Influence of nutrient and light management on postharvest quality of lettuce (lactuca sativa L.) in soilless production systems.

Mandizvidza, Tonderai Clive (2017-03)

Thesis (MScAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Despite the ease in manipulating plant growth and development variables, meticulous management is required to achieve high yields and good quality crops in a soilless system. A deep understanding of the intricacies involved in plant growth and development will aid in optimizing these variables to achieve desired yield and crop quality with subsequent effect on postharvest quality. Therefore manipulating and managing plant growth and development variables should be considered as pivotal in a soilless production system. For that reason, other techniques such as foliar fertilization have been employed in an attempt to enhance crop growth and development during production to increase productivity and crop quality. The aim of this study was to assess how manipulation and management of nutrient solutions (different cation concentrations), light intensity levels and foliar fertilization in a hydroponic system affect postharvest quality. The study on nutrient cation concentrations was conducted in a tunnel whilst light intensity study was conducted in a controlled glasshouse at the University of Stellenbosch in the Western Cape Province of South Africa. To evaluate the effect of light intensity levels, two lettuce types (cos and iceberg) were exposed to three different light intensities, control of 450 μmol m-²s-1 (19.44 mol m-²d-1), 60% of control at 270 μmol m-²s-1 (11.66 m-²d-1), 40% of control at 180μmol m-²s-1 (7.78 m-²d-1). Overall visual appearance was considered using plant height (mm) and cos lettuce reaching significant height at 60% and 40% LI. A significant interaction was observed with regards to texture parameter with cos lettuce generally outperforming iceberg. In the second trial, nutrient solutions with different cation concentrations were evaluated. Two lettuce types (cos and iceberg) were cultivated hydroponically with nutrient solutions containing Ca⁺² as 45% of the total cations (S 1) compared to low Ca⁺² of 20% of the total cations (S 2) and high Ca⁺² of 60% of the total cations (S 3) all at an EC of 1.30 mS cm-1. Based on the nutrient composition, the increase or decrease in cation concentration affected the uptake of nutrients with adverse effects on nutritional values of crops. Variation was largely due to nutrient availability at different concentrations for plant absorption and use. Lastly, foliar fertilization of Ca based boron, nitrogen and silicate sprays on rocket and red oak lettuce revealed interactions between the foliar treatments (CaN, CaB and CaSi) and plant types (red oak lettuce and rocket) on the fresh weight (yield) of plants grown hydroponically and differences in means with regard to total moisture and weight loss were also observed for treatment and crop variety effect. The results in this thesis make a valuable contribution to our understanding of manipulating and management of soilless production system with adverse effects on postharvest.

AFRIKAANS OPSOMMING: Ten spyte daarvan dat dit relatief maklik is om die groei en ontwikkeling van plante te manipuleer in ʼn grondlose stelsel is noukeurige bestuur steeds nodig ten einde 'n hoë opbrengs en 'n goeie kwaliteit gewasse te verkry. ;n Goeie begrip van die kompleksiteit betrokke by groei en ontwikkeling van plante sal help met die optimalisering van hierdie veranderlikes om sodoende die oesopbrengs en kwaliteit te verbeter. Daarom is dit uiters belangrik om plant groei en ontwikkeling noukeuring te manipuleer en te bestuur in 'n grondlose produksie stelsel. Om dié rede word ander tegnieke soos blaartoediening van nutriente tydens produksie gebruik in 'n poging om groei en ontwikkeling en kwaliteit te verbeter. Die doel van studie was om te bepaal hoe manipulasie en bestuur van voedingsoplossings (verskillende katioon konsentrasies), ligintensiteit en blaar bemestingspeile in 'n hidroponiese stelsel na-oes gehalte beïnvloed. Die studie oor voedingstowwe katioon konsentrasies is uitgevoer in 'n tonnel terwyl die ligintensiteit studie uitgevoer in 'n beheerde glashuis by die Universiteit van Stellenbosch in die Wes-Kaap Provinsie van Suid-Afrika. Om die effek van ligintensiteit vlakke op twee blaarslaai kultivars (cos en ysberg) te evalueer is plante blootgestel aan drie verskillende ligintensiteite; ʼn kontrole van 450 mol m-²s-1 (19.44 mol m-²d-1), 60% van die kontrole, 270 umol m-²s-1 (11.66 m-²d-1), en 40% van die kontrole teen 180μmol m-²s-1 (7.78 m m-²d-1). Algehele visuele voorkoms is geassesseer deur planthoogte (mm) te bepaal en cos slaai wat ʼn beduidende toename toon by 60% en 40% ligintensiteit behandelings. 'n Beduidende interaksie is waargeneem ten opsigte van tekstuur as kwaliteit parameter waar oor die cos slaai beter gevaar het as ysberg slaai. In die tweede stel proewe is voedings oplossings met verskillende konsentrasies (katioon konsentrasies) geëvalueer. Twee blaarslaai kultivars (cos en ysberg) is hidroponies verbou. Voedingsoplossings waar Ca⁺² 45% van die totale katione opmaak(S 1) teenoor ʼn oplossing waar Ca⁺² slegs 20% ot die total katione opmaak (S 2) en ʼn oplossing waar Ca⁺² 60% van die totale katione opmaak (S 3) almal teen 'n EG van 1.30mS cm -1 is toegedien. Op grond van die voedingstof samestelling het ʼn toename in die katioon konsentrasie die opname van voedingstowwe geaffekteer wat ʼn nadelige uitwerking op voedingswaarde van gewasse gehad het. Dit was waarskynlik grootliks te wyte aan die variasie op die beskikbaarheid van voedingstowwe vir plante asook die opname van elemente. Laastens, blaar bemestings van Ca, Boor, stikstof en silikaat bespuitings getoets op slaai in ʼn hidroponiese sisteem. ʼn Interaksies tussen die blaarbespuitings (CaN, CaB and CaSi) en planttipes ten opsigte van die vars gewig (opbrengs), en vogverlies na-oes is aangeteken. Die resultate in hierdie tesis lewer 'n waardevolle bydrae tot ons begrip van hoe om gewasse te bestuur en te manipuleer ten einde opbrengs en kwaliteit te verbeter.

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