摘要:

Winter cover crop studies were conducted for 17 years with cotton grown on a Dubbs‐Dundee soil complex at the University of Arkansas Delta Branch Experiment Station. This experiment was established in 1972 to investigate the changes induced by winter cover crops of rye, vetch, and lupine. The rye and lupine were later changed to rye + vetch and rye + crimson clover, resp. Cotton yield responses to cover crops were found to be highly dependent on the growing season. Although the cover crops averaged a seedcotton yield increase, certain years had drastic yield reductions. This experiment was not designed with sufficient scope to address why yield responses occurred as they did. Soil physical properties of hydraulic conductivity, water retention, porosity, and proportion of large pores were found to be measurable changed by having winter cover crops. In general the change in soil physical properties resulting from the cover crops would result in faster infiltration and transmission of water, more stored water, less crusting, better ability of soil to ameliorate and degrade herbicides and improve soil tilth. The change in these properties may be too small to result in practically cost effective changes. However, it would seem reasonable to assume that if current trends continue the impact would eventually become large enough to become a major concern.

ISSN:0010-3624    

DOI:10.1080/00103629409369250

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The chelate, DTPA, has heen shown to be an effective extraction agent for the micronutrients from peat‐based soilless media. Multiple applications of 2 mM DTPA extracted 95 ppm iron (Fe) after one week and then declined to 16 ppm Fe while 0.2 mM DTPA extracted Fe which increased to 16 ppm after three weeks. Leachate Fe concentrations from 0.02 mM DTPA and 0.02 mM FeDTPA were similar, increasing from 1 to 2 ppm. Leachate Fe concentrations from 0.2 mM FeDTPA increased from 7 to 14 ppm, however, 0.2 mM DTPA decreased from 9 to 3 ppm. The 0 DTPA treatment had a constant 0.1 ppm Fe in the leachates. Manganese (Mn) was rapidly extracted from the medium. Leachate concentration of both copper (Cu) and zinc (Zn) increased slightly above applied concentrations. There were no differences in dry weight or total micronutrient content among geranium(Pelargonium x hortorum’Aurora') grown with either DTPA or FeDTPA treatments 0.2 mM and below.

ISSN:0010-3624    

DOI:10.1080/00103629409369251

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new calibration of the Mehlich 3 soil test for potassium (K) is proposed for the Mississippi Delta area, based on leaf analyses and K deficiency symptoms in cotton plants. The calibration reflects the need to supply adequate K concentrations to plants during the fruiting period of greatest K demand. The lowest levels and highest percent of sites exhibiting K‐deficiency symptoms were associated with the fifth week of flowering; or at the peak bloom stage of plant growth. The fifth week of flowering was selected to base soil and plant evaluations for K needs. A 1.5% leaf K level was selected as the critical leaf K level (the level that plants experience a nutrient deficiency and yield reductions), based on visual leaf K‐deficiency symptoms observed in plants 95% of the time. Leaf K concentrations below 1.51% identifies K‐deficiency symptoms in the upper leaves through eight weeks of flowering. A simplified equation [Topsoil K (lb/A) = 480 + 5 x CEC (Milliequivalents/100g soil)] defines critical soil test K concentrations with respect to the cation exchange capacity (CEC) in soils. This equation can be used to determine present topsoil K needs for cotton in the Mississippi Delta area based on a 1.5% critical leaf K level during the fifth week of flowering.

ISSN:0010-3624    

DOI:10.1080/00103629409369252

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Murphy and Riley method for phosphorus (P) determination is used with almost all commonly used soil P extractants, but few tests for the effects of extractants itself on the indicator species have been reported. In practice, it is important to know the period of stability of the indicator species and the range of P and extractant concentrations that produce reliable results. In this study, a series of tests was conducted over a range of extract volumes to determine indicator species stability and to identify factors affecting it. Three soil P extradants (Mehlich‐3, Bray‐I, and Modified Truog) and three soils were tested at different levels of extract volume, solution pH, and P concentration. In our tests, Bray‐I and Modified Truog did not interfere with the stability of the indicator species under conditions commonly used for soil P determinations. Mehlich‐3 caused fading of the blue color at low P concentrations and precipitation of a blue compound at high P concentrations. This instability was most pronounced when Mehlich‐3 extradant volumes exceeded 2 mL in 50 mL final solutions with P concentrations greater than 0.4 mg/L. The EDTA and NH4NO3contained in Mehlich‐3 both contributed significantly to the observed instability. Our results indicate that use of the Murphy and Riley method with untested extradants can produce unreliable P determinations, especially when soil extract volumes are high relative to the total volume of the colored solution.

ISSN:0010-3624    

DOI:10.1080/00103629409369253

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effects of storage on soluble phosphorus (P) fractions in water extracts of two soils, and standard solutions of inorganic and organic P compounds have been quantified. The water extracts were obtained from a peaty podzol and an iron humus podzol and contained about 140 and 270 μg P/dm3, respectively. The standard solutions contined 100 μg P/dm3. Storage conditions investigated included different types of containers (glass and polythene), different temperatures (4, 22, and ‐12°C), and times. Hydrolysis of dissolved condensed phosphorus (DCP) and dissolved organic phosphorus (DOP) compounds in the water extract of the soils and standard solutions were observed at 4 and 22°C after one day. Total dissolved phosphorus (TDP) in the standard P solutions was not significantly affected by storage. However, TDP in water extracts of soils decreased significantly when the solutions were stored in polythene at 22°C. The loss of P after 15 days was 56 and 31% in the extracts from the peaty podzol and iron humus podzol, respectively. In relation to the storage of samples frozen at ‐12°C, freeze‐thawing the water extracts of the soils or standard solutions did not affect their P composition. Storage of a water extract of the peaty podzol in polythene at 4°C for 74 days did not affect TDP but MRP increased by 60% at the expense of both DOP and DCP.

ISSN:0010-3624    

DOI:10.1080/00103629409369254

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nitrogen (N) in forest soil extracts and surface waters may be dominantly in organic compounds as dissolved organic nitrogen (DON). Due to various difficulties associated with measuring total N (as TKN) by the Rjeldahl digest, this important vehicle for nutrient movement is rarely monitored. By coupling two relatively new methods and optimizing them for use in soil studies, we developed an alternative method for measuring DON. Analysis of pure compounds and field samples shows that persulfate oxidation combined with conductimetric quantification of nitrate (NO3) provides a highly accurate measure of dissolved N content. With relatively inexpensive equipment and reagents, a single technician can digest and assay over a hundred samples a day. This rapid, simple, and accurate assay may make it possible to routinely monitor DON where it had previously been impractical. This in turn could substantially enhance understanding about the form and quantity of N involved in nutrient fluxes.

ISSN:0010-3624    

DOI:10.1080/00103629409369255

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The amount of phosphorus (P) dissolved in a closed‐incubation system, in soils receiving Christmas Island grade‐A phosphate rock (CIPR), Gafsa phosphate rock (GPR), and triple superphosphate (TSP), as measured by extraction with 0.5M NaHCO3(APb) or 0.5M NaOH (AP) and expressed as ?Pb/?P*100 (PDP) was compared to P uptake (?Ps) bySetariain a glasshouse experiment. There was no direct relationship between APs and PDP for CIPR, GPR, and TSP added at 50 and 150 mgP/kg soil to three Malaysian soils (Bungor, Kundor, and Segamat) during a 10‐month period. Averaged across soils, rate of addition, and P sources, ?Ps was 17% higher than PDP. Overestimation of PDP by ?Ps could be due to the ability of the roots ofSetariato use more of the P which is dissolved from the three P sources and then chemisorbed, than can be extracted by the NaHCO3reagent. The chemisorbed P pool is extractable using 0.5M NaOH. There was a close relationship between ?Ps and ?P, with a correlation coefficient of 0.85**. Residual P, determined by Pb method after each harvest, successfully predicted Ps bySetariain the subsequent harvest with correlation coefficients varying between 0.74* and 0.99** for CIPR, GPR, and TSP in five soils (Bungor, Durian, Kundor, Segamat, and Tok Yong). The critical Pb values ranged from 5 for Durian to 10 mgP/kg soil for Kundor.

ISSN:0010-3624    

DOI:10.1080/00103629409369256

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The amounts of sulfur (S) mineralised in three soils incubated in both open (i.e. leached) and closed systems increased with time over the period of the incubation. However, the rates and patterns of S release differed with the soil type and incubation technique used. The pattern of S mineralisation during the open incubation was a rapid release of S in the first two weeks, followed by a slightly slower almost linear rate of release for the remainder of the incubation. The pattern of S release during the closed incubation was slightly curvilinear. In the short term, the closed system released similar or greater amounts of S than the open system. However, in the long term, more S would be mineralised in the open than that in the closed system. Conditioning (i.e. pre‐incubation of air‐dried samples) did not significantly affect the amounts of S mineralised in the soils incubated in the open system, but did in two soils incubated in the closed system.

ISSN:0010-3624    

DOI:10.1080/00103629409369257

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In a study with fifty peaty growing media some water extracts were tested on their ability to estimate the chemical composition of the “soil”; solution. The chemical and physical characteristics of the growing media differed widely. The soil solution was prepared by pressing out 30–50% of the the water from the growing media exactly brought on a water content equal to the water content at a pressure head value of‐1.0 kPa. The water extracts compared were, the press extract of growing media brought by a quick method on a water content at a pressure head of‐1.0 kPa and an extract prepared from a 1:1.5 (v/v water/growing medium) suspension. In the extracts all the likely anions and cations were determined. The correlation coefficients for the relationships between the analytical data of the soil solution and the analytical data of the extracts varied between 0.975 and 0.993 for the extract prepared from the media quickly brougt to a water content at a pressure head of‐1.0 kPa and between 0.912 and 0.992 for the extract prepared from a 1:1.5 suspension. So both extracts are a suitable aid to estimate the chemical composition of the soil solution. The extraction methods compared are discussed on their suitability for routine soil testing purposes. An overall view for the interpretation of the analytical data is presented.

ISSN:0010-3624    

DOI:10.1080/00103629409369258

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A simple method was developed for measuring phosphorus (P) mineralisation in soil using an anion exchange membrane. Labile inorganic phosphate was first removed from the soil by means of the membrane. The soil samples were then filtered on GF/C papers and incubated moist under aerobic conditions for seven days at 39°C. The inorganic phosphate produced during incubation was extracted using a second extraction with the anion exchange membrane to give a measure of phosphorus mineralisation. The method was applied to 17 soil samples taken from Inceptisols, Andisols, and Spodosols under pasture and pine forest.

ISSN:0010-3624    

DOI:10.1080/00103629409369259

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor