Horticulture 102: Soil Water and Nutrients Lecture 16

[Teresa Koenig]

Slide #: 1 Slide Title: Intro Information Slide

Title: Lecture 16 – Soil Water and Nutrients Speaker: Teresa Koenig Created by: Teresa Koenig, Kim Kidwell

Audio: [Introduction music] Slide #:2 Slide Title: Soil Water and Nutrients

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Audio: [Introduction music] Slide #: 3 Slide Title: Soil texture has two effects on soil moisture availability:

1. Size of soil pores: water is lost from the largest pores (sand) first. 2. The total amount of surface area per unit mass associated with the particles (clay has more surface area per gram).

Audio: If you remember from our last lecture we defined soil texture as a percentage by weight of sand, silt, and clay sized particles in the soil. Soil texture has two effects on soil moisture availability. The first is the size of soil pores. Water is lost from the largest pores first, and these would be the sand sized particles. Second, soil texture also affects soil moisture availability due to the total amount of surface area per unit mass associated with the particles. So for example, clay has more surface area per gram and holds water more tightly than sandy or silt particles. Slide #:4 Slide Title: Surface forces that account for the retention for water by soil particles:

1. Adhesion: the attraction of water molecules to soil particle surfaces. 2. Cohesion: the attraction of water molecules for one another

Audio: Surface forces that account for the retention of water by soil particles are adhesion and cohesion. Adhesion is the attraction of water molecules to soil particle surfaces. Cohesion is the attraction of water molecules to one another. Slide #: 5

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Slide Title: How does surface tension affect water movement in soils:

Example: clay vs. sand?

Audio: So how does surface tension affect water movement in soils. For example in a clay soil versus a sandy soil. Slide #:6 Slide Title: [no title]

The size of the particles (texture) determines the amount of water a soil can hold.

Smaller particles hold water more tightly due to smaller pore size and greater surface area.

Audio: The size of the particles or texture determines the amount of water a soil can hold. Smaller particles hold water more tightly due to smaller pore size and greater surface area. Slide #: 7 Slide Title: [no title]

Example: Water bonds stronger to clay particles than to sand particles due to the smaller pores and higher surface area in clay.

Water leaches farther in: Sandy loams > loams > clay loams

Audio: For example, Water bonds stronger to clay particles than to sand particles due to the smaller pores and higher surface area in clay. Water leaches further in sandy soils than it does in loam soils and water leaches further in loom soils than it does in clay soils. Slide #:8 Slide Title: Forms of soil water

1. Gravitational (free) water: remains in the soil only temporarily and moves down through the soil due to the force of gravity.

Runs through the soil so quickly that plants do not have an opportunity to absorb it.

Audio: There are several different forms of soil water. Gravitational or free water remains in the soil only temporarily and moves down through the soil due to the force of gravity. The problem is that gravitational water runs through the soil so quickly that plants do not have an opportunity to absorb it.

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Slide Title: [no title]

2. Available (capillary) water: Water held in small pores (spaces) between soil particles and present as films (layers) around the soil particles.

Can be absorbed by plant roots.

Audio: Available or capillary water is water held in the small pores between soil particles. It is present as a film layer around the soil particles. Available water can be absorbed by plant roots. Slide #:10 Slide Title: [no title]

3. Hygroscopic (bound, unavailable) water: is held so tightly by the soil particles, plant roots cannot extract it.

Audio: Hygroscopic is bound, unavailable water. This water is held so tightly by the soil particles that plant roots cannot extract it. Slide #: 11 Slide Title: [no title]

The strength with which water adheres to soil particles depends on the soil texture and structure.

Audio: The strength with which water adheres to soil particles depends on the soil texture and soil structure. Slide #:12 Slide Title: [no title]

1. The more sand present in the soil, the more easily water can pass through it. 2. The higher the clay percentage, the smaller the particles and pore spaces.

Audio: The more sand present in the soil, the more easily water can pass through it. The higher the clay percentage, the smaller the particles and pore space and the less easily the water can pass through it. Slide #: 13 Slide Title: [no title]

Water is held more tightly to clay than sand so less water runs through a clay type soil than a sandy soil.

Audio: Water is held more tightly to clay than sand so less water runs through a clay type soil than a sandy soil.

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Slide #:14 Slide Title: We are most concerned about water that is available to the plant:

1. Field capacity (FC): all the gravitational water has moved through the soil and the pore space is filled with only the water the soil can hold against the force of gravity.

Audio: We are most concerned about water that is available to the plant. Field capacity is when all the gravitational water has moved through the soil and the pore space is filled with only the water the soil can hold against the force of gravity. Slide #: 15 Slide Title: [no title]

Field capacity represents water present in the soil after gravitational water is removed

Audio: Field capacity represents water present in the soil after gravitational water is removed. Slide #:16 Slide Title: [no title]

2. Permanent Wilting point (PWP): Plant can no longer extract water from the soil and it begins to wilt.

Audio: The permanent wilting point (PWP) refers to the point at which the plant can no longer extract water from the soil and it begins to wilt. Slide #: 17 Slide Title: [no title]

Clay has a higher PWP because it has more hygroscopic water than the other soil types.

Smaller particles hold water more tightly than larger particles, which make it more difficult for the plant roots to absorb it.

Audio: Clay has a higher PWP because it has more hygroscopic water than the other soil types. Smaller particles hold water more tightly than larger particles, which make it more difficult for the plant roots to absorb it. Slide #:18 Slide Title: [no title]

3. Available Water (AW) = Field Capacity – Permanent Wilting Point

Audio: Field capacity minus permanent wilting point gives us the available water for the plant.

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Slide #: 19 Slide Title: [no title]

4. Saturation capacity: All pores are completely filled with water.

The saturation capacity of sand is much lower than clay.

i.e. clay soils have much more water in them than sandy soils.

Audio: When all pores are completely filled with water the soil has reached saturation. The saturation capacity of sand is much lower than clay meaning clay soils have much more water in them than sandy soils. Slide #:20 Slide Title: [no title]

Plants don’t grow well in clay soil because the high water level decreases the amount of oxygen available.

Plants (roots) need oxygen to grow

Audio: Plants don’t grow well in clay soil because the high water level decreases the amount of oxygen available. Plants including the roots need oxygen to grow. Slide #: 21 Slide Title: Salinity (Soluble Salts)

A bulk measure of soluble inorganic elements such as sodium, calcium, magnesium, chloride, sulfate and bicarbonate.

Salty soils are a problem in arid regions or in poorly drained soils

Audio: We are going to change our focus a little bit and talk about soluble salts and how these influence both the soil and plant growth. Soluble salts are a bulk measure of soluble inorganic elements such as sodium, calcium, magnesium, chloride, sulfate and bicarbonates. Salty soils are a problem in arid regions or in poorly drained soils. Slide #:22 Slide Title: [no title]

Salts originate from:  Mineral weathering  Inorganic fertilizers and manures  Irrigation waters  Other sources

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Audio: Soluble salts originate from mineral weathering, inorganic fertilizers and manures, irrigation waters and other sources Slide #: 23 Slide Title: [no title]

Salts cause “chemical drought” which is similar to water stress

Or, may be caused by specific ion toxicities (sodium, chloride)

Audio: Salts cause what we call “chemical drought” which is similar to water stress. Or, salt problems may be caused by specific ion toxicities such as sodium or chloride. Slide #:24 Slide Title: Salt problems can be solved by:

- Selecting salt tolerant vegetation - Leaching salts out of soil with clean water

Audio: Salt problems can be solved by selecting salt tolerant vegetation or leaching salts out of the soil with clean water. Slide #: 25 Slide Title: Plants vary in salt tolerance

Salt tolerant plants have developed mechanisms to tolerate or exclude salts

[scale of soil salinity with the following food sources exemplified on the scale: berries, beans, carrots, alfalfa, corn, beets, bluegrass, tall fescue, cottonwood, barley]

Audio: Plants vary in their tolerance to salt. Crops such as berries, beans, carrots, alfalfa, and corn are sensitive to soluble salts. Tall fescue, cottonwood trees and especially barely are more tolerant of high salt levels. These salt tolerant plants have developed mechanisms to tolerate or exclude salts. It is important for you to know the salt level in your soils and the general salt tolerance of your potential crops when choosing plants for your situation. Slide #:26 Slide Title: Soil fertility a. Organic matter (OM): plants obtain some of their mineral nutrient requirements and much of their nitrogen from the decomposition of organic materials such as roots, stems, leaves, and animal manure.

Audio: The last part of the lecture we will focus on soil fertility. Plants obtain some of their mineral nutrient requirements and much of their nitrogen from the decomposition of organic matter such

6 as roots, stems, leaves, and animal manure. Slide #: 27 Slide Title: Decaying OM also supports bacteria and fungi which aid in:

a. Bringing insoluble soil minerals into solution b. Improving the physical condition of the soil

Audio: Decaying organic matter also supports bacteria and fungi which aid in bringing insoluble soil minerals into solution and improving the physical condition of the soil. Slide #:28 Slide Title: b. Mineral Nutrition:

Essential elements: Plants require these to grow and develop properly. [photograph of a growing crop]

Audio: When we talk about mineral nutrition we are referring to the essential elements required for plants to grow and develop properly. Slide #: 29 Slide Title: Types of Nutrients:

1. Macronutrients: Required in largest quantities

If adequate amounts are not present, the plant will show dramatic deficiency symptoms.

Ex. Leaf chlorosis or necrosis, yellowing around leaf edges or between veins

Audio: Now we are going to look at the various types of nutrients, both macronutrients and micronutrients. Macronutrients are required in the largest quantities. If adequate amounts are not present, the plant will show dramatic deficiency symptoms. Examples of plant deficiency symptoms are leaf chlorosis, necrosis, or yellowing around leaf edges or between veins. This yellowing between the veins is referred to as interveinal chlorosis.

Slide #:30 Slide Title: a. Primary Macronutrients: N, P, and K

1. Referred to as primary because they are most frequently found to be deficient 2. Primary components of most fertilizers

Audio: The primary macronutrients are nitrogen, phosphorus and potassium. These are referred to as primary because they are most frequently found to be deficient and they are the primary components of most fertilizers.

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Slide #: 31 Slide Title: b. Secondary Macronutrients: Ca, Mg and S.

May also be required in quantities nearly as great as N, P, and K; Soils are not found to be deficient in these elements as often as they are for the primary nutrients.

Audio: Secondary macronutrients are calcium, magnesium, and sulfur. These nutrients may also be required in quantities nearly as great as nitrogen, phosphorus and potassium. However, soils are not found to be deficient in these elements as often as they are for the primary nutrients. Slide #:32 Slide Title: 2. Micronutrients:

Required in small quantities

If adequate amounts are not present, the plant will show deficiency symptoms.

Ex. Leaf chlorosis or necrosis, yellowing around leaf edges, or between veins

Audio: Micronutrients are required in small quantities. If adequate amounts are not present, the plant will show deficiency symptoms. These symptoms may be leaf chlorosis or necrosis, yellowing around leaf edges, or between veins. Depending on the specific nutrient deficiency, the symptoms might occur on older leaves or newly developed leaves. Slide #: 33 Slide Title: a. List of micronutrients

Molybdenum (Mo) Boron (B) Copper (Cu) Iron (Fe) Manganese (Mn) Zinc (Zn) Chorine (Cl)

Audio: The plant micronutrients are Molybdenum, Boron, Copper, Iron, Manganese, Zinc, and Chorine. Slide #:34 Slide Title: Sources of Nutrients

 Inorganic fertilizers  Manures, composts, and other organic materials/fertilizers  Green manures (legumes and others) o Peas, vetch, rye, oats, wheat, barley

Audio:

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Potential sources of plant nutrients are inorganic fertilizers, manures, composts, and other organic materials/fertilizers and green manures. Examples of green manures are crops such as peas, vetch, rye, oats, wheat, barley. Green manure crops are commonly nitrogen fixing legumes. Slide #: 35 Slide Title: Types of Fertilizers

 Chemical fertilizers  Organic fertilizers (bone meal, compost, manure, etc.)  Green manures

Audio: Chemical or synthetic organic, such as bone meals, compost and green manures are potential types of fertilizers. Slide #:36 Slide Title: Fertilizer label and “grade”

3 numbers always appear on the label to describe the fertilizer content

The numbers refer to: % Nitrogen (N) %Phosphorus (P2O5) %Potassium (K2O)

Audio: 3 numbers always appear on the label to describe the fertilizer content. The numbers refer to percent nitrogen, percent phosphorus as P2O5, percent potassium and K2O. Slide #: 37 Slide Title: How Much Fertilizer do I Need to Apply?

Estimate the amount of fertilizer needed based on soil test results, crop needs, and area to receive fertilizer.

Most fertilizer recommendations are in pounds per 1000 square feet, or pounds per acre.

Audio: When determining the amount of fertilizer needed, estimate the amount based on soil test results, crop needs, and area to receive fertilizer. Most fertilizer recommendations are in pounds per 1000 square feet, or pounds per acre. Slide #:38 Slide Title: Organic Nutrient Sources

 Much lower concentrations of nutrients o Example: 2-2-2 for composts  Good sources of organic matter  Much high rates of application needed than inorganic fertilizers (10 to 50 times higher)  Slow release materials (and unpredictable)

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 May need to supplement with inorganic nitrogen fertilizer

Audio:  Organic nutrient sources contain much lower concentrations of nutrients. For example, 2- 2-2 for many composts. And those three numbers are nitrogen, phosphorus and potassium. They are good sources of organic matter but require much high rates of application needed than inorganic fertilizers, sometimes 10 to 50 times higher. They are slow release materials which can be unpredictable and may need to be supplemented with inorganic nitrogen fertilizer.

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