• Authors:
    • Isla, R.
    • Ellsworth, J. W.
    • Blackmer, A. M.
    • Kyveryga, P. M.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 2
  • Year: 2004
  • Summary: Soil temperature at the time of application has been the primary factor used to predict rates of nitrification and assess the risks associated with losses of N applied in the fall as anhydrous ammonia in the Corn Belt. We report studies assessing the importance of soil pH as a factor affecting nitrification rates and losses of this N before corn (Zea Mays L.) begins rapid growth in June. Data were collected in a series of field studies conducted during 4 yr. Anhydrous ammonia was applied in the fall after soils had cooled to 7.5. Significant relationships between soil pH and percentage nitrification were observed each year. Means of measurements made in mid-April (when planting begins) indicated 89% nitrification of fertilizer N in soils having pH > 7.5 and 39% nitrification of this N in soils having pH < 6.0. The finding that soil pH influenced when nitrification occurred helps to explain why the effects of nitrification inhibitors have been variable in this region. Significant relationships between soil pH and recovery of fertilizer N as exchangeable NH4+ and NO3- were observed in years with above-average rainfall before samples were collected in April. The effects of soil pH on nitrification, therefore, influenced the amounts of NO3- lost by denitrification or leaching during spring rainfall. The observed effects of pH on nitrification rates suggest that economic and environmental benefits of delaying application of fertilizer N may be greater in higher-pH soils than in lower-pH soils.
  • Authors:
    • Lal, R.
  • Source: Science
  • Volume: 304
  • Issue: 5677
  • Year: 2004
  • Summary: The carbon sink capacity of the world's agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossil fuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.
  • Authors:
    • Harveson, R. M.
    • Burgener, P. A.
    • Blumenthal, J. M.
    • Baltensperger, D. D.
    • Lyon, D. J.
  • Source: Crop Science
  • Volume: 44
  • Issue: 3
  • Year: 2004
  • Summary: ummer fallow is commonly used to stabilize winter wheat (Triticum aestivum L.) production in the Central Great Plains, but summer fallow results in soil degradation, limits farm productivity and profitability, and stores soil water inefficiently. The objectives of this study were to quantify the production and economic consequences of replacing summer fallow with spring-planted crops on the subsequent winter wheat crop. A summer fallow treatment and five spring crop treatments [spring canola (Brassica napus L.), oat (Avena sativa L.) + pea (Pisum sativum L.) for forage, proso millet (Panicum miliaceum L.), dry bean (Phaseolus vulgaris L.), and corn (Zea mays L.)] were no-till seeded into sunflower (Helianthus annuus L.) residue in a randomized complete block design with five replications during 1999, 2000, and 2001. Winter wheat was planted in the fall following the spring crops. Five N fertilizer treatments (0, 22, 45, 67, and 90 kg N ha-1) were randomly assigned to each previous spring crop treatment in a split-plot treatment arrangement. The 3-yr mean wheat grain yield after summer fallow was 29% greater than following oat + pea for forage and 86% greater than following corn. The 3-yr mean annualized net return for the spring crop and subsequent winter wheat crop was $4.20, -$6.91, -$7.55, -$29.66, -$81.17, and -$94.88 ha-1 for oat + pea for forage, proso millet, summer fallow, dry bean, corn, and spring canola, respectively. Systems involving oat + pea for forage and proso millet are economically competitive with systems using summer fallow.
  • Authors:
    • Lewis, D. T.
    • Reedy, T. E.
    • Martens, D. A.
  • Source: Global Change Biology
  • Volume: 10
  • Issue: 1
  • Year: 2004
  • Summary: Conversion of former agricultural land to grassland and forest ecosystems is a suggested option for mitigation of increased atmospheric CO2. A Sharpsburg prairie loess soil (fine, smectitic, mesic Typic Argiudoll) provided treatments to study the impact of long-term land use on soil organic carbon (SOC) content and composition for a 130-year-old cropped, pasture and forest comparison. The forest and pasture land use significantly retained more SOC, 46% and 25%, respectively, compared with cropped land use, and forest land use increased soil C content by 29% compared with the pasture. Organic C retained in the soils was a function of the soil N content (r=0.98, P<0.001) and the soil carbohydrate (CH) concentration (r=0.96, P<0.001). Statistical analyses found that soil aggregation processes increased as organic C content increased in the forest and pasture soils, but not in the cropped soil. SOC was composed of similar percentages of CHs (49%, 42% and 51%), amino acids (22%, 15% and 18%), lipids (2.3%, 2.3% and 2.9%) and unidentified C (21%, 29% and 27%), but differed for phenolic acids (PAs) (5.7%, 11.6% and 1.0%) for the pasture, forest and cropped soils, respectively. The results suggested that the majority of the surface soil C sequestered in the long-term pasture and forest soils was identified as C of plant origin through the use of CH and PA biomarkers, although the increase in amino sugar concentration of microbial origin indicates a greater increase in microbial inputs in the three subsoils. The practice of permanent pastures and afforestation of agricultural land showed long-term potential for potential mitigation of atmospheric CO2.
  • Authors:
    • Palm, C.
    • King, J.
    • Verchot, L.
    • Wassmann, R.
    • Mosier, A.
  • Source: Environment, Development and Sustainability
  • Volume: 6
  • Issue: 1-2
  • Year: 2004
  • Summary: Tropical soils are important sources and sinks of atmospheric methane (CH4) and major sources of oxides of nitrogen gases, nitrous oxide (N2O) and NOx (NO+NO2). These gases are present in the atmosphere in trace amounts and are important to atmospheric chemistry and earth's radiative balance. Although nitric oxide (NO) does not directly contribute to the greenhouse effect by absorbing infrared radiation, it contributes to climate forcing through its role in photochemistry of hydroxyl radicals and ozone (O3) and plays a key role in air quality issues. Agricultural soils are a primary source of anthropogenic trace gas emissions, and the tropics and subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. The soil microbial processes responsible for the production and consumption of CH4 and production of N-oxides are the same in all parts of the globe, regardless of climate. Because of the ubiquitous nature of the basic enzymatic processes in the soil, the biological processes responsible for the production of NO, N2O and CH4, nitrification/denitrification and methanogenesis/methanotropy are discussed in general terms. Soil water content and nutrient availability are key controls for production, consumption and emission of these gases. Intensive studies of CH4 exchange in rice production systems made during the past decade reveal new insight. At the same time, there have been relatively few measurements of CH4, N2O or NOx fluxes in upland tropical crop production systems. There are even fewer studies in which simultaneous measurements of these gases are reported. Such measurements are necessary for determining total greenhouse gas emission budgets. While intensive agricultural systems are important global sources of N2O and CH4 recent studies are revealing that the impact of tropical land use change on trace gas emissions is not as great as first reports suggested. It is becoming apparent that although conversion of forests to grazing lands initially induces higher N-oxide emissions than observed from the primary forest, within a few years emissions of NO and N2O generally fall below those from the primary forest. On the other hand, CH4 oxidation is typically greatly reduced and grazing lands may even become net sources in situations where soil compaction from cattle traffic limits gas diffusion. Establishment of tree-based systems following slash-and-burn agriculture enhances N2O and NO emissions during and immediately following burning. These emissions soon decline to rates similar to those observed in secondary forest while CH4 consumption rates are slightly reduced. Conversion to intensive cropping systems, on the other hand, results in significant increases in N2O emissions, a loss of the CH4 sink, and a substantial increase in the global warming potential compared to the forest and tree-based systems. The increasing intensification of crop production in the tropics, in which N fertilization must increase for many crops to sustain production, will most certainly increase N-oxide emissions. The increase, however, may be on the same order as that expected in temperate crop production, thus smaller than some have predicted. In addition, increased attention to management of fertilizer and water may reduce trace gas emissions and simultaneously increase fertilizer use efficiency.
  • Authors:
    • Tan, C. S.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Soil & Tillage Research
  • Volume: 79
  • Issue: 1
  • Year: 2004
  • Summary: The influence of soil and crop management practices on soil aggregation is well documented; however very little information is available on the impact of aggregation on biological processes such as greenhouse gas emissions. Soils (Ap horizon of a Brookston clay loam) were sampled in the spring of 2002 from two treatments in a long-term study (established in 1959). The treatments included continuous corn (Zea mays L.) and the corn phase of a 4-year crop rotation which included corn-oats (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa. The continuous corn (CC) treatment was plowed every fall whereas the rotation corn (RC) treatment was plowed 2 out of the 4 years (in the fall following second year alfalfa and following corn). The objectives were to determine the impact of crop rotation and continuous corn on aggregate size distribution, and the influence of aggregate size on CO2 and N2O production through denitrification. The soil samples were separated into six aggregate size fractions (<0.25, 0.25-0.50, 0.50-1.0, 1.0-2.0, 2.0-4.0, and 4.0-8.0mm diameter) using a dry sieving procedure. Each aggregate size fraction was separated into two subsamples with one subsample left intact and the other ground to <0.15mm (100-mesh sieve). The intact and ground aggregates from each size fraction were incubated anaerobically using the acetylene inhibition technique and carbon dioxide (CO2) and nitrous oxide (N2O) production (denitrification) were determined. Nitrate was added and thus not limiting in the incubations. In both cropping treatments, the 2–4mm aggregate size was the dominant size fraction (~35-45% of the soil by weight) followed by the 1-2mm size fraction (~20-25% of the soil by weight). Crop rotation increased both CO2 and N2O production (denitrification) and the proportion of <2mm diameter aggregates compared to continuous corn. For intact aggregates, CO2 production decreased with increasing aggregate size, while N2O production (denitrification) increased with increasing aggregate size. When the aggregates were ground, CO2 production was independent of the original aggregate size, while N2O production (denitrification) decreased as the size of the original aggregates increased. This study demonstrates that both the size distribution of natural soil aggregates and soil grinding can have substantial impacts on the CO2 and N2O production through denitrification.
  • Authors:
    • Perfect, E.
    • Herbeck, J.
    • Murdock, L.
    • Grove, J. H.
    • Dí­az-Zorita, M.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 6
  • Year: 2004
  • Summary: The development of well-structured soils is a goal for achieving sustainable and productive agricultural systems. Nevertheless, the maintenance of soil structure in continuous no-till (NT) soils has sometimes been thought to induce soil conditions that are detrimental to crop yields. The objectives of this research were to characterize the effects of periodic tillage disruption in otherwise NT systems on soil properties and the yields of winter wheat (Triticum aestivum L.), double-cropped soybean [Glycine max (L.) Merr.], and maize (Zea mays L.) in rotation and to determine if soil structural changes occurring in tilled soils are independent of changes in other soil properties. A field experiment was established in 1992 on a Huntington silt loam soil (Fluventic Hapludoll) at the University of Kentucky Research and Education Center in Princeton (KY) under a NT crop sequence with two seedbed preparation methods for winter wheat, (a) NT or (b) chisel plus disk tillage (Till). In fall 2000, similar soil chemical properties were observed between disrupted and continuous NT systems over the 0- to 20-cm layer. The geometric mean diameter of dry fragments and the soil water content retained between 0.0003 and 0.03 MPa water potential was greater in NT soils than in soils tilled for winter wheat. Tillage for winter wheat enhanced winter wheat yields (4.2% increase), mostly under low-yielding conditions, but it resulted in a reduction of subsequent summer crop yields (i.e., 3.7% for soybean and 7.0% for maize). The yields obtained in our study translate to an economic benefit for the continuous NT system. Net returns per hectare were estimated to be $73 higher for the winter wheat/double-crop soybean-maize rotation under NT than under Till treatments. The differences in maize yields between NT and tilled treatments were attributed to a better water supply in NT soil due to the maintenance of a larger number of mesopores and a great hydraulic conductivity. In the absence of significant changes in other physicochemical properties, periodic tillage appears to disrupt soil structure, which negatively affects crop productivity.
  • Authors:
    • USDA-ARS
    • Clapp, C. E.
    • Linden, D. R.
    • Allmaras, R. R.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 4
  • Year: 2004
  • Summary: Soil organic carbon (SOC) is sensitive to management of tillage, residue (stover) harvest, and N fertilization in corn (Zea mays L.), but little is known about associated root biomass including rhizodeposition. Natural C isotope abundance ({delta}13C) and total C content, measured in paired plots of stover harvest and return were used to estimate corn-derived SOC (cdSOC) and the contribution of nonharvestable biomass (crown, roots, and rhizodeposits) to the SOC pool. Rhizodeposition was estimated for each treatment in a factorial of three tillage treatments (moldboard, MB; chisel, CH; and no-till, NT), two N fertilizer rates (200 and 0 kg N ha-1), and two corn residue managements. Treatments influenced cdSOC across a wide range (6.8-17.8 Mg C ha-1). Nitrogen fertilization increased stover C by 20%, cdSOC by only 1.9 Mg C ha-1, and increased rhizodeposition by at least 110% compared with that with no N fertilizer. Stover harvest vs. stover return reduced total source carbon (SC) by 20%, cdSOC by 35%, and total SOC. The amount of stover source carbon (SSC) responded to tillage (MB > CH > NT), but tillage affected the amount of cdSOC differently (NT > CH > MB). Total SOC was maintained only by both N fertilization and stover return during the 13-yr period. The ratio of SC in the nonharvestable biomass to SSC ranged from 1.01 to 3.49; a ratio of 0.6 conforms to a root-to-shoot ratio of 0.4 when the root biomass includes 50% rhizodeposits. Tillage controlled the fraction of SC retained as cdSOC (i.e., humified; 0.26 for NT and 0.11 for MB and CH), even though N fertilization, stover harvest, and tillage all significantly influenced SC. Decomposition of labile rhizodeposits was a major component of the nonhumified fraction. Rhizodeposition was as much as three times greater than suggested by laboratory and other controlled studies. To understand and manage the entire C cycle, roots and rhizodeposition must be included in the analysis at the field level.
  • Authors:
    • Lowenberg-DeBoer, J.
    • Bongiovanni, R.
    • Anselin, L.
  • Source: American Journal of Agricultural Economics
  • Volume: 86
  • Issue: 3
  • Year: 2004
  • Summary: The objective of this study is to determine the potential for using spatial econometric analysis of combine yield monitor data to estimate the site-specific crop response functions. The specific case study is for site-specific nitrogen (N) application to corn production in Argentina. Spatial structure of the yield data is modeled with landscape variables, spatially autoregressive error and groupwise heteroskedasticity. Results suggest that N response differs by landscape position, and that site-specific application may be modestly profitable. Profitability depends on the model specification used, with all spatial models consistently indicating profitability, whereas the nonspatial models do not.
  • Authors:
    • Feller, C.
    • Oliver, R.
    • Lesaint, S.
    • Villenave, C.
    • Girardin, C.
    • Blanchart, E.
    • Azontonde, A.
    • Barthès, B.
  • Source: Soil Use and Management
  • Volume: 20
  • Issue: 2
  • Year: 2004
  • Summary: Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12-year experiment on three maize cropping systems under manual tillage: traditional no-input cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass 13C. In T, NPK and M changes in soil carbon at 0±40 cm were ±0.2, +0.2 and +1.3 tC ha±1 yr±1, with residue carbon amounting to 3.5, 6.4 and 10.0 tC ha±1 yr±1, respectively. After 12 years of experimentation, carbon originating from maize in litter-plus-soil (0±40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter-plus-soil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter-plus-soil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied.