Are Organic Fertilizers Really Organic?

The organic movement has a foothold in the turfgrass and ornamental industry. The same industry brewing for decades in home vegetable gardens, and then with small-scale producers, has emerged as a significant market percentage for commercial landscapers. Homeowners are asking for “organic” landscape plants, organic methods of controlling pests and applications of “organic” fertilizer to their landscapes.

            Alternative methods for producing and maintaining ornamentals and turfgrass have been around for a long, long time. In the past, very few residential clients were willing to pay for the additional costa associated with the product. That may be changing thanks to local food movements and organic agriculture¹. The word “organic” has become synonymous with “wholesome” and “safe”.

            Organic has a different meaning in landscape horticulture industry. Organic can mean sources that are not synthetic or conventional. Organic amendments, such as municipal and animal sources of biosolids, can be applied to improve soil physical and chemical properties which in turn can improve turfgrass establishment rates, growth, and quality. We know, for instance, that in poor or marginal soils the incorporation of compost improves soil properties, increases soil nutrients and consequently improves plant growth. In soils with a naturally higher percentage of organic matter these improvements are less noticeable.

            Research at Colorado State University evaluated the effects of applying composted dairy manure as topdressing to Kentucky bluegrass. Researchers applied compost at the rates of 13.3, 26.6 and 40 cubic yards to the acre. Applying composted manure as topdressing to established bluegrass in 2003 through 2004 improved the soil’s physical properties and nutrient content.

Effects of Compost Topdressing on Turf Quality and Growth of Kentucky Bluegrass

            Although nothing new, the application rates are important. The two higher rates improved turfgrass overall quality and allowed the grass to retain color in the fall, early winter and green up faster in the spring. Not bad for a product that is not considered a fertilizer.

            During the hot summer months the two higher application rates produced about 50% more clippings. The researchers concluded that compost improves turf quality and shoot growth via its action as a slow-release fertilizer.

            More turfgrass clippings sound like a potential landscaper’s nightmare but there is a positive side to this “problem”.  Increased amounts of clippings in summer months helps suppress the incidence of hot weather diseases. Infected leaf blades are removed through regular mowing and mulched back into the turfgrass sward or removed from the property.

            Disease suppression by composts, composted biosolids and compost teas in vegetable crops has been documented fairly well. But research has been conducted on the suppressive effects of composts, such as biosolids, on turfgrass diseases as well, dating back 20 years or more.

            This research shows promise to “organic” gardeners by reducing the application of fungicides, synthetic fertilizers and other chemicals to home lawns. Composts show promise in controlling turf diseases such as Pythium, summer patch, brown spot, dollar spot, red thread, necrotic ring spot and others.  Reductions in the applications of pesticides such as fungicides, directly supports the “organic” movement whether it is truly organic or not.

            Researchers at Texas A and M University, from 2005 through 2008, demonstrated the benefits from composts used for soil improvement and nutrient enrichment can be transferred from the sod farm to newly established landscapes. Previous studies with sod that recycled manure-based soil amendments as topdressing indicates that 77% of the phosphorus and 47% of the nitrogen might be removed and transported in a single sod harvest.

Effects of Composted Biosolids and Nitrogen on Turfgrass Establishment, Sod Properties, and Nutrient Export at Harvest

            About one quarter of the cubic yard of composted biosolids was incorporated to rootzone depth in a cubic yard of native soil when establishing Tifway bermudagrass sod. Researchers measured that five times more nitrogen and seven times more phosphorus was available to turfgrass grown in biosolids compared to grass grown without biosolids.

            After two sod harvests, all of the nitrogen and phosphorus applied from the biosolids was removed with the sod. These nutrients were transferred, with the sod, to the landscape.

            Although not demonstrated, researchers claimed that this could result in faster establishment times and better turfgrass cover in a shorter period of time. This, of course, would reduce the amount of fertilizers needed during sod establishment. Another coup for the organic movement.

            They also found that sod established with biosolids was lighter in weight than sod grown without biosolids. Biosolids-grown sod contained more water but less native soil than sod without biosolids. This helped preserve the native soil. Less fuel is needed for transporting the sod. Organics, are you listening?

            Composts, when used as a fertilizer, releases nutrients slowly, acting like a slow-release fertilizer. When establishing turfgrass in sod farm operations, rapid turfgrass establishment is important so a rapid release of nutrients, particularly nitrogen, is needed.

            This was not going to happen with compost-amended soils. So the researchers applied either 50 or 100 pounds of nitrogen per acre at the time of sprigging (establishment) to supplement the slowly-released nutrients contained in the compost.

            Because of the application of supplemental nitrogen, the time between harvests in biosolids-amended soil plus fertilizer was reduced 60% compared to the time needed for sod grown with biosolids only.

            Similarly, other researchers reported better turf coverage and density when a two to three inch depth of compost was incorporated to a 6 inch soil depth compared to soil without compost. They attributed these responses to improvements in the soil’s physical properties such as better pore spaces, greater rooting depth and improved drainage.

            Composts can be over-applied to landscapes. This can become a serious environmental concern to surface waters such as irrigation ponds and waterways. When composts high in nutrients such as nitrogen are applied to turfgrass as topdressing, researchers have found a significant amount of nitrogen can be transported to these waterways.

            Incorporation of composts to a greater depth should reduce the amount of nutrients removed compared with topdressing. Incorporation of composts to greater depths should allow for less frequent applications as well which would save money. In addition, soil incorporation of biosolids should reduce the potential for runoff of nutrients after establishing in urban landscapes.

¹USDA “trademarked” the term “organic” into its National Organic Program in The Organic Foods Production Act of 1990. This federal act required USDA to develop national standards for organic products and was codified in 2000 (Code of Federal Regulations at 7 C.F.R. 205). So far, it has only been applied to food crops. http://www.ams.usda.gov/AMSv1.0/nop

Bob Morris, Consultant for Viragrow, Inc.

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