摘要:

The effect of different intensities of water stress imposed during the first three weeks of grain filling were determined on the protein content, protein composition and bread volume of three spring wheat cultivars. Water stress was induced by watering the plants with a nutrient solution containing 0%, 15% and 22.5% polyethylene glycol (PEG 6000). Water stress generally decreased the protein content and bread volume by decreasing the production of the reserve proteins, gliadin and glutenin. The lower PEG-concentration had a more pronounced effect than the higher concentration, because the effect of the higher concentration on the production of protein, relative to non-protein components, was less than that of the lower PEG concentration. In this study cultivars did not differ in their response to different intensities of water stress.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634335

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The accuracy of different models for simulating the area of mature leaves on the main stem (PLA) of maize using thermal time was investigated. The accuracy of sub-models for simulating the area of individual mature leaves (LAn) and the number of mature leaves (Xn) was also determined. Measured data from six fully irrigated crops (three cultivars planted on two dates), as well as from independent data extracted from the literature, were statistically compared with simulated values. PLA was best simulated using an exponential function for the Xn submodel together with a bell-shaped function for the LAn sub-model. The average simulation error of the most reliable complete PLA model was 16%.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634336

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The potential of threeLrgenes in the wheat lines RL6080 (Thatcher*6/Lr29), RL6081 (Thatcher*8/Lr37) and RL6082 (Thatcher*6/Lr35) was evaluated in field experiments. Leaf rust reaction types on flag leaves of lines withLr29, Lr35orLr37varied between resistance and moderate susceptibility. Severity ratings on these lines did not exceed 5%. Leaf rust infection reduced grain mass in Thatcher by 10.4% whereas lines withLr29, Lr35orLr37did not sustain significant losses (+1.0, 2.6 and 1.0%, respectively). According to grain and flour protein concentration, flour yield, loaf volume and the baking strength index, no deleterious quality characteristics appeared to be genetically associated withLr29, Lr35orLr37. The dough development time of RL6080 was shorter, and that of RL6081 longer than the control.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634337

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Phosphorus (P) sorption poses a severe constraint on the ability of many soils to supply adequate amounts of P to plants. In an effort to quantify the P sorption capacities of soils in Natal, P sorption isotherms of 50 topsoils from a number of localities in the province were established. The amount of P sorbed at a solution P level of 0.2 mg P L−1, defined as the standard P requirement, varied from 5 to 1174 mg kg−1. Standard P requirement was greatest in highly weathered clay soils and lowest in sands. Various soil parameters were correlated with standard P requirement and isotherm slope at 0.2 mg P L−1. Oxalate-extractable aluminium, organic matter and sample density gave the best correlations. Because the method for the determination of sorption isotherms is tedious and does not lend itself to routine use, the feasibility of predicting the isotherm slope by near infra-red reflectance spectroscopy was also investigated. Preliminary results were encouraging and a calibration based on the samples used in this study yielded anr2of 0.82 and a residual standard deviation of 184.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634338

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Controlled environment studies have indicated that the reaction of hematoxylin with Al-stressed roots can be used as the basis for a rapid and reliable test for Al tolerance in perennial ryegrass. Preliminary screening experiments identified a high degree of variability in the intensity of hematoxylin stain found in the root apex of plants subjected to a uniform Al treatment (24 h; 100μM Al). In the more intensely stained roots, visual symptoms of Al toxicity were observed in those regions of the axial structure of the root where the stain was most pronounced. These symptoms (thickening of the root and distortion) were notably absent from the less intensely stained roots. In subsequent growth experiments, plants segregated according to root growth reactions in solutions containing 0 - 150μM Al into clearly defined Al-tolerant and Al-sensitive populations which corresponded with the initial assessments made in hematoxylin. Plants from different cultivars which were initially considered to show similar levels of Al tolerance (hematoxylin test) did not perform equally well in the growth experiments. These differences implied that plants which exhibit Al tolerance in hematoxylin do not necessarily have good root growth characteristics. This finding is discussed in the context of improving and updating procedures directed at identifying germplasm adapted to growing on acid, Al-toxic soils. The magnitude of the differences in root growth reactions in the presence of Al between Al-tolerant and Al-sensitive plants suggests that the genetic resources available in perennial ryegrass are sufficient to support a conventional breeding programme directed at improving the Al tolerance of this species.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634339

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

This study is part of an investigation into the effect of cultivation on the organic matter content of topsoils (0 - 200 mm) from commercial farms practising dryland agriculture in the summer rainfall area of South Africa (24°-30°S; 24°-30°E). The aim was to examine the effects of cultivation, period of cultivation and soil properties on potential mineralizable and residual inorganic N as parameters of the nitrogen fertility of the soils under discussion. Virgin and cultivated soils were sampled at 50 sites. Of these, 27 were located within five ecotopes. The sites in each ecotope varied as to cultivation period. The remaining 23 sites were chosen to obtain a wider range of climatic conditions and soil properties. Incubation tubes, packed in triplicate with a mixture of a soil and filter sand, were leached before incubation (residual inorganic N) and again after 2, 5, 9, 14 and 22 weeks of incubation (mineralizable N) at 30°C with 0.01 M CaCl2. The data was used to calculate cumulative net mineralization after 22 weeks (N22), nitrogen mineralization potential (N0) and rate constant (k). Pairedt-tests showed that cultivation had a significant negative effect on mineralization characteristics, viz. a decrease of 48.5% in N2237.6% inN0and 22.6% in k. Residual inorganic N during sampling did not differ significantly between virgin (18.3 mg kg−1) and cultivated (15.5 mg kg−1) soils. Plant-availableN, the sum ofN22and residual inorganic N differed significantly between virgin (61.9 mg kg−1) and cultivated (38.8 mg kg−1) soils. Although unique for each ecotope, the decline ofN22was rapid during the first few years of cultivation. Thereafter the rate decreased until an equilibrium was reached after 15 - 45 years of cultivation. The decline ofN22in ecotopes from the warmer, drier areas was higher than in the ecotopes from the cooler, wetter areas, but the percentage loss was larger in the latter areas. This reduction in nitrogen fertility status of cultivated soils may result in unsustainable crop production.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634340

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The applicability of fixed recropping intervals for crops that are sensitive to atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-striazine) was assessed. Atrazine carry-over was monitored 12 and 24 months after its application at six different rates to maize (Zea maysL.) grown in eight trials at six sites. The rotational test species were dry beans (Phaseolus vulgarisL. cv. Teebus) and sunflower (Helianthus annuusL. cv. SO 222). Yield reductions indicated the carry-over of phytotoxic atrazine residues. At 12 months after treatment dry bean yield was significantly reduced at one site and sunflower yield at six, on plots previously treated with the atrazine rates recommended for maize. During the next season significant yield reductions (dry beans 38%; sunflower 29%) occurred only on the single montmorillonite soil (pH 7.8). The relatively high tolerance of the dry bean cultivar in most soils at the first assessment is not reflected in the single recropping period of 18 months that is currently recommended for both species. Current recropping intervals for sensitive crops could be refined by assigning flexible intervals that are based on the herbicide's expected dissipation rate in a particular soil, as well as on the tolerance of the follow-up crop.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634341

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Concern has been expressed that reduced tillage systems may lead to excessive soil compaction, with a negative impact on crop growth. The objectives of this study were to determine the effects of different tillage systems, namely, minimum tillage (disc and sweep), chisel plough and conventional tillage (plough) on soil bulk density, penetrometer resistance and yield. These effects were determined over a three-year period (1991/1992 and 1992/1993 seasons) on an Avalon sandy clay loam soil in the central Orange Free State. Results indicated that soil water content at planting was similar for the different tillage systems, except for slight differences in the upper soil depths. Penetration resistance and bulk density increased from a depth of 130 mm down to 290 mm of the soil using disc and sweeps compared with conventional tillage and chisel plough treatments. However, in the deeper soil zones, the tillage system did not consistently influence either bulk density or penetration resistance. At a depth of 400 mm, conventional tillage and chisel ploughing resulted in a lower bulk density than minimum tillage. The tillage operations for minimum tillage probably led to compaction in the deeper soil zone. Penetration resistance in the deeper soil zone in all tillage systems restricted rooting, but differences due to the tillage treatment were not sufficient to markedly influence the yield.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634342

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

A number of maize genotypes reportedly resistant to various stem borer species were evaluated for resistance to the maize stalk borer,Busseola fusca, and the spotted stem borer,Chilo partellus. Based on larval mass gain after two weeks of feeding on plants grown under greenhouse conditions, genotypes of both yellow and white kemel types were found to be significantly more resistant than the resistant standard Mp706. Pronounced resistance to both borer species was observed in breeding material developed by CIMMYT, whereas the Mississippi inbred line Mp708 was identified as a new source of resistance toC. partellusonly. The level of resistance to B.fuscain Mp706 seemed to be negatively affected by reducing the photoperiod.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634343

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor