• Authors:
    • Hayes, R. M.
    • McClure, M. A.
    • Yin, X. H.
  • Source: Agricultural Sciences
  • Volume: 3
  • Issue: 2
  • Year: 2012
  • Summary: Nitrogen concentration in the ear leaf is a good indicator of corn (Zea mays L.) N nutrition status during late growing season. This study was done to examine the relationship of late-season ear leaf N concentration with early- to mid-season plant height of corn at Milan, TN from 2008 to 2010 using linear, quadratic, square root, logarithmic, and exponential models. Six N rate treatments (0, 62, 123, 185, 247, and 308 kg.N.ha -1) repeated four times were implemented each year in a randomized complete block design under four major cropping systems: corn after corn, corn after soybean [Glycine max (L.) Merr.], corn after cotton [Gossypium hirsutum (L.)], and irrigated corn after soybean. The relationship of ear leaf N concentration determined at the blister growth stage (R 2) with plant height measured at the 6-leaf (V6), 10-leaf (V10), and 12-leaf (V12) growth stages was statistically significant and positive in non-irrigated corn under normal weather conditions. However, the strength of this relationship was weak to moderate with the determination coefficient (R 2) values ranging from 0.21 to 0.51. This relationship was generally improved as the growing season progressed from V6 to V12. Irrigation and abnormal weather seemed to have adverse effects on this relationship. The five regression models performed similarly in the evaluation of this relationship regardless of growth stage, year, and cropping system. Our results suggest that unlike the relationship of corn yield at harvest with plant height measured during early- to mid-season or the relationship of leaf N concentration with plant height when both are measured simultaneously during early- to mid-season, the relationship of late-season ear leaf N concentration with early- to mid-season plant height may not be strong enough to be used to develop algorithms for variable-rate N applications on corn within a field no matter which regression model is used to describe this relationship.
  • Authors:
    • Pruessner, E. G.
    • Stewart, C. E.
    • Follett, R. F.
    • Kimble, J. M.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 5
  • Year: 2012
  • Summary: Soils of the US Great Plains contain enormous stocks of soil organic carbon (SOC) and soil organic nitrogen (SON) that are vulnerable to predicted climate and land use change. Climate change scenarios predict a 2.2 degrees C to 3.6 degrees C (4 degrees F to 6.5 degrees F) increase and more variability in precipitation across most of the United States. This study quantifies management effects (native grassland, Conservation Reserve Program [CRP], and cropped) on SOC and SON stocks across the region and assessed soil variables (soil texture, cation exchange capacity and others) and climatic drivers (precipitation and temperature) to predict future changes in carbon (C) and nitrogen (N) stocks. Across all sites, cropped land had significantly lower C and N stocks in the 0 to 5 cm (0 to 2 in) and 0 to 10 cm (0 to 3.9 in) depths than native sites, while CRP sites were intermediate. Mean annual temperature (MAT), the ratio of mean annual precipitation to potential evapotranspiration (MAP:PET), soil bulk density (BD), and clay content were important covariates for SOC and SON stocks within land use. Soil C and N stocks under all three land uses were strongly negatively related to MAT and positively related to MAP:PET, suggesting that they are equally vulnerable to increased temperature and decreasing water availability Based on these empirical relationships, a 1 degrees C (1.8 degrees F) increase in MAT could cause a loss of 486 Tg SOC (536 million tn) and a loss of 180 kg SON ha(-1) (160 lb SON ac(-1)) from the top 10 cm (3.9 in) of soil over 30 years, but the decrease will be mediated by water availability (MAP:PET). Combined, increased temperature and conversion from CRP to cropland could decrease the existing SOC sink, but improved soil management and increased water availability may help offset these losses in the US Great Plains.
  • Authors:
    • Kratochvil, R. J.
    • Forrestal, P. J.
    • Meisinger, J. J.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: Evaluation of corn ( Zea mays L.) N management and soil residual NO 3-N late in the growing season could provide important management information for subsequent small grain crops and about potential NO 3-N loss. Our objective was to evaluate the ability of several late-season corn measurements, which have been advocated to assess N management, to identify sites with elevated soil residual NO 3-N. These crop-based measurements were collected at three reproductive phases and included normalized difference vegetative index (NDVI) at 10 site-years and green-leaf number and chlorophyll (SPAD) meter readings at six of these sites. The corn stalk nitrate test (CSNT) and postharvest soil residual NO 3-N were measured at all sites. Four levels of N were applied, ranging from N deficient (0 or 67 kg N ha -1) to excessive (269 kg N ha -1). The CSNT was positively ( p<0.001) correlated with residual NO 3-N, although residual NO 3-N was not always low at CSNT values <2.0 g NO 3-N kg -1, where drought reduced production. Drought stress was a major factor influencing excess N supply and residual soil NO 3-N. Canopy measurement values at growth stages R3-R4, including NDVI, which can be measured remotely, were effective indicators of drought stress. Across sites, relative canopy readings best predicted relative grain yield when collected at R3-R4, underscoring the importance of reference strips. Use of remotely measured NDVI would allow policymakers to identify drought sites in the late summer and target them for cover crop planting, thus reducing potential winter NO 3-N losses in humid regions.
  • Authors:
    • Eigenberg, R. A.
    • Hubbard, R. K.
    • Powell, J. M.
    • Torbert, H. A.
    • Woodbury, B. L.
    • Albrecht, S. L.
    • Sistani, K. R.
    • Wienhold, B. J.
    • He, Z. Q.
    • Larkin, R. P.
    • Griffin, T. S.
    • Vandemark, G.
    • Honeycutt, C. W.
    • Fortuna, A. M.
    • Wright, R. J.
    • Alldredge, J. R.
    • Harsh, J. B.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 1
  • Year: 2012
  • Summary: Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy ( Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha -1. Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.
  • Authors:
    • Verfaillie, J.
    • Deverel, S. J.
    • Sonnentag, O.
    • Detto, M.
    • Hatala, J. A.
    • Baldocchi, D. D.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 150
  • Year: 2012
  • Summary: The Sacramento-San Joaquin Δ in California was drained and converted to agriculture more than a century ago, and since then has experienced extreme rates of soil subsidence from peat oxidation. To reverse subsidence and capture carbon there is increasing interest in converting drained agricultural land-use types to flooded conditions. Rice agriculture is proposed as a flooded land-use type with CO 2 sequestration potential for this region. We conducted two years of simultaneous eddy covariance measurements at a conventional drained and grazed degraded peatland and a newly converted rice paddy to evaluate the impact of drained to flooded land-use change on CO 2, CH 4, and evaporation fluxes. We found that the grazed degraded peatland emitted 175-299 g-C m -2 yr -1 as CO 2 and 3.3 g-C m -2 yr -1 as CH 4, while the rice paddy sequestered 84-283 g-C m -2 yr -1 of CO 2 from the atmosphere and released 2.5-6.6 g-C m -2 yr -1 as CH 4. The rice paddy evaporated 45-95% more water than the grazed degraded peatland. Annual photosynthesis was similar between sites, but flooding at the rice paddy inhibited ecosystem respiration, making it a net CO 2 sink. The rice paddy had reduced rates of soil subsidence due to oxidation compared with the drained peatland, but did not completely reverse subsidence.
  • Authors:
    • Kurz, W. A.
    • Birdsey, R. A.
    • McConkey, B. G.
    • Dejong, B.
    • Heath, L. S.
    • West, T. O.
    • Wei, Y. X.
    • McGuire, A. D.
    • Stinson, G.
    • Turner, D. P.
    • Hayes, D. J.
    • Jacobson, A. R.
    • Huntzinger, D. N.
    • Pan, Y. D.
    • Post, W. M.
    • Cook, R. B.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 4
  • Year: 2012
  • Summary: We develop an approach for estimating net ecosystem exchange (NEE) using inventory-based information over North America (NA) for a recent 7-year period (ca. 2000-2006). The approach notably retains information on the spatial distribution of NEE, or the vertical exchange between land and atmosphere of all non-fossil fuel sources and sinks of CO 2, while accounting for lateral transfers of forest and crop products as well as their eventual emissions. The total NEE estimate of a -327252 TgC yr -1 sink for NA was driven primarily by CO 2 uptake in the Forest Lands sector (-248 TgC yr -1), largely in the Northwest and Southeast regions of the US, and in the Crop Lands sector (-297 TgC yr -1), predominantly in the Midwest US states. These sinks are counteracted by the carbon source estimated for the Other Lands sector (+218 TgC yr -1), where much of the forest and crop products are assumed to be returned to the atmosphere (through livestock and human consumption). The ecosystems of Mexico are estimated to be a small net source (+18 TgC yr -1) due to land use change between 1993 and 2002. We compare these inventory-based estimates with results from a suite of terrestrial biosphere and atmospheric inversion models, where the mean continental-scale NEE estimate for each ensemble is -511 TgC yr -1 and -931 TgC yr -1, respectively. In the modeling approaches, all sectors, including Other Lands, were generally estimated to be a carbon sink, driven in part by assumed CO 2 fertilization and/or lack of consideration of carbon sources from disturbances and product emissions. Additional fluxes not measured by the inventories, although highly uncertain, could add an additional -239 TgC yr -1 to the inventory-based NA sink estimate, thus suggesting some convergence with the modeling approaches.
  • Authors:
    • Stewart, J. S.
    • Menge, B. A.
    • Gouhier, T. C.
    • Iles, A. C.
    • Haupt, A. J.
    • Lynch, M. C.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 2
  • Year: 2012
  • Summary: Eastern boundary current systems are among the most productive and lucrative ecosystems on Earth because they benefit from upwelling currents. Upwelling currents subsidize the base of the coastal food web by bringing deep, cold and nutrient-rich water to the surface. As upwelling is driven by large-scale atmospheric patterns, global climate change has the potential to affect a wide range of significant ecological processes through changes in water chemistry, water temperature, and the transport processes that influence species dispersal and recruitment. We examined long-term trends in the frequency, duration, and strength of continuous upwelling events for the Oregon and California regions of the California Current System in the eastern Pacific Ocean. We then associated event-scale upwelling with up to 21 years of barnacle and mussel recruitment, and water temperature data measured at rocky intertidal field sites along the Oregon coast. Our analyses suggest that upwelling events are changing in ways that are consistent with climate change predictions: upwelling events are becoming less frequent, stronger, and longer in duration. In addition, upwelling events have a quasi-instantaneous and cumulative effect on rocky intertidal water temperatures, with longer events leading to colder temperatures. Longer, more persistent upwelling events were negatively associated with barnacle recruitment but positively associated with mussel recruitment. However, since barnacles facilitate mussel recruitment by providing attachment sites, increased upwelling persistence could have indirect negative impacts on mussel populations. Overall, our results indicate that changes in coastal upwelling that are consistent with climate change predictions are altering the tempo and the mode of environmental forcing in near-shore ecosystems, with potentially severe and discontinuous ramifications for ecosystem structure and functioning.
  • Authors:
    • Busscher, W. J.
    • Novak, J. M.
    • Ippolito, J. A.
    • Ahmedna, M.
    • Rehrah, D.
    • Watts, D. W.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 4
  • Year: 2012
  • Summary: The use of biochar has received growing attention because of its ability to improve the physicochemical properties of highly weathered Ultisols and Oxisols, yet very little research has focused on its effects in Aridisols. We investigated the effect of low or high temperature (250 or 500°C) pyrolyzed switchgrass ( Panicum virgatum L.) biochar on two Aridisols. In a pot study, biochar was added at 2% w/w to a Declo loam (Xeric Haplocalcids) or to a Warden very fine sandy loam (Xeric Haplocambids) and incubated at 15% moisture content (by weight) for 127 d; a control (no biochar) was also included. Soils were leached with 1.2 to 1.3 pore volumes of deionized H 2O on Days 34, 62, 92, and 127, and cumulative leachate Ca, K, Mg, Na, P, Cu, Fe, Mn, Ni, Zn, NO 3-N, NO 2-N, and NH 4-N concentrations were quantified. On termination of the incubation, soils were destructively sampled for extractable Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Zn, NO 3-N, and NH 4-N, total C, inorganic C, organic C, and pH. Compared with 250°C, the 500°C pyrolysis temperature resulted in greater biochar surface area, elevated pH, higher ash content, and minimal total surface charge. For both soils, leachate Ca and Mg decreased with the 250°C switchgrass biochar, likely due to binding by biochar's functional group sites. Both biochars caused an increase in leachate K, whereas the 500°C biochar increased leachate P. Both biochars reduced leachate NO 3-N concentrations compared with the control; however, the 250°C biochar reduced NO 3-N concentrations to the greatest extent. Easily degradable C, associated with the 250°C biochar's structural make-up, likely stimulated microbial growth, which caused NO 3-N immobilization. Soil-extractable K, P, and NO 3-N followed a pattern similar to the leachate observations. Total soil C content increases were linked to an increase in organic C from the biochars. Cumulative results suggest that the use of switchgrass biochar prepared at 250°C could improve environmental quality in calcareous soil systems by reducing nutrient leaching potential.
  • Authors:
    • Garten, C. T.,Jr.
    • Keller, J. K.
    • Iversen, C. M.
    • Norby, R. J.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 5
  • Year: 2012
  • Summary: Increased partitioning of carbon (C) to fine roots under elevated [CO 2], especially deep in the soil profile, could alter soil C and nitrogen (N) cycling in forests. After more than 11 years of free-air CO 2 enrichment in a Liquidambar styraciflua L. (sweetgum) plantation in Oak Ridge, TN, USA, greater inputs of fine roots resulted in the incorporation of new C (i.e., C with a depleted delta 13C) into root-derived particulate organic matter (POM) pools to 90-cm depth. Even though production in the sweetgum stand was limited by soil N availability, soil C and N contents were greater throughout the soil profile under elevated [CO 2] at the conclusion of the experiment. Greater C inputs from fine-root detritus under elevated [CO 2] did not result in increased net N immobilization or C mineralization rates in long-term laboratory incubations, possibly because microbial biomass was lower in the CO 2-enriched plots. Furthermore, the delta 13CO 2 of the C mineralized from the incubated soil closely tracked the delta 13C of the labile POM pool in the elevated [CO 2] treatment, especially in shallower soil, and did not indicate significant priming of the decomposition of pre-experiment soil organic matter (SOM). Although potential C mineralization rates were positively and linearly related to total SOM C content in the top 30 cm of soil, this relationship did not hold in deeper soil. Taken together with an increased mean residence time of C in deeper soil pools, these findings indicate that C inputs from relatively deep roots under elevated [CO 2] may increase the potential for long-term soil C storage. However, C in deeper soil is likely to take many years to accrue to a significant fraction of total soil C given relatively smaller root inputs at depth. Expanded representation of biogeochemical cycling throughout the soil profile may improve model projections of future forest responses to rising atmospheric [CO 2].
  • Authors:
    • Alves, B. J. R.
    • Follett, R. F.
    • Halvorson, A. D.
    • Jantalia, C. P.
    • Polidoro, J. C.
    • Urquiaga, S.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 6
  • Year: 2012
  • Summary: Ammonia (NH 3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH 3-N loss from four urea-based N sources (urea, urea-ammonium nitrate [UAN], SuperU, and ESN [polymer-coated urea]) surface band applied at a rate of 200 kg N ha -1 to irrigated, strip-till corn production systems for 2 yr using semi-static chambers (semi-open and open) to measure NH 3-N loss. The efficiency of the semi-static chambers in estimating NH 3-N loss under field conditions was determined using 15N labeled urea applied at rates of 50, 100, and 200 kg N ha -1. Both chamber types had similar NH 3-N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH 3-N volatilization from surface-applied N fertilizers to a range of 0.1 to 4.0% of total N applied. SuperU, which contains a urease inhibitor, had the lowest level of NH 3-N loss when compared to the other N sources. Analyzed across years, estimated NH 3-N losses for the N sources were in the order: ESN=UAN > urea > SuperU. Both years the results showed that measurement time may need to be increased to evaluate NH 3-N volatilization from polymer-coated urea N sources such as ESN. The open-chamber method was a viable, low cost method for estimating NH 3-N loss from small field plot N studies.