Sunshine Weekly Weeder Newsletter
31 December 2015
Everyone should have their hours in the Virtual Green Binder by the end of today, Thursday 31st December. If you haven't entered them you will be charged, see website above for more information.
I have excerpted the following from aggie-horticulture.tamu.edu/vegetable/guides/texas-vegetable-growers-handbook, as it contains valuable information for any gardener. There are a selection of topics covered which generally help most gardeners. Note that the information is not exclusively for organic gardeners. As Sunshine is solely an organic garden, do not use non-organic chemical solutions.
-- V. A. Haby, Marvin L. Baker, and Sam Feagley
Soil is a habitat for plants. As such, the soil's physical, chemical, and biological properties affect plant growth. The physical properties of a soil largely determine the ways in which it can be used. The size, shape, and arrangement of the primary soil particles are known as the physical properties of soil. Other important physical properties center on these such as the size and shape of the spaces between the particle arrangements, called the pore space, which has a direct effect on the movement of air and water, the ability of the soil to supply nutrients to plants, and the amount of water available to the plant.
The proportions of the four major components of soils, inorganic particles, organic materials, water, and air, can vary greatly from place to place and with depth. The amount of water and air in a soil can also fluctuate widely from season to season. However, the physical characteristics of the solid components, inorganic and organic particles, are essentially unchanging.
Chemical properties of soils are important in that, along with their physical and biological properties, they regulate the nutrient supplies to the plant. Without these nutrients supplied by the soil or applied as inorganic fertilizers, organically by manures, and other vegetative materials, plant growth would cease.
The biological properties of the soil are dictated by the macroorganisms and microorganisms. Good physical and chemical properties supply the right environment and sufficient nutrients to the organisms for optimal biological activity. This in turn improves the soil physical and chemical properties through improved structure and nutrient cycling.
Important Definitions and Considerations
Soil Structure: The arrangement of the primary soil particles into clusters or masses called aggregates.
Primary Soil Particle: Mineral particles sizes including sand (0.05 to 2 mm), silt (0.002 to 0.05 mm), and clay (<0.002 mm.)
Soil Porosity: The ratio of the volume that is not occupied by soil particles to the bulk volume of the soil is called soil porosity. It is the degree to which the soil mass is permeated with pores or cavities.
Pore Space: The solid soil particles (minerals and organic matter) occupy about 50% of the total volume in a soil. The remaining space, the voids between the solid particles and between the aggregates, is called the pore space. The pore space is the volume occupied by water and the soil air.
Soil Air: Water and air occupy the soil pores in varying amounts. The amount and composition of the air in a soil has important direct and indirect effects on vegetable growth. Soil air differs from the atmosphere above the soil in that it usually contains 10 to 100 times as much carbon dioxide, slightly less oxygen, and is saturated with water vapor.
Soil Air Movement: Air enters and leaves the soil through cracks in the soil and through the pores at the surface of the soil. Saturation of the pores with water limits the movement of oxygen into and carbon dioxide out of the soil. This condition can occur from over-watering or from poor drainage of excess water down through the soil profile. A waterlogged condition can severely damage or kill the roots of plants. It is not the water that inflicts the injury, but the lack of oxygen. Therefore, drainage of excess water from a soil is important to vegetable growth.
Soil Water: Water moves through the pore spaces of a soil. The pore spaces are also where water is retained for plant use. Sandy soils tend to have a preponderance of large pores whereas clayey soils are much smaller. During and following the entry of rain and irrigation water, sandy soils with their larger pores, usually conduct water more rapidly than clayey soils. For that reason, sandy soils retain less water for plant use. The loam textures have the highest plant available water.
Drainage: The rate at which water moves from the root zone is known as drainage. If the soil is kept excessively wet for long periods of time, oxygen cannot reach the roots and damage can occur. Sometimes a soil layer exists in the profile that restricts the downward movement of water. In these cases drainage is slowed or stopped because a water table forms above the restricting layer.
Soil Organic Matter: Organic matter is a temporary product or a stage in a natural cycle of decay or decomposition of plant and animal residue. Soil organic matter is dynamic. It changes continually through further decomposition. The amount of organic matter affects the physical properties of soil. Organic matter acts as biological "glue" that cements individual soil particles together into aggregates. Thus, it affects soil structure and the retention and movement of water and air into, in and out of the soil. Dead plant matter provides food for microorganisms that in turn die and make a contribution to the total organic content of the soil. Some organisms such as earthworms while feeding on organic matter modify the structure of the soil and improve its porosity.
Soil Temperature: The temperature of soils varies at different depths and seasons of the year. The changes are determined by the amount of the radiant energy that reaches the soil surface and by the thermal properties of the soil. Dark soils absorb a much higher proportion of radiant energy than do light colored soils. Energy that has been absorbed is disposed of in one or more of the following ways by reradiation to the atmosphere; by heating of the air above the soil by convection; by increasing the temperature of the surface soil; or by conduction to the deeper soil layers.
Soil Crusts: Soil crusts are formed by the desiccation of a thin layer of dispersed surface soil. Such crusts frequently have considerable mechanical strength and may keep vegetable seedlings from emerging or cause injury to the stems of established plants.
Soils and Plant Roots
Of equal importance are the quantitative aspects of the soil as a habitat for plant roots. It is necessary that nutrients, air, and water are present in optimum concentrations for normal root development and plant growth. It is also necessary that enough of them be present throughout the growing season to meet plant needs.
The depth of soil available for rooting is a major physical factor that influences vegetable growth. Severe limitations are placed on the ways in which the soil can be used when the rooting volume is restricted by bedrock, cemented layers, a high water table, or other root barriers.
The effective depth of a soil is determined by the total thickness of the soil layers that can be readily penetrated by plant roots. The roots of most vegetable crops will penetrate to a depth of 3 feet or more if soil conditions permit. A desirable soil should be favorable for the reception, transmission, and storage of water to a depth of at least 42 inches. The ability of a soil to withstand drought is related to its depth and chemical composition. Plant nutrients stored in the subsoil are used by plants if roots can reach them.
There are 20 essential chemical elements (plant nutrients) known to be required for normal vegetable growth. These elements can be supplied by either organic or commercial inorganic fertilizers. Carbon, hydrogen, and oxygen from air and water, and nitrogen from organic and inorganic sources are four plant nutrients which make up 95% of plant solids. Although the atmosphere consist of 78% nitrogen as N2, this form is unavailable for plant use. However, certain bacteria that live symbiotically in nodules on the roots of legumes are able to take nitrogen from the air and fix it in a form available to plants.
The other 16 essential elements, iron, calcium, phosphorus, potassium, copper, sulfur, magnesium, manganese, zinc, boron, chlorine, molybdenum, cobalt, sodium, silicon and vanadium, are supplied to plants by the soil. With the exception of nitrogen and phosphorus, most alkaline, clay type soils usually contain enough of these elements for vegetable production. In acid sandy soils, nitrogen, phosphorus, potassium, calcium, magnesium and, at times, sulfur and boron may need to be added for successful crop production. Cobalt, sodium, silicon, and vanadium have been proven essential for only a few plants.
Iron chlorosis, a deficiency of iron in the plant, can be corrected by applying chelated iron or iron sulfate to the soil or foliage. The term chelate comes from the Greek word claw. Chelates are chemical bonds (claws) that help hold metal ions, such as iron, in solution so that plants can absorb them. Different chemicals, from relatively simple natural chelates like citrate, to more complex manufactured chemicals, can act as chelates. When a chelated metal is added to the soil, the nutrient held by the chelate will remain available to the plant longer than if the sulfate salt is applied to the soil. Most nutrients do not require the addition of a chelate to help absorption. Only a few of the metals, such as iron and zinc, benefit from the addition of chelates. The types of chelate used will depend on the nutrient needed and the soil pH. Iron is normally applied foliarly, just wetting the leaf, using a 2% iron solution. This is because the soil binds with the iron so rapidly that as much as 10 to 15 lb of iron may not meet the plant iron requirement. Zinc can be applied foliarly using a 0.5% zinc solution or applied to the soil. The chelated form works best for soil application. The sulfate or chelated form can be used for foliar application.
The word organic applied to fertilizers simply means that the nutrients contained in the product are derived solely from the remains or a byproduct of a once living organism. Urea is a synthetic organic fertilizer, an organic substance manufactured from inorganic materials. Cottonseed meal, blood meal, bone meal, hoof and horn meal, and all manures, are examples of organic fertilizers. Most of these products packaged as fertilizers will have the nutrient ratios stated on the package labels. Some organic materials, particularly composted manures, and sludge, are sold as soil conditioners. Although nutrients are present in small amounts, these products do not have a nutrient guarantee. Most contain one or more of the three major nutrients in low concentrations, although you may find some fortified with nitrogen, phosphorous or potassium for a higher analysis. In general, organic fertilizers release nutrients over a fairly long period; the potential drawback is that they may not release enough of their principal nutrient at a time to give the plant what it needs for best growth. Because organic fertilizers depend on soil organisms to mineralize and release nutrients, most of them are effective only when soil is moist and soil temperature is sufficiently warm for the soil organisms to be active.
Cottonseed meal is a byproduct of cotton production. As a fertilizer, it is somewhat acid in reaction. Formulas vary slightly, but generally contain 7% nitrogen, 3% phosphorous, and 2% potassium (Table 19 in Appendix). Nutrients in cottonseed meal are more readily available to plants in warm soils, but there is little danger of burn.
Blood meal is dried, powdered blood collected from cattle slaughterhouses. It is a rich source of nitrogen, so rich, in fact, that is may do harm if used in excess. The vegetable producer must be careful not to exceed the recommended amount suggested on the label. In addition to nitrogen, blood meal supplies some essential trace elements, including iron, as a well rounded fertilizer.
Fish emulsion, a well rounded fertilizer, is a partially decomposed blend of finely pulverized byproducts form processing fish for human consumption. No matter how little it is used, the odor is intense, but it dissipates within a day or two. Fish emulsion is high in nitrogen, and is a source of several trace elements.
Manure varies in nutrient content according to the animal source and its diet but a fertilizer ratio of 1-1-1 (as N2-P2O5-K2O) is typical. Manures are best used as soil conditioners instead of nutrient suppliers. Horse, cow, pig, chicken, and sheep manures are commonly available. The actual nutrient content varies widely. The highest concentration of nutrients is found when manures are fresh. As it is aged, leached or composted, nutrient content is changed.
Even though fresh manures have the highest amount of nutrients, vegetable producers should use composted forms of manure to ensure a lesser amount of salts, thereby reducing the chance of burning plants. Fresh manure should not be used where it will contact tender plant roots. Typical rates of manure application vary from a low 70 pounds per 1,000 sq. ft (1.5 T/A) to a moderate level of 185 pounds per 1,000 sq. ft (4.0 T/A). Rates over 345 pounds per 1,000 sq. ft (7.5 T/A) should be considered excessive for most manures. Cow manure can be applied up to 925 pounds per 1000 sq. ft (20 T/A). These rates should be applied only once every two years. These rates are based upon dry weight.
Two rules should be kept in mind when applying a fertilizer during hot weather and when soil moisture is limited:
- Do not over apply nitrogen fertilizers
- Make sure adequate moisture is present after applying fertilizers high in salts.
Plant Nutrient Deficiency Symptoms
Plants which become excessively deficient in one or more nutrients will display those deficiencies with distinctive discoloration patterns on the leaves and/or by characteristic leaf and stem distortions. However, even before these deficiency symptoms become visible, the plant can be suffering from a nutrient deficiency which is sufficiently severe to cause yield reduction. Soil testing and plant tissue analysis are two common techniques which may be used to prevent nutrient deficiencies in plants. Plant nutrients may be classed as mobile or immobile relative to the plant's reaction to nutrient deficiencies. Nitrogen, phosphorus, potassium and magnesium are considered mobile nutrients. When the soil becomes deficient in these nutrients, actively growing plants will remove them from the older leaves and mobilize them to the young, actively growing leaves. Therefore, deficiencies of these four nutrients are first observed in the older leaves.
All other nutrients are classified as immobile because they are not readily resolubilized from the older leaves and moved to the new growth. Deficiencies of these nutrients will first appear in the new growth.
From this information, if the deficiency is showing on older leaves, compare it with the symptoms described for nitrogen, phosphorus, potassium and magnesium. Deficiencies showing on new growth will be from any of the other secondary and micronutrients.
Classes & Meetings
Compost for Beginners
January 9 @ 10:00 am - 12:00 pm
Compost isn't just a pile of dead leaves! It's a vital community of microorganisms that work to add vital nutrients, moisture, and structure to your soil. Travis County Master Gardener Sheryl Williams will explain the basic science of how compost is created, what materials you can use to make compost, types of compost containers and which to choose, plus what type of compost is best for your garden. Join the tour of the Zilker Botanical Garden Compost Demonstration area to compare different types of compost systems - please dress appropriately.
Seminar is free
Zilker park entrance fee is $2 per adult, $1 per child (ages 3-12) or seniors (age 62 & over), $3 for non-Austin Residents. Cash or check accepted.
For more information contact: Texas A&M AgriLife Extension Service - Travis County,512-854-9600
What to Plant in January
Early to Mid-month: Asparagus crowns
Officer and Zone Coordinator Contacts - Sunshine Garden
- President - Jeff Monks email@example.com
- Vice President - Jim Willmann firstname.lastname@example.org
- Secretary - Shannon Posern email@example.com
- Treasurer - Caroline Limaye firstname.lastname@example.org
- Director - Michael Hall email@example.com
- Director - Kay McMurry firstname.lastname@example.org
- Director - Katy Davis email@example.com
- Zone 1, Martin Morales firstname.lastname@example.org
- Zone 2, Katy Davis email@example.com
- Zone 3, Ludmila Voskov firstname.lastname@example.org
- Zone 4, Ila Falvey email@example.com
- Zone 5, Mary Gifford firstname.lastname@example.org
- Zone 6, Charlotte Jernigan email@example.com
- Zone 7, Jing Li firstname.lastname@example.org
- Zone 8, Irina Kadukova email@example.com
- Zone 9, Kerry Howell firstname.lastname@example.org
- Zone 10, Christopher Schroder email@example.com
- Weekly Weeder Newsletter - Margaret Powis firstname.lastname@example.org
- Plant Sale - Michael Hall email@example.com
- TSBVI Liason & Volunteer Coordinator - Janet Adams jartdaht@gmailcom
- Plot Rental - Kay McMurry firstname.lastname@example.org
- Compost Coordinator - Janet Adams email@example.com
- Compost Tea - Jennifer Woertz firstname.lastname@example.org
- Education Committee - Shannon Posern email@example.com
- Carpentry & Repairs - Robert Jarry firstname.lastname@example.org
- Water Leak Repairs - Steve Schulz email@example.com
- Tools & Wheelbarrows - Bob Easter firstname.lastname@example.org
- Compost Tea - Jennifer Woertz email@example.com
- Website Coordinator - Sharon Rempert firstname.lastname@example.org
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