摘要:

Retentivity data for 409 South African soils were obtained from several sources. Water retained at matric potential values of 0,−1,−3,−10,−30,−100,−500 and−1500 kPa was determined from the retentivity curve for each soil core. Retentivity at each matric potential value was related to clay, silt, (or clay plus silt), fine sand and bulk density using multiple regression analysis. For the combined data, R2values ranged from 0,59 at−3 kPa to 0,86 at−1500 kPa. Using data from a single source, R2values ranged from 0,55 at−1 kPa to 0,93 at - 50 kPa.

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634212

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

In an experiment conducted outdoors, usingCitrus jambhiriplants, we obtained comparativein situdew point hygrometer, Psychrometer and pressure chamber water potential measurements. Partial abrasion of the leaf cuticle was effected prior to sealing thermocouple hygrometers against leaf surfaces. Contrary to common belief, the dewpoint hygrometric technique was found to be affected by leaf conductance, and therefore cannot be considered isopiestic. Dewpoint hygrometric water potential values were generally lower than corresponding pressure chamber or psychrometric measurements.S. Afr. J. Plant Soil1986, 3: 156–160

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634213

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

'n Aantal sonneblombasters is vergelyk by drie plantpopulasies oor twee seisoene te Ermelo, Sandvet en Warmbad. Die doel was om die kompensasievermoëvan kultivars te bepaal vir 'n swak stand. Onder laepotensiaal-toestande was die kultivar X plantpopulasie-interaksie nie beduidend nie, wat aantoon dat kultivars soortgelyk op plantpopulasie reageer het. Onder mediumpotensiaal- toestande het die vinnige kultivars hoër populasies benodig om 'n hoëopbrengs te gee en onder hoëpotensiaal- toestande is plantpopulasie 'n belangrike faktor wat die prestasie van kultivars beïnvloed. Die kultivars AS 504, SNK 25 en SO 323 het relatief goed presteer oor al drie populasies en onder hoë- sowel as laepotensiaal-toestande, wat aantoon dat hierdie kultivars geskik is vir gevalle waar Standprobleme met sonneblom kan voorkom.S.-Afr. Tydskr. Plant Grond1986, 3: 161–164

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634214

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Severe lodging in maize lands on Cedara on the 24 February 1985 was caused by a rainstorm registering Force 10 on the Beaufort scale. Large differences in lodging existed between plots in three tillage trials. In two identical primary tillage trials, four different systems of soil preparation were being compared; in the other, direct drilling was being compared to ripping with a specialized slant-legged plough. In all three cases, standability under direct drilling was more than double that under any other treatment. It appears that the firm soil condition occurring at the surface under direct drilling provides better anchorage for the maize roots, thus preventing severe root lodging. Stem lodging constituted a greater proportion of total lodging under direct drilling than under the other tillage treatments.S. Afr. J. Plant Soil1986, 3: 165–170

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634215

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Die oesindeks van mielies is bepaal in vier veldproewe. Verskille tussen mieliekultivars het voorgekom. Kultivars wat hoëgraanopbrengste gelewer het in 'n kultivarproef, het ook deurgaans hoëoesindekswaardes gehad. In 'n langtermyn- bemestingsproef het behandelings wat kalium ontvang het, hoër oesindekse gelewer as diésonder kalium, terwyl stikstofbemesting die oesindeks verlaag het. By lae plantpopulasies kon geen duidelike patroon in oesindekswaardes waargeneem word nie, maar met verhoging van die plantbevolking bo 30 000 plante ha−1het die oesindeks in 'n wisselende mate afgeneem by al die kultivars wat ondersoek is. Dit het bygedra tot die verskynsel dat die rangorde waarin kultivars ten opsigte van graanopbrengs presteer het, verander het met verandering in plantbevolking. Die noodsaaklikheid om in mielieproewe ook die biologiese opbrengs (en dus oesindeks) te bepaal, word beklemtoon.S.-Afr. Tydskr. Plant Grond1986, 3: 171–175

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634216

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Two naturally-occurring polyacetylene derivatives are found inTagetes minutaL. andBidens bipinnataL. which, when released into the soil, may affect crop growth. They are alpha- terthienyl in roots ofT. minutaand phenylheptatriyne in leaves ofB. bipinnata.Soil samples were collected from a lot where pure stands of the two weeds were found to be growing. Similar soil was also sampled for control purposes, where the two weeds did not occur. The effect of aqueous extracts, taken from the weed-infested soils, on seed germination of seven horticultural crop species was determined in the laboratory. Nine crop plant species were also grown in pots containing the sampled soil. The species were: carrot, cucumber, lettuce, maize, onion, radish, squash, sunflower and tomato. Seed germination was delayed by aqueous extracts from the weed- infested soils. Where soil was infested withTagetesduring the previous season, dry mass of top growth and plant height of all the test plants were greatly reduced. Soil from an earlierTagetesinfestation had less of an effect on growth, with carrot and maize growing normally and growth of cucumber stimulated. Soil from aBidensinfestation significantly affected the eight plant species tested, although not to such a marked degree as soil from a recentTagetesinfestation.S. Afr. J. Plant Soil1986, 3: 176–180

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634217

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

The concept of irrigating in excess of plant water requirement to restrict soil profile salinity to acceptable limits is well established. The tolerable upper salinity limit is used to calculate the leaching requirement. This upper limit is determined mainly by crop salt sensitivity and acceptable yield decrease. It is proposed that when salinity limits are such that reduced yields result, then plant water use is also reduced. Should the crop be irrigated according to water requirements for non-saline conditions, the leaching fraction will be higher than planned. A degree of self-adjustment in the leaching fraction can thus be expected. Calculations were carried out to confirm and demonstrate the importance and applications of this concept.S. Afr. J. Plant Soil1986, 3: 181–184

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634218

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Several experiments have been done at Cedara in attempts to control broadleaved weeds in unfilled lands during winter. A number of herbicide treatments were tested on Conyza spp.,Coronopus didymus, Gnaphaliumspp.,Hypochoeris radicata, Oenothera roseaandTaraxacum officinale.Where moisture conservation is an objective, these weeds, which grow during the winter, must be controlled. The most promising herbicide mixtures or combinations tested include glyphosate, paraquat and/or 2,4-D together with appropriate wetting agents. For example, consistent broad-spectrum control has been achieved with an initial application of 2,4-D + wetting agent, followed 8–10 days later by paraquat + a wetting agent.S. Afr. J. Plant Soil1986, 3: 185–188

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634219

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

Monitoring for many years of the soils of an effluent disposalsite inthe eastern Transvaal has shown that the disposal of alkaline and saline effluents on red sesquioxic clays has not appreciably affected soil permeability but has brought about high ESP levels (<40%) and moderate salinity in the lower subsoil horizons. The soil in these horizons remains permeable even after complete removal of electrolytes by leaching. It was found that although ESP increased with depth, the pH of the saturated pastes remained unusually low and that within the soil profile, pH decreased with Increasing ESP. Furthermore, in spite of moderate salinity in the lower subsoils, the exchange complex did not appear to be fully base saturated when CEC was determined by the ammonium acetate method (pH 7) in spite of soil pH being close on 7. In an attempt to find a reason for these apparent anomalies, five subsoil samples with ESP's ranging from 13 to 45 were selected from two profiles and leached with successive small quantities of deionized water. It was found that this removed not only the normal free water-soluble salts but also significant amounts of apparently adsorbed sodium, thus reducing ESP and further lowering base saturation. This was accompanied by only a small rise in soil pH, by about 0,3 to approximately 7,1.S. Afr. J. Plant Soil1986, 3: 189–192

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634220

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor

摘要:

A field trial is described, in which the response ofLupinus albusandL. angustifoliusto three levels of P and five of K was measured. The P level of the soil was moderate, but the K content was extremely low. Both species responded only slightly to P and K; significant differences were only obtained in stubble yield. The latter results suggest somewhat better response to both elements in Lalbusthan inL. angustifolius.It was concluded that lupins have an unusually efficient K uptake mechanism. Protein content and protein production of the tops and seed did not suggest any effect of the fertilizer treatments on the efficiency of nitrogen fixation. Findings of the P, K, Ca and Mg content of the tops of Lalbusat the late bud stage and the seed of both species are also reported.S. Afr. J. Plant Soil1986, 3: 193–197

ISSN:0257-1862    

DOI:10.1080/02571862.1986.10634221

出版商:Taylor&Francis Group    

年代:1986

数据来源: Taylor