Cover crop effect on soil carbon fractions under conservation tillage cotton   总被引：1，自引：0，他引：1  

Upendra M. Sainju  Harry H. Schomberg  Bharat P. Singh  Wayne F. Whitehead  P. Glynn Tillman  Sharon L. Lachnicht-Weyers 《Soil & Tillage Research》2007,96(1-2):205-218

Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on soil C fractions at the 0–150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90 Mg C ha⁻¹ greater in rye + blend than in other cover crops in 2001 but was 1.15–2.24 Mg C ha⁻¹ greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50–150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150 mm was greater with rye + blend than with crimson clover and at 0–50 mm was greater in March than in December 2002. The PCM at 0–50 and 0–150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0–50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24 g CO₂–C ha⁻¹ d⁻¹ but MBC increased by 90–224 g CO₂–C ha⁻¹ d⁻¹ from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1 kg C ha⁻¹ d⁻¹, and PCM decreased by 10 g CO₂–C ha⁻¹ d⁻¹ with rye to 79 g CO₂–C ha⁻¹ d⁻¹ with blend, but MBC increased by 13 g CO₂–C ha⁻¹ d⁻¹ with blend to 120 g CO₂–C ha⁻¹ d⁻¹ with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring.  相似文献   

Formation and stability of foam made with various potato protein preparations   总被引：1，自引：0，他引：1  

van Koningsveld GA  Walstra P  Gruppen H  Wijngaards G  van Boekel MA  Voragen AG 《Journal of agricultural and food chemistry》2002,50(26):7651-7659

In the present study, foam-forming and -stabilizing properties of potato proteins were studied using whipping and sparging tests. The soluble potato proteins are mainly composed of patatin and protease inhibitors. The whipping tests showed that less foam was formed from untreated patatin than from the protease inhibitors, but patatin foam was much more stable. The foam-forming properties of patatin could be strongly improved by partial unfolding of the protein. Whipping tests, at both low (0.5 mg/mL) and high (10 mg/mL) protein concentration, also indicated that foams made with an ethanol-precipitated protein isolate were more stable than those made with beta-casein and beta-lactoglobulin. More generally, it can be concluded that when proteins are used as a foaming agent, a high concentration is required, because the protein available is inefficiently used. Also, there are several variables that may all, in different ways, affect both foam formation (amount of foam, bubbles size distribution) and foam stability. These variables include the type and concentration of protein, solvent conditions (pH, I), and the method used to make the foam.  相似文献   

Observed flow compensation associated with the MOC at 26.5 degrees N in the Atlantic   总被引：3，自引：0，他引：3  

Kanzow T  Cunningham SA  Rayner D  Hirschi JJ  Johns WE  Baringer MO  Bryden HL  Beal LM  Meinen CS  Marotzke J 《Science (New York, N.Y.)》2007,317(5840):938-941

The Atlantic meridional overturning circulation (MOC), which provides one-quarter of the global meridional heat transport, is composed of a number of separate flow components. How changes in the strength of each of those components may affect that of the others has been unclear because of a lack of adequate data. We continuously observed the MOC at 26.5 degrees N for 1 year using end-point measurements of density, bottom pressure, and ocean currents; cable measurements across the Straits of Florida; and wind stress. The different transport components largely compensate for each other, thus confirming the validity of our monitoring approach. The MOC varied over the period of observation by +/-5.7 x 10(6) cubic meters per second, with density-inferred and wind-driven transports contributing equally to it. We find evidence for depth-independent compensation for the wind-driven surface flow.  相似文献   

Value-laden knowledge and holistic thinking in agricultural research     

Donald M. Vietor  Harry T. Cralle 《Agriculture and Human Values》1992,9(3):44-57

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Electron tunneling through organic molecules in frozen glasses     

Wenger OS  Leigh BS  Villahermosa RM  Gray HB  Winkler JR 《Science (New York, N.Y.)》2005,307(5706):99-102

Reaction rates extracted from measurements of donor luminescence quenching by randomly dispersed electron acceptors reveal an exponential decay constant of 1.23 per angstrom for electron tunneling through a frozen toluene glass (with a barrier to tunneling of 1.4 electron volts). The decay constant is 1.62 per angstrom (the barrier, 2.6 electron volts) in a frozen 2-methyl-tetrahydrofuran glass. Comparison to decay constants for tunneling across covalently linked xylyl (0.76 per angstrom) and alkyl (1.0 per angstrom) bridges leads to the conclusion that tunneling between solvent molecules separated by approximately 2 angstroms (van der Waals contact) is 20 to 50 times slower than tunneling through a comparable length of a covalently bonded bridge. Our results provide experimental confirmation that covalently bonded pathways can facilitate electron flow through folded polypeptide structures.  相似文献   

Temporal variability of the Atlantic meridional overturning circulation at 26.5 degrees N   总被引：4，自引：0，他引：4  

Cunningham SA  Kanzow T  Rayner D  Baringer MO  Johns WE  Marotzke J  Longworth HR  Grant EM  Hirschi JJ  Beal LM  Meinen CS  Bryden HL 《Science (New York, N.Y.)》2007,317(5840):935-938

The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5 degrees N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 +/- 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 10(6) cubic meters per second). Interannual changes in the overturning can be monitored with a resolution of 1.5 Sv.  相似文献   

Use of time-activity budgets to measure early progress of a social attraction restoration project     

Peter J. Kappes  Gerard J. McChesney  Michael W. Parker  Harry R. Carter  Stephen W. Kress  Richard T. Golightly 《Biological conservation》2011,(1):620-626

Social attraction is a useful technique for re-establishing or relocating waterbird colonies and other species groups. However, little information exists regarding how newly attending individuals behave when the social environment is influenced predominantly by artificial stimuli. To help assess early progress of colony re-establishment, we compared time-activity budgets of common murres (Uria aalge) at a social attraction site (Devil’s Slide Rock; DSR) in central California with two nearby reference colonies during the first 3 years (1996–1998) of efforts. Murres at all colonies spent over 95% of their time engaged in resting, comfort, courtship, and alert activities during the pre-breeding period and over 88% of their time in similar activities during the breeding period. Although patterns were similar overall, comparisons of pooled and year-specific time budget data revealed significant differences between all three colonies, especially during pre-breeding. Murres at DSR typically engaged in comfort behaviors less frequently and in alert and courtship behaviors more frequently than reference colonies. Differences likely were due to recent re-establishment, including lower bird densities and higher proportions of non-breeders and first-time breeders at DSR, along with other factors such as disturbance. Results indicate that newly attracted birds at DSR behaved “normally” even though the social environment was influenced predominantly by artificial stimuli. Furthermore, re-established breeding in the first year of efforts, subsequent colony growth, and high productivity reflected successful restoration efforts. Thus, time-activity budgets can provide important measures of early progress of social attraction efforts and as such can be used to inform adaptive management decisions.  相似文献   

Effect of pesticide fate parameters and their uncertainty on the selection of 'worst-case' scenarios of pesticide leaching to groundwater     

Vanderborght J  Tiktak A  Boesten JJ  Vereecken H 《Pest management science》2011,67(3):294-306

BACKGROUND: For the registration of pesticides in the European Union, model simulations for worst‐case scenarios are used to demonstrate that leaching concentrations to groundwater do not exceed a critical threshold. A worst‐case scenario is a combination of soil and climate properties for which predicted leaching concentrations are higher than a certain percentile of the spatial concentration distribution within a region. The derivation of scenarios is complicated by uncertainty about soil and pesticide fate parameters. As the ranking of climate and soil property combinations according to predicted leaching concentrations is different for different pesticides, the worst‐case scenario for one pesticide may misrepresent the worst case for another pesticide, which leads to ‘scenario uncertainty’. RESULTS: Pesticide fate parameter uncertainty led to higher concentrations in the higher percentiles of spatial concentration distributions, especially for distributions in smaller and more homogeneous regions. The effect of pesticide fate parameter uncertainty on the spatial concentration distribution was small when compared with the uncertainty of local concentration predictions and with the scenario uncertainty. CONCLUSION: Uncertainty in pesticide fate parameters and scenario uncertainty can be accounted for using higher percentiles of spatial concentration distributions and considering a range of pesticides for the scenario selection. Copyright © 2010 Society of Chemical Industry  相似文献   

Seed Dimensions in the Subspecies and Cultivar-groups of Cucurbita pepo     

Harry S. Paris  Haim Nerson 《Genetic Resources and Crop Evolution》2003,50(6):615-625

Seed samples of 174 accessions of pumpkins, squash, and gourds of Cucurbita pepo were measured for length, width, and thickness. Mean seed length ranged from 8.8 to 23.3 mm, mean seed width from 5.0 to 12.5 mm and mean seed thickness from 1.2 to 3.8 mm. The seeds of the edible-fruited cultivar-groups of C. pepo subsp. pepo (Pumpkin, Vegetable Marrow, Cocozelle, Zucchini) were longer, wider, and thicker than those of their counterparts of C. pepo subsp. texana (Acorn, Crookneck, Scallop, Straightneck). The small-fruited, inedible gourds had the smallest seeds. Of the edible-fruited C. pepo subsp. pepo, the Pumpkin Group (round fruits) possessed the longest and flattest seeds whilst the Zucchini Group (long, uniformly cylindrical fruits) possessed the shortest and thickest seeds. The samples tested also differed greatly in mean values for relative dimensions. Length-to-width ratio ranged from 1.5 to 2.5, length-to-thickness ratio from 3.7 to 8.2, and width-to-thickness ratio from 2.0 to 4.9. The Pumpkin Group, followed by the Cocozelle Group (long, bulbous cylindrical fruits) and the Vegetable Marrow Group (short, tapered cylindrical fruits), had seeds of the highest length-to-width ratio. The seeds of the four edible-fruited groups of C. pepo subsp. pepo differed significantly from one another in their length-to-thickness and width-to-thickness ratios. The seeds of the Pumpkin Group and the wild Mexican gourd (C. pepo subsp. fraterna) differed greatly in their dimensions but were most similar to one another in their relative dimensions. In C. pepo, seed size is positively associated with fruit size and seed shape is inversely associated with fruit shape.  相似文献   

Identification of metallic-smelling 1-octen-3-one and 1-nonen-3-one from solutions of ferrous sulfate     

Lubran MB  Lawless HT  Lavin E  Acree TE 《Journal of agricultural and food chemistry》2005,53(21):8325-8327

Taste threshold tests of ferrous sulfate (FeSO4) solutions have been confounded by the presence of putative odorants. To detect the presence of odorants released from these solutions solid-phase microextraction (SPME) was used to collect volatiles in the headspace above FeSO4 solutions. Gas chromatography-olfactometry of samples collected over three time periods (1, 5, and 16 h) and at two temperatures (22 and 37 degrees C) revealed the presence of several metallic-smelling odorants in the headspace. Using authentic standards, two of the odorants were conclusively identified as 1-octen-3-one and 1-nonen-3-one. Trace levels of other odorants were also detected, but dilution experiments indicated that 1-nonen-3-one was at least 10 times more potent than anything else released from the solutions. 1-Octen-3-one and 1-nonen-3-one are excellent candidates for the metallic odor responses often observed in threshold testing of solutions of FeSO4.  相似文献