ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Movement of water through well developed calcic horizons, present in many North American Great Plains soils, is critical to groundwater recharge and crop water management; however, information about the hydraulic properties of these horizons is scarce. This study was conducted to measure physical and hydraulic properties of a calcic layer under an Acuff fine sandy loam (fine-loamy, mixed, thermic Aridic Paleutolls) in the southern Great Plains near Lubbock, TX. Site characterization included bulk density, particle size distribution, and water retention measurements. The saturated hydraulic conductivity (Ks) was measured with the constant head method and estimated from infiltration rate data fitted to three models. Unsaturated hydraulic conductivity (K(&thetas;v)) was calculated using measured and estimated values of Ksand the measured soil water retention curve (&thetas;v(h)). Mean bulk density was 1.44 ± 0.2 Mg m-3, and the textural classes of the calcic layer with and without carbonates were clay and sandy loam, respectively. The measured vertical Ksof 0.87 x 10-5m s-1and model estimated Ksof 1.20 x 10-5m s-1were consistent with the Ksof a coarse textured soil. However, measured (&thetas;v(h)) was consistent with a fine textured soil. These data suggest that a calcic horizon would not greatly impede water movement, but drain rapidly instead. For example, water reaching the caliche layer from excess irrigation will drain rapidly below the root zone. Ground water recharge from draining surface basins (playa lakes or unsealed water treatment lagoons) would not be hindered.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

High soil Zn concentrations can cause Zn toxicity in peanuts, which diminishes productivity and can be fatal to plants. The objectives of this study were (i) ot determine the interactive effects of soil texture, pH, and Zn rates on the distribution of Zn among fractions in kaolinitic Coastal Plain soils, and (ii) to relate soil Zn fractions to Zn uptake by peanut (Arachis hypogaeaL.) plants. Four soils were selected for this study: Lakeland sand, Tifton loamy sand, Greenville sandy clay loam, and Greenville sandy clay. Zinc sulfate was applied at three rates (0, 20, and 40 mg Zn/kg soil), and limestone was applieid at four rates to each soil in a factorial design. Peanut plants were grown in a greenhouse for 10 weeks. Duplicate soil samples were fractionated for Zn by a sequential technique. Total Zn was determined by digestion with HF, HCI, and HNO3. The sum of Zn fractions was not significantly different from the total soil Zn. The percentage of Zn in the exchangeable and organic matter faractions was higher in the coares-textured soils, and the percent in the crystalline Fe oxide fraction was greater in the fine-textured soils. Application of Zn increased the amount of Zn in the soluble forms, specifically, the exchangeable, organic matter, and Mn oxide fractions. Liming redistributed Zn from the exchangeable fraction to less soluble fractions. The amount of Zn in the exchangeable fraction was best correlated with CEC, but the sum of fractions was best correlated with the clay percentage. Plant Zn concentrations were most highly correlated with the exchangeable fraction. Because of toxic Zn effects, plant weight was lower at high Zn availability, which led to positive correlations of plant weight with Zn in the relatively plant-un-available forms.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Causal modeling was used to study mechanims involved in pH, P, and Mo interactions in three soils, to determine the relative importance of several variables to an endogenous variable and to decompose the simple Pearson correlations into direct, indirect, simple noncausal, and spurious effects. Solutions varying in pH and concentrations of P and Mo were reacted with a clay, a loam, and a sand soil. Supernatant was analyzed for pH and concentrations of Ca, Si, Mo, P, Fe, and Al. Dissolutions of Ca (CaD), dissolution/desorption of Si (SiD), and sorption of P (Ps) and Mo (Mos) were calculated. Logarithm values of CaD, SiD, and MoSand pH were used to build the structure equations using Psand MOsas endogenous variables.The causal modeling showed that there existed reciprocal relationships between Mosand Psand that Moswas influenced more by Psthan vice versa. Significance of such reciprocal effects varied in the three soils. In general, decreases in Mosdid not occur until Psincreased to 17, 16, and 15 mmol kg-1soil in the clay, the loam, and the sandy soil, respectively. The effects of pH and SiDon Moswere more significant in the sandy soil than in the loam and/or in the clay soil. The relative importance (absolute standardized coefficient) of variables to Moswas in the decreasing order of Ps, Mo, pH, CaD, and SiDin the clay, of pH, Mo, SiD, Ps, and CaDin the loam, and of SiD, pH, Ps, Mo, and CaDin the sandy soil. In some cases, the direct effects of the pH, SiD, CaD, Mo, and P on Ps or Moswere counterbalanced by their indirect and/or noncausal effects, resulting in small Pearson correlation coefficients. The causal modeling and the ion activity products of some Ca-P and Ca-Mo minerals suggested that Mo retention was primarily a process of adsorption in the three soils and that P adsorption was the principal reaction in the clay soil, while both adsorption and precipitation controlled P reaction in the loam and the sandy soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Crop rotation is a major factor in maintenance of soil productivity in cropping systems, but the role of mycorrhizal fungi has been little considered. A tall fescue (Festuca arundinaceaSchreb.) sod heavily infected with theAcremonium coenophialumendophyte was plowed, and pearl millet (Pennisetum americanumLeeke) or crabgrass (Digitaria sanguinalis(L.) Scop.) was grown. Pearl millet produced more shoot dry matter and was more heavily colonized than crabgrass, and soil populations of mycorrhizal fungi were usually higher with pearl millet. Associated with the production of pearl millet and crabgrass were radical changes in the mycorrhizal fungal community. Populations of eight of 19 species decreased, four of them not detected at the end of the season. Populations of nine increased, five of them not detected at the beginning of the season. Field host and time affected species richness, dominance, and diversity; but only time affected equitability. This study suggests that crop rotation may be used to manage the mycorrhizal fungal community. Managing these fungi may be important if individual species or biotypes are found to be pathogenic or mutualistic.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

A gradient in plant species diversity was investigated to determine how soil chemical properties limit the distribution of desert plants. Species-poor communities (lacking succulents) growing on basalt-derived soils were compared with richer communities on soils that developed on basalt or quartz diorite. Species richness and density were determined in three 100-m2quadrats at five sites. Soil samples were collected from A (0–10 cm) and B (10–30 cm) layers near the center of each quadrat. Leaves of species growing in or near quandrats were collected as indicator tissue. Elemental concentrations were measured in soil saturation extracts and leaf tissue digests. Surface soils were non-saline and had near-neutral pH. Soil saturation extracts were high in NaCl and adequate in Ca but low in N, P, B, K, Mg, S, and Fe. Leaves of indicator plants (Viguieraspp.) were high in K, Ca, and Na, medium in B, and low in Mg, P, and some micronutrients. Analysis of variance revealed that the Ca: Mg ratio in the soil solution differed significantly between sites and was lowest at species-rich sites. Simple regression revealed a moderate positive dependence of species richness on Mg in the soil solution and a negative dependence of species richness on soil solution Ca:Mg. But a marked dependence was found when species diversity (Shannon-WeinerH‘ Index) was regressed on Ca: Mg in the soil solution. These results indicate that the geographic ranges of desert species (and of succulents in particular) can be restricted by even moderate Ca in the rooting medium when Mg is critically low. Magnesium concentration in leaves of species studied in Baja California was among the lowest, and Ca: Mg ratios among the highest ever reported in desert plants.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Graphite, in an aqueous nitrogen (N) suspension of urea ammonium nitrate (UAN), was applied to snow covering dryland winter wheat in either February or March to determine impacts on wheat yield, soil temperature, available soil moisture, and N movement in soil. Field experiments were established on soils with slopes of 1–2% in both the Pocatello Valley and Soda Springs areas of southern Idaho. Snow depths ranged from 40–65 cm at treatment application. Soil water content was determined with a neutron probe. Thermocouples were used to measure soil temperature in each plot following snowmelt from control plots. Soil water differences were observed between the graphite treatment and the control to a soil depth of 90 cm in the spring. Soil temperature fluctuation following snowmelt was greater where graphite influenced snow melt. There was a tendency for higher initial soil tempratures (above 0°C) with the graphite treatments compared with the control. These higher temperatures were observed for over 20 days and to a depth of 20 cm. Increased wheat yields were observed with graphite-N applications over snow compared with similar fall or spring N application treatments. These higher yields were likely the result of increased soil temperature and soil water content as a function of controlled (pulsed) snow-melting with graphite.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID