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,
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?
Basics - How it Works from Bradfield Organics® (Adobe