Taking care of the soil is essential |
Everyone is looking to get the most value from everything they do. With the ever-tightening squeeze between farm inputs and crop prices, it just makes good sense to reevaluate where the added fertilizer is going each year.
The purpose of adding
nutrients to soil is to create an environment for healthy and profitable plant
growth. It has long been known that
well-nourished plants are better able to resist disease and insects, use water
more efficiently, produce more abundant and higher quality yields, and offer a
better economic return. It remains the
goal to get as much of the applied nutrients into the plant where they can be productive.
Healthy crop of mandarins |
Nutrients become depleted
when they removed from the soil in every harvested crop- but there are also
other things happening that cause nutrients to become less available to
plants. An overview is presented here,
but more details are available from your local crop advisor.
Potash
Almonds in stoney ground |
When potash fertilizers are
added to a field, they quickly dissolve in soil water and the potassium cation
(K+) becomes held on the negatively charged sites on clays and
organic matter. Potassium is retained on
these cation exchange sites until another cation comes along to replace it. Since K is not held as strongly as some other
cations (such as calcium or magnesium), it can slowly move down in the soil-
especially in very sandy soils and in high rainfall areas. In most soils however, added K remains close
to where it is applied and stays available for plant uptake year after
year.
Phosphate
Phosphorus (P) fertilizer generally
has the greatest solubility and availability for plant uptake immediately after
being added to soil. Soon after
application, P fertilizers begin to react with the soil solution and soil
minerals to form less soluble compounds.
The chemistry of P in the soil governs these reactions and over time,
less soluble and less available compounds are formed. All added P, whether commercial fertilizer or
organic sources such as manure, eventually undergo these soil reactions.
Onions have a shallow root system |
Soil testing is the best
technique for determining the nutrient value of these older P compounds and for
predicting the need for any additional fertilizer required to meet the plants
nutritional needs.
Application of P fertilizer
in a concentrated zone or band is one simple technique that is useful in
delaying these soil reactions and improving nutrient availability. New additives are being developed that may
also prove beneficial. Special attention
should be taken to avoid conditions where P can be lost in surface runoff.
Nitrogen
Nitrogen (N) is the most
difficult to manage of the primary plant nutrients. It undergoes many complicated biological and
chemical transformations that make it a challenge to keep it in the rootzone
where is needed. The primary goal is to
get the added N into the plant, where it is essential for many metabolic
processes, such as chlorophyll formation and protein synthesis.
Soil processes change in wet conditions |
Unfortunately, a significant portion of the
added N can be lost as a gas through ammonia volatilization from
surface-applied fertilizer or through denitrification from wet soils. Nitrate is mobile in the soil solution and
may be carried beyond the rootzone in water passing through the soil. A significant amount of added N fertilizer is
used by the soil microbes in building soil organic matter. Special attention is needed for N fertilizer
management because of its numerous pathways of loss, and the high plant
requirement for vigorous growth. Plant
tissue testing can provide an indication of the nutritional status and the need
for mid-season additions.
Nitrogen-deficient lettuce |
Each of these nutrients is
frequently viewed as a separate management issue- due to their diverse behavior
and unique soil reactions- but it is essential that all three are managed as a
package in order to provide balanced nutrition for the plant. When any one of these nutrients is in short
supply, the other two will not be used efficiently and plant performance will
suffer.
One view of the complex processes in soil |
FERTILIZERS ARE IMPORTANT IN OLD AGE AND NEW AGE ALSO
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