摘要:

Calcareous soils often need supplemental manganese (Mn) to support optimum plant growth, but some reports show that the apparent recovery of applied Mn is very low in such soils, i.e., nearly all of the applied Mn is retained in the soil. This experiment was conducted to find the relationship between the retained Mn and selected properties of calcareous soils. Eleven surface (0–20 cm) soil samples with pH ranging from 7.7 to 8.1 and calcium carbonate equivalent (CCE) ranging from 20 to 50% were used in the Mn adsorption study. Two‐gram subsamples of each soil were equilibrated with 20 mL of 0.01M CaCl2solutions initially containing 10 to 200 mg Mn L‐1. The Mn that disappeared from solution (after 6 h shaking at 25°C) was considered as adsorbed (retained) Mn. The adsorption data showed a highly significant fit to Freundlich and also to the two‐surface Langmuir adsorption isotherms. The coefficients of both isotherms showed significant positive correlations with cation exchange capacity (CEC), organic matter (OM), and CCE of the soils indicating that OM and calcium carbonate are the sites of Mn retention in calcareous soils. Comparison of the adsorption data of this experiment with those of plant Mn uptake of the same soils (published earlier) shows that as the Langmuir second surface adsorption maxima (maximum retention capacity) of the soils increase the plant Mn concentration and uptake decrease.

ISSN:0010-3624    

DOI:10.1080/00103629809370008

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A relatively low‐cost digital measurement system configured with off‐the shelf components (a standard consumer High 8‐mm camcorder, video cassette recorder, video monitor, desktop computer with image capture board, and image analysis software) has been used in applications from benchtop stem length and leaf area measurements to aerial imaging for precision agriculture applications. However, preliminary research identified a systematic error in estimating leaf area using this system, which further investigation revealed to be caused by the internal calibration method used. Further research was needed to determine appropriate calibration methods for length and area measurements using this system. Length measurements were very accurate and repeatable using a vertical (i.e., parallel to the axis of objects) two‐point calibration. Two‐point (vertical, horizontal or diagonal) calibration led to over‐ or under‐estimation of area, but three‐point calibration yielded very accurate measurements of area and percent coverage. This system proved to be a versatile and useful method of measuring many plant size parameters.

ISSN:0010-3624    

DOI:10.1080/00103629809370009

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The preparation of an air‐dry river‐clay soil as reference soil material for pH and extractable nutrients with a 0.01 M calcium chloride (CaCl2) solution and the homogeneity testing are described. Recommended values for pH and the concentrations of ammonium‐nitrogen (NH4‐N), total soluble nitrogen (N), phosphorus (P), sodium (Na), potassium (K), and magnesium (Mg) using the unbuffered 0.01M CaCl2are given. With respect to nitrate‐nitrogen (NO3‐N), the sample proved not to be sufficienctly homogeneous. The certified soil sample has also been used as a sample in the International Soil‐Analytical Exchange (ISE), a continuous proficiency testing scheme. The values found by the ISE laboratories compared well with the certified values.

ISSN:0010-3624    

DOI:10.1080/00103629809370010

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Accurate determination of orthophosphate (P) in soil solutions is a prerequisite for rigorously assessing soil P availability for plants as well as the potential risk of P transfer to water bodies. Although P is usually measured on extracts filtered at 0.45 μm, little is known on the potential interfences due to the presence of colloidal particles. This work was conducted to study the influence of colloidal particles on P concentration by measuring it both by the phosphoantimonylmolybdenum blue colorimetry and ion chromatography in soil water extracts filtered at 0.45, 0.2, or 0.025 μm. Results strongly suggest that direct measurements with colorimetry might lead to an overestimation of the P concentration due to the solubilization of P‐containing particles in the acid medium prevailing in the solution during colorimetric essay. In the present study, the largest overestimations were observed in soil extracts rich in iron (Fe) and aluminum (Al) that had been filtered at 0.45 μm, on the opposite this overestimation remained lower but constant for the three levels of filtration in the studied calcareous soil. Ion chromatography constantly underestimated P concentration especially when the solutions were rich in Al and Fe. This underestimation could not be related to the presence of dissolved polyvalent cations in the solution and, therefore, might be accounted for by the sorption of P at the surfaces of colloids. In order to limit these interferences, it is proposed to measure P concentration by colorimetry after a filtration of the solution through a 0.2‐ or 0.025‐um membrane, instead of a 0.45‐μm filter. In some cases for instance for soil solutions rich in calcium phosphate particles, it might be advisable to determine P concentration with ion chromatography.

ISSN:0010-3624    

DOI:10.1080/00103629809370011

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Uses of lime‐stabilized biosolids in container media or topsoil formulations may be limited by alkalinity imparted by lime added for reductions in vector attraction and pathogens and for suppression of odors. This experiment was conducted to assess the suitability of quicklime‐stabilized biosolids mixed with calcareous or noncalcareous sand and with sulfur or aluminum sulfate as acidifying agents for development of synthetic topsoil for turfgrass(Lolium perenneL.) production. Grass emergence and growth were inhibited in media that were not amended with an acidifying agent. Additions of aluminum sulfate were more effective in acidification than sulfur, causing an immediate drop in pH, whereas additions of sulfur required about 2 months for a depression in media pH. With time, electrical conductivities were higher in media with additions of sulfur than in media with additions of aluminum sulfate. Calcareous sand mixed with biosolids (2 sand: 1 biosolid, v: v) gave a better medium for growth of turfgrass than noncalcareous sand mixed with biosolids. Calcareous sand flocculated biosolids, whereas noncalcareous sand dispersed them. Results suggest that calcareous sand and aluminum sulfate are effective agents for diluting and acidifying biosolids for development of a suitable topsoil medium for turfgrass production.

ISSN:0010-3624    

DOI:10.1080/00103629809370012

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In order to monitor barley and weed development on a loamy sand soil subjected to different agronomic practices, field experiments were conducted for three growing seasons (1992–95) in a semi‐arid agrosystem in central Spain. For eight years, independent plots were managed with three crop sequences: barley (Hordeum vulgareL.)?vetch(Vicia sativaL.); barley? sunflower (Helianthus annuusL.); and a barley monoculture. In all cases, two tillage systems were implemented: no‐tillage and conventional tillage. In the years with standard rainfall (400 mm) an improvement in growth‐related cultivation variables and yield components of barley were observed in plots under barley?vetch rotation and/or conventional tillage. In drier conditions (<350 mm) the growth rate, crop yield and yield components of barley tended to improve under the no‐tillage system. Barley?vetch rotation and/or conventional tillage increased nitrate‐nitrogen (NO3‐N) content in barley plants. Similar results were found for the concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). In addition, the plots under crop rotation showed a weed biomass with a high concentration of N, K, and Ca in comparison with plots under monoculture. The lack of spring herbicide treatment in the no‐tillage plots led to a 3‐fold increase in weed density compared with the plots under conventional tillage.

ISSN:0010-3624    

DOI:10.1080/00103629809370013

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two soil tests commonly used to characterize the availability of soil phosphorus (P) are Bray P1 (B1) and Mehlich 3 (M3) extradants. The objective of this investigation was to compare M3‐ and B1‐extractable P levels in a Starr clay loam (fine‐loamy mixed thermic Fluventic Dystrochrepts) amended with relatively low to high surface applications of poultry litter (PL). The following eight treatments were applied to the soil for pasture renovation in 1991 and 1992: 1) a control, 2) P application as monocalcium phosphate [Ca(H2PO4)2‐H2O], 3) P application as Ca(H2PO4)2‐H2O and nitrogen (N) application as ammonium nitrate (NH4NO3) and urea, and 4) five levels of poultry litter (PL) based on N content. The five P levels as PL were 56.6, 113.2, 169.8, 226.4, and 283.0 kg ha‐1in 1991, and 49.2, 98.5, 147.7, 196.9, and 246.1 kg ha‐1in 1992, respectively. Soil samples were obtained from the 0‐ to 5‐cm layer in the spring of 1992 and 1993 for extractable P determination. Levels of P extracted from all treatments by the M3 and B1 extractants were linearly correlated both years (r2=0.96 in 1991 and r2=0.99 in 1992). However, M3 extracted more P from the PL treatments, whereas B1 extracted more P from the control, P application, and N and P application treatments. Curvilinear relationships were obtained between P uptake and levels of either M3‐ or B1‐extractable P for the PL treatments (r2=0.713 for M3 and 0.663 for B1 in 1991 and r2=0.925 for M3 and 0.933 for B1 in 1992). These close relationships in 1992 between extractable P and uptake of P for the PL‐ treated soils indicate that both the B1 and M3 extractants could be used to evaluate excess P in PL‐amended soils.

ISSN:0010-3624    

DOI:10.1080/00103629809370014

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The majority of soils in Africa are phosphorus (P) deficient, but the high cost of water‐soluble P fertilizers limits their use by resource‐poor farmers. A low‐cost alternative is to use phosphate rocks. We evaluated the effectiveness of Egyptian phosphate rock (EPR) relative to triple superphosphate (TSP) applied at 0, 15, 30, 45, and 60 kg P ha‐1to annualTrifoliumspecies grown on a P‐deficient Vertisol. The fertilizers were applied once and their effects were followed on seven consecutive annual clover crops. Clover responded to P at all the rates used. Significant (P<0.05) P effects on clover P content and DM yields were observed up to the fourth crop. Over all the seven crops, EPR was 89% as effective as TSP in increasing herbage DM and 93% as effective in increasing herbage P content. Its substitution rates were 79% for DM yield and 86% for clover P content. Therefore, EPR was highly reactive and its use could elevate the P status of the P‐deficient Vertisols and increase feed and livestock productivity in the Ethiopian highlands.

ISSN:0010-3624    

DOI:10.1080/00103629809370015

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The accuracy of phosphorus (P) fertilizer recommendations can be improved by knowing the soil buffering capacity. Field estimates of the change in Mehlich‐3 P per unit of P applied after one year, termed the Field Mehlich‐3 P Buffer Coefficient (M3PBC), were available from five Ultisols and five Oxisols. Specific surface area (SSA), clay content, and iron (Fe) and aluminum (Al) extractable by both citrate‐bicarbonate‐dithionite (CBD) and oxalate (Oxa) were determined on these soils and the results related to the Field M3PBC. The Field M3PBC was highly correlated linearly with SSA and clay content. Also, Field M3PBC was related well with CBDFe, CBDAl, and their summation. Neither OxaFe, OxaAl, nor their summation was correlated with Field M3PBC. The relationship between Field M3PBC and these factors was exponential. Specific surface area and clay gave the best relationships, but Field M3PBC could also be predicted from the CBD summation of Fe and Al, CBDFe alone, or CBDAl alone, in that order. Knowledge of CBD‐extractable Fe and/or Al can be used to establish the rate of fertilizer required to increase the Mehlich‐3 P to a sufficient level on Ultisols and Oxisols. An estimate of CBDFe is available from soil survey data and it should be applicable within a region.

ISSN:0010-3624    

DOI:10.1080/00103629809370016

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The malachite green method was sometimes used to determine low concentrations of inorganic phosphate due to its high sensitivity. The aim of this work was to test the suitability of this method for the determination of phosphorus (P) extracted by various reagents, e.g., KCl 0.01–1.20M, CaCl20.01–0.1M, Na2SO40.01–0.40M, NaHCO30.1M at pH 8.5, and NaOH 0.1M+NaCl 1M. The malachite green method was also compared with the traditional molybdenum blue method on 35 soil extracts. Color development reached stability within 2 hrs and was stable for up to 24 hrs for dilute solutions. For concentrated solutions the stability was inversely proportional to the concentration of the reagent. Salt concentration appeared to have no effect on absorbance in KCl extracts of up to 1.2M and in Na2SO4extracts of up to 0.05M. Higher concentrations of sodium sulfate induced flocculation and precipitation of the dye complex, as did CaCl2above 0.04 M. A strong correlation was found between the malachite green and the molybdenum blue method. The malachite green method can be used for P determination in soil extracts when appropriate time of color development is provided and salt concentration is taken into account.

ISSN:0010-3624    

DOI:10.1080/00103629809370017

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor