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Urban Wild

Lawns are more than just grass. There is an amazing array of life that lives above the ground, among the grass blades and below the soil surface. Stopping for a minute to look deeper into our lawns we see complex relationships between many organisms. Understanding those relationships and identifying those living processes that occur will help you have a healthy and green lawn.

Grass, as with all plants, needs certain things to live. They are light, air, water, nutrients and soil.

Light: the sun provides A constant source of natural light.

Air: Grass blades and roots need air to be healthy. There are spaces in the root zone, when not occupied by water, where the plant takes in carbon dioxide and oxygen is released. Air space is created by roots dying and decomposing, small and large organisms foraging for food (i.e., bacteria, protozoa, earthworms, insects, and spiders), the freezing and thawing of the soil, or by aerating the soil.

Water: Whether added by Mother Nature or us, lawns need water to live. Soil water effects plant growth, the transportation of nutrients, moderates soil temperature, dilutes toxins, acts as a pathway for soil organisms and as a source of hydrogen for the plants.

Water moves through the soil by the pull of gravity. As water percolates down it displaces the air in the macro pores found in the soil. As the macro pores fill, water is moved into the micro pores by the way of capillary action. Capillary action is a sponge like action. Water is held in the micro pores waiting to be used by the plants.

The types or classifications of soil water:

Gravitational Water: Found in the macro pores of the soil. This type of soil water drains quickly past the root zone and is not available to plants.

Capillary Water: Found in the micro pores of the soil. This type of water is taken up by capillary action into the plants by way of their roots. Water stays in these pores until it is used by the plants or is removed by evaporation. Capillary water is the only water that plants can use.

Hydroscopic Water: Found in the micro pores of the soil. This type of water is not available to plants. The water molecules are bound so tightly to the soil particles that the capillary action of the plant roots can not break the bond.

Knowing how water moves through the soil is important as it can help you correctly water your lawn. Over watering wastes water because once the macro and micro pores are full any additional water added runs over the surface of the soil. This run off carries with it the lawn care products that are not absorbed by the plants and is a major source of non-point pollution that effects the health of our water ways. Under watering fail to fill the macro pores in the soil which in turn fails to fill the micro pores which holds the water that will be available to the plants roots. Under watering also encourages the plants roots to stay near the surface wear they are susceptible to the affects of drought.

Nutrients: There are 17 nutrients needed by plants to be healthy. Macronutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, carbon hydrogen, and oxygen are used in large quantities by plants. The essential micronutrients used in relatively small amounts are iron, manganese, boron, molybdenum, copper, zinc, chlorine and cobalt. Organic lawn fertilizers contain most of these marconutrients. Micronutrients in the form of greensand, granite meal or kelp meal are sometimes added as well.

Plants also fertilize themselves by the decay cycle. The dead and dying organic material is consumed by organisms such as millipedes, beetles, mite, and earthworms. These creatures physically and chemically break the plant tissue into simpler components. Proteins found inside the plant material are consumed then released in the form of nitrogen compounds that can then be absorbed by the plant's roots. Phosphorus, potassium, calcium, magnesium and other minerals are also supplied this way.

Organic matter does more than just feed the system. Organic matter adds surface area in the soil where nutrients can attach themselves, preventing them from being leeched through the soil. Organic matter increases the soil ability to hold water near plant roots where it is needed most. The holes created by burrowing organisms allow increased air movement, allowing more efficient gas exchange.

Organic matter is considered anything that lives or did live in the soil. This includes plant material, fungus, and the micro and macro organisms. Organic matter has been likened to batteries, in that it acts as a storehouse for the energy that is used to run the biological processes.

Without a steady input of organic matter, such as grass clippings and leaves in the fall, lawns will need supplemental nutrients in the form of lawn fertilization.

Soil: The physical properties of the soil are those that can be evaluated by sight or by feel. Soil is made up of about 50% solids and 50% pore space. The pore space is filled with either air or water. The solid space is made up of organic and mineral soil particles. The organic matter averages 5% while the mineral content of the soil solids are approximately 45%.

The mineral content of soil solids is described as the physical properties of the soil. The two most important properties of a lawn soil are the soil's texture and structure.

Soil Texture: Soil texture is described as being the relative size of the soil particles, i.e. the relative amounts of sand, silt and clay. In central Ohio our soils have a high clay content which has both positive and negative attributes. The high clay content is good because nutrients can easily attach themselves to the clay and remain in the soil for plant absorption. However, clay tends to hold water and become very hard when it dry preventing root expansion and water drainage.

Soil Structure: Soil structure is the physical shape of the soil when it is broken apart. The shape is created by the effect of the surrounding organic matter on the soil particles. Soil aggregates are used to describe some of the soil structures. The two most common soil aggregates in central Ohio are granular and blocky. Soils rich in organic matter will have porous, granular structure. Soils low in organic matter tend to have hard, compacted soils, which limits root growth. Good soil structure is more important to plants than soil texture.
The roots of plants and the organisms that live around the root zone create granular aggregates. This happens when organic gums from the decomposition of the plant material bind the soil particles together. When granular soil is present it shows that the plants living there have excellent drainage and aeration. Blocky soils are those that form distinct sides when disturbed. These aggregates are generally found under the root zones of plants. To change blocky soils into granular soils, organic matter needs to be added.