• Authors:
    • Robertson, G. P.
    • Kravchenko, A. N.
    • Basso, B.
    • Senthilkumar, S.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 6
  • Year: 2009
  • Summary: Temporal changes in soil C content vary as a result of complex interactions among different factors including climate, baseline soil C levels, soil texture, and agricultural management practices. The study objectives were: to estimate the changes in soil total C contents that occurred in the past 18 to 21 yr in soils under agricultural management and in never-tilled grassland in southwest Michigan; to explore the relationships between these changes and soil properties, such as baseline C levels and soil texture; and to simulate C changes using a system approach model (SALUS). The data were collected from two long-term experiments established in 1986 and 1988. Georeferenced samples were collected from both experiments before establishment and then were resampled in 2006 and 2007. The studied agricultural treatments included the conventional chisel-plow and no-till management systems with and without N fertilization and the organic chisel-plow management with cover crops. Total C was either lost in the conventional chisel-plowed systems or was only maintained at the 1980s levels by the conservation management systems. The largest loss in the agricultural treatments was 4.5 Mg ha(-1) total C observed in the chisel-plow system without N fertilization. A loss of 17.3 Mg ha(-1) occurred in the virgin grassland sod. Changes in C content tended to be negatively related to baseline C levels. Under no-till, changes in C were positively related to silt + clay contents. The SALUS predictions of soil C changes were in excellent agreement with the observed data for most of the agricultural treatments and for the virgin soil.
  • Authors:
    • Jarecki, M. K.
    • Lal, R.
    • Ussiri, D. A. N.
  • Source: Soil & Tillage Research
  • Volume: 104
  • Issue: 2
  • Year: 2009
  • Summary: Nitrous oxide (N2O) and methane (CH4) emitted by anthropogenic activities have been linked to the observed and predicted climate change. Conservation tillage practices such as no-tillage (NT) have potential to increase C sequestration in agricultural soils but patterns of N2O and CH4 emissions associated with NT practices are variable. Thus, the objective of this study was to evaluate the effects of tillage practices on N2O and CH4 emissions in long-term continuous corn (Zea mays) plots. The study was conducted on continuous corn experimental plots established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. The experimental design consisted of NT, chisel till (CT) and moldboard plow till (MT) treatments arranged in a randomized block design with four replications. The N2O and CH4 fluxes were measured for 1-year at 2-week intervals during growing season and at 4-week intervals during the off season. Long-term NT practice significantly decreased soil bulk density (rho(b)) and increased total N concentration of the 0-15 cm layer compared to MT and CT. Generally, NT treatment contained higher soil moisture contents and lower soil temperatures in the surface soil than CT and MT during summer, spring and autumn. Average daily fluxes and annual N2O emissions were more in MT (0.67 mg m(-2) d(-1) and 1.82 kg N ha(-1) year(-1)) and CT (0.74 mg m(-2) d(-1) and 1.96 kg N ha(-1) year(-1)) than NT (0.29 mg m(-2) d(-1) and 0.94 kg N ha(-1) year(-1)). On average, NT was a sink for CH4, oxidizing 0.32 kg CH4-C ha(-1) year(-1), while MT and CT were sources of CH4 emitting 2.76 and 2.27 kg CH4-C ha(-1) year(-1), respectively. Lower N2O emission and increased CH4 oxidation in the NT practice are attributed to decrease in surface rho(b), suggesting increased gaseous exchange. The N2O flux was strongly correlated with precipitation, air and soil temperatures, but not with gravimetric moisture content. Data from this study suggested that adoption of long-term NT under continuous corn cropping system in the U.S. Corn Belt region may reduce GWP associated with N2O and CH4 emissions by approximately 50% compared to MT and CT management.
  • Authors:
    • VandenBygaart, A. J.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 4
  • Year: 2009
  • Summary: Comments on "Regional study of no-till effects on carbon sequestration in the Midwestern United States"
  • Authors:
    • Oberholzer, H.
    • Reiser, R.
    • Leifeld, J.
  • Source: Agronomy Journal
  • Volume: 101
  • Issue: 5
  • Year: 2009
  • Summary: Organic farming practices are regarded as being beneficial for the environment by promoting soil quality and sequestering soil organic carbon (SOC). We studied SOC dynamics in the long-term field experiment DOK in Switzerland. The experiment compares three organically fertilized treatments under conventional (CONFYM), bioorganic (BIOORG), and biodynamic (BIO-DYN) management, and two systems with (CONMIN) or without (NOFERT) mineral fertilizer. We analyzed measured SOC time series from 1977 to 2004 and applied soil fractionation, radiocarbon dating, and modeling with the carbon model RothC. The SOC declined significantly in most parcels, but was not systematically different between systems. Initial SOC contents correlated with soil texture and were identified as being important with respect to the change rate. The SOC loss was at the expense of mineral-associated carbon whereas the more labile fractions increased. The overall decline was explained by reduced carbon inputs since commencement of the experiment and was most pronounced in NOFERT and CONMIN. The model satisfactorily simulated the dynamics of most of the treatments for both initialization with equilibrium runs or measured SOC fractions. Carbon loss in CONFYM was not fully captured by the model. Composition of organic fertilizers depended on the particular management, and a model adjustment of their relative stability improved the match between model and measurements. Model runs without management effects indicated that the observed increase in temperatures at the experimental site does not induce a change in SOC. Overall, the study does not support a benefit of organic farming on SOC contents compared with conventional systems with manure.
  • Authors:
    • Moreno, F.
    • Murillo, J. M.
    • López-Garrido, R.
    • Melero, S.
  • Source: Soil & Tillage Research
  • Volume: 104
  • Issue: 2
  • Year: 2009
  • Summary: Short- and long-term field experiments are necessary to provide important information about how soil carbon sequestration is affected by soil tillage system; such systems can also be useful for developing sustainable crop production systems. In this study, we evaluated the short- and long-term effects of conservation tillage (CT) on soil organic carbon fractions and biological properties in a sandy clay loam soil. Both trials consisted of rainfed crop rotation systems (cereal-sunflower-legumes) located in semi-arid SW Spain. In both trials, results were compared to those obtained using traditional tillage (TT). Soil samples were taken in flowering and after harvesting of a pea crop and collected at three depths (0-5, 5-10 and 10-20 cm). The soil organic carbon fractions were measured by the determination of total organic carbon (TOC), active carbon (AC) and water soluble carbon (WSC). Biological status was evaluated by the measurement of soil microbial biomass carbon (MBC) and enzymatic activities [dehydrogenase activity (DHA), o-diphenol oxidase activity (DphOx), and beta-glucosidase activity (beta-glu)]. The contents of AC and MBC in the long-term trial and contents of AC in the short-term trial were higher for CT than TT at 0-5 cm depth for both sampling periods. Furthermore, DHA and beta-glucosidase values in the July sampling were higher in the topsoil under conservation management in both trials (short- and long-term). The parameters studied tended to decrease as depth increased for both tillage system (TT and CT) and in both trials with the exception of the DphOx values, which tended to be higher at deeper layers. Values of DHA and beta-glu presented high correlation coefficients (r from 0.338 to 0.751, p <= 0.01) with AC, WSC and TOC values in the long-term trial. However, there was no correlation between either TOC or MBC and the other parameters in the short-term trial. In general, only stratification ratios of AC were higher in CT than in TT in both trials. The results of this study showed that AC content was the most sensitive and reliable indicator for assessing the impact of different soil management on soil quality in the two experiments (short- and long-term). Conservation management in dryland farming systems improved the quality of soil under our conditions, especially at the surface layers, by enhancing its storage of organic matter and its biological properties, mainly to long-term. (C) 2009 Elsevier B.V. All rights reserved.
  • Authors:
    • Horwath, W.
    • Kallenbach, C.
    • Assa, J.
    • Burger, M.
  • Year: 2009
  • Authors:
    • Paustian, K.
    • Rice, C.
    • Grove, J.
    • Alley, M.
    • Duiker, S. W.
    • Burras, L.
    • Liebig, M.
    • Lal, R.
    • Franzleubber, A.
  • Year: 2009
  • Summary: The Chicago Climate Exchange (CCX®) Agricultural Best Management Practices - Continuous Conservation Tillage and Conversion to Grassland Soil Carbon Sequestration Offset Project Protocol outlines the process and requirements for Project Proponents to register greenhouse gas (GHG) emission reductions resulting from voluntary conservation tillage practices and/or grassland planting. CCX General Offsets Program Provisions, the CCX Offset Project Verification Guidance Document, and CCX Offset Project Protocols can be downloaded by visiting www.theccx.com. Requests for further information or comments may be directed to offsets@theccx.com.
  • Authors:
    • Smith, D. L.
    • Ma, B.-L.
    • Rochette, P.
    • Madramootoo,C.
    • Zhou, X.
    • Mabood, F.
    • Almaraz, J. J.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 1
  • Year: 2009
  • Summary: Agriculture has an important potential role in mitigating greenhouse gas emissions (GHG). However, practices that reduce CO2 emissions from soils and increase the soil organic C level may stimulate N2O emissions. This is particularly critical in Quebec where heavy soils and a humid climate may limit the adoption of agricultural practices designed to mitigate GHG. The objective of this work was to study the effects of two tillage and N fertilization regimes on CO2 and N2O fluxes and the seasonal variability in emissions of these gases, associated with corn (Zea mays L.) grown in southwestern Quebec. Different seasonal emission patterns of CO2 and N2O were observed. Higher N2O fluxes occurred during the spring and were associated with precipitation events, while higher CO2 fluxes occurred in mid-season and were related to temperature. Conventional tillage (CT) had greater peaks of CO2 emissions than no-till (NT) only after disking in the spring. Once corn was established, differences between tillage systems were small. Peaks of N2O emission occurred in both systems (NT and CT) following N application. Plots receiving 180 kg N ha-1 in both tillage systems had large peak of N2O emission rates during the wettest parts of the season. The CT and NT systems generally had similar cumulative CO2 emissions but NT had higher cumulative N2O emissions than CT. Our findings suggests that changing from CT to NT under the heavy soil conditions of Quebec may increase GHG, mainly as result of the increase in N2O emission. This negative effect of NT could be reduced by avoiding fertilizing when precipitation is more intense.
  • Authors:
    • McNeill, A.
    • Sommer, R.
    • Ibrikci, H.
    • Ryan, J.
  • Source: Advances in Agronomy
  • Volume: 104
  • Year: 2009
  • Summary: This review examines the varied aspects of N in the soils and cropping systems as reflected by research at The International Center for Agricultural Research in the Dry Areas (ICARDA) in Syria in collaboration with other countries of the West Asia-North Africa region, especially in Morocco and other countries north and south of the Mediterranean. The synthesis, therefore, reflects a broad overview of conditions that impinge an N nutrition of crops and the evolution of N research achievements since the advent of commercial fertilization over three decades ago. With few exceptions, the soils of the Mediterranean region are low in organic matter and consequently in the reserves of total N, thus posing a limit of growing crops without fertilizer N or biological N fixation (BNF) through legumes. Soil calibration studies established the value of the soil nitrate test as a predictor of crop response with field trials to establish application rates for the main crops. Applicability is influenced by depth of sampling and the extent of mineralization. Dryland crop responses to N varied widely throughout the region from 30 to 150 kg N ha -1, being dependent on soil N status and seasonal rainfall as the major determinant of yields. Splitting the N application was only advantageous in higher rainfall areas. Residual N from BNF by food and forage legumes influenced soil N supply for cereals and relative responses to N fertilizer. The contribution of rhizobia fixation to all the major legumes was quantified using 15N along with management factors that influenced BNF by legumes. Where legumes were newly introduced to a region, rhizobial inoculation was considered necessary. With cereal responses to fertilizer N, differences between varieties were highlighted. Where urea or ammonium-N fertilizers were used, volatilization was the main loss mechanisms rather than leaching or denitrification. Considerable work was done on N use within crop rotation systems and components of the N cycle defined along with inputs from urine and feces from grazing animals. Forage legumes were shown to enhance total soil N and both labile and biomass N, with the least influence from fallow. These N forms were shown to fluctuate during the year as moisture and temperature conditions changed. Fertilizer N use had a positive effect on grain quality with increased protein, as well as soil organic matter (SOM) and thus soil quality. The significant change of the gradual introduction of supplemental irrigation in traditional rainfed cropping areas and its implications for use of models to describe the complex nature of N in dryland cropping systems was described. With the likelihood of a continuation of intensification of the dryland cropping systems in the Mediterranean region, N fertilizer use will inevitably increase and along with it the need for greater use efficiency in the interest of production economics and the environment. While limited use has been made of modeling of N, this approach is likely to be of more significance in integrating the varied facets of N under Mediterranean cropping conditions.
  • Authors:
    • White, P. M.
    • Rice, C. W.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 1
  • Year: 2009
  • Summary: One goal of soil C sequestration is to increase the mass of C stored in agricultural soils. Reducing soil disturbance, e.g., no-till management, facilitates soil fungal growth and results in higher C sequestration rates; however, the specific mechanisms associated with short-term plant residue C and N retention are less clear. We applied 13C- and 15N-enriched grain sorghum ( Sorghum bicolor) residue to no-till (NT) and conventional tillage (CT) soils, and measured the 13C and 15N retention in the soil and in aggregate fractions, along with soil microbial dynamics, during a growing season. The field site was located at Ashland Bottoms near Manhattan, Kansas. The added plant residue mineralized rapidly in both tillage systems, with similar decomposition kinetics, as indicated by 13C data. Mass balance calculations indicated that approximately 70% of the added 13C was mineralized to CO 2 by 40 days. The total Gram positive and Gram negative bacteria and fungal phospholipid fatty acids were higher under NT 0-5 cm during the most active period of residue mineralization compared with the CT 0-5 or 5-15 cm depths. No changes were observed in the NT 5-15 cm depth. The >1000-m aggregate size class retained the most 13C, regardless of tillage. The NT >1000-m aggregates retained more 15N at the end of the experiment than other NT and CT aggregates size classes. Data obtained indicate higher biological activity associated with NT soils than under CT, and increased retention of plant residue C and N in macroaggregates.