1

Mark L. McFarland

Professor and Soil Fertility SpecialistTexas A&M AgriLife Extension Service

College Station, Texas

Soils and Soil Fertility Management

Four Principal Components of Soil

Air Mineral

Water Organic Material

Solid Soil

Variation in Soils- Geology- Climate- Vegetation

2

Soil Properties Physical properties

• Texture• Structure

Chemical properties• Cation exchange capacity (CEC)• Soil reaction (pH)

3

SAND

Very Coarse 2.0 – 1.0 mm

Coarse 1.0 – 0.5 mm

Medium 0.5 – 0.25 mm

Fine 0.25 – 0.1 mm

Very Fine 0.1 – 0.05 mm

.05 - .002 mm

LessThan

Soil Texture(Diameters of individual soil particles)

.002 mm

SILT

CLAY

4

SoilTexture

Sand

Loam

Silt

Clay

Permeability

High

Medium

Low

Low

WaterRetention

Low

Medium

High

High

Soil Physical Properties

Soil Structure

Formation of soil “aggregates” (clods)Opens soil surface to allow water, air,

nutrients, and roots to move.

5

kAcidic

Basic

Neutral

Expected pH Range in Soils

6

Effect of pH on Plant Nutrient Availability

Crops:AsparagusBeetsCabbageSweet CornPumpkinsTomatoesBlueberriesStrawberries

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Optimum pH Range for Vegetable Crops

Preferred pH Ranges of Various Plants

7

Ca++

Na+

Ca++

H+K+

Mg++

NO3-

Cl-

SO4=

NO3-

Soil Water

• Likes repel• Unlikes attract

Cation Exchange Capacity(The Nutrient Supplying Power of Soil)

Clay particles

Organic matter

Plant Nutrition

Factors Affecting Fertilizer Management

Plant species

Type and intensity of use

Soil characteristics (texture)

Residual nutrient status

Boron

Calcium

Carbon

Chlorine

Cobalt

Copper

Hydrogen

Iron

Magnesium

Manganese

Molybdenum

Nitrogen

Oxygen

Phosphorus

Potassium

Silicon

Sulfur

Vanadium

Zinc

Essential Elements for Plant Growth

8

Essential Elements Found to Limit Plant Growth in the Field

Primary Nutrients: Nitrogen, Phosphorus, Potassium

Secondary Nutrients:Calcium, Magnesium,

Sulfur

Micronutrients: Boron, Chlorine, Copper,

Iron, Manganese, Zinc

Annual Nutrient Removal in Clippings(lbs./1,000 ft2)

Nutrient Bermuda St. Augustine

Nitrogen 12.0 7.0Phosphorus 2.3 1.5Potassium 8.5 5.0

Calcium 4.6 3.3Magnesium 4.3 1.5Sulfur 1.4 1.0

Zinc 0.046 0.023Manganese 0.012 0.007

Primary

Secondary

Micro’s

9

Soil TestingThe Key to Nutrient Management

A soil test is a chemical extraction that provides an index to estimate the nutrient supplying power of a soil

– Identifies the degree of deficiency or sufficiency of a nutrient

The Best and Proper Fertilizer to Use is the One Based on a Soil Test!

There is no standard fertilizer product, nutrient ratio or rate of application for yards, gardens, etc.

– Each crop, location and year can and often will be different.

10

Types of Fertilizers

Single Nutrient“Simple Fertilizers”

Multinutrient“Mixed Fertilizers or Complexes”

Fertilizers Must Always BeUsed Properly

Nutrient Contamination of Water

Nitrogen and Phosphorus:

– Needed by all plants for optimum growth and production.

– Runoff into creeks, streams, lakes can cause excessive plant growth  (eutrophication).

11

IMPAIRMENT:

•Bacteria• Water quality

does not support designated use of contact recreation.

CONCERNS:

•Nutrients (nitrogen and phosphorus)• Portions exhibit

elevated nutrient levels.

Plum Creek

Lockhart

Impairments in Texas

1,214 water bodies surveyed for the 2010 report

12

Fertilizer Analysis

15-5-10

– State Law – commercial fertilizers must have a label identifying the materials guaranteed analysis (grade)

– Guaranteed Analysis – minimum weight (%) of each nutrient contained in the fertilizer

Fertilizer Grade

15 - 5 - 10

% Nitrogen % Phosphate % Potash

(N) (P2O5) (K20)

Fertilizer Grade & Ratio

Grade: 15 - 5 - 10

Ratio: 3 : 1 : 2

13

Primary Nutrients

Nitrogen

Phosphorus

Potassium

BiologicalFixation Plant & Animal

Wastes

Ammonium

NitriteNitrate Leaching Loss

Denitrification

Nitrate Reduction

Protein

AtmosphericNitrogen

IndustrialFixation

AtmosphericFixation

The Nitrogen Cycle

NitrogenCharacteristics and Functions

Available Forms: Nitrate (NO3-), Ammonium (NH4

+)

Movement in Soil: NO3- can leach

NH4+ won’t leach

Functions in Plant: Part of Amino Acids Proteins

Part of chlorophyll molecule

14

15

Excess Nitrogen

Reduced root growth.

Excess water use.

Reduced cold tolerance

Thatch accumulation.

Disease and insect susceptibility.

Brownpatch

Nitrogen Fertilizer Sources

Inorganic, soluble sources

Inorganic slow release

Organic (slow release)

16

Soluble Nitrogen Sources

Material % N

Urea 45-0-0

Ammonium sulfate 21-0-0

Potassium nitrate 13-0-45

Slow Release Nitrogen Sources

Coated Products Reacted Products

Sulfur coated urea IBDU

Polymer coated urea Ureaformaldehyde

Polymer/sulfur Methylene Urea

coated urea Ureaform

Organic Products

Municipal biosolids Food processing by products

Composts Animal manures

Growth Response

10

8

6

4

21 2 3 4 5 6 7 8

Weeks After Fertilization

Col

or R

atin

g

17

PhosphorusCharacteristics and FunctionsAvailable Forms

Primary orthophosphate (H2PO4-)

Secondary orthophosphate (HPO42-)

Movement in Soil:Very immobile; Will not leach or volatilizeTends to accumulate/build up in soils.

Functions in Plant:Stimulates early growth & root formationHastens maturity and promotes seed production

18

Excessive Phosphorus* phosphorus induced zinc deficiency

Phosphorus Fertilizer SourcesInorganic % P2O5

Triple superphosphate (TSP) 46Monoammonium phosphate (MAP) 48Diammonium phosphate (DAP) 46

Organic

Biosolids 3 – 4Animal manures < 1 – 3Bone meal 12 - 14

PotassiumCharacteristics and Functions

Available Forms:Potassium ion (K+)

Movement in Soil: Does not leach/volatilize

Functions in Plant:Increases water use efficiencyIncreases disease resistanceImproves cold hardiness

19

Potassium Fertilizers

Grade

Source Formula (% K2O)

Potassium chloride KCl 0-0-60

Potassium sulfate K2SO4 0-0-54

Potassium nitrate KNO3 0-0-46

K Mag KMgSO4 0-0-22

Secondary Plant Nutrients

Calcium (Ca)

Magnesium (Mg)

Sulfur (S)

20

Essential Micronutrients

Zn Fe Cu Mn B Cl Mo

Needed in very small amounts

Most micronutrients come from decomposition of O.M.

Increase in soil pH decreases micronutrient availability (Except Mo and Cl)

21

Name That Deficiency?

Taking Soil Samples Soil tests are only as accurate as the

samples on which they are based.

Samples must be representative of the area to be cropped.

22

Taking Good Soil Samples Take 10-20 cores for each management area (yard,

garden, flower beds).

Place cores in clean plastic bucket, and mix thoroughly.

Put 2 pints in bag and mail immediately to laboratory.

XX

XX

X

X

XX

Xsandy spot

drainage

23

Non-Traditional Products

24

Categories of Non-Traditional Products

Soil conditioners

Soil activators (biological inoculants)

Wetting agents

Plant stimulants and growth hormones

Mineral nutrient sources used in an unconventional manner

Effects of Two Soil Activatorson Crop Yields

Fertility Soybean Peanut Corn Bermuda Rice TomatoTreatment KY LA FL OK Al KY TX UnfertilizedCheck 32 26 649 3240 80 87 1.99 2244 7775Medina 31 25 914 3493 86 87 1.95 2189 8501Supernate 32 24 599 --- 87 85 1.86 2178 7312

FertilizedCheck 31 25 1060 3463 123 127 2.31 6155 11450 Medina 32 24 814 3189 126 127 2.22 6185 10226Supernate 33 26 829 ---- 125 126 2.15 6128 11549

* Weaver et al., 1974.