摘要:

Seedlings of Troyer citrange[Poncirus MollataL. Raf.×Citrus sinensisL. Osbeck] (Tro), Citrus volkameriana (Vol), Carrizo citrange[Poncirus trifoliataL. Raf.×Citrus sinensisL. Osbeck], (Car) and Rough lemon [Citrus jambhiriLush.] (Rie) were tested for tolerance to chloride in irrigation water, ranging from 0 to 1147 mg L−1chloride, as NaCI. Based on the occurrence of toxicity symptoms on the leaves, Vol was the most tolerant to CI, followed by Rle. Decrease in dry mass of shoots and roots with increased chloride levels again showed Vol to be the most tolerant rootstock followed by Rle. Tro and Car were the most sensitive to chloride. The shoot: root ratio increased with increasing chloride levels indicating that more shoots were produced in relation to roots at increasing chloride levels. The percentage chloride in the leaves showed a constant increase with increasing CI levels to the point where leaf drop occurred.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634344

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Die behoefte in Suid-Afrika aan stikstofbemestingsriglyne wat op 'n meer fundamentele basis berus, het aanleiding gegee dat drie veldproewe in die 1992/93 groeiseisoen begin is. Residuele NO3-N is na oes (Julie 1993) en voor plant (November 1993) op dieptes van 0–300 mm en 300–600 mm bepaal. Die gemiddelde residuele NO3-N voor plant (0–600 mm) was 4. 3 en 2. 8 mg kg−1vir behandelings wat onderskeidelik deur peulplante en mielies sonder stikstofbemesting, voorafgegaan is. Die stikstofvoordeel van eenjarige peulplante is meetbaar as residuele NO3-N voor plant, aangesien data van mielies na mielies en mielies na peulplante dieselfde ver- wantskap tussen relatiewe opbrengs en residuele NO3-N beskryf het. Residuele NO3-N voor plant het 81% van die variasie in relatiewe opbrengs (van behandelings waar geen stikstof toegedien is nie) verklaar terwyl residuele NO3-N na oes slegs 34% van die variasie in relatiewe opbrengs verklaar het. Die residuele NO3-N oor 600 mm het 00k beter met relatiewe opbrengs gekorreleer as residuele NO3-N oor 300 mm. Stikstoftoediening kon slegs 29% van die variasie in relatiewe opbrengs verklaar, maar toegediende plus residuele NO3-N het 72% van die variasie in relatiewe opbrengs verklaar. Dit is 'n aanduiding dat die bepaling van residuele NO3-N onontbeer- lik is vir stikstofbemestingsaanbevelings. Na kombinasie van data met diévan Van der Walt&Du Preez (1991) is 'n betekenisvolle empiriese verwantskap verkry, waar 59% van die variasie in relatiewe opbrengs deur toegediende plus residuele NO3-N verklaar word. Hierdie verwantskap verteenwoordig data van ses seisoene en nege lokaliteite en kan gebruik word om residuele NO3-N by bemestingsaanbevelings in berekening te bring.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634345

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Four field trials were conducted over three seasons to determine the optimum plant growth stages for single and follow-up insecticide applications for the control ofChilo partellusin grain sorghum. The insecticide was applied at various vegetative and reproductive plant growth stages. Different infestation levels were obtained by using different planting dates. A significant infestation level×treatment interaction (P<0.001) was observed. Yield losses ranged between 10.7% and 24.7% for the most effective single application and 3.9% and 48.0% for the most effective follow-up application. The most efficient single application was at the mid-whorl or flag leaf stage. The most efficient follow-up application involved the flag leaf stage application combined with either a boot or soft dough stage application. An increase in infestation levels resulted in an increase in the efficacy of mid-whorl stage applications. Applications before the flag leaf stage appear to be necessary when approximately 20% of the plants exhibit whorl damage. The necessity for different control strategies for specificC. partellusinfestation situations is emphasized.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634346

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effect of foliar application of molybdenum (Mo) on grain dormancy was examined in six wheat cultivare at four sites. Application of 100 mg L−1Mo at flag leaf stage significantly increased grain Mo content at all sites and reduced germination at three sites. Alpha-amylase activity of the grain harvested from ears that had been subjected to 0, 12, or 24-h simulated rain was significantly reduced by the Mo application. Molybdenum also reduced grain nitrate concentrations in all cultivars at all sites. It is concluded that an application of Mo at the flag leaf stage will significantly ameliorate sprout damage in wheat.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634347

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Annual ryegrass (Lolium multiflorumLAM. cv. Midmar) pastures were established on three sites, representing the Avalon, Katspruit and Inanda soil forms, with cut-plot experimentation over a period of four years (1987 - 1990). Nitrogen fertilizer was top-dressed at 0, 200, 300 or 400 kg N ha−1y−1and at intervals of 4 or 6 weeks. The dry matter (DM) yield data indicates that there was little justification for applying more than 40 kg N ha−1per application in autumn, and more than 50 kg N ha−1per application during spring. In addition, pastures top- dressed 4-weekly, at the above rates, produced yields equal or superior to equivalent annual rates applied on a 6-weekly application interval. With the increase in environmental concern about nitrates leaching into ground waters, and the potential for excessive applied N to accumulate to potentially toxic levels in pastures, the adoption of large infrequent applications of N is questioned.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634348

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Unless corrected, soil acidity and K deficiency frequently limit growth of intensive temperate pastures on highly weathered soils in South Africa. A field trial, with Italian ryegrass (cv. Midmar), was established on a Himeville sandy clay loam (typic Hapludox) for two seasons to test the possibility that Na applications could assist in the correction of these problems. Four levels of Na, lime and K were applied in an unreplicated 43factorial design. Significant responses to all treatments were recorded. In the first season, the response to 200 kg ha−1Na as NaCI was 1526 kg dry matter ha−1: Sodium responses were possibly due to enhanced P uptake, or Na substitution for K, or a combination of the two mechanisms. No consistent lime×Na interaction was observed. The need for continual monitoring of K levels in intensively used pastures was highlighted. Also shown was the important effect of K and Na on the mineral balance of the herbage produced: Potassium depressed herbage Ca, Mg and Na concentrations, and Na depressed herbage Ca and Mg where herbage K was low, but had no effect on herbage K. Where soil P and K reserves are marginal, production of ryegrass pastures in the cool part of the season may benefit from Na applications.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634349

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

Normal fertilizer placement, two placements deeper than normal, a broadcast application and a non-fertilized control were compared to maximize production in a stubble tillage system. Root growth was evaluated at three growth stages from tassel initiation to flowering during the 1986/87 and 1987/88 growing seasons. Fertilizer placed in the soil stimulated deeper rooting, particularly during early vegetative growth stages. The lowest total root length was measured in no-fertilizer and broadcast treatments. No differences in total evapotranspiration were associated with treatments. The percentage of available water in the top 0.3 m soil was less than, 25% for most of the active growing period while in the 0.3–0.6-m soil layer available water generally exceeded 25%. This lead to the conclusion that fertilizer placed in the deeper soil layer is accessible to the plants for a longer period.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634350

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor

摘要:

'n Afname van 4–70% in die totale S van bogronde as gevolg van bewerking het die vraag laat ontstaan hoe hierdie verlies verband hou met die periode van bewerking en of so 'n verwantskap tussen ekotope verskil. Bewerkte en nabygeleëekwivalente onversteurde gronde (0–200 mm) is by 50 lokaliteite, wat verspreid in die somerreënvalgebied voorkom (24°- 30°S en 24°- 30°0), gemonster. Die lokaliteite is geselekteer om 'n groot variasie in klimaatstoestande, grond- eienskappe en bewerkingsperiodes te verkry. Die tempo van swawelverlies is hoog gedurende die eerste paar jaar van bewerking, waarna dit afneem, totdat 'n nuwe ewewig bereik word. Die afnamepatroon van totale S het tussen ekotope verskil. Die persentasie verlies was groter in gronde met 'n hoër totale S, terwyl hierdie gronde, wat meestal in koeler gebiede met hoër reënval voorkom, ook langer neem om 'n nuwe ewewig te bereik as gronde met 'n laer totale S, wat meestal in warmer gebiede met 'n laer reënval voorkom.

ISSN:0257-1862    

DOI:10.1080/02571862.1995.10634351

出版商:Taylor&Francis Group    

年代:1995

数据来源: Taylor