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Identification of soil and biological factors in crop rotation systems with significance to wheat crop performance in the Overberg production area of South AfricaHuman, Hans Jurie 03 1900 (has links)
Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2008. / A two year experiment (2004-2005) was conducted at the Tygerhoek Experimental Farm near
Riviersonderend in the Western Cape Province of South Africa. The effect of different crop
rotation systems on soil properties, disease and insect pests, weed populations, wheat growth,
yield and quality in the wheat crop phase, included in these crop rotation systems, was
determined. This trial was part of a long term crop rotation experiment started in 2002.
This trial was laid out as a block design with four replications. Crop rotation systems included
wheat, barley, canola, lupins and pasture phases which consisted of medics and clovers planted
collectively. Soil samples were taken at each replication for N-incubations for determination of
mineral N (NO3
- -N plus NH4
+ -N) at 0-150 mm soil depth. A basic soil chemical analysis was
done at 0-150 mm and 150-300 mm soil depths, respectively. Each sub-plot (replication)
consisted of a 3 m2 block that was divided into a 1.5 m2 block for harvest and smaller 0.25 m2
blocks for samples that were taken at different growth stages throughout both seasons. Dry
mass and nitrogen (N) content of different plant components, leaf area index, disease symptoms
and pest damage were recorded from each sample.
Trends in basic soil chemical properties mostly differed between crop rotation systems during
different seasons while similar trends in soil mineral nitrogen occurred. Highest soil mineral N
levels occurred after one or two consecutive years of pasture while levels after a lupin phase
were disappointingly low in both seasons. These high soil mineral N levels showed similar trends
to wheat grain quality and some wheat yields, while the most influencing factors on wheat grain
yield were probably soil physical properties. Soil mineral N after canola was high during plant
after which levels were much lower than many other crop rotation systems. This occurrence will
probably need a re-evaluation of N fertilizing programs if the same trends are found in similar, but
longer trials.
Lolium spp. was the most prominent weed that occurred in both seasons at some crop rotation
systems seemingly with no direct effect from crop rotation. Highest disease incidence mainly from Septoria spp. and Puccinia spp. occurred, particularly in wheat/wheat rotations, except for
Puccinia which showed high ratings of disease symptoms in all crop rotations in the drier 2004
season. Lower ratings occurred in crop rotation systems when wheat was preceded by nonwheat
crops. Insect pest damage showed no similar trends indicating no direct effect of crop
rotation on these pests and/or effective control from applied pesticides in both seasons.
It was concluded that climate was one of the most influencing factors affecting differences and
seem to be the main cause for different trends found between these two seasons in similar crop
rotation systems. A similar trial with longer duration than this one is thus needed to obtain
conclusive trends. This also indicates the importance of integration of crop rotation and
management practices that are most optimal during dry and wet seasons, thus limiting risk.
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Morphological and physiological responses of spring wheat (Triticum aestivum L.) to spatial arrangementsTolmay, John Peter Cleggenett 12 1900 (has links)
Thesis (PhD(Agric) (Agronomy))--Stellenbosch University, 2008. / The adoption of the no-till planting method brought about changes to the way the wheat crop is
established in the Mediterranean climate of the Western Cape. Row widths have to increase
from the normal narrow rows (170-180 mm) to at least 250 mm to allow for sufficient stubble
handling. Furthermore, planters are designed to place seed accurately in the soil at uniform
depth, which may increase seedling survival rates. The main objective of this study was to
determine the influence of the use of wide row widths on yield, the components of yield and
grain quality parameters and to revisit planting density recommendations to be used with the notill
planting method.
On-farm, producer managed trials which included cultivars, row widths and planting density
treatments were planted at Riversdale, Swellendam and Caledon in the Southern Cape region
and at Moorreesburg and Hopefield in the Swartland during the 2004 to 2006 production
seasons. All trials were factorial RCB designs with split-split plot arrangements. Grain yield,
grain protein, hectolitre mass (HLM) and the yield components, seedlings m-2, seedling survival
(%), number of heads m-2, number of heads plant-1, number of kernels head-1 and thousand
kernel mass (TKM) were determined at all sites in 2005 and 2006.
Seedling survival rates of 80% were easily achieved in all trials with the exception of Caledon and Swellendam in 2005. The no-till planting method may be efficient to improve on survival rates of 50-70% found with the conventional planting methods. The yield component response that raised the most concern was the clear trend of the reduction in the number of heads m-2 as row widths increased, which was significant in eight out of the nine experiments. The number of heads plant-1 decreased significantly as planting density increased in all experiments. Cultivars
differed in the grain quality parameters grain protein (%) and HLM but were influenced minimally
by the other treatments. Reductions in grain yield occurred in three out of eight trials in the
Southern Cape and in three out of six trials in the Swartland, with reductions of between 6.8%
and 33% in some seasons. The risk of yield loss due to wide row widths could not be excluded
by this study and therefore the row widths used by producers should remain as narrow as
practically possible. Grain yield response to increasing planting density differed between the two regions. No significant yield benefits were found in any of these trials if planting densities were increased above 175 target plants m-2. Planting densities may be reduced to between 70 and 87.5 kg seed ha-1 to achieve this target if the crop is planted in time and seedling survival rates of at least 80% can be achieved.
