Cabbage waste biochar and potting mixture in improving growth of Ocimum basilicum and water retention of soil

Abstract

Biochar is a carbon rich product produced through the pyrolysis of waste biomass which can enrich soil nutritional value, physical properties as well as plant development. This study investigated the use of cabbage waste biochar and potting mixture (PM) in different proportions to analyze and compare their relative improvement of soil physical properties and effect on basil (Ocimum basilicum) plant growth. Biochar produced at 360 °C, soil and PM were characterized for various parameters including pH, electrical conductivity (ECe), elemental composition, including carbon (C), hydrogen (H), nitrogen (N), fixed carbon (FC) and ash contents. Surface and chemical analysis was also conducted using FT-IR, XPS, and SEM on these three materials. Two types of tests were performed on basil plants. The first is a test of the effects of biochar on improving sandy soil where biochar is compared with PM and a combined biochar + PM treatment at two different loadings (2%, 6%). The second is the application of biochar when added to PM as a growing media at 4% loading for a period of 2 months. The first test results revealed a clear improvement in plant growth and water retention abilities of sandy soil when amended with either biochar or PM. Although the addition of 6% biochar negatively impacted the germination and early growth of the plants by the end of the test (day 60) biochar amendments clearly outperformed control or their relative PM comparisons. For 6% biochar the plant height was increased by 214%, the leaf length by 152%, fresh biomass by 274%, and number of leaves by 420% compared to the control treatment. The chlorophyll, carotenoid contents, membrane stability index (MSI), and leaf relative water contents (%) were also enhanced by high biochar alone and the combined PM and biochar application. The combined treatment of 6% biochar + 6% PM improved the germination by 85% and reduced the early growth stress caused by the 6% biochar loading when applied alone. The same treatment increased plant height by 179%, leaf length by 120%, fresh biomass by 443%, and number of leaves by 325% compared to the control. There was also an increase in the nutrient uptake of potassium, manganese, and zinc (Zn) by plants with the application of biochar and PM and a decrease in the uptake of aluminium. The largest change in nutrient uptake from the control was observed in 6% biochar treatment, though similar results were obtained for zinc and manganese in the case of the combined 6% biochar + PM treatment. The high water retention in the drainage was observed with the combined treatment of biochar + PM in both incubation (98%) and planted pot experiments (90%). The combined application of biochar + PM is also more efficient against evaporation at different temperatures than the control treatment. Therefore, this study suggests that the mutual application of biochar and PM is a good approach in retaining more water into the soil, maximizing overall biomass productivity and in ameliorating early growth stress caused by biochar alone. Biochar only treatments provided comparable or better performance in most parameters studied, with exception of slightly lower water retention and a lower biomass production. The plants with biochar only addition however had larger leaves, higher plants and better micronutrient composition. In the test of 4% biochar applied to potting mixture no discernable differences were observed between biochar and control conditions with regards to growth or water retention. These results indicate that biochar, and biochar + PM are effective amendments for improving agriculture in sandy soils, but biochar may not provide advantages in soils of existing high quality.

Date of Award	2021
Original language	American English
Awarding Institution	HBKU College of Science and Engineering