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DIE WEDLOOP NA HOER
PROTEIEN IN SOJABONE
Saamgestel deur/Compiled by: Jan Dreyer
THE RACE TO SECURE
HIGHER PROTEIN CONTENT
IN SOYBEANS
Inhoudsopgawe
01
Inleiding
01
Kultivar en plantfaktore
01
Stikstofvoorsiening
02
Stikstofbinding
02
Omgewingsfaktore wat proteïenvlakke beïnvloed
02
Verbouingspraktyke wat proteïenvlakke beïnvloed
03
Opsommend
03
Bronne
Index
04
Introduction
04
Cultivar and plant factors
04
Nitrogen supply
04
Nitrogen fixation
05
Environmental factors that affect protein levels
05
Growing practices that affect protein levels
06
Summary
06
Sources
01
Die wedloop na hoer prote en
in sojabone
INLEIDING
edurende die afgelope vyf jaar het die produksie van sojabone in Suid-Afrika in só ‘n mate
toegeneem dat hierdie skitter-gewas nou sy
regmatige plek as een van die groottes in die
akkerbouwêreld kan inneem.
G
Tesame met hierdie verhoogde belangstelling, het die
klem ook sterker op verskeie kwaliteitseienskappe begin
val waaraan sojabone moet voldoen om veral in die
veevoermark sy prima status te behou. Proteïeninhoud
van die graan en uiteindelik die proteïeninhoud van
sojaboonkoek is vir die veevoerbedryf van groot belang.
Die vraag is dus hoe die proteïeninhoud van graan deur
verskillende faktore beïnvloed word.
KULTIVAR EN PLANTFAKTORE
Daar word jaarliks landswyd ‘n uitgebreide kultivarevaluasieprogram deur die Landbounavorsingsraad
uitgevoer. Die inligting in hierdie uitgebreide verslag toon
duidelik hoe kultivars in proteïeninhoud verskil, maar
ook hoe dieselfde kultivars tussen gebiede kan verskil.
Hou ook in gedagte dat daar ‘n verband tussen olie- en
proteïeninhoud van sojaboongraan bestaan. As die olie
hoog is, daal die persentasie proteïen, en andersom. Die
gemiddelde olie-inhoud van nagenoeg 20% en proteïen
van 40% is dus nie ‘n konstante nie.
Wat interessant is, is die feit dat die proteïeninhoud in
‘n enkele plant kan verskil. Dit is egter nie van praktiese
belang nie. So ook het kultivareienskappe, soos byvoorbeeld bepaalde en onbepaalde groeiwyses, ‘n beperkte
invloed op proteïenkonsentrasies in sojaboongraan.
STIKSTOFVOORSIENING
Sojabone het die vermoë om minerale stikstof (N)
uit die grond te onttrek of N te verkry deur ‘n simbiotiese N-binding met behulp van ‘n aangepaste entstof
(Bradyrhizobium japonicum-bakterieë). Uiteraard is ‘n
kombinasie van dié twee stelsels moontlik.
Verskeie buitelandse datastelle is ontleed om ‘n
prentjie te kry van die relatiewe bydrae van N-binding
en minerale-opname. Indien slegs bogrondse groei in
ag geneem word, is die bewyse sterk dat N-binding
in die meeste gevalle nie alleen in die vraag na N kan
voorsien nie. As die ondergrondse dele (wortels) egter
bygevoeg word, dan balanseer die N-som tot ‘n mate.
Wat egter belangrik is, is die feit dat hoe hoër die
graanopbrengs raak, hoe meer neig die N-binding om
‘n kleiner persentasie van die N-behoefte van die plant
te voorsien.
Te veel N in die bogrond het egter ‘n negatiewe invloed
op die N-binding. Belangrik is egter die feit dat die Nbinding vanaf die vroeë reproduktiewe fase (blomstadium) tot selfs ná die saadontwikkelingsfase (R6) ‘n
groot invloed op die proteïenpersentasie van sojaboonsaad het. Gedurende hierdie periode behoort alles
moontlik gedoen te word om optimale groei te verseker.
Onkruidkompetisie behoort dus beperk te word; so
ook alle negatiewe aspekte wat die plant se groei kan
benadeel, soos byvoorbeeld blaarsiektes.
In ‘n studie met verskillende N-draende bemesting, is
gevind dat ammoniumnitraat, ureum en ureum plus
swael (S) almal die N-binding verminder het. Hierdie
vermindering is duidelik bevestig deur verminderde
nodulegewig, die aantal nodules en hul massa. Swaelbyvoegings het nie, soos verwag, deurgaans ‘n opbrengsverhoging tot gevolg gehad nie.
Aanvullende N word redelik algemeen gebruik. Dit bly
egter riskant waar groot hoeveelhede toegedien word.
Die literatuur dui verskillende limiete aan, maar dit
wil voorkom of ongeveer 20 kg N die boonste grens
mag wees. Minerale N in die grond word makliker deur die plant opgeneem en vereis minder
energie as stikstofbinding deur bakterieë. Waar
N dus wel toegedien word, bly dit ‘n balanstoertjie om die beste van twee wêrelde
te verseker.
02
Die wedloop na hoer prote en
in sojabone (vervolg)
STIKSTOFBINDING
Ekonomiesgesproke is sojabone se vermoë om N te bind
een van die groot pluspunte van die gewas. Voeg hierby
die feit dat effektiewe N-binding die beste versekeringspolis vir ‘n goeie opbrengs is asook die hoogste proteïenkonsentrasie in die graan verseker.
Effektiewe N-binding is slegs moontlik as daar nie ‘n
oormaat N (veral nitrate) in die bogrond teenwoordig is
nie. Die grond se pH behoort neutraal te wees, terwyl
Molobdeen (Mo) in baie gevalle ‘n vereiste is. Met al
hierdie vereistes in plek, is enting met die regte stam
(ras) (WB 74) van Rhizobium ‘n vereiste. Nie alleen
moet die konsentrasie van die bakterieë hoog genoeg
wees nie, maar dit moet verkieslik op die saad of naby
genoeg aan die saad in klam grond geplaas word.
Direkte sonlig, hoë temperature en droë grond sal die
bakterieë laat vrek; tesame daarmee sal die moontlikheid vir ‘n goeie opbrengs en hoë proteïeninhoud ook
verdwyn. Die stoor van die entstof voorplant en die
hantering op die land is dikwels deurslaggewend vir
goeie resultate. Temperature in store en voertuie is dikwels so hoog dat baie bakterieë vrek selfs nog voordat
dit in die grond beland.
Simbiotiese N-binding vind plaas waar wortelhare teenwoordig is en waar sojabone ‘n chemiese sein uitstuur
wat deur die bakterieë erken en beantwoord word. Die
proses is baie sterk aan goeie vogvoorsiening gekoppel.
‘n Neutrale pH is ideaal, omdat dit die toeganklikheid
van die meeste noodsaaklike mikro-elemente bevoordeel wat N-binding aanhelp.
OMGEWINGSFAKTORE WAT
PROTEÏENVLAKKE BEÏNVLOED
Daar is baie uitsonderings op die reël, maar oor die
algemeen is proteïenvlakke hoër hoe warmer die
omgewing. In die noorde van China is proteïenvlakke
laer as in die suide, wat nader aan die ewenaar lê.
Dieselfde geld vir die VSA. Een verklaring vir hierdie
probleem mag laer grondtemperature wees wat die Nbinding beperk.
Relatief hoë temperature en droë toestande tydens
die graanvulperiode sal proteïenvlakke verhoog ten
koste van olie, maar ook die saadopbrengs laat daal.
Verskeie kritiese temperatuurstudies is wêreldwyd
gedoen. Waar proteïenvlakke van sojabone by 29°C
met dié by 35°C vergelyk is, het proteïenvlakke met
4% gestyg en olievlakke met 2,6% gedaal by die hoër
temperatuur. Dit was geldig oor verskillende vogpeile.
Dit wil voorkom of die temperatuurgrens iewers tussen
25°C en 28°C is. Bokant 28°C styg proteïenvlakke en
daal die olie-inhoud. Daar is ook sprake dat verkorte
daglengtes proteïenkonsentrasies verhoog, omdat
die tempo van N-translokasie daardeur verhoog word.
Temperature het ook ‘n beduidende invloed op proteïensamestelling.
VERBOUINGSPRAKTYKE WAT
PROTEÏENVLAKKE BEÏNVLOED
Alle verbouingsaspekte wat verseker dat optimale sojaboongroei plaasvind, sal opbrengs, en in die meeste
gevalle ook proteïenvlakke, verhoog.
Die optimalisering van bemesting is waarskynlik die
beste metode wat ‘n produsent kan volg om die maksimum opbrengs te kry, maar ook om in die meeste
gevalle die hoogste proteïeninhoud in sojabone te
bewerkstellig. ‘n Algemene riglyn om in gedagte te hou,
is die volgende: Elke ton sojaboonsaad benodig tussen
60 kg en 70 kg Stikstof (N), tussen 6 kg en 9 kg
Fosfaat (P), 20 - 40 kg Kalium (K), 4 kg Kalsium en
6 kg Swael (S). Voeg hierby die uiters belangrike
mikro-elemente wat vir optimale groei en proteïensintese noodsaaklik is.
Dit is veral Mo wat aandag vereis. Plaaslike
werk wat deur Mark Farina en medewerkers
in KwaZulu-Natal gedoen is, dui op die
verhoging in proteïeninhoud van saad
met die toediening van veral P en Mo.
Volgens hierdie studie is P vir 57%
van die variasie wat in totale proteïenproduksie voorgekom het, verantwoordelik.
03
Die wedloop na hoer prote en
in sojabone (vervolg)
Molobdeen is uiters noodsaaklik vir N-binding, hoewel dit
in klein hoeveelhede benodig word. Blaarbespuiting kan
werk, hoewel saadbehandeling ook gedoen word met
moontlikke risiko vir swakker stikstofbinding. Optimale
bemesting is met planttyd noodsaaklik, aangesien nagenoeg 80% van die totale voedingstowwe tussen 50 en
100 dae na-opkoms opgeneem word. Die nodules begin
ook eers ná ongeveer ‘n maand funksioneer – indien vog
voldoende is en die temperatuur nie te laag daal nie.
Kalium is veral belangrik in die vervoer van voedingstowwe, die waterverbruik van die plant en fotosintese. Hierdie element verhoog proteïeninhoud, waarskynlik omdat
dit knoppiesvorming bevoordeel.
Slegs 20% van die kalsium wat deur die plant opgeneem
word, word deur die saad verwyder; tog speel hierdie
element ‘n belangrike rol in N-binding. Dit het waarskynlik iets te doen met die selmembrane wat om die knoppies vorm ná wortelinfeksie.
Swael se rol is belangrik in die sintese van aminosure
en dus ook proteïen in die saad. Slegs die helfte van die
opgeneemde S vind hul weg na die saad.
Sink kan beperkend wees, wat die ensiemsisteem van
die plant kan benadeel en gevolglik minder proteïen tot
gevolg sal hê.
Enting met die voorgeskrewe bakterieë is noodsaaklik,
so ook die behandeling van die saad en entstof voorof tydens plant. Die konsentrasie van bakterieë en die
plasing daarvan om goeie simbiose te verseker, is van
kritieke belang. Neem kennis dat N-binding steeds die
mees effektiewe en goedkoopste manier is om N in die
plant te kry.
Temperatuurmanipulasie ten einde proteïenvlakke te
verhoog, is moontlik deur later te plant, maar dit sal in die
meeste gevalle onprakties wees, veral omdat opbrengste
meestal daal soos wat planttye aangeskuif word.
OPSOMMEND
Maak seker dat alle verbouingsaspekte waaroor daar
beheer is, optimaal toegepas word. Hierdeur verseker
die produsent ook dat die proteïenvlakke so hoog as
moontlik sal wees.
BRONNE
• Boerma, H.R. and Specht, J.E., Co-Editors, 2004.
Soybeans: Improvement, Production and Uses, Third
Edition
• Gous, R.M. and Griessel, M., 2012 – Literature Review
• Farina, M.P.W., Thibaud, G.R. and Channon, P., 1997 –
Factors Affecting the Response of Soybeans to Molybdenum application: Final Report
• Singh, G., 2010 – The Soybean Botany Production and
Uses
Pamflet geborg deur die Proteïennavorsingstigting.
04
The race to secure higher
protein content in soybeans
INTRODUCTION
uring the past five years the production of soybeans in South Africa has increased to such an
extent that this celebrated crop can now take its
rightful place as one of the most important crops
in our country.
D
With this increased production, more emphasis now
needs to be placed on improving some essential quality
characteristics in soybeans if its prime status in the animal feed market is to be retained. Protein content of the
grain and protein content of the oilcake is of considerable importance for the animal feed industry. The question
is thus how the protein content of grain are affected by
different agronomic factors.
CULTIVAR AND PLANT FACTORS
Every year the Agricultural Research Council conducts
an extensive cultivar evaluation programme. The information contained in the council’s comprehensive report
shows clearly how cultivars differ in terms of protein content, but also how the content of the same cultivar differs
when grown in different areas. The average protein
content of soybeans is about 40% and the oil content
about 20%, but these amounts are not constant, seeing
as there is a link between the oil and protein content of
soybean grain: When the oil content is high, the amount
of protein is reduced and vice versa.
It is interesting to note that the protein content of the
grain sometimes differs within a single plant, although
this is not of practical concern. Cultivar characteristics,
such as determinate and indeterminate growth habits,
also have a limited effect on protein concentrations in
soybean grain.
Various international data sets have been analysed to
obtain a picture of the relative contributions of mineral
uptake and N fixation. There is strong evidence to suggest that N fixation alone cannot provide fully for the N
demand required for plant growth above the ground. If
the parts that grow below ground (roots) are included,
the N total balances to a certain degree. What is important though is that the proportion of N supplied through
fixation declines as grain yield increases. However, too
much N in the upper soil level has a negative effect on
N fixation.
N fixation plays an important role in determining the
amount of protein deposited in the soybean from the
early reproductive (flowering) phase through to the
seed development phase (R6). During that period,
everything possible should be done to ensure optimal
growth. Weed competition should be limited, as should
diseases that affect the leaves and all other aspects
that could negatively affect plant growth.
A study, in which various N containing fertilisers were
compared, showed that ammonium nitrate, urea and
urea plus sulphur (S) all reduced N fixation, resulting in
reduced nodule weight, number of nodules and nodule
mass. In contrast with expectations, sulphur additives
did not always lead to yield increases.
N supplementation is used fairly generally, but this
practice is risky if large quantities are used. Various
limits are given in the literature, but it seems as if approximately 20 kg N/ha may represent the upper limit.
Mineral N is taken up from the soil more easily than
what it “costs” to manufacture N through fixation. It
thus remains a balancing act when adding mineral
N, to ensure the best of both worlds.
NITROGEN FIXATION
NITROGEN SUPPLY
Soybeans have the ability to both take up mineral nitrogen (N) from the soil and to fix N by means of a symbiotic relationship with an adapted inoculum (Bradyrhizobium japonicum bacterium).
In an economic sense the ability of
soybeans to fix N remains one of the
biggest advantages of the crop. Additionally, effective N fixation is the
best assurance for a good yield and the
highest protein concentrate in the grain.
05
The race to secure higher protein
content in soybeans (continued)
Effective N fixation is possible only if there is not an
excess of N (particularly nitrates) in the upper soil
layer. The soil pH should be neutral, and in many cases
Molybdenum (Mo) is required. Once all these aspects
are in place, inoculation with the correct Rhizobium
genus (WB 74) needs to take place. Not only should
the bacterial concentration be sufficient, but it should
also be placed on the seed or in close proximity to the
seed in moist soil to ensure effective inoculation. Direct
sunlight, high temperatures and dry soil will kill the
bacteria, which will reduce the potential for a good yield
and high protein content. The conditions during storage
of the inoculum before planting and handling during
planting are critical if good results are to be achieved.
Temperatures during storage and in vehicles during
transportation are often so high that bacteria die even
before being placed in the soil.
Symbiotic N fixation takes place if root hairs are present and when soybeans send a chemical signal recognised and responded to by bacteria. The process is
strongly linked to adequate soil moisture conditions. A
neutral pH is ideal, because it increases the accessibility to most of the essential micro-elements and assists
with N fixation.
ENVIRONMENTAL FACTORS THAT
AFFECT PROTEIN LEVELS
There are many exceptions to the rule, but generally
protein levels are higher in warmer environments. In
the north of China, protein levels are lower than in
southern China, which is closer to the equator. The
same principle applies in the USA. One possible reason for this may be that lower soil temperatures limit
N fixation.
Various critical temperature studies have been conducted globally, which have shown that relatively high
temperatures and dry conditions during the grain filling
period increase protein levels at the expense of oil, but
seed yield is also reduced under these conditions. In
one study, protein levels of soybeans grown at 29°C
were 4% higher and oil levels 2,6% lower than those
grown at 35°C. These results were similar over a range
of moisture levels. It seems as if the upper temperature
limit is between 25°C and 28°C. At temperatures above
28°C, protein levels increase and oil levels decrease. It
also seems that shorter day lengths may increase protein concentration by increasing the rate of N translocation. Temperatures also have a significant effect on the
composition of protein.
GROWING PRACTICES THAT AFFECT
PROTEIN LEVELS
All agronomic aspects that ensure optimal soybean
growth will increase yield and, in most cases, also
protein levels.
Optimising fertilisation is probably the best method
available to producers to ensure maximum yield and
in most cases this also ensures the highest protein
content in soybeans. Remember, a general guideline is
that each ton of soybean seed requires between 60 kg
and 70 kg nitrogen (N), 6 kg and 9 kg phosphate (P),
20 to 40 kg potassium (K), 4 kg calcium and 6 kg sulphur (S). In addition, many micro-elements are essential for optimal growth and protein synthesis.
Mo requires particular attention. Local work conducted
by Mark Farina and co-workers in KwaZulu-Natal demonstrated that the protein content of seed increased
after the addition of P and Mo. According to that study,
P is responsible for 57% of the variation in total protein
production.
Molybdenum is vital for N fixation, although it is required in small quantities. Spraying leaves could
work, although seed treatment is also possible
although it may adversely affect nitrogen fixation. Optimal fertilisation during planting is
essential, seeing as about 80% of total
nutrients are taken up between 50 and
100 days after sprouting. The nodules
also start functioning about a month
later, but only if moisture is sufficient
and temperatures do not drop too low.
06
The race to secure higher protein
content in soybeans (continued)
Potassium is particularly important for the transport of
nutrients, water consumption and photosynthesis in the
plants. These elements increase protein content probably because they promote the formation of nodules.
Only 20% of the calcium taken up by the plant is
removed by the seed and yet this plays an important
role in N fixation. It is probably involved with the cell
membranes that form around the nodules after root
infection.
Sulphur plays an important role in the synthesis of
amino acids and therefore also in seed protein. Only
half of the sulphur taken up finds its way to the seed.
Zinc can be inhibitive and can be a disadvantage to the
enzyme system of the plant, leading to reduced protein.
Inoculation with the required bacteria is vital, but so is
the treatment of seed and inoculum before and during planting. The bacterial concentration used and the
placement of bacteria to ensure good symbiosis are of
critical importance. Remember that N fixation remains
the most effective and cost efficient means of introducing N to the plant.
SUMMARY
Ensure that all agronomic aspects that may be controlled are applied optimally. For producers, this will
ensure that protein levels will be as high as possible.
SOURCES
• Boerma, H.R. and Specht, J.E., Co-Editors, 2004 Soybeans: Improvement, Production and Uses, Third Edition
• Gous, R.M. and Griessel, M., 2012 – Literature Review
• Farina, M.P.W., Thibaud, G.R. and Channon, P., 1997 –
Factors Affecting the Response of Soybeans to Molybdenum application: Final Report
• Singh, G., 2010 – The Soybean Botany Production and
Uses
Pamphlet sponsored by the
Protein Research Foundation.
Temperature manipulation to increase protein levels is
possible by delaying planting, but is impractical in most
cases, particularly because yields are mostly reduced if
planting is delayed.
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