MICROSYSTEMS FOR RAPID EVALUATION OF PLANT GROWTH RESPONSE TO ORGANIC AMENDMENTS

Abstract

Organic matter (OM)-based amendments offered to farmers vary greatly in their source, properties, and effectiveness. Some of these are produced from natural organic resources, whereas others originate from recycled organic waste, in part as an environment-friendly low-cost alternative to waste disposal. Stimulatory effects of OM on plant growth have been noticed in many systems, but a few reports have indicated negative effects. Many factors and interactions dictate plant response to these materials, and not all are well understood. Procedures that can be used to evaluate OM composition and characteristics that might affect plant growth are complicated and expensive. Deleterious effects of OM additions are frequently associated with a nonmature status of the decomposing material, but maturity is difficult to define. Evaluation of humic substances (HS)-based products is even more complex and needs improvement of the available methodologies. This article presents two simple versatile bioassay methods carried out in microplates or pouches for screening and evaluating soluble organic products for agronomic and horticultural use. To illustrate the two methods, we present microplate experiments with creeping bentgrass (Agrostis palustris Huds.) that provide an evaluation of plant response to N rates spanning from deficient to excessive levels (0.9-57.6 mg N L−1) and to 11 different soluble HS products. The pouch method is presented by soybean (Glycine max L.) and corn (Zea mays L.) experiments that evaluate plant response to two HS and determine whether it is related to Fe or Zn mediation by the tested substances. The two methods are shown to be sensitive for nutritional factors and could effectively rank various OM materials frombeing deleterious to stimulatory to plant growth.