摘要:

Researchers traditionally conduct fertilizer experiments on small, replicated areas at university or governmental research centers. This approach has two problems: (1) extrapolation of the results to large cropped fields requires taking into account the impacts of spatial variability of soil properties on the optimum amount and type of fertilizer to apply and (2) farmers have limited access to the research work, particularly in developing countries, which limits the information transfer needed for farmers to adopt the recommended fertilizer techniques. With these problems in mind, field and laboratory investigations were conducted on a farmer's field to study the spatial patterns of some soil properties and wheat yield using geostatistics for determination of fertilizer rates. The field was divided into four parallel transects, and soil samples were collected at 15‐m intervals along each transect. These soil samples were analyzed for different physical and chemical properties. A uniformity trial was conducted on wheat in the field. Classical statistical and geostatistical techniques were used to describe the variability in measured soil properties and wheat yield. Most of the soil properties and wheat yield had a very high coefficient of variation. Variability in soil properties and wheat yield was best described by a linear model. The potential wheat yield was estimated using the relationship between wheat yield and lime content, and was used in determining nitrogen (N) fertilizer rates for different areas. The effects of soil variability on crop growth and profitability of fertilizer used were also demonstrated to the farmers.

ISSN:0010-3624    

DOI:10.1080/00103629809369963

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A sequential extraction procedure was used to assess the availability of selenium (Se) from four Scottish soils which may receive sewage sludge and a sewage sludge that may be applied to agricultural land. The procedure identified two exchangeable (available) and three non‐exchangeable Se fractions. The exchangeable fractions were defined as soluble (0.25M KCl) and ligand exchangeable (0.1M KH2PO4). The non‐exchangeable fractions were defined as acid‐extractable (4M HCl), oxidizable (dissolution in KClO3and concentrated HNO3), and residual (dissolution in HF and HNO3). The fraction of Se defined as acid‐extractable is not readily available for plant uptake, but has the potential to become available through chemical and microbial mobilization. The total Se was also determined for each soil and the sewage sludge by a one step digestion procedure using HNO3and HF acids. The determination of Se in the individual fractions was performed by isotope dilution‐mass spectrometry using76Se. The total Se in the soils ranged from 0.5–0.8 ug g‐1and less than 5% was available. The sewage sludge had a total Se of 3.55 μg g‐1, but <4% was available for uptake with a further 5% potentially available. The sum of the Se concentrations in the fractions was in good agreement (92–108%) with the total Se concentrations found by the one step digestion. With the likely increase of disposal of sewage sludge to land, the method provides a means of assessing the bioavailability of Se for plant uptake from sewage sludge and sludge amended soil.

ISSN:0010-3624    

DOI:10.1080/00103629809369964

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An investigation was conducted to study the effect of humic (HA) and fulvic acid (FA) on the dissolution of aluminum phosphate (AlPO4) and iron phosphate (FePO4), to analyze the dissolution products, and assess their availability to plants. The rate of dissolution was determined by shaking 10 mg of Al‐ or FePO4with 0 to 800 mg L‐1of HA or FA solutions at pH 7.0 for 0 to 192 hours. The phosphorus (P) concentration was measured in the extracts by spectrophotometry, whereas the nature of P‐humic acid complexes was determined by31P NMR analysis. Availability of dissolution products was studied by growing corn plants in aerated hydroponic solutions receiving treatments of 50 mg Al‐ or FePO4and 0 to 800 mg L‐1of HA or FA at pH 5.0. The results indicated that the amount of P released by HA or FA increased with time. Humic acid was more effective than FA in dissolving the metal phosphates. The31P NMR analysis showed that the dissolution products contained free orthophosphates and minor amounts of P‐humic acid complexes. This confirms the role of HA as a powerful chelator of Al and Fe, liberating in this way the orthophosphate anions. Corn plants grown in hydroponics, with AlPO4or FePO4as the source of P, exhibited better growth performance when HA or FA are present.

ISSN:0010-3624    

DOI:10.1080/00103629809369965

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In the San Luis Valley of south central Colorado, winter cover crops (WCC) are used to reduce soil erosion and scavenge residual soil‐N. Some San Luis Valley farmers are beginning to use WCC as a source of over‐winter or early‐spring grazing. Common WCC used by farmers, wheat(Triticum aestivumL.) and rye(Secale cerealeL.) are reported to accumulate high levels of nitrate nitrogen (NO3‐‐N) in aboveground biomass that can be toxic to animals. Evaluation and calibration of a quick Cardy Meter2Sap Test (CMST) for determination of NO3‐‐N status in the field will facilitate the management of these WCC. Field and growth chamber studies were conducted to correlate the CMST with laboratory procedures and with plant and soil parameters. In field and growth chamber studies, the CMST was correlated with standard dry tissue NC3‐‐N laboratory analysis (P<.001) and with soil inorganic N content (P<.05). These field and growth chamber studies show that the CMST can be a tool in helping farmers identify fields where WCC aboveground biomass is accumulating potentially toxic levels of NO3‐‐N. Additionally, plant parameters such as nitrogen uptake, biomass, and grain yield of WCC grown under growth chamber conditions were correlated with the CMST readings conducted at the growth stage, Feekes five (P<.05). The growth chamber results suggest that if WCC are grown for grain production, the CMST can help identify the needs for additional nitrogen (N) fertilizer application at Feekes five.

ISSN:0010-3624    

DOI:10.1080/00103629809369966

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A kinetic approach was developed to indicate the inherent capacity of aquatic plants to absorb heavy metals. The concept was based on the hypothesis that heavy metal uptake by plants follows a first‐order mathematical model depending on the heavy metal concentration in the biomass of this plant. This method enabled the evaluation of two parameters: (i) the specific metal uptake rate (k) and (ii) the maximum specific content (Epl,8) of this metal in the aquatic plant. The specific uptake rate coefficient of the metal depended upon the concentration of the metal in the liquid phase, as can be seen from a Michaelis‐Menten‐type equation. This equation has two constants: (i) a maximum specific metal uptake rate (kmax) and (ii) a Kscoefficient. The maximum specific uptake rate coefficient was useful in the evaluation of the ability of different aquatic plants to absorb specific heavy metal, as well as in the evaluation of the selectivity of absorption between two or more metals by the plant. The maximum specific heavy metal content can be used for quantitative evaluation of an aquatic plant's ability to select this heavy metal. The ability of an aquatic plant to clean its aquatic environment from the metal can be evaluated in terms of the Ks‐coefficient. An example of this kinetic approach is given by usingApium nodiflorum.Experimental data from an aquatic system ofApium nodiflorumwere collected and applied to the proposed kinetic approach for the estimation of parameters Epl,8kmaxand Ksof the proposed kinetic model, whereas the adequacy of the model was examined by simulating a real process and comparing the predicted and measured values using χ2‐test.

ISSN:0010-3624    

DOI:10.1080/00103629809369967

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629809369968

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An investigation was conducted to study physical and chemical change at two adjacent soil sites, one used for irrigated cotton since 1972 (cultivated) and the other for traditional grazing and browsing (uncultivated). The soil at each site, a clayey Vertisol was described and sampled for physical and chemical analyses. The result showed that the surface layer of the uncultivated soil was denser and more compact than that of the cultivated soil. Soil porosity and moisture build‐up were lower in the uncultivated than in the cultivated soil. Due to percolation of irrigation water and leaching of soluble salts, salinity, concentration of soluble cations, anions, and exchangeable cations were slightly higher at the lower soil depths in the cultivated than in the uncultivated soil. The exchangeable sodium percentage (ESP) also followed the same trend. Correlation coefficient between the values of electrical conductivity, soluble and exchangeable cations, sodium adsorption ratio (SAR), and ESP were more significant for the cultivated than for the uncultivated soil. Cultivation has reduced organic matter levels by 15%.

ISSN:0010-3624    

DOI:10.1080/00103629809369969

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The efficiency of Mehlich‐3 reagent as an extractant for aluminum (Al) and iron (Fe) was studied in Galician coal mine soils, in the process of reclamation. Mehlich‐3 Al and Fe values were compared to those from other Al and Fe tests and with phosphorus (P) sorption. The soils are very heterogeneous, consisting mainly of carbonaceous and non‐carbonaceous clays and shales, which are often rich in pyrite. Some of them have been amended with topsoil or fly ash. One hundred forty samples, from 0 to 15 or 15 to 30 cm, were analyzed. The pH values ranged from 2.7 to 8.4; oxalate and pyrophosphate Al from 0 to 1.17%, and 0.02 to 0.58%, respectively; and oxalate and pyrophosphate Fe from 0.02 to 2.25% and 0 to 1.28%, respectively; PSI (P sorption index) values varied between 0 and 55.1. The Mehlich‐3 Al values ranged from 24 to 2600 mg kg‐1. A close relationship was observed between Mehlich‐3 and oxalate Al values (r=0.77), although the regression line tended to be curvilinear. Mehlich‐3 Al was better correlated than oxalate Al to pyrophosphate Al (r=0.66 vs. r=0.59) and also to pH‐NaF (r=0.89 vs. r=0.74). The Mehlich‐3 Al is almost as good as oxalate Al in estimating non‐crystalline Al, the correlation coefficients between log PSI and log (Mehlich‐3 Al) or log (oxalate Al) being 0.51 and 0.57, respectively. The Mehlich‐3 Fe correlated to available (r=0.63), exchangeable (r=0.65) and soluble Fe (r=0.66), but not to non‐crystalline Fe.

ISSN:0010-3624    

DOI:10.1080/00103629809369970

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Crop residue management influences the soil physical, chemical, and biological environment. Our objective was to examine, in unfertilized rotation systems and a semi‐arid environment, the effects of cultural practices on soil nitrate, nitrogen (N) in plant tissue, and yield of rainfed grain sorghum [Sorghum bicolor(L.) Moench]. Field experiments conducted on a wheat‐sorghum‐fallow (WSF) rotation system included conventional tillage plus furrow diking (FD), conventional tillage (CT), no‐tillage with wheat(Triticum aestivum)residue maintained on the plots (NT+), and no‐tillage with residue removed (NT‐). Wheat residues in FD and CT plots were incorporated during tillage operations. Treatments were imposed 2 weeks before seeding of sorghum. Soil water was measured at three growth stages of sorghum: emergence, flowering, and harvest. The FD and NT+ treatments resulted in increased storage of growing season precipitation, which subsequently produced higher sorghum grain yield. Diking resulted in about 44 mm more stored soil water at emergence and about 770 kg ha‐1more sorghum grain yield than the CT treatment. The NT+ treatment also resulted in significant increases in water storage (42 mm) and sorghum grain yield (870 kg ha‐1) compared to NT‐ treatment. Furrow diking resulted in greater (P≤0.05) soil NO3‐N at the 30‐ to 60‐cm depth at flowering. Concentrations of N in leaf, stover, and grain were greater in plants with FD than with other treatments. Available soil water, soil NO3‐N, sorghum leaf‐N concentration, and grain and stover yields were noticeably responsive to cultural practices.

ISSN:0010-3624    

DOI:10.1080/00103629809369971

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The release of soil phosphorus (P) to solution has been described by extraction of soil with iron (Fe)‐oxide coated paper strips. Little information is available, however, on where this P is coming from. The effect of removal of reversibly adsorbed soil P on the distribution of inorganic P forms was investigated for 12 Italian soils. Phosphate was removed from these soils by Fe‐oxide strips after incubation with P (0 and 100 mg P kg‐1) for 90 days. With no applied P, 3 to 17% of the total soil active P [saloid‐P, aluminum‐phosphate (Al‐P), iron‐phosphate (Fe‐P), and calcium‐phosphate (Ca‐P) was removed by the Fe‐oxide strips. The change in strip‐P following P addition (100 mg kg‐1soil), ranged from 12.9 to 53.5 mg P kg‐1, with P coming almost entirely from the active P fractions. A close relationship between the changes in desorbed strip‐P after P equilibration and soil P sorption index (SI) was found for the studied soils (r2=0.96). Thus, the release of soil P for plant uptake or transport in runoff was a function of the amount of “actively”; sorbed P and an estimate of P sorption.

ISSN:0010-3624    

DOI:10.1080/00103629809369972

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor