摘要:

It is essential to study the relationships of soil water and plants in desert areas for determining available soil water for plants, scheduling best irrigation management practices, deciding the suitable artificial vegetation density, and for selecting drought‐tolerating and water‐saving plants. In this study more than 100 lysimeters were installed to measure evapotranspiration and water‐use efficiency of five desert xerophyte species:Elaeagnus angustifolia, Hedysarum scoparium, Tamarix ramosissima, Caragana korshinskii, andHaloxylon ammodendron. The lysimeters were used to simulate evaporation of desert soils and transpiration of desert plant species with various groundwater depths and surface water supply conditions. The experimental data showed that the amount of transpiration, indexes of transpiration and evapotranspiration, and water‐use efficiency were different with different groundwater depths, plant species and plant ages. More than 80% of the total annual transpiration of the plants and more than 70% of the total annual evaporation from the desert soil occurred from June to September. Hence irrigation should be implemented during the 4 months in the experimental area. The measured data indicated that about 90% of the annual precipitation were evaporated from the bare soil; thus the choices of water‐saving plant species became critical. Our analyses suggest thatHalexylon ammodendronandCaragana korshinskiiare water‐saving as well as drought‐tolerating plant species, therefore, should be recommended for afforesting the desert area.

ISSN:0010-3624    

DOI:10.1080/00103629809369924

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A straightforward procedure is described for soil organic carbon (C) measurement in soil samples that may contain carbonates by using the Leco CR‐12 Carbon Analyzer. At a temperature of 840°C, a measured oxygen flow of 3.6 L min‐1, lancing flow of 1.0 L min‐1, soil organic C content can be directly measured on 0.20 to 0.40 g of samples, which have previously been ground to pass 40‐mesh sieve, for most medium‐ and fine‐textured soils. The organic C is combusted and measured within 2 min. A larger sample size of up to 2.5 g is suggested for sandy soils of low organic C content.

ISSN:0010-3624    

DOI:10.1080/00103629809369925

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Portable electrodes for rapid quantitative determination of nitrate‐N (NO3‐N) in plant sap have recently been developed, thus enabling a quick assessment of the crop nitrogen (N) status. The intent of this study was to provide diagnostic criteria necessary for the interpretation of petiole sap NO3‐N concentrations for potato(Solanum tuberosumL.). Specific objectives were to characterize the relationship between potato petiole sap NO3‐N concentration and petiole NO3‐N determined by conventional dry weight analysis, and to establish NO3‐N sufficiency ranges (NSR) for irrigated potatoes based on sap analyses associated with maximum and 85–95% of maximum yield. A four‐year experiment was conducted on a loamy sand soil (Udic haploboroll) at the Sand Plain Research Farm, Becker, Minn. Ten treatments consisting of various rates and times of N application were evaluated. Recently matured leaves were collected every 10 to 14 days, and petioles were split for sap NO3and dry tissue NO3analysis. Two portable NO3electrodes, the Cardy and Hach meters, designed for quick tests, and a fixed laboratory method, the Wescan, were used to determine sap NO3‐N concentrations. Dry petiole NO3‐N and petiole sap NO3‐N were linearly and significantly related, with regression coefficients r2=0.91, 0.92, and 0.93 for the Cardy, Hach, and Wescan methods, respectively. Nitrate‐N sufficiency ranges determined with the Cardy were 50 mg L‐1higher than those determined with the Hach. During the vegetative/tuber initiation stage (15–30 days after emergence), NSR were 1350–1450, and 1300–1400 mg L‐1for the Cardy and Hach, respectively. As the season progressed, the NSR decreased. During the tuber bulking period (30–75 days after emergence), NSR were 600–1350 mg L‐1for the Cardy and 550–1300 mg L‐1for the Hach. At maturity, NSR were less than 600 and 550 mg L‐1for the same respective electrodes. Petiole sap NO3‐N determined by either the Cardy or Hach methods can be a quick and useful tool to assess potato N status.

ISSN:0010-3624    

DOI:10.1080/00103629809369926

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Numerous chemical species of aluminum (Al) occur in acid soils and simple but accurate methods are needed to characterize phytotoxicity. Kinetic reaction studies between Al and ferron were used to separate Al into instantaneously reactive (Ala), metastable (Alb), and non‐reactive (Alc) fractions in soil solutions of two North Carolina Ultisols. Relative root growth of field‐grown corn (Zea maysL.) was used to assess rhizotoxicity of kinetically measured Al forms. Reaction of Albwith ferron conformed to first order kinetics, with rate constant values ranging from 0.53 to 9.13 minute‐1. The Alafraction correlated significantly with Al reacting in 30 seconds (r2=0.99), but the former averaged 10% less than the latter. Both Alaand Al reacting in 30 seconds correlated significantly with the Albfraction (r2≥0.89), but not with the Alcfraction (r2<0.1). Correlation exercises between ferronreactive Al fractions and various Al species predicted by the GEOCHEM‐PC speciation program revealed a strong relationship between Alaand the sum of activities of Al3+, Al(OH)2+, and A1(OH)2+, suggesting an instantaneous reaction of these species with ferron. The Alaand Abfractions correlated significantly with root growth. The Alcfraction did not correlate significantly with root growth and may be relatively less toxic. Further soil solution studies may be required to ascertain the nature of actual Al species measured in the Alaand Abfractions.

ISSN:0010-3624    

DOI:10.1080/00103629809369927

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of waterlogging and subsequent drying on pH, Eh, dissolved oxygen (DO), water soluble ions, exchangeable cations, cation exchange capacity (CEC), and phosphorus sorption capacity (Pmax) in three soils were studied (krasnozem, sandy loam, and highly organic material from a Melaleuca wetland). Fifty grams of each soil were mixed with 75 mL of distilled water, and left in a waterlogged state for 21 days. After removing a sample of the ponded water and sediment for analysis, the remaining water was discarded and the soils allowed to dry at room temperature for 21 days. All soils demonstrated a decrease in Eh, PO4, NO3and DO, and an increase in pH, soluble organic carbon (SOC), iron (Fe), manganese (Mn), NH4, calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na), in the solution phase due to waterlogging, but the magnitudes of change were greatest in soils with the higher levels of organic matter. Increases in Fe and Mn were attributed to the dissolution of Fe and Mn oxides under chemically reducing conditions. Increases in Ca, Mg, K, and Na were attributed to increased solubility of organic carbon, and from increased competition for the CEC sites due to elevated Fe and Mn concentrations. Increases in CEC due to the presence of colloids with variable charge were largely balanced by Fe and Mn. Mineralization of organic nitrogen (N) by anaerobic bacteria, and the absence of DO, was considered responsible for the accumulation of water soluble NH4. Decreases in water soluble NO3and PO4due to waterlogging were attributed to denitrification and sorption by amorphous Fe(OH)2, respectively. Reoxidation by drying caused increases in Eh and DO, decreases in exchangeable Fe and Mn, but had no significant effect on pH, exchangeable cations or CEC. Waterlogging nearly doubled Pmaxin the krasnozem A horizon and wetland soils, and produced only small changes in the other soils. Sorption by freshly precipitated Fe(OH)2is considered the major mechanism increasing PO4sorption.

ISSN:0010-3624    

DOI:10.1080/00103629809369928

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A growth model is needed which will account for time of planting and stage of growth for annual grasses and for time of season and harvest interval for perennial grasses. A linear intrinsic growth function was assumed previously which described response of dry matter accumulation to harvest interval for a warm‐season perennial. Field data indicated that this model was appropriate for intervals up to about six weeks. Beyond this range yields peaked and then declined with increased interval. This article assumes a linear‐exponential intrinsic growth function which more accurately describes the data and removes the restriction on harvest interval. The model describes dependence of dry matter accumulation on time of season and harvest interval for a warm‐season perennial Coastal bermudagrass(Cynodon dactylon). Mean time and standard deviation of the distribution are independent of harvest interval. The model also accounts for time of planting and time in the season for the warm‐season annual corn(Zea mays)as related to dry matter and plant nitrogen (N) accumulation. The resulting analytical functions can be used to estimate values on a pocket calculator without need for finite difference procedures.

ISSN:0010-3624    

DOI:10.1080/00103629809369929

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Little is known about the phosphorus (P) status of non agricultural soils, although some sites in drylands are potentially important for the production of desert truffles, a mycorrhizal association that may overcome the fertility deficiency. In this work we described the fertility characteristics with special emphasis on the P status of some natural desert truffle stands. The soils have poor fertility characteristics and the total P contents range from 32 to 273 mg Kg‐1. The P fractionation shows fairly variable amounts of organic P, while the proportions of the other fractions are related to the soil chemical properties. The available P contents are also variable, but generally high if compared with the critical levels for optimal yields of crops. The water availability of these soils is likely to be an important factor to be kept into account when evaluating the P availability.

ISSN:0010-3624    

DOI:10.1080/00103629809369930

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Ryegrass was grown under greenhouse conditions in pots containing two types of calcareous soil. After 8 harvests, the soil was left in the pots for a simulated fallow period, then reseeded with ryegrass, from which 4 further harvests were obtained. The manganese (Mn) content in the soil samples, taken before seeding and after intensive cropping, was fractionated chemically and physically. Although different trends were apparent in the different fractions, ryegrass cropping enhanced the overall mobilization of soil Mn, which easily surpassed the cumulative Mn uptake. The organically bound Mn and clay‐associated Mn fractions released significant amounts of the element, whereas the behavior of exchangeable Mn, Fe‐oxide associated Mn and sand‐associated Mn fractions varied in the two different soils studied. The silt‐associated Mn fractions increased significantly in both soils.

ISSN:0010-3624    

DOI:10.1080/00103629809369931

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In many areas, continual application of fertilizer and manure has increased soil phosphorus (P) to levels that are of environmental rather than agronomic concern. More information is needed on the long‐term residual availability of soil P to make more reliable P management recommendations. Three Italian soils with a wide range in phosphorus adsorption properties were equilibrated for 91 days with different rates of fertilizer P to obtain similar levels of soil extractable Mehlich 3‐P (M3‐P). After equilibration, P was desorbed from the soils using ten successive extractions with iron oxide‐impregnated paper strips, Mehlich3 extractant, and water solution (Psol). At similar levels of M3‐P contents (57±6 mg P kg‐1soil), more P was released from the soil with higher P sorption index (SI) than from the soil with lower SI, indicating that a greater available P content was necessary from low P sorbing soils to maintain a given rate of P release. Soil M3‐P and Psol decreased in the course of P removal, and a close linear relationship was found between the decrease in soil M3‐P and P released onto the strips (r=0.99; P<0.1%). Furthermore, soil with the highest P buffer power presented the lowest variation in M3‐P and soil P solution values, and changes in M3‐P per unit of P removed were significantly related to soil SI (r=0.97; P<5%). The data suggest that the successive soil P extraction procedure carried out using Fe oxide‐impregnated paper strips may provide a reliable laboratory method for characterizing P desorption from soils and easily estimating residual soil P availability.

ISSN:0010-3624    

DOI:10.1080/00103629809369932

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Use of sewage sludge on cropland may contribute to nitrate leaching or runoff from fields if mineralization of organic nitrogen (N) is not in synchrony with crop N uptake. Differences in sludge application method may influence sludge N use efficiency. A two‐year field experiment was conducted to determine how method of applying lime‐stabilized digested sewage sludge in the spring affected seasonal patterns of soil mineral N. Sludge rate was such as to supply 157 kg ha‐1plant available N as determined by State of Maryland regulations. Corn (Zea mays) yield in year 2 and corn earleaf N at tasseling in both years were significantly lower for surface‐incorporated sludge than for injected sludge, although equivalent N was applied to both. Vertical distribution of soil ammonium‐N and nitrate‐N within the surface 30 cm of soil in year 2 suggested that, compared to injected sludge, surface‐incorporated sludge lost more nitrate by leaching before the period of rapid plant N uptake. Release of nitrate was delayed by at least one month with injected as compared to surface‐incorporated sludge. In both years, soil pH and electrical conductivity measured about one month after sludge application were sufficiently high to inhibit nitrification in the injected sludge band. Residual mineral soil N remaining in the upper 30 cm of soil after plant N uptake ceased in fall was greatest with injected sludge in both years. Delayed nitrification in the injected band should be considered in planning method and timing of sludge applications to cropland.

ISSN:0010-3624    

DOI:10.1080/00103629809369933

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor