nutrients and is the main source of water for plants.
season there shouldn’t be too much nitrogen and phos-
Essential nutrients are made available to the roots of
phorus left in highly soluble forms or enriching the soil’s
plants through the soil solution. The air in the soil,
surface. Leaching and runoff of nutrients are most likely
which is in contact with the air above ground, provides
to occur after crops are harvested and before the follow-
roots with oxygen and helps remove excess carbon
ing year’s crops are well established.
dioxide from respiring root cells. When mineral and
We also want the soil to have good tilth so that plant
organic particles clump together, aggregates are formed.
roots can fully develop with the least amount of effort.
They create a soil that contains more spaces, or pores, for
A soil with good tilth is more spongy and less compact
storing water and allowing gas exchange as oxygen enters
than one with poor tilth. A soil that has a favorable and
for use by plant roots and soil organisms and the carbon
stable soil structure also promotes rainfall infiltration
dioxide (CO2) produced by organisms leaves the soil.
and water storage for plants to use later. For good root
Farmers sometimes use the term soil health to
growth and drainage, we want a soil with sufficient
describe the condition of the soil. Scientists usually use
depth before a compact soil layer or bedrock is reached.
the term soil quality, but both refer to the same idea—
We want a soil to be well drained, so it dries enough in
how good is the soil in its role of supporting the growth
the spring and during the following rains to permit timely
of high-yielding, high-quality, and healthy crops? How
field operations. Also, it’s essential that oxygen is able to
would you know a high-quality soil from a lower-quality
reach the root zone to promote optimal root health—and
soil? Most farmers and gardeners would say that they
that happens best in a soil without a drainage problem.
know one when they see one. Farmers can certainly tell
(Keep in mind that these general characteristics do not
you which of the soils on their farms are of low, medium,
hold for all crops. For example, flooded soils are desirable
or high quality. They know high-quality soil because it
for cranberry and paddy rice production.)
generates higher yields with less effort. Less rainwater
We want the soil to have low populations of plant
runs off, and fewer signs of erosion are seen on the better-
disease and parasitic organisms so plants grow bet-
quality soils. Less power is needed to operate machinery
ter. Certainly, there should also be low weed pressure,
on a healthy soil than on poor, compacted soils.
especially of aggressive and hard-to-control weeds. Most
The first thing many might think of is that the soil
soil organisms are beneficial, and we certainly want high
should have a sufficient supply of nutrients throughout
amounts of organisms that help plant growth, such as
the growing season. But don’t forget, at the end of the
earthworms and many bacteria and fungi.
thInK LIKe A root!
If you were a root, what would you like from an ideal soil? Surely you’d want the soil to provide adequate nutrients and to be porous with good tilth, so that you could easily grow and explore the soil and so that soil could store large quantities of water for you to use when needed. But you’d also like a very biological y active soil, with many beneficial organisms nearby to provide you with nutrients and growth-promoting chemicals, as well as to keep potential disease organism populations as low as possible. You would not want the soil to have any chemicals, such as soluble aluminum or heavy metals, that might harm you; therefore, you’d like the pH to be in a proper range for you to grow. You would also not want any subsurface layers that would restrict your growth deep into the soil.
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent