Kale seedlings grew better in a blend of peat and coconut coir than in the pure peat or coconut coir.
Sustainable Agriculture Student Research Project
Coconut Coir as Potting Soil Alternative to Peat: Biochar, Wool Pellets, |
Introduction
Peat is a cheap, yet unsustainable resource widely used for growing crops. Peatlands sequester carbon as they build up organic matter deposits over thousands of years. They contain 30% of the world’s soil carbon. When peatlands are disturbed by fire, clearing, or drainage, carbon is released and oxidized into carbon dioxide, a greenhouse gas. Previous research has shown that coconut coir, biochar, wool pellets, and wollastonite have the potential to replace peat in potting soil for crop growth.
Coconut coir is a waste product from the coconut industry that is high in organic matter and mineral content. Coir has similar physical and chemical properties to peat, so it has potential as a peat alternative. Biochar is made from organic waste or biomass that has been partially combusted. Biochar can increase soil water holding capacity, pH levels, and crop growth. Wool is a waste product from the sheep farming industry, and it is a natural source of carbon and nitrogen. Wool is fibrous, so it is slow to break down, improving water holding capacity, bulk density, nutrient availability, and soil aggregation. Wollastonite is a mineral that increases plant yield through fertilization, raises pH levels in soil, and adds plant available calcium to soil, while simultaneously reducing greenhouse gas emissions. Coconut coir, biochar, wool pellets, and wollastonite are sustainable alternatives that could potentially allow crop growth without impeding the environment and contributing to climate change.
Objective
- Compare coconut coir to peat as a growing medium base
- Evaluate biochar, wool pellets, and wollastonite as amendments
Methods
- Location: Passive Solar Growing Dome, KPU Farm, Garden City Lands, Richmond, BC
Table 1. KPU Farm standard potting soil recipe (2024)
| Ingredient | Weight (kg) |
|---|---|
| Peat | 41.9 |
| Perlite | 15.9 |
| Vermiculite | 13.0 |
| Limestone | 0.56 |
| Coconut coir | 5.5 |
| Gaia Green Fertilizer (4-4-4) | 3.3 |
Treatments
Base Growing Media
- Peat (control)
- Coir (100%)
- Peat/Coir (50:50)
Amendments
- None (100%)
- Biochar (6%)
- Wool Pellet (6%)
- Wollastonite (6%)
- Biochar/Wool Pellet (3:3)
- Biochar/Wollastonite (3:3)
- Wollastonite/Wool Pellet (3:3)
- Biochar/Wollastonite/Wool Pellet (2:2:2)
Crop
- Kale (cv. Black Magic)
Seeding Method
- Compostable plant pots
- Plastic trays
Steps
Treatments were mixed using KPU’s potting soil recipe (Table 1). Base growing media replaced peat in original recipe. Amendments were added in addition to Gaia 4-4-4 fertilizer in the same quantity. Recipes were poured into compostable plant pots in plastic trays in order of experimental design. Pots were hand seeded with two kale seeds per pot. Plants were kept in the passive solar growing dome for seven weeks and watered as needed. Pots were thinned if more than one seed germinated in week two.
Experimental Design
Completely randomized factorial design with two factors (base growing medium and amendment) and three replicates (Table 1).
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Data Collection
- Leaf area
- Dry weight of roots and shoots (g/plant)
Statistical Analysis
- All data were tested for normality using the Shapiro-Wilk Test
- Total dry weight (g) and root:shoot ratio data were analyzed by ANOVA
- Leaf area data were analyzed using a Repeated Measures ANOVA with base and amendment as Between Subject Factors and dates (Oct. 11, Oct. 22, and Oct. 31) as Repeated Measures Factors
- All analyses were conducted using the jamovi (v. 2.4.11.0) interface for R statistical software
- Tukey’s Honestly Significant Difference test was used to compare differences between treatments (α = 0.05).
Results
Amendment had a significant effect on the root:shoot ratios of kale seedlings (p = 0.021) (Table 2, Fig. 2). Base growing medium had no significant effect (p = 0.531) and there was no interaction between base medium and amendment (p = 0.066) on the root:shoot ratios of kale seedlings.
Table 2. ANOVA table testing for effects of base growing media, amendments, and their interactions on root:shoot ratios.
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Root:shoot ratio was higher in media amended with biochar or biochar and wollastonite than in media amended with wool pellets (p = 0.044) (Fig. 1).
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The total dry weight of kale seedlings differed between growing media bases (p=0.005) and amendments (p=0.021), and there was an interaction between these factors (p =0.009) (Table 3).
Table 3. ANOVA table testing for effects of base growing media, amendments, and their interactions on dry weight of kale seedlings.
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The total dry weight of kale was higher in the peat/coir blend than in media based on pure peat or pure coir (Fig. 4).
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There was a significant interaction between the effects of growing medium and amendment on total dry weight. Dry weight was highest when plants were grown in unamended peat, an unamended blend of peat and coir, or a blend of peat and coir amended with biochar or wollastonite. Dry weight was lowest when plants were grown in coir amended with a blend of biochar, wollastonite and wool; or in peat amended with wollastonite, a blend of biochar and wollastonite, or a blend of biochar, wollastonite and wool (Fig. 5). Other treatment combinations did not differ significantly from the highest or lowest treatments.
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Repeated measures ANOVA detected a strong effect of date on leaf area (p < 0.001), indicating kale growth over time (Table 6, Figure 6). Leaf area was also affected by media base (p = 0.009), amendment (p < 0.001), and interactions between base and amendment (p < 0.001). Leaves were larger on plants growing in a blend of peat and coir than in media based on either peat or coir alone (Figure 6).
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Conclusion
- Kale seedlings grew best in media based on a blend of coconut coir and peat
- None of the tested amendments increased growth of kale seedlings
- Biochar and wollastonite amendments did not reduce growth in the peat/coir blend
- Peat can be partially, but not entirely, replaced with coconut coir in growing media without reducing growth
Acknowledgements
Thank you to Dr. Michael Bomford for his help and support throughout my experiment. Thank you to Georg Janssen from Preterra BioCarbon Solutions Ltd. for his generous donation of biochar to my experiment. Thanks to Sahar Zandieh, Ben Alles, and the farm crew for answering my questions. Thanks to my classmates Talia Parfeniuk and Kayla Buttress for helping me with data collection.
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