摘要:

Grain yield for 21 maize cultivars common to 10 localities and three harvesting seasons was used to compare the Finlay-Wilkinson and the additive main effects and multiplicative interaction (AMMI) methods of studying interactions in multi-site trials. Both methods showed variability and unpredictability with respect to year-to-year results. Each method considered the data from different points of view, bringing to light various aspects of the variability contained in the data. The cultivars were loosely ordinated by the AMMI method along a gradient representing length of growing season in two years out of three and also when the years were analysed jointly. In order to maximize the predictive ability of the AMMI method, selection should be made using the AMMI 0 scale of treatment estimators because of its minimal sampling variance.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634384

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

A commercially available salinity sensor (model EM-38 of Geonics Ltd., Canada) has been developed for diagnosing and quantifying soil salinity in the field. There is a need, however, to calibrate the instrument reading against a more commonly used measure of soil salinity. Linear regression equations are reported that allow the interpretation of field instrument readings in terms of electrical conductivity of the saturation extract (ECe) measured in the laboratory. Instrument measurements and soil samples were taken at some 110 sites on various irrigation schemes distributed across South Africa. Samples were analysed in the laboratory and soils categorized according to texture, water status and salinity distribution with depth. Calibration equations were developed firstly by relating field instrument readings, taken either in the vertical or horizontal position, to a depth-integrated ECevalue which was weighted for depth according to instrument response. Secondly, the mean of the readings taken in the vertical and horizontal positions at each site was related to the arithmetic mean ECefor the 0- to 1.2-m soil depth. A set of 12 linear regression equations was established in the first approach, and eight in the second. Two of the relationships showed statistical significance at the 5% level, the remainder at the 1% level. These equations enable the user of the EM-38 to derive a realistic index of soil salinity in terms of ECe, but calibration of the instrument for local soil conditions is preferable.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634385

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

The South African bread wheat cultivar Tugela has consistently displayed effective field resistance to leaf rust, caused byPuccinia reconditaRob. ex Desm. f. sp.tritici.Based on its pedigree and adult plant reaction to leaf rust, it has been assumed that Tugela contains theLr34gene for resistance toP. reconditaf. sp.tritici.Evaluation of wheat seedings at 10°C and 20°C suggested that Tugela has two genes for resistance, one of which is only expressed at 10°C. Tugela primary leaf infection types at 10°C and measurement of latent period, uredinium density and uredinium size on flag leaves strongly resembled those on RL6058 (Thatcher/Lr 34). To determine the number ofLrgenes and confirm the presence ofLr34, Tugela was crossed with Thatcher (leaf rust susceptible) and RL6058. F2and F3populations from each cross were tested as seedlings for segregation of resistance to pathotype UVPrt3 at 10°C. Two dominant genes were indicated by the segregation ratios of Tugela×Thatcher F2plants (χ215:1= 0.56) and F3families (χ27:8:1= 0.67). The presence ofLr34was confirmed in all 590 Tugela×RL6058 F2seedlings tested. Tugela×Thatcher F2plants, inoculated with pathotype UVPrt9 during flag leaf and ear emergence stages of growth, indicated segregation of a single gene (χ23:1= 0.19) for resistance when tested at low glasshouse temperature. All Tugela×RL6058 adult F2plants were resistant in this environment. Field tests with F3families from both crosses confirmed glasshouse results. This study indicated that Tugela containsLr34and an unidentifiedLrgene.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634386

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

An intercropping trial involving four legumes, three maize planting densities and two legume planting times was undertaken at Dembela Wacho in the Sidamo region of Ethiopia during the 1987 growing season. The objective was to explore the potential of intercropping maize(Zea mays)with legumes within the existing Borana cropping system. The legumes examined were cowpeas(Vigna unguiculata), lablab(Lablab purpureus), cassia (Cassia rotundifolia)and centro(Centrosema schottii). In an‘average’growing season for the area, maize grain yield decreased by about 30% when intercropped with both cowpeas and lablab. The effect of cassia and centro was not significant. Legume planting time showed a significant effect on maize grain yield only when the legumes were cowpeas and lablab. Maize grain yield increased by 43% and 36% for cowpeas and lablab respectively when planted 20 days after the maize was sown. Maize planting density had a significant effect on maize grain yield in that yield increased with increased plant population. However, the increase in grain yield was not proportional to the maize planting density. The dry matter yield followed the trend of the grain yield. These results showed that intercropping was more advantageous than sole cropping of maize. Delaying the planting time of cowpeas and lablab after that of maize is recommended, while cassia and centro could be planted together with maize. The best maize planting density under the given conditions was about 55 000 plants ha−1.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634387

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

An intercropping trial of maize (Zea mays) with two dual-purpose and two forage legumes was undertaken at Dembela Wacho in the Sidamo region of Ethiopia during the 1987 growing season. The objective was to explore the potential of intercropping in order to improve food security, provide high-quality livestock feed and improve soil stability within the existing Borana cropping system. The legumes examined were two annual dual-purpose legumes, cowpeas (Vigna unguiculata) and lablab (Lablab purpureus), and two forage legumes, cassia (Cassia rotundifolia) and centro (Centrosema schottii). The other treatments imposed were four maize planting densities (0, 20, 35 and 50 thousand plants per hectare) and two legume planting times (at maize planting and 20 days later). Cowpeas produced 55% more grain than lablab. Maize planting density did not affect legume grain yield, but monoculture legume grain yield was about twice that of the intercropped ones. Monoculture cowpea grain yield was reduced by 44% when the planting time was delayed by 20 days while the reduction of lablab was only 12%. On the other hand, lablab grain yield was reduced by 56% due to delayed sowing in the intercrop situation. The dry matter yield of cowpeas and lablab was significantly higher than that of cassia and centro. Monoculture legume dry matter yield was significantly higher than the intercropped legume dry matter yield in all cases. The annual combined maize and legume grain and dry matter yields were higher than those in monoculture, thus showing yield advantages for intercropping. The perennial forage legumes did not appear to reduce maize yield when sown at the same time, suggesting that this practice could be a useful strategy in the last year of a cereal cropping cycle to prevent future soil erosion.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634388

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

The aim of this study was to evaluate the relative water content and the reduction of 2,3,5-triphenyltetrazoliumchloride, as indicators of drought stress and drought tolerance in spring wheat cultivars(Triticum aestivumL.) grown in the Western Cape. Drought stress was induced in two cultivars with known drought tolerance, namely, Gamtoos (drought tolerant) and SST 66 (slightly drought sensitive), as well as in two cultivars with unknown drought tolerance, namely, Nantes and SST 44. To assess the effect of growth stage on the reaction of the cultivars to drought stress, stress was induced during pre-anthesis and also during anthesis. Relative water content patterns for the different cultivars showed clear genotypical differences during pre-anthesis and, to a lesser extent, during anthesis. A positive correlation between the ability to maintain relative water content levels and drought tolerance was found for Gamtoos and SST 66. The results obtained with the reduction of 2,3,5-triphenyltetrazoliumchloride during drought stress showed only minor genotypical differences, and no correlation could be shown between the degree of reduction and drought tolerance.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634389

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effect of six crop rotation systems, planted under conventional and reduced tillage, on root and stalk rot and grain yield of sorghum was studied. The systems were applied for five seasons until 1991/92 when the effects of the systems were compared. Neither tillage, nor rotation, or the interaction of both had a significant effect on sorghum root rot. Stalk rot at harvest was significantly lower and grain yields significantly higher with minimum tillage (main effect) compared with conventional tillage. No significant rotation effect or tillage×rotation interactions were observed for both variables.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634390

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

Die doel met hierdie ondersoek was om die atmosferiese en grondstikstofopname deur die groeiseisoen van sojabone vas te stei, te bepaal in watter plantdele die N afkomstig van die twee bronne versamel, of dit later na die saad getranslokeer word en of 'n nie-nodulerende kultivar as verwysingsplant gebruik kan word om met vertroue die atmosferiese N-binding te bepaal. 'n Potproef met drie nodulerende en een nie-nodulerende sojaboonkultivar is uitgevoer. Die grond-N is vooraf met15N verryk en gestabiliseer. Plante is op vol-blom, peulvorming, peulvul en met oesrypheid gemonsteren vir totale N en15N ontleed. Gedurende die eerste 5–6 weke na opkoms is die beskikbare grond-N vir vegetatiewe groei benut. Na nodulering en gedurende die reproduserende fase het biologiese N-binding versnel om 'n piek 10 weke na opkoms te bereik. Met peulvul het die biologiese N-binding afgeneem om teen 'n lae, konstante tempo atmosferiese N te bind. Die opname van grond-N is in hierdie stadium minimaal en N is uit die vegetatiewe dele na die peule en saad getranslokeer. Ongeveer twee-derdes van die N in die plante en sowat 80% in die peule en sade is van atmosferiese oorsprong. In vergelyking met die15N-isotooptegniek, het die konvensionele metode N-binding onderskat.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634391

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor