C-SB-SB-OCL sequence enhanced nutrient cycling efficiency, while N fertilization resulted in a trade-off between its positive effect on biological productivity and negative effect on nutrient cycling efficiency.

Evaluation of soil quality is essential to determining the sustainability of land management systems. Previous work has sought to identify soil quality assessments for evaluating soil conditions within the context [...]

A correlation analysis of the influence of long-term controlled wheel traffic on soil respiration in ridge-till shows that alterations in physical and chemical conditions are responsible for the variations in microbial activity. Ridge-till decreases chemical, fuel and labor inputs compared to traditional tillage systems. Soil respiration is substantially affected by position, depth and water filled pore space. Soil respiration is present uptill 7.5 cm and reduces below that.

The soil characteristics of a ridge tillage system were studied to determine the influence of long-term controller tractor wheel traffic. The influence of major position and depth position on soil characteristics was primarily due to the management-linked activities of tractor wheel traffic and ridging. An extremely compact soil condition in the traffic interrow resulted from wheel traffic. Ridge-tilled fields must be viewed and handled, not as a single unit but as soil zones, because three separate soil zones are caused by wheel traffic and ridging.

Archived soil samples are an important resource for quantifying changes in soil attributes over decadal time scales. Herein, we describe a soil archive at the USDA-ARS Northern Great Plains Research Laboratory (NGPRL) near Mandan, ND with the intent of encouraging research collaboration through utilization of the archive. Over 5000 samples are included in the NGPRL soil archive, ranging in age from 4 to 90 yr. Samples were derived from both grazing and cropping studies, with the former being conducted near Mandan, and the latter as a part of an evaluation of soil C and N change at multiple locations throughout the Great Plains. Most samples are associated with soil depths above 30.5 cm, although 10 locations from the Great Plains evaluation possess archived soils below I am for native vegetation treatments. Collaborative research opportunities using the NGPRL soil archive abound, and may include characterizations of soil organic matter fractions, micronutrients, and soil acidity. Scientists interested in engaging in collaborative research efforts are encouraged to contact the authors of this report. Abbreviations: LTSE, long-term soil experiment; NGPRL, Northern Great Plains Research Laboratory.

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]