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Biomass production, yield and quality response of spring wheat to soil tillage, crop rotation and nitrogen fertilisation in the Swartland wheat producing area of South AfricaMaali, Safiah Hasan 03 1900 (has links)
Thesis (PhD(Agric) (Agronomy))--University of Stellenbosch, 2003. / 108 leaves printed on single pages, preliminary pages i-vi and numbered pages 1-1 to 1-5 to 9-1 to 9-3. Includes bibliography, list of abbreviations and 22 figures in color. Digitized at 300 dpi grayscale and 300 dpi 24-bit Color to pdf format (OCR), using an HP Scanjet 8250 Scanner. / ENGLISH ABSTRACT: A long term experiment was conducted at the Langgewens Experimental Farm, near Malmesbury in the Western Cape province of the Republic of South Africa. The
effect of soil tillage, crop rotation and nitrogen fertiliser rates on mineral-N levels in
the soil, nitrogen levels in plants, wheat growth and yield components, grain yield as
well as quality parameters of spring wheat were determined.
Although the tillage treatments tested were initiated in 1976, present crop rotations
and nitrogen application rates were only applied since 1990. Most of the data that are
discussed however was recorded during the 1997 to 2001 period.
The trial was designed as a randomised complete block with a split-plot arrangement
and four replicates. Main plots were tillage methods namely conventional tillage
(CT), tine tillage (TT), minimum tillage (MT) and no tillage (NT). Crop rotations
used were continuous wheat (WW) and wheatl lupin/wheat/canola (WLWC). Both soil and crop data were
recorded.
The results of this study showed the differences in total mineral-N content of the soil.
N-contents of wheat, wheat growth and yield components as well as wheat quality
parameters were found between tillage treatments, crop rotations used as well as N-
fertiliser rates applied. Response however, varied largely between years due to annual
variation in especially total precipitation and distribution of rainfall. The inclusion of
a legume crop (lupin) and canola in the rotation with wheat was found to have only a
small effect probably due to the fact that lupins were grown once in a four year cycle
only.
Application of different nitrogen rates did increase the mineral-N in the soil, but the
effect did not last very long in most years due to either N-leaching or plant uptake. To
ensure sufficient mineral-N levels, late application of N-fertiliser will therefore be
needed. Minimum tillage or reduced tillage performs better than conventional tillage
in low rainfall years. In general these tillage systems should be combined with crop
rotation to ensure that yields are comparable to that obtained with conventional
tillage. / AFRIKAANSE OPSOMMING:
Die ontwikkeling, graanopbrengs en bakkwaliteit van koring (Tritium aestivum L.) in reaksie
teenoor gewasratasie, metode van grondbewerking en N-bemestingspeil is in 'n lang tennyn
sllldie op Langgewens Proefplaas, naby Malmesbury in die Weskaap provinsie van die
Republiek van Suid-Afrika, bepaal.
Hoewel die verskillende grand bewcrkingsmetodes sedert 1976, en gewasrotasies en
slikstofpeile sedert 1990 toegepas is, is daar in hierdie studie gekonsentreer op data wal
gcdurcnde die periode 1997-2001 ingesamel is.
Die eksperiment is as 'n randomiseerde blok ontwerp met vier bewerkingsmetodes nl.
konvcnsionele bewerking (CT), tand bewerking (TT). minimum bewerking (MT) en geen
bewerking (NT), twee gewasratasies nl. monokuhuur koring (WW) en
koring/lupienelkoringiCanola (WLWC) en drie N-peie (60 kg N ha- ', 100 kg N ha- 1
, 140 kg N
ha- I uitgevoer. Aile stikstof is in die vorm van kalksteen-ammoniumnitraat toegedien.
Die reaksie van beide grondfaktore soos die minerale N inhoud en gewaskomponente 5005
biomassa produksie, opbrengs en kwaliteit teenoor bogenoemde faktore het '0 goeie
korrelasie getoon met die heersende klimaatstoestande.
Lae reenval jare (gebiede) sal volgens hierdie stlldie die grootste voordeel verkry met minder
intensiewe grand bewerkingstelsels. terwyl 'n frekwensie van meer as een peulgewas per
siklus van 4 jaar nodig sal wees om grondvrllgbaarhcidsvlakke betekenisvol te verhoog.
Stelsels van rninder intensiewe grondbewerking is ook tot 'n grater mate deur gewaswisseling
bevoordeel as konvensionele melOdes van grondbewerking.
Hocwel minerale-N vlakke in grond deur verskillende N-peile be'lnvloed is, was die
efTektiwiteit van toedienings laag en het verdeelde tocdienings groat voordele ingehou.
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