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Soil and Plant Evolution - A TerraSoil Overview

TerraSoil

03 Aug 2024

The Evolution of Plants and Optimal Soil Conditions

What is Soil?

Soil is a dynamic natural body composed of mineral particles, organic matter, water, air, and living organisms. It is a vital component of the Earth’s ecosystem, supporting plant growth, regulating water flow, and cycling nutrients. Soil health is crucial for sustainable agriculture and environmental quality.

Components of Soil

Soil consists of several components:

Mineral Particles: These include sand, silt, and clay, derived from the weathering of rocks.
Organic Matter: Decomposed plant and animal residues that provide nutrients and improve soil structure.
Water: Essential for nutrient transport and microbial activity.
Air: Occupies the pore spaces between soil particles, providing oxygen for root and microbial respiration.
Living Organisms: Includes bacteria, fungi, nematodes, and earthworms that contribute to soil health and fertility.

Soil Formation

Soil formation, or pedogenesis, is a complex process influenced by five main factors: parent material, climate, organisms, topography, and time. Weathering of parent material, such as rocks, combines with organic matter from living organisms to form soil. Over time, these processes lead to the development of distinct soil horizons.

Particle Size and Organic Matter Content

The particle size of soil influences its texture, which in turn affects water retention, drainage, and aeration. Soil texture is classified based on the proportion of sand, silt, and clay:

Sand: Large particles that provide good drainage but poor nutrient retention.
Silt: Medium-sized particles that retain nutrients and moisture well.
Clay: Small particles that hold water and nutrients but may hinder drainage and aeration.

Organic matter improves soil structure by binding particles together, enhancing porosity, and increasing water as well as nutrient retention. It also provides a food source for soil micro-organisms.

The Importance of Aluminosilicates

Aluminosilicates are minerals composed of aluminum, silicon, and oxygen. They are abundant in clay minerals and play a crucial role in soil fertility. These minerals help retain essential nutrients like potassium, calcium, and magnesium, making them available to plants. They also improve soil structure and water-holding capacity.

Natural Growing Media Types

Natural growing media found in nature include:

Loam: A balanced mixture of sand, silt, and clay, ideal for most plants.
Peat: Organic material derived from decomposed plant matter, commonly used for its high water retention.
Compost: Decomposed organic matter that enriches soil with nutrients and improves structure.
Vermiculite and Perlite: Mineral-based media that enhance aeration and drainage.

Evolution of Plant Roots

Plant roots evolved to efficiently extract water and nutrients from the soil. The development of root hairs increased the surface area for absorption. Symbiotic relationships with mycorrhizal fungi further enhanced nutrient uptake, particularly phosphorus. These adaptations allowed plants to colonize diverse soil environments.

Plant-Soil Fauna Interactions

Plants and soil fauna work together in extracting nutrients from soil particles. Mycorrhizal fungi form symbiotic relationships with plant roots, extending their reach into the soil and increasing nutrient absorption. Soil microorganisms decompose organic matter, releasing nutrients in a form that plants can absorb. This mutualistic relationship is essential for soil fertility and plant health.

Plant Root Exudates

Root exudates are organic compounds secreted by plant roots into the soil. These exudates include sugars, amino acids, and organic acids, which attract beneficial microbes and enhance nutrient availability. Root exudates can also alter soil pH, making certain nutrients more accessible to plants.

The Role of Organic Matter

Organic matter is crucial for soil health. It improves soil structure, increases water-holding capacity, and provides a reservoir of nutrients. Organic matter also supports a diverse soil micro-biome, which plays a key role in nutrient cycling and disease suppression. However, both excessive and insufficient organic matter can lead to soil health issues, such as poor drainage or low fertility. The typical content in naturally occurring soil is between 2 to 10%, 4-5% for the most productive farms, and up to around 17% in Chernozem or related soil types.

Problems of Organic Matter Imbalance

Having too much organic matter can lead to anaerobic conditions, promoting the growth of harmful pathogens. On the other hand, too little organic matter results in poor soil structure, reduced nutrient availability, and lower microbial activity. Maintaining a balanced level of organic matter is essential for optimal soil health and plant growth.

Soil Classifications

Soil Classification	Main Characteristics	Color	Nutrient Deficiency or Excess	Climate Type	Countries Location
Oxisols	Highly weathered, low fertility, rich in iron and aluminum oxides	Red, yellow	Deficiency in phosphorus, potassium, and calcium	Tropical	Brazil, Indonesia, Nigeria
Aridisols	Dry, low organic matter, often saline or alkaline	Light gray, pale brown	Deficiency in nitrogen and organic matter	Arid	USA (Southwest), Egypt, Australia
Mollisols	Thick, dark topsoil rich in organic matter, highly fertile	Dark brown, black	Often well-balanced but can have nitrogen deficiency	Temperate grasslands	USA (Midwest), Ukraine, Argentina
Alfisols	Moderately leached, clay-enriched subsoil, fertile	Brown, grayish-brown	Can be deficient in nitrogen and phosphorus	Temperate	USA (Eastern), Western Europe, Russia
Ultisols	Strongly leached, acidic, low fertility	Red, yellow	Deficiency in calcium, magnesium, and potassium	Humid subtropical	USA (Southeast), China, India
Entisols	Young soils with little profile development, variable fertility	Variable (depending on parent material)	Variable (depending on parent material)	Variable	Worldwide (recent deposits, floodplains)
Histosols	Organic soils, high in organic matter, often waterlogged	Dark brown, black	Excessive organic matter, potential for phosphorus deficiency	Wetlands	Canada, Finland, Indonesia
Spodosols	Acidic, sandy soils with organic-rich layer overlying iron/aluminum oxides	Ash-gray surface, dark subsoil	Deficiency in nitrogen, phosphorus, potassium, calcium, and magnesium	Cool, humid	Northern USA, Russia, Scandinavia
Andisols	Volcanic ash soils, high water-holding capacity, fertile	Black, dark brown	Generally fertile but can be deficient in phosphorus	Volcanic regions	Japan, New Zealand, Pacific Northwest (USA)
Vertisols	High clay content, significant expansion and contraction with moisture	Dark gray, black	Deficiency in nitrogen and phosphorus	Seasonal wet and dry	India, Australia, Sudan
Chernozem	High organic matter, very fertile, rich in humus	Black	Rarely deficient, sometimes phosphorus	Temperate grasslands	Ukraine, Russia, Canada
Terra Preta	Man-made, high charcoal content, extremely fertile	Black	Very fertile, rarely deficient	Tropical	Amazon Basin (Brazil)

Conclusion

Understanding soil composition, formation, and the interactions between plants and soil organisms is crucial for optimizing growing conditions and ensuring sustainable agriculture. By maintaining soil health through proper management practices, we can support robust plant growth, enhance soil fertility, and contribute to environmental sustainability.

References

Guo, M. (2021). Soil Health Assessment and Management: Recent Development in Science and Practices. Soil Systems.
Peteira, B., & Ciancio, A. (2021). Functional Diversity of Soil Nematodes in Relation to the Impact of Agriculture—A Review. Diversity.
Idris, S., et al. (2021). Testing the accuracy of Soil Testing Kit® Transchem. Agro-Science.
Winnick, M. J., Bargar, J. R., & Maher, K. (2018). A Molecular Investigation of Soil Organic Carbon Composition across a Subalpine Catchment. Soil Systems. DOI: 10.3390/soils2010006.
NASA Earth Observatory. Soil Composition Across the U.S. Retrieved from earthobservatory.nasa.gov.
Brady, N. C., & Weil, R. R. (2016). The Nature and Properties of Soils. Pearson.
FAO (2015). World Reference Base for Soil Resources 2014. International soil classification system for naming soils and creating legends for soil maps.
FAO (2015). World Reference Base for Soil Resources 2014. International soil classification system for naming soils and creating legends for soil maps.
Glaser, B., & Birk, J. J. (2012). State of the scientific knowledge on properties and genesis of anthropogenic dark earths in central Amazonia (terra preta de índio). Geochimica et Cosmochimica Acta.
FAO. (2006). Guidelines for Soil Description. Rome: Food and Agriculture Organization of the United Nations.
https://impellobio.com/blogs/inoculants/rootexudates