摘要:

A number of seed vigour tests were conducted on two groups of maize seed lots. One group consisted of six seed lots of different cultivars while the other group consisted of six sub-lots of one cultivar, artificially aged for different periods. Seed vigour tests included in the study were, a low temperature germination test (incubation in rolled paper towels at 13°C), the soil cold test, the accelerated ageing test and an osmotic stress test. The results of the vigour tests were correlated with the emergence of the seed lots in four field trials representing different sets of environmental conditions. The low temperature germination test was found to have the greatest overall predictive value for field emergence. The advantages and disadvantages of the low temperature germination test compared with the soil cold test, which has gained wide acceptance as a standard seed vigour test for maize, are discussed.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634570

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Die ondersoek is onderneem om vas te stei of nitraatontledings gebruik kan word om die huidige stikstof- bemestingsriglyne in die westelike mielieproduserende gebiede te verfyn. Verskeie stikstofbemestingsproewe is by verskillende terreine in die gebiede uitgevoer. By elk van die 14 proewe is die opbrengsreaksie van mielies tot verskillende peile van stikstoftoediening gemeet. Die nitraatkonsentrasie van die grond oor drie diepte-intervalle is ook biepaal by 11 van die 14 proewe voordat dit bemes is. Die resultate het getoon dat die nitraatkonsentrasie van grond met planttyd 'n betekenisvolle bydrae maak tot die opbrengs wat gerealiseer het. Daarom is daar ook 'n hoëkorrelasie tussen nitraatkonsentrasie en relatiewe opbrengs van die zero behandelings gekry. Die korrelasiekoëffisiënte neem toe met toenemende diepte-intervalle van grondmon-sterneming. Drumpelkonsentrasies is bereken waaronder daar verseker 'n opbrengsreaksie met stikstofbe- mesting sal wees asook waarbo daar geen opbrengsreaksie met stikstofbemesting sal wees nie. Hierdie drumpelwaardes kan in die praktyk geïmplementeer word om die huidige riglyne vir stikstofbemestingaanbevelings te verfyn sodat die bemestlng in die mielieproduserende gebiede meer koste-effektief gemaak kan word.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634571

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Single applications of insecticide againstChilo partellusat different times in the pre-flowering stages of maize and from early whorl to soft dough stage in grain sorghum were compared with multiple applications. Based on yield and the incidence of damaged plants, late treatments were more beneficial than early treatments. Two serial applications would have sufficed to eliminate the greater part of the observed yield loss. The cost- benefit ratio seemed to favour a reduction in the number of applications currently recommended for maize, although more than one application seemed to be needed in grain sorghum.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634572

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

To calculate nutrient requirement it is necessary to know how much of that nutrient must be applied to overcome any buffering effects and raise the test value to a desired level. A glasshouse study was conducted on a wide range of Natal soils to establish this information for phosphorus. The upper 200-mm depth at 54 sites was sampled. Soils varied greatly in texture (4–83% clay), organic carbon (0.2–9.2%) and clay mineralogy (kaolinitic-sesquioxic through to illitic and smectitic). Soil from each site was treated with four levels of P and taken through a number of wetting and drying cycles over a six-week period. Analysis for P using the Ambic, Bray no. 1 and Truog extradants showed that the quantity of applied P (kg ha−1) required to raise the soil test value by a unit amount (1 mg L−1), i.e. the P requirement factor, varied greatly for the different soils. The range in values for these three extradants was 2.5–37.9; 2.0–17.7; and 2.3–30.3, respectively. The level of P sorption was found to be strongly related to clay content, and soils rich in 2:1 minerals showed surprisingly high P sorption.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634573

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Die oogmerk van die studie was om die verwantskappe tussen maksimum nitrifikasietempo (Kmaks) en relevante eienskappe van die gronde vanaf die sentrale besproeiingsgebiede uit te wys. Die verloop van nitrifikasie is in agt gronde, afkomstig van die gebiede, gemonitor na toediening van (NH4)2SO4teen die ekwivalent van 100 kg N ha−1aan beide die bo- en ondergronde. Eerste-orde vergelykings is gebruik om Kmakste bereken vanaf die NO3-N wat oor tyd geproduseer is. Die maksimum nitrifikasietempo's van die gronde is betekenisvol deur die nitrifiserende populasie (r= 0.73) en katioonadsorpsievermoë(r=0.75) beïnvloed. In beide gevalle neem Kmakslogaritmies toe met toenemende waardes van nitrifiserende bakterieëen katioonadsorpsievermoë. Alhoewel in sommige gevalle betekenisvol, beïnvloed grond-pH en organiese koolstof Kmaksminder, 'n Variasie van 72% in Kmaksword met katioonadsorpsievermoë, pH en organiese koolstof as veranderlikes in meervoudige regressie verklaar.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634574

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Missing weather data is a very real problem when using daily-incrementing crop growth simulation models. This is especially true in the case of daily air temperature and solar radiation data. The aim of this study was to compare two simple methods of supplementing the input weather record, and to determine whether the estimates could be used with confidence in the case of the CERES-Maize model. Wet and dry day monthly means of daily maximum and minimum temperature and sunshine duration were calculated for four long-term weather stations in Natal. Ordinary monthly means of these elements were also computed. The two sets of means, which were calculated from the most recent 5 years of the weather record, were appended program-matically to daily rainfall data for the preceding 10 years of the weather record, in each case replacing totally the observed daily temperature and sunshine duration values. The weather files thus created were then used as inputs to the CERES-Maize plant-growth model. Yield, flowering date and maturity date estimates so gained were compared with similar estimates over the same period using real temperature and sunshine data. Yield estimates based on supplemented data compared excellently with those using the full weather record, with mean percentage differences for the four sites ranging from 1.23% to 9.34%. Yield estimates based on wet and dry day means for the weather record were slightly better than those derived using ordinary monthly means. This was also true in the case of the flowering and maturity date estimates.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634575

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

The objective of this study was to obtain information on the nutrient uptake patterns of winter wheat(Triticum aestivumL.) grown under normal irrigation farming conditions. Except for irrigation scheduling, 13 farmers were allowed to follow their normal farming practices. At each site biomass production, nutrient content of the top growth and root length were measured regularly throughout the growing season, starting 35–45 days after planting. The nutrient content of the soils was determined on samples collected 35–45 days after planting at 300-mm depth intervals to a depth of 1.8 m. As early as 40 days after planting the concentration of N, P and Ca in wheat plants started to decrease, while the concentration of K, Mg and S started to decrease 10–20 days later. Accumulation of the nutrients in plants increased until 120 days after planting and then stabilized at an average of about 214, 40, 326, 33, 21 and18kg ha−1for N, P, K, Ca, Mg and S, respectively. Nutrient uptake rates reached a maximum between 60 and 100 days after planting. The maximum nutrient uptake rates for N, P, K, Ca, Mg and S were respectively, 3.90; 0.69; 7.47; 0.60; 0.35 and 0.32 kg ha−1day−1. The root length weighted mean N, P, K and S content of a well-rooted soil for a 1.5-m depth corresponding with these maximum nutrient uptake rates was 20, 11, 139 and 4 mg kg−1, respectively.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634576

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Data from maize cultivar trials at Vaalharts over a five-year period were used to evaluate the level of resistance to maize streak virus (MSV) in commercial maize hybrids, and to determine the potential value of such resistance. Maize hybrids presently grown in South Africa showed varying degrees of resistance to MSV. In general, yellow maize hybrids displayed a wide range of genetic variability, from resistant to highly susceptible,whereaswhite maize hybrids were mostly highly susceptible. Calculated resistance indices on a scale from 1 (resistant) to 5 (highly susceptible) proved very useful in quantifying genetically-based plant reaction to MSV infection. Hybrids ranked consistently similar, both within and throughout all seasons. The relationship between yield loss due to MSV infection and resistance indices was positively correlated.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634577

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

The simplest crop development model assumes a linear relationship between temperature (x) and rate of development (y) and can be written as y =β1+β2x +€. In crop development models non-linear functions of the parametersβ1andβ2have certain physical meanings. For example TO=−β1β2is the‘apparent’threshold temperature at which development begins to take place; while k=1/β2is the value of the summation constant, the number of degree days, or the sum of the daily temperature remainder indices required for the crop to pass through the phonological phase in question. In this article statistical inferences (hypothesis testing and the construction of confidence intervals) on TOand k are made in the case of five wheat cultivars, namely, Wilge, Betta, Karee, Scheepers 69 and SST 102. It is concluded that there were no real differences between threshold temperatures and summation constants for the cultivars considered.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634578

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor

摘要:

Die oogmerk met die studie was om die omvang van urease-aktiwiteite in die besproeide grondevas te stelen watter grondparameters dit beïnvloed. Die verloop van hidrolise is in agt gronde, afkomstig van die sentrale besproeiingsgebiede, gemonitor na toediening van ureum teen die ekwivalent van 100 kg N ha−1aan beide die bo- en ondergronde. Tydens inkubasie by 30°C Is die ureumstikstof op gereeide tydsintervalle gemeet. Die data is gebruik om die urease-aktiwiteite van die verskillende gronde te bereken. Die urease- aktiwiteit in die bogronde het gevarieer tussen 1.23 en 7.37 mg N kg−1grond uur−1en in die ondergronde tussen 0.80 en 11.10 mg N kg−1grond uur−1. Al die ureum wat aan die bogronde toegedien is, is na 10–49 uur gehidroliseer en diéaan die ondergronde na 8–76 uur. Gedurende hierdie periodes kan loging van ureum plaasvind weens oormatige reën en/of besproeiing. Gedurende hidrolise van ureum het die pH-waar- des van sommige gronde met meer as een eenheid gestyg wat 'n aanduiding is dat groot hoeveelhede NH3kan vorm wat danóf vervlugtigóf fitotoksies vir saad en saailinge kan wees. Die gevaar van ammoniakver- vlugtiging en-vergiftiging is ongeveer 10–43 uur na ureumtoediening die grootste. Die urease-aktiwiteite van die gronde het die beste gekorreleer met klei-inhoud, terwyl goeie korrelasies ook met organiese koolstof- en totale stikstofinhoudeen met katioonadsorpsievermoëgevind is.

ISSN:0257-1862    

DOI:10.1080/02571862.1991.10634579

出版商:Taylor&Francis Group    

年代:1991

数据来源: Taylor