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Fertilizers

Michael Rowell

Fertilizers

“a fertilizer is a plant food”

Make plants grow bigger & betterCorrect deficiencies in plant diet

Do not get confused: Plants and animals feed differently

Some important differencesAnimal (“grandson”)

• Eat complex foods which are broken down into smaller units and reassembled into new products

• Move about to find food.

• Selective uptake of food due to 4 senses.

• High body temperature to aid in digestion, growth and mobility.

• Produce high amounts of waste as solid, liquid, gases (carbon dioxide) and heat.

• Grown from “within” have specialized organs.

• Reproduce sexually to make a small replica.

• Life cycle extends over many years.

Plant (“ Joe Tomato”)

• Use carbon dioxide, water & minerals and build them into complex things using sun’s energy

• Not mobile; “rooted” to the spot

• Mainly unselective uptake of food.

• Grow at prevailing temperature thus have variable growth rate and often need dormant periods.

• Produce small amounts of waste mainly as oxygen, water and leakage from roots

• Grow from tips of shoot & roots (meristems)

• Reproduce sexually by seed or vegetatively

• Variable life cycles; annual, biennial & perennial

How a plant works

The Leaf: Green in colour and with holes (stomata) on the surface let air in and water out. More pores on lower than upper surface to reduce water loss.

Photosynthesis:Green pigments intercept sun light and capture energy to break water molecules into hydrogen and oxygen; release most of the oxygen. Chemical “power” stored as bound hydrogen and special phosphates. Carbon, hydrogen & oxygen react with minerals to make all the things plant needs to grow.

Flower & seeds

Stem for support &

transport of water and nutrients

Root for support & uptake of water and minerals

Helper microbes

Plants with different life cycles may feed differently

• Annual– Germinate, grow, flower, fruit and seed in one year

Grains, peas, beans, & corn

• Biennial– Year 1: Germinate, grow then rest & conserve

nutrients maybe underground (things we harvest)– Year 2: Produce flowers and seed

Carrot, cabbage, beet, celery etc

• Perennial– Grow, flower and fruit each year over many years of life Asparagus,

rhubarb, cranberry, raspberries, & apples

What Types of Food Do Plants Need?

Needed in Large AmountsCarbon (from carbon dioxide in the air) Hydrogen & oxygen (largely water from the soil).Major Nutrients: [essential & often in short supply] Nitrogen, Potassium & PhosphorusMacro Nutrients: [essential but not so often in short supply] Sulphur, Calcium and Magnesium

Needed in Small AmountsMicronutrients: Iron, Copper, Manganese, Zinc, Boron, Molybdenum & NickelBeneficial in small amounts but often not sure why: Sodium, Chlorine,

Selenium, Chromium, Cobalt & Silicon

What things are detrimental?

• “Heavy metals” such as lead, mercury, cadmium

• Aluminum in very acidic soils

• Essential food elements in too large amounts

• High sodium in saline soils

• Acid or alkaline soils where nutrient elements may become toxic while others unavailable for plant growth

Veggies from the farmer’s market or my garden taste better than from the supermarket.

If that is true, does it have anything to do with fertilizers?

But, plant roots are unable to tell the origin of the nutrients they take up.

Some possible reasons for better taste & nutritional value

– Commercial plant varieties are developed for: • rapid growth • high yield • disease resistance• transportability• cosmetic appearance

• all possibly detrimental to taste and nutritional value

Some more reasons

– Supermarket produce is often harvested too early to avoid spoilage in transit. The result is hard pears, tasteless strawberries, unripe tomatoes etc.

– “Factory farming” pushes high yield/low cost through high water uptake, irrigation with water of perhaps poor quality, and unbalanced nutrient supply by using synthetic fertilizers of specific nutrient content.

Organic farming probably supplies a better balanced nutrition for plants by providing

nutrients in the correct amount at the right time

Fertilizer Timeline

Horses, oxen and other “beasts of burden” produced vast amounts of manure that were used in farming.

Advances in understanding composting lead to better use of animal manures.

Von Liebig stated that plants grew by using carbon dioxide from the air and by taking up minerals through the roots. The mineral that was in the relatively shortest supply limited the growth of the plant. This better understanding of plant nutrition lead to exploitation of many natural deposits as fertilizers (nitrates, phosphates, potash, guano from seabirds & bats).

Industrial by-products were found to be valuable fertilizers (basic slag, tannery & slaughterhouse wastes).

A synthetic fertilizer industry developed that produced products that were of superior value to previous natural products (super phosphate; urea, ammonia & ammonium nitrate from nitrogen and natural gas).

Environmental concern over pollutants and residues from manufactured fertilizers lead to increased use of “organic” or “green” products.

Types of Fertilizers

• Organic Fertilizers [derived from once living things]

– Animal manures (steer, sheep, chicken, horse etc.)

– Composted materials (mushroom, animal or garden origin)

– Animal by-products (bone and fish meal, dried blood, sewage sludge)

– Plant products (alfalfa, kelp, corn & cottonseed meals; seaweed)

Types of Fertilizers

• Inorganic Fertilizers [were never alive]

– Natural • (rock phosphate, green sand, guano, Chile

saltpetre, potash, gypsum, lime, shells.)

– Synthetic • (urea, ammonium nitrate, super phosphate,

anhydrous ammonia, coated pellets like osmocote.)

Types of Fertilizers

• Soil Conditioners or Amendments[do other things than just adding nutrients]

• Lime• Gypsum• Farmyard Manures• Sulphur• Composts

Shapes, Sizes and Forms

• Pellets– Single compound– Blended mixtures

• Slow-release granules, spikes

• Soluble Powders

• Ground Organic Products

Numbers on the Bag

Concentrated fertilizers have to be labelled to show the amount of different nutrients

However it is confusing!!The first three numbers refer to the % amount of nitrogen,

phosphorus & potassium

Nitrogen is OK but the actual amount of phosphorus is only

44% of its number & potassium is only 83% of its!

Thus 10-15-19 is actually closer to

10-7-16

Fortunately all the amounts of micronutrients like iron, copper and boron are expressed as their real percentages

Most packaged organic fertilizer give a list of the ingredients though many synthetic products do not

Examples of “Green” Inorganic Products

• Green Sand– A mineral mined from ancient marine deposits– Rich in potassium, magnesium and Iron– Slow release source of other micronutrients– May improve moisture holding if contains clay

• Dolomite Lime– Naturally occurring mineral deposit– Contains calcium & magnesium carbonates– Used to correct soil acidity– Slow release of calcium & magnesium

Examples of “Green” Organic Fertilizers

• Alfalfa Meal– Approximately 3-1-2 – Good source of nitrogen & potassium– Nutrients released over 3-4 months

• Kelp Meal– Made from seaweed, 1-0-2, a useful source

of potassium– Also rich in iron, copper, boron and other

micronutrients– Major nutrients released more rapidly than

alfalfa meal

Plants can’t move, you have to place the food where they can get it

• Mix it into the soil [incorporation]– Often done before seeding, even the previous year

• Scatter it over the surface [broadcast]– Less efficient; better if you mix it into the surface

• Place it in between plant rows on surface [side dress]– Get it to roots by rainfall or watering

Plants can’t move, you have to place the food where they can get it

• Place it to one side of the seed or roots [band]– More often done with special equipment in commercial farming

• Water it onto the soil [fertigate]– Watering can , drip irrigation, special hose pipe attachments

• Water it over the plants [foliar feed]– Not efficient for general feeding but might be used to correct a

nutrient deficiency quickly

Salts and pH

• Plants do not grow well if the soil is salty– Inorganic fertilizers can add soluble salts– Organic fertilizers are less of a problem– Slow release fertilizers add salts more slowly

• Plants tend to grow best between slightly acid and alkaline conditions.– At extreme acidity or alkalinity growth processes are

impeded and nutrients may become less available or present in too high amounts

– Lime is needed to correct acidity

Summary Looks around you; plants grow on most soils without intervention. Look around you, plants grow on most soils. However, growth is limited by the

nutrient in the relatively shortest supply. Plants grow better if you add fertilizers. Unlike animals, plants make all their material needs without complex supplements. Make up your own mind which type of fertilizers you want to use. Organic fertilizers release nutrients more slowly than inorganic ones. With all fertilizers several small applications are more efficient than one large one. Plants can’t move; place fertilizers where the plant can get to it. If you are buying a fertilizer make sure you read the label carefully. Many organic

fertilizers may boost their nutrient content by adding inorganic compounds that you may not want to use.

Plant roots withdraw simple minerals from the soil for growth and have a limited ability to take up large molecules.

Be wary of claims of big benefits due to things like live microbes, enzymes, vitamins, hormones and humates.

Live microorganisms in products are unlikely to survive long in the soil.