What Is Loam Good For?
The basis for a good garden is the soil available for plants to grow in. Soil needs to have proper drainage qualities, acceptable pH for the plants you're raising, water-holding capacity, and the ability to provide nutrients essential for proper plant growth. If you are fortunate, you'll have loam soil. Loam is a soil type that contains all three of the basic soil particles: silt, clay and sand. Basic loam soil has about equal amounts of all three, and is the ideal garden soil. It's good for plants in multiple ways.
Soil quality depends on not just the soil particle size, but also the sizes of the pores left between the soil particles. The pores provide spaces for water to move through the soil. Loam is good because the three kinds of soil particles have different sizes. Sand particles are about 1/16 inch in diameter and tend to be rounded. Silt and clay particles are flatter, thinner and finer. Silt particles are less than the size of a period on a printed page and clay particles aren't visible without microscopy. When they're combined, they offer a variety and abundance of pore spaces for water to drain through. In a good loam soil, 40 to 60 percent of the soil volume consists of the spaces between the particles.
Proper Root Aeration
The spaces between the particles of loam soil are also good for providing oxygen to the plant roots. The above-ground green plant parts can photosynthesize and produce oxygen as a waste product of photosynthesis that they use when they need to break down sugars to grow. Plant roots don't have photosynthetic capabilities to make their own food, and they rely on getting oxygen from the soil to grow and stay alive. Loam soil has so many spaces between the particles that good supplies of both air and water are held in them to nourish roots. Without proper aeration, roots don't have enough oxygen to stay alive, root cells die, and root rot moves in to feed on decaying tissues.
Plants need 13 essential mineral nutrients in order to grow, and they get these primarily from soil. The clay particles of loam soil help hold on to plant nutrients instead of letting them move with the water and leach through the soil, washing away from the root zone. The flatter clay particles have more surface volume, offering places for the plant nutrients to latch onto. There's an electrical attraction involved, with negatively charged places on clay particles attracting positively charged plant nutrients. Clay soils can hold more nutrients, but they're not as good as loam because they have poor drainage and aeration.
The texture of soil is important for plant health. Soil types that form horizontal plates or hard, massive clods are difficult for roots to grow through and for water and air to move through. Loam furnishes the ideal texture, called crumb or granular texture, for root growth. It also provides places for soil organisms to live. Loam soil contains a wealth of microscopic life such as bacteria, fungi and one-celled animals called protozoa. They're essential to recycling nutrients and decomposing organic matter. They interact with each other and with plants in beneficial ways, such as soil mycorrhizas and bacteria that attach to plant roots and help with nutrient availability.
- Penn State Extension: Soil Quality -- Introduction to Soils
- University of California Santa Barbara: UCSB ScienceLine: Why Do Plants Need Oxygen?
- North Carolina Department of Agriculture & Consumer Services: Plant Nutrients
- Soil Net: Secondary: Microfauna and Microflora
- Royal Horticultural Society: Mycorrhizal Fungi
- University of Hawaii: Introduction to Rhizobia
- Pudue University: What Is Loam?
- fralo/iStock/Getty Images