ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

A batch equilibration study evaluated the influence of naturally occurring low-molecular-weight mono- and diprotic aliphatic acids on the rate of Al and SO42−release in a Cecil soil (Typic Hapludult). We adjusted the pH of the organic acids (OAs) and of the soil suspension (3.8% w/w) to pH 4.0 and allowed them to equilibrate thermally before the experiment. After rapid addition of OAs to the soil suspension, we took solution samples at various time intervals and analyzed for Al, SO42−, and OA concentration. The initial concentration of OA in suspension was 1 × 10−5mol liter−1. Both Al and SO42−release followed pseudo-first-order kinetics, whereas OA adsorption obeyed simple first-order kinetics. The rate of Al release (k1) was more rapid for the diprotic OA treatment (20.4 × 10−8mol s−1), as was SO42−release (1.63 × 10−8mol s−1), compared to the monoprotic OA treatment. The rate of Al release varied inversely with OA chain length and the distance between - COOH functional groups. The addition of substituent - OH groups between the - COOH groups further reducedk1. A similar trend was observed for the rate of SO42−release (k1) into solution. Monoprotic OAs were more rapidly adsorbed to the particle surfaces than were diprotic OAs. We postulate that removal of Al and SO42−from solution occurs via selective mineral precipitation.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

This study had two principal objectives. The first was to evaluate the Kelowna and EDTA- and DTPA-modified multiple-element extractants for determining available P in acid and calcareous soils. The second was to determine the relevance of some associations between plant and test data for evaluating extractants. To achieve these ends, we evaluated the precision of relationships between extracted soil P and relative yield, tissue P concentration, and P uptake data by means of regression, correlation, and graphing techniques. Three ryegrass cuts were gathered on 41 soils-30 with pH < 7.0 and 11 with higher values to 7.9-to obtain data. Available-P levels in soils ranged from 9 to 96 μg of P per ml of soil (Kelowna); these produced relative yields, without P fertilization, of 44 to 97%. Average tissue P concentrations varied between 0.20 and 0.52%. Relationships between available P and relative yield, or tissue P, data were generally curvilinear and linear, respectively. Available-P values determined with the Kelowna and KEDTA solutions were as precisely related to relative yield and tissue plant data as values obtained with the Mehlich II & III, Olsen, and KDTPA-solutions. However, soil test values collected with two new solutions, consisting of 0.25NHOAc and either 0.001MEDTA (AAEDTA) or 0.005MDTPA (AADPTA), were more precisely related to yield. These solutions may provide more reliable estimates of crop response to P fertilization. The merits of various approaches of evaluating test procedures for determining available P are discussed in the text.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Using first-order kinetics we describe the release of nutrients by coated slow-release fertilizer (SRF). Plotting the logarithm of the concentration of intact fertilizer in the soil [log(Q0-Qt), whereQt, is the amount applied andQt, is the amount released at timet] versus the time yielded a straight line, as predicted. The rate constants of SRF release at different temperatures are linearly related to the water vapor pressure:K=A·Pw+BwherePwis the vapor pressure andAandBare constants.We conclude that the rate-determining step in the nutrient release out of SRF is the migration of vapor from the soil into the fertilizer granule. The very mild effect of soil moisture on the rate of nutrient release is consistent with the proposed mechanism. We discuss the possibility of predicting nutrient release from SRF using the derived relationships.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

