• Authors:
    • Suyker, A. E.
    • Verma, S. B.
  • Source: Agricultural and Forest Meteorology
  • Volume: 148
  • Issue: 3
  • Year: 2008
  • Summary: In this paper, we present results from 4 years (May 2001-May 2005) of water and energy flux measurements made in a no-till, irrigated maize-soybean rotation system in eastern Nebraska, USA. The peak green leaf area index (LAI) reached 6.0 and 5.5 in maize (2001 and 2003, respectively) and 5.7 and 4.4 in soybean (2002 and 2004, respectively). The dependence of evapotranspiration (ET) on leaf area was consistent with previous studies. There was a nearly linear relationship between the daily ET/ET o (where ET o is the reference evapotranspiration over a grass reference crop) and LAI until a threshold LAI (between 3 and 4). Above this threshold LAI, the ET/ET o was virtually independent of LAI. The cumulative growing season (planting to harvest) evapotranspiration was 544 and 578 mm for maize, and 474 and 430 mm for soybean. The interannual variability in the growing season ET totals correlated very well with the number of days when the LAI was greater than 3. The non-growing season period (harvest to subsequent planting) contributed between 20 and 25% of the annual ET totals for both crops. The maximum canopy surface conductance ( Gsmax) was 29 mm s -1 for maize in both years, 41 mm s -1 for soybean in 2002 (peak LAI=5.7) and 36 mm s -1 for soybean in 2004 (peak LAI=4.4). The variability in Gsmax was largely explained by the leaf nitrogen concentration, consistent with the literature.
  • Authors:
    • Egbert, S. L.
    • Wardlow, B. D.
  • Source: Remote Sensing of Environment
  • Volume: 112
  • Issue: 3
  • Year: 2008
  • Summary: Improved and up-to-date land use/land cover (LULC) data sets that classify specific crop types and associated land use practices are needed over intensively cropped regions such as the U.S. Central Great Plains, to support science and policy applications focused on understanding the role and response of the agricultural sector to environmental change issues. The Moderate Resolution Imaging Spectroradiometer (MODIS) holds considerable promise for detailed, large-area crop-related LULC mapping in this region given its global coverage, unique combination of spatial, spectral, and temporal resolutions, and the cost-free status of its data. The objective of this research was to evaluate the applicability of time-series MODIS 250 m normalized difference vegetation index (NDVI) data for large-area crop-related LULC mapping over the U.S. Central Great Plains. A hierarchical crop mapping protocol, which applied a decision tree classifier to multi-temporal NDVI data collected over the growing season, was tested for the state of Kansas. The hierarchical classification approach produced a series of four crop-related LULC maps that progressively classified: (1) crop/non-crop, (2) general crop types (alfalfa, summer crops, winter wheat, and fallow), (3) specific summer crop types (corn, sorghum, and soybeans), and (4) irrigated/non-irrigated crops. A series of quantitative and qualitative assessments were made at the state and sub-state levels to evaluate the overall map quality and highlight areas of misclassification for each map. The series of MODIS NDVI-derived crop maps generally had classification accuracies greater than 80%. Overall accuracies ranged from 94% for the general crop map to 84% for the summer crop map. The state-level crop patterns classified in the maps were consistent with the general cropping patterns across Kansas. The classified crop areas were usually within 1-5% of the USDA reported crop area for most classes. Sub-state comparisons found the areal discrepancies for most classes to be relatively minor throughout the state. In eastern Kansas, some small cropland areas could not be resolved at MODIS' 250 m resolution and led to an underclassification of cropland in the crop/non-crop map, which was propagated to the subsequent crop classifications. Notable regional areal differences in crop area were also found for a few selected crop classes and locations that were related to climate factors (i.e., omission of marginal, dryland cropped areas and the underclassification of irrigated crops in western Kansas), localized precipitation patterns (overclassification of irrigated crops in northeast Kansas), and specific cropping practices (double cropping in southeast Kansas).
  • Authors:
    • Pridham, J. C.
    • Entz, M. H.
