THE YIELD AND LAND RECLAMATION PROBLEMS OF AGRICULTURAL LAND OF ŠEMOVEC AREA

The detailed soil survey, land reclamation and crop production investigations are made for 706 hectars of Šemovec area. Investigated area belongs to the rather flat river Drava alluvial valley. The soils are semigley and hypogley with maximum height of groundwater talble for semigley soils 1—2 meters and for hypogley less than 1 meter. Changes in groundwater levels including water table are caused by changes in groundwater storage of unconfined phreatic aquifer and due to reduced natural water regime of river Drava and water regime of river Plitvica channel. The texture of semigley and hypogley topsoil is mostly silty loam while unconfined aquifer is mixture of gravel and sand (graf. 1). Effective soil depth vary from shallow (20—60 cm) to deep (more than 100 cm). Average content of available soil water is 150 mm/m (graf. 4) while infiltration rate of surface layers is very high. The primary source of water of semigley topsoil is rainfall. In general the rainfall in this humid area vary widely m respect to amount and frequency (graf. 2, 3). The present crop production is mostly extensive due to crop rotation and yields. The present land suitability for intensive crop production is evaluated in respect to suitable (S-1, S-2, S-3) and unsuitable (N-1, N-2) land classes. Limitations for intensive crop production are mostly due to some combinations of fertility status, effective soil depth and unregulated soil water regime. There are two land reclamation units. One priority for agroamelioration of 642 hectars (semigley) and another one of priority for agro and hydroamelioration of 58 hectara (hypogley). Land reclamation must be done in order to some combinations of soil loosening, soil fertilization (450 kg PgOg and KgO), supplementary irrigation (due to maximum monthly deficit of available soil water approximately 78 mm including net hydromodul 0,29—0,311/sec/ha), introduction of new crop rotations and soil drainage