摘要:

A drainage experiment was conducted to determine the time-dependence of soil-water retention during drainage of a quasi-uniform column of Lakeland sand and similar columns to which phosphatic clay was added as an amendment or a layer. Phosphatic clay was observed to increase and prolong water retention in the soil. Saturated hydraulic conductivity of the column with soil amended with 5 percent phosphatic clay in the surface 30 cm was 13 cm/hr as compared to 25 cm/hr for the quasi-uniform column of Lakeland sand. Drainage from the column with a 1-cm-thick layer of phosphatic clay and the column with a 2-cm-thick layer of phosphatic clay aggregates was greatly restricted. The nonaggregated phosphatic clay layer provided nearly constant impedence to flow across the layer, whereas successive water desaturation of the larger pores in the layer aggregates resulted in a time-dependent impedence to water flow. At saturation the hydraulic conductivities of the aggregated and nonaggregated clay layers were calculated to be 5.0 and 0.8 cm/hr, respectively. Maximum hydraulic head gradients across the aggregated and nonaggregated clay layers were 4 and 13, respectively. Values of unsaturated hydraulic conductivity calculated from soil-water characteristic curves for the Lakeland sand and measured water-saturated hydraulic conductivity were in good agreement with values measured experimentally from the soil columns.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The weathering of hornblende, augite, phlogopite, muscovite, albite, and andesine as influenced by exchangeable cations Ca, Mg, K, Na, NH4, Al, and H was studied for two years under laboratory conditions. Portions were analyzed for mobilized Ca, Mg, Na, K, Fe, and Al after the first and second years. Since the weathering products were accumulated, equilibrium conditions were almost reached during the first year, causing a retardation of the weathering process during the second year.The weathering was accompanied by a consumption of H ions which substantially increased the pH of the H- and Al-saturated samples. There were great differences between the minerals as to the pH increase and the pH values recorded at the end of the experiment. After two years H-saturated hornblende had a pH of 8.2, while H-saturated muscovite was still acid with a pH of 4.4. In the case of H-saturated augite and andesine, the pH increases exceeded two pH units at the end of the experiment, but for H-saturated muscovite the pH increase was only 0.5 pH units.Contrary to the other ions studied, extractable amounts of Al and Fe were found to decrease during the second year. The reason is supposed to be precipitation of hydroxides, followed by a gradual recrystallization to more resistant compounds of the type gibbsite and goethite, respectively. Hence, it is not possible to estimate the total mobilization of these ions.The release of the base cations Ca, Mg, K, and Na in relation to the total amounts present has been used as an index of stability. Based on the release from initially Ca-, Mg-, K-, and Na-saurated samples, the following stability sequence could be arranged: Hornblende < Augite < Albite < Muscovite < Phlogopite < Andesine.In the case of hornblende and augite as much as 3 and 2 percent, respectively, of the total content of base cations were mobilized during two years of weathering.No consistent specific effect on the weathering by the exchangeable Ca, Mg, K, and Na was found.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Results of a field experiment comprising soil application of elemental sulfur, ferrous sulfate, and gypsum, along with a control and foliar sprays of 0.1 percent H2SO4, FeSO4, sequestrene 138-Fe, MnSO4, and ZnSO4along with no spray showed that soil application of 250 kg/ha of elemental sulfur and foliar sprays of H2SO4and FeSO4increased cowpea yields by 38.0, 32.6, and 33.4 percent, respectively. The increase in grain yield of cowpea was associated with the increase in leaf contents of sulfur, nitrogen, and a, b, and total chlorophyll. Soil application of gypsum or FeSO4was only 82 percent as effective as elemental sulfur. The results show that chlorosis in cowpea does not represent any deficiency of iron or other micronutrient, and that it is on account of low supply of active sulfur. Since yield increases with soil application of elemental sulfur and foliage application of 0.1 percent H2SO4or FeSO4are of the same magnitude, an application of H2SO4is recommended to prevent chlorosis and increase crop yield of cowpea as the treatment is almost costless. The beneficial results of FeSO4, MnSO4, ZnSO4, etc., reported in the past seem to be on account of inadvertent supply of sulfur and/or low pH of salt solutions which jointly increase physiological availability of iron at the site of biosynthesis of chlorophyll.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Methylated and unmethylated hexane and ether extracts of raw humus were oxidized by potassium permanganate at pH 9–10. Methylated ether extract gave 6 benzenecarboxylic acid methyl esters, 6 methoxy-benzenecarboxylic acid methyl esters, 3,4-dimethoxy-benzoic acid methyl ester, and 6 dicarboxylic acid dimethyl esters among other products. No methoxy or dimethoxy derivatives were found after oxidation of unmethylated hexane or ether extracts or methylated hexane extract. These extracts gave benzenecarboxylic acid methyl esters and dicarboxylic acid dimethyl esters. All extracts yielded fatty acids; the hexane extract was found to contain 17 percent and the ether extract 11 percent of straight chain fatty acids, free or esterified. For both extracts the molar distribution of the acids, C12-C33, was approximately the same, with C24and C22dominating. Both extracts yielded significant amounts of 1(a),3(a)-dimethylcyclohexane-1(e),2(e),3(e)-tricarboxylic acid trimethyl ester by oxidation. 1(a),3(a)-Dimethyl-2(e)-carbomethoxymethyl-cyclohexane-1(e),3(e)-dicarboxylic acid dimethyl ester was also found from the ether extract.A number of the compounds isolated have also been found after oxidation of other humic fractions, thus indicating a certain similarity in composition between especially the ether extract and these fractions. Compared to the other humic fractions the ether extract, and even more the hexane extract, yields a significantly higher amount of aliphatic structures.It is concluded that the resinous part of the ether extract contains little and the hexane extract none of the condensed phenolic structures usually present in soil organic matter. Both extracts contain cyclic aliphatic systems, probably of the abietic acid type or transformation products of this type of compound. The results indicate that both extracts also contain aromatic rings substituted or linked together by aliphatic chains of the length 6–8 CH2units.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Laboratory studies were performed to see the effect of initial soil moisture content, method of placement (spread on the soil surface or mixed in the entire soil), and nature of amendment (gypsum or calcium chloride) on the extent of precipitation of soluble carbonates and changes in soil properties of a highly sodic soil upon leaching. The results showed that when gypsum or calcium chloride were mixed in the entire soil, all the soluble carbonates were precipitated but only a small portion of the soluble carbonates were precipitated when the soil was leached after surface application of the amendment. For this reason also, the exchangeable calcium content and the soil hydraulic conductivity were improved to a greater extent in the case of surface application treatment when the amount of amendment applied was reduced to half compared to the treatment where the amendment was mixed in the entire soil. The results have been discussed to suggest that for the determination of gypsum requirement of soils containing soluble carbonates, the latter should be eliminated by washing with 20 ml of 60 percent ethanol prior to the determination by following Schoonover's procedure.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The feedback effect of plant residues on soil organic matter is of current interest in many agricultural systems due to recent large increases in crop yields.Computer-based numerical methods which fit differential equations to data allow the plant yield-soil organic matter relations in crop sequential experiments to be examined more fully.The equationdN/dt = -K1(t)*N+K2+K3(t)*Y(t) whereNis soil organic nitrogen,Y(t) is plant yield at timet, K2is a constant noncrop addition term, andK1(t) andK3(t) are decomposition and addition crop coefficients which vary with the stage of the sequential experiment, has been fitted to soil and plant yield data from the Morrow and Sanborn plots. Coefficients of the above model and three restricted variants of it were estimated by least squares, using soil nitrogen and crop yield data over 50 to 63 years. Statistical comparisons of the models were also made.From the equations the relationships between equilibrium soil levels and crop yields were calculated and the feedback effect of increasing crop yield on soil nitrogen level was estimated.At Morrow, increasing corn yields in a continuous corn system had negligible feedback effects on soil N level. However, some feedback effects were shown by oats and clover.At Sanborn, oats had the greatest feedback effect of the four crops examined. In this experiment timothy had the least feedback effect.Manure in both experiments substantially increased soil equilibrium levels.The value of quantitative estimates of feedback effects and the need for additional soil data in understanding changes in agricultural ecosystems are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Atriplex confertifolia(Torr, Frem.) Wats. seedlings were grown in soil irrigated with different salt levels. Maximum yields were obtained with a 50 me/liter NaCl treatment. Higher salt levels produced large, succulent leaves showing symptoms of nitrogen deficiency. Physiological effects of salt were noted as decreased chlorophyll, soluble protein, and nitrate and loss of nitrate reductase activity. Salt also reduced the uptake of Mg, K, and P. Net carbon assimilation rates were reduced presumably from salt-induced increases in respiration. Leaf water potential was decreased greatly by the salt levels, but transpiration levels at leaf temperature of 20°C did not correspond in that they were quite insensitive to salt levels. At 30°C, transpiration rates decreased with increasing salt indicating an improved water use efficiency.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Potentiometric and counter-ion adsorption techniques were used to study the effects of pH, electrolyte concentration, and phosphate treatment on charges associated with a Typic Gibbsihumox and a Typic Hydrandept. The methods did not agree on either the isoelectric points or the net charges associated with the soils. Furthermore, neither method provided data at pH 7 that are close to those obtained during routine cation exchange capacity determinations. The Gibbsihumox fit the definition of a constant surface potential colloid in terms of the combined Nernstian-Stern theory treatment better than the Hydrandept did. The latter fit the definition well when its surfaces acquired larger magnitudes of negative charge due to KH2PO4treatment.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Several mathematical models have been developed to describe water uptake by plant root systems. These models usually incorporate one or more of the assumptions that water is proportional to rooting density, to soil hydraulic conductivity, and to the water potential difference between the root surface and that in bulk soil midway between two adjacent roots. An experiment was conducted with cotton (Gossypium hirsutum) at the Auburn rhizotron to test the validity of these three assumptions. Soil water potential, soil hydraulic conductivity, water uptake, and rooting density were measured or estimated as functions of soil depth and time. Average plant water potential for a water extraction period was estimated from pressure chamber and continuous stem diameter measurements. The assumption that water uptake is proportional to rooting density was valid. However, there appeared to be a large resistance in the pathway from root epidermis to root xylem. The other two assumptions must be modified to include this resistance. Therefore, water uptake was proportional to the water potential difference between root xylem and bulk soil and to the hydraulic conductivity of the combined soil-root pathway. There was no depth-of-roots effect on the validity of these relationships.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The gamma density probe is a useful instrument for measuring water content in small volumes of soil. Essentially, the gamma probe measures the density of the soil and water between a source and a detector. To transpose the gamma densities into water content, the dry bulk density of the soil is needed. A nondestructive method for estimating dry bulk densities for use with the gamma probe is proposed. The procedure is based on the assumption that water content values in a field dry condition were more stable than the dry bulk density values and could be transferred from one point to another. The procedure was successfully used on three areas in Reynolds Creek Experimental Watershed in Southwest Idaho.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID