• Authors:
    • Chorover, J.
    • Chadwick, O. A.
    • Sanderman, J.
    • Kramer, M. G.
    • Vitousek, P. M.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 8
  • Year: 2012
  • Summary: Soils retain large quantities of carbon, thereby slowing its return to the atmosphere. The mechanisms governing organic carbon sequestration in soil remain poorly understood, yet are integral to understanding soil-climate feedbacks. We evaluated the biochemistry of dissolved and solid organic carbon in potential source and sink horizons across a chronosequence of volcanic soils in Hawai'i. The soils are derived from similar basaltic parent material on gently sloping volcanic shield surfaces, support the same vegetation assemblage, and yet exhibit strong shifts in soil mineralogy and soil carbon content as a function of volcanic substrate age. Solid-state 13carbon nuclear magnetic resonance spectra indicate that the most persistent mineral-bound carbon is comprised of partially oxidized aromatic compounds with strong chemical resemblance to dissolved organic matter derived from plant litter. A molecular mixing model indicates that protein, lipid, carbohydrate, and char content decreased whereas oxidized lignin and carboxyl/carbonyl content increased with increasing short-range order mineral content. When solutions rich in dissolved organic matter were passed through Bw-horizon mineral cores, aromatic compounds were preferentially sorbed with the greatest retention occurring in horizons containing the greatest amount of short-range ordered minerals. These minerals are reactive metastable nanocrystals that are most common in volcanic soils, but exist in smaller amounts in nearly all major soil classes. Our results indicate that long-term carbon storage in short-range ordered minerals occurs via chemical retention with dissolved aromatic acids derived from plant litter and carried along preferential flow-paths to deeper B horizons.
  • Authors:
    • Kronholm, S.
    • Capel, P.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 6
  • Year: 2012
  • Summary: Carbon is cycled to and from large reservoirs in the atmosphere, on land, and in the ocean. Movement of organic carbon from the terrestrial reservoir to the ocean plays an important role in the global cycling of carbon. The transition from natural to agricultural vegetation can change the storage and movement of organic carbon in and from a watershed. Samples were collected from 13 streams located in hydrologically and agriculturally diverse watersheds, to better understand the variability in the concentrations and loads of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the streams, and the variability in watershed yields. The overall annual median concentrations of DOC and POC were 4.9 (range: 2.1-6.8) and 1.1 (range: 0.4-3.8) mg C L -1, respectively. The mean DOC watershed yield (SE) was 256.8 kg C ha -1 yr -1. The yields of DOC from these agricultural watersheds were not substantially different than the DOC yield from naturally vegetated watersheds in equivalent biomes, but were at the low end of the range for most biomes. Total organic carbon (DOC + POC) annually exported from the agricultural watersheds was found to average 0.03% of the organic carbon that is contained in the labile plant matter and top 1 m of soil in the watershed. Since the total organic carbon exported from agricultural watersheds is a relatively small portion of the sequestered carbon within the watershed, there is the great potential to store additional carbon in plants and soils of the watershed, offsetting some anthropogenic CO 2 emissions.
  • Authors:
    • Ippolito, J. A.
    • Lentz, R. D.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: Carbon-rich biochar derived from the pyrolysis of biomass can sequester atmospheric CO 2, mitigate climate change, and potentially increase crop productivity. However, research is needed to confirm the suitability and sustainability of biochar application to different soils. To an irrigated calcareous soil, we applied stockpiled dairy manure (42 Mg ha -1 dry wt) and hardwood-derived biochar (22.4 Mg ha -1), singly and in combination with manure, along with a control, yielding four treatments. Nitrogen fertilizer was applied when needed (based on preseason soil test N and crop requirements) in all plots and years, with N mineralized from added manure included in this determination. Available soil nutrients (NH 4-N; NO 3-N; Olsen P; and diethylenetriaminepentaacetic acid-extractable K, Mg, Na, Cu, Mn, Zn, and Fe), total C (TC), total N (TN), total organic C (TOC), and pH were evaluated annually, and silage corn nutrient concentration, yield, and uptake were measured over two growing seasons. Biochar treatment resulted in a 1.5-fold increase in available soil Mn and a 1.4-fold increase in TC and TOC, whereas manure produced a 1.2- to 1.7-fold increase in available nutrients (except Fe), compared with controls. In 2009 biochar increased corn silage B concentration but produced no yield increase; in 2010 biochar decreased corn silage TN (33%), S (7%) concentrations, and yield (36%) relative to controls. Manure produced a 1.3-fold increase in corn silage Cu, Mn, S, Mg, K, and TN concentrations and yield compared with the control in 2010. The combined biochar-manure effects were not synergistic except in the case of available soil Mn. In these calcareous soils, biochar did not alter pH or availability of P and cations, as is typically observed for acidic soils. If the second year results are representative, they suggest that biochar applications to calcareous soils may lead to reduced N availability, requiring additional soil N inputs to maintain yield targets.
