摘要:

Cultivation caused, without exception, a decline in the organic matter content of dryland soils in the central regions of South Africa. The question arose as to how cultivation affects the organic matter content of irrigated soils from these regions. The main aim, therefore, was to quantify the effect of cultivation on the organic matter content of soils from three irrigation schemes with virgin soils serving as reference. Virgin and cultivated topsoils (0–200 mm) were sampled from seven sites at Riet River, eight sites at Ramah and six sites at Vaalharts. The sites at each irrigation scheme represented varying periods of cultivation. Soil samples were analysed for particle size distribution, pH, exchangeable Na, K, Mg and Ca, extractable P and Zn, CEC, organic C and total N. The K, P and Zn contents differed significantly between virgin and cultivatedsoils:K decreased, while P and Zn increased with cultivation and irrigation. Organic C and total N significantly increased at seven sites and decreased at eight sites as a result of cultivation and irrigation. At another three sites only one of organic C or total N changed significantly and at the remaining three sites cultivation and irrigation had no significant effect. Neither cultivation and irrigation history, nor soil properties provided a clear explanation for these contrasting findings. The gain of soil organic matter at five sites from Ramah and two sites from Vaalharts could possibly be attributed to enhanced biomass turnover on these irrigated lands

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635080

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Protein banding patterns of seed obtained by sodium dodecyl sulphate Polyacrylamide get electrophoresis (SDS-PAGE) or acid polycrylamide gel electrophoresis (A-PAGE) were used to distinguish between differentCyclopiaspecies (‘heuningbostee’). An electrophoretic formula was determined for each species using relative band mobility and the number of protein bands Distinctive band patterns were obtained enabling the species to be identified using either SDS-PAGE or A-PAGE Banding patterns showed that this technique can be used as a tool for taxonomic classification ofCyclopiaspecies.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635081

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Leaching of atrazine [6-chloro-N-ethyf-N′-(methylethyl)-1,3,5-triazine-2,4-dlamine] and terbuthylazine [6-chloro- N-(1,1-dirnelhylethyt)-N′-ethyl-1,3,5-triazlne-2,4-diamine] was studied in 23 soils by means of the soil thick-layer leaching method. The equivalent of 4 kg ai ha−1of both herbicides was leached with water equivalent to 129 mm rain Distances leached were measured qualitatively in bioassays with the test plantTnfolium repensL. Leaching distances in different soils varied from 6–20 cm for atrazine, and from 2–16 cm for terbuthylazine. Atrazine leached at least 10 cm in 13 soils, while terbuthylazine did not move from the zone of application in 12 soils. Of the five soil properties assessed by means of simple regression, organic matter content (%C) and P-reversion were significantly correlated with the leaching distance of atrazine, and %C with the mobility of terbuthylazine. Relationships between herbicide leaching and either total clay content or soil pH were relatively weak. The combination of organic matter content and soil pH in multiple regression analysis gave the best prediction of leaching for atrazine (R=0.85) and terbuthylazine (R= 0.42). It is suggested that the regression models incorporating % C and pH be used for rapid ranking of soils regarding their leaching indices for the two compounds The models may prove useful for preliminary identification of soils which are prone to leaching of the herbicides.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635082

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Urea fertilizers may lose N by ammonia volatilization when applied in the field. In order to reduce this loss, modified urea compounds are being used. Not all of them reduce ammonia loss and improve crop yields. A field study was conducted to evaluate the comparative advantage of cogranulated urea-urea phosphate (340 g N kg−1, 73 g P kg−1) over urea (460 g N kg−1) and ammonium nitrate (350 g N kg−1) when supplied as nitrogen fertilizers to maize. The fertilizer granules were applied at rates of 67, 134 and 202 kg N ha−1, as surface-broadcast or soil-incorporated treatments. Fertilizer application increased crop yields and nitrogen uptake, but the sources were not significantly different from each other. Increasing nitrogen supply up to 134 kg N ha−1improved maize yield and nitrogen uptake. Incorporating the fertilizer with the soil was not better than surface application. The data available suggest that maize responded to cogranulated urea-urea phosphate, urea and ammonium nitrate similarly.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635083

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The volatilization of ammonia following applications of urea fertilizers to soils may release significant amounts of N into the atmosphere and reduce the plant available N. This study compared ammonia loss from urea phosphate (170 g N kg−1, 190 g N kg−1), cogranulated urea-urea phosphate (340 g N kg−1, 73 g P kg−1), urea (460 g N kg−1) and ammonium nitrate (350 g N kg−1) granular fertilizers applied to the soil surface at 60, 120 and 200 mg N kg−1soil. Soil moisture contents were adjusted to 100% and 25% of field moisture capacity at the beginning of the experiment. Ammonia losses from cogranulated urea-urea phosphate and urea were similar, being as much as 7.8% of applied nitrogen in 14 days. Urea phosphate and ammonium nitrate exhibited significantly lower ammonia losses. As the amount of N applied increased, corresponding ammonia loss increased. An initial soil moisture at 25% field moisture capacity caused the fertilizers to lose more ammonia than when the soils were initially at 100% field moisture capacity. The data suggest that urea phosphate has a lower ammonia volatilization potential than urea, but increasing the urea to phosphoric acid mole ratio to achieve a higher N analysis (cogranulated urea-urea phosphate) suppresses the effect of phosphoric acid and raises the ammonia volatilization potential.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635084

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Monogenic resistance in wheat (Triticum aestivumL.) to leaf rust, caused byPuccinia reconditaRob. ex. Desm. f. sp.tritici, has generally not been durable. Durable resistance, as well as an improved expression of resistance, have been associated withLrgene combinations. In this study, the assumption thatLr12andLr13may interact to condition improved resistance to leaf rust, was investigated. Four Thatcher (Tc) x RL6011 F3lines (13/12–3, 13/12–9, 13/12-19 and13/12–40), homozygous for bothLr13andLr12, were selected and their leaf rust resistance compared with the parents (CT263 [=TcLr13] and RL6011 [=TcLr12]), the single gene linesTc/13–22and TC/12–16, and Thatcher. In addition to infection type studies in seedlings and adult plants, lines were compared according to macroscopic components of resistance, as well as disease ratings in the field. Flag leaf infection type studies showed thatLr12is effective against most pathotypes ofP. reconditaf. sp.triticioccurring in South Africa. Conversely,Lr13is ineffective against the dominant pathotypes, implying that the gene has no value as a monogenic source of resistance. Based on the fact that several pathotypes are avirulent to these genes, they should be manipulated with relative ease in local breeding programmes directed at utilizing these sources in combination with otherLrgenes. Infection types on the flag leaves of lines carrying bothLr12andLr13often displayed chlorosis and necrosis. These ratings on primary and flag leayes, as well as the quantitative components latent period, uredium density and uredium size, did not indicate clear differences between the digenic lines and the most resistant parent. In the absence of a pathotype virulent to both genes, the combination lines were resistant in the field. Data obtained were not conclusive in suggesting pronounced resistance enhancement due to combiningLr12withLr13.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635085

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Survival and efficacy of monoculture inoculants ofFlavobaderiumsp. andRhodococcus chlorophenolicusto bioremediate PCP-contaminated soil were examined under sterile and non-sterile conditions. Both species effected ≥ 40% catabolism in four weeks although inoculant survival was significantly higher withR. chlorophenolicus.Supplements of bark chips or distillery waste with the inoculant did not, initially, promote bioremediation. PCP additionper seeffected enrichment of indigenous catabolic populations and this was promoted by the presence of wood chips. Both aerobic and anaerobic enrichments were successful and PCP mineralization under both conditions was recorded. Under anoxic conditions, dehalogenation of o-substituents was dominant although some meta-chlorines were removed. Provisional evidence of two separate isomer-specific dehalogen-ating populations was obtained.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635086

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fifteen maize inbred lines were evaluated for resistance to ear rot, using artificial inoculation of plants with isolates ofStenocarpella maydisfrom 13 localities in the South African maize production area. Five inbreds and four isolates were common to the four seasons of evaluation. The inbreds B37, D0620Y and E739 showed levels of resistance superior to that of the standard Hill. Isolates provided inconsistent infection levels in different years. All interactions were significant, with seasonal effects predominating over the genotype x isolate interaction.

ISSN:0257-1862    

DOI:10.1080/02571862.1997.10635087

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor