摘要:

We measured actual infiltration rates (i) during a prolonged infiltration test in a field soil and noted thatifluctuates with time (t). The plot ofiagainsttreveals thatineither becomes asymptotic with thetaxis nor attains a constant (zero or nonzero) value whentis large.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We conducted laboratory and pot experiments to study the effect of different qualities of irrigation water having various Mg/Ca ratios (2, 4, 8, and 16), SAR (10, 25, and 50) and electrolyte concentrations (20 and 80 meq/L) on the physicochemical properties of soils and on the yield and chemical composition of wheat, using four soils of different texture, clay mineralogy, and degree of calcareousness. The Mg/Ca ratio in the exchange complex increased with an increase in Mg/Ca ratio and decreased with an increase in SAR of the leaching water. The increasing proportion of Mg over Ca in the irrigation water at a given SAR and electrolyte concentration increased the sodicity and the degree of dispersion of the soil, and its effect was more pronounced at higher SAR than at lower SAR. The deteriorating effect was found to be more in the alluvial soil than in the black soil because of greater CaCO3content in the latter soil. A significant reduction was noticed in the grain and dry matter yields of wheat with an increase in Mg/Ca ratio and electrolyte concentration of the irrigation water. The effects were more pronounced in the heavy black clay soil dominated with montmorillonitic clay mineral than in the alluvial soil having illitic clay mineral. Further, the concentration of Na, Mg, and P increased and that of Ca and K decreased both in the grain and the straw with an increase in the Mg:Ca ratio of the irrigation water.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We prepared water-soluble fulvic acid-copper and fulvic acid-iron complexes, with fulvic acid:metal ratios of 1:0.5 and 1:1, at pHs 4 and 6. After the complexes were freezedried, we characterized them by chemical, spectroscopic (infrared, electron spin resonance, and Mössbauer), x-ray, and thermal (differential thermal analysis) methods.The major FA functional groups involved with metal complexing were COOH and phenolic OH groups. Electron spin resonance (ESR) data showed that substantial portions of the metals in the complexes formed inner sphere complexes with the FA. The Cu in all complexes was divalent, whereas the Fe was trivalent. From x-ray diffraction patterns, it appeared that metals brought FA “molecules” closer together by bridging adjacent FA “molecules.” The thermal stability of FA decreased as it complexed with metals. Apparently, the complexing of Cu and Fe exerted strains on the structure of the FA, thereby lowering its resistance to thermal decomposition. The data presented here provide evidence that at least portions of the Cu and Fe are strongly complexed by the FA.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Decomposition of sewage sludge in soil is mediated by microbial populations. The facility with which the decomposition is carried out is influenced by several factors, one being the sludge's content of toxic metals. The objectives of this investigation were to determine the effects of three concentrations, in micrograms per gram of soil, of sludge-borne cadmium (111, 1, 0.1), chromium (556, 44, 1), and copper (556, 78, 11) on bacterial numbers, ATP content, and distribution of major fungal genera in an agricultural soil suited for the disposal of sewage sludge.Bacteria were stimulated initially in the 78 and 11 μg/g Cu treatments and in the 1 μg/g Cr treatment. Restriction of bacterial growth occurred in the 556 μg/g Cu and 556 μg/g Cr treatments. Cadmium treatments exhibited counts similar to controls initially, but were reduced after 2 weeks' incubation. After 25 days, bacterial counts in controls were higher than in all but two metal treatments.Fungal intergenus relationships were altered in all but Cr treatments.ATP estimates indicated that biomass increased initially, but, by 1 week, was reduced in Cu treatments. ATP in Cr treatments paralleled the initial stimulation, but, by 2 weeks, gave lower estimates than controls. Cadmium treatments showed similar trends in bacterial counts and measured ATP.Results indicated that metal-laden sewage sludge affected soil microbial populations quantitatively or qualitatively, which could influence the capacity of these soil populations for nutrient cycling.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We estimated the phosphate sorptivity of 290 samples (topsoil and subsoil) from 9 orders and 26 great groups of theSoil Taxonomy, in terms of the Bache and Williams index. Among these samples, entisols, alfisols, mollisols, and ultisols generally had lower than average sorption indices, and vertisols higher than average. Samples from histosols, inceptisols, oxisols, and spodosols varied greatly in sorption index, but there is usually an explanation for this variation in terms of a property or properties considered at the family level of theSoil Taxonomy.Some statistical evidence is given to show that the variation in sorption index within soil series is usually considerably less than the variation in a more diverse collection of soil samples.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The mathematical, two-dimensional model described here allows study of the effects of soil surface shape, produced by different cultivation techniques, upon soil temperatures. It uses a terrain-following coordinate system and considers environmental conditions, soil physical characteristics, and the slope and aspect of the surface.I compare calculated temperatures with observed ones in a ridge, a furrow, and a horizontal surface and show that soil temperatures are significantly influenced by both slope and aspect. The results indicate that the numerical model predicts the soil temperatures accurately in the three soil shapes tested.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Increased nitrogen loss from leaching, denitrification, or volatilization with reduced or no-till farming may offset potential energy savings from reduced field operations. Nitrification inhibitors have effectively reduced N losses in conventional tillage and may increase the energy efficiency and yield resulting from N applied to no-till corn. For 3 years, we studied corn produced by no-till farming to determine the effects of inhibiting nitrification of spring-applied N with nitrapyrin or etradiazole on corn yield and N use efficiency. Low grain yields obtained without N fertilization indicated that only low levels of residual or mineralizable N were available for corn growth. The importance of incorporating N in the soil was indicated, because plants fertilized with 28 percent N solution injected into soil produced 20 percent more grain than plants fertilized with broadcast 28 percent N or urea. The highest grain yield was achieved with anhydrous NH3. Plants fertilized with surface-applied N fertilizers showed symptoms of N deficiency by 30 days postpollination. Inhibiting nitrification of injected NH3or 28 percent N solution generally increased corn yields compared with N without the inhibitor. Nitrification inhibitors have a good potential to improve N use efficiency and grain yields by reducing losses of applied ammoniacal N in no-till corn production systems.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We observed low nutrient levels and poor productivity in andic soils overlying glacial till with differential percolation characteristics in northwestern Montana. The objective of this study was to determine whether variation in the subsurface percolation rate of underlying glacial till significantly affected (1) the nutrient content of the andic surface soil and (2) timber production on the andic soils. Twenty sample sites supporting 50-year-old stands of western larch (Larix occidentalisNutt.) were selected on the Kootenai National Forest. Grouping of the soils was based on slow, (25.4 cm/h) internal subsoil (till percolation). Soil nutrient concentrations and availabilities, tree growth indicators, xylem sap nutrient contents, and tree moisture stress were measured. The results supported the hypothesis that the rate of subsoil percolation affected the overall fertility of andic soils. Tree growth was affected by the subsoil percolation rate as it related to moisture availability. There is some evidence that trees on the slowly draining sites that had the best juvenile growth were growing more slowly with age because of nutrient depletion in the shallow andic soil where the roots were confined by compacted silts. Trees on the rapidly draining sites were growing better with age, because the roots were able to penetrate more broadly into the underlying gravel that was not strongly compacted.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID