Soil compaction connected with tractor traffic leads to changes in roots morphology and decreased plant yields of both annual and perennial forage plants. The aim of this study was to quantify the effect of soil compaction on alfalfa herbage production and root growth. A pot experiment with different levels of soil compaction was conducted in 2007-09. Plant yield and root morphology such as root length density (RLD), mean root diameter (MD), specific root length (SRL), and root dry matter (RDM) were determined.
Root dry matter distribution in uncompacted soil was uniform in the investigated soil layers. In compacted soil the main root matter was located in the upper soil layer. Generally, roots were also much longer in the upper soil layer (0-10 cm) than below 10 cm. The value of RLD decreased in treatments with a higher degree of compaction. It was observed that roots in more compacted soil were thinner than in uncompacted. Based on the results in herbage production, the reaction of plant yield to soil compaction can be described as positive. In the first year of the experiment (2007), soil compaction caused a significant decrease in plant yield. However, in 2008 and 2009 the opposite effect was noticed when yields were significantly higher in strongly compacted soil than in less compacted.