Mycorrhizas for Forestry and Agriculture

This chapter provides an introduction to the concepts and procedures that would be required to plan. initiate. monitor and analyse experiments involving mycorrhizal inoculation or fertilizer application treatments. The following discussion is concerned primarily with larger field trials required in plantation forestry. but most principles apply equally to smaller experiments conducted in the glasshouse or nursery. and are also relevant to experiments with horticultural or agricultural crops. or native plants grown to restore degraded habitats. Sound experimental design can be more critical in field experiments than in nursery or glasshouse experiments. for the following reasons. I. The establishment of large-scale field experiments is very labourintensive. time-consuming. and expensive. 2. Biological resources required for mycorrhizal experiments (e.g. inoculum of appropriate fungi) can be difficult to produce or expensive to obtain. 3. Experiments are conducted on a long time-scale. due to the life span of trees and plantation rotation intervals. so several years of tree growth may be required before treatment differences are established. 4. Field experiments inherently have larger sources of variability than glasshouse experiments due to spatial variability in site factors. and are influenced by climatic factors which cannot be controlled. Thus, while it is always important to take a great deal of care when designing experiments, this is even more critical for field experiments as logistical and time constraints may make it impossible to replace an experiment which has failed. There are many alternative approaches to deSigning, implementing and analysing experiments. The purpose of this section is not to explore all the possibilities, but to briefly describe the types of experiments we and others have used to examine response to mycorrhizal and nutrient treatments. A rather elementary approach is used initially as a basis for discussing some of the important aspects of design and analysis. Simple examples are presented to illustrate basic concepts. Principles used for the design and analysis of experiments have been described in a number of books. which should be consulted for further information (e.g. Zar 1984, Mead 1988, Snedecor & Cochran 1989. Williams & Matheson 1994). Chapter 7 Field Experiments