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1.
2.
Cochran LC 《Science (New York, N.Y.)》1946,104(2699):269-270
3.
H. P. Collins A. Alva R. A. Boydston R. L. Cochran P. B. Hamm A. McGuire E. Riga 《Biology and Fertility of Soils》2006,42(3):247-257
Sodium N-methyldithiocarbamate (metam sodium) and 1,3 dichloropropene are widely used in potato production for the control of soil-borne
pathogens, weeds, and plant parasitic nematodes that reduce crop yield and quality. Soil fumigation with metam sodium has
been shown in microcosm studies to significantly reduce soil microbial populations and important soil processes such as C
and N mineralization. However, few published data report the impact of metam sodium on microbial populations and activities
in potato production systems under field conditions. Fall-planted white mustard (Brassica hirta) and sudangrass (Sorghum sudanense) cover crops may serve as an alternative to soil fumigation. The effect of metam sodium and cover crops was determined on
soil microbial populations, soil-borne pathogens (Verticillium dahliae, Pythium spp., and Fusarium spp.), free-living and plant-parasitic nematodes, and C and N mineralization potentials under potato production on five soil
types in the Columbia Basin of Eastern Washington. Microbial biomass C was 8–23% greater in cover crop treatments compared
to those fumigated with metam sodium among the soil types tested. Replacing fumigation with cover crops did not significantly
affect C or N mineralization potentials. Cumulative N mineralized over a 49-day laboratory incubation averaged 18 mg NO3-N kg−1 soil across all soil types and treatments. There was a general trend for N mineralized from fumigated treatments to be lower
than cover-cropped treatments. Soil fungal populations and free-living nematode levels were significantly lowered in fumigated
field trials compared to cover-cropped treatments. Fumigation among the five soil types significantly reduced Pythium spp. by 97%, Fusarium spp. by 84%, and V. dahliae by 56% compared to the mustard cover crop treatment. The percentage of bacteria and fungi surviving fumigation was greater
for fine- than coarse-textured soils, suggesting physical protection of organisms within the soil matrix or a reduced penetration
and distribution of the fumigants. This suggests the potential need for a higher rate of fumigant to be used in fine-textured
soils to obtain comparable reductions in soil-borne pathogens. 相似文献
4.
Earth tides can trigger shallow thrust fault earthquakes 总被引:6,自引:0,他引:6
We show a correlation between the occurrence of shallow thrust earthquakes and the occurrence of the strongest tides. The rate of earthquakes varies from the background rate by a factor of 3 with the tidal stress. The highest correlation is found when we assume a coefficient of friction of mu = 0.4 for the crust, although we see good correlation for mu between 0.2 and 0.6. Our results quantify the effect of applied stress on earthquake triggering, a key factor in understanding earthquake nucleation and cascades whereby one earthquake triggers others. 相似文献
5.
A knowledge of the nutrient dynamics that occur with land use changes, e.g., in clearing forests for farmland, is useful in choosing the most efficient soil and fertilizer management practices. To determine net in situ P and N mineralization and nitrification rates of forest floor materials and their nutrient value for agricultural crops, plastic bags containing different materials (moss, O horizon, and A horizon) collected from a subarctic black spruce (Picea mariana Mill.) forest were incubated for 2 years in their respective forest horizons and at 7.5 cm depth in a nearby fallow field. Net amounts of P and N mineralized were highest in moss and were similar in forest and field when the temperature and moisture content were similar, but smaller in forest when the water content was higher. Net nitrification was negligible in O and A horizon material but significant in moss during the 2nd year, occurring sooner and producing higher NO
inf3
sup-
levels in the field (171 mg ha-1) than in the forest (13 mg ha-1). Moss P and N mineralization rates were correlated in the fallow field. Temperature, moisture content, and substrate quality were important factors controlling P and N dynamics of forest floor materials in a subarctic fallow field and native forest. In subarctic regions, incorporation and mineralization of forest floor materials could provide an early source of N and P (70 and 17 kg ha-1, respectively) for succeeding agricultural crops. 相似文献
6.
Farmer CG Cochran RC Simms DD Klevesahl EA Wickersham TA Johnson DE 《Journal of animal science》2001,79(9):2276-2285
Two experiments were conducted to quantify the impact on forage use and performance of varying supplementation frequency of cattle consuming forage diets across a range of frequencies. In both experiments, a common supplement was used that contained a relatively high concentration of CP (43%) and was fed at the following frequencies: 1) 2 d/wk; 2) 3 d/wk; 3) 5 d/wk; and 4) 7 d/wk. In Exp. 1, 120 Hereford x Angus cows (BW = 537 kg) grazing winter tallgrass-prairie range were supplemented at the various frequencies from December 7 until calving (average calving date = 3/7/99). All treatments provided the same quantity of supplement on a weekly basis (12.74 kg, as-fed) but divided the amount delivered on a given day equally among the number of supplementation events for that treatment. Less BW was lost from December 7 through calving (linear effect, P = 0.02) as frequency of supplementation increased, but the magnitude of difference in weight change was relatively small. Body condition responded similarly through early February (linear effect, P = 0.02), although treatment effects were not as distinct at calving (cubic effect, P = 0.11). In Exp. 2, 16 ruminally fistulated Hereford x Angus steers (BW = 257 kg) were blocked by weight and assigned to one of the four frequencies of supplementation. Steers were offered tallgrass prairie hay (73.5% NDF, 4.8% CP) ad libitum and were supplemented at a rate (relative to BW) similar to that of the cows in Exp. 1. Increasing frequency of supplementation increased (linear effect, P < or = 0.02) forage OM intake, OM and NDF digestion, and digestible OM intake. However, the most prominent differences in forage OM intake tended (cubic effect, P = 0.07) to occur with the two extreme frequencies of supplementation. In conclusion, forage use was improved with an increased frequency of supplementation, but the impact on performance is not likely to be large unless extreme differences in frequency occur. 相似文献
7.
V. L. Cochran 《Biology and Fertility of Soils》1991,10(4):227-232
Summary The mass loss and N dynamics of barley stems and leaves, placed on the soil surface or buried, were examined over two summers. There was little difference in mass loss or N dynamics in straw placed 7.5 or 15 cm deep. However, the surface straw lost mass much more slowly and immobilized more N for a longer time than the buried straw. Filter paper had a slow rate of mass loss initially, but once started, lost mass much more rapidly than either the barley stems or leaves. Loss of mass was closely correlated with the cellulose loss in straw, whether buried or placed on the soil surface. The sustained rate of mass loss was 6.3 and 7.0% month-1, respectively, for surface and incorporated leaves compared with 3.5 and 4.3% month-1, for surface and incorporated stems. The greater loss sustained by the leaves was attributed to a lower lignin content rather than a higher N content, because the addition of N to the straw after 30 days in the field failed to increase CO2 evolution. Maximum net N immobilization occurred within 30 days for all the barley straw, except for the stems placed on the ground surface, which did not reach maximum N immobilization until the second summer. Immobilization and mineralization of N were estimated for a 3000 kg ha-1 grain crop. Surface straw immobilized 3.8 kg N ha-1 in the 1st year and 9 kg N ha-1 in the 2nd year, whereas incorporated straw immobilixed 3.5 kg N hs-1 in the 1st year and mineralized 4.5 kg N ha-1 in the 2nd year. Thus, in Alaska, residue management does not affect N fertilizer requirements in the 1st year, but an additional 13.5 kg N ha-1 is required for surface residues in the 2nd year. 相似文献
8.
Ten low (LSC) and 10 high (HSC) serving capacity yearling bulls were exposed individually to 25 naturally cyclic (N) cows for 3 d (average mating load) and subsequently to 9 estrus-synchronized (S) cows for 1 d (heavy mating load) in a randomized complete block design consisting of 10, 4-d blocks. Bulls were fitted with vibracorders and temperature acquisition modules to record grazing activity and body temperature (BT), respectively. During the N cow treatment, LSC bulls had fewer (P less than .05) services per cow and a higher mount to service ratio than HSC bulls, and LSC bulls tended (P = .12) to graze less total time than HSC bulls (7.8 vs 9.0 h/d, respectively). However, both groups of bulls exhibited similar diurnal grazing patterns with two major daily grazing periods; the first (0400 to 1300) peaked early in the morning (0600) and the second (1700 to 2200) occurred in late afternoon and evening. During the S cow treatment, LSC and HSC bulls did not differ (P = .60) in grazing time or pattern, but similar mating activity was exhibited by both SC groups while exposed to S cows. Bulls grazed little during the hottest part of the day (1300 to 1700), and LSC and HSC bulls spent only 2.2 and 2.4 h, respectively, grazing during dark, cooler periods near midnight. Body temperature did not differ between SC groups and averaged 39.3 degrees C during N cow treatment and 39.4 degrees C during S cow treatment. Body temperature had a distinct, monophasic diurnal pattern in bulls exposed to an average mating load.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
9.
Samples from two experiments were used to evaluate the potential of ADL and alkaline peroxide lignin (APL; isolated by sequential, alkaline hydrogen peroxide [AHP] incubation and ADL extraction) for predicting digestibility of warm-season grass diets. Experiment 1 evaluated the influence of level of sorghum grain supplementation on utilization of immature bluestem-range grasses, and Exp. 2 evaluated the influence of supplemental protein x energy level interaction on the utilization of dormant bluestem-range grasses. Internal markers isolated in feed, orts and feces were 1) ADL and 2) APL with AHP incubation either before (APL-PRE) or after (APL-POST) the acid detergent extraction step in the ADL procedure. Organic matter digestibility (OMD) was calculated from the ratio of marker consumed to marker excreted for each internal marker and was compared with OMD from total collection. For Exp. 1 a treatment x marker interaction was observed (P less than .01). The APL-PRE procedure yielded OMD coefficients similar (P greater than .10) to total collection values within most treatments, but OMD coefficients from APL-POST and ADL differed (P less than .05) from total collection within all treatments except at the highest level of supplementation. For Exp. 2, predicted OMD values from ALP-PRE were similar (P greater than .10) to total collection values, whereas OMD predictions from APL-POST and ADL were different (P less than .01) from total collection. In conclusion, APL appears promising as an internal marker for bluestem-range grasses if AHP incubation is incorporated before the acid detergent extraction in the ADL procedure. 相似文献
10.
OBJECTIVE: To compare the levels of mRNA expression of cycooxygenase (COX)-1 and COX-2 in the digital laminae of normal horses and horses in the developmental stages of laminitis experimentally induced by administration of black walnut extract (BWE). SAMPLE POPULATION: Samples of mRNA extracted from the digital laminae of 5 control horses and 5 horses at the onset of leukopenia after administration of BWE. PROCEDURE: Specimens of laminae were collected from anesthetized horses prior to euthanasia. Expression of COX-1 and COX-2 mRNA in laminae of control and affected horses was evaluated via real-time quantitative polymerase chain reaction techniques. RESULTS: Expression of COX-2 mRNA was significantly increased in the BWE-treated group, compared with that in control horses. In contrast to COX-2 regulation, COX-1 mRNA expression was not significantly different between groups. Interestingly, despite consistent clinical signs such as leukopenia in all BWE-treated horses, distinct differences in COX-2 mRNA expression were detected among those 5 horses (compared with values for control horses, the increase in COX-2 mRNA expression ranged from no increase to a 30-fold increase). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that there was a significant upregulation of COX-2 mRNA expression during the developmental stages of laminitis, with no significant change in expression of the COX-1 isoform. These data appear to provide support for aggressive use of nonsteroidal anti-inflammatory drugs in horses at risk for laminitis; further investigation into the clinical value of selective COX-2 inhibitors for treatment of laminitis in horses appears to be warranted. 相似文献