摘要:

The presence of surface competing cations and pH are expected to have an influence on the cation adsorption-desorption behavior of soils. In this study, we evaluated the adsorption-desorption behavior of K+in the presence of solution Ca2+(binary) or in the presence of solution Ca2+plus NH4(ternary) and the adsorption-desorption behavior of NH+4in the presence of solution Ca2+(binary) or in the presence of solution Ca2+plus K+(ternary). The soils selected for the study were the Eden, Lowell, and Nicholson soils from Northern Kentucky. These soils are generally known to give poor yield response to fertilizer application. It was shown that potassium adsorption was suppressed by solution NH+4while NH+4adsorption was greatly enhanced by solution K+. Adsorption of K+and NH+4also increased as pH increased. Ammonium desorption, on the other hand, decreased in the presence of solution K+relative to that in the absence of solution K+, increased at the medium pH tested, but decreased at the highest pH tested. Furthermore, in general, fixation accounted for most of the adsorbed K+or NH+4. The results suggested that-predicting exchange or apparent fixation behavior of monovalent cations based on ion size and charge for soils containing vermiculite type minerals is difficult. Experimental exchange data are needed to make accurate binary or ternary cation exchange predictions in such soil systems

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Metribuzin [4-amino-6-(1–1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] is a widely used soil-applied herbicide, and its dissipation was assessed using undisturbed soil columns to simulate field conditions. Metribuzin (technical grade and14C-labeled dissolved in 0.1MCaCl2) was applied to the soil (Dundee loam) surface at a concentration equivalent to 0.68 kg metribuzin ha−1. Water was added to the surface at 1, 8, 15, 22, 29, and 36 days after treatment. Chloride (Cl−) and14C were measured in the effluent. Twenty-four hours after each leaching, three cores were randomly selected, sectioned at 0–3.3-, 3.3–6.6-, and 6.6–10-cm depth increments, and analyzed. Metribuzin mineralization was monitored weekly by trapping14CO2-C in 0.5MNaOH. The pattern of Cl−appearance in the effluent indicated possible preferential flow. Metribuzin degradation in the 10-cm profile followed first-order kinetics, with parent metribuzin being the dominant extractable species until the last 14 days when a composite of unidentified polar metabolites was prevalent. Metribuzin was the primary single component measured in the effluent until 37 days after application. However, from 9 days after herbicide application through the remainder of the experiment, the fraction of total applied14C present as metabolites (summation of known metabolites diketometribuzin [DK], deaminated metribuzin [DA], and deaminated diketometribuzin [DADR] and unidentified polar metabolites) exceeded metribuzin in the effluent. As an average over time, the 3.3–6.6-cm section contained the most methanol unextractable14C

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

A major scientific challenge for modern agriculture is control of off-site effects on the water resource. In the Valle Central of Costa Rica, coffee plantations may leach fertilizer-derived NO−3to groundwaters, as a result of high fertilization rates (annually ∼270 kg/ha as N), highly permeable and well structured Andisols, and high rates of annual runoff (>1000 mm). The objective of this study was to examine several aspects of the nitrification and NO−3adsorption that control NO−3leaching from these highly productive soils. Monthly collections from four Andisols indicated that soil NO−3varied seasonally, with NO−3accumulating to about 280 kg/ha in the upper meter of soil during the 5-month dry season. Soil NO−3was reduced during wet season months, even though fertilization was confined to the wet season. During these months, soil NO−3averaged about 140 kg/ha as N in the upper meter of soil, apparently reduced by wet season leaching, root uptake, and, possibly, dentrification. Field and laboratory incubations at different soil moisture and temperature regimes demonstrated how soil microflora mineralized N and nitrified NH+4at relatively high rates, even at low water potentials, e.g.,−3can be adsorbed by these allophanous Andisols, especially at low pH (up to about 5 cmol/kg at pH−3to groundwater; however, the effectiveness of adsorption as a protection of groundwater quality is probably limited due to high inputs of fertilizer N and to liming management of coffee soils that maintains relatively high soil pH. Additional research into the coffee N cycle and fertilizer efficiency in coffee is needed to ensure high coffee productivity and to protect aquifer water quality in the Valle Central

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Electron Spin Resonance (ESR) measurements were performed on particle size fractions of high and low humifiedSphagnum fuscumandCarex rostrata. Each peat sample was divided into seven particle size groups, where the size varies between >2.0 andCarexpeat type class and the low humifiedSphagnumpeat, slightly worse with the high humifiedCarexpeat and the high humifiedSphagnumpeat types. Many of the dependent variables were well modeled, and unknown test samples were correctly predicted

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Growing season (March-October) water table levels were measured over a 4-year period, and soil profiles were described along a gradient of upland to wetland pitch pine-dominated sites in the New Jersey Pinelands. These sites were associated with very poorly to somewhat poorly drained soils of the Lakewood sand catena. Although several profile attributes were more closely associated with specific ranges of water table levels, few features were, limited to a specific hydrologic regime. O and A horizon thickness and frequency of very dark gray to black A horizons generally decreased along the wet to dry hydrosequence. E horizon thickness was variable and unrelated to water table level. Bh horizons with values and chromas of 2 or 3 characterized soils with first quartile water tables from 15.1 to 60 cm from the surface. Chromas of 1–4 dominated all but the driest soils. Relatively bright high chroma, horizons, with or without low chroma mottling (chromas ≤ 2), were most common in soils with first quartile water levels greater than 45 cm from the surface, yet they also occurred in some of the most frequently saturated soils. In most cases, low chroma mottles as well as the lower surface of high chroma horizons without mottling were found at or below the highest water level recorded during the study period. These results suggest that soil features are not absolute indicators of water table level in somewhat poorly drained and very poorly drained soils of the Lakewood catena. A dual parameter approach that considers both soil features and vegetation to determine water levels provides a more accurate estimate of hydrologic conditions in these soils. Estimates based on one parameter should not be discounted when that parameter clearly characterizes hydrologic regime

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The objectives of this study were to (i) develop a semiempirical model to predict the changes in clay stabilization after the introduction of forages, (ii) assess the model using data from different soils, and (iii) determine the influence of soil properties on clay stabilization. Dispersible clay (DC) measurements were made at monthly intervals during the 1989, 1990, and 1991 growing seasons on seven soils under continuous conventionally tilled corn and forage treatments established in 1989. The influence of cropping treatment, time of sampling, water content (Θ) at sampling, and the interaction of these terms onDCwas significant for each soil atP= 0.05. Using the variation inDCwith Θ over time, a semi-empirical model was developed to predict the changes in the amount of clay stabilized by forages. The model parameters described (i) the rate at which clay stabilization occurred and (ii) the maximum potential amount of clay stabilized. The rate was characterized by half-life (t1/2) for the stabilization process. TheR2for the best fit of the model ranged from .48 to .84, and the fit was significant for each soil atP= 0.05. The projectedt1/2for clay stabilization ranged from 3.55 to 9.12 years. The maximum potential amount of clay stabilized ranged from 0.55 to 4.51%. Thet1/2decreased with increasing clay and organic matter contents and pH, whereas an opposite trend was observed for the maximum potential amount of clay stabilized. The model provided a framework for assessing the influence of changes in cropping practices and soil properties on clay stabilization

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID