Soil Science

KAMINSKY, RAY ; MULLER, WALTER H.

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A new technique for extracting potential phytotoxic materials from soils is presented and discussed. This technique features the use of water and a chelating agent (Na2EDTA at pH 7.5) as the primary levers of extraction, and, therefore, avoids the use of denaturing alkaline conditions. Stress is placed on extraction mechanisms that accord with the natural circumstances governing the basic ecology of plant and soil systems. Thus, availability, with respect to the uptake of organic soil compounds by plants, is discussed, as is a recommendation for sampling soil at the time these compounds are introduced. The application of the above to the study of allelopathy is discussed.

MULLER, R. N.; TISUE, G. T.

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A modified elutriation procedure is described for the physical separation of soils and sediments based on particle size. The size distribution of fractions obtained by this method is directly verified and indicates that acceptable separation of silts and clays may be obtained. Studies of plutonium distribution with particle size indicate that the greatest concentrations are in the smaller size classes, which are most subject to erosional transport.

SAEED, M. ; FOX, R. L.

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Four acid soils from Hawaii and three calcareous soils from Pakistan were used to study the effect of suspension pH on Zn solubility. The soils, at different pH values, were equilibrated with added Zn for 6 days at 25°C. After equilibration, Zn concentrations in the supernatants were determined by atomic absorption spectrophotometry. The effect of suspension pH was quantitatively evaluated by plotting the negative log Zn in solution (pZn) against pH. A linear relationship was observed up to pH 7.0 for acid soils. As the system passed neutrality, a general increase was noted in the amounts of Zn in solutions for the soils high in organic matter. The increase in Zn solubility over the alkaline range was assumed to be due to dispersion of organic matter, which either released complexed Zn or provided chelating agents for added Zn and reduced adsorption or precipitation.

REHM, G. W.; SORENSEN, R. C.

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Several researchers have determined the effect of direct application of N to soybeans with conflicting results. This study was designed to allow measurement of the residual effects of repeated applications of fertilizer to previous corn crops on soybean yields. Treatments, including row spacings, plant populations, and rates of N and P for corn, were repeated from 1968 through 1972 on a Judson silt loam. Soil samples to a 180-cm depth were collected in the fall of 1972 and analyzed for NO3--N and acid-soluble P. Inoculated soybeans were then planted in 1973.

ELSEEWI, AHMED A.; ELATTAR, H. A.; DAOUD, A. M.

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Soluble Na, expressed in terms of sodium adsorption ratio, SAR, and its relationships to exchangeable sodium ratio, ESR, and to exchangeable sodium percentage, ESP, were examined in 31 surface soil samples from the Nile Delta. Empirical equations for SAR-ESR and SAR-ESP relationships were developed and compared to those obtained by the U.S. Salinity Laboratory Staff and by Bower. Excellent agreement was observed between all equations employed and between them and the actual data. Proportions of exchangeable sodium predicted by the U.S. Salinity Laboratory equations were, however, lower than the observed values at the low and at the high levels of SAR. The difference was, nevertheless, within 5 units of ESP, and does not seem to impair the validity of the SAR concept.

SALARDINI, A. A.; MURPHY, L. S.

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Effects of Fe sources, levels of added Fe, and incubation time on the availability of micronutrients in a slightly acid (normal) and a calcareous (Fe-deficient) soil were determined. Twenty, 40, and 80 ppm Fe, as Fe-EDDHA,1Fe-PF, and Fe-LS, were mixed with soils and incubated at field capacity at room temperature. DTPA extraction of soil samples collected at 1,2,4, and 8-week intervals indicated that, in general, proportional Fe recovery decreased with increasing Fe application. After 8 weeks, Fe recovery from Fe-EDDHA applied to the normal soil at rates of 20, 40, and 80 ppm Fe was 46, 34, and 21%, respectively. Iron retention by the soil increased with time, and was higher in Fe-deficient soil than in normal soil. Iron-EDDHA was found to be the most stable compound in both soils. Iron-PF was more stable in Fe-deficient soil than Fe-LS, and the reverse was true in the normal soil. Extractable Mn increased with increasing Fe application. Extractable Zn and Cu varied with soil and source of Fe. Iron-LS produced the highest increase in extractable Cu and Zn; Fe-PF increased Mn, but Fe-EDDHA had little or no influence on extractable soil micronutrients. The results generally suggest that Fe-EDDHA has a superior efficiency to Fe-LS and Fe-PF in both soils. The results also confirm the suitability of DTPA as a soil extractant for available Fe.

BARKER, S.

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From the results of 123 field experiments conducted in the major beet-growing areas of Turkey, the Mitscherlich-Bray calibration equation, log (100-y) = log100–0.018b1- 0.0084 x, was obtained to represent the relationship between the percentage sugar beet yield under irrigated conditions (y) and Olsen soil test value (b1) and the amount of fertilizer phosphorus (x), both expressed in kg P2O5/ha, for a 40-cm x 25-cm planting pattern and a plowdown application of 16–18% superphosphate in late fall. The variations in soil, climate, weather, length of growing period, and maximum yield level were found not to change significantly the constants 0.018 and 0.0084 used in the equation. For the average maximum yields of 42–58 t/ha obtained in different growing areas, phosphorus fertilization aimed at practically the maximum yield was found to be economical under the current fertilizer and beet prices.

KEISLING, T. C.; DAVIDSON, J. M.; WEEKS, D. L.; MORRISON, R. D.

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Under field conditions, the validity of many predictions concerning the movement of soil water and solute depends on the inherent variability of the soil parameters used in making the predictions. Data concerning the natural variability of many physical parameters of soils are lacking. A single soil series was studied over a land area 7.3 km in radius. Estimates were made of how some physical properties of soil vary with depth and with large and small land areas. Estimates of the number of samples required to achieve a given precision for each soil parameter were also made. The variability arising from location to location was found to be the major influence on the variation of soil-water conductivity. Restricting sampling to a radius of 5.6 km or sampling within morphological horizons reduced the variance of the soil-water conductivity. A range of 1 to 56 locations was required to achieve a standard deviation equal to 10% of the mean for the different physical properties of soil measured.

SIDHU, A. S.; RANDHAWA, N. S.; SINHA, M. K.

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Thermodynamic parameters (δF, δH, and δS) governing the adsorption of zinc were determined in soils that differed in physical and chemical properties. The adsorption of zinc in these soils conformed to the linear form of the Langmuir equation. The adsorption maximum, a constant related to bonding energy and differential buffering capacity of soils for zinc, was calculated from the experimental data. The sequential desorption of sorbed zinc by indifferent electrolytes, complexing agents, and acids provided a measure of different chemical pools of zinc in these soils. Higher values of entrophy change in Faridkot sandy loam and Laungowal loam than in the other two soils suggest the possibility of specific adsorption of zinc in these two soils. The adsorption maxima of Zn were related to the clay contents of these soils. Similarly, the differential buffering capacity of zinc in these soils also shows a relationship with their clay contents. A supply parameter combining the quantity, intensity, and buffering capacity of zinc was calculated from the experimental data, and it provides a relative measure of the Zn-supplying capacity of soils. A highly significant relationship between the supply parameter and the uptake of zinc by wheat was noted. The cumulative desorption of Zn was inversely related to the differential buffering capacity of these soils.