摘要:

A new potentiometric method for cation exchange capacity (CEC) determination in soils is proposed. Studied on Spanish soils of different physical, chemical, and miner-alogical characteristics, the methodology consists of acid saturation of a powdered sample suspension by conventional batch equilibration, with a strongly cationic exchange resin in acid form, and potentiometric CEC determination by displacement of titratable acidity retained in samples with 1 N BaCl2solution at pH 8.1 (standard conditions or other concentration and pH previously selected). The exchange process was performed in an automatic ti-trator under standardized conditions, keeping the initial pH and concentration of the salt solution practically unchanged by automatically controlled addition of Ba(OH)2. It is applicable to all soils studied, including calcareous, gypsiferous, and saline samples, with a standard deviation (SD) less than 5%, permitting the CEC determination at different pH and ionic concentration using the same treated sample, and an automatic recording of the exchange process.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Using five Argentinian soils, we studied the ability of the Colwell, the Olsen and the Bray-1 tests to reflect four factors that affect the availability of phosphate. The four factors were: the amount and solubility of native P present; the amount of P added; the period of contact between soil and phosphate; and the capacity of the soil to retain P. Phosphate was added to the soils, and they were incubated at a range of temperatures for periods of up to 60 d.Appreciable native P was extracted from some of the soils, especially by the Colwell method. At zero added P there was, for one soil, a slight decrease in P extracted with increasing incubation. For the others there was little change. This contrasted with previous studies, which showed that, on prolonged incubation, these soils released phosphate to the soil solution. In most cases, the proportion of the added P extracted increased as the level of addition increased. This occurred even when there was no prior incubation. It was therefore due to a nonlinear sorption reaction despite the presence of the reagents rather than to a faster reaction at low levels of addition of P. The amount of P extracted from the soil decreased as the period and temperature of incubation increased. These effects of level of addition and of time and temperature were closely described by functions that described the increase with time of both the retention of added P and the amount of native P that was potentially extractable. The recovery of added P decreased as the capacity of the soil to sorb P increased. The effects of both time and P sorption were reflected differently by the different soil tests. The vigorous conditions of the Colwell test resulted in a smaller effect of both the period of incubation and of P sorption.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Phosphorus (P) sorption at equilibrium concentrations of 0.1–2 ppm in 0.01MCaCl2by 42 samples of highly acidic surface layers of Ultisols and Inceptisols from three major geomorphological regions of the Niger Delta of Nigeria, West Africa, conformed to the Langmuir isotherm. Langmuir sorption maxima and sorption at 0.2 ppm equilibrium P concentration ranged from 100–767 μ P/g soil and 30–240 fig μ P/g soil, respectively, indicating that the soil samples have low to medium P fertilizer requirements. No significant difference in sorption capacities among the soils of the three geomorphological regions or the two soil orders was noticed.Sorption capacities were significantly correlated with percentages of clay and silt, surface area, and different forms of Fe and Al, but not with pH or organic matter. Multiple regression equations relating P sorption to exchangeable Al, amorphous Al, amorphous Fe, and crystalline Fe are presented, and the relative contributions of these factors in the soils of the three geomorphological regions are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

We established a greenhouse study on five different Venezuelan soils to evaluate the external phosphorus (P) requirement of cowpea (Vigna unguiculata var. Tuy). The external requirement for the various soils was almost identical (approximately 1.00 μg/ml) and independent of edaphic factors, such as texture and mineralogy. The values differ greatly from those previously reported for the same species growing in a high P-fixing Hawaiian soil. We propose that pot effect, variety differences, and the presence (or absence) of my-corrhizal associations influence the differences between these external P requirements.The external P requirement of crops, in conjunction with P sorption curves, provides a rational basis for P fertilizer requirements. However, because the value is not a single-valued constant, affected by many biotic and abiotic factors, much more information should be accumulated before it can be widely recommended as a common fertilizing technique.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The high cost of15N-labeled fertilizers encourages the use of field plots having minimum size. If plot size is reduced too much, however, lateral movement of N near the plots by mass flow or diffusion within the soil or by translocation through plant roots can become a significant source of error in determinations of fertilizer N recovery. This study was initiated to assess the importance of lateral movement of labeled fertilizer when unconfined plots are used to determine recovery of fertilizer. Corn grain samples were collected at various positions inside and outside15N plots, and the15N contents of these samples were determined. The data were fit to mathematical models to estimate the extent to which lateral movement of fertilizer N caused errors in determined values of fertilizer recovery for the first, second, and third crops following fertilization. These models also were used to predict the plot size needed for similar15N-tracer studies in the future. The results of these studies indicate that15N plots having a size of 2 by 2 m are sufficiently large for determining recovery of fertilizer N for corn crops under most conditions. Where lateral movement of fertilizer N in soils is suspected to be a problem, we recommend collection of a few plant samples outside the15N plots as insurance against misleading conclusions concerning fertilizer N recovery.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Roots link all processes above and below the ground surface during plant growth. They are necessary to cover transpiration demands and define a sink term crucial to the determination of soil salinity and moisture distribution over depth.This paper presents a model to dynamically distribute root biomass over depth, so that water uptake rate is maximized. Biological factors affecting the morphology of the root system are also considered. The solute concentration profile is used for predicting osmotic effects on the behavior of the roots. The root growth works within the framework of a dynamic crop growth model that partitions biomass in root and shoot in a synergistic environment of depth-varying soil salts and moisture.A case study shows that soil salinity and irrigation practice can create a variety of observed root systems.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

This report describes a tensiometer designed to be used for soil water sampling. Variations in the design include a solenoid transducer tensiometer for monitoring metric potentials at depths in excess of 10.3 m and instrumentation to automatically re-circulate fluid in the tensiometer. The designs were evaluated to determine whether their response to matric flow was “soil-limited” or “tensiometer-limited,” as defined by Towner (1980). In a dry silt, the response time was soil-limited, but was tensiometer-limited in a wet silt and in a wet and dry sand. The effects of 11 mg/L of O2dissolved in 236 ml of water and a 2-mm-diameter bubble upon the response time, compared with an ideal fluid, was calculated. Only a dry silt with dissolved oxygen in the tensiometer fluid was found to be soil-limited; a wet silt and a dry and wet sand were tensiometer-limited. The response time was affected more by gas in the tensiometer fluid than by the measurement device (Bourdon gauge or pressure transducer).

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The presence of many organic industrial and agricultural chemicals in urban storm-water runoff has been documented in various reports. The purpose of this 3-yr study was to determine the nature and possible accumulation of organic pollutants in the soils of retention/recharge basins designed to manage and conserve urban storm runoff water in a semiarid climate.There was no evidence of the accumulation of organophosphorous pesticides in the soils of five study basins. Of the organo-chlorine pesticides tested, chlordane was usually detected in surface soils. The highest concentration of chlordane was 2.7 mg kg−1soil and decreased with depth to−1below 24 cm. DDT and DDE (mixed isomers) were not detected in any soil samples. Lindane was found only once in a turfed basin in the 0 to 2-cm depth at a concentration of 20 μg kg−1soil. Oil and grease and total phenols were usually detected at low concentrations that generally decreased with depth. Concentrations of 48 semivolatile priority pollutants were below their analytical detection limits. Analyses for 43 purgeable compounds were also below detection limits except for two organic compounds (toluene and methyl cyclohexane) found in one soil sample from one basin. The polychlorinated biphenyl—Arochlor 1260—was detected in four of seven surface soils at concentrations−1soil.The results of this study indicate that pollution of the soils beneath the cited urban runoff retention/recharge basins by organic compounds was insignificant with the possible exception of chlordane. There was no evidence of man-made organic compounds having an unfavorable impact on the plants in the basins or on the use of the turfed basins for recreation during dry summer months.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID