A Happy Soil for Happy Gardeners
If you’re anything like me (a soil geek), you are probably already looking at seed catalogues and planning your gardening activities for the coming growing season. I find the months leading up to actually planting a garden go by quickly and it takes self-discipline to stay on track to be ready for those first warm days of spring when the sunshine and soil beckon.
So what are your favourite vegetable seeds to grow in your garden? Add a comment below and tell me what you plan to grow this year.
If you are with me on planning your garden, I’d like to share some “soil geek” stuff – particularly about how plant roots function in healthy and robust soil. Have a look at the following diagram:
Figure 1. Plant Roots, Nutrients, Moisture, Microbiology, and Soil Matrix Triangular Relationship
Understanding this relationship is important if we hope to create the ideal growing conditions for flowers, lawns, vegetables, and all of the cultivars we are hoping to grow.
Most of us know that plants need nutrients and moisture and we diligently provide these inputs every year by going out and purchasing chemical and/or organic fertilizers, following the application instructions and then waiting for rain or turning on our sprinklers. However, nutrients and moisture are but one component of three important needs roots have to support healthy plant growth. The other two are healthy living biological life and a soil matrix that contains carbon materials like humus and charcoal (biochar) where nutrients and moisture can be stored.
Now, it is possible to get plants to grow without these other two elements, but unless we have a hydroponic system where nutrients and moisture are being carefully metered to the plants, the plant roots will be challenged to find and make use of the nutrients that are applied to the soil.
A good example of how microbiology (in this case mycorrhizal fungi) feeds plant roots is illustrated in this 5 minute YouTube video:
A diverse population of beneficial fungi and bacteria are important “carriers” of moisture and nutrients for plant roots. Yes, roots can function without them, but the optimum growing environment will always include them.
The ingredients of the soil — i.e. sand grains, silt, humus (dead plant material), clay, and soil organic carbon (SOC) – all play an important role in enabling the roots to uptake nutrients. Furthermore, micro-organisms living in the soil also enable roots to uptake nutrients. In fact: micro-organisms (bacteria and fungi) are better at feeding roots than roots left on their own.
Now for some microbiology!
The key requirement for nutrients to be available to both the roots and the microbiology is “solubility”. Roots, bacteria, and fungi can take up only nutrients that have been in solution with water. Biochar plays an important role in this process because it can support the solubilisation of nutrients with the large surface area of biochar’s pore structure as seen in the adjacent diagram. Moreover, the pores themselves make excellent storage locations for moisture. Together, moisture stored (absorbed) in biochar pores and nutrients stored (adsorbed) along its cellular walls become more available for roots, bacteria, and fungi. Mycorrhizal fungi provide path ways that connect nutrients and moisture stored inside biochar particles to the roots.
To be clear, biochar particles are not a necessary component for soil nutrients to be made available for plants. That would be a vast over statement! Roots can access nutrients directly as long as long as the root itself comes in contact with nutrients that are in solution. In this case, the soil must be moist and solubilized nitrogen, phosphorous, and/or potassium (the top three macro nutrients), must be directly available to the plant roots; but if the soil is dry and the nutrients are in a crystalized solid form, they will not be available to the plant roots. In fact, nutrients that have not been adsorbed onto some type of surface area can easily be washed away in the rains — the fate of soils with too little soil organic carbon content in the form of dead plant or microbial material. Adding rich compost, worm castings, humus rich soil, and biochar can provide the surface area needed to hold onto (by adsorption) precious nutrients.
If you skipped the microbiology lesson, don’t miss this part!
3 Crucial reasons you do or do not need biochar in your spring garden:
- Soils that are already rich in organic content such as compost, dead plant material, wood chips, mulch, etc. will not benefit greatly from adding biochar. They already have the surface area needed to make nutrients available for plants.
- Soils that lack nutrients in a form that can be solubilized will not feed plants until the solid nutrients in organic materials in the soil are broken down by microbial life, fungi, bacteria, worms, and other soil life. Biochar will help to attract these micro organisms and soil life, and give them a safe home.
- Soils that lack organic carbon from dead plant and microbial life will benefit from biochar additions but only if adequate nutrients are available in the soil. It is the soil life in the form of bacteria, fungi and earthworms that perform the work of converting solid organic material into these necessary solubilized nutrients.
In conclusion, all of the soil components shown in Figure 1 are necessary for healthy plant growth to occur. Biochar plays an important role for soils that have lost organic carbon and/or need to attract health microbes. Biochar also helps to maintain the organic carbon at a healthy level between additions of compost.
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Watch for our next newsletter to learn more about how any soil type can be improved for healthy plant growth.
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