摘要:

Control of wild oats (Avena sterilisssp.ludovicianaNyman) with tralkoxydim {2-[1-(ethoxyimino)propyl]-3- hydroxy-5-(2,4,6-trimethylphenyl) cyclohex-2-enone} in a tank mix with MCPA (2-methyl-4-chloro phenoxy acetic acid) and/or bromoxynil (3,5-dibromo-4-hydroxybenzonitrile-octanoate and heptanoate esters) was determined under controlled conditions. Tralkoxydim alone and combinations with bromoxynil and MCPA were applied at different rates and growth stages of wild oats. Fresh leaf mass was determined at various intervals. Growth control of wild oats was significantly reduced by as much as 21% by the addition of MCPA at the lower rates of tralkoxydim. Antagonism occurred at both application stages and was first detected 7 days after herbicide application. Addition of bromoxynil did not reduce the effect of tralkoxydim drastically. The tralkoxydim alone and the combination of tralkoxydim plus bromoxynil plus MCPA controlled wild oats satisfactorily.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634592

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The objective of this study was to obtain information on the Cu, Fe, Mn and Zn uptake patterns of wheat (Triticum aestivumL.) grown under normal irrigation farming conditions. Except for irrigation scheduling, the 13 farmers on whose farms the study was conducted were allowed to follow their normal farming practices. At each site biomass production and nutrient content of the top growth were measured regularly throughout the growing season, starting 35–45 days after planting. The concentration of Cu and Zn started to decrease from 40 days after planting, while the concentration of Fe and Mn increased until 50 days after planting and then started to decrease. Accumulation of Cu, Fe, Mn and Zn in the whole plant reached a maximum during caryopsis at about 150 days after planting. The maximum accumulation for Cu, Fe, Mn and Zn was 145, 3 984, 934 and 124 g ha−1, respectively. Uptake rates for Cu, Fe and Mn reached a maximum just before anthesis at about 115 days after planting. The maximum uptake rate for Zn occurred just after four leaves were fully unfolded on the main stem at about 75 days after planting. The maximum uptake rates were 2.75, 91.67, 14.67 and 2.18 g ha−1day−1for Cu, Fe, Mn and Zn, respectively.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634593

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Severe K nutritional problems in maize (Zea maysL.) and soyabean (Glycine max(L) Merr.) are common on the strongly K-fixing gleysols of east Croatia, Yugoslavia. There is, however, little information currently available regarding the K fertilizer requirements of these soils. The work reported here was conducted to obtain this information. Maize and soyabean were grown for three seasons in experiments incorporating seven initial K application rates (125, 275, 460, 650, 835, 1 580 and 2 220 kg ha−1). In the second and third seasons equal rates of K (125 kg ha−1) were applied to all plots. Both maize and soyabean responded dramatically. In the first season yield responses were curvilinear in nature, but by the third season responses were linear and K nutrition was clearly inadequate, even at the highest rate of K application. Soil and plant analytical data generally mirrored these effects and it is apparent that severe fixation of applied K resulted in a massive K requirement. Further work is needed to establish whether band placement of applied K will help to alleviate K-fixation problems more economically.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634594

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Field trials consisting of different tillage and soil fertility treatments were conducted to study possible causes of yield decline of monoculture winter wheat in the eastern Orange Free State. Soil fumigation with methyl bromide enhanced plant growth, reducedPythiuminfections and increased grain yields in both clean-tilled (mouldboard-ploughed) and minimum-tilled (stubble-mulch) plots.Pythium irregulärewas frequently isolated from scutellum tissue of young wheat seedlings. Roots of older plants were commonly infected withp. arrhenomanes.Higher yields were obtained under conventional tillage than under minimum tillage. Nitrogen amendments retarded growth and reduced yields in clean-tilled plots, but not in minimum-tilled plots. Phosphorus seems to act as a buffer to the damaging effects ofPythium, minimizing the combined effect of infection and phosphorus deficiency. The yield depression of wheat in minimum-tilled soil is attributed toPythiumdamage rather than to Phytotoxins previously isolated from unweathered straw.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634595

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Acid, P-deficient soils with a large capacity to immobilize P favour the rapid decomposition of apatite. Such soils are widespread in the east of South Africa and the possibility exists that Langebaan rock phosphate (Langfos) may be a more cost-effective source of P than superphosphate on these soils. This study compared the effectiveness of granular Langfos to that of double superphosphate in a pot experiment using a strongly P-fixing Balmoral clay (Typic Haplorthox) and a weakly P-fixing Avalon sandy loam (Plinthic Paleu- dult). Five rates of double superphosphate (0, 100, 250, 500 and 1 000 mg P kg−1) and six of Langfos (0, 100, 250, 500, 1 000 and 2 000 mg P kg−1) were compared at three lime rates. Three consecutive crops of maize (Zea maysL.) were grown for periods of four weeks. The average of the initial response slopes from the relationship between cumulative yield and P applied for the different lime applications showed that the effectiveness of Langfos relative to superphosphate was 10% and 18% for the Balmoral and Avalon soils, respectively. Lime had relatively little effect on plant response to superphosphate on the Balmoral, but had a marked positive effect on the Avalon. The response to Langfos was negatively affected by lime on the Balmoral, but only slightly so on the Avalon. These results suggest that granular Langfos will be more effective in acid sandy soils than in acid clay soils but that it is not an effective substitute in either for water-soluble P fertilizers.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634596

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

The aim of the study was to compare N uptake from initially-applied NH4+and NO3- ions and to compile a balance sheet for applied fertilizer N. In a pot experiment, maize, sorghum and sunflower plants were grown in succession, each for c. 6 weeks, to utilize the mineral N. The treatments were: NH4{NO3}, {NH4}NO3, {NH4}{NO3} and a zero N control, each replicated four times. The ions in brackets were labelled with15N, Although the applied ammonium nitrate was labelled in three different ways, the same quantity of N was applied initially and similar quantities of total N and soil N were together taken up by the three crops. The N recoveries from the two individual ions, however, differed. Results indicated that on average 75.8% of the initially-applied labelled NH4+-N was utilized by the vegetative tops of the three crops, this being significantly lower than the 85.9% of the labelled NO3-N utilized. The maize (1st) crop utilized 45.2%, the sorghum (2nd) crop 23.2% and the sunflower (3rd) crop 12.5% of the ammonium nitrate. When both NH4+and NO3- ions were labelled the N recovery corresponded with the sum of the findings where the ions were separately labelled. The accumulated N uptake by the successive crops from the soil reserves was higher where the soil was fertilized with ammonium nitrate when compared with the controls. The balance sheet took the N in the planted seed and the mineralization of soil N into account. It appeared that the addition of ammonium nitrate stimulated the mineralization of humus in the fertilized pots. The total soil analysis at the end of the experiment indicated that, on average, 17.7% of the fertilizer N remained in the pot soil. Eventually 100%, on average, of the applied ammonium nitrate could be accounted for in the N balance.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634597

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Sunflower,Helianthus annuusL., is an insect-pollinated crop and the different insect taxa visiting the flowering head play a role of greater or lesser importance in cross-pollination. Species diversity, abundance and behaviour of insects visiting commercial sunflower during flowering are reported for three sites in the Transvaal during 1985–87. The conventional strip-counting method was used to determine diversity and abundance, while notes on behaviour were taken at the same time. The mean number of insects per 100 capitula was 45, 147 and 64 at Settlers, Pretoria and Hartbeesfontein, respectively. Indigenous honeybees,Apis mellifera saltellataLepeletier, were the most common in all study areas (71%, 86% and 46%, respectively). Other well-represented taxa includedHeliothis armigeraHübner (American bollworm larvae),Asiylus atro- maculatusBlanchard (spotted maize beetles), Diptera (flies) and Hemiptera (bugs). Solitary bees were rare.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634598

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Tomato and lettuce seedlings were exposed to 1 or 3 mm of simulated rainfall containing the auxin-type herbicide 2,4-D iso-octyl ester. They were then evaluated weekly for damage according to symptoms and chlorophyll content. In addition, dry matter production was determined at the end of the three- week growth period. The herbicide threshold concentration for causing the symptoms‘stem, leaf and petiole bending’on tomato seedlings and‘duck's foot-type leaves’on lettuce seedlings was found to be 10 pg L−1. Significant reduction of the dry mass of the above-ground plant parts began with 10 ng L−1of the herbicide. Further dry mass seems the only parameter measured that is sensitive to application volume. There was a significant decrease in chlorophyll content at 10 mg L−1of the herbicide. It was deduced that neither chlorophyll content nor dry mass can be used as markers for auxin-type herbicide damage.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634599

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Rest-breaking agents less toxic than the commercially-used DNOC/winter-oil and less expensive than hydrogen cyana- mide were tested on Golden Delicious in a high density planting in a region of warm winters. Some combinations of mineral oil and cyanamide were as effective in promoting budbreak as both DNOC/oil and cyanamide but neither treatment improved fruit set or fruit size 12 weeks after treatment, relative to the control. Rest-breaking treatments are seen as one aspect of tree manipulation rather than a direct means of increasing production.

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634600

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor

摘要:

Daily potential surface radiation values were calculated for selected South African weather stations. These were used, together with various air temperature parameters, to derive regression equations to estimate actual surface solar radiation at sites lacking the required instrumentation. A single regression equation for the whole country proved more effective than several region-specific expressions. The equation was assessed at 27 widely-ranging sites which had not been used in the regression analysis. According to Willmott's Index of Agreement (D), solar radiation estimates were best in the winter rainfall region (D≥0.92) but were quite acceptable for the rest of the country (D≥0.78).

ISSN:0257-1862    

DOI:10.1080/02571862.1992.10634601

出版商:Taylor&Francis Group    

年代:1992

数据来源: Taylor