Better Landscaping Today Newsletter

Volume 3, Issue 6 June 2000

RESEARCH EXPLAINS WHY ORGANIC AMENDMENTS CAN SOMETIMES BE TOXIC TO TRANSPLANTS - NEED IS SHOWN FOR BETTER SOIL MANAGEMENT

Inconsistent results in the use of compost to amend soils was the subject of a report from Israel . Yoram Avnimelech, Avraham Cohen and Dan Shkedi from the Faculty of Agricultural Engineering in Haifa Israel reported their results of plant growth in the September 1990 issue of SOIL TECHNOLOGY. In some cases compost caused definite improvement in soil properties and plant growth, but in other cases, no positive results were found. The goals of the study were to find the causes, to predict the response and to determine optimal application methods.

They found that very low amounts of organic amendments were unable to improve soil properties and plant growth. As the application rate was increased, favorable results were observed. However, if the rate exceeded an optimal value, toxic effects were observed. The optimal rate in most of their studies is equivalent to between 0.2 and 1 cubic yard of amendment per 1,000 square feet.

Since laboratory experiments give consistent soil improvement only when the soil is well aerated, the authors concluded that the toxicity, when it occurs, results from insufficient soil aeration. If the applied organic amendments do not quickly condition the soil and increase the porosity, the level of aeration could be worse with the application of' organic matter. Increasingly high levels of organic matter progressively increase the moisture content of most soils which decreases the supply of soil oxygen. In addition, the decomposition of applied organic amendments consumes oxygen. Anaerobiosis could result. The decomposition of organic matter changes under various conditions. Under some conditions, humic compounds are formed that improve soil, while under others, organic acids are formed that are injurious. Excessive amounts of decomposable organic matter with changes in soil aeration cause a change in the metabolism. If the soil below the surface smells putrid, there are severe problems.

Also observed was a loss of nitrate nitrogen due to denitrification with high application rates of organic matter due to the lack of aeration. Another problem was the fact that the positive results decreased with time. They usually lasted for one growing season only.

These studies indicate the need for better soil aeration, especially when organic matter is used. The best technique is to use a soil conditioner that functions like humus but does not decompose like organic amendments. In lieu of consuming oxygen, much more oxygen is provided because of increased porosity. These effects are achieved with Soil Drain/P.A.M. The soil is immediately conditioned when it is used. In addition the organic amendments which are applied are made even more effective because of the improved aeration and the formation of beneficial compounds. Research results from around the world have validated this successful technique. Organics can be used in transplanting if PAM is used also.

Landscape professionals have often debated the value of organic amendments in backfill for transplants and in other soil preparation activities. The information presented here indicates clearly the nature of the so-called dilemma. Organic amendments can be useful only with well aerated soil. Again, the simultaneous use of the Soil Drain/P.A.M. soil conditioner with organic matter is an excellent means of assuring proper soil aeration. Synergistic responses to both Soil Drain/P.A.M. and organic amendments are obtained when used together.

Successful landscaping requires the utilization of the proper techniques that give good porosity and a high degree of aeration. They are now available for your use.