• Authors:
    • de Moura, R. L.
    • Klonsky, K. M.
    • Peacock, W. L.
    • Hashim-Buckey, J. M.
    • Vasquez, S. J.
  • Source: University of California Cooperative Extension Publication
  • Year: 2007
  • Authors:
    • Mitchell, J. P.
    • Horwath, W. R.
    • Veenstra, J. J.
  • Source: Soil Science Society of America Journal
  • Volume: 71
  • Issue: 2
  • Year: 2007
  • Summary: Conservation tillage (CT) and cover cropping (CC) are agricultural practices that may provide solutions to address water and air quality issues arising from intensive agricultural practices. This study investigated how CT and CC affect soil organic matter dynamics in a cotton(Gossypium hirsutum L.)-tomato (Lycopersicon esculentum Mill.) rotation in California's San Joaquin Valley. There were four treatments: conservation tillage, no cover crop (CTNO); conservation tillage with cover crop (CTCC); standard tillage, no cover crop (STNO); and standard tillage with cover crop (STCC). After 5 yr, the top 30 cm of soil in CTCC had an increase of 4500 kg C ha(-1), compared with an increase of 3800 kg C hat in STCC from initial soil C content in 1999. To enhance our understanding of C dynamics in CT systems, we pulse-labeled cotton with (CO2)-C-13 in the field and followed the decomposition of both the roots and the shoots through three physical fractions: light fraction (LF), which tends to turnover quickly, and two relatively stable C pools-intraaggregate LF (iLF) and mineral-associated carbon (mC). Soil under CT treatments retained more of the cotton-residue-derived C in LF and iLF than ST 3 mo after placement in the field. These differences disappeared after 1 yr, however, with no discernable differences between CT and ST regardless of CC. In California's Mediterranean climate, CT alone does not accumulate or stabilize more C than ST in tomato-cotton rotations, and the addition of cover crop biomass is more important than tillage reduction for total soil C accumulation.
  • Authors:
    • Venterea, R. T.
  • Source: Global Change Biology
  • Volume: 13
  • Issue: 8
  • Year: 2007
  • Summary: Nitrite (NO2-) can accumulate during nitrification in soil following fertilizer application. While the role of NO2- as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil-to-atmosphere fluxes as a function of NO2- levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N2O production rate (PN2O)toNO2- was observed at concentrations below 60 ugNg-1 soil in both nonsterile and sterilized soils. Rate coefficients (Kp) relating PN2O to NO2- varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in Kp across all samples. Abiotic processes accounted for 31-75% of total N2O production. Biological reduction of NO2- was enhanced as oxygen (O2) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO3-)-reduction, and the reduction of N2O itself, were only stimulated at O2 levels below 5%. Greater temperature sensitivity was observed for biological compared with chemical N2O production. Steady-state model simulations predict that NO2 - levels often found after fertilizer applications have the potential to generate substantial N2O fluxes even at ambient O2. This potential derives in part from the production of N2O under conditions not favorable for N2O reduction, in contrast to N2O generated from NO3- reduction. These results have implications with regard to improved management to minimize agricultural N2O emissions and improved emissions assessments.
  • Authors:
    • Adee, E. A.
    • Nafziger ,E. D.
    • Hoeft, R. G.
    • Lal, R.
    • Jagadamma, S.
  • Source: Soil & Tillage Research
  • Volume: 95
  • Issue: 1-2
  • Year: 2007
  • Summary: Agricultural soils can be a major sink for atmospheric carbon (C) with adoption of recommended management practices (RMPs). Our objectives were to evaluate the effects of nitrogen (N) fertilization and cropping systems on soil organic carbon (SOC) and total N (TN) concentrations and pools. Replicated soil samples were collected in May 2004 to 90 cm depth from a 23-year-old experiment at the Northwestern Illinois Agricultural Research and Demonstration Center, Monmouth, IL. The SOC and TN concentrations and pools, soil bulk density (rho(b)) and soil C:N ratio were measured for five N rates [0 (N-0), 70 (N-1), 140 (N-2), 210 (N-3) and 280 (N-4) kg N ha(-1)] and two cropping systems [continuous corn (Zea mays L.) (CC), and corn-soybean (Glycine max (L.) Merr.) rotation (CS)]. Long-term N fertilization and cropping systems significantly influenced SOC concentrations and pools to 30 cm depth. The SOC pool in 0-30 cm depth ranged from 68.4 Mg ha(-1) for N-0 to 75.8 Mg ha(-1) for N-4. Across all N treatments, the SOC pool in 0-30 cm depth for CC was 4.7 Mg ha(-1) greater than for CS. Similarly, TN concentrations and pools were also significantly affected by N rates. The TN pool for 0-30 cm depth ranged from 5.36 Mg ha(-1) for N-0 to 6.14 Mg ha(-1) for N-4. In relation to cropping systems, the TN pool for 0-20 cm depth for CC was 0.4 Mg ha(-1) greater than for CS. The increase in SOC and TN pools with higher N rates is attributed to the increased amount of biomass production in CC and CS systems. Increasing N rates significantly decreased rho(b) for 0-30 cm and decreased the soil C:N ratio for 0-10 cm soil depth. However, none of the measured soil properties were significantly correlated with N rates and cropping systems below 30 cm, soil depth. We conclude that in the context of developing productive and environmentally sustainable agricultural systems on a site and soil specific basis, the results from this study is helpful to strengthening the database of management effects on SOC storage in the Mollisols of Midwestem U.S. (c) 2007 Elsevier B.V. All rights reserved.
  • Authors:
    • Reicosky, D. C.
    • Lachnicht Weyers, S.
    • Franzluebbers, A. J.
    • Johnson, Jane M. -F
  • Source: Environmental Pollution
  • Volume: 150
  • Issue: 1
  • Year: 2007
  • Summary: Agriculture is a source for three primary greenhouse gases (GHGs): CO2, CH4, and N2O- It can also be a sink for CO2 through C sequestration into biomass products and soil organic matter. We summarized the literature on GHG emissions and C sequestration, providing a perspective on how agriculture can reduce its GHG burden and how it can help to mitigate GHG emissions through conservation measures. Impacts of agricultural practices and systems on GHG emission are reviewed and potential trade-offs among potential mitigation options are discussed. Conservation practices that help prevent soil erosion, may also sequester soil C and enhance CH4 consumption. Managing N to match crop needs can reduce N2O emission and avoid adverse impacts on water quality. Manipulating animal diet and manure management can reduce CH4 and N2O emission from animal agriculture. All segments of agriculture have management options that can reduce agriculture's environmental footprint.
  • Authors:
    • Boast, C. W.
    • Ellsworth, T. R.
    • Mulvaney, R. L.
    • Khan, S. A.
  • Source: Journal of Environmental Quality
  • Volume: 36
  • Issue: 6
  • Year: 2007
  • Summary: Intensive use of N fertilizers in modern agriculture is motivated by the economic value of high grain yields and is generally perceived to sequester soil organic C by increasing the input of crop residues. This perception is at odds with a century of soil organic C data reported herein for Morrow Plots, the world's oldest experimental site under continuous corn (Zea mays L.). After 40 to 50 yr of synthetic fertilization that exceeded grain N removal by 60 to 190%, a net decline occurred in soil C despite increasingly massive residue C incorporation, the decline being more extensive for a corn-soybean (Glycine max L. Merr.) or corn-oats (Avena sativa L.)-hay rotation than for continuous corn and of greater intensity for the profile (0-46 cm) than the surface soil. These findings implicate fertilizer N in promoting the decomposition of crop residues and soil organic matter and are consistent with data from numerous cropping experiments involving synthetic N fertilization in the USA Corn Belt and elsewhere, although not with the interpretation usually provided. These are important implications for soil C sequestration because the yield-based input of fertilizer N has commonly exceeded grain N removal for corn production on fertile soils since the 1960s. To mitigate the ongoing consequences of soil deterioration, atmospheric CO2 enrichment, and NO3- pollution of ground and surface waters, N fertilization should be managed by site-specific assessment of soil N availability. Current fertilizer N managment practices, if combined with corn stover removal for bioenergy production; exacerbate soil C loss.
  • Authors:
    • Kucharik, C. J.
  • Source: Soil Science Society of America Journal
  • Volume: 71
  • Issue: 2
  • Year: 2007
  • Summary: Conservation Reserve Program (CRP) prairie restorations can sequester soil C and N, but the varied effects of soil order and ecosystem age are uncertain. Soil bulk density (Db) (0-20 cm) and soil organic C (SOC) and total N at 0 to 5, 5 to 10, and 10 to 25 cm were measured at 39 paired CRP-crop sites in Wisconsin to quantify SOC and N stock changes as a function of prairie age (4-16 yr) and soil order (Alfisols and Mollisols). Several important outcomes were found regarding land conversion to CRP: (i) soil Db decreased on Alfisols (-0.12 {+/-} 0.11 g cm-3, P < 0.0001) but not Mollisols; (ii) SOC sequestration rates were not significantly different between Mollisols (49.7 {+/-} 64 g C m-2 yr-1) and Alfisols (43.9 {+/-} 86 g C m-2 yr-1), but were only detectable (P < 0.05) in the upper 5 cm; (iii) whole SOC and N to a depth of 25 cm did not change significantly; (iv) the annual average SOC sequestration rate declined (P < 0.05) as prairie age increased (from 72 {+/-} 105 to 13 {+/-} 25 g C m-2 yr-1 for youngest to oldest age groupings); and (v) short-term SOC and N increases could be lost with time. These data suggest that there may be a discontinuity between the intensity of continuing management that is needed for sustained, long-term SOC increases in planted prairies and the resources that the CRP has available to achieve this level of ecosystem functioning.
  • Authors:
    • Kimble, J. M.
    • Stewart, B. A.
    • Follett, R. F.
    • Lal, R.
  • Source: Soil Science
  • Volume: 172
  • Issue: 12
  • Year: 2007
  • Summary: World soils have been a source of atmospheric carbon dioxide since the dawn of settled agriculture, which began about 10 millennia ago. Most agricultural soils have lost 30% to 75% of their antecedent soil organic carbon (SOC) pool or 30 to 40 t C ha-1. The magnitude of loss is often more in soils prone to accelerated erosion and other degradative processes. On a global scale, CO2-C emissions since 1850 are estimated at 270 +/- 30 gigaton (billion ton or Gt) from fossil fuel combustion compared with 78 +/- 12 Gt from soils. Consequently, the SOC pool in agricultural soils is much lower than their potential capacity. Furthermore, depletion of the SOC pool also leads to degradation in soil quality and declining agronomic/biomass productivity. Therefore, conversion to restorative land uses (e.g., afforestation, improved pastures) and adoption of recommended management practices (RMP) can enhance SOC and improve soil quality. Important RMP for enhancing SOC include conservation tillage, mulch farming, cover crops, integrated nutrient management including use of manure and compost, and agroforestry. Restoration of degraded/desertified soils and ecosystems is an important strategy. The rate of SOC sequestration, ranging from 100 to 1000 kg ha-1 year-1, depends on climate, soil type, and site-specific management. Total potential of SOC sequestration in the United States of 144 to 432 Mt year-1 (288 Mt year-1) comprises 45 to 98 Mt in cropland, 13 to 70 Mt in grazing land, and 25 to 102 Mt in forestland. The global potential of SOC sequestration is estimated at 0.6 to 1.2 Gt C year-1, comprising 0.4 to 0.8 Gt C year-1 through adoption of RMP on cropland (1350 Mha), and 0.01 to 0.03 Gt C year-1 on irrigated soils (275 Mha), and 0.01 to 0.3 Gt C year-1 through improvements of rangelands and grasslands (3700 Mha). In addition, there is a large potential of C sequestration in biomass in forest plantations, short rotation woody perennials, and so on. The attendant improvement in soil quality with increase in SOC pool size has a strong positive impact on agronomic productivity and world food security. An increase in the SOC pool within the root zone by 1 t C ha-1 year-1 can enhance food production in developing countries by 30 to 50 Mt year-1 including 24 to 40 Mt year-1 of cereal and legumes, and 6 to 10 Mt year-1 of roots and tubers. Despite the enormous challenge of SOC sequestration, especially in regions of warm and arid climates and predominantly resource-poor farmers, it is a truly a win-win strategy. While improving ecosystem services and ensuring sustainable use of soil resources, SOC sequestration also mitigates global warming by offsetting fossil fuel emissions and improving water quality by reducing nonpoint source pollution. (C) 2007 Lippincott Williams & Wilkins, Inc.
  • Authors:
    • Pimentel, D.
    • Lal, R.
  • Source: Soil & Tillage Research
  • Volume: 93
  • Issue: 2
  • Year: 2007
  • Summary: A 2007 editorial about biofuels from crop residues in the journal Soil & Tillage Research.
  • Authors:
    • Chen, C. -C.
    • Schneider, U. A.
    • McCarl, B. A.
    • Lee, H. -C.
  • Source: Mitigation and Adaptation Strategies for Global Change
  • Volume: 12
  • Issue: 4
  • Year: 2007
  • Summary: The world is moving toward efforts to reduce net greenhouse gas emissions. Reduction efforts may involve the agricultural sector through options such as planting of trees, altering crop and livestock management, and increasing production of biofuels. However, such options can be competitive with domestic food production. In a free trade arena, reduced domestic food production could stimulate increased production and exports in other countries, which are not pursuing net emission reductions. As a consequence, emission reduction efforts in implementing countries may be offset by production increases stimulated in other countries. We examine the competitive effects of agriculturally related emission reduction actions on agricultural production and international trade. In doing this, we employ the assumption that U.S. emission reduction caused cost increases will also occur in other reducing countries. We consider emission reduction: 1) unilaterally by the U.S., 2) by all Kyoto Protocol Annex B countries, and 3) globally. The results, which are only suggestive of the types of effects that would be observed due to the simplifying cost assumptions, indicate compliance causes supply cutbacks in regulated countries and increases in non-regulated countries. The study results show that producers in regulating countries are likely to benefit and consumers lose due to commodity price increases.