The effect of soil residue cover on medicago pasture establishment and production under conservation agricultural practices

Le Roux, Andries Abraham (2015-04)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Annual medic pastures play an important role in conservation agriculture (CA) practices in the Western Cape, because of the beneficial role it plays in rotation systems and the fact that it can re-establish on its own. In the Overberg medic pastures are the main pasture short rotation crop, but farmers in recent years shifted away from including medics. This was due to unsuccessful re-establishment and a visible decrease in dry matter production. This trend started after CA practices were implemented for a few years. A field study conducted during 2013 investigated medic re-establishment and production following a wheat, barley, oat and medic pasture production year ( WM, BM, OM and MM) of which residues were left on the soil surface at different cover percentage levels (100%, 75%, 50%, 25% and 0%). The objective of this study was to determine what the effect of different amounts of residues was on annual medic re-establishment and production. Data from this study suggest that management of annual medic pastures should aim to re-sow the medic pasture if plant count drops below 78 pants per square meter. Weed management is of cardinal importance as it competes for resources, light and space and decrease medic pasture re-establishment and production. The data also indicates that the wheat/medic sequence is the best option when applying a short cash crop/annual pasture cropping system. Producers should manage their animals to ensure that a 50% to 75% cover is left on top of the soil following the grazing of residues during the summer months. The study in 2013 should have been replicated, but due to the low levels of re-establishment and production a decision was made to re-plant the trial sites. The field study conducted during 2014 investigated the medic/clover establishment and production following a re-plant. Medics were replanted following a W, B, O and M season, respectively. Residues again were manipulated to different cover percentages (100%, 75%, 50%, 25% and 0%). The objective was again to look at the amount and type of residues on medic/clover establishment and production following re-plant. Data from this study indicated that it might be advisable for annual medic/clovers to be re-sown after a cereal production year rather than a medic pasture year. With the production of medic/clover pastures not being affected by the residue cover percentage, a 100% residue cover following re-plant is best in rotations, if the optimal effect of CA wants to be observed. If animals are included in the production cycle, grazing of residues during summer months can occur until 50% cover is left. Soils will take longer to reach its potential, but by including animals the gross margin is more stable year on year. Two supplementary studies were conducted to investigate the germination of annual medics under controlled conditions. The objectives of the first supplementary study was to investigate the physical barrier effect of residues at different percentage cover (100%, 75%, 50%, 25% and 0%) and a possible allelopathic action from different types of residues (wheat, barley, oat and medic) on the annual medic cultivar Cavalier (one of the cultivars used during 2014 field re-plant). The different amounts of residue had no significant effect on percentage emergence of Cavalier. The 0% residue cover having the slightly higher germination could be because there are no physical obstructions preventing seedlings to establish. The different types of residue cover had no significant effect on the germination of annual medics, as the germination under wheat, barley, oats and medic residues did not differ from the control. The control had a slightly higher germination percentage (85%), while germination under residues was just below the recommended germination rate of 80-85%. This could be an indication of allelopathy from residues. The objective of the second supplementary study was to investigate the allelopathic effects of different residue leachates (wheat, barley, oat and medic) at different levels of concentrations (100% leachate, 75%, 50%, 25% and distilled water being the control) on Cavalier germination. The interaction between leachate type and concentration were significant. Low levels of leachate concentration did not have a significant impact on medic germination when compared between each other and the control. When the concentration percentage was increased differences were detected. Cavalier germination decreased drastically when medic leachate concentration increased, indicating allelopathic effects. Cavalier germination followed the same trend, just not as drastic, when wheat leachate concentration increased. This indicates that wheat could also have a negative allelopathic effect. With oat leachate Cavalier germination did not decrease except when 100% concentrate was used, which could indicate a small allelopathic effect. Cavalier germination following barley leachate showed no effect as concentration increased, even showing the odd increase. Depending on repeatability or follow-up studies of these experiments, data suggest that re-plant of medic pastures is beneficial if plant count drops below sustainable levels. Management of weeds during the medic pasture year improves production. Annual medic pastures should be re-planted following a cereal production year rather than a previous pasture year. Thus single medic rotations are preferred, for example WMWM rotation. Greater amounts of residues are beneficial for CA effects, but allelopathic effects of wheat and oat residues should be taken in consideration during re-establishment and residue levels should be lowered.

AFRIKAANSE OPSOMMING: Eenjarige medic weidings speel ʼn belangrike rol in bewaring landbou (CA) praktyke in die Wes Kaap, vanweë sy vermoë om jaarliks op sy eie te hervestig en sy voordelige rol in rotasie stelsels. Eenjarige medic weidings is tans die hoof kort rotasie gewas in die Overberg, maar boere is tans besig om dit uit die rotasie uit te sluit. Dit is as gevolg van lae hervestiging sowel as die opvallende afname in produksie. Hierdie waarnemings het na ʼn paar jaar na die toepassing van CA praktyke begin. Gedurende 2013 is daar ʼn veldstudie voltooi rakende medic weiding hervestiging en produksie wat na ʼn koring, gars, hawer en medic weiding produksie jaar volg (WM, BM, OM en MM). Gedurende die studie is stoppels by verskillende persentasie vlakke van bedekking op die grond gelaat (100%, 75%, 50%, 25% en 0% bedekking). Die doel van die studie was om die invloed van verskillende tipes en hoeveelhede stoppels op die hervestiging en produksie van eenjarige medic weidings vas te stel. Data van hierdie studie dui aan dat jaarlikse medic weidings so bestuur moet word dat medics in die Overberg area se plant telling nie laer as 78 plante per vierkante meter daal nie. Onkruid bestuur is van kardinale belang, omdat dit kompeteer met medics en veroorsaak ʼn verlaging in hervestiging en opbrengs. Data dui ook aan dat ʼn koring/medic stelsel die beste opsie is wanneer ʼn kort kontant gewas/eenjarige weiding gewas stelsel toegepas word. Produsente moet hul vee so bestuur dat ʼn 50 tot 75% stoppel bedekking gedurende die somer maande oorgelaat word na beweiding. Die herhaling van die 2013 veld studie was van plan, maar ag gevolg van lae hervestiging en produksie was die proef kampe oor geplant. Die veldstudie in 2014 was medic/klawer vestiging en produksie na herplanting ondersoek. Die medic/klawer saad is geplant na ʼn koring, gars, hawer en medic weiding seisoen onderskeidelik. Stoppels is weereens na verskillende bedekking persentasies verander (100%, 75%, 50%, 25% en 0% bedekking). Die doel was om te kyk wat die effek van verskillende tipes en hoeveelhede stoppels op eenjarige medic/klawer weiding is na herplant. Data wys dat medic/klawer weidings verkieslik herplant moet word na ʼn graan produksie jaar as ʼn medic weiding produksie jaar. Die medic/klawer weiding is nie geaffekteer deur die hoeveelheid stoppels op die grond oppervlakte nie, dus is ʼn 100% stoppel bedekking verkieslik vir optimale CA effekte. As diere in die sisteem teenwoordig is, kan stoppels bewei word gedurende die somer maande tot ʼn 50% bedekking bereik word. Grond sal langer vat om sy potensiaal te bereik, maar die jaarlikse bruto marge sal meer stabiel wees. Twee aanvullende studies is onderneem en ontkieming van eenjarige medics is ondersoek onder beheerde toestande. Die doelwit van die eerste aanvullende studie was om te kyk na die fisiese versperring effek van stoppels by verskillende persentasie bedekking (100%, 75%, 50%, 25% en 0%) en ʼn moontlike allelopatiese effek van verskillende tipe stoppels (koring, gars, hawer en medic) op die eenjarige medic kultivar Cavalier. Verskillende hoeveelhede stoppels het geen beduidende uitwerking op die vestiging van Cavalier gehad nie. Die 0% stoppel bedekking het ʼn effens hoër vestiging gehad. Dit kon wees as gevolg van geen fisiese versperring wat die saailing verhoed om te vestig nie. Die verskillende tipes stoppels het geen beduidende uitwerking op die ontkieming van eenjarige medics nie, die vestiging onder koring, gars, hawer en medic stoppels het nie statisties verskil van die kontrole nie. Die kontrole het wel ʼn effense hoër persentasie vestiging gehad (85%), terwyl die vestiging onder die stoppels onder die aanbevole koers van 80-85% was. Dit kan dalk ʼn allelopatiese effek van die stoppels aandui. Die doel van die tweede aanvullende studie was om die allelopatiese effek van die verskillende tipes stoppels (koring, gars, hawer en medic) by verskillende vlakke van konsentrasie (100%, 75%, 50%, 25% van die onverdunde loogsel en gedistilleerde water as kontrole) op Cavalier ontkieming. Daar was ʼn beduidende interaksie tussen tipe en konsentrasie loogsel. Met lae konsentrasie vlakke van loogsel was daar nie ʼn werklike impak op Cavalier ontkieming tussen die verkillende tipes en die kontrole nie. Slegs wanneer die konsentrasie persentasie verhoog is, is verskille waargeneem. Cavalier ontkieming het drasties af geneem soos die medic loogsel konsentrasie toegeneem het, wat ʼn negatiewe allelopatiese en verhoogde osmolaliteit effek wys. Cavalier ontkieming het dieselfde tendens gewys wanneer koring loogsel konsentrasie verhoog was, maar nie so drasties soos medic loogsel. Dit dui daarop dat koring ook ʼn negatiewe allelopatiese effek wys. Met hawer loogsel het Cavalier ontkieming slegs by die 100% konsentrasie pyl afgeneem, wat op ʼn lae allelopatiese effek dui. Cavalier ontkieming onder gars loogsel het geen verandering gewys as konsentrasies toegeneem het nie, en het selfs ʼn toename in ontkieming in party gevalle ondergaan. Afhangend van herhaling of op-volg studies van hierdie eksperimente, wys die data dat dit voordelig is om medic weidings te herplant as plant telling onder 78 plante per vierkante meter daal. Die bestuur van onkruid tydens die medic weidings jaar verbeter opbrengs. Eenjarige medic weidings moet herplant word na ʼn graan produksie jaar liewer as ʼn vorige weidings jaar. Medics moet dus in ʼn eenjarige rotasie stelsel wees, byvoorbeeld WMWM rotasie. Meer stoppels is voordelig vir CA promosie, maar allelopatiese stowwe van koring en hawer stoppels moet in ag geneem word en stoppels moet verlaag word vir hervestiging.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97055
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