摘要:

Drie grondwaterregimes (20, 50 en 70% onttrekking van plantbeskikbare water) is gedurende herfsaanplan- tings in 1987 en 1988 op Up-to-date aartappels toegepas om die invloed daarvan op groei en ontwikkeling te ondersoek. Twee fisiologiese parameters van plantwaterstremming, naamlik, fotosintesetempo en stomatadiffusieweerstand, is gedurende die 1988 groeiseisoen gemonitor. Vegetatiewe ontwikkeling is deur waterstremming vertraag en al die groeikomponente van veral die 70% onttrekkingsregime is negatief beïnvloed. Plante van die 20% regime het hoër gemiddelde fotosintesetempo's as gestremde plante getoon. 'n Betekenisvolle positiewe korrelasie (R2= 0.83) is tussen totale opbrengs en gemiddelde fotosintesetempo deur die groeiseisoen verkry. Stomataweerstand, sowel as fotosintesetempo, het as goeie indikators vir die voorkoms van plantwaterstremming gedien. Gemiddelde stomataweerstand het 'n negatiewe korrelasie (R2= 0.88) teenoor totale opbrengs getoon.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634613

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Drie besproeiingsbehandelings (20, 50 en 70% onttrekking van plantbeskikbare water) is toegepas ten einde die optimum peil van grondwateronttrekking by aartappels te bepaal. Die proef is gedurende die 1987 en 1988 herfsseisoene uitgevoer. Totale waterverbruik van behandelings is bereken en knolopbrengs, -grootteverspreiding en -kwaliteit is na oes geëvalueer. Die hoogste totale opbrengs en persentasie groot knolle is by die plante van die 20% regime verkry en die laagste by die plante van die 70% regime. Gereelde watertoediening het oor die algemeen tot 'n geringe verlaging in knolkwaliteit gelei. Die gemiddelde waterverbruiks- doeltreffendheid van die 50% regime was die hoogste.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634614

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The objective of this study was to obtain information on the inflow of N, P, K, Ca, Mg, S, Cu, Fe, Mn and Zn to the roots of wheat (Triticum aestivumL.) grown under normal irrigation farming conditions. Except for irrigation scheduling, the eight farmers on whose farms the study was conducted were allowed to follow their normal farming practices. At each site biomass production, nutrient content of the top growth and root length were measured regularly throughout the growing season, starting 35–45 days after planting. The inflow of all ten nutrients increased with the age of the crop, reaching a maximum somewhere between four fully unfolded leaves and anthesis, whereafter it decreased. The maximum inflow values for N, P, K, Ca, Mg and S were respectively, 113.0, 17.7, 187.0, 17.1, 8.9 and 8.3μg m−1day−1. In the case of Cu, Fe, Mn and Zn the maximum inflow values were 46.4, 1 493.4, 249.8 and 68.3 ng m−1day−1respectively. In the period when maximum inflow occurs, namely, 70–110 days after planting, the nutrient supply capacity of the irrigated soils will be exploited to the utmost due to a limited root length. It seems that under local circumstances a root length of only 4–5 km m−2is sufficient for adequate nutrient absorption during peak inflow, providing the water regime of the soils is kept at field capacity.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634615

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Little or no information is available on the contribution of individual subterranean nodes to the storage root formation in sweet potatoes. Therefore, two field trials were conducted where apical vine cuttings of various cultivars were planted vertically or horizontally, with three or five nodes beneath the soil surface, and storage root formation was monitored. The same potential for storage root formation existed at the various subterranean nodes provided that the plant material had been cut equidistant from the two nodes. The differentiation of potential storage roots at the basal node was stimulated when vines were cut directly below a node. Only a small percentage of these roots eventually developed into storage roots. The number, length and diameter of the storage roots, as well as the storage root stalk length decreased progressively at the lower nodes. There was no benefit in planting at depths where more than three nodes were below the soil surface. The limited differentiation and development of storage roots at the lower nodes may be ascribed to soil physical factors, although factors such as assimilate partitioning may also play an important role.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634616

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of four seed treatments and storage period of treated seed on the germination, coleoptile length and emergence of five winter wheat genotypes was investigated. The first trial was conducted under controlled conditions to determine the effect of triadimenol, terbuconazole, flutriafol + thiabendazole and carboxin + thiram-treated seed at recommended rates on the germination and coleoptile length of five genotypes, viz. Betta, Tugela, Molen, T85/21 and Karee. A second trial was conducted under field conditions to determine the percentage emergence of Betta and T85/21 treated with the same seed treatments and planted 30 mm and 60 mm deep. Significant seed treatment×genotype×storage period interactions for germination occurred. All seed treatments had an effect to varying degrees on the germination of genotypes after the nine- month storage period but not on the seed treated directly prior to germination. Significant seed treatment×genotype×storage interactions occurred for coleoptile length. Triadimenol and flutriafol + thiabendazole consistently reduced coleoptile length while terbuconazole only reduced coleoptile length alter the nine-month storage period. Carboxin + thiram had no detrimental effect on coleoptile length. No significant second or first order interactions occurred for seedling emergence, but the seed treatment effect was highly significant.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634617

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Synthetic sex pheromone formulations of the maize stalk borer,Busseola fusca(Fuller) were compared in different trap designs with a light trap for efficiency in describing seasonal moth activity. Omni-directional traps were superior to conventional delta traps for both quantitative and qualitative estimations of moth populations. While pheromone traps tended to over-estimate moth numbers during periods of diminished moth populations, the possibility of using pheromone trapping systems to identify seasons of potentially severe infestations seems to be feasible. Descriptions of two effective omni-directional trap designs are provided.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634618

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect ofChito partellus(Swinhoe) on growth and yield of maize was investigated in two field experiments, using artificial infestation in cages. The first experiment consisted of five infestation levels, viz. 0, 15, 30, 45 and 60 eggs per plant. Plants were infested 3 weeks after emergence. The second experiment involved infestation on five occasions, viz. 2, 4, 6, 8 and 10 weeks after plant emergence, with a single infestation level of 30 eggs per plant. Results from both experiments indicated that whorl damage increased until 2 weeks after infestation, with minimal increases recorded at later stages. Levels and times of infestation were both non-linearly related to yield loss, the slope being positive for levels and negative for time of infestation. The level of whorl damage 2 weeks after infestation proved reliable for the estimation of yield losses. The economic threshold was determined as 40% plants with visible whorl damage.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634619

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Normal fertilizer placement, two deeper than normal, broadcast and no fertilizer treatments were compared in a stubble tillage system in the north-western Free State. Plant growth, as indicated by leaf area, leaf dry mass and stem dry mass, was evaluated at three intervals until flowering during the three growing seasons of 1985/86 to 1987/88. Tillering and grain yield were measured at harvest. The deeper than normal placement of fertilizer gave up to an 11% increase in yield in the drier years (345 mm and 356 mm rainfall) but not in the wetter year (869 mm rainfall). Deeper placement initially resulted in poorer plant growth, but had the best plant growth at flowering. Deeper placement also resulted in less tillering.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634620

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Larvae of the bagwormEumeta hardenbergi(Bourgogne) (Lepidoptera: Psychidae) are reported for the first time to feed on the leaves and bark of guayule(Parthenium argentatumGray) plants which were being examined as a potential source of natural rubber in Pietermaritzburg, Natal, South Africa. Plant damage due to the removal of stem shoots for bag construction by a light infestation of larvae was assessed. Subsequent losses in rubber yield were estimated to be c. 100 kg ha−1. An unidentified bagworm was also found feeding on guayule leaves. Both species of bagworm should be considered as potential pests of guayule plantations in areas of southern Africa.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634621

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor