Issue No. 3, Article 8/April 23, 2010
Are These Products the Real Deal?
This spring I have been answering questions from farmers who want to use the very best products available in the market to ensure good crop yields. The most common question is, Do they work? Typical promotional claims are that a product replaces commercial fertilizer, makes nutrients in the soil more available, costs less than traditional fertilizers, supplies micronutrients, or is "natural." While some of the claims may be true for some products, more often they are untrue, or at best partially true.
The first important distinction to make is that, in general, soil additives are not fertilizers; they have little or no nutrient content, and they do not display guaranteed analysis labels as do fertilizers (e.g., 10-34-0). Those promoting soil additives typically use testimonials from farmers and present data from suspect sources, showing either a substantial increase in yield or a small (2 to 4 bushel/acre) increase.
When high yields are being advertised, remind yourself: You get what you pay for. I would ask myself, If a product is capable of producing such yield increases, why is so inexpensive? And if the yield increase is only a few bushels, it is within the inherent variability of most field studies--you can't be sure the additive was responsible.
The types of products being advertised fall into three broad categories: soil activators, wetting agents or surfactants, and soil conditioners.
Soil activators. Some products are said to introduce beneficial organisms or stimulate existing soil microbes. While these so-called soil activators might increase microbial activity, their effect compared to that of what is already present in the soil can be considered a drop in the bucket that does not translate into improved yield.
Wetting agents or surfactants. These products are successfully used to improve the surface coverage of insecticides and herbicides by reducing water surface tension. However, there is no basis for using them to improve water infiltration and retention in the soil or to loosen compacted soil.
Soil conditioners. These materials are designed to improve the physical condition of the soil and thus enhance aeration, root growth, and water infiltration and retention. Products in this category are being advertised heavily this year, a result of the fact that many fields received substantial compaction during last year's wet planting and harvesting seasons. Products in this category typically contain humates and humic acid, or some other type of organic material mixed with inorganic elements such as rock phosphate, limestone, or other mined mineral that has been ground.
One soil amendment receiving heavy attention this year is gypsum, or calcium sulfate (CaSO4). Most gypsum sold as a soil amendment has about 22% calcium and 17% sulfur by weight. Much of the gypsum available in Illinois comes from power plants or is a byproduct of other industrial activities. Depending on the source, gypsum can have many trace metals and impurities. This material is sometimes confused with limestone (CaCO3). That can be a serious mistake since gypsum does not react with hydrogen ions (H+), and thus it makes no change in soil acidity like limestone does. Gypsum is moderately soluble; when dissolved in water it produces calcium ions (Ca2+) that interact with the exchange sites of the soil and sulfate ions (SO42-) that stay dissolved in soil water. The value of gypsum as a fertilizer in Illinois is related to sulfur, if sulfur is deficient in a particular field. Calcium, while an important nutrient, is not limiting in Illinois.
Since gypsum has calcium, which is a divalent cation (two positive charges), it can help improve soil structure. In essence, a calcium ion can hold two negatively charged soil particles by magnetic (electrostatic) attraction. On the other hand, monovalent cations (one positive charge) cannot help improve soil structure. In the case of sodium (Na+) that has a large ionic size, the presence of excess sodium can actually degrade soil structure. In places where this is a problem, such as dry areas in the western U.S. where crops are irrigated, gypsum is often used as a source of calcium that can displace sodium ions out of the soil exchange sites. Once sodium and other salts are removed from the exchange site, the soil can be flushed with water. This works well in soils with good permeability in the subsoil because the water can move sodium and other salts below the rooting zone. Soils in Illinois do not have sodium problems, so applying gypsum is very unlikely to significantly improve structure or permeability of the soil. Organic matter, which also acts as a "glue" to keep soil particles attached, is a very important component of good soil structure. Soils in Illinois generally have good organic matter content, which likely plays a much more important role in soil structure than additions of gypsum would. Even if gypsum helps improve structure and permeability, it is not going to magically relieve heavy compaction created by equipment. And the tendency is to think that if a little gypsum helps some, a lot would help more; this can be a problem because a large application of calcium could displace important nutrients, such as potassium K+, out of the soil exchange sites, which would then be leached out of the soil. In brief, I do not recommend using gypsum as a way to relieve soil compaction.
The best approach to take with new products is caution. If the product is claimed to make nutrients more available in the soil, ask yourself this: If the product increases the availability of a particular nutrient, how is it possible to increase yields (as is being advertised) in a field where that nutrient is already present in ample quantities?
Another point to consider is whether you have problems with this nutrient in your field: have you seen micronutrient deficiencies? More often than not you will find that you do not need the product; if you do discover that you are lacking in a particular nutrient, it is better to invest in products that have been proven over time. The people promoting new products are well versed in sales techniques and can be very persuasive. If you become convinced that you really need a product, or you are simply curious to find out how well it works, take a conservative approach; apply it only on an experimental basis so you can be your own judge. The extension specialists at the University of Illinois are ready to provide guidelines on how to set up an experimental trial and to give unbiased advice when asked about new products.
An additional resource that may be useful is the Compendium of Research Reports on Use of Non-traditional Materials for Crop Production. This electronic compendium contains abstracts, data, and reports on a number of nontraditional products marketed for use in crop production in the north-central region of the U.S. that have been tested by scientists in state agricultural experiment stations. Not all products (especially those that are only newly advertised) are included. However, be aware that often a seemingly new product is an old product with a new name; where that is the case, research may already be available. You can search for products by name or for types of product (surfactants, foliar additives, seed coatings, wetting agents, microbial enhancers, etc.). The compendium is provided by the North Central Region NCR-103 committee on nontraditional soil amendments and growth stimulants; it can be accessed for free.--Fabián G. Fernández