Factors that have an influence on splitting of malting spring barley (Hordeum vulgare L.)

Carstens, Louis Wilhelm (2020-03)

Thesis (MScAgric)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: In South Africa barley (Hordeum vulgare L.) is the second most produced small grain crop, where most of the barley is used by the beer-brewery industry for malting purposes. The Southern Cape (dryland) and Northern Cape (irrigation) is South Africa’s two main barley production areas. The term “splitting” refers to when the grain is cracked open through the pericarp, aleurone or testa, exposing the starchy endosperm. Split grain can result in non-uniform malt, the formation of foam in steep tanks or possible fungal growth, which is not suitable for the brewing process. This was recently detected in barley produced in the Northern Cape and consequently threatens the beer-brewing industry of South Africa. Some studies suggest that splitting is caused by abnormal climatic conditions or high nitrogen (N) application during the later stages of crop development. However, there is a lack of information regarding the causes of the splitting of barley under South African conditions. Therefore, the aim of this study was to identify such factors by investigating the influence of temperature, water stress, different light intensity conditions, and the rate of nitrogen application on a low-risk (Cristalia) and a high-risk (Overture) cultivar for splitting during different growth stages. Pot trials were conducted in a glasshouse at the Welgevallen Experimental Farm in Stellenbosch. For the temperature experiment, temperatures were lowered by 10°C at grain filling; maintaining 15°C/5°C for a week and then transferred back to normal growing conditions. The nitrogen experiment involved a total of 100 kg N ha-1 (low N), 150 kg N ha-1 (control) and 200 kg N ha-1 (high N) divided into increments and applied at planting, six weeks after planting and grain filling respectively. The shade experiment entailed no shading (control), 40% and 60% shade introduced at the end of tillering and removed at early milk development. For the water experiment, normal daily irrigation was applied until stem elongation after which low, medium and high water stress treatments were introduced. The effect of the treatments on vegetative and reproductive growth parameters and grain quality was determined. Low temperature during grain filling and high rate of nitrogen fertiliser resulted in an increase in splits. Different shade levels and water stress had minor effects on splitting. Therefore, a follow-up trial was conducted the next year where the combined influence of temperature and nitrogen on splitting was tested. It involved low-temperature conditions for three hours during grain filling. Nitrogen rates only differed at grain filling (0, 30, 40, 50 and 60 kg N ha-1) with a standard nitrogen rate applied at planting and six weeks after planting respectively. It was found that only nitrogen had a significant (p < 0.05) effect on splitting, as rates above 40 kg N ha-1 during grain filling resulted in an increase in split grain. The results of this study will aid in finding methods to prevent splitting of barley in the future.

AFRIKAANSE OPSOMMING: Gars (Hordeum Vulgare L.) is die tweede belangrikste kleingraangewas wat in Suid-Afrika geproduseer word, waar die meeste gars gebruik word vir die vermoutingsproses deur die bierbrou industrie. Die twee hoof gars produksie areas in Suid-Afrika is die Suid-Kaap (droëland) en die Noord-Kaap (besproeiing). Splitsing is die term wat gebruik word om die toestand waar graan deur die perikarp, aleuroon en testa oopkraak en die styselagtige endosperm blootgestel word, te beskryf. Dit affekteer die vermoutingsproses deur oneweredige ontkieming, die vorming van skuim in fermentasietenke of moontlike groei van swamme. Dit was onlangs in gars wat in die Noord-Kaap geproduseer word waargeneem en gevolglik hou dit ‘n bedreiging vir die bierbrou industrie van Suid-Afrika in. Sommige studies stel voor dat splitsing deur abnormale klimaatsomstandighede of hoë stikstoftoedienings gedurende die latere stadiums van gewasontwikkeling veroorsaak word. Daar is wel ‘n tekort aan inligting rakende die oorsake van splitsing van gars onder Suid Afrikaanse toestande. Daarom is die doel van die studie om sulke faktore te identifiseer deur die impak van temperature, waterstremming, verskillende vlakke van lig-intensiteit en die vlak van stikstoftoedienings op ‘n lae risiko (Cristalia) en ‘n hoë risiko (Overture) kultivar vir splitsing gedurende verskillende groeistadiums te toets. Potproewe is in ‘n glashuis by die Welgevallen-proefplaas in Stellenbosch uitgevoer. Vir die temperatuureksperiment is temperatuur verlaag met 10°C gedurende graanvul om 15°C/5°C vir ‘n week te handhaaf waarna dit na normale groei-omstandighede teruggeplaas is. Die stikstofeksperiment het behels dat ‘n totaal van 100 kg N ha-1 (lae N), 150 kg N ha-1 (kontrole) en 200 kg N ha-1 (hoë N) opgedeel en onderskeidelik tydens plant, ses weke na plant en tydens graanvul toegedien is. Die skaduwee-eksperiment het bestaan uit geen skaduwee (kontrole), 40% en 60% skaduwee wat aan die einde van halmvorming toegevoeg is en weer met vroeë melk-ontwikkeling verwyder is. Tydens die water-eksperiment is ‘n normale daaglikse besproeiing tot en met stamverlenging toegedien waarna dit deur lae, medium en hoë waterstres behandelinge opgevolg is. Die impak van die behandelinge op die vegetatiewe en reproduktiewe groei-parameters en graankwaliteit is bepaal. Die lae temperatuur gedurende graanvul en hoë stikstoftoedienings het ‘n verhoogde impak op splitsing gehad. Die impak van verskillende skaduwee-vlakke en waterstres op splitsing was minimaal. Daarom is ‘n opvolgproef die volgende jaar uitgevoer waar die gekombineerde impak van temperature en stikstof getoets is. Dit het behels dat lae temperatuurtoestande vir drie ure tydens graanvul toegepas is. Die stikstofvlakke het slegs verskil gedurende graanvul (0, 30, 40, 50 en 60 kg N ha-1), terwyl ‘n standaard stikstofvlak toegedien was met plant en ses weke na plant onderskeidelik. Daar is gevind dat slegs stikstof ‘n betekenisvolle invloed op splitsing gehad het aangesien vlakke bo 40 kg N ha-1 gedurende graanvul ‘n verhoging in splitsing tot gevolg gehad het. Die resultate van hierdie studie sal dus help om metodes te vind om splitsing van gars in die toekoms te voorkom.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108129
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