摘要:

The phonological submodel of the PUTU wheat crop growth model was refined to account for the variation in sensitivity to vernalization and photoperiod. Crop development rate was simulated in five phenological phases making use of temperature and photoperiod. Base values of temperature, photoperiod and vernalization were determined for 22 cultivars currently grown in the RSA. After calibration the submodel was verified for two cultivars. It was shown on average to calculate accurately the date of flag leaf maturity and start of anthesis to within six and five days, respectively, of the true date. It was concluded that the phenological submodel of PUTU wheat crop growth model functioned satisfactorily.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634581

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

A refined leaf growth submodel was incorporated in an existing wheat crop growth model. The submodel calculated daily green leaf area expansion per plant by taking into account plant population, crop age, interplant competition, temperature and crop water status. After calibration, the submodel was tested against independent data. Statistical comparisons between simulated and observed green leaf area index through several growing seasons yielded an index of agreement of 0.88. The mean absolute difference between simulated and observed maximum green leaf area index was 21% of mean observed values. The submodel performed satisfactorily over a wide range of weather conditions, plant populations and cultivars.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634582

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

A submodel for simulating daily grain growth was incorporated in an existing wheat crop growth model. The submodel calculated daily potential grain growth from green leaf area index, plant population and crop stage. Simulated daily potential grain growth was reduced by excessively high or low temperatures or water stress during the period heading to end of anthesis. Actual daily grain growth was calculated using daily potential growth, temperature and crop water status prevailing on the given day. Daily accumulation of grain growth from anthesis to physiological maturity yielded final grain mass. After calibration of the model, it was tested against 19 sets of independent final grain yield data. Statistical validation yielded an index of agreement of 0.91 and a mean absolute error of 20%. The results indicate that the PUTU989 grain growth submodel calculated final grain yield satisfactorily.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634583

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

'n Bewegende gemiddelde daaglikse minimum nagtemperatuur, T[mbar][nbar](per vyf dae) is oor 8–15 j vir 23 weer- stasies bereken wat verspreid in die katoenproduserende gebiede van die Republiek van Suid-Afrika aanwesig is. As onderste temperatuurdrempel, of basistemperatuur waarby groei van katoen staak, is 13°C aanvaar. Die daaglikse verandering van T[mbar][nbar]oor die periode vanaf 3 September tot 30 Mei aan elke lokaliteit is met 'n regressievergelyking beskryf. Die gemiddelde intreedatum van 13°C nagtemperatuur in die lente en die uittreedatum daarvan in die herfs, is vir elke lokaliteit bepaal. Katoengebiede op hoogtes van 900 tot 1 200 m bo seevlak ondervind 'n skerp daling in gemiddelde T[mbar][nbar]na die middel van die jaar, i.e. 16 Januarie, en die uittreedatum van 13°C kom in 60% van die jare teen die einde van Maart in meeste gebiede voor. Dit beperk die lengte van die groeigeisoen vir katoenproduksie.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634584

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

The influence of five different plant densities on whorl damage, internal damage, tillering and yield of grain sorghum under attack byBusseola fuscawas evaluated over two seasons, using artificial infestation of three egg batches (90 eggs) per 5-m row. No difference in the number of tillers produced by infested and uninfested rows was observed and tillering was negatively related to plant density. No difference in the incidence of whorl damage existed between the different treatments. The lowest incidence of dead heart occurred at the lowest plant density. Initial plant density did not have a significant effect on either the degree of internal damage or the number of internally-damaged stems caused by moderate infestations ofB. fusca.Yields were significantly reduced by infestation in one season only. This was attributed to the effect of climatic conditions more favourable for growth.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634585

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

A regression model with which the leaf water potential (LWP) of wheat can be estimated from soil water content and potential evapotranspiration was developed from data generated during 1986. This model was used during the 1988 wheat season to decide when to relieve crop water stress by irrigation. Seven values of LWP, viz.−1.2;−1.4;−1.6;−1.8;−2.0;−2.2 and−2.4 MPa were considered as possible threshold values for irrigation. The soil water content, determined twice weekly, was used to estimate actual evapotranspiration. Midday LWP was determined on selected cloudless days and found to be most suitable as an irrigation timing criterion for several reasons. Firstly, the ratio evapotranspiration/pan evaporation was at least as well related to LWP as to soil water status. Secondly, strong relationships between grain yield, seasonal evapotranspiration, peak evapotranspiration rate and threshold LWP exist, and finally, indications are that yields near the upper limit of the evapotranspiration-yield relationship are ensured. Leaf water potential for irrigation timing purposes could be satisfactorily estimated by the model if calibrated over a sufficiently large range of leaf water potentials. The threshold potential for maximum water use efficiency was−1.82 MPa and for maximum yield−1.44 MPa.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634586

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

The economic optimum harvest age for sugar-cane depends to a large extent on how rates of photosynthesis and respiration change with age. A simple model of the carbon balance in which a constant photosynthetic efficiency was assumed, accounted to a large extent for dry matter accumulation by cv. NCo376 grown under irrigation. Rain-fed crops of this cultivar were simulated by linking the model of the carbon balance to the CERES-Maize water balance routine. The combined model was validated with data from a comprehensive growth analysis experiment undertaken by staff of the SASA Experiment Station in the 1960's. Dry matter accumulation was explained satisfactorily without changing the coefficients for gross photosynthesis (Pg= 0.082 PAR MJ m−2), maintenance (0.242 Pg) or growth respiration (0.003×total phytomass). Leaf area index and leaf appearance data indicated that the assumptions regarding leaf area development were valid. The observed fluctuations in water content of the top 300 mm of soil were well explained by the CERES-maize water balance but the gypsum block resistance readings in deeper layers indicated the presence of water that on some occasions was not explained by the model. It was concluded that the sucrose accumulation rate on many farms may have declined because of the recent reduction in the age at harvest in the sugar industry.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634587

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

The utilization of initially-applied15N-labelled ammonium and nitrate nitrogen by wheat plants grown in soil was investigated in a pot experiment under controlled growth chamber conditions. The application rate was approximately 140 kg N ha−1) and the treatments consisted of {NH4}NO3, NH4{NO3}, {NH4NO3}, {NH4}2- SO4, K{NO3} and nil nitrogen. The ions in brackets ({ }) indicate those enriched with15N toc.5 atom %. On average, according to the isotope technique, 67.24±2.48% of the nitrogenous fertilizer was utilized by wheat. Significantly more nitrate N was recovered in the plants than ammonium N. Furthermore, when fertilized, less soil nitrogen is utilized by the plants compared with the controls, and the application of nitrate suppressed the uptake of soil N more than when ammonium N was applied. The results confirmed that, on average, the conventional method of determining fertilizer recovery by difference yielded lower values (47.49±8.93%) than those obtained with the tracer technique.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634588

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Die invloed van benfurakarb saadbehandeling op kieming by mieliesaad is onder gunstige en suboptimale temperatuur sowel as na opberging en in waterstrestoestande ondersoek. Konsentrasies van 1 350 en 1 800 g a.b. 100 kg−1saadmassa en opberging na behandeling lei tot verlaging in kiemingspersentasie en kiemingstempo. Saad wat met 1 350 g a.b. 100 kg−1saad en meer behandel is weerstaan opberging swakker as toedienings van 900 g a.b. 100 kg−1saadmassa. Ongunstige kiemingstemperatuur (13°C) en waterstres lei tot verminderde verdraagsaamheid vir benfurakarb behandeling wat vererger word deur voorafopberging. Benfurakarb kan met relatiewe veiligheid teen 900 g a.b. 100 kg−1saadmassa toegedien word.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634589

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Letaba, NIK2 and OR19 were released for commercial cultivation in the R.S.A. in 1989. Letaba has potential as a dryland cultivar in the Springbok Flats and northern Natal. NIK2 is intended for cultivation under irrigation in the same areas and has fibre properties comparable with those of Acala 1517–70. OR19 was developed at Upington and has high resistance toVerticillium dahliae(Kleb). It is intended for areas withVerticilliumproblems and where the red leaf disorder occurs.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634590

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor