Over the weekend a group of thinkers working with Post
Carbon Institute have been discussing the mineral content of rain. Often
when we discuss minerals and rain we are talking about the manner in which
minerals and inorganic nutrients are readily leached from the soil. Leaching is when minerals are not able to hold
in the soil and are thus washed out by the natural flow of groundwater. A soil’s
tendency to leach is influenced by the way that the soil is tilled, cropped,
and fertilized.

For instance, inorganic fertilizers provide crops with plant
available nutrients in the form of chemicals like nitrate (NO₃^-).
The problem is that nitrate readily washes out of the soil if the plants are
unable to utilize it before heavy rains. Many farmers are beginning to realize that
heavy fertilizer application in the fall amounts to a waste of money since a majority
of the nutrients are lost by spring due to sever washout by winter rains or
spring snow melt.

Leaching of minerals also occurs when soil is left bare to
face winter rains. In this case, leaching is accompanied by a loss in top soil
from the process of erosion. Imagine rain drops as tiny explosions on bare
soil, blasting minerals loose, collecting in water particles, and flowing away
as surface runoff.

Fortunately, farmers do not need to resign to the fact that
rains always mean a loss in minerals and nutrients. By cover-cropping and the
addition of compost, a farmer can protect the soil from direct rainfall and increase
the organic matter in the soil in the form of root biomass. Roots and organic matter
create a healthy habitat for soil microbes that play a key role in mineralizing
soil nutrients and forming soil aggregates that resist leaching.

One great benefit to having a diverse soil food web of
fungi, bacteria, and protozoa is because organic minerals are “sequestered” in
the biomass/bodies of microbes and recycled through in their metabolic
processes. Instead of washing out of the soil, the minerals actually become the
body of bacteria and fungi! In a series of food chain and energy exchanges the
minerals in the soil are converted from one form to the next; changing from plant
detritus to the body of a soil organism, then to metabolic wastes of that
organism and into plant available forms of, and then consumed and incorporated into
the body of another soil microbe. All these changes occur in and around in the
rhizosphere (root-zone) of plants, and demonstrate an interconnected web of
energy and nutrient cycling and nutrient retention.

Also consider the fact that bacteria and fungi create a natural
glue that sticks to everything. Through the production of “glomulin”, nutrients
are retained and soil aggregates are formed. As organic matter is decomposed, the
biology in the soil help to form stable negatively charged humic (humus)
molecules which bind together with positively charged cat ions, electrically holding
minerals and preventing them from leaching. Important cat ions retained in
colloidal humus particles include: calcium, iron, magnesium, potassium, sodium,
and copper.

As you can see, there is a lot happening below the
soil, and farmers and gardeners have an opportunity to utilize cover crops, compost,
soil biology, and appropriate timing of fertilization to prevent soil erosion
and leaching of nutrients.

Broadcasting a Cover Crop of Crimson Clover in October to Protect Bare Soil from Winter Rain

Recently Sown Cover Crop of Legumes mixed with Rye and Barley Provides Root Biomass and Use Boilogy to "Fix" Nitrogen from the air