To clarify the effect of the heat wave that accompanies the passage of a fire on some chemical parameters related to soil fertility and plant growth, we subjected two soils, classified as a sandy loam and a silty clay, respectively, to artificial heating under controlled conditions. We arranged the heating program according to the true thermal reactions occurring in the soils, which were previously detected by differential thermal analysis. The heating of soils had a variable effect on pH, with a decrease up to 220°C and a sharp increase after 700°C. Heating produced a continuous decrease of the cation exchange capacity (CEC) in both soils. The effect of the heat on organic matter content, total nitrogen, and organic phosphorus was similar, with a little decrease up to 220°C; beyond this value the organic matter was burned up, the total nitrogen was volatilized, and the organic phosphorus was mineralized and transformed into the inorganic form. N-NH4, on the contrary, increased up to 220°C and then decreased very sharply; at 460°C it was barely detectable. Similar behavior was shown by the available P, which peaked at 460°C. Water-extractable cations showed various behaviors. Ca increased to a peak at 220°C; after a decrease at 460°C Ca increased drastically at 900°C. Mg showed an increase to a peak at 220°C followed by a continuous decrease to complete unextractability at 700° and 900°C. K extractability increased progressively, with a maximum peak at 700°C. The extractability of Na increased to a maximum at 220°C and then decreased continuously to a very low level at 900°C.Heating to 170°C had no effect on plant and root growth and dry matter production. On the contrary, heating to 220° and 460°C, respectively, improved plant height and dry matter production of both tops and roots but not root extension. Further heating at 700° and 900°C resulted in a reduction in plant height, root extension, and dry matter production.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We measured aggregate stability index and particle size on three fields differing in tillage regime. Field I was conventionally tilled, Field II was in transition between conventional and nontillage regimens, and Field III was in native pasture. We studied the spatial distribution of aggregate stability index and particle sizes using variography, kriging, and cokriging. With weighted least squares we fit variogram and cross-variogram models to experimental variograms and then determined the best models by the leaving-one-out method (“jackknifing”) of cross-validation.Using the average estimation variance as a criterion for comparison, we found that cokriging is only minimally better than kriging as an interpolator. Cokriging performed better when the covariables were highly correlated. Aggregate stability index was not correlated to texture in field I and was only slightly correlated with silt and clay in field III.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We studied the particle size distribution of the sandy fraction separated from the horizons of an Oxisol-Spodosol sequence in Amazonia (Brazil). All of the soils have developed from the same parent material, but great contrasts occur among the end members of the sequence. Oxisols are 10 to 20% sand, whereas Spodosols are 90% sand. In spite of very different pedogenetic pathways the sandy fraction shows the same particle size distribution in Oxisols as in Spodosols.A simulation with a computer makes it possible to understand this better. The same particle-size-distribution curve may be obtained either by means of a strong dissolution, leading to a loss of more than 50% of quartz sand, or by a moderate fragmentation (no loss of sand), which is in fact linked to the dissolution process. We conclude that particle-size-distribution curves of sand are not an adequate test in tropical soils.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Soil solution compositional analysis is widely used to evaluate plant growth response and environmental fates of chemicals, but little is known regarding the influence of sample storage techniques on the composition of displaced soil solution. We conducted this research to determine the effects of time of incubation (storage at room temperature) on soil solution composition of Ultisol Ap and B horizons that had been maintained field-moist or had been air-dried and rewet. We analyzed soil solutions displaced immediately after soil sampling or over a 32-day period of incubation for pH, electrical conductivity, dissolved organic carbon, and total concentrations of SO4, Cl, NO3, Ca, Mg, K, Na, Si, and Al. Soil solution composition was frequently influenced by the interaction of sample treatment (field-moist versus air-dried and rewet) and time of incubation. The effects of sample storage were most pronounced in A horizon samples, where higher organic C and microbial activity resulted in greater variation in soil solution composition in comparison to soil solutions from B horizons. It is difficult to identify any one combination of sample treatment and time of incubation which most closely corresponds to the composition of soil solution obtained immediately after sampling. Samples stored field-moist and displaced after 2 or 4 days of incubation, however, seemed to result in the most consistent composition for the bulk of components determined. The variation in soil solution composition anticipated as a result of sample storage should be recognized and carefully dealt with when soil solution composition is used as a diagnostic measure.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

The topography of the Appalachian region strongly influences the environment for plant growth. We conducted a field study in 1984 and 1985 on a Gilpin silt loam soil association in Preston County, West Virginia, to determine soil and environmental factors controlling corn (Zea maysL.) yield differences among landscape positions. Four plots were established at each of nine locations including summit, shoulder (N, E, S, W aspects), and backslope (N, E, S, W aspects). Athough common management practices were used throughout the field, silage, yields (65% moisture) were 15.3 to 43.0 Mg/ha in 1984 and 22.2 to 36.6 Mg/ha in 1985. Grain yields (15% moisture) were 3.1 to 8.2 Mg/ ha in 1984 and 4.0 to 7.6 Mg/ha in 1985. Poor silage and grain yields were associated with higher clay content and lower organic C in the A horizon, lower plant “available water” in the 0− to 15-cm depth interval, and possible subsoil acidity problems. Mean “available water” as represented by the difference between gravimetric water determined over time and water retained at 1500 kPa was a good predictor of silage yield. Soil water was apparently the most important factor controlling corn production differences in this study. The ability to predict soil water relationships on the landscape would hasten the development of successful agronomic management practices for the hilly Appalachian region.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

The topography of the Appalachian region strongly influences the environment for plant growth. We conducted a field study in 1984 and 1985 on a Gilpin silt loam soil in West Virginia to determine soil and environmental factors controlling corn (Zea maysL.) yield differences among landscape positions. Four plots were established at each of nine locations including summit, shoulder (N, E, S, W aspects), and backslope (N, E, S, W aspects). Although common management practices were used throughout the field, corn yields varied significantly among positions. Mean “available water”as represented by the difference between gravimetric water determined over time and water retained at 1500 kPa (Kilopascal) was the most important factor controlling corn production.The objectives for this study were to determine the relationships between soil physical properties, surface curvature, and precipitation catch on the distribution of soil water, with emphasis on the surface layer (0–15 cm depth). Available water was always lower at the backslope sites than at summit or shoulder sites. Higher clay content and lower infiltration capacity were associated with lower available water. Precipitation catch differences strictly followed the same pattern as available water between shoulder sites and summit. A cokriging analysis indicated that surface curvature may be useful for spatial representation of available water throughout the study site.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID