摘要:

Maize was grown under controlled conditions in a pot experiment to determine how drought sensitivity would be affected by differential soil fertilities. Soil was obtained from a fertilization field trial where soil fertility differences developed over a period of 45 years. Four water stress treatments were applied in the pot experiment. Grain yield was determined as a measure of the stress reaction. Plants with nitrogen, phosphorus and potassium deficiencies were apparently less tolerant to water stress conditions than well fertilized plants. As could be expected, plants were more sensitive to drought during the reproductive phase than during the vegetative phase. However, the differences in sensitivity were much more for plants with nutrient deficiencies. The results implied that nitrogen, phosphorus and potassium played a beneficial role in the drought adaptation mechanisms of the well fertilized plants.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634487

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Ondersoek is ingestel na die invloed van relatief lae toedienings van kalium, asook drogingstemperatuur, op die vermoëvan die kleifraksie van 'n Arcadia-grond, versadig met kalsium of magnesium, om kalium vas te lê. Die verskil in reaksie tussen die behandelings van die Ca- en Mg-kleisisteme was betekenisvol. Alhoewel hierdie smektiet swellende klei aan uitdroging onderwerp moet word alvorens kalium in die tussenlaag ruimtes vasgevang kan word, word heelwat kalium uit die uitruilbare fraksie onttrek onder klam toestande. Hierdie verskynsel kan aan 'n chemiese binding tussen kalium en die kleimineraal toegeskryf word. In die geval van die kontrole en die laagste K-peil het lugdroging 'n vrystelling van kalium uit beide kleisisteme tot gevolg gehad. Verhoogde drogingstemperatuur het 'n gepaardgaande verhoging in die hoeveelheid kalium wat vrygestel word tot gevolg. 'n Verhoging in kaliumtoediening het gelei tot 'n afname in die hoeveelheid kalium wat uit die kristalstruktuur vrygestel word. In die geval van die hoogste K-toedienings van 10,24 mmol(+)kg−1is kaliumvaslegging by alle uitdrogingsbehandelings op beide die Ca- en Mg-versadigde kleie waargeneem, Binne die gebied van kaliumtoedienings wat algemeen in die praktyk toegepas word, dit is 1,28–2,56 mmol(+) kg−1(100–200 kg K ha−1), word hoogstens 12,5% van die toegediende kalium aan die uitruilkompleks onttrek (geen uitdroging). Met lugdroging kan daar binne hierdie gebied eerder 'n vrystelling van kalium verwag word.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634488

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Plant available water (PAW) is the amount of water in the soil profile available for crop use. When irrigation management is based on a percentage depletion of PAW accurate estimates of PAW are essential and it is important that factors affecting the magnitude of PAW are taken into account. The effect of fertilization and irrigation on PAW of wheat was investigated in the long-term fertilization and irrigation experiment of the University of Pretoria.In situPAW determinations revealed large differences between treatments, with well fertilized wheat being able to extract more water from the profile than nutrient deficient wheat. Reduced water supply also tended to increase PAW. Differences were attributed to the effect of the treatments on rooting depth and density. Results show that certain managerial practices such as irrigation scheduling and fertilization can influence PAW, which accentuates the need forin situdeterminations rather than laboratory determinations of PAW where accurate estimates are needed.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634489

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Pre-emergence herbicides were tested for relative phytotoxicity to Nemaguard peach seedlings (Prunus persica) in a sand culture. Typical symptoms, phytotoxicity ratings, growth and regrowth parameters were recorded. Diuron, the mixture diuron plus terbacil (1:1), terbutryne and norflurazon were rated phytotoxic at concentrations as low as 1 mg−1with little recovery in the regrowth. Terbacil and simazine caused moderate initial phytotoxicity at concentrations up to 3 mg l−1but the seedlings showed recovery in the regrowth. Oryzalin at 6 mg l−1and higher caused stunting of growth, especially with the regrowth, while trifluralin, pendimethalin, napropamide and prodiamine proved to be relatively safe to peach seedlings at concentrations up to 6 mg l1.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634490

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Treatment of barley plants with 2,4-D, when the main tiller apical meristem was in the late vegetative or double ridge stage, resulted in the production of various abnormalities including missing spikes, branched spikes, whorls of spikelets and paired spikelets instead of the normal alternate arrangement, 90°turn in the plane of the spike and the production of double seeds.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634491

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Early maize development is generally less rapid in the cooler soils of tillage systems which maintain large amounts of crop residues (stubble) on the soil surface. However, soil water storage tends to increase with increasing amount of surface cover, and therefore, a study was conducted in which uniformly distributed maize stubble (92% cover) was raked away from the planter rows to produce 0, 80 and 320-mm bare soil bands (BSB) over the seed-rows, or ploughed under in accordance with standard fallow period field management practices (conventional tillage). Maximum and hourly mean soil temperatures measured in the seedzone (50-mm depth) during the planting to tassel initiation period increased with increase in width of BSB and approached the values measured under the bare surface of conventional tillage (CT). However, soil water contents decreased with increasing BSB and played the dominant role in reducing the number of days from planting to 80% maize emergence, with fewer days being required as BSB decreased. Rates of leaf area development increased with increasing maximum and hourly mean soil temperatures (or width of BSB). AlthoughCThadthemost favourable soil temperatures forseedlingestablishment, low soil water contents, particularly during early growth, reduced plant vigour and grain yield.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634492

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Aluminium (Al) is a major component of most soils and is a limiting factor to sustained crop production in many regions. The amelioration of Al toxicity is of theoretical as well as practical interest in our understanding of mechanisms of toxicity. The effect of Al and calcium (Ca) on root length, shoot and root dry mass of two soybean (Glycine max(L.) Merr) cultivars, Hill and Forrest, was evaluated in a nutrient solution culture experiment. The experiment consisted of a factorial design comprising varying levels of Ca (50, 250, 1 250 and 2 500μM Ca as CaSO4. 2H20), Al (0, 148, 296 and 588μM Al as AI2(SO4)3. 18H20) and the two soybean cultivars. At pH 4,0 these treatments resulted in predicted activities of monomeric Al species in solution in the range of 16–92μM for Al3+, 47–257μM for AISO4+, 1,6–9,3μM for AIOH2+and 0,1–4,6μM for AI(OH)2. Very poor correlations were observed between measured plant growth parameters and individual monomeric Al species in solution, this being ascribed to the interactive effect of Ca on Al phytotoxicity and the presence of the less phytotoxic species AISO4+. However, highly significant coefficients of determination were found where both the molar activities of Ca2+: AI3+and the ratios of Ca: AI on a concentration basis were considered. Increasing Al levels in solution significantly depressed Ca, Mg, P, Mn and Zn concentrations in the shoots. No relationship between Al concentration in the shoots and the activities of various monomeric Al species was observed. A highly significant quadratic function (R2= 0,956) was found between the Ca concentration in the shoots and the ratio of the molar activities of Ca2+: AI3+.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634493

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Bioassays with grain sorghum (Sorghum bicolorL. Moench) cultivar NK222 were conducted in a glasshouse. Thirty-four natural soils were used in each of two experiments with alachlor [2-chloro-2′,6′-diethyl-N- (methoxymethyl) acetanilide] and metolachlor [2-chloro-6′-ethyl-N-(2-methoxy-1-methylethyl)acet-otoluidide] respectively. Linear regression analyses were performed to determine the importance of certain soil properties in the prediction of herbicide bioactivity. The order of importance for alachlor bioactivity was as follows: % C>clay %≥CEC P reversion≥soil pH; and for metolachlor: % C>clay % 3 CEC>soil pH>P reversion. Inclusion of either clay content or P reversion with % C in multiple regression equations significantly increased the predictability of alachlor and metolachlor bioactivity. Organic matter content affected alachlor and metolachlor phytotoxicity, despite the relatively low organic matter levels generally found in South African soils.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634494

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

The nature of the resistance of guar to attack by the root parasiticA. vogeliiwas investigated, it was found that although seed of the parasite was induced to germinate in the presence of stimulants, radicle elongation was prevented owing to substances inhibitory to the germination OfAmaranfhus caudal us(L.). This effectively prevented penetration of the parasite into the tissue of the host. In this way guar couid act as a catch crop by eliminatingA, vogeliiseed from the soil in a process of suicidal germination. Indications of a resistance to penetration was also found. Chromatographic investigation of the stimulant as well as the inhibitor revealed almost co-eluting compounds on a Fractogel column.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634495

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor

摘要:

Sphagnumpeat moss is used in most countries as a casing material in the cultivation ofAgaricus bisporus.Since South Africa has no peat moss, suitable substitutes for it have to be found. Nine potential materials were screened as casing media of which topogenous peat, paper pulp and spent compost gave encouraging results and were further investigated. Apart from mushroom production, various physical, chemical and microbiological properties of the substrates were compared. Weathered spent compost and topogenous peat gave the highest mushroom yields.

ISSN:0257-1862    

DOI:10.1080/02571862.1989.10634496

出版商:Taylor&Francis Group    

年代:1989

数据来源: Taylor