摘要:

Nitrogen mineralization potentials were determined using an undisturbed-soil incubation procedure. The purpose of this study was to evaluate the above-mentioned method as an index of soil nitrogen availability. Undisturbed soil samples (0–150 and 150–300 mm) of a limed (pH 7.3) and an equivalent non-limed (pH 4.9) soil were incubated at 30°C and field water capacity. After every consecutive 10-day period, four samples of each treatment/depth combination were removed, dried and analysed for mineral N content. This was conducted over a period of 60 days. Distinction was made between changes in NH4+and NO3-contents of the incubated soil, assuming the NO3−release represented N release from the soil due to high nitrification rates. The release of NO3−was depicted by a straight-line regression, where the slope was equal to the rate constant of mineralization (k). The mineralization potential (NO) was assumed to be the maximum mineral N content obtained in the soil during incubation. Comparing the amount of CO2that evolved per unit NO3−released, it was found that the mineralizing microbial activity was lower, but more efficient in releasing N at pH 7.3 than at pH 4.9. Both ammonification and nitrification proved to be pH-sensitive processes. Although unsatisfactory for making fertilizer recommendations, the total N content of the soil was found to be a good indication of its N mineralization potential. The method used in this study gave no indication of the fraction ofN0that is released during the different seasons. The use of undisturbed samples makes this method cumbersome because of the large number of samples needed to accommodate a large spatial variability component.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634372

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

Proteins were extracted and separated by SDS-PAGE from leaves of scions and rootstocks of differentVitiscultivars. Banding patterns were used to identify the different cultivars after extraction of the proteins with a medium containing Tris-HCI (0.68 M, pH 7.8), SDS (2%),β-mercaptoethanol (5%), glycerol (10%) and PEG 20 000 (2%). Electrophoretogram formulae using relative band mobility and staining intensity of the different bands were calculated for the different cultivars. No differences in Rm values were found between individual scion or rootstock cultivars but the technique can be used to distinguish between scion and rootstock cultivars.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634373

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

A study of seed development and maturation in edible dry bean cv. Teebus was conducted on field-grown plants. Mass maturity (maximum seed dry mass) occured 43 days after flowering (DAF) when seed moisture content was 52%. Harvest maturity (at a seed moisture content of 12.7%) was reached 15 days after mass maturity (58 DAF). Fresh seeds produced 90.5% normal seedlings at 30 DAF (13 days before mass maturity), when they had acquired only 48% of their maximum dry mass. Only 3% of rapidly dried seeds produced normal seedlings at this stage. Maximum seed quality (as determined by normal germination and conductivity of steep water), as well as maximum desiccation tolerance, were attained 5 days after mass maturity when seed moisture content was 34%. Respiration initially increased sharply, followed by a relatively constant high level for several days, after which it diminished to near zero levels when moisture content was 16.8% (5 days before harvest maturity). ATP content followed much the same pattern, but the seeds still contained a relatively large amount of this compound (39 nmol seed−1) when respiration had declined to a negligible value.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634374

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

Three methods of directional insecticide application againstBusseola fuscaandChilo partellusinfestations in the late growth stages of sorghum and maize were compared over two seasons. An insecticide mixture consisting of endosulfan and deltamethrin was applied 10 days after artificial inoculation of plants with newly hatched larvae of both species. Treatments consisted of insecticide applications, directed into the whorl (during the flag-leaf stage), onto the sides of plants, or a split application directed both into the whorl and onto the sides of plants. The last treatment was also applied at double the dosage rate, to determine the possible dilution effect resulting from split applications. Reduced dosage rate into the whorls, resulting from the split application, did not result in reduced efficacy of control. Species x treatment interactions occurred in maize and sorghum. Side applications of insecticide were ineffective in both crops. Whorl and split applications were effective and showed similar control of larval numbers in maize, while whorl applications provided best control in sorghum. Split applications resulted in the lowest yield losses in maize and sorghum. The efficacy of the various treatments is discussed in relation to ecological differences between the two borer species.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634375

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor

摘要:

A total of 877Triticumaccessions (27 species) were screened for resistance to leaf rust (Puccinia reconditaf. sp.tritici) using mixed inoculum of pathotypes UVPrt2, UVPrt3, UVPrt8, UVPrt9 and UVPrt13. Of these, 206 accessions were resistant/moderately resistant to all races. An attempt was made to cross each resistant accession with common wheat and to determine if resistance is expressed sufficiently in the presence of wheat genomes. Seventy nine accessions have not yet been crossed successfully, while the remaining 127 (representing 19 species) were crossed with common wheat. A number of transfer attempts failed in the F, as a result of suppression of resistance (44 accessions) or formation of embryoless or non-viable seeds/seedlings (13 accessions). The resistance of 70 hybrids is fully expressed and these are now in various stages of back-crossing to wheat. The resistance was confirmed by retesting the species sources of the 70 successful combinations with the individual leaf rust pathotypes.

ISSN:0257-1862    

DOI:10.1080/02571862.1996.10634376

出版商:Taylor&Francis Group    

年代:1996

数据来源: Taylor