长期秸秆还田对白浆土物理性质及水稻产量的影响

【目的】明确长期秸秆还田对白浆土土壤物理性质及水稻产量的影响。【方法】开展秸秆还田长期定位试验。试验设置4个处理,分别为对照(CK),单施秸秆(S),秸秆+化肥(SNPK),单施化肥(NPK)。在2005年后连年处理,并于试验处理前和2010年、2015年试验处理期间调查土壤容重、硬度、孔隙、三相组成以及水稻产量。【结果】白浆土长期秸秆还田有利于水稻产量提高,10年产量平均,秸秆还田配施肥料处理水稻产量比对照和秸秆单独还田处理增产275.70%和133.23%,比单施化肥处理增产14.17%。秸秆还田处理水稻产量在还田第5—10年平均产量比第1—5年有增加趋势;长期秸秆还田可以改善土壤物理性质,降低土壤容重、硬度,还田10年后,秸秆还田配施化肥处理土壤容重低于化肥单施、秸秆单施及对照处理,SNPK处理0—20、20—30 cm土层土壤容重与对照相比分别降低6.34%和10.00%,与还田5年后同类处理相比仍呈下降趋势;秸秆还田配施化肥处理土壤硬度10年后在10、20、30 cm土层与处理前相比分别降低为26.87%、5.68%和4.62%,在20—30 cm土层与对照相比差异显著,还田10年与5年后相比有下降趋势,其他处理变化不明显;还田5年后,秸秆还田配施化肥处理在0—20、20—30、30—40 cm土层土壤固相比例与对照相比分别下降8.82%、8.36%和3.65%,还田10年后分别下降10.87%、10.61%和4.67%,10年后要比5年后下降幅度大,秸秆还田配施化肥比秸秆单施和化肥单施处理下降幅度大;长期秸秆还田可以增加土壤有效孔隙的数量,在处理间和年限间差异极显著,还田10年后,在0—20、20—30、30—40 cm土层秸秆还田配施化肥土壤有效孔隙比对照增加28.86%、63.85%和23.40%,在20—30 cm和30—40 cm土层比化肥单施增加12.55%和62.96%,在0—20、20—30、30—40cm土层比秸秆单施增加19.68%、56.52%和24.46%;与还田5年后相比,土壤有效孔隙度均呈现增加的趋势。【结论】长期秸秆还田可以改善白浆土不良物理性状,降低白浆层的容重、硬度,增加土壤总孔隙度和有效孔隙的比例,提高水稻产量。秸秆还田年限越长改善土壤不良物理性质效果越明显。单独进行秸秆还田改善土壤效果不明显,秸秆还田配施肥料处理效果明显;在不同处理上,秸秆还田配施化肥处理既有改土效果,又可提高水稻产量,而单施化肥和单独秸秆还田均达不到此类效果。     

The 1882 tilefish kill — a cold event in shelf waters off the north-eastern United States?

A mass mortality of `warm-water' tilefish in the Middle Atlantic Bight between April and August of 1882 suggests an episode of extreme cold in the shelf waters off the north-eastern United States. This cooling is hypothesized to be a consequence of enhanced equatorwards transport of cold water in the Labrador Current, coincident with a minimum in the North Atlantic Oscillation (NAO) index during the early 1880s.
Although there is little direct evidence for this historical event, an analogue for the 1880s cooling is found in the 1960s, at the most recent NAO-index minimum. Post-1945 observations in the Middle Atlantic Bight / Gulf of Maine region reveal changes in winter baroclinic circulation between cool and warm decades, with greater equatorward penetration of south-westwards flow along the shelf-edge during the cool 1960s. Over the period 1934–77, the NAO is found to account for 17% of the interannual variance in Labrador Current transport around the Grand Banks.
Proxy evidence for the cold episode of the early 1880s is sought. Records of bottom temperature in the Middle Atlantic Bight region are reconstructed using stable oxygen isotopic analysis on the annual bands of shells of a bivalve mollusc ( Arctica islandica ) and an empirical model of covariability with local air temperature. The result is confirmation of the presence of anomalously cold water during the early 1880s.     

Alfalfa establishment without tillage as influenced by insecticide and vegetation suppression

Conventional alfalfa ( Medicago sativa L.) establishment methods may create considerable potential for erosion. Conservation tillage practices that result in stand establishment without disturbing the soil greatly would be beneficial in reducing soil losses. Thus, field experiments were conducted to evaluate the success of alfalfa establishment without tillage in a perennial grass sod. Variables included rate of carbofuran (2, 3-dihydro-2, 2-dimethyl-7 benzofuranyi methylcarbamate) insecticide and control of existing vegetation with chemicals. Establishment without tillage was compared with a conventional method of establishment. Carbofuran at 1.1 kg ha⁻¹ applied in the row with the seed, when compared with a control, increased yields during the year of planting but no response was observed in the year after seeding. Yields of alfalfa established without tillage using either glyphosate ( N -(phosphonomethyl)glycine) or paraquat (1,1-dimethyl-4, 4-bipyridinium chloride) for sod suppression were equivalent to or better than yields obtained from conventional sowings except for the 2 April sowing. Paraquat was more effective for tall fescue (Festuca arundinacea Schreb.) suppression when applications were made on 26 April after spring tiller emergence was complete than on 2 April when some of the tillers may have been protected from the spray by basal sheath tissue.
Broadcast application of paraquat resulted in higher alfalfa yields and decreased non-alfalfa components due to more complete sod suppression than application in bands over the row.     

Efficiency of Tree Crowns and Stemwood Production at Different Canopy Leaf Densities

Variation in the unit leaf rate in trees, i.e. the weight ofwood increment per unit of leaf area, arises from disproportionatechanges in their rates of net photosynthesis and in the allocationof carbohydrates. Changes in unit leaf rate in response to variationsin canopy density were investigated in a thinning experimentestablished in a 36 year-old Douglas fir forest. Tree growthwas estimated from increment cores and leaf area by linear correlationwith sapwood basal area. Net assimilation and mean growth ofindividual trees expressed as basal area and volume decreasedin direct proportion to increase in canopy density from 3.6to 12.0 m²m^–2 of projected leaf area. These relationshipswere linear with multiple correlation coefficients (r²)0.97. Net stand increment, in contrast to unit leaf rate, culminatedas projected leaf area approached 6 m²m^–2 and decreasedat the higher canopy densities due to mortality. The approachdeveloped in this paper could be applicable in predicting growthin response to various silvicultural treatments.     

IMAGING DIAGNOSIS—NECROTIZING MENINGOMYELITIS AND POLYARTHRITIS

A vaccinated 2-year-old female neutered Weimaraner had bilateral pelvic limb ataxia that progressed over 12 h. The dog became nonambulatory, with signs of pain on palpation of the lumbar spine. The dog also developed multiple joint effusions. On magnetic resonance (MR) imaging, there was a diffuse, asymmetric T2-hyperintensity in the thoracolumbar spinal cord which was characterized by contrast enhancement. Lumbar cerebrospinal fluid (CSF) analysis had an elevated white blood cell count and protein. On the basis of MR images and CSF analysis, a presumptive diagnosis of diffuse myelitis was made. The dog became paraplegic and was euthanized. Postmortem examination confirmed the presence of myelitis with vasculitis and nonerosive polyarthritis.     

Verification of immunofluorescence colony-staining of Erwinia carotovora subsp. atroseptica by reisolation and immunodiffusion or PCR

In this study, the reliability and efficiency of three procedures for verification of IFC-positive colonies of Erwinia carotovora subsp. atroseptica were compared: (1) PCR amplification, (2) reisolation on a non-selective medium (trypticase soy agar) followed by direct immunodiffusion (TSA-DID), developed for isolation of target and cross-reacting bacteria, and (3) reisolation on a selective medium (crystal-violet pectate) and characterization of selected isolates with Ouchterlony double diffusion (DLCVP-ODD), developed for isolation of pectinolytic Erwinia spp. The reliability of a PCR amplification procedure for characterization of E.c. atroseptica was evaluated. Specific amplification products could be produced from DNA of all 187 European strains of the bacterium, while no amplification products were obtained from DNA of four distinctive serological groups of bacteria cross-reacting with antibodies against E.c. atroseptica , nor from DNA of randomly selected saprophytic bacteria isolated from potato peel extracts. All 60 immunofluorescent-positive target colonies from a potato peel extract with added E.c. atroseptica tested were positive by PCR compared with 68 and 72% successful determinations by TSA-DID and DLCVP-ODD, respectively. PCR enabled verification of fluorescent colonies from IFC preparations of naturally infected seed lots with an efficiency of 93%, compared with 48 and 71% successful determinations by TSA-DID and DLCVP-ODD, respectively. It is concluded that PCR is useful for routine confirmation of the identity of fluorescent colonies in IFC.