摘要:

Twenty bulked soil samples will define the average pH of 1 ha of a soil type. Air-drying shortly after collection is needed to prevent development of acidity during moist storage. Determining pH in the clear supernatant of a mixture of 0.01MCaCI2and soil shaken for 1 h gives highly reproducible values that are a good estimate of field pH. Threefold changes in sampling volumes had a very small effect on variance, so sample size does not strongly influence the error associated with sample collection.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

We studied clay mineralogy and differences in oxidic ratio and CEC of selected low-activity clay soils in temperate and tropical regions. Samples were collected from six Ultisols in Georgia (Bradson, Cecil, Davidson, Decatur, Greenville, and Madison soils). Two Oxisols (Cibinong and Sitiung) and four Ultisols (Ciomas, Jasinga, Jonggol, and Kedunghalang soils) were sampled in Indonesia. The samples from A, Bt, and B horizons were analyzed for CEC by the NH4OAc and NH4Cl methods, effective CEC (ECEC), and oxidic ratio ((extractable Fe2O3% + gibbsite%)/ clay%). Clay mineralogy was studied by x-ray diffraction (XRD), and gibbsite concentrations were measured by differential thermal analysis (DTA). Iron oxide was extracted from the soils by the dithionitecitrate-bicarbonate (DCB) procedure, and the concentration was determined in the extract by atomic absorption spectroscopy. The results indicated that the Bt horizons of the soils in Georgia had values for CEC(NH4OAc) and ECEC ranging from 14.7 to 28.9 and 8.1 to 11.9 cmol(+)kg-1clay, respectively. With the exception of the Decatur soil, the oxidic ratio of the Bt horizons of the Georgia soils was >0.20, which could qualify them for placement in the oxidic mineralogy class, provided their quartz content would support it. The Davidson soil, especially, exhibited CEC and ECEC values within the requirement limits for both kandic and oxic horizons. These chemical properties were related closely to the clay mineralogy, which was composed of large amounts of kaolinite and especially gibbsite. Some hydroxy-A1-interlayered clays were also detected. In comparison, the Bt and B horizons of the soils in Indonesia, with oxidic ratios <0.20, were less oxidic in nature. On a soil basis, the Indonesia soils were generally higher in CEC values than the six Georgia soils. These differences in chemical characteristics were attributed to a variation in soil mineralogy, indicating the absence of quartz and considerably lower amounts of sesquioxides, but larger kaolinite contents, in the Indonesian than in the Georgian soils.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

In a study of soils from a chronosequence in southern New Mexico, where CaCO3accumulation is primarily derived from aeolian input, P adsorption was greatest in the most highly calcic horizons and least in horizons of clay and oxyhydroxide accumulation. Similarly, adsorption capacity was most highly correlated with CaCO3content. Iron and Al oxyhydroxide contents increased with increasing soil age, and absolute levels were as high as in calcareous soils developed in more humid conditions. Calcium carbonate appears to be the primary geochemical agent capable of the fixation and retention of P within the soil profile in this ecosystem.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

We investigated the effects of three intervals (5, 10, and 20 d) and four total amounts of irrigation water (120, 240, 360, and 480 mm) applied at two rates (3 or 6 mm/d)3on intermittent evaporation, soil moisture distribution, and salt redistribution through saline-sodic clay soil columns with initial zonal distribution of salts. The results indicated that after a threshold period, which was longer for the lower rate of water application, cumulative evaporation (E) increased with decrease in irrigation interval. In accordance with previous findings,Ewas a linear function of the square root of time, i.e.,E=ct, wherec, under the experimental conditions, is largely determined by the amount of water applied per irrigation. The transmission zone of the moisture distribution profiles lengthened and the wetting front advanced deeper, and consequently salt leaching improved as time progressed and as the irrigation interval and the amount of water applied increased. The sodium adsorption ratio profiles qualitatively followed the electrical conductivity, EC1:5, redistribution patterns. The depth of the wetting front and the amount of the water stored accounted for 97.4 and 96.8% (r.001= 0.872) of the variability of the depth of the desalinized zone, respectively. The amount of the stored water accounted for 68% (r.01= 0.765) of the variability of the weighted mean EC1:5of the desalinized zone.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Nitrogenase activity and population dynamics of isolated free-living aerobic bacterial diazotrophs enriched from soil were monitored upon salt addition after 3 to 24 d of preincubation. Three series of salt treatments were employed in this study: (1) KCl, NaCl, CaCl2, and MgCl2varying from 0 to 30 meq/100 g soil or 100 ml medium, (2) three anionic forms, Cl-, CO32-and SO42-combined with K+, Na+, Ca2+, and Mg2+upon single addition (10 meq/100 g soil or 100 ml medium), and (3) different combinations of salt mixtures (homocationic and heteroionic) at the same single addition. In all cases, the applied salts inhibited diazotroph numbers; however, survival was evident even at the highest salt levels. The intensity of inhibition was higher in the salinized culture medium than in soil. Nitrogenase activity, as determined by acetylene reduction, followed a similar pattern as the cell densities of diazotrophs in the salinized soil. The extent of inhibition in regard to cell population density and nitrogenase catalysis was as follows: (1) among the Cl-salts, CaCl2> KCl > NaCl > MgCl2; (2) coion treatments, CO32-> Cl-> SO42-with the degree of inhibition varying with accompanying cations, Mg2+being the least inhibitory; and (3) combination of salt mixtures (homocationic) Cl-plus CO32-> SO42-plus CO32-and (heteroionic) Na2CO3plus CaSO4being the most inhibitory, and MgCO3plus K2SO4being the least.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

In laboratory trials I tested the efficacy of FeSO4·7H2O (0.05, 0.1, 0.2, 0.3, and 0.5% Fe2+) alone and in combination with polyacrylamide (0.05, 0.10, and 0.2% PAM) and urea formaldehyde (0.50 and 0.75% UF) as soil conditioners in light-textured soils. Four soils varying in texture from sand to silt loam were used in the study.Individual application of FeSO4had no effect on dry aggregation (<2-mm diameter). However, sand aggregation with PAM and UF was enhanced with the prior application of FeSO4; the effect was greater with PAM.Applications of either FeSO4or UF alone were effective only in improving the water stability of aggregates <2 mm in diameter. For increasing the stability of aggregates <8 mm in diameter, a combined application of FeSO4and UF was needed. The combination of FeSO4and PAM was also more effective in stabilizing aggregates of sand <8 mm in diameter than PAM alone, except in alkaline sand. Nevertheless, the beneficial effect of FeSO4on aggregate stability was higher with UF than with PAM. A new index of soil aggregation, called thestability quotient, is proposed and discussed.In general, a treatment of 0.3% Fe2+plus either 0.75% UF or 0.1% PAM was quite effective in aggregating light-textured soils. Without FeSO4, 0.2% PAM was needed to give the same results, and UF was completely ineffective as a soil conditioner.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Organic matter can accumulate in surface soil when reduced tillage methods are used. This in turn can influence the plant-availability of micronutrients. This paper reports an incubation study carried out to determine the effects of organic matter and micronutrient addition (Mn, Cu, and Zn) on the distribution of Mn, Cu, Fe, and Zn among soil fractions. Eight topsoils were treated with 0, 20, and 50 g/kg of ground straw and none or one level of the above combined metals. After 5 mo, soils were extracted sequentially to determine metals in the exchangeable, organic, Mn oxide, amorphous Fe oxide, crystalline Fe oxide, and residual fractions. Metals were also extracted using Mehlich 1, Mehlich 3, and DTPA.Increasing organic matter caused Mn and Fe to move from the less soluble forms to more plant-available forms (exchangeable and organic). Oxidation-reduced effects are the probable mechanism of this movement. Copper was not affected significantly. Increasing organic matter caused Zn to increase in the Mn and Fe oxide fractions at the expense of the Zn in the other fractions. Released Zn may have been occluded in these fractions or been strongly adsorbed. Added metals were evident in the exchangeable and organic fractions. Metals extracted with Mehlich 3 increased with increases in organic matter, but the other extractants did not consistently show this pattern. Correlations between metals in the fractions and that extracted by the extractants showed that the soil test extractants were solubilizing the metals from the exchangeable and organic fractions. These results demonstrate that accumulated organic matter near the soil surface can increase plant availability of Mn and Fe and possibly decrease the availability of Zn by causing a redistribution of elements between soil fractions.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

The author found liquid contrast media suitable for x-ray radiography on soil pore structure. A method of infiltrating a contrast medium into a soil sample was also investigated. As a result, it became possible to observe the macropores in a 4-cm cube of a soil sample stereoscopically. The procedure for this new method is introduced in this paper, and the stereoradiographs of macropores in several Japanese soils obtained by this method are shown. The following conclusions are derived from the stereoradiographs of the 4-cm cube samples: (1) the minimum pore diameter recognizable in the radiographs is around 50 μm; (2) because this method reveals macropores by infiltrating liquid contrast media into the soil sample, the results of radiography mainly show images of continuous macropores. These images show the important pores that contribute to water percolation and aeration and somewhat to water retention in the soils; (3) the structure of continuous macropores in a soil where plants have grown is very similar to the configuration of the root system of the plants. That is, the macropore structure is characterized by channel networks composed of tubular pores.

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1988

数据来源: OVID