Carbon dioxide and oxidative techniques to improve growth and yield of beetroot, Swiss chard and green beans

Abstract

The current population of almost 8 billion is projected to reach 9.55 billion by 2050 and will cause a greater demand for food. Dietary changes will further add to the demand for food.. To meet the growing demand, food production will have to be increased between 60 -110%. Intensification and land clearing are two methods that have been developed to increase yield and to close the yield gap, however, there are negative problems associated with them. Genetic manipulation, management and production practices are mainly focused on to increase yield. The release of additional oxygen and carbon dioxide in close proximity to plants or the improvement of existing CO2 and O2 fertilization are techniques that can be explored further as a possible solution to the yield gap problem. Main purpose of this study was to investigate the application of additional carbon dioxide and oxygen on plant growth and yield. In this study a quantitative research approach was taken to determine the effects of the CO2 and O2 treatments on plant growth and yield. In the preliminary pot trial additional CO2 was given to the bean plants via a calcium carbonate and hydrochloric acid reaction as well as via a carbon dioxide tablet treatment on the soil surface. In the second trial, the same treatments were applied to the beans, beetroot and Swiss chard plants. The reactions took place within Boston round bottles planted into the pots next to the plants. Unfortunately, due to COVID-19 the CO2 tablet treatments were terminated as no new stock could be imported. Weekly plant growth measurements, photosynthetic measurements, stomatal conductance and laboratory analyses of the leaf material (stomatal density, chlorophyll concentration) were measured. Other measurements such a root length, root mass, biomass and yield were taken at the end of the trial or per harvest (bean pods, edible part of the beetroot). The data was analysed to determine whether the means were significantly (P<0.05) affected by the treatments. Initially the treatments in the preliminary trial showed promise in increasing plant height, chlorophyll A and B concentrations and stomatal density; however, the soil treatment affected the plant roots and soil electrical conductivity (EC), which caused the plants to die. In the second pot trial both the beans and beetroot had grown under an elevated CO2 concentration showed improved growth but varied between the crops for example, only beans showed increased height, beans and beetroot had improved root and biomass growth, it greatly affected the shoot to root ratio in Swiss chard, the number of pods per bean plant and yield in all crops except for Swiss chard. Calcium carbonate in the second pot trial improved bean and beetroot plant growth. The plant growth parameters, bean yield and beet measurements did not differ significantly between the control (ambient glasshouse) and the plants receiving the additional CO2 through CaCO3. The field study consisted of beans, beetroot and Swiss chard plants grown in an open field at plot scale. The plant leaves were sprayed with two concentrations (0.5 and 0.1 ml L-1) of hydrogen peroxide at two application rates (once and twice a week) to determine whether additional O2 would improve not only plant growth but also yield. The foliar applications of hydrogen peroxide were found to be effective in increasing plant height in all three crops. The biomass and yield of Swiss chard plants treated weekly with the low H2O2 concentration were positively affected whereas the bean biomass was improved with the weekly application of the high H2O2 concentration. Regardless of application rate the beetroot leaf area index and biomass improved with the low H2O2 concentration treatment whilst yield increased under the high H2O2 concentrations. The stomatal density in all three crops were unaffected by any of the treatments. The photosynthetic pigments (chl A, -B and total carotenoid concentration) increased overall in all the treatments of the bean plants. The beans treated weekly with the low H2O2 concentration resulted in greater photosynthetic pigment concentrations regardless of application rate. The beetroot plants had a similar reaction in its photosynthetic pigments than the beans except that it was with the higher H2O2 concentration applied twice a week. The Swiss chard plants treated weekly with the low H2O2 concentration resulted in the increase of its photosynthetic pigments. Beetroot and Swiss chard plants were grown in a suspended, non-circulating hydroponic pot system. A pump system was built to aerate the nutrient solution with either pure oxygen, carbon dioxide or air (21% oxygen) to determine if plant growth and yield would improve. The beetroot and Swiss chard plants aerated with air resulted in the best plant and root growth among the treatments. The beetroot plants that were aerated with pure oxygen resulted in the greatest biomass weight followed by those aerated with carbon dioxide. In conclusion, the application of additional CO2 to plants grown in pots, the foliar application of hydrogen peroxide to plants grown in open fields and aerating the nutrient solution of a hydroponic system with carbon dioxide or oxygen showed promising results but should be studied further.