Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Protein and oilseed production in the winter rainfall region of South Africa
(primarily the Southern and Western Cape) is well below the potential for
the area. One possible method of increasing production is to convince
producers that the inclusion of protein and oilseed rotational crops will
enhance the sustainability of wheat production systems. A project to
investigate, quantify and elucidate the effect of canola (Brassica napus),
lupins (Lupinus angustifolius) and medics (Medicago spp.) on subsequent
wheat (Triticum aestivum) production as well as their influence on soil
fertility in respect to nitrogen was initiated in 1999. The long- term
rotational crop system experiment on Langgewens experimental farm
near Malmesbury, provided the infrastructure for the project.
During the 1999 and 2000 wheat-growing seasons, 50m2 plots were
demarcated in wheat fields where wheat, lupins, canola or medics were
produced in 1998 and 1999 respectively. Each plot was cleared of all
vegetation and received no fertilizer N. In these fallow plots, soil samples
were collected at three to four week intervals and the available nitrate-N
and ammonium-N content of the topsoil (0-15cm depth) and the subsoil
(15-30cm depth) were determined.
Additional soil samples were also taken from the topsoil on 09/03/2000
after a summer fallow period. These samples were taken on plots that
were subjected to a wheat crop in 1999, but were preceded by either
wheat, canola, lupins or medics in 1998. The soil samples were then
subjected to a 60-day incubation period at 15°C while being maintained at
75% of their water holding capacity. Mineral N was determined after 0, 3,
7, 15, 30, 45 and 60 days of incubation. Large variation in the nitrogen
contents observed made it difficult to always obtain significant
differences. The results of the soil investigations however indicate that
the inclusion of lupins and medics in wheat cropping systems in the Swartland could help to limit the decline of mineral N in the soil profile,
experienced within a growing season. This will therefore enable farmers
to reduce fertilizer inputs without facing soil mineral N depletion.
Plant samples were also collected from wheat plots during the 1999
growing season on three occasions (23/06/99 (growth stage 5), 5/08/99
(growth stage 15), 14/09/99 (growth stage 23)). Plots were selected to
represent the same treatments as in the soil sampling procedure during
the growing season of 1999 as described above. Plant and tiller numbers
of a 0.25m2 sub sample from each plot were counted and leaf area was
determined, whereafter the dry material was weighed. The percentage
nitrogen content in the leaves and stems were subsequently determined
using Near Infra-Red Spectroscopy. In terms of vegetative growth, little
difference was observed. A significant increase in nitrogen content of
wheat plants growing in plots where wheat and canala were grown in
1998 was observed in the second plant sampling (growth stage 15) and
this was attributed to higher nitrogen topdressing. However, on the third
sampling date on 14/9/1999 (growth stage 23), the difference was no
longer evident. The most important conclusion to make from this study, is
that farmers can probably save on fertilizer inputs when including lupins
and medics in their wheat production systems, without risking poorer
wheat growth.
At growth stage 28, a 0.25m2 sub sample of wheat plants was removed at
a randomly chosen point in each of the plots described above. Ears and
grains were subsequently counted. The wheat remaining on the plots
were then harvested at the end of October 1999 using a plot combine.
Subsequently the yield, hectolitre mass, thousand grain mass and %
crude protein was determined from samples of harvested grain from each
plot. The % flour and % bran extraction were then determined whereafter
the % flour protein was determined. Micro bread loafs were baked to
estimate the loaf volume. Flour and dough properties were also tested
using the Falling Number System, mixograph and alveograph. Wheat in
cropping systems consisting of legume phases such as lupins and medics, required less nitrogen fertilizer application to achieve statistically
the same yield, flour and dough properties. These crop rotations can
therefore be considered as more ecologically sustainable and
economically viable for the Swartland. This study was aimed at determining the effect of different crop rotations
on soil fertility, and because clear soil fertility trends take time to form,
this study was probably too short to obtain fully significant differences. / AFRIKAANSE OPSOMMING: Proteïen- en oliesaad produksie in die winter reënval streek van Suid
Afrika (hoofsaaklik die Suid- en Weskaap) is ver benede die potensiaal vir
die streek. Een moontlike manier om die produksie hiervan te verhoog is
om produsente in hierdie streek te oortuig dat die insluiting van proteten
en oliesaad gewasse die volhoubaarheid van koring verbouingstelsels sal
verhoog. Na aanleiding hiervan, is In projek in 1999 van stapel gestuur
om die effek van canola (Brassica napus), lupiene (Lupinus angustifolius)
en medies (Medicago spp.) op daaropvolgende koring (Triticum aestivum)
produksie, asook die invloed daarvan op grondvrugbaarheid in terme van
stikstofinhoud, te ondersoek. Die langtermyn wisselbouproef op
Langgewens proefplaas naby Malmesbury, het as infrastruktuur vir die
ondersoek gedien.
Gedurende die 1999 en 2000 koring groeiseisoene is 50m2 plotte in
koringkampe gekies waarop koring, canola, lupiene en medies
geproduseer is in onderskeidelik 1998 en 1999. Hierdie plotte is skoon
gehou van plantegroei en het ook geen stikstof in kunsmisvorm gekry nie.
Met drie tot vier week intervalle is grondmonsters op hierdie plotte
versamel in die bogrond (0-15cm diep) en ondergrond (15-30cm diep),
waarna die beskikbare nitraat-N en ammonium-N konsentrasie bepaal is.
Adissionele grondmonsters van die bogrond is ook geneem op 9/03/2000
na In somer braak periode. Hierdie monsters was geneem op persele wat
blootgestel was aan In koringproduksie in 1999, maar voorafgegaan is
deur koring, canola, lupiene en medies in 1998. Hierdie monsters is dan
vir 60 dae geïnkubeer teen 15°C en 75% van die grond se water
houvermoeë. Minerale N inhoud bepalings is gedoen na 0, 3, 7, 15, 30,
45 en 60 dae van inkubasie. Groot variasie in die minerale stikstof
inhoud, het die verkryging van herkenbare tendense en konstante
statistiese verskille belemmer. Die resultate wat verkry is dui egter dat
die insluiting van lupiene en medies in koring produksie stelsels in die Swartland, hoër minerale N vlakke in die grond handhaaf en dit kan boere
gevolglik in staat stelom kunsmis insette te besnoei sonder dat
grondvrugbaarheid verswak.
Op 23/06/99 (groeistadium 5), 5/08/99 (groeistadium 15) en 14/09/99
(groeistadium 23) is plantmonsters versamel van koringpersele. Hierdie
persele is gekies om die behandelings van die grondmonsterontledings
soos hierbo beskryf, te verteenwoordig. Plante en halms van 'n 0.25m2
area uit die persele is getel en die blaaroppervlaktes is bepaal, waarna
die droëmateriaal massa van die area bepaal is. Die persentasie
stikstofinhoud van die blare en stingels was daarna bepaal. In terme van
vegetatiewe groei was daar nie groot verskille te bespeur nie.
Betekenisvolle hoër stikstof inhoud van koringblare in plotte waar daar in
die vorige jaar canola en koring verbou was, is in die tweede planttrekking
(groeistadium 15) gevind en dit is toegeskryf aan die hoër stikstof
kopbemesting wat daardie behandelings ontvang het. Teen die derde
monsterneming op 14/09l99 (groeistadium 23), was hierdie verskille nie
meer in die ontledingsdata te sien nie. Die afleiding wat van hierdie
studie gemaak is, is dat boere moontlik stikstofbemesting kan verminder
as hulle lupiene en medies in hulle koring produksiestelsels inbring,
sonder om die risiko van swakker groei te verhoog.
Op 20/10/99 (groeistadium 28) is 0.25m2 plante van elke koringperseel
verwyder waarna die are en die korrels getel is. Die koring wat nog op
die persele was is teen die einde van Oktober 1999 met 'n
perseelstropertjie geoes. Opbrengs, hektoliter massa, duidendkorrel
massa en % ru-proteïene is daarna bepaal. Volgende is die % meel en %
semel ekstraksie bepaal waarna die % meelproteïene bepaal is. Mikro
broodjies is ook gebak om die broodvolume te bepaal. Meel en deeg
eienskappe is ook getoets met die Falling Number System, mixogram en
alveogram. Koring in produksiestelsels met peulplant fases (lupien en
medies in hierdie geval), het minder N toediening nodig gehad om
statisties dieselfde opbrengs, meel- en deeg eienskappe te verkry. Lupien en medic gebaseerde wisselbou praktyke in die Swartland kan
gevolglik as meer ekologies volhoubaar en ekonomies haalbaar
bestempelword.
Hierdie studie het gepoog om die invloed van wisselbou op
grondvrugbaarheid te ondersoek. Sodanige veranderings neem egter tyd
en daarom is dit waarskynlik nog te gou om werklike grondvrugbaarheids
verskille waar te neem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52455 |
| Date | 03 1900 |
| Creators | Wessels, Pieter Gerhardus Wilhelmus |
| Contributors | Pieterse, P. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 87 p. : ill. |
| Rights | Stellenbosch University |
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