• Authors:
    • Rolston, D. E.
    • van Kessel, C.
    • King, A. P.
    • Six, J.
    • Lee, J.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 3
  • Year: 2006
  • Summary: There is a lack of understanding of how associations among soil properties and management-induced changes control the variability of greenhouse gas (GHG) emissions from soil. We performed a laboratory investigation to quantify relationships between GHG emissions and soil indicators in an irrigated agricultural field under standard tillage (ST) and a field recently converted (2 yr) to no-tillage (NT). Soil cores (15-cm depth) were incubated at 25{degrees}C at field moisture content and 75% water holding capacity. Principal component analysis (PCA) identified that most of the variation of the measured soil properties was related to differences in soil C and N and soil water conditions under ST, but soil texture and bulk density under NT. This trend became more apparent after irrigation. However, principal component regression (PCR) suggested that soil physical properties or total C and N were less important in controlling GHG emissions across tillage systems. The CO2 flux was more strongly determined by microbial biomass under ST and inorganic N content under NT than soil physical properties. Similarly, N2O and CH4 fluxes were predominantly controlled by NO3- content and labile C and N availability in both ST and NT soils at field moisture content, and NH4+ content after irrigation. Our study indicates that the field-scale variability of GHG emissions is controlled primarily by biochemical parameters rather than physical parameters. Differences in the availability and type of C and N sources for microbial activity as affected by tillage and irrigation develop different levels and combinations of field-scale controls on GHG emissions.
  • Authors:
    • Liu, X. J.
    • Reule, C. A.
    • Halvorson, A. D.
    • Mosier, A. R.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 4
  • Year: 2006
  • Summary: The impact of management on global warming potential (GWP), crop production, and greenhouse gas intensity (GHGI) in irrigated agriculture is not well documented. A no-till (NT) cropping systems study initiated in 1999 to evaluate soil organic carbon (SOC) sequestration potential in irrigated agriculture was used in this study to make trace gas flux measurements for 3 yr to facilitate a complete greenhouse gas accounting of GWP and GHGI. Fluxes of CO2, CH4, and N2O were measured using static, vented chambers, one to three times per week, year round, from April 2002 through October 2004 within conventional-till continuous corn (CT-CC) and NT continuous corn (NT-CC) plots and in NT corn-soybean rotation (NT-CB) plots. Nitrogen fertilizer rates ranged from 0 to 224 kg N ha-1. Methane fluxes were small and did not differ between tillage systems. Nitrous oxide fluxes increased linearly with increasing N fertilizer rate each year, but emission rates varied with years. Carbon dioxide efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. The CT soils were smaller net sinks for GWP than NT soils. The determinant for the net GWP relationship was a balance between soil respiration and N2O emissions. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when appropriate crop production levels are achieved, net CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer.
  • Authors:
    • Bremer, D.
  • Year: 2006
  • Summary: 1) Quantify the magnitude and patterns of nitrous oxide (N2O) fluxes in turfgrass; and 2) determine how nitrogen (N)-fertilization rates, N-fertilizer types, and irrigation affect N2O fluxes.
  • Authors:
    • Benvenuti, S.
    • Macchia, M.
  • Source: Italian Journal of Agronomy
  • Volume: 1
  • Issue: 1
  • Year: 2006
  • Summary: Little information is available on the stale seedbed effect on seedbank reduction. This weed management is of increasing interest overall in organic agricultural systems where is no possible to use herbicides. The emergence dynamics and related seedbank reduction were evaluated following adoption of two different stale seedbed techniques (with or without irrigation), made during the spring-summer season in 2001 in organic agricultural systems. As expected, emergence was strongly stimulated by irrigation and soil tillage. When the no-tillage technique was adopted (control), the absence of soil disturbance resulted in extremely low emergence levels, associated with a reduction in the number of the relative species. Consequently, analysis of the residual seedbank of the shallow layer (0-10 cm) of the control (no-till) showed only small reduction (about 1%). In contrast, the tillage-only experiment led to a reduction of about 5% in the same soil layer. However only with the irrigation, a drastic reduction in the amount of seeds (roughly half) was achieved. In particular, grasses showed the highest seedbank reduction rates. Despite this different effectiveness of the stale seedbed techniques, the soil layers at greater depths (10-20 and 20-30 cm) were found to be completely unaffected, independently of the agronomic practices carried out. Qualitative analysis of exhumed seeds demonstrated that greatest "forcing of germination" (tillage+irrigation) resulted in a percentage increase of "deep-dormant" seeds as a consequence "non-dormant" seeds decrease. Although stale seedbed appeared to be only partially effective, we believe that if this agrotechnique is properly carried out and repeated at the appropriate times, it promises to be successful in agricultural systems where herbicides are excluded.
  • Authors:
    • Yang, H. S.
    • Amos, B.
    • Burba, G. G.
    • Suyker, A. E.
    • Arkebauer, T. J.
    • Knops, J. M.
    • Walters, D. T.
    • Cassman, K. G.
    • Dobermann, A.
    • Verma, S. B.
    • Ginting, D.
    • Hubbard, K. G.
    • Gitelson, A. A.
    • Walter-Shea, E. A.
  • Source: Agricultural and Forest Meteorology
  • Volume: 131
  • Issue: 1-2
  • Year: 2005
  • Summary: Carbon dioxide exchange was quantified in maize ( Zea mays)-soybean ( Glycine max) agroecosystems employing year-round tower eddy covariance flux systems and measurements of soil C stocks, CO 2 fluxes from the soil surface, plant biomass, and litter decomposition. Measurements were made in 3 cropping systems: (a) irrigated continuous maize; (b) irrigated maize-soybean rotation; and (c) rainfed maize-soybean rotation during 2001-2004. The study was conducted at the University of Nebraska Agricultural Research and Development Centre near Mead, Nebraska, USA. Because of a variable cropping history, all 3 sites were uniformly tilled by disking prior to initiation of the study. Since then, all sites are under no-till, and crop and soil management follow best management practices prescribed for production-scale systems. Cumulative daily gain of C by the crops (from planting to physiological maturity), determined from the measured eddy covariance CO 2 fluxes and estimated heterotrophic respiration, compared well with the measured total above and belowground biomass. Two contrasting features of maize and soyabean CO 2 exchange are notable. The value of integrated gross primary productivity (GPP) for both irrigated and rainfed maize over the growing season was substantially larger (ca. 2:1 ratio) than that for soyabean. Also, soyabean lost a larger portion (0.80-0.85) of GPP as ecosystem respiration (due, in part, to the large amount of maize residue from the previous year), as compared to maize (0.55-0.65). Therefore, the seasonally integrated net ecosystem production (NEP) in maize was larger by a 4:1 ratio (approximately), as compared to soyabean. Enhanced soil moisture conditions in the irrigated maize and soyabean fields caused an increase in ecosystem respiration, thus eliminating any advantage of increased GPP and giving about the same values for the growing season NEP as the rainfed fields. On an annual basis, the NEP of irrigated continuous maize was 517, 424, and 381 g C m -2 year -1, respectively, during the 3 years of our study. In rainfed maize, the annual NEP was 510 and 397 g C m -2 year -1 in years 1 and 3, respectively. The annual NEP in the irrigated and rainfed soyabean fields were in the range of -18 to -48 g C m -2. Accounting for the grain C removed during harvest and the CO 2 released from irrigation water, our tower eddy covariance flux data over the first 3 years suggest that, at this time: (a) the rainfed maize-soybean rotation system is C neutral; (b) the irrigated continuous maize is nearly C neutral or a slight source of C; and (c) the irrigated maize-soybean rotation is a moderate source of C. Direct measurement of soil C stocks could not detect a statistically significant change in soil organic carbon during the first 3 years of no-till farming in these 3 cropping systems.
  • Authors:
    • R,Leuning
    • IE,Galbally
    • K,Kelly
    • R,Edis
    • Y,Li
    • D,Turner
    • D,Chen
  • Source: 4th International Symposium on non-CO2 Greenhouse Gases
  • Year: 2005
  • Authors:
    • Kelly, K.
    • Baigent, R.
    • Eckard, R.
    • Weeks, I.
    • Leuning, R.
    • Phillips, F.
    • Barker-Reid, F.
    • Gates, W.
    • Grace, P.
    • Galbally, I.
    • Meyer, M.
    • Bentley, S.
  • Source: Environmental Sciences
  • Volume: 2
  • Issue: 2-3
  • Year: 2005
  • Authors:
    • Ding, H.
    • Edis, R.
    • Zhang, Y.
    • Chen, D.
    • Li, Y.
  • Source: Global Biogeochemical Cycles
  • Volume: 19
  • Year: 2005
  • Authors:
    • Ginting, D.
    • Eghball, B.
  • Source: Soil Science Society of America Journal
  • Volume: 69
  • Issue: 3
  • Year: 2005
  • Summary: Field experiments were conducted to determine optimal time during the day for N 2O flux determination and to evaluate the effects of wheel traffic and soil parameters on N 2O fluxes following urea ammonium nitrate (UAN) injection and summer UAN fertigations. The experiments were located on silty clay loam soils under no-till irrigated continuous corn of eastern Nebraska. Three approaches were used. First, near-continuous N 2O flux measurements were made in non-wheel-tracked (NWT) interrows in four 24-h periods during the growing season of 2002. Second, point measurements of N 2O flux were made in the wheel-tracked (WT) and NWT interrows at five dates during the growing season of 2002. Third, point measurements of N 2O fluxes and soils (nitrate, ammonium, moisture, and temperature) were made in the NWT interrows from 2001 to 2004. The differences between point vs. continuous flux measurements (<8 g N 2O-N ha -1 d -1) and between the WT vs. the NWT (<3.7 g N 2O-N ha -1 d -1) were not significant. The means of N 2O daily flux within 60 d after injection (period of high soil N) in the first, second, and third year were 26.8, 21.2, and 28.0 g N 2O-N ha -1 d -1, respectively. The means during low soil N were 9.24, 4.05, and 7.50 g N 2O-N ha -1 d -1, respectively. Summer fertigations did not increase N 2O flux. Under the conditions of this study, optimal point measurement for N 2O daily flux can be made any time during the day at the NWT interrows. Among the soil parameters, soil nitrate dynamics in the injection zone correlates best with N 2O fluxes.
  • Authors:
    • Paustian, K.
    • Breidt, F. J.
    • Ogle, S. M.
  • Source: Biogeochemistry
  • Volume: 72
  • Issue: 1
  • Year: 2005
  • Summary: We conducted a meta-analysis to quantify the impact of changing agricultural land use and management on soil organic carbon (SOC) storage under moist and dry climatic conditions of temperate and tropical regions. We derived estimates of management impacts for a carbon accounting approach developed by the Intergovernmental Panel on Climate Change, addressing the impact of long-term cultivation, setting-aside land from crop production, changing tillage management, and modifying C input to the soil by varying cropping practices. We found 126 articles that met our criteria and analyzed the data in linear mixed-effect models. In general, management impacts were sensitive to climate in the following order from largest to smallest changes in SOC: tropical moist>tropical dry>temperate moist>temperate dry. For example, long-term cultivation caused the greatest loss of SOC in tropical moist climates, with cultivated soils having 0.58 ± 0.12, or 58% of the amount found under native vegetation, followed by tropical dry climates with 0.69 ± 0.13, temperate moist with 0.71 ± 0.04, and temperate dry with 0.82 ± 0.04. Similarly, converting from conventional tillage to no-till increased SOC storage over 20 years by a factor of 1.23 ± 0.05 in tropical moist climates, which is a 23% increase in SOC, while the corresponding change in tropical dry climates was 1.17 ± 0.05, temperate moist was 1.16 ± 0.02, and temperate dry was 1.10 ± 0.03. These results demonstrate that agricultural management impacts on SOC storage will vary depending on climatic conditions that influence the plant and soil processes driving soil organic matter dynamics.