  • Authors:
    • Kunkel, K.
    • Reddy, K. R.
    • Gao, W.
    • Xu, M.
    • Liang, X. Z.
    • Schmoldt, D. L.
    • Samel, A. N.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Climate variability and changes affect crop yields by causing climatic stresses during various stages of the plant life cycle. A crop growth model must be able to capture the observed relationships between crop yields and climate stresses before its credible use as a prediction tool. This study evaluated the ability of the geographically distributed cotton growth model redeveloped from GOSSYM in simulating U.S. cotton ( Gossypium hirsutum L.) yields and their responses to climate stresses during 1979 to 2005. Driven by realistic climate conditions, the model reproduced long-term mean cotton yields within 10% of observations at the 30-km model resolution across virtually the entire U.S. Cotton Belt and correctly captured the critical dependence of their geographic distributions on regional climate characteristics. Significant correlations between simulated and observed interannual variations were found across 87% of the total harvest grids. The model also faithfully represented the predictive role of July to August air temperature and August to September soil temperature anomalies on interannual cotton yield changes on unirrigated lands, with a similar but weaker predictive signal for irrigated lands as observed. The modeled cotton yields exhibited large, positive correlations with July to August leaf area index. These results indicate the model's ability to depict the regional impact of climate stresses on cotton yields and suggest the potential predictive value of satellite retrievals. They also provide a baseline reference for further model improvements and applications in the future study of climate-cotton interactions.
  • Authors:
    • Liebman, M.
    • Cambardella, C. A.
    • Loecke, T. D.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 93
  • Issue: 1
  • Year: 2012
  • Summary: Understanding how the quality of organic soil amendments affects the synchrony of nitrogen (N) mineralization and plant N uptake is critical for optimal agronomic N management and environmental protection. Composting solid livestock manures prior to soil application has been promoted to increase N synchrony; however, few field tests of this concept have been documented. Two years of replicated field trials were conducted near Boone, Iowa to determine the effect of composted versus fresh solid swine manure (a mixture of crop residue and swine urine and feces produced in hoop structures) on Zea mays (maize) N uptake, in situ soil net N mineralization, and soil inorganic N dynamics. Soil applications of composted manure increased maize N accumulation by 25 % in 2000 and 21 % in 2001 compared with fresh manure applications (application rate of 340 kg N ha(-1)). Despite significant differences in net N mineralization between years, within year seasonal total in situ net N mineralization was similar for composted and fresh manure applications. Partial N budgets indicated that changes in soil N pools (net N mineralization and soil inorganic N) in the surface 20 cm accounted for 67 % of the total plant N accumulation in 2000 but only 16 % in 2001. Inter-annual variation in maize N accumulation could not be attributed to soil N availability. Overall, our results suggest that composting manures prior to soil application has no clear benefit for N synchrony in maize crops. Further work is required to determine the biotic and abiotic factors underlying this result.
  • Authors:
    • Lucas, S. T.
    • Weil, R. R.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 4
  • Year: 2012
  • Summary: Permanganate (KMnO 4) oxidizable C (POXC), an estimate of labile soil C, was evaluated for use as a soil test to identify soils that may respond positively to soil organic matter (SOM) management. We hypothesized that soils lower in POXC would be more likely than soils higher in POXC to show increased crop productivity in response to practices that increase SOM. At four sites, paired fields of the same soil but contrasting management history (cropping vs. sod) were studied. Fields with sod history tested higher in total organic C (TOC) and POXC than fields with cropped history. Permanganate-oxidizable C was strongly related to TOC ( r=0.94). We examined crop stover, grain, and biomass responses to two cover crop treatments within each field: winter rye ( Secale cereale L.) or no rye. After at least 1 yr of treatment, there was a significant negative correlation between relative stover response to rye and POXC ( r=-0.60) at sites with finer textured soils. After at least 2 yr of treatment, crop responses to rye showed a significant negative correlation with POXC and TOC. The strongest relationships to POXC occurred in the stover response at two sites with finer textured soils (Keedysville: r=-0.74; Holtwood: r=-0.84). Permanganate-oxidizable C was comparable to TOC at predicting crop responses to rye. These results suggest that POXC may be a useful test for identifying soils where improved SOM management is likely to improve productivity. The rapid, simple POXC methodology enables on-site or laboratory soil testing.
  • Authors:
    • Maltais-Landry, G.
    • Lobell, D. B.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 2
  • Year: 2012
  • Summary: Evaluating the contribution of weather and its individual components to recent yield trends can be useful to predict the response of crop production to future climate change, but different modeling approaches can yield diverging results. We used two common approaches to evaluate the effect of weather trends on maize ( Zea mays L.) and wheat ( Triticum aestivum L.) production in 12 U.S. counties, and investigate sources of disparities between the two methods. We first used the Decision Support System for Agrotechnology Transfer (DSSAT) model from 1984 to 2008 to evaluate the contribution of weather changes to simulated yield trends in six counties for each crop, each county being located in one of the top 10 U.S. producing states for that crop. A parallel analysis was conducted by multiplying inter-annual weather sensitivity of county-level yields with observed weather trends to estimate weather contributions to empirical yield trends. Weather had a low (maize) to high (wheat) contribution to simulated yield trends, with rain having the largest effect. In contrast, weather and rain had lower contributions to empirical yield trends. Along with evidence from previous studies, this suggests that DSSAT may be too sensitive to water thus inflating the importance of rain. Moreover, the time period used to compute yield trends also had a large effect on the importance of weather and its individual components. Our results highlight the importance of using multiple computation approaches and different time periods when estimating weather-related yield trends.
  • Authors:
    • Zabinski, C. A.
    • Burgess, M. H.
    • Miller, P. R.
    • Jones, C. A.
    • McCauley, A. M.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 92
  • Issue: 3
  • Year: 2012
  • Summary: Crop-fallow systems dominate many semi-arid agricultural regions despite fallow's negative effects on soil and water quality. Annual legumes grown as a fallow-replacement crop, and terminated prior to maturity, can reduce these negative effects without substantially decreasing plant available water for the subsequent crop. Interest in growing legume green manures (LGMs) in synthetically-fertilized systems is increasing in the northern Great Plains of North America, partly due to the N-fixing capabilities of legumes; however, little is known about the effects of planting and termination time on N fixation amounts in the region. A 2-year field study was initiated in southwest Montana to determine the effects of planting time (spring or summer) and termination time (e.g. flower or pod) on the amount of N fixed by field pea (Pisum sativum cv. Arvika) and lentil (Lens culinaris cv. Richlea). Two methods, N-15 natural abundance and N difference, were used to quantify N fixation, with wheat or in-crop weeds as reference plants. In 2009, N fixed by spring-planted lentil was higher by pod than flower (P = 0.03). Termination time did not affect the amount of N fixed by spring-planted pea, despite more biomass by pod than flower. In 2010, both spring-planted crops fixed more N by pod than flower (P < 0.01) and more N was fixed by spring-planted than summer-planted crops (P < 0.01). These results should prove useful to growers interested in selecting management practices that optimize N fixation of LGMs.
  • Authors:
    • Koch, J. B.
    • McCorkle, D. S.
    • Muth, D. J.
    • Bryden, K. M.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 4
  • Year: 2012
  • Summary: This study developed a computational strategy that utilizes data inputs from multiple spatial scales to investigate how variability within individual fields can impact sustainable residue removal for bioenergy production. Sustainable use of agricultural residues for bioenergy production requires consideration of the important role that residues play in limiting soil erosion and maintaining soil C, health, and productivity. Increased availability of subfield-scale data sets such as grain yield data, high-fidelity digital elevation models, and soil characteristic data provides an opportunity to investigate the impacts of subfield-scale variability on sustainable agricultural residue removal. Using three representative fields in Iowa, this study contrasted the results of current NRCS conservation management planning analysis with subfield-scale analysis for rake-and-bale removal of agricultural residue. The results of the comparison show that the field-average assumptions used in NRCS conservation management planning may lead to unsustainable residue removal decisions for significant portions of some fields. This highlights the need for additional research on subfield-scale sustainable agricultural residue removal including the development of real-time variable removal technologies for agricultural residue.
  • Authors:
    • White, J. W.
    • Kimball, B. A.
    • Ottman, M. J.
    • Wall, G. W.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: Possible future increases in atmospheric temperature may threaten wheat (Triticum aestivum L.) production and food security. The purpose of this research is to determine the response of wheat growth to supplemental heating and to seasonal air temperature from an unusually wide range of planting dates. A field study was conducted at Maricopa, AZ, where wheat was planted from September to May over a 2-yr period for a total of 12 planting dates. Supplemental heating was provided for 6 of the 12 planting dates using infrared heaters placed above the crop which increased canopy temperature by 1.3°C during the day and 2.7°C during the night. Grain yield declined 42 g m -2 (6.9%) per 1°C increase in seasonal temperature above 16.3°C. Supplemental heating had no effect on grain yield for plantings in winter (Dec./Jan.) since temperatures were near optimum (14.9°C). However, in spring (Mar.) plantings where temperature (22.2°C) was above optimum, supplemental heating decreased grain yield from 510 to 368 g m -2. Supplemental heating had the greatest effect in the early fall plantings (Sept./Oct.) when temperature was slightly below optimum (13.8°C) and mid-season frost limited the yield of unheated plots to only 3 g m -2 whereas yield of heated plots was 435 g m -2. Thus, possible future increases in temperature may decrease wheat yield for late plantings and shift optimum planting windows to earlier dates in areas of the world similar to the desert southwest of the United States.