摘要:

Movement of NH3plus NH4+from nitrogen fertilizers, band placed either as crystals or as granules in alkaline soils, was determined. The pH values of these soils, whereof the clay contents ranged from 7,6 to 49,9%, were adjusted to approximately 8,8. Fertilizers like (NH4)2SO4, LAN, urea, MAP and DAP were band placed in these soils with different water contents at different bulk densities. The application level was equivalent to 60 kg N ha−1. After a contact period of 14 days the movement of NH3plus NH4+was determined. The distances that NH3plus NH4+moved from the plane of application varied between 45 and 100 mm. The results indicate that the movement of NH4+was small compared to the movement of NH3. The major factor that controlled the degree of NH3movement in soil was the quantity of NH4+converted to NH3. The conversion of NH4+to NH3was governed by the variable soil properties and the type of fertilizer. Both diffusion and convection contributed to the movement of NH3.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634252

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Four months before planting a crop of maize, a study was commenced on a well-drained clay loam soil to test the effect of tillage and surface maize residue on soil water storage. Tillage main plots were split into bare (residue removed) and residue-covered sub-plots. At commencement, all plots were irrigated to field capacity to a depth of 600 mm. Initially, large positive differences in soil water storage developed due to residue cover in the tilled treatments (chisel and disc respectively), but this advantage tended to diminish during the prolonged dry period. Tillage accelerated drying of the surface soils, and the resultant dry layers restricted movement of subsoil water to the surface, causing lower rates of evaporation during long, dry periods. The relatively faster rates of water loss from the covered and bare direct-drill (DD) sub-plots during the dry winter was ascribed to the continuous micropores linking the subsoil and soil surface, which promoted supply of subsoil water to the surface. Residue cover was most effective in reducing stage-one evaporation, but when the rainless period exceeded about 2 weeks, the moister soils under residue resulted in rates of evaporation which equalled and then exceeded those of bare soils. Surface residues were most effective in increasing soil-water storage when rainfall frequency was high just prior to planting, with greater storage where residue cover was higher. Among the bare sub-plots, DD had the driest profiles at planting, whereas the tilled profiles were drier where soil disturbance had been greater.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634253

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The growth and water use of three sugar cane cultivars, NCo376, N12 and N14, were measured under varying degrees of water stress controlled by means of a movable rain shelter. Plots of a first ratoon cane crop were allowed to desiccate on two occasions until about three leaves remained alive oh each stalk. Other plots were irrigated regularly. Destructive and non-destructive measurements were used to estimate daily increments in the wet mass of the cane stalks. Although in the unstressed plots the three cultivars each showed similar maximum cane growth rates (approximately 1,3t ha−1d−1), the peak growth rate was reached by cultivar N14 first and by N12 last. Cane growth rate decreased rapidly as a result of water stress but recovery in growth rate was almost complete two weeks after the stress was relieved. N12 used less water than the other two cultivars in unstressed conditions but no differences between the cultivars were apparent under stressed conditions. The water use efficiency (WUE) of unstressed sugar cane in the stalk elongation stage varied from about 0,03 to 0,3 tc ha−1mm−1. The WUE was reduced by water stress but rapidly recovered to control levels after water stress was relieved.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634254

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Bemestingsproewe is by drie lokaliteite oor vier seisoene uitgevoer deur 'n ongerepliseerde 43-gestrengelde faktoriaaluitleg te gebruik. Peile het gewissel van 0 tot 150 kg N ha−1, 0 tot 45 kg P ha−1, 0 tot 60 kg K ha−1by twee lokaliteite en by die derde is dieselfde N- en P-peile gebruik, maar die derde faktor was kalk met peile wat gewissel het van 0 tot 6 000 kg ha−1. Die resultate toon dat 'n saadopbrengs van 1 300 kg ha−1verkry kan word sonder N-bemesting, terwyl 'n saadopbrengs van 2 000 kg ha−160 kg N-bemesting ha−1benodig. Reaksiekrommes is gepas. Op 'n enkele uitsondering na was daar geen beduidende P- en K-reaksies waar die grondfosfor- en kaliumvlakke van 10 tot 60 mg kg−1(Bray 2) en 0,3 tot 0,5 me 100 g−1onderskeidelik was nie. Die gevolgtrekking word dus gemaak dat 10 mg kg−1P (Bray 2) en 0,3 me 100 g−1K in die grand voldoende is vir opbrengste van tot 2 000 kg ha−1. Kalk het slegs die saadopbrengs verhoog waar die pH (KCl) minder as 4,6 was.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634255

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The cotton breeding program in the Republic of South Africa is conducted at the localities Loskop, Upington and Vaalharts. Preliminary results from breeding trials indicated that a finer but more mature fibre could be produced at Vaalharts as compared to the other two localities. This might be advantageous to the rotor spinning industry. Inanalyses ofvariance over seasonsandlocalities, the order of magnitude of the GxE interaction variances was G×L

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634256

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The mycorrhizal relationship ofPaulownia taiwanianawas investigated on trees from six sites. The species exhibits an endomycorrhizal relationship. Soil spore counts and root colonization levels varied appreciably both between and within sites. Soil from the site with the lowest coefficient of variation for both variables was chosen for a pot trial to investigate the reliance ofP. taiwanianaon its fungal symbionts. Growth ofP. taiwanianain the pots was significantly increased by methyl bromide disinfestation of the soil before planting, through the removal of nematodes. This treatment also reduced the mycorrhizal spore count of the soil. Inoculation with a mycorrhizal fungus failed to improve the growth over and above that of the uninoculated plants. Fertilizer increased the growth of the pot plants, but reduced the nutrient level of the tissues expressed as a percentage of the dry mass. It seems unlikely that the perfection of an artificial inoculation technique forP. taiwaniananurseries could be economically justified.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634257

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

In sitruskwekerye word vegetatiewe groei gestimuleer deur die konsentrasie van voedingstowwe in die groeimedium so hoog moontlik te handhaaf. Dit kan egter te hoëkonsentrasie teweegbring. In die ondersoek is gevind dat growwe- skilsuurlemoensaailinge (GS) optimaal groei waar sproeibemes was met 'n gebalanseerde voedingsoplossing, waarvan die elektriese geleiding (EG) 150 mS m−1was. Troyer citrange (TC) het die beste by 'n EG van 450 mS m−1gegroei. Periodieke ongunstige toestande waar die EG nie optimaal was nie, het groei ook onderdruk. Die EG van 'n blaarekstrak was 'n goeie aanwyser van die EG van die voedingsoplossing vir GS maar swakker vir TC. Die asinhoud van die blare was egter deurgaans 'n swak aanwyser van die EG van die voedingsoplossing.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634258

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Nitrogen losses from nine nitrogen fertilizers, applied to four different topsoil samples, were compared in the laboratory. Total N losses were determined 28 days after application, as a difference between the extractable soil nitrogen initially and after 28 days. The ammonia volatilized during this period was determined. By subtracting this ammonia nitrogen loss from the total nitrogen loss, the‘denitrification’loss was estimated. Ammonia volatilization was important from aqua ammonia, urea or UAN for two soil samples with a clay content of 9,5% and 32,3%, and if the soil pH (H2O) increased above 7,0 as a result of fertilizer application.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634259

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Crust formation and infiltration rates and their dependence on the exchangeable sodium percentage (ESP) of South African (SA) soils, with kaolinite and illite as the dominant clay minerals, were studied by subjecting them to simulated rain. The final infiltration rate (FIR) values of these soils at ESP ca. 2,5 were compared to values reported for Israeli soils having similar clay content but with smectite as the dominant clay mineral. The SA soils have higher FIR values, which indicates that they were less affected by raindrop impact than the smectitic (Israeli) soils. It is therefore suggested that kaolinitic and illitic soils are less dispersive than smectitic soils. The effect of ESP on infiltration was found also to depend on the clay mineralogy of the soil. The FIR values of the kaolinitic soil with no smectite were only slightly affected by ESP. When smectite was present in kaolinitic soil, the susceptibility of the soil to sodicity, as reflected by crust formation, increased. The illitic soil was found to be more susceptible to sodicity and hence to crusting than any of the kaolinitic soils.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634260

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

A diallel study of the variability for yield that remained after an effort to exclude some of the factors known to contribute strongly to yield variation in the Winter Rainfall Region, was done. Overdominance resulted in strong heterosis effects which persisted in the F2. Little or no additive variation was expressed across the five environments sampled, while highly significant specific combining ability effects were evident.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634261

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor