摘要:

Replacement intercropping trials with maize and dry beans were conducted to provide information which could lead to a cropping strategy that would reduce the risk of rainfed crop production in the Ciskei. Attention is focused on the problem of analysing intercropping experiments. It was concluded that more than one method of analysis was necessary. The gross yields obtained as well as the competition effects in terms of the proportion harvested rather than the proportions sown must be examined. Replacement intercropping of maize and beans does not appear to provide a strategy for reducing the risk of rainfed cropping in Ciskei.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634226

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

Maize was grown under field conditions, applying conventional farming practices. Atrazine was sprayed pre- emergence at concentrations of 1,25 I ha−1ai. and 5 I ha−1ai. Severe phytotoxicity symptoms were visible from the first- to about the sixth-leaf stage i.e. 25–30 days after planting in the maize plants treated with 5 I ha−1atrazine. The growth rate of atrazine-treated maize plants was inhibited during this period, whereafter it recovered. No effect on subsequent fresh mass accumulation could be detected when comparing treated plants with the control after about 40–45 days after planting. The inhibition of growth during the early developmental stages had no negative effect on the final yield. Hydroxylation of atrazine as detoxifying mechanism seems to play the major role in the case of root-absorbed atrazine up to approximately 25–30 days after planting.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634227

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

'n Ondersoek het aangetoon dat 'n hoogsbetekenisvolle (r= 0,96) verwantskap bestaan tussen waterverbruik van 'n volwasse sitrusboom en vruggroeitempo. Waterverbruik bereik 'n maksimum van 80–90 l/dag gedurende die periode Desember tot einde Maart, dit is dieselfde tyd wanneer vruggrootte snel toeneem. Sikluslengte van besproeiing speel 'n belangrike rol in vruggroei. 'n Kort sikluslengte lewer egalige vruggroei en dus groot vrugte. Die verskille in vruggrootte tussen twee seisoene vir 'n behandeling waarin geen vogstremming voorgekom het nie, is toegeskryf aan klimaatsverskille veral gedurende die vroeëdeel van die seisoen (Sept.–Jan.). Vruggroeitempo neem snel toe bokant 26°C.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634228

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

Volatilization losses of NH3from five fertilizers, namely (NH4)2SO4, LAN, urea, MAP and DAP were determined. The fertilizers were applied to a Bainsvlei soil of which the pH was adjusted to 6,5; 7,6; 8,3 and 9,1. The application levels were equivalent to 0, 15, 30, 60, 120 and 240 kg N ha−1. After a contact period of three days NH3losses were determined. Ammonia was lost from all fertilizers under all treatments. The losses increased with increasing pH values and levels of application. These five nitrogen-containing fertilizers differ significantly from each other with regard to volatilization of NH3. They can be ranked in order of increasing NH3losses as follows: LAN

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634229

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

This paper discusses data obtained from a long-term N, P, K field experiment with maize (ZeamaysL.) on a Normandien clay loam (Plinthic Paleudult) near Newcastle, Natal. After eight seasons plots were split, sub-plots being allowed either to rundown or continuing to receive annual P applications. Soil samples were obtained shortly after fertilization each season and P soil tests were related to final grain yield. The results obtained indicate that although yield maxima varied from 3 000 kg ha−1in the dry 1981/82 season to over 6 500 kg ha−1in the more favourable 1983/84 season, there was no meaningful difference in the optimum P soil test using either the Ambic, modified Truog or Bray 1 extractants. Furthermore, the relationship between yield and soil test was identical for residual P subplots and those which received annual applications of fertilizer P.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634230

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

Four tillage treatments ranging from conventional mouldboard ploughing through to direct-drilling were repeated during the second season of an ongoing experiment. At commencement of the new season, differences in plant- available water (PAW) in the top 600 mm of the soil profile were non-significant. Following primary tillage, a strong trend of lower PAW with increasing degree of tillage was observed until just before anthesis, and again midway through grain-filling. These differences were attributed mainly to reduced evaporation prior to planting under the greater maize residue cover on the less disturbed soil. Residue cover at planting was 83% on the direct-drill, 21% on the chisel, 15% on the chisel&disc, and 4% on the mouldboard ploughed treatments. Maximum soil temperatures at 50 mm depth increased with decreasing residue cover which resulted in quicker seedling emergence, and leaf area development during early vegetative growth. The soil water storage advantage and slower initial growth in the direct-drill treatment was associated with highest yield of 7,6 t ha−1.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634231

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

The objective of these experiments was to evaluate the usefulness of the excised leaf water retention capability (ELWRC) technique for screening grain sorghum genotypes for drought resistance. Seven genotypes were planted in a randomized block consisting of four replications. The plants were kept under severe moisture stress. In addition to their ELWRC, the canopy temperature, diffusive resistance, transpiration and yield potential was measured. Significant differences between genotypic means were obtained for ELWRC and yield potential only. These were significantly correlated (r =0,89). Correlations between the other characteristics are discussed. Only additive genetic variation was detected for ELWRC in a partial diallei of three female and nine male inbred lines. It was concluded that ELWRC was a satisfactory screening technique for drought resistance of the sorghum genotypes included in these experiments.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634232

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

Two toposequences derived from granite in the Mt. Garnet area, North Queensland, were examined to determine the detailed soil - landform relationships in order to facilitate subsequent broad-scale mapping of the soil resource. The dominant landsurface feature is gently sloping, concave footslopes covered by relatively thick colluvial deposits. It is assumed that these footslopes are attributable to a retreating midslope as well as the colluviation of materials during dry periods of the Late Mid- to End-Pleistocene. Granulometrie parameters indicated a single source of parent material for the footslope soils, although there would seem to be a temporal discontinuity between the A and B horizons. The distribution patterns of the footslope soils (varying from Griffin, Shepstone to Longlands forms) could be explained by means of a simple catenary model, in which profile hydrology, caused by a water surplus generated by the physical environment, played the major role. In extent, the footslope is dominated by the Shepstone form comprising greyish coarse sands abruptly overlying reddish, apedal, mesotrophic clays and loams.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634233

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

Nitrogen transformations and losses from three nitrogenous fertilizers, urea, urea ammonium nitrate (UAN) and limestone ammonium nitrate (LAN), when applied to four South African soils, were compared in a laboratory study. The highest losses on all these soils were experienced when urea was applied, followed by UAN solution and then LAN. It also appears that a relationship exists between N volatilization and the change in pH of the soil. The lower the buffer capacity or clay content of the soil, the greater the pH change and the nitrogen losses. In the case of LAN, the pH did not rise to above 7 in any of the four soils and no ammonia volatilization was detected. Explanations for the nitrogen losses are proposed and supported with chemical reactions. High soil surface temperatures may result in accelerated mass flow and ammonia volatilization. On the other hand, it was shown that nitrites or nitrous acid promoted denitrification, especially when LAN was applied.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634234

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor

摘要:

A relationship was observed between seedling growth rate and seedling emergence under conditions of soil capping. Coleoptile and root growth rates were strongly influenced by the origin of the seed sample and the genotype involved, whereas genotype×environment interactions were small and not significant. A test-cross analysis revealed the presence of strong epistatic effects for the characters coleoptile growth rate and coleoptile diameter. Both additive and dominance variation contributed strongly to the total genetic variation for coleoptile growth rate, while the - dominance appeared to be ambidirectional. Genetic variation for coleoptile diameter was found to be predominantly additive. Whereas both traits were expected to respond well to selection, no consistent correlations with simple plant characteristics could be established, a situation that may limit the utilization of the observed genetic differences through indirect selection.

ISSN:0257-1862    

DOI:10.1080/02571862.1987.10634235

出版商:Taylor&Francis Group    

年代:1987

数据来源: Taylor