Use of biostimulants to assess the production of the underutilised legume, Bambara groundnut

Thesis (MScAgric)--Stellenbosch University, 2021.

ENGLISH ABSTRACT: Underutilised crops are an important part of local diets but have not been fully adopted in modern agriculture. Often, they are cultivated in marginal lands with low, if any, nutrients. The need for underutilised crop research becomes apparent not only because a big portion of plant based human food is mainly derived from a limited number of staple crops. With the threat of global warming and associated more extreme weather, and indirect impacts such as crop diseases, reliance on a few crops is a major challenge to food and nutritional security. Moreover, existing deficiencies of key vitamins and minerals pose a serious constraint to livelihoods, more especially in rural areas. Bambara groundnut (Vigna subterranea (L) Verdc.) is one of the crops that could be used to increase food production. With a reported high drought tolerance, Bambara groundnut is cultivated across Africa, but its full potential has not been realised and its agronomic performance scantily documented. Therefore, two greenhouse experiments, using two landraces of Bambara groundnut, were conducted at the Welgevallen experimental farm, Stellenbosch University, Stellenbosch. The aim was to investigate the effect of different biostimulants on the growth performance of Bambara groundnut. The specific objectives were to: (1) Evaluate the effect of different biostimulants on agronomic plant performance, (2) Assess the effects of biostimulants on the nutritional composition of Bambara groundnut seeds. The study consisted of five treatments (untreated control, chicken manure fertiliser, Kelpak®, humic substance and Moringa leaf extract, n=6 replicates each), conducted in a tunnel production system. Biostimulant treated plants reached 50% flowering significantly earlier that the control and fertiliser treated plant. Plants treated with Kelpak® showed significantly higher plant height, larger leaf area, and higher leaf dry matter relative to control and other treatments. Treatment with humic substance and Moringa leaf extracts resulted in higher yield parameters, number of pods per plant, 100-seed weight, and total seed yield were the highest in humic substance treated plants followed by Moringa leaf extract. Therefore, the humic substance showed the highest harvest index percentage relative to the other treatments. Of the three biostimulants treatments, Kelpak® treated plants produced the lowest seed yield. Using multiple linear regression we found that variation in total seed yield could be explained by the input of treatment, particularly humic substance and Moringa. Kelpak® was found to not have a significant effect on seed yield but rather on plant height and dry shoot mass, indicating better suitability to growing leafy vegetables than grain. The nutrient composition was improved under Moringa and humic substance treatment, meaning that these two factors not only improved plant growth and productivity but maintained the nutritional composition of Bambara. Therefore, biostimulant application positively influenced Bambara groundnut growth, development, and yield without compromising the nutritional content of the crop seeds. Therefore, biostimulants alongside appropriate levels of fertilization may be used to enhance the production of Bambara groundnut crops, and other underutilised and neglected crops. However, the results need to be validated by investigating the remaining landraces of Bambara groundnut. Keywords: Bambara groundnut, biostimulants, underutilised crops, landraces.

AFRIKAANSE OPSOMMING: Alhoewel onderbenutte gewasse ʼn belangrike deel van plaaslike diëte uitmaak, word dit nie ten volle in die hedendaagse landbou opgeneem nie. Dit word dikwels op marginale grond met min, indien enige, voedingstowwe verbou. Daar is ʼn duidelike behoefte aan navorsing oor onderbenutte gewasse, nie net omdat ʼn groot deel van plantgebaseerde voedsel vir mensgebruik hoofsaaklik van ʼn beperkte getal stapelgewasse afkomstig is nie. In die lig van die gevaar van aardverhitting en verwante meer ekstreme weer, en indirekte impakte soos gewassiektes, is die afhanklikheid van enkele gewasse ʼn groot uitdaging vir voedsel- en voedingsekerheid. Origens plaas die bestaande gebrek aan belangrike vitamiene en minerale ʼn ernstige stremming op lewensbestaan, veral in landelike gebiede. Die Bambara-grondboontjie (Vigna subterranea (L) Verdc.) is een van die gewasse wat gebruik kan word om voedselproduksie te verhoog. Na berig word, is die Bambara-grondboontjie, wat regoor Afrika verbou word, hoogs weerstandig teen droogte, maar die volle potensiaal daarvan is nog nie verwesenlik nie en die agronomiese prestasie daarvan is karig gedokumenteer. Daarom is twee kweekhuisproewe met twee landrasse van die Bambara-grondboontjie by die Welgevallen-proefplaas van die Universiteit Stellenbosch gedoen. Die doel was om die effek van verskillende biostimulante op die groeiprestasie van die Bambara-grondboontjie te ondersoek. Die spesifieke doelstellings was: (1) om die effek van verskillende biostimulante op agronomiese plantprestasie te evalueer, en (2) om die effekte van biostimulante op die voedingsamestelling van Bambara-grondboontjiesaad te bepaal. Die studie het bestaan uit vyf behandelings (onbehandelde kontrole, hoendermisbemesting, Kelpak®, humusstof en moringablaar-ekstrak; n=6 replikate elk), wat in ʼn tonnelproduksiestelsel uitgevoer is. Plante wat met biostimulante behandel is, het 50% blomvorming aansienlik vroeër as die kontrole- en messtofbehandelde plant bereik. Plante wat met Kelpak® behandel is, het aansienlik groter plantgrootte, groter blaaroppervlak en meer droë blaarmaterie in vergelyking met die kontrole en ander behandelings getoon. Behandeling met humusstof en moringablaar-ekstrakte het hoër opbrengsparameters, getal peule per plant en 100-saadgewig tot gevolg gehad, en totale saadopbrengs was die hoogste in plante wat met humusstof behandel is, gevolg deur moringablaar-ekstrak. Die humusstof het dus die hoogste oesindekspersentasie in vergelyking met die ander behandelings getoon. Van die drie biostimulant-behandelings het Kelpak®-behandelde plante die laagste saadopbrengs gelewer. Met behulp van meervoudige lineêre regressie is bepaal dat variasie in totale saadopbrengs deur behandelingsinset, veral humusstof en moringa, verklaar kon word. Daar is bevind dat Kelpak® nie ʼn noemenswaardige effek op saadopbrengs het nie, maar wel op plantgrootte en droë lootmassa, wat op beter geskiktheid vir blaargroente as graan dui. Die voedingsamestelling het verbeter met moringa- en humusstofbehandeling, wat beteken dat hierdie twee faktore nie net plantgroei en produktiwiteit verbeter het nie, maar ook die voedingstofsamestelling van die Bambara-grondboontjie gehandhaaf het. Die gebruik van biostimulante het dus die groei, ontwikkeling en opbrengs van die Bambara-grondboontjie positief beïnvloed sonder om die voedingsinhoud van die gewassade in die gedrang te bring. Biostimulante kan dus saam met geskikte vlakke bemesting gebruik word om die produksie van Bambara-grondboontjiegewasse en ander onderbenutte en afgeskeepte gewasse te verbeter. Die geldigheid van die resultate moet egter bepaal word deur die res van die landrasse van die Bambara-grondboontjie te ondersoek. Sleutelwoorde: Bambara-grondboontjie, biostimulante, onderbenutte gewasse, landrasse.

Masters