soil basics - how it works


2. Water Uptake

Plants need water as part of their cells. Indeed, plant tissue is about 80 to 90% water. This water is the substance in which the various molecules and ions that perform metabolic activities (such as photosynthesis, food transport, cell maintenance, growth and reproduction) are dissolved and transported. Water is also the substance in which the soil’s nutrients are dissolved and carried into the plant.

Plants are constantly losing water via “transpiration” through thousands of tiny pores (“stomata”) in the leaves and by leakage of root exudates through the tips of the roots. Plants do have some ability to regulate the size of their stomata and slow down water loss, but obviously water must be continually provided to the plant by absorption through the roots to maintain optimal health. The constant movement of water upward from the roots to the leaves serves to carry nutrients from the soil to all parts of the plant and to help cool the leaves during hot weather. Plants vary in their water needs – while a cactus will lose only microscopic amounts of water in a day, a corn plant may lose up to two quarts!

In the soil, water fills pore spaces between soil particles. In moist soil, about half of the total soil water is able to be absorbed (“available water”) and about half is too tightly held on soil particles to be used (“unavailable water”). The composition of the soil is a major factor in availability of water to plants. Soils with a high clay content hold a higher percentage of the total water as unavailable water, but their total water supply will be considerably larger than sandy soils. High clay soils are also subject to compaction, which can impede the development of strong, deep root systems. Sandy soils will be short on total water-holding capacity and may not have the humus content necessary to support nutrition and water provision needed by many plants. Use of fertilizers such as Bradfield products that contribute organic matter to soils can increase the available water and reduce the compaction of clay soils and increase the total water capacity and nutrient content of sandy soils.

Salts in soils also affect root water uptake. The higher the salt level, the more difficult it is for the plant to draw water from the soil. Excessive use of inorganic, high-salt fertilizers (such as potassium chloride or ammonium nitrate) can increase salt levels so high that plant growth is negatively impacted. Use of natural fertilizers avoids this salt build-up and maintains water availability.

The faster the rate of transpiration from the leaves, the faster the plant must draw water through the roots to keep up. Plants need much more water when weather is sunny, humidity is low, or the wind is strong. Under these conditions, if the soil’s supply of available water is low, either due to low capacity or low availability, plants will begin to wilt. This is one reason why a soil’s structure and humus content are so important: to improve water movement and availability. Inorganic fertilizers do nothing to enrich the organic matter or humus content of a soil and therefore do nothing to improve the supply of water to plants. Indeed, the potential for salt build-up will result in a negative impact on available water over time. A soil rich in organic matter will not only be optimal for water availability, it will encourage growth of dense, deep root systems that are better able to withstand periods of water shortage. Use of natural Bradfield fertilizers helps to build soil organic matter, ultimately resulting in stronger, healthier plants!


Zimmer, Gary. 2006. Soil Basics: How It Works. Acres U.S.A.

Transport in Plants.

Soil Basics - How it Works

1. The Symbiotic Decay-Nutrition Cycle

2. Water Uptake

3. Ions, Nutrition and all that “Scary” Chemistry

4. Who are these Microbes, and what are they doing in my Soil?

Download Soil Basics - How it Works from Bradfield Organics® (Adobe Acrobat Required)


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