  • Source: Agronomy Journal
  • Volume: 100
  • Issue: 5
  • Year: 2008
  • Summary: The success of organic wheat ( Triticum aestivum L.) production can be severely inhibited by weed and disease pressures. This study sought to determine the effectiveness of wheat intercrop mixtures in suppressing weeds and diseases and increasing grain yield and net return. Field experiments were conducted on organically managed land in 2004 and 2005 and three representative intercrop systems were tested: wheat with other cereals [oats ( Avena sativa L.), barley ( Hordeum vulgare L.), and spring rye ( Secale cereale L.)]; wheat and noncereal seed crops (flax [ Linum usitatissimum L.], field pea [ Pisum sativum L.], oriental mustard [ Brassica juncea L.]); and wheat and cover crops (red clover [ Trifolium pratense L.], hairy vetch [ Vicia villosa L.], annual ryegrass [ Lolium multiflorum Lam.]). The cereal intercrop systems provided no consistent yield benefit over wheat monocultures. Results from noncereal-wheat intercrops were variable. Wheat-flax reduced the wheat crop to unacceptable levels but was capable of reducing wheat flag leaf disease levels. Wheat-field pea resulted in the lowest disease levels, yet had inconsistent yields, and more weeds than wheat monoculture. Wheat-mustard did not reduce weeds or diseases, but it was capable of high grain yields and net returns, though usually hampered by flea beetle ( Phyllotreta cruciferae) attack. The effect of cover crops on wheat was affected by environment. Wheat-red clover and wheat-hairy vetch did demonstrate the ability to maintain high wheat grain yield in certain site-years. In conclusion, wheat intercrop mixtures provided little short-term benefit over monoculture wheat in this study.
  • Authors:
    • Shipitalo, M.
    • Bonta, J.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 6
  • Year: 2008
  • Summary: Paper mills generate large amounts of solid waste consisting of fibrous cellulose, clay, and lime. Paper mill sludge (PMS) can improve reclamation of surface-coal mines where low pH and organic-carbon levels in the spoil cover material can inhibit revegetation. When applied at high rates, however, PMS may adversely impact the quality of surface runoff. Therefore, we applied PMS at 0, 224, and 672 dry Mg ha -1 to 22.1*4.6-m plots at a recently mined site and monitored runoff for a total of 13 mo. The zero-rate plots served as controls and received standard reclamation consisting of mulching with hay and fertilization at planting. Compared to the control plots, PMS reduced runoff fourfold to sixfold and decreased erosion from 47 Mg ha -1 to
  • Authors:
    • Krupinsky, J. M.
    • Tanaka, D. L.
    • Merrill, S. D.
    • van Donk, S. J.
  • Source: Transactions of the ASABE
  • Volume: 51
  • Issue: 5
  • Year: 2008
  • Summary: Residue cover is very important for controlling soil erosion by water and wind. Thus, the wind erosion prediction system (WEPS) includes a model for the decomposition of crop residue. It simulates the fall rate of standing residue and the decomposition of standing and flat residue as a function of temperature and moisture. It also calculates residue cover from flat residue mass. Most of the data used to develop and parameterize this model have been collected in the southern USA. We compared WEPS-simulated residue cover with that measured in south-central North Dakota for 50 two-year cropping sequences from nine crops species that were grown using no-till management. Measured data included residue mass at the time of harvest and residue cover just after seeding the next spring.
  • Authors:
    • Wei, C. F.
    • Tang, X. H.
    • Wang, Z. F.
    • Luo, Y. J.
    • Gao, M.
  • Source: Pedosphere
  • Volume: 18
  • Issue: 5
  • Year: 2008
  • Summary: The effect of different tillage systems on the size distribution of aggregates and organic carbon distribution and storage in different size aggregates in a Hydragric Anthrosol were studied in a long-term experiment in Chongqing, China. The experiment included three tillage treatments: conventional tillage with rotation of rice and winter fallow (CT-r) system, no-till and ridge culture with rotation of rice and rape (RT-rr) system, and conventional tillage with rotation of rice and rape (CT-rr) system. The results showed that the aggregates 0.02-0.25 mm in diameter accounted for the largest portion in each soil layer under all treatments. Compared with the CT-r system, in the 0-10 cm layer, the amount of aggregates >0.02 mm was larger under the RT-rr system, but smaller under the CT-rr system. In the 0-20 cm layer, the organic carbon content of all fractions of aggregates was the highest under the RT-rr system and lowest under the CT-rr system. The total organic carbon content showed a positive linear relationship with the amount of aggregates with diameter ranging from 0.25 to 2 mm. The storage of organic carbon in all fractions of aggregates under the RT-rr system was higher than that under the CT-r system in the 0-20 cm layer, but in the 0-60 cm soil layer, there was no distinct difference. Under the CT-rr system, the storage of organic carbon in all fractions of aggregates was lower than that under the CT-r system; most of the newly lost organic carbon was from the aggregates 0.002-0.02 and 0.02-0.25 mm in diameter.
  • Authors:
    • Nelson, R. G.
    • Larson, J. A.
    • De La Torre Ugarte, D. G.
    • Marland, g.
    • Tyler, D. D.
    • Hellwinckel, C. M.
    • Wilson, B. S.
    • Brandt, C. C.
    • West, T. O.
  • Source: Soil Science Society of America Journal
  • Volume: 72
  • Issue: 2
  • Year: 2008
  • Summary: To manage lands locally for C sequestration and for emissions reductions, it is useful to have a system that can monitor and predict changes in soil C and greenhouse gas emissions with high spatial resolution. We are developing a C accounting framework that can estimate C dynamics and net emissions associated with changes in land management. One component of this framework integrates field measurements, inventory data, and remote sensing products to estimate changes in soil C and to estimate where these changes are likely to occur at a subcounty (30- by 30-m) resolution. We applied this framework component to a midwestern region of the United States that consists of 679 counties approximately centered around Iowa. We estimated the 1990 baseline soil C to a maximum depth of 3 m for this region to be 4117 Tg. Cumulative soil C accumulation of 70.3 Tg was estimated for this region between 1991 and 2000, of which 33.8 Tg is due to changes in tillage intensity. Without accounting for soil C loss following changes to more intensive tillage practices, our estimate increases to 45.0 Tg C. This difference indicates that on-site permanence of soil C associated with a change to less intensive tillage practices is approximately 75% if no additional economic incentives are provided for soil C sequestration practices. This C accounting framework offers a method to integrate inventory and remote sensing data on an annual basis and to transparently account for alternating annual trends in land management and associated C stocks and fluxes.
  • Authors:
    • Kay, B. D.
    • Wander, M. M.
    • Drury, C. F.
    • Yang, X. M.
  • Source: Pedosphere
  • Volume: 18
  • Issue: 4
  • Year: 2008
  • Summary: Three long-term field trials in humid regions of Canada and the USA were used to evaluate the influence of soil depth and sample numbers on soil organic carbon (SOC) sequestration in no-tillage (NT) and moldboard plow (MP) corn (Zea mays L.) and soybean (Glycine max L.) production systems. The first trial was conducted on a Maryhill silt loam (Typic Hapludalf) at Elora, Ontario, Canada, the second on a Brookston clay loam (Typic Argiaquoll) at Woodslee, Ontario, Canada, and the third on a Thorp silt loam (Argiaquic Argialboll) at Urbana, Illinois, USA. No-tillage led to significantly higher SOC concentrations in the top 5 cm compared to MP at all 3 sites. However, NT resulted in significantly lower SOC in sub-surface soils as compared to MP at Woodslee (10-20 cm, P = 0.01) and Urbana (20-30 cm, P < 0.10). No-tillage had significantly more SOC storage than MP at the Elora site (3.3 Mg C ha(-1)) and at the Woodslee site (6.2 Mg C ha(-1)) on an equivalent mass basis (1350 Mg ha(-1) soil equivalent mass). Similarly, NT had greater SOC storage than NIP at the Urbana site (2.7 Mg C ha(-1)) on an equivalent mass basis of 675 Mg ha-1 soil. However, these differences disappeared when the entire plow layer was evaluated for both the Woodslee and Urbana sites as a result of the higher SOC concentrations in NIP than in NT at depth. Using the minimum detectable difference technique, we observed that up to 1500 soil sample per tillage treatment comparison will have to be collected and analyzed for the Elora and Woodslee sites and over 40 soil samples per tillage treatment comparison for the Urbana to statistically separate significant differences in the SOC contents of sub-plow depth soils. Therefore, it is impracticable, and at the least prohibitively expensive, to detect tillage-induced differences in soil C beyond the plow layer in various soils.
  • Authors:
    • Parkin, T. B.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 4
  • Year: 2008
  • Summary: It is generally recognized that soil N2O emissions can exhibit pronounced day-to-day variations; however, measurements of soil N2O flux with soil chambers typically are done only at discrete points in time. This study evaluated the impact of sampling frequency on the precision of cumulative N2O flux estimates calculated from field measurements. Automated chambers were deployed in a corn/soybean field and used to measure soil N2O fluxes every 6 h from 25 Feb. 2006 through 11 Oct. 2006. The chambers were located in two positions relative to the fertilizer bands--directly over a band or between fertilizer bands. Sampling frequency effects on cumulative N2O-N flux estimation were assessed using a jackknife technique where populations of N2O fluxes were constructed from the average daily fluxes measured in each chamber. These test populations were generated by selecting measured flux values at regular time intervals ranging from 1 to 21 d. It was observed that as sampling interval increased from 7 to 21 d, variances associated with cumulative flux estimates increased. At relatively frequent sampling intensities (i.e., once every 3 d) N2O-N flux estimates were within {+/-}10% of the expected value at both sampling positions. As the time interval between sampling was increased, the deviation in estimated cumulative N2O flux increased, such that sampling once every 21 d yielded estimates within +60% and -40% of the actual cumulative N2O flux. The variance of potential fluxes associated with the between-band positions was less than the over-band position, indicating that the underlying temporal variability impacts the efficacy of a given sampling protocol.
  • Authors:
    • Patton, J.
    • Zhang, Q.
    • Vanni, M. J.
    • Renwick, W. H.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 5
  • Year: 2008