From klier@cobra.uni.edu Thu Jun 16 23:33:43 EDT 1994 Article: 35611 of rec.gardens Path: bigblue.oit.unc.edu!concert!gatech!howland.reston.ans.net!vixen.cso.uiuc.edu!newsrelay.iastate.edu!cobra.uni.edu!klier From: klier@cobra.uni.edu Newsgroups: rec.gardens Subject: Fertilizer FAQ Message-ID: <1994Jun15.173345.28688@cobra.uni.edu> Date: 15 Jun 94 17:33:45 -0500 Organization: University of Northern Iowa Lines: 487
>From the rec.gardens archives at sunsite.unc.edu (use gopher or telnet, look under sustainable agriculture)
FERTILIZER FAQL
Initial writing by Kay Klier, using materials from a wide variety of sources. Primarily written from the point of view of NPK. Needs work on using green manures and cover crops as nutrient sources, since I mainly use them to add organic matter.
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Fertilizers are materials that contain appreciable amounts of plant nutrients. Probably the most familiar categories of fertilizer are "chemical" vs. "organic": these could better be termed synthetic vs. natural.
The synthetic fertilizers consist almost entirely of nitrogen, potassium and phosphorus (the three nutrients most likely to be in short enough supply to limit growth), in forms that are readily utilized by plants. In contrast, the natural fertilizers are more likely to have significant amounts of micronutrients (trace minerals) and the macronutrients are likely to be in forms that are not as readily absorbed-- they are in forms that must first be metabolized by soil microorganisms before they are available to plants. There may also be significant bulk: useful for tilth improvement.
Thus the synthetic fertilizers are "fast", while the natural fertilizers tend to be more "time release". Some people feel that synthetic fertilizers "poison" the soil, and will not use them in any instance; others feel that synthetics are perfectly acceptable if used properly.
Synthetic fertilizers can be one of the major sources of groundwater pollution (as can runoff from manure piles): the nitrogen is in such a soluble form that it tends to leach from the point of application. Overfertilization of natural bodies of water tends to lead to algal blooms and subsequent death of fish from oxygen depletion. High nitrate levels in drinking water can cause reduction in oxygen carrying capacity in red blood cells. Reduced oxygen levels can cause retardation in young children and fetuses. If you apply a highly soluble fertilizer, please use it thoughtfully.
II. PLANT NUTRIENTS
Besides carbon, hydrogen and oxygen, the essential minerals for most plants are: Chemical Element Symbol Available form:
It is relatively rare for soils to be deficient in copper, zinc, molybdenum or chlorine. If needed, the micronutrients plus magnesium are often applied as a chelated mixture. Sequestrene is a common US brand.
III. WHAT IS A COMPLETE FORMULA FOR PLANTS?
Different plants require different proportions of nutrients, but you can get some idea of the general requirements by looking at one of the commonly used research formulations: Knop's solution with Nitsch's micronutrients. This will support hydroponic growth: (soil-less culture)
IV. NUMBERS ON THE FERTILIZER SACK
The three numbers on a commercial fertilizer bag are in the order NPK: nitrogen, phosphorus, potassium (=kalium). The actual numbers are percentages: 20-20-20 fertilizer is 20% (by weight) nitrogen, 20% phosphorus, 20% potassium.
When choosing a fertilizer formulation, choose a balanced fertilizer for most purposes, one in which the three numbers are approximately equal. If you wish to favor growth of leaves over flowers (for instance for a leafy vegetable crop, or a lawn, choose a fertilizer with a higher first number; for flowers or fruits, choose a higher middle number, for better root growth, choose a higher last number. NPK: leaves: flowers: roots
V. CALCULATING AMOUNTS TO APPLY
Typically, a soil test will tell you that X pounds per thousand square feet will be required for a certain level of productivity (those who are fortunate enough to think metric can use appropriate units). As an example, consider someone who has just gotten a recommendation to apply 3 lbs of N per thousand square feet, in a divided (spring and fall) application. Our hapless homeowners wish to get their money's worth from the new mower he purchased for their 20,000 sq ft bluegrass lawn.
To determine how many square feet a bag of fertilizer will cover at 1 lb per 1000 sq ft, multiply the weight of the bag by the percentage nitrogen on the label, then multiply by 1000. Assume this 30-1-1 fertilizer is sold in 40 lb sacks. One bag will cover 40 * .30 * 1000 = 12,000 sq ft at that rate.. But since we want 3 lbs N per 1000 sq ft, one sack will cover 4,000 sq ft, and our homeowners will buy 5 sacks of fertilizer (20,000sq ft/(4,000 sq ft/sack)) and use 3 sacks in the spring and 2 in the fall...
Quickly absorbed fertilizers should be applied only when a plant is about to begin a growth spurt, or during heavy growth. You should not fertilize heavily just before a plant will be going into dormancy (this may keep the plant from "hardening off" properly, and can result in winter damage. If you choose to use "high management" on a plant (heavy fertilization), you should also count on increasing water to the plant. If you anticipate major insect damage (perhaps a hatch of grasshoppers), decrease fertilization: tender plant tissues are more subject to damage than tissues that grew more slowly. In general, a _slightly_ "hungry" plant is more resistant to pests and diseases than an overfed one.
Overfeeding can also result in salts building up in the soil. The salt build-up decreases the water potential of the soil, and can actually reach the point that a plant cannot extract enough water from a moist but salinized soil. These soils must be "cured" by leaching with tremendous amounts of water.
Although a "proper" fertilization regime would include soil and plant analyses, most of us guesstimate fertilizer requirements. A cautious approach to guesstimation is to observe the plants for nutrient deficiency symptoms (you'll need to compare to photos often found in basic agronomy, horticulture or botany texts). If any are suspected, apply a weak fertilizer and observe for increased growth. If this is observed, you can repeat the application. Stop as soon as any signs of overfertilization (weak, floppy growth, all leaves and no flowers, salt burned leaves) are observed.
Slow release fertilizers can be applied at almost any time, and there is relatively little danger of "burning" the plants. Notable exceptions are urine or fresh manures, which can be very high N. Composted manures are less "lively".
A. COMMERCIAL FORMULATIONS
Because these generally have lower analyses than commercial fertilizers, generally much larger quantities are applied. This has the advantage of improving soil tilth by adding organic matter, and these generally require no additional micronutrient correction. You can also get a fair amount of exercise spreading and digging in a natural fertilizer. Another common way to use these fertilizers is as a "tea", an infusion of (for instance) manure in water. Water is added to a container of manure, the contents stirred and allowed to settle, then the water siphoned off for use, often on potted plants. Additional water can be added and the process repeated.
VIII. FERTILITIES VS. SOIL AMENDMENTS
Natural fertilizers are often used not just for their nutritive value, but to improve soil tilth. Commercial fertilizers are generally not useful for tilth improvement. However, other soil amendments, like gypsum or agricultural lime, affect the availability of soil nutrients by their effect on soil pH.
IX. APPROXIMATE ANALYSES OF COMMONLY AVAILABLE NATURAL FERTILIZERS AND SOIL AMENDMENTS.
A. SEED MEALS
B. MANURES
D. STEM AND LEAF PRODUCTS
X. EXPERIENCES WITH VARIOUS FORMULATIONS
Newsgroups: rec.gardens,misc.rural From: ron@mlfarm.com (Ronald Florence) Subject: Re: Fertilizer FAQ Date: Tue, 17 Aug 1993 13:51:14 GMT
klier@iscsvax.uni.edu writes:
Besides carbon, hydrogen and oxygen, the essential minerals for most plants are: Chemical Element Symbol Available form:
SECONDARY
MICRONUTRIENTS
The FAQ was clearly intended for rec.gardens, and not for misc.rural, but it might be useful to add that boron is an important element in assuring growth of forage legumes like alfalfa and ladino clover.
One other mineral which can be important to the health of animals fed on forage is selenium. The soils in many areas of the United States are low in selenium; animals raised on hay or pasture from these soils can suffer from selenium/vitamin-E defficiency (White Muscle Disease), a chronic muscular dystrophy that ultimately affects the heart muscles. The condition can be relieved by injections of vitamin-E and selenium, or by diet supplements. I don't know whether selenium can be added to deficient soils.