EFFECTS OF HUMUS THICKNESS LAYER ON DRAINAGE RUNOFF

The article presents the influence of fluctuation of the main climatic factors over time on drainage runoff, the analysis of drainage runoff distribution in the course of a year. The size of drainage runoff depends on meteorological conditions of the year, the most important of which are the precipitation quantity and air temperature, however, the soil characteristics conditions are very important factor too. The impact of humus on heavy-textured soil is multiple, since not only moisture regimes, biological activity, sorption capacity, chemical and biological characteristics, stability of plant nutrition are related with its quantity. This study presents drainage runoff dynamic in two contrasting humus thickness layers systems (in soil with thickened (up to 40–50 cm) humus layer and with humus layer of natural thickness (20–30 cm) during various seasons) during 1989–2012 years of a long-term experiment in Centre Lithuania. It was found that the thicker layer of soil humus substantially improves the drainage performance. The field with the thickened humus content drainage runoff ranged higher amplitude than the field in all seasons, with a natural layer of humus. It is determined that the lowest quantity of precipitation in the researched territory during the research period is in spring and winter but the highest – in summer and autumn. During the research period the highest drainage runoff in the field with thickened humus layer was during winter season (46%), in the field with humus layer of natural thickness – in winter and spring almost the same (32– 33%).