Midwest Vegetable Guide - 2022 - 14

Soil Fertility and Nutrient Management
Soil Fertility and Nutrient
Management
Reviewed by Liz Maynard and Ajay Nair - Aug 2021
Soil tests aid vegetable growers with their soil fertility and
fertilizer application programs. Soil tests are most useful
when growers keep accurate records for each field that
include the amount of fertilizers and other soil amendments
they applied, crop yields, and rotations. These records allow
growers to determine trends in soil fertility and crop response
to applied fertilizers over several years.
Efficient vegetable production relies on growers adjusting
lime and fertilizer applications to their soils' existing pH and
fertility levels. Growers can increase their net returns if they
maintain proper soil fertility, which can reduce crop losses
from physiological disorders. Applying nutrients based on
crop needs and existing soil nutrient levels also reduces the
movement of nutrients into groundwater and surface waters.
Take soil samples at the same time each year, preferably in
the fall or early spring. Soil pH varies seasonally, so
comparing winter and summer samples is difficult. A typical
soil test for plants usually determines pH, lime index (also
called buffer pH), available Bray P1 phosphorus (P),
exchangeable potassium (K), calcium (Ca), magnesium (Mg),
and cation exchange capacity. It also includes the percent
base saturation of Ca, Mg, and K.
In addition to the routine pH test, growers should test soils
that are susceptible to large variations in soil pH for salt pH.
The salt pH provides a more accurate estimate of the true
acidity in these soil types by simulating the effects of
fertilizer salts on soil pH.
There are also tests to determine organic matter and other
nutrients, including sulfur (S), manganese (Mn), boron (B),
and zinc (Zn). Some labs test for microbial activity and
water-soluble carbon, which can predict the release of
nitrogen and phosphorus from organic sources.
Your land-grant university or extension service can provide
you with a list of soil testing labs in your area.
Soilless Growing Media
Test soilless growing media used in transplant or crop
production for pH and total soluble salts before using it.
Request a test specifically for " soilless media " from the lab.
If the crop will be grown in soilless media more than a
month, regularly test the media or plant tissue to catch any
nutrient imbalances that may affect crop growth and yield.
14
Interpretation of Standard Soil Test
Results
Soil pH (sometimes called active soil acidity) is based on the
pH scale, which measures the acidic or basic reaction of the
soil. A pH less than 7 is acidic; a pH greater than 7 is
alkaline. When soil pH is too low
for good crop growth, adding lime will raise the pH. Natural
processes and agricultural practices tend to lower pH over
time, so it is important to measure it every year or two. When
soils are alkaline, the testing laboratory may recommend
applying sulfur (S) to lower the pH to a level that allows
nutrient availability in the soil.
Lime index (sometimes called " buffer pH " ) measures reserve
soil acidity. The lime index is used to make limestone
recommendations. It usually takes lime four to six months to
correct soil acidity. Your land-grant university or extension
service can provide you with liming recommendations
specific your state.
Phosphorus may be reported as P (phosphorus) or P2O5
(phosphate). The units for P and other nutrient values may be
given as parts per million (ppm) or pounds per acre. The
value is an estimate of the amount of phosophorus in the soil
that the plant can use for growth. Applying P2O5 fertilizer at
100 pounds per acre will increase the soil P test level by
about 10 pounds per acre.
Potassium may be reported as K (potassium) or K2O
(potash). The test value estimates the amount of K available
per acre. About 50 percent of the potassium applied in
fertilizers is fixed in the soil and is not immediately available
to plants - this can vary by soil type and clay content. Soil K
declines due crop removal,leaching, and soil erosion.
Calcium (Ca) and magnesium (Mg) soil test values
represent the amount of Ca and Mg available in the soil. Ca
and Mg values generally are low when soils are acidic.
Levels are usually sufficient when pH and the lime test index
are at proper levels.
Cation exchange capacity (CEC) is a measure of the soil's
ability to hold exchangeable cations such as hydrogen (H),
Ca, Mg, K, sodium (Na), iron (Fe), and aluminum (Al). CEC
is measured in terms of milliequivalents (meq) per 100 grams
of soil. Soil type and soil organic matter determine CEC.
Clay-, silt- and loam-type soils generally have a higher CEC
than sandy soils because they have many more exchange sites
to hold cations. High-CEC soils generally hold nutrients
better than low-CEC soils. High-CEC also lose smaller
amounts of nutrients due to leaching.
Midwest Veg Guide 2022
Midwest Vegetable Guide - 2022

Table of Contents for the Digital Edition of Midwest Vegetable Guide - 2022
