ISSN:0010-3624    

DOI:10.1080/00103629409369072

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629409369073

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629409369074

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629409369075

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The development and current status in South Africa of soil and plant analysis for fertilizer advisory purposes is reviewed. Data obtained from governmental and private laboratories indicate that from 1966 to 1992 the number of soil and plant samples analysed annually increased by approximately 180 % and 470 %, respectively. Plant analyses increased exponentially, but countrywide analysis of soil samples has not increased since 1982. An inadequate soil test calibration base in many parts of the country, a scarcity of soil fertility researchers, and extractant and procedural differences among laboratories are considered to have been largely responsible. Advisory laboratories in those regions supported by ongoing field research programmes have shown continual growth in analytical output and farmer demand. In these areas, the intensity of soil sampling compares favourably with that in developed countries, but in other important cropping areas the intensity of sampling has stabilized at about 90 ha sample. Over 80 % of all plant analyses are conducted by laboratories serving high value deciduous and subtropical fruit industries, industries better able to make use of internationally established analytical norms. While there is an urgent need for expanded soil test calibration research for annual row crops, it is doubtful that this need will be easily satisfied. The availability of funds for such research is declining and the publication demands on young researchers make long‐term field studies decidedly unattractive.

ISSN:0010-3624    

DOI:10.1080/00103629409369076

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Soil testing in Brazil is done by about 180 laboratories, of which 167 provided the statistical information used in this paper. There are few differences in analytical procedures for the macronutrients and soil acidity. All laboratories determine exchangeable Ca, Mg, and K. Two thirds of the laboratories use Mehlich No. 1 solution to determine P whereas the other third extract the element from soils with an ion exchange resin procedure, introduced in Brazil in 1983. The pH is determined either in water or in 0.01 M CaCl2. For lime requirement, the analytical data used is either exchangeable aluminum, SMP buffer pH, or cation exchange capacity and soil base saturation. Some laboratories determine also S, micronutrients, clay content, and electrical conductivity. Soil samples analyzed increased from 267 thousand in 1972 to 719 thousand in 1989. Private laboratories increased their share from 34% to 48% in this period. Sao Paulo State had the largest increase in the number of soil samples analyzed during the last decade, increasing from 65 thousand samples in 1982 to 255 thousand samples in 1989. Plant analysis is increasing in importance and about 40 laboratories analyzed around 100 thousand samples in 1991.

ISSN:0010-3624    

DOI:10.1080/00103629409369077

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The increasing demand for analytical data from laboratories in the field of soil and plant analysis and the increasing possibilities of modern instrumentation (speed and multi‐element determinations) ask for a reconsideration of the conventionally used analytical methods together with stronger requirements for quality control.

ISSN:0010-3624    

DOI:10.1080/00103629409369078

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Cropping, horticultural industries, and pastoral enterprises based on improved pastures occupy only a small percentage of Australia's land mass. The major part of Australian agriculture is confined to limited zones, usually within 500 km of the coast, due to rainfall and limited irrigation potential. This is in stark contrast to the United States with its productive mid‐west agricultural belt.

ISSN:0010-3624    

DOI:10.1080/00103629409369079

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Although the literature is replete with guidelines as to how soil and plant samples should be obtained, soil sampling remains a fragile link in the soil testing process, and interpretation of plant analytical data is often fraught with uncertainty. There is unquestionably a need to re‐examine currently accepted procedures and to identify aspects which might lead to an improvement in the quality of samples submitted to advisory laboratories. This paper discusses some of the weaknesses in soil sampling identified in Natal, South Africa, and an aspect of plant sampling usually overlooked, but deserving of much closer examination. None of the issues discussed are uniquely original, but all have had an impact on soil testing and plant analysis in South Africa and may well have application elsewhere. Aspects of soil sampling discussed include the sampling tool, the influence of subsoil properties on the value and meaning of topsoil analytical data, and heterogeneity in farmer fields and experimental plots. Choice of sampling tool is considered to be an issue of particular importance, since sample quality Is strongly related to the labour and time required to obtain samples and many of the tools popularly employed are not conducive to high intensity sampling. A sampler is described which has all the attributes of other acceptable equipment, but which is particularly easy to use. The importance of subsoil properties is evaluated by examining the influence of subsoil acidity, K distribution in the profile and vertical K movement on topsoil‐based fertilizer recommendations. Brief discussion is included on the effects of soil heterogeneity in farmer fields on sample integrity and of implement carry‐over of nutrients in long‐term calibration trials. Plant sampling is examined in the light of fortuitously acquired findings on the influence of soil moisture on nutrient uptake by maize. Data presented demonstrate that variations in soil water content several weeks prior to sampling may invalidate commonly accepted tissue content norms. These data might help to elucidate anomalous findings and encourage re‐examination of an issue considered to be fundamentally important to the diagnosis of plant nutritional status.

ISSN:0010-3624    

DOI:10.1080/00103629409369080

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Universal extractant is a term used to designate reagents or procedures to extract several elements or ions to assess soil fertility status or levels of toxicity. Ideally, universal extractants should be rapid, reproducible, inexpensive, adaptable to soils from different regions, and the extraction of the nutrients should be from the labile forms that supply plant roots. Most extractants in use fall short of these requirements and are in reality multinutrient extractants, given priority to the laboratorial convenience. The most commonly used “universal” extractants are known as Morgan, Mehlich No. 1, Mehlich No. 3, and AB‐DTPA, but there are other multinutrient extractants, such as 1 M neutral ammonium acetate, TEA‐DTPA, and ion exchange resin. None of these are able to extract all elements determined in soil testing laboratories, nor are they always efficient for all nutrients. Nitrogen, S, B, and Mo are usually not determined by these extractants and require single nutrient extractions. The elements commonly extracted for soil analysis are P, K, Ca, Mg, Na, Zn, Cu, Fe, Mn, and occasionally Cd, Ni, Cr, and Pb. Phosphorus is the most difficult extractable element since any extracting solution present lower correlations with the more complicated and not much used ion exchange resin extraction. The exchangeable cations, K, Ca, Mg, and Na are rather easily determined with most extractants. For Zn, Cu, Mn, Fe, Cr, Cd, Ni, and Pb, the most effective extractants are those containing DTPA. Among the non‐conventional soil test methods, the extraction with ion exchange resin is one of the most promising alternatives.

ISSN:0010-3624    

DOI:10.1080/00103629409369081

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor