Characterizing soil fertility by ion diffusive flux measurements

Summary The general acceptance of diffusion as a rate-limiting step in transferring ions to plant roots was considered in characterizing soil fertility. Soil ion diffusive flux measurements to an exchange resin were measured with two soil: resin cells, one with untreated soil, the other with the same soil fertilized with P, K, and Cl. The P, K, and Cl that diffused to the resin of each cell was extracted and determined. Using only these measurements and some simplifying assumptions of diffusion theory, calculations were made of the soil's P and K solution concentration, adsorbed concentration, a capacity factor, transmission factor, and quantity of fertilizer needed to attain any desired flux. Excellent to fair correlations existed between these calculated values and traditionally measured chemical quantities. Plant uptake of P and K was generally well correlated with diffusive flux measurements as well as traditional chemical measurements.Contribution from the Western Region, Agricultural Research Service, U.S. Department of Agriculture; and the Montana Agricultural Experiment Station, Bozeman, Montana, submitted as Station Paper No. 654, Journal Series.Soil Scientist, Snake River Conservation Research Center, Kimberly, Idaho; Professor of Chemistry, and Professor of Soils, Montana State University, Bozeman, respectively.     

Relation of solute and sorbed boron to the boron hazard in irrigation water

Summary The current criteria for evaluating the boron (B) hazard of irrigation water for specified crops are based on the concentration of B in the irrigation water without consideration of soil properties or the leaching fraction. Experiments were conducted to determine the influence of B sorption capacity on plant uptake of B at rates of 0.1, 2.5, 5.0 and 10.0 ppm B in the irrigation water with a leaching fraction of 0.5. A relatively B sensitive crop, oats (Avena sativa), was grown on four arid-region soils of varying B sorption capacities. The results show that B in solution rather than sorbed B influenced B toxicity. Contribution from the Department of Soils, Water and Engineering, The University of Arizona, Tucson, Arizona 85721. Arizona Agricultural Experiment Station No. 2508. Research Associates and Associate Professor, respectively. The senior author is currently at the Department of Soils and Irrigation, American University of Beirut Beirut, Lebanon.     

Changes in extractable organic phosphorus in soil in the presence and absence of plants

Summary The effect of cropping on soil organic phosphorus was investigated in laboratory and greenhouse work with six soils. Successively lower contents of extractable organic phosphorus were found in samples that had been (a) airdried initially and stored in that condition, (b) incubated in a moist condition but without a crop, and (c) planted to four successive crops, the roots of the crops being removed before analysis of the soil. These differences were statistically significant. Samples of rhizosphere soil taken after the fourth crop did not yield significantly different amounts of extractable organic phosphorus than did bulk samples of cropped soil taken at the same time. Extractable organic and inorganic phosphorus in the soils were not significantly affected by drying the soil before each crop.Journal Paper No. J-5916 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 1183.Former Rockefeller Fellow and Professor, respectively. The senior author is now Associate Professor, Department of Soils, Punjab Agricultural University, Ludhiana, Punjab.     

Salt distribution around roots of wheat under different transpiration rates

Summary Magnitude of Na and Cl accumulation around wheat roots was studied under different transpiration conditions in a loamy sand soil salinized with sodium chloride to an electrical conductivity of 4.1 mmho/cm in the saturation extract. A significant correlation was observed between rate of water loss per unit root length and Na and Cl content of the soil closely adhering to the roots. Under high transpiration condition, maximum ion accumulation occurred in the apparent free space of roots followed by the soil closely adhering to the roots. Results indicate that salt concentration at the root surface is markedly altered under the influence of transpiration rate such that under high transpiration conditions, the plant roots may be exposed to a much higher salt concentration than that anticipated from an analysis of the bulk soil samples.Department of Soil and Water EngineeringDepartment of Soils     

Influence of iron on the uptake of phosphorus by maize

Summary Experiments were carried out with maize in solution culture at three different iron levels at each of which P solubilities were varied through a relatively wide range (upto 80 per cent). Studies were made of the interactions between iron and phosphorus in their effects upon the dry matter production, iron and phosphorus uptake. The results revealed that iron above 5 mg per litre adversely affected the growth as well as P uptake. At higher P solubility levels, translocation of iron from the roots to the shoots was reduced, indicating an internal inactivation of iron by the phosphorus. Assistant Professor, Department of Soil Science, Tamil Nadu Agricultural University Coimbatore 641003 South India Professor and Head of Institut fur Pflanzenern?hrung, Weihenstephan 805 Freising, W. Germany Professor and Head of Institut fur Pflanzenern?hrung, Weihenstephan 805 Freising, W. Germany     

The possibility of predicting solute uptake and plant growth response from independently measured soil and plant characteristics

Summary A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented. Growth rate is linked to the nutrient level of the photosynthetic tissues, which is assumed to control changes in the net assimilation rate, the leaf area per unit shoot weight, the shoot: root ratio, the root surface area, and the distribution of nutrient between root and shoot. The uptake of nutrient depends on the concentration of nutrient at the root surface, the root surface area and its absorbing power. All these relationships may be determined in stirred solution culture. A method of applying this information to soil grown plants is suggested.Soil Science Laboratory, Department of Agricultural Science, University of Oxford     

Preliminary evaluation of H2SO4 application methods to soils

Summary The effects of sulfuric acid application to soils and water on growth and chemical composition of sorghum (Sorghum bicolor) were compared in a greenhouse experiment using high sodium bicarbonate irrigation water. Significant increases in dry matter yield and plant uptake of P en Fe were produced only by soil treatment of calcareous soils.Contribution from the Department of Soils, Water and Engineering, The University of Arizona, Tucson, Arizona 85721, as Technical Paper No. 2320. This work was supported by the Arizona Mining Association.Research assistants and Professor     

Characterization of soil phosphorus by anion exchange resin adsorption and P32-equilibration

Summary Adsorption of phosphate by the anion-exchange resin Dowex-2 was investigated. The resin adsorbed small quantities of P from solution quantitatively. The rate of P-adsorption by resin agitated in solution was proportional to the P-concentration in solution, and was independent of the rate of diffusion of adsorbed P in the resin. When 1 g of soil was shaken continuously with 1 g of resin in 100 ml of water, the rate of P-adsorption by the resin was controlled by the rate of P-release from the soil. Quantities of P adsorbed from soil by resin after different lengths of time were less than those equilibrated with P³² during the same time intervals. The curves showing quantity of P adsorbed vs. time could be satisfactorily described by the hypothesis that there were three simultaneous reactions differing in rate, each reaction being first-order with respect to P. The same was true of the P³²-equilibration data, except that the rate of the slowest reaction was apparently independent of time. In a group of 16 soils, the correlation between P adsorbed by the resin in 2 hours and P-availability to plants in the greenhouse, measured by the isotope-dilution method of Fried and Dean, was 0.95. The corresponding correlation between P extracted by the 0.25N HCl — 0.03N NH₄F extractant of Bray and Kurtz was 0.91.Joint contribution from the Iowa Agricultural Experiment Station and the Eastern Soil and Water Management Section, U.S. Department of Agriculture. Journal Paper No. J-2639 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project No. 1183.Graduate Assistants, Professor of Soils, and Associate Professor of Chemistry, respectively.     

A common chemical extractant for estimating plant-available zinc in different soil types (peaty,red and alluvial)

Summary Relative efficiency of five chemical extractants for the extraction of available Zn in four different soils and its uptake by rice seedlings was studied in a pot culture experiment. The Zn extracted by dithizone-ammonium acetate showed a significant relationship with plant uptake whereas the values for other extractants except NH₄OAc (pH4.8) did not approach the level of significance. Among the soil properties studied, pH and CaCO₃ correlated negatively and organic matter and CEC positively with Zn uptake by rice plants.Contribution from the Soil Science and Agricultural Chemistry Dept., Banaras Hindu University, Varanasi-221005, India.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.Lecturer and Research Scholar of the Soil Science and Agricultural Chemistry Department, respectively.     

The contact-exchange theory amended

Summary Experimental data have been presented showing that over a three-month period the rate of cation uptake by kidney bean plants from a substrate containing both adsorbed cations and cations in solution is equal to that from a solution only, provided the ions in the solution are in thermodynamic equilibrium with those in the adsorbed from. These data, in conjunction with presentations in the literature which would seem to validate the contact-exchange theory, have been critically analyzed. It has been concluded that while probably correct in assuming contact-exchange between ions adsorbed at or near the surfaces of plant root and exchanger, the contact-exchange theory should be amended so as to recognize that the rate at which this exchange proceeds is a function of the diffusivity of the medium for, and the thermodynamic state of the ions in the various phases of the nutritional environment of the roots. The faster rate of ion-uptake by contact-effect (surface-migration) than by diffusion and adsorption, as frequently reported, is considered to be typical of unequilibrated ionic conditions, whereas a corresponding equal rate of uptake is held to be accounted for by assuming the existence of thermodynamic equilibrium between the ions in the various phases of the system. This equilibrium, naturally, cannot be but approximate because of the occurrence of a driving force prompting locomotion of ions. Under the equilibrium conditions thus specified, the ionic environment of the plant root is entirely characterized by the ionic composition of the solution phase. This deduction may serve to show that under certain conditions the same interpretative value may be placed on the outcome of soil- and solution-culture studies.Contribution from the U.S. Salinity Laboratory, Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture, Riverside, California, in cooperation with the 17 Western States and Hawaii.     

Effect of sulfuric acid on sodium-hazard of irrigation water

Summary The sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and saturated hydraulic conductivity were measured under laboratory conditions in one neutral and four calcareous soils using simulated alkaline irrigation waters having salt concentrations ranging from 7 to 39 meq/l with the SAR from 3.8 to 8.4. Sulfuric acid was applied to the waters at sufficient rates to prevent calcium precipitation under an open system, ranging from 2.1 to 4.7 meq/l. At these acid rates, the pH of irrigation waters remained above neutral. This treatment reduced SAR and ESP in all cases tested, and increased the hydraulic conductivity of some soils when the SAR of the original irrigation waters was greater than approximately 7. The experimentally determined SAR was then compared with the values predicted based on some of the existing theories. The results indicated that the conventional method to estimate SAR with adjustment using the pH_C index of Langelier overestimates the effect of HCO₃ ^-, whereas the equation based on carbonate equibria gives a reasonable prediction of SAR in waters containing HCO₃ ^- as well as H₂SO₄. The SAR calculated by the latter method was also linearly related to the measured ESP with an equation, ESP=0.761 SAR, r²=0.986.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.Arizona Agr. Exp. Sta. J. No. 2449. Contribution from the Department of Soils, Water and Engineering. The University of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Association.     

Accumulation and toxicity of chloride in bean plants

Summary Chloride tends to accumulate in tissues, particularly leaves, of some plants to toxic levels. Chloride accumulation in plants is closely related to Cl concentration in the external solution and the genotype.An experiment was conducted to study the rate of Cl accumulation in bean plants under greenhouse conditions and to determine the toxic levels of this anion in the leaves of red kidney beans. Plants were grown in large tanks containing a basal nutrient solution, salinized with either NaCl or Na₂SO₄ to produce 80 meq/l solutions of these two salts. Control plants were grown in nonsalinized nutrient solutiosn. Salt-treated plants were harvested at different time intervals and analyzed. Chemical analysis of leaves showed that accumulation of chloride was different from that of other ions derived from salines. The leaf-Cl accumulation was shown to be dependent on Cl concentration of the culture solution as well as the duration of the experiment. The data also revealed two processes of rapid Cl accumulation in the leaves of bean plants when a relatively high concentration of this ion is present in the external solution. These are: (a) a rapid Cl accumulation occurring between transplanting and the first harvest; (b) a second rapid Cl accumulation occurring after the fourth harvest to the end of the experiment leading to a toxic concentration of Cl in the leaves. The second rapid absorption period was absent for the other ions derived from salines.     

Mineral Uptake in Fusarium oxysporum f. sp. vasinfectum

A method for growing Fusarium oxysporum, a mycelial fungus, and a technique for its use in mineral uptake studies have been described. Some general characteristics of the uptake process were determined. The fungus, grown for 54 hours, was found to take up as much K as 15 to 20 meq/100 g dry weight in 2 to 4 hours from a solution of 5 meq/l KCl. Approximately 3 to 5 meq of this uptake was readily removed by a CaCl₂ rinse. The uptake was only slightly sensitive to pH over the range of 4 to 9. Below pH 4 uptake dropped rapidly. The age of the culture appeared to be the dominant factor in determining the rate of uptake. In contrast to other fungi, the presence of glucose during uptake was detrimental to K uptake. Conditions unfavorable for metabolic activity as low temperature, anaerobiosis, or the presence of DNP markedly reduced the uptake rate. Although the fungus took up Na from single salt solutions nearly as well as K, the latter ion was much preferred in mixtures of the two ions. The organism showed no significant metabolic uptake of Ca or Cl. During uptake from KCl solutions, the organic acid content increased. The increase, chiefly in succinic acid and to a lesser extent in acetic and citric acids, amounted to about half the K uptake. The remainder of the K taken up was correlated with a roughly equivalent efflux of cellular Mg.     

Studies on the mucilaginous layer of barley (Hordeum vulgare) roots

The nature and composition of the external, mucilageneous layer of barley roots was studied by extraction methods and electron microscopy. Barley roots were extracted with chloramphenicol-supplemented water at 35°C, with NH₄Cl at various concentrations and with pectinase solutions. The kinetics of transfer of bacteria, total and reducing sugars, proteins, Ca⁺⁺ and K⁺ was studied, and the removal of the mucigel from the extracted roots was followed under the electron microscope. Within 2 to 3 hours of treatment with water, the rate of release of sugars, ions, proteinaceous material and bacteria, was reduced to almost zero. Increasing concentrations of ammonium chloride enhanced transfer of ions to the extracting solution but affected sugar extraction to a lesser extent. Electron micrographs of ammonium chloride-extracted roots revealed that the amorphous, rather than the fibrillar fraction of the mucigel was removed. At 10³ meq of NH₄Cl, distortion of the epidermal layer of the extracted roots was observed. With pectinase as an extractant, there was some enhancement of sugars and ions transfer from the roots to the extracting solution. Electron micrographs showed that the main site of extraction of pectinase was the boundary layer between the root surface and the mucigel. Paper chromatography of the acid hydrolyzate of the water extracted, ethanol-precipitated fraction showed the presence of compounds identical in Rf values to D-glucose, D-arabinose, D-glucuronic acid and D-galacturonic acid. Present methods available for the extraction of the mucigel do not allow the differentiation between extracted pectic compounds which originate from the internal root tissue, and the mucigel. re]19751128 Dept. of Field Crops Dept. of Soil and Water Sciences Dept. of Microbiology and Phytopathology     

The effects of root temperature and Ca supply on the growth and transpiration of cotton seedlings (Gossypium hirsutum,L.)

Summary Cotton seedlings were germinated in either tap water or a CaSO₄ solution and then grown for two days in nutrient solutions containing 0.1, 1.0, or 10.0 me Ca/1. They were then transferred to cultures having the same Ca variables and the roots subjected to temperatures of 26, 18, 15 and 12°C for four days. The fresh weight of all plant parts and leaf area increased with increasing root temperatures and with increasing Ca levels, the effect of Ca being most pronounced at the higher temperatures. The dry weight was increased by increasing root temperature; the effect of Ca was rather small. Water use increased with increasing temperature and was higher for the lowest Ca level than for the higher levels. The results emphasize the overriding effect of low temperature on water uptake. Calcium had little effect on the growth depression resulting from low root temperatures. Joint contribution from the Agronomy Department, Mississippi Agricultural Experiment Station, State College and the Soil Science Department, North Carolina Agricultural Experiment Station, Raleigh. Published with the approval of the Directors of Research as Journal Contribution No.1530 and Paper No.2389 of the Journal Series, respectively. This is a report of research conducted while the author was on sabbatical leave at North Carolina State University, February 1–September 10, 1965.     

Role of root systems of eastern larch and white spruce in response to flooding

Abstract. Soil flooding causes rapid reductions in transpiration, stomatal conductance and photosynthesis of many woody plants, which can decrease growth and ultimately result in plant death. This study was conducted to determine the role of the root system in the flooding response. Eastern larch ( Larix laricina ) seedlings were grown in Plexiglas tubes in which water uptake by flooded and unflooded roots was measured independently. Further flooding studies were conducted with eastern larch and white spruce ( Picea glauca ) in which stems were girdled. Root hydraulic properties were analysed using pressure-flow relationships. Transpiration rates of partially flooded plants declined more slowly than fully-flooded plants. Water uptake by unflooded roots of partially flooded seedlings increased momentarily with flooding. After lOd, flooding caused little change in root hydraulic conductance, a decrease in root system reflection coefficient, and an increase in osmotic permeability. Stem girdling had little effect on stomatal conductance and transpiration in comparison to flooding effects. The response of plant tops to flooding appears to be xylem-mediated and in proportion to the amount of root system flooded. Root hydraulic conductance appears to be unaffected by flooding except for a possible temporary increase on the first day following flooding treatments.     

Nitrogen-tillage-residue management

Summary NCSWAP (nitrogen and carbon cycling in soil, water and plant) is a simulation model of the soil-crop-water system which integrates water flow dynamics, crop growth, N transformations, tillage and residue effects, soil temperature, and solute transport. A small plot field study was initiated in May of 1980 to determine the effects of N rate (2 or 20 g N/m²), tillage (rototill or no-till), and residue management system (residue return or noresidue) on soil parameters, and maize (Zea mays L.) production.Significant differences due to treatments (N rate, tillage, and residue) were not detected in 1981 for the measured soil-plant parameters including soil moisture, yield, and N uptake. Therefore, two representative treatment combinations (N rates of 2 or 20 g N/m²-tilled-no residue) characterized the field research data. Calculated and observed data sets were compared for several parameters including: (1) soluble NO₃–N, (2) N leaching losses (3) plant total-N and¹⁵N, (4) root growth, (5) soil moisture, and (6) fertilizer efficiency.The objectives of this study were to initiate the validation process of the model NCSWAP, and to illustrate how NCSWAP can be used as a research tool to infer operational characteristics of the N cycle.Contribution of the Soil and Water Management Research Unit, USDA-ARS, and the Department of Soil Science, University of Minnesota, St. Paul, MN 55108. Minn Agric. Exp. Sta., Sci. J., Ser. Paper 13907.Senior Laboratory Technician; Research Chemist, USDA-ARS and Professor; Professor of Soil Microbiology; and Soil Scientist, USDA-ARS and Assistant Professor; all Department of Soil Science, University of Minnesota, respectively. Inquiries about NCSWAP should be sent to J. A. E. Molina.     

Genetic analyses for certain plant and ear characters in pearl millet top-crosses

Summary Combining ability and the genetics of tiller number, days taken to flower and ear thickness were studied in top-cross progenies of pearl millet. General combining ability seemed to be more important for all the characters. The prevalence of epistatic variation, presumably of the type additive x additive, additive x dominance and dominance x dominance gene effects, with a non-significant contribution of additive and dominance components of genetic variance, was observed for tiller number. For days taken to flower, the importance of additive genetic variance was greater than that of the dominance component with directional dominance towards the recessive allele. However, for ear thickness, the existence of additive genetic variability together with the additive x additive type of genic interaction was suggested.An appreciable effect of epistasis on and ₁ components was observed for tiller number, whereas this effect was not so marked for other characters.The author is grateful to Dr. D. S. Athwal, formerly Professor and Head (now Assistant Director, The International Rice Research Institute, Los Banõs, Laguna, Philippines), Department of Plant Breeding, Punjab Agricultural University, Ludhiana, for providing the facilities.     

Maximale Salzkonzentrationen in der rhizosphären Bodenlösung junger Zuckerrüben

Zusammenfassung In Salzb?den wird das Wasserpotential der Rhizobodenl?sung (wurzelnahe Bodenl?sung) durch die transpirationsabh?ngige Akkumulation leichtl?slicher Salze erniedright. Aus Bodenl?sungen niedriger Wasserpotentiale ist die Wasseraufnahme der Pflanze gering bzw. wird ganz eingestellt. Wurzeln junger Zuckerrübenpflanzen konnten noch aus Bodenl?sungen mit 900–1000 meq NaCl/l (≜≈−3,8 MPa bis−4,2 MPa) die zum überleben erforderliche Wassermenge aufnehmen, da sich die Bl?tter durch Aufnahme von Na-und Cl-Ionen an extreme Salzbedingungen adaptierten. Für Pflanzen, die mit etwa 2,5 meq Na/g TS und etwa 1,5 meq Cl/g TS im Pro? an weniger extreme Bodensalzgehalte angepa?t waren, wurden maximale Konzentrationen der Rhizobodenl?sung von 650 bis 750 meq NaCl/1 (≜≈−2,7 MPa bis −3,1 MPa) ermittelt. Es ist anzunehmen, da? in der Rhizobodenl?sung von Pflanzen mit potentiell h?chsten Wachstumsraten, aber geringer Salzadaption, deutlich niedrigere Salzkonzentrationen in der Rhizobodenl?sung ermittelt werden.

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Maximum salt concentrations in the rhizospheric soil solution of young sugar beets

Summary Due to transpiration easily soluble salts accumulate in the rhizospheric soil solution (soil solution in close vicinity of the roots) and reduce the water potential. The uptake of water by roots is lower or might even be ceased from soil solutions of low water potentials. Roots of young sugar beets were able to absorb enough water to survive even from soil solutions of 900–1000 meq NaCl/1 (≜≈−3.8MPa to−4.2 MPa), as their leaves were adapted to extreme salinity by uptake of Na-and Cl-ions. For plants less adapted to extreme soil salinity containing 2.5meq Na/g DM and 1.5 meq Cl/gDM maximum salt concentration of 650 to 750 meq NaCl/l (≜≈−2.7 MPa bis −3.1 MPa) were found in the rhizospheric soil solution. Most probably the maximum salt concentration is much lower around roots of plants high in growth potential, but less adapted to saline soils.

     

Uptake of solutes by multiple root systems from soil

Summary A procedure is put forward for calculating the plant uptake of solutes supplied by diffusion and mass flow to the randomly dispersed roots of a developing root system. The model was tested as follows: (a) for a constant root density, and both transport processes—against a more accurate numerical solution of the same system (b) for an increasing root density, and for supply by diffusion only—by electrical simulation using the analog described in Part I. In both cases, results obtained by the two types of calculation were in close agreement. A less accurate method which includes both supply mechanisms and does not require a computer is presented, and compared with an electrical simulation when there is no mass flow. Agreement is within 20 per cent. The model should be useful for predicting plant nutrient uptake from soil, and may be of special interest to modellers of the whole plant system. re]19720905 Soil Science Laboratory, Department of Agricultural Science ,University of Oxford Present address: Department of Plant Sciences,University of Leeds