摘要:

Early detection of nitrogen deficiency on annual agricultural crops can assist the management of N-fertilization to improve crop yields. Low altitude aerial photography is an inexpensive means to assess crop canopy radiation in the near infrared range. In this study, different Nitrogen experiments were laid out on cotton, tobacco and wheat. Nitrogen rates on the tobacco and cotton were 0.50, 100, 150 and 200 kg N ha1. On a wheat experiment the rates of N were 0.60, 120 and 180 kg N ha−1with4times of application after planting. All these experiments were conducted in 1992 and 1996. Infrared aerial photographs and multi spectral videography were taken of the experiments at certain times using remotely piloted aircraft. These images were processed on a computer and classified into classes of high- and low-N categories using image processing software. A portable spectrometer operating in the 770 nm to 920 mn range was also used to assess N deficiency by measuring the reflected radiation of wheat canopies 70 days after planting. Interception of Photosynthetically Active Radiation (PAR) was used to assess the biomass of wheat over time. Light reflection in the near infrared wavelengths from airborne CIR photography and the 853 nm band from multi spectral videography correlated well with the N rates on the different crops. Spectrometric reflection provided the best detection of N-deficiency at the 779 nm wavelength. The PAR measurements followed the same correlation with N-rates. The results showed that CIR airborne photography, multi spectral videography and spectrometric reflectance provide a practical and economical means of assessing crop N status when standardized with an in-field reference.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634847

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Die voginhoud van sonneblomsaad(Helianthus annunsL.) wat vir persing gebruik word, wissel tussen 5.5% (ongeveer die laagste inhoud waartoe saad natuurlik droog) en 10% (die hoogste toelaatbare inhoud vir berging). Die doel van die ondersoek was om vas te stel hoe die voginhoud van twee saadmonsters wat natuurlik droog die dopbaarheid beinvloed, met die spoed van die dopper gestel vir minimalisering van ongedopte saad plus fynmateriaal. Die saad van twee kultivars wat by Heilbron gedurende 1996/97 gekweek is, is gebruik. Die saad is gelaat om natuurlik te droog en ontdopping is met tussenposes met 'n laboratoriumdopper uitgevoer. Die resultate toon dat droer saad 'n laer dopperspoed as natter saad vereis. Dopbaarheid het van 88 tot 95% toegeneem met 'n saadvogafname van 9.5 tot 5.7%. Terselfdertyd het die produksie van fynmateriaal, wat 'n verlies aan olie en protei'en meebring, vir die twee monsters verskillend toegeneem. Indien die verlies van fynmateriaal voorkom kan word, sal ontdopping die hoogste wees by die laagste moontlike voginhoud.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634848

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Voor die olie van sonneblomsaad(Helianthus annuusL.) uitgepers word, word dit ontdop om onder andere die kwaliteit van die oliekoek so hoog moontlik te kry. Dopbaarheid, of die gemak van ontdopping, het 'n positiewe verwantskap met saadgrootte. Aangesien saadmonsters 'n samestelling van verskillende saadgroottes is en elk moontlik 'n unieke dopperverstelling vereis, bestaan die moontlikheid dat indien elke grootteklas teen sy unieke optimale dopperspoed gedop word, die effektiwiteit van die verwerkingsproses verbeter kan word. Vier saadmonsters is in grootteklasse van < 3, 3–3.5 en > 3.5 mm geskei. Die drie grootteklasse en 'n ongesifte monster is teen 'n voorafbepaalde optimale dopperspoed ontdop en elk is in 'n fyn-, kernryke en dopryke fraksie geskei en geweeg. Die persentasie dop wat verwyder is (die dopbaarheid), is bereken en die olie- en proteieninhoud van die kernryke fraksies is bepaal. Die gedopte en ongedopte monsters is vergelyk deur middel van die Student-t-toets met kontraste. Saadbron het die oorheersende invloed op die saadkwaliteitparameters vir verwerking getoon. 'n Beperkte voordeel is deur te sif teweeggebring, deurdat die potensieel herwinbare olie vir slegs twee van die vier monsters met 9% verhoog is en vir een verlaag is, terwyl die hoeveelheid en proteieninhoud van die potensiele oliekoek vir slegs een monster verhoog is. Weens verskille in die dopbaarheid, is met die sif van die saad daarin geslaag om drie potensiele oliekoeke van elke monster te produseer, waarvan die proteien- inhoud met tot 5.5 persentasiepunte verskil het.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634849

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An experiment was conducted at the University of Queensland Redland bay Farm (27°37′ S, 153°17′ E) in southeast Queensland, Australia to study response of groundnut cultivars [Improved Virginia Bunch, NC-7, Q18801 (Virginia types), TMV-2, McCubbin and Red Spanish (Spanish types)] to different plant population densities (6.3, 11.1, 25.0 and 100.0) arranged in square spacings. The objective was to study plant physiological and morphological characteristics associated with the optimum plant population density among groundnut cul- tivars. Leaf area index (LAI), interception of photosynthetically active radiation (PAR), total dry mass (TDM), dry mass (DM) partitioning, economic yield and yield components were measured. The results show that TDM and economic yield were both maximized at 25 plants m−2in all cultivars and so were the radiation use efficiency (Ec), crop growth rate (CGR) and DM partitioning'toTeproductive components (pods and kernels). Overall, variation in economic yield (kernel DM) was determined by pod harvest index (HI), kernel HI, ratio of pod to peg plus pod number, kernel number per pod and kernel size. Most of these components were maximized at the optimum plant population density.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634850

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The objectives of this study were to compare the infection of wheat heads byFusarium graminearumand F.crookwellenseand to determine the effect of temperature on head blight development induced by these species. Scanning electron microscopy of spikes of the wheat cv. Palmiet revealed no differences in the infection process between F.graminearumand F.crookwellense.In glasshouse experiments, F.graminearumwasmore pathogenic than F.crookwellenseat constant ± 22°C and ± 24.6°C, whereas F.crookwellensewas more pathogenic at ± 13.8X. Both species caused more severe head blight at 22°C and 24.6°C than at 13.8°C.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634851

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The effect of four tillage systems on grain yield of maize, incidence of diseases and production costs was investigated for a Hutton soil in the Natal Midlands from 1982 to 1995. The four tillage systems were no-till (NT), reduced tillage (R, T and R2T) and conventional tillage (CT). Mean grain yields were not significantly affected by tillage system. Compared with the other systems, NT negatively affected final plant densities, by about 2000 plants ha1. The incidence of ear rot caused byStenocarpellaspp. was not significantly affected by tillage systems, although NT resulted in reduced ear rot incidence in seven out of 13 years. Spraying fungicide for control of grey leaf spot(Cercospora zeae-maydis)improved yields over 100% for NT and in reduced tillage systems during a wet season, compared to 80% increase with CT. During a drier season spraying had no significant effect on grey leaf spot. In the long term, NT was economically more profitable and less risky than the CT system.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634852

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Metolachlor (2—chloro—6′—ethyl—N-(2—methoxy—1—methylethyl)acet—o—toluidide) / flumetsulam (2′6′—difluoro—5-methyl[1,2,4] triazolo [1,5—a] pyrimidine—2—sulfonanilide) mixtures were evaluated in 77 field experiments in maize (ZeamaysL.), groundnuts(Arachis hypogaeaL.), soya beans(Glycine max(L.) Merr and dry beans(Phaseolusspp). Many broadleaf weeds, includingTribulus terrestris, were selectively controlled with a 50:1 mixture. Application rates varied, depending on soil type, from 744 g ai. ha1metolachlor + 15 g a.i. ha−1flumetsulam on sandy soils to 1673 g a.i. ha-1metolachlor + 34 g a i. ha1flumetsulam on soils with more than 40% clay. Full rotational flexibility exists for field crops on the Highveld after the application of metolachlor/flumetsulam mixtures.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634853

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Information on the effects of El Nino on local climate and sugarcane production will assist planning and management. The objective of this study was to investigate the relationship between the southern oscillation index (SOI) and rainfall and sugarcane yields in South Africa. Probabilities of low rainfall more than doubled during summers with a consistently negative SOI phase during November. February rainfall was worst affected. Factors other than climate confounded the historical relationship between El Nino and sugarcane yields. Simulation studies to exclude non-climatic factors indicated that cane yields are reduced by significant margins following seven out of nine El Nino events. Results show that the phase of the SOI during spring is a reasonably reliable indicator of low rainfall during the subsequent midsummer and of low yields during the subsequent milling season.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634854

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Nassella tussock(Stipa trichotomaNees) is a perennial grass weed that seeds prolifically, resulting in build-up of a large soil seed bank. Due to it's vigorous growth it has the potential to spread rapidly in disturbed environments and overgrazed areas. Field trials were initiated in a dense nassella tussock infestation to assess the influence of various adjuvants (Citowett, Frigate and Reverseal 9) on the herbicide activity of tetrapion (sodium 2, 2, 3, 3-tetrafluoropropion) and to monitor subsequent seedling establishment. Reverseal 9 was the only adjuvant that significantly increased the efficacy of tetrapion at 0.44kg ai ha1, but this level of control achieved (75%) was not considered adequate for large-scale nassella tussock control operations. The next higher rate of tetrapion (0.88 kg ai ha1) was effective in achieving nearly total mortality (98%) with or without the addition of Reverseal 9. This rate also restricted establishment of nassella tussock seedlings for up to 23 months after initial application. Further studies with tetrapion/Reverseal 9 combinations are recommended in an attempt to reduce the current registration rate of tetrapion (0.88kg ai HEN), thereby saving costs and reducing the negative impact on desirable grasses and subsequent veld rehabilitation.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634855

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Maize streak virus (MSV) was first studied by Storey in Kenya in the 1920s and resistance transferred into East African maize in the 1960's. Yet the majority of farmers of East Africa are still growing streak-susceptible maize. At the International Institute of Tropical Agriculture (IITA) in Nigeria, an effort to incorporate streak resistance as an integral part of a holistic maize improvement program was begun in 1975. By 1979, usable resistance had been found and methods of large scale field challenge devised, and used routinely in the development of populations targeted at three major ecological zones in tropical Africa. Methods were continuously improved and resistant open pollinated varieties and hybrids produced that are now used on a large scale by farmers in West Africa. The strategy for success was based on: 1) Avoidance of virus strain specificity; 2) Large scale vector rearing and field infestation to ensure early infection; 3) Selection only for tolerance when infected; and 4) Not separating virus resistance selection from simultaneous selection for yield, adaptation, and resistance to other diseases important in each target ecology. The result was maize genotypes that exhibit low field incidence (tolremicity) and are tolerant (yield well even if diseased). The approach and methods have been extended to many interested national maize improvement programs and adopted by them. We believe that this form of tolerant resistance remains effective wherever deployed in Africa and thus that it has not ‘broken down’.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634856

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor