Midwest Vegetable Guide - 2022 - 15

Soil Fertility and Nutrient Management
Here are the typical CEC ranges of various soil types:
Soil Texture CEC Range
Sands
Silts
Clays
5-15
8-30
25-50
Organic soils 50+
Base saturation is the percentage of the total CEC occupied
by basic cations such as Ca, Mg, and K. Base saturation is
related to soil pH and soil fertility. On acid soils, the percent
base saturation of Ca and Mg is low. The saturation of the
different cations is important because plants take up some
cations more easily than others. The base saturation for Ca
should be 60 percent or more; Mg should range between 10
and 15 percent; K should range from 1 to 5 percent. Excess
levels of one cation can reduce the uptake of another. Some
soil scientists believe that there should be specific Ca:Mg
ratios and Mg:K ratios (2:1). Most horticulturists believe that
if base saturation levels are at the minimum levels suggested
here, then it is not important to maintain specific proportions
or ratios.
Crop Nutrient Requirements
Vegetable crops require 17 essential elements (nutrients) for
development and reproduction. In addition to carbon (C),
hydrogen (H), and oxygen (O), plants need macronutrients in
large concentrations and micronutrients in relatively small
concentrations.
Each crop has a crop nutrient requirement (CNR) for
particular nutrients. The CNR is defined as the total amount
of the nutrient (in pounds per acre) the crop requires to
produce optimum economic yield. The concept of optimum
economic yield is important in vegetable production, because
applying a certain amount of a nutrient might produce a lot of
biomass, but may produce negligible marketable product due
to small fruit size, small number of fruits, or large number of
culls and small number of marketable fruits. Always consider
fruit number, size, and quality in the CNR concept for
vegetable production.
The best way to achieve the CNR is to begin with a soil test.
The results from a soil lab analysis include recommendations
for the amount of lime or sulfur needed to balance the soil
pH, and indicate the amount of fertilizer needed to deliver the
CNR.
Macronutrients
Nitrogen (N), phosphorus (P), and potassium (K) are the
primary macronutrients, and they are commonly applied in
fertilizers for field vegetable production. Plant nutrient
recommendations are often given as pounds of N, pounds of
phosphate (P2O5) and pounds of potash (K2O) per acre.
It is up to growers to figure how much fertilizer or product
they must apply to meet the suggested recommendations.
This can be tricky, because growers may need more than one
kind of fertilizer product to meet the recommendations.
Fertilizer products are required to list the percent N, P2O5,
and K2O equivalent they contain - and the products are
listed in the order: N-P-K. For example, a fertilizer labeled
10-10-10 contains the equivalent of 10 percent N, 10 percent
P2O5, and 10 percent K2O. So a pound of this fertilizer would
contain 0.1 pound each of N, P2O5, and K2O. Urea labeled
46-0-0 contains 46 percent N, 0 percent P2O5, and 0 percent
K2O. Potassium chloride (muriate of potash) labeled 0-0-60
contains 0 percent N, 0 percent P2O5, and 60 percent K2O.
Organic fertilizers are also labeled this way - a 3-2-2
product contains 3 percent N, 2 percent P2O5, and 2 percent
K2O. It is important to note that some of the N and P in
organic fertilizers require warm, moist soil and microbial
activity before it is available to plants.
Let's say a nutrient recommendation calls for 100 pounds of
N and 100 pounds of K2O per acre.
A grower could meet that recommendation by using 217
pounds of urea (217 pounds of urea X 0.46 N = 100
pounds of N) and 167 pounds of potassium chloride (167
pounds of potassium chloride X 0.60 K2O = 100 pounds of
K2O).
A grower could also meet that recommendation by using
1,000 pounds of premixed 10-10-10 fertilizer (1,000 pounds
of fertilizer X 0.10 N = 100 pounds of N; 1,000 pounds of
fertilizer X 0.10 K2O = 100 pounds of K2O).
But that same fertilizer would also supply 100 pounds of
P2O5 that is not needed. So, using such a fertilizer could be a
waste of money and could pollute surface or ground water.
If you choose a premixed fertilizer, select the ratio of
nutrients that comes closest to the amount of recommended
nutrients. It is not necessary to be exact as long as any
differences are reasonable. If you can't get to the
recommended nutrient application using premixed fertilizers,
it is fine to first make a base application using a standard
fertilizer ratio, and then apply individual elements to reach
the recommended nutrient levels.
For example, you can supply extra N with urea or urea
ammonium nitrate (UAN) solution; you can supply extra K
with muriate of potash. Custom-blended fertilizers can be
made to almost any desired ratio.
Nitrogen (N)
Standard soil tests aren't very useful for predicting how much
N fertilizer you need to apply to optimize yield and qualilty.
N fertilizer recommendations account for the soil type,
amount of organic matter in the soil, field history, and crop.
The recommendations in this guide are based on data from
Midwest Veg Guide 2022
15
Midwest Vegetable Guide - 2022

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