摘要:

The moisture characteristic and the unsaturated hydraulic conductivity are calculated from the measured water pressures at different depths in a soil core and the weights during evaporation at the top of the core. The measured water pressure is assumed to represent the mean pressure in a layer of a certain thickness, and the moisture characteristic is assumed to be described with sufficient accuracy by a polynom. The tangent of the polynom in each pressure interval is solved from a set of equations.Assuming the hydraulic conductivity-water pressure relationship can be described by an exponential relationship with varying constants in the different pressure ranges, the constants can be solved from measured water pressure at two depths and three sequential moments, and the rate of change in water content below some defined depth in the core during two sequential time periods.Up to ten cores can be handled at the same time. Measuring at a core can be started and stopped at any time. The water pressure at different depths is measured with one pressure transducer, connected with a scannivalve; the weight is measured with a straingauge load cell; and the data are recorded on a magnetic cassette tape. The recorded data are processed by a computer and stored on a magnetic disc.If the saturated conductivity is relatively high, a steady-state infiltration method is applied to determine the unsaturated hydraulic conductivity at high water contents.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The mechanisms of bonding of Mn2+, Cu2+, and VO2+in humic acid extracted from a mineral soil were investigated by electron spin resonance spectroscopy. The Mn(H2O)62+ion appeared to retain its inner hydration sphere upon adsorption, and was adsorbed at the organic surface by electrostatic attraction. Both Cu2+and VO2+entered into rigid surface complexes with oxygen ligands of organic functional groups, however, losing rotational mobility. The different bonding mechanisms of these transition metal ions are explained in terms of ligand field effects. No evidence of highly covalent metal-organic bonds was found.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The relation of potentially mineralizable soil nitrogen, No, to the oxidative release of NH4-N from soil organic matter during extraction with acid KMnO4was investigated, using 62 soils. Included in the study were members of 8 soil orders comprising 43 noncalcareous and 19 calcareous soils. Soils were extracted with 1NH2SO4solutions of 0.05 and 0.1NKMnO4(HOx) and with 1NH2SO4(H) alone for 1 h at room temperature, and amounts of NH4-N released were determined. The expression HOx - H denotes the quantity of NH4-N released owing to partial oxidation of soil organic matter. Later, a more direct and simpler procedure for determining oxidative NH4-N release was adopted, in which soils were preextracted with 1Nacid, and the soil residues were extracted with acidic KMnO4.Regression equations that may be useful in predicting Nofrom the oxidative release of NH4-N were developed. Amounts of NH4-N released by oxidation with 1NH2SO4solutions of 0.05 and 0.1NKMnO4, respectively, were approximately one-third and one-half of No. We conclude that the NH4-N was derived from oxidation of the soil organic N fraction most readily susceptible to biological mineralization.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The mineral composition of perennial plant species from widely separated sites in the Mojave Desert varied among sites, but variation between species was more pronounced. According to the nutritional status, species have been classified into different categories each of which includes species characteristically rich or poor in a given element. The close relationships between the nutritional status of these species and their sociological relations, as reflected by the principal component analyses, are evaluated. The frequency of correlation between the concentration of the different element pairs across the different species studied has been evaluated and discussed. Stress has been focused on Ca-Zn relations, with an 80 percent frequency of positive correlation. The causal factor or factors behind this high percentge of positive correlation frequency have been suggested. Linear correlation coefficients between plant composition and soil variables were also obtained.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The objectives of this study were to evaluate the effect of changes in soil pH on the plant availability of soil phosphorus and the interaction between Mn and Al accumulation and P response of tomato and corn plants.Yield response of tomato plants grown in pots to the level of P in soils was affected by soil pH. Plants in soils with pH values of 6.3, 6.7, or 7.2 produced maximum growth if the soil solution P level had been adjusted to 0.2 ppm. At lower soil pH values, 5.1, 5.3, and 5.7, yield increased up to 0.8 ppm, the highest solution P level employed; this yield, nevertheless, was still below that for higher pH values. By contrast, the effect of P fertilizer on corn hardly varied at different pH levels.Evidence of Mn and/or Al toxicity on tomatoes is presented. Apparent toxicity was lessened by high levels of P. A threshold toxicity level of 450 ppm Mn in tomato tops is proposed.Soil P solubility as measured by phosphate sorption isotherms did not change over a range of soil pH between 5.1 and 7.2.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

An abandoned feedlot was cropped to corn (Zea maysL.) and alfalfa (Medicago sativaL.) to prevent excess buildup and deep percolation of NO3-N from the organic and NH4-N accumulations from the feedlot operation. To eliminate part of the N and salt accumulations, 15 cm of surface material was removed from half the plots and replaced with field soil. Alfalfa production was 14.1 and 11.8 metric tons/ha, and corn forage production was 8.0 and 6.7 metric tons/ha, from the intact surface and removed surface treatments, respectively. Nitrogen uptake was two and one-half to three times greater for alfalfa than for corn, which was reflected by the NO3-N content of the respective soil profiles. Nitrate-N content of the corn forage exceeded 2000 ppm (above the acceptable limit for livestock consumption), whereas the alfalfa averaged only 857 ppm, which would allow using it as a feed without ensiling. Nitrate buildup in the soil profiles was greater when the surface material remained in place; our results indicated that with proper cropping, however, either method would prevent excess NO3-N accumulation.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The relation of potentially mineralizable soil nitrogen, Noto hydrolytic and oxidative release of NH4-N from soil organic matter by extraction with alkaline permanganate was investigated using 62 soils representing several major agricultural regions in the United States. The NH4-N was recovered by steam-distilling 1-g samples of soil during extraction of 4 min with several concentrations of NaOH and KMnO4in different combinations. The same concentrations of NaOH and KMnO4, were used to determine amounts of NH4-N released by hydrolysis (B) during steam distillation. Oxidative release was estimated as the difference between total NH4-N produced during alkaline permanganate extraction (BOx) and that derived by NaOH distillation. These NH4-N fractions were determined using inital NaOH concentrations ranging from 0.25 to 0.625N, alone or with amounts of KMnO4ranging from 0.032 to 0.5 g/10 ml of extractant. For all combinations of NaOH and KMnO4, the correlation coefficients relating B and BOx consistently were high (r= > 0.9). Correlations between the independent variables B and (BOx - B), ranged fromr= 0.17 to 0.90. Multiple regressions of Noon B and BOx were associated with coefficients of multiple correlation, R, that were relatively constant (generally, 0.8 to 0.9), despite the diversity of reagent concentrations used for extraction. THese and other considerations indicate that the NH4-N released by NaOH hydrolysis (B) and by KMnO4oxidation (BOx - B) was derived, in large part, from the same soil organic sources (e.g., amides, amines, amino acids, and amino sugars). With few exceptions, correlations of Nowith BOx were as good as, or better than, simple correlations of Nowith B or (BOx - B). Thus, the extra effort required for separate NaOH and NaOH-KMnO4extractions would not appear to be justified. The alkaline permanganate methods thus far reported by various investigators, as well as modifications evaluated in this study, offer a less precise and reliable basis for predicting Nothan does acid permanganate extraction for measuring oxidative release of NH4-N.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID