Organic Fertilizers: Of Trends, Science and Chickens

Trends are fascinating and exhilarating phenomena. They allow pundits the opportunity to pontificate upon things which may never happen but are nonetheless given great credence due to the expertise of the pontificator. Trends tend to focus on the minutia of a far greater whole, and more likely than not are short-lived. Trends are fun to watch and a delight to participate in. Trends define goals and give us hope to better ourselves and our communities. We want to become a trendsetter due to its elitism and social stature. We want to follow trendsetters because there's safety in numbers. But lurking in the hallowed halls of this intermittent euphoria lays danger. Nothing can disappear quicker than Elvis Presley sideburns then to follow a trend and ignore the science behind it.

2010 promises to promote trends in: Sustainability; Frugality; "Blue Gold"; "Water Wars"; Edible Urbanism, and Walkable Neighborhoods. Making a reappearance, if not resurgence, from previous years will be anything that's organic. We all know that organic is both good and better - our moms told us so. So do the vendors hawking organic anything in the hallowed passageways of our conventions and seminars. This is especially true of fertilizers, and we are being led to believe that if it is organic it is superior to chemical fertilizers. But as it relates to organics, specifically in fertilizer, just because it came out of the end of a chicken does not make it more environmentally efficient or friendly.

Fertilizers and fertilization are arguably the most misunderstood component of landscape architectural specifications in landscape notes, and in landscape maintenance specifications and implementation. While there are a plethora of components to understanding and writing specificity for fertilizers (e.g. soil pH, Cation Exchange Capacity, percent of organic matter, estimated nitrogen release, analysis versus ratio, derivations of elements, runoff probabilities, and much, much more) the focus here is directed to the mathematics and science of fertilizers as it relates to organic components. Specifying fertilizers and applying them is a great matter of mathematics.

In order for something to be labeled organic it must contain the molecule of carbon. If it has carbon it is organic. Plants need at least 15 different elements for their growth processes. They require large quantities of carbon, hydrogen, and oxygen, which they obtain from the air and water. Nitrogen, potassium, phosphorus, calcium, magnesium, and sulfur also are used in considerable quantity by a plant. These elements may not be present in sufficient supply or in the proper form. For example, air is 4/5 nitrogen gas, but only the clovers and similar leguminous plants with nodule bacteria in their roots can use it. All other plants must have nitrogen in combined form such as is found in nitrate salts, ammoniacal salts, and certain other fertilizer materials. Additionally, there is a group of elements (referred to as micro elements) iron, copper, manganese, zinc, boron, and molybdenum that are all essential for normal plant growth. Whenever any element is in short supply for plant growth, it must be furnished by some type of fertilization.

The derivation of organic compounds most often are associated with natural organics and include: cottonseed meal; castor pomace; hoof meal; dry fish scraps; activated sewage sludge; bone meal; hull meals, and garbage tankage. Animal manures are used primarily for their soil-conditioning value, and only secondarily for their plant food content. Typical examples of animal manure include horse, cow, sheep, and chicken. About 4 pounds of fresh manure equals one pound of dry fertilizer. Following are the nutrient breakdowns of nitrogen, phosphorus, and potash for the aforementioned animal manures:

You will note that chicken manure has a very rapid rate of nitrogen availability, and can "burn" a landscape if applied at the proper rate.

All plant species require a certain amount of fertilizer to be applied per 1000 ft.² to correct deficiencies or for optimum performance. As an example, warm season grasses may typically call for 4 pounds of nitrogen to be applied annually per 1000 ft.² of area. The application problem becomes how much actual fertilizer should be applied on 1000 ft.² to ensure that 1 pound of actual nitrogen is applied. The answer is to divide the first number on the bag of fertilizer into 100. The answer gives you how many pounds of that actual fertilizer must be applied on 1000 ft.² to ensure that 1 pound of actual nitrogen has been applied. As an example, let's take the fertilizer analysis 6-6-6. If you divide the first number (which represents the pounds of nitrogen in 100 pounds of fertilizer) into 100, the answer is 17 pounds. So, 17 pounds of the 6-6-6 fertilizer must be evenly distributed on 1000 ft.² of turfgrass to apply 1 pound of actual nitrogen. If you want to apply four pounds of actual nitrogen, then 68 pounds of actual fertilizer must be applied on 1000 ft.² to give you 4 pounds of actual nitrogen. Naturally, you would not want to apply that much fertilizer at one time, and practically it would be almost impossible to do so. Applying 15 pounds of actual fertilizer to 1000 ft.² is indeed a remarkable accomplishment. But the take-home lesson is that if you were going to apply processed organic manure, say cow manure, (which contains 4 pounds of nitrogen), you would have to apply 25 pounds of this fertilizer to achieve 1 pound of actual nitrogen.

The fertilizer analysis is the weight representation of nitrogen, phosphorus, and potassium found in the material which you are applying. 6-6-6 is an example of a fertilizer analysis. The mathematical relationship of the fertilizer analysis is known as the fertilizer ratio. The ratio of the 6-6-6 analysis fertilizer is 1-1-1. Which means that if you apply 1 pound of nitrogen you are also applying, by default (like it or not), 1 pound of potassium and 1 pound of phosphorus. In the example of the cow manure, which has an analysis of 4-1-3, if you apply 25 pounds of actual fertilizer material you would only be applying about one 1/4 pound of phosphorus and 3/4 pound of potassium. Typically, this would not nearly be sufficient amounts to correct deficiencies of phosphorus or potassium in soils.

Organic fertilizers are considered natural and more environmentally friendly; however, defining the benefits of natural versus manufactured fertilizer components and derivatives becomes a rapidly moving and elusive target. Whether a fertilizer is natural or manufactured it must go through a chemical conversion process in soils to become available to plants. A natural fertilizer is thought of as a slow release fertilizer and therefore embraces the vision of low run-off probabilities. But slow release and run-off are not necessarily linked at the hip. A slow release fertilizer, natural or manufactured, can be applied to a slope where runoff is likely to occur during heavy rainfall or irrigation pressures. A manufactured, organic fertilizer can release exponentially slower than a natural fertilizer. A classic example is the fertilizer Milorganite (a 6-2-0 analysis fertilizer from the acronym Milwaukee organic nitrogen). Everybody recognizes this fertilizer as organic, safe, and slow release. The organic part is correct as it is processed sewage from the good people of the City of Milwaukee, Wisconsin. The safe part is negated by the warning not to use it on edible crops, and the slow part (as in slow-release) is accurate when compared with other organic fertilizers. However, a manufactured organic nitrogen fertilizer, ureaformaldehyde (UF, 36-0-0), is approximately 6 times "stronger" than Milorganite, is safer to use, and 2/3 of it releases as slow as or slower than Milorganite. Further, Milorganite takes approximately 16 pounds of material applied on 1000 ft.² to equal 1 pound of actual nitrogen whereas UF takes only 3 pounds to equal 1 pound of actual nitrogen. When it comes to run-off issues, 3 pounds is more desirable than 16 pounds applied on 1000 ft.². Another way to look at this issue of run-off, or for that matter groundwater contamination, is that it would take over 700 pounds per acre of Milorganite to accomplish what 132 pounds per acre of UF would accomplish.

The issue of the remaining elements needed for proper plant performance is seldom, if ever addressed in terms of organic, yet run-off from the nutrient phosphorus is a looming problem in our environment. Potassium leeches as readily as or more readily than water insoluble organic nitrogen, yet the only method to produce slow release potassium is to coat it with, as an example, sulfur. Phosphorus and potassium from natural sources, such as chicken manure, leach as quickly as if chemically processed from sulfate of potash or from ammonium phosphate, yet the latter chemically processed nutrients are applied at far less a rate of application than their organic counterparts.

There is also the issue of odoriferous assaults on the senses of our urban end users checking the bottom of their shoes as they trespass through our urban landscapes. Organic fertilizers applied at proper rates also attract undesirable wildlife - not an oxymoron when applied to the damage done by these creatures when foraging into turfgrass and landscape ornamental beds in search of the organic sources. The negative byproducts of organic fertilizers, including nauseous smells and uninvited wildlife, can remain for weeks in a landscape setting.

Before signing onto the trend of using organic fertilizers and specifying them in your landscape notes, look into the research-back data, science, and mathematics of fertilizers and fertilization. Understand and realize that the successful and environmentally friendly approach to fertilization includes applying the right material at the right time, in the right manner, and at the right rate.

Joe Samnik is a consulting arborist with Expert Tree Consultants and is entering his 40th year of private practice. He is an approved LA CES educational Provider.