ABSTRACT
Summary Half-rotted older roots and active younger ones both are present in abundance in forage grass, and both types assist in soil aggregate formation in their own rhizosphere. Italian ryegrass (Lolium multiflorum Lam.) was grown in quartz sand for 12 weeks in glass boxes placed in phytotron. In experiment 1, three boxes were opened after 4, 8, and 12 weeks of growth. Root weight was measured, and quantity of sand adhering to the roots was weighed. One hundred times more sand was found adhering to roots after 12 than after 4 weeks. When converted to root basis, weights at 8 weeks and 12 weeks both were around 2 g, or 10 times greater than at 4 weeks. In experiment 2, the distribution of pectic substance on root surfaces and points in contact with the surrounding sand was ascertained by application of ruthenium-red solution. Adhesive strength of the pectic substance was measured using glass plates and was found to be 15-20g/single adventitious root. Total adhesive strength of the roots of each plant increased in proportion to root number. From the experiments, it was concluded that active forage grass roots excrete a pectic substance causing adhesion of soil particles in the surrounding area, acting as a first step in anchoring the plant. As the active root system expands, the quantity of pectic substance excreted increases rapidly, and the adhesive action affects a wider area, thus leading to aggregate formation.
