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Ibrahim, Illani Zuraihah (2025) Effects of biostimulants on germination, agronomic performance, and nutritional quality of Pakchoi (Brassica rapa L. subsp. chinensis) cultivars in organic cultivation. PhD thesis, University of Nottingham.

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Abstract

Organic farming is increasingly recognized as a sustainable alternative to conventional agriculture, offering significant environmental benefits, enhancing soil health, and supporting long-term ecosystem resilience. However, organic production often faces inherent challenges, including lower yields and reduced crop size, primarily due to limited nutrient availability, the absence of synthetic growth enhancers, and natural pest pressures. While biostimulants have emerged as promising tools to improve plant productivity in an eco-friendly manner, their application within organic systems remains underexplored, particularly concerning their effects on crop physiology, phytochemical attributes, and soil fertility.

This study aimed to evaluate the effects of biostimulant application and in combination with biochar on seed germination, growth performance, physiological traits, root morphology, phytochemical quality, nutrient uptake, and soil chemical properties of Pakchoi (Brassica rapa L. subsp. chinensis) under organic cultivation. The research was structured in three phases: laboratory trials, controlled glasshouse experiments, and field studies. In the laboratory, nine Pakchoi cultivars were subjected to seed priming treatments including hydropriming (distilled water for 1, 3, and 6 hours), biopriming with Biostimulant C (1% v/v), and nutripriming with Biostimulants A and B (0.2% and 0.4% v/v) using a completely randomized design (CRD) with three replications. Hydropriming (1–3 hours) yielded the highest germination rates (95.9–97.6%), while nutripriming with Biostimulant A (0.2%) produced the longest roots (63.22 mm). Biopriming with Biostimulant C significantly improved shoot length (28.33 mm) and seedling fresh weight (0.93 mg). Among cultivars, KCC18157-J and KCC18334-F showed the strongest early growth and root performance, respectively.

Subsequently, a glasshouse study using a randomized complete block design (RCBD) with five replications assessed the impact of priming and biostimulant treatments on seedling development. Results showed significant improvements in plant height, leaf number, leaf area, fresh and dry biomass, and chlorophyll content among bioprimed and biostimulant-treated plants. Enhanced physiological parameters, including net photosynthetic rate (Pn), stomatal conductance (gs), and chlorophyll fluorescence (Fv/Fm), were observed. Root morphological traits as total root length, surface area, volume, and tip number were markedly increased, leading to improved water and nutrient uptake. Correlation analyses highlighted strong positive associations between root development, shoot biomass, and photosynthetic efficiency. Based on overall seedling performance, two cultivars, KCC18425-K (white-stemmed) and 9116-H (green-stemmed), were selected for field trials.

Field experiments were conducted using a factorial RCBD to evaluate the combined effects of biopriming, biostimulant application, and biochar on plant performance and soil fertility. Results confirmed that the combination treatment significantly enhanced plant growth, with fresh weight increasing by 26.4% and chlorophyll content by 18% relative to controls. Shoot number and leaf area were also significantly improved. Phytochemical analysis revealed an increase of up to 30% in total phenolic content, along with elevated vitamin C, crude protein, and fibre levels, indicating improved nutritional and functional quality. Root analysis showed increased root length, surface area, and branching. Biochar supplementation enhanced soil total nitrogen (+20%), organic carbon (+18%), and cation exchange capacity (CEC) (+15%) without adversely affecting pH or electrical conductivity.

Overall, the integration of microbial biostimulants, seed biopriming, and biochar amendments synergistically improved seedling establishment, physiological vigour, nutrient uptake efficiency, and soil fertility, while also enhancing the phytochemical profile of Pakchoi. These findings offer a strong foundation for the practical adoption of biostimulant-based technologies in organic vegetable systems and underscore their potential to increase yield and quality under low-input, sustainable farming practices.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Singh, Ajit Ali, Asgar Sparkes, Debbie
Keywords:	biostimulants; organic farming; seed biopriming; Pakchoi (Brassica rapa); soil fertility
Subjects:	S Agriculture > S Agriculture (General)
Faculties/Schools:	University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Biosciences
Item ID:	81175
Depositing User:	Ibrahim, Illani Zuraihah
Date Deposited:	26 Jul 2025 04:40
Last Modified:	26 Jul 2025 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/81175

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