Nuutti Kiljunen, Aki Jouhiaho

Faculty of Forestery, University of Joensuu

Vladimir Siounev, Gennadi Davidkov

Petrozavodsk State University

1. INTRODUCTION

There has been a lot of interest on soil damages caused by logging operations during last decades. In Finland, the research on this topic has concentrated mostly on the rut formation in strip roads. Soil compaction has not been so popular aim of study here though in many countries it has been considered very important. Results from foreign studies can not necessarily be generalized to Finnish conditions due to differences in soil properties etc.

In Taiga Model Forest area there will be comparative studies of logging damages between Scandinavian and Russian logging technologies. One part of the logging damage study is soil compaction. Research work will be done near village Matrosy about 30 km from Petrozavodsk.

2. MATERIALS AND METHODS

Weight of logging machines will be estimated by information from the manufacturers of the machines and by measuring the weight of the timber carried by the forwarder or skidder. The weight distribution between front and rear axles have to be estimated, too. The ground pressure of the machine will be calculated by dividing the weight (kg) of the machine by the contact area of its wheels. The contact area ca be estimated by scattering small grained material (dust) around the wheels

and measuring the undusted area caused by the wheels.

The soil compaction and rut formation measurements will be done on sample lines, where a string will be used as a reference line for measurements (Meek 1996). Sample lines will be passed different times, so that the effect of passing times can be taken into consideration. According to Meek (1996) and Jansson and Johansson (1998) it can be estimated that after seventh or eighth pass more passes will compact soil no more. It can be reasonable to pass different lines for example 3, 6, and 8 times. When establishing the sample lines, it is very important that differences in soil condition are taken into consideration.

Fig. 1. String as a reference line on sample line

Penetration resistance of soil will be measured by a cone penetrometer in different depths between 5 cm. Soil samples will be taken into metal cores in different depths between 10 cm. The deepest measurement point will be 50 cm below soil surface. Penetrometer measurements have to be repeated after few months so that possible age hardening can be noticed.

In soil sampling, it is reasonable to find simple methods, which have a strong correlation to the growth resistance of roots, though. Corns (1987) noticed in his studies with four different types of mineral soils, that there was a strong connection between bulk density of soil and growth speed of tree roots. Anyhow, Wasterlund (1985) presented, that bulk density alone is a poor indicator of root growth speed. Alakukku and Elonen (1994) used porosity as third indicator of soil compaction in addition with penetration resistance and bulk density. Wasterlund (1985) found out that the share of macropores of all soil pores is more reliable indicator of root growth speed that soil porosity itself. Jansson and Johansson (1998) considered pores over 50 m m as macropores, eventhough usually limit is 30 m m.

Measurement line

Fig. 2. Sampling method for soil samples and penetrometer measurements.

Soil samples for measuring the bulk density will be taken by metal cores which are pressed into soil in different depths. Cores are closed by plugs to prevent the water evaporation before measurement. Samples for measuring the soil moisture content will be taken at the same time to plastic bags. Moisture content samples will be weighed and weighed again after drying for 24 hour in 110 °C. Soil moisture content has reasonable effect on pehetrometer measurements.