SOIL CONTENT OF MINERAL NITROGEN AFTER INTERCROPPING DETERMINED IN AUTUMN AND SPRING

The paper presents the results of studies carried out over 2004-2007, whose aim was to determine the effect of undersown crops and stubble catch crops used for mulching on the content of nitrogen mineral forms in the soil profiles of autumn and spring. The field experiments were conducted at the Experimental Farm in Zawady, owned by the University of Natural Sciences and Humanities in Siedlce. The following treatments were examined: control (no undersown or catch crops), an undersown crop with its biomass plowed down in autumn (red clover, red clover + Italian ryegrass, Italian ryegrass), stubble catch crop with its biomass plowed down in autumn (phacelia), and stubble catch crop whose biomass was used as a spring-incorporated mulch (phacelia). The content of nitrate and ammonia ions was determined in two soil layers (0-30 and 30-60 cm) twice, i.e. in autumn and spring. The results demonstrated that the undersown crops and catch crops reduced the soil amount of mineral nitrogen in autumn, but increased the mineral nitrogen content in spring. The highest soil concentration of nitrate and ammonia ions was recorded in spring following red clover incorporation. When the soil surface was mulched with a stubble catch crop of phacelia in autumn and winter, the mineral nitrogen content significantly dropped in spring as compared to autumn incorporation. The topsoil had a higher content of mineral nitrogen compared with the subsoil.