摘要:

Five pecan[Carya illinoensis(Wang.) K. Koch] cultivars, commercially recommended for the Transvaal middleveld areas were evaluated for nut quality (nut size, kernel %, kernel colour, nut shape and shell thickness). New South African grading standards are suggested for nut size and kernel % in order to bring the South African standards into line with the U.S.A. and world standards. Using these revised South African standards the grading of the five cultivars according to nut size was as follows: Mahan, extra large; Ukulinga, large; Barton and Success, medium; and Moore, small (average of 16 years). The grading of these cultivars according to kernel % was medium (52,6% to 54%) except Moore which was poor (47,2%). The average length: width ratio for all cultivars is 2,0 (3 years, average). The kernel colour ratings were between 3 and 4 for all cultivars except Success (4–5), which was acceptable and not too dark. The shell thickness varied from thick to medium for the five cultivars, averaging about 960μm.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634238

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The major physical properties that control the penetration resistance of soils are the degree of soil compaction, water content and particle size distribution. Sandy soils with well-sorted particle size distributions and low cohesivity compact and consolidate easily under pressure. Six soil samples with predominantly fine sand fractions and clay contents varying between 8 and 20% silt plus clay were selected to determine the relationships among penetration resistance, relative bulk density and water content. Penetration resistance was measured using a constant-rate penetrometer. The relative bulk density given by the ratio between bulk density and maximum ASTM bulk density was used as the parameter representing the level of compaction. Curves relating penetration resistance to water content at different relative bulk densities and to relative bulk density at different water contents were determined for each soil. All the variables were incorporated into a multiple regression equation. This equation can be used to calculate the penetration resistance of fine sandy apedal soils at specific bulk density, water content and silt- plus-clay content values.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634239

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

A production function is derived and calibrated forDigitaria erianthahay production in the Highveld region of the RSA. A procedure is described that optimizes this function for nitrogen and phosphorus application rates within economic and risk constraints at different expected rainfall levels. Risk analysis points to more definite optimal rates than classical optimization alone. It was also found that experiments with all treatments near the optimum, or production functions without definite yield limits, could lead to recommendation of too high application rates.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634240

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Die invloed van agt verskillende plantreshoeveelhede (0–3 500 kg ha−1), sowel as verskiHende tipes plantreste (graansorghum- en mieliereste) op onkruiddodereffektiwiteit is ondersoek in 'n glashuisproef. Onkruiddodereffektiwiteit is bepaal deur middel van 'n indikatorplant,Avena sativa.Droëmassaopbrengs en planttellings van die indikatorplant is as veranderlikes gemeet. Die aanwesigheid van verskillende tipes plantreste tydens onkruiddodertoediening het dodereffektiwiteit nie betekenisvol be'invloed nie, terwyl 'n toename in plantreshoeveelheid dodereffektiwiteit wel betekenisvol beïnvloed het.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634241

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Two-year-old peach trees, grown in sand culture were destructively sampled over a period of 14 months, to determine the uptake of phosphorus, potassium, calcium and magnesium in the new growth (leaves, fruit and new shoots) and in the permanent structure (roots, wood and bark). Samples were taken at three-weekly intervals and the accumulation during five distinct phenological stages, i.e. bud-break, termination of shoot elongation, harvest, commencement of leaf fall and completion of leaf fall, was examined. The total content of these elements increased from bud-break or shortly afterwards, through the period of shoot elongation until harvest. P content again increased during the leaf-senescence period, while Ca content increased initially but declined sharply during leaf fall, which lasted six weeks. Mg content declined rapidly during this period. K content declined after harvest, remained constant for a period and then declined rapidly during the leaf-fall period. The leaves of the young peach tree contained the largest proportions of the K, Ca and Mg content in the tree. Leaf fall therefore accounted for most of the losses during the leaf-fall period. Peach fruit contained relatively large quantities of K which were removed during harvest.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634242

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Yield testing in early generations of wheat breeding programmes is limited by large numbers of lines and small amounts of seed. This paper compares yield testing using conventional row plots, hill plots and small single-ear plots. The effects of smaller plot size are compensated for by increasing the number of replications when moving from row plots, through hill plots to ear plots. Statistics derived from standard ANOVA's revealed small ear plots to be as useful as larger hill or conventional row plots in assessing the yield potential of lines. In spite of rather large genetic as well as environmental coefficients of variation, ear plots had a lower intra-class correlation coefficient than hill plots or row plots while the repeatability value of ear plots was higher than that of hill or row plots. Spearman rank correlation coefficients showed a highly significant correspondence in the ranking of trial entries in the three systems tested.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634243

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Pineapples can be rapidly multiplied and propagated by means of crown sections in a peatmoss and vermiculite mixture (2:1). Each section can produce a new plantlet within 65 days and the development of dormant buds may be promoted by the removal of the daughter plant. Crown expiants could produce daughter plants under glasshouse or ambient conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634244

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Die aktiwiteit van atrasien is in biotoetse onder gekontroleerde toestande ondersoek in 43 gronde vanaf 29 lokaliteite geleëin die somerreënvalstreek van Suid-Afrika. Sojabone en hawer is in afsonderlike proewe as toetsgewas gebruik. Geselekteerde grondeienskappe is met atrasienaktiwiteit gekorreleer. In beide proewe het % C, fosforvaslegging en klei-inhoud atrasienaktiwiteit goed voorspel, terwyl katioonuitruilvermoëen pH deurgaans swakker voorspellers was. In meervoudige regressie-analises is die grootsteR2-waarde verkry met 'n kombinasie van % C, P-vaslegging en klei-inhoud. Inagneming van % C, P- vaslegging en klei-inhoud by die gebruiksvoorskrifte vir atrasien behoort die risiko verbonde aan die gebruik daarvan op sekere gronde aansienlik te verminder en/of die effektiwiteit van onkruidbeheer te verhoog.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634245

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

A wheat crop growth model (Singels, 1983) was refined and used to calculate annual grain yield from weather data for 45 seasons in the Bloemfontein area. Five different levels of profile-available water capacity were used as soil input parameter. Other input parameters were kept constant at optimum levels. The average yield and gross margin were calculated for the different hypothetical soil types as were probabilities for positive gross margins. Results indicated that successful wheat production is possible on soils with a profile-available water capacity between 92 mm and 112 mm. Below 92 mm the low water storage capacity of soils limits yields. Soils with an available water capacity of more than 100 mm m−1(clays and loams) under certain circumstances experience profile water deficits at planting as a result of climatic conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634246

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Ten einde 'n geskikte metode op 'n tyd- en kostebasis te vind vir die roetine-ontleding van nornikotien in tabakmonsters, is twee tegnieke van individuele alkaloïedbepalings vergelyk. Met die dunlaagchromatografiese metode kon sewe verskillende alkaloïedes in een van die monsters wat ontleed is waargeneem word terwyl die gaschromatografiese metode slegs nikotien en nornikotien kon waarneem. Die verskille in die persentasies nikotien en nornikotien van die drie uitgesoekte monsters wat volgens die prosedures van die twee metodes ontleed is, is binne perke van 'n 10%-variasie en vergelyk baie gunstig. Vir die roetine-ontleding van nornikotien in tabakmonsters word die dunlaagchromatografiese metode aanbeveel.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634247

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor