• Authors:
    • Reinsch, T. G.
    • Mays, M. D.
    • Walsh, M. G.
    • Shepherd, K. D.
    • Brown, D. J.
  • Source: Geoderma
  • Volume: 132
  • Issue: 3-4
  • Year: 2006
  • Summary: There has been growing interest in the use of diffuse infrared reflectance as a quick, inexpensive tool for soil characterization. In studies reported to date, calibration and validation samples have been collected at either a local or regional scale. For this study, we selected 3768 samples from all 50 U.S. states and two tropical territories and an additional 416 samples from 36 different countries in Africa (125), Asia (104), the Americas (75) and Europe (112). The samples were selected from the National Soil Survey Center archives in Lincoln, NE, USA, with only one sample per pedon and a weighted random sampling to maximize compositional diversity. Applying visible and near-infrared (VNIR) diffuse reflectance spectroscopy (DRS) to air-dry soil (<2 mm) with auxiliary predictors including sand content or pH, we obtained validation root mean squared deviation (RMSD) estimates of 54 g kg-1 for clay, 7.9 g kg-1 for soil organic C (SOC), 5.6 g kg-1 for inorganic C (IC), 8.9 g kg-1 for dithionate-citrate extractable Fe (FEd), and 5.5 cmolc kg-1 for cation exchange capacity (CEC) with NH4 at pH=7. For all of these properties, boosted regression trees (BRT) outperformed PLS regression, suggesting that this might be a preferred method for VNIR-DRS soil characterization. Using BRT, we were also able to predict ordinal clay mineralogy levels for montmorillonite and kaolinite, with 88% and 96%, respectively, falling within one ordinal unit of reference X-ray diffraction (XRD) values (0-5 on ordinal scale). Given the amount of information obtained in this study with ~4x103 samples, we anticipate that calibrations sufficient for many applications might be obtained with large but obtainable soil-spectral libraries (perhaps 104-105samples). The use of auxiliary predictors (potentially from complementary sensors), supplemental local calibration samples and theoretical spectroscopy all have the potential to improve predictions. Our findings suggest that VNIR soil characterization has the potential to replace or augment standard soil characterization techniques where rapid and inexpensive analysis is required.
  • Authors:
    • Al-Kaisi, M.
  • Source: Integrated Crop Management
  • Volume: IC-496
  • Issue: 11
  • Year: 2006
  • Authors:
    • Hunt, P. G.
    • Novak, J. M.
    • Frederick, J. R.
    • Bauer, P. J.
  • Source: Soil & Tillage Research
  • Volume: 90
  • Issue: 1-2
  • Year: 2006
  • Summary: Tillage affects the ability of coarse-textured soils of the southeastern USA to sequester C. Our objectives were to compare tillage methods for soil CO2 flux, and determine if chemical or physical properties after 25 years of conventional or conservation tillage correlated with flux rates. Data were collected for several weeks during June and July in 2003, October and November in 2003, and April to July in 2004 from a tillage study established in 1978 on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults). Conventional tillage consisted of disking to a depth of approximately 15 cm followed by smoothing with an S-tined harrow equipped with rolling baskets. Conservation tillage consisted of direct seeding into surface residues. Flux rates in conservation tillage averaged 0.84 g CO2 m-2 h-1 in Summer 2003, 0.36 g CO2 m-2 h-1 in Fall 2003, 0.46 g CO2 m-2 h-1 in Spring 2004, and 0.86 g CO2 m-2 h-1 in Summer 2004. Flux rates from conventional tillage were greater for most measurement times. Conversely, water content of the surface soil layer (6.5 cm) was almost always higher with conservation tillage. Soil CO2 flux was highly correlated with soil water content only in conventional tillage. In conservation tillage, no significant correlations occurred between soil CO2 flux and soil N, C, C:N ratio, pH, bulk density, sand fraction, or clay fraction of the surface 7.5 cm. In conventional tillage, sand fraction was positively correlated, while bulk density and clay fraction were negatively correlated with soil CO2 flux rate, but only when the soil was moist. Long-term conservation tillage management resulted in more uniform within- and across-season soil CO2 flux rates that were less affected by precipitation events.
  • Authors:
    • Lucier, A.
    • Pregitzer, K.
    • Birdsey, R.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 4
  • Year: 2006
  • Summary: This paper reviews the effects of past forest management on carbon stocks in the United States, and the challenges for managing forest carbon resources in the 21st century. Forests in the United States were in approximate carbon balance with the atmosphere from 1600-1800. Utilization and land clearing caused a large pulse of forest carbon emissions during the 19th century, followed by regrowth and net forest carbon sequestration in the 20th century. Recent data and knowledge of the general behavior of forests after disturbance suggest that the rate of forest carbon sequestration is declining. A goal of an additional 100 to 200 Tg C/yr of forest carbon sequestration is achievable, but would require investment in inventory and monitoring, development of technology and practices, and assistance for land managers.
  • Authors:
    • Hons, F.
    • Dou, F.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 6
  • Year: 2006
  • Summary: Management practices that alter plant residue production and distribution influence SOC (soil organic carbon) dynamics. The objectives of this study were to investigate the impacts of tillage, cropping system, and N fertilizer application on SOC and soil N pools through physical fractionation of a central Texas soil after 20 years. Nitrogen fertilizer application and no-tillage (NT) significantly increased wheat ( Triticum aestivum) straw yield. Compared with conventional tillage (CT), SOC under NT in surface (0-5 cm) samples was 38, 69, and 68% greater for continuous wheat (CW), wheat-soyabean ( Glycine max)-sorghum ( Sorghum bicolor) rotation (SWS), and double-cropped wheat-soyabean (WS), respectively. The greatest SOC was observed in WS under NT with N fertilizer application, and the lowest occurred in CW under CT without N. Increased cropping intensity increased SOC compared with monoculture. Nitrogen fertilizer application only significantly increased SOC sequestration under NT. No-tillage increased SOC concentration in all physical size fractions compared with CT. Increased cropping intensity and N fertilizer application significantly increased SOC sequestration in most size fractions only under NT. Intraparticulate organic matter C (IPOM-C) was proportionally more affected by tillage than total SOC, indicating that this fraction was more sensitive to management. Carbon concentrations in all size fractions were significantly correlated with each other as well as SOC. Our results indicated that NT associated with enhanced cropping intensity and N fertilizer application sequestered greater SOC and soil total N.
  • Authors:
    • Gallagher, L.
    • Armentrout, D.
    • Kratochvil, R.
    • Sardanelli, S.
    • Everts, K.
  • Source: Plant Disease
  • Volume: 90
  • Issue: 4
  • Year: 2006
  • Summary: Experiments using soil-incorporated cover crops and amendments of poultry litter (PL) and PL compost to suppress root-knot (RKN) and root-lesion nematodes were conducted in response to increasing nematode populations in Maryland's potato production areas. Identical experiments were established in microplots infested with Meloidogyne incognita or Pratylenchus penetrans. Treatments consisted of 12 3-year rotational sequences comprising potato (year 1) and cucumber (year 2) followed by a moderately RKN-resistant or susceptible soyabean cultivar, castor bean, grain sorghum, or sorghum sudangrass; PL or PL compost were amended to some of the RKN-susceptible soyabean and sorghum sudangrass plots. In the third year of the rotation, potato followed by soyabean was planted in all 12 treatments. The RKN-resistant soyabean, castor bean, sorghum sudangrass, and fallow or tillage decreased the populations of M. incognita compared with microplots where RKN-susceptible soyabean had been grown. However, RKN populations quickly recovered. Root-lesion nematode was reduced in the spring of 2001 following application of high rates of PL and PL compost in 2000. In the fall of 2001, sorghum sudangrass alone or in combination with PL or PL compost, grain sorghum, or fallow or tillage reduced root-lesion nematodes compared with either soyabean cultivar. No treatment affected root-lesion nematode the following year. The use of cover crops and PL compost is an effective method to reduce nematode populations only if successively incorporated into rotational cropping sequences.
  • Authors:
    • Sweeney, D.
    • Kilgore, G.
    • Whitney, D.
    • Schwab, G.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 3
  • Year: 2006
  • Summary: Reduced- and no-tillage seedbed preparation methods coupled with broadcast P applications lead to an accumulation of available P in the surface 0- to 5-cm soil layer and a depletion of available P deeper in the profile. A 3-yr study determined the effects of tillage and fertilizer P management on P uptake and grain yield for P-stratified soils. Tillage practices were moldboard plow (once at the start of the study followed by reduced tillage), reduced tillage (disk followed by field cultivation), and no-tillage. Four P management methods were imposed: (i) no P; (ii) 20 kg P ha -1 applied as a surface broadcast; (iii) 20 kg ha -1 applied as a banded starter, 5 cm to the side and 5 cm below the seed; or (iv) 20 kg ha -1 applied in a deep placed band, 13 to 15 cm on 0.7-m centers. The one-time moldboard plowing produced higher early season dry matter yields for corn ( Zea mays L.), wheat ( Triticum aestivum L.), and soybean [ Glycine max (L.) Merr.] compared with the no-tillage system, but tillage effects on final grain yield were inconsistent. Subsurface placement of P generally increased P uptake and grain yield of corn and sorghum [ Sorghum bicolor (L.) Moench], but had little effect on grain yield of soybean. Results indicate that subsurface applications of P fertilizers should be considered if soil test P is highly stratified within the surface 0- to 15-cm layer and the 15-cm composite is medium or below for available P.
  • Authors:
    • Sisson, J.
    • Kirkham, M.
    • Sweeney, D.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 3
  • Year: 2006
  • Summary: Annual row crop production on the naturally occurring claypan soils of the eastern Great Plains may require field operations during somewhat wet conditions and this potentially results in soil compaction by the commonly-used, heavy-weight tractors and equipment. The objectives of this experiment were (i) to determine if compaction reduced yield and growth of soybean [ Glycine max (L.) Merr.] and grain sorghum [ Sorghum bicolor (L.) Moench] grown on a claypan soil (fine, mixed, thermic Mollic Albaqualf) and (ii) to determine the effect of wheel tracks on selected soil properties and whether chisel plow tillage could reduce wheel-track compaction. Compaction treatments were (i) ALL - all of the plot compacted, (ii) WT - wheel-track compaction, (iii) WTC - wheel-track compaction followed by a chisel tillage operation, and (iv) NO - no intentional compaction. In general, it took until the third year of annually repeated compaction in the ALL treatment to reduce crop growth and yields compared with the NO compaction treatment. Even though nearly half of the area was compacted each year in the WT treatment, few measured crop parameters decreased. In wheel tracks, soil penetrometer resistance and bulk density increased and air permeability decreased compared with out of tracks. However, chisel tillage appeared to eliminate the compaction by reducing penetration resistance and bulk density and increasing air permeability to values similar to out of tracks. Thus, compaction of claypan soils may not often be a problem for producers in this area, especially if occasional chisel tillage is included to remove possible compacted zones.
  • Authors:
    • Boyles, S. B.
    • Nelson, R. G.
    • Rice, C. W.
    • Williams, J. R.
    • Pendell, D. L.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 4
  • Year: 2006
  • Summary: This study examined the economic potential of no-tillage versus conventional tillage to sequester soil carbon by using two rates of commercial N fertilizer or beef cattle manure for continuous corn (Zea mays L.) production. Yields, input rates, field operations, and prices from an experiment were used to simulate a distribution of net returns for eight production systems. Carbon release values from direct, embodied, and feedstock energies were estimated for each system, and were used with soil carbon sequestration rates from soil tests to determine the amount of net carbon sequestered by each system. The values of carbon credits that provide an incentive for managers to adopt production systems that sequester carbon at greater rates were derived. No-till systems had greater annual soil carbon gains, net carbon gains, and net returns than conventional tillage systems. Systems that used beef cattle manure had greater soil carbon gains and net carbon gains, but lower net returns, than systems that used commercial N fertilizer. Carbon credits would be needed to encourage the use of manure-fertilized cropping systems.
  • Authors:
    • Tolbert, V. R.
    • Mays, D. A.
    • Nyakatawa, E. Z.
    • Green, T. H.
    • Bingham, L.
  • Source: Biomass and Bioenergy
  • Volume: 30
  • Issue: 7
  • Year: 2006
  • Summary: Renewable energy sources such as bioenergy crops have significant potential as alternatives to fossil fuels. Potential environmental problems arising from soil sediment and nutrient losses in runoff water from bioenergy crops need to be evaluated in order to determine the sustainability and overall feasibility of implementing bioenergy development strategies. This paper discusses runoff, sediment, N, and total P losses from agricultural land (continuous cotton (Gossypium hirsutum L.)) converted to short-rotation sweetgum (Liquidamber styraciflua L.) plantations with and without fescue (Festuca elatior L.) and switchgrass (Panicum virgatum L.) bioenergy crops, compared to corn (Zea mays L.), on a Decatur silt loam soil in north Alabama, from 1995 to 1999. Runoff volume was significantly correlated to total rainfall and sediment yield in each year, but treatment differences were not significant. Sweetgum plots produced the highest mean sediment yield of up to 800 kg ha(-1) compared to corn and switchgrass plots, which averaged less than 200 kg ha(-1). Runoff NH4+ N losses averaged over treatments and years for spring season (3.1 kg ha(-1)) were three to five times those for summer, fall, and winter seasons. Runoff NO3- N for no-till corn and switchgrass plots in spring and summer were five to ten times that for sweetgum plots. No-till corn and switchgrass treatments had 2.4 and 2.1 kg ha(-1) average runoff total P, respectively, which were two to three times that for sweetgum treatments. Growing sweetgum with a fescue cover crop provides significantly lower risk of water pollution from sediment, runoff NH4+ N, and NO3- N. (c) 2006 Published by Elsevier Ltd.