Eight-year (2000-2007) field studies on the effectiveness of controlled drainage in loam sandy soil were carried out in the Lowland of Middle Lithuania. The plot, which has existing subsurface water removal systems operated as conventional drainage was readjusted for the water table management. Two separate systems - 4.9 hectares free drainage (FD) and 5.4 hectares controlled drainage (CD) were arranged. A water level control structure with a riser column and hand operated rigid flap door was installed in the outlet of drainage collector in the manhole at the junction of two collectors. The water table level was allowed to rise to the maximum of 68 cm above the drains. Measurements to record the water table depth, drain outflow quantity and quality were performed. It was determined that in the CD system the annual drainage outflow lasted shorter by 40-62%, at the same time it was reduced by 25% and nitrate leaching - by 20-28% lower in comparison with the drainage operating in an ordinary regime. These indicators varied depending on weather conditions. The water table control in single-acting drainage systems is feasible and has a positive hydrological and environmental impact.

The objective of this study was to evaluate the main plant nutrient: mineral nitrogen (NH4 + -N and NO3 -N) dynamic in soil under fertilizing for obtaining high grain yields of winter wheat (Triticum aestivum L.) and to determine relationships between nutrient uptake and winter wheat productivity. The field study was carried out at the Research and Study farm ‘Vecauce’ of the Latvia University of Agriculture for two years 2012/2013 and 2013/2014 with winter wheat variety ‘Kranich’. Different nitrogen application rates (0, 85, 153, 150, 175, 180 and 187 kg haE-1) and timing were used for winter wheat. The content of nitrates NO3 -N and ammonium nitrogen NH4 -N was determined in the soil layers 0-0.20 m, 0.20-0.40 m, 0.40-0.60 m. Nitrogen management strategy during the plant growth period based on soil Nmin evaluating can improve N use efficiency and reduce environmental contamination. The maximum of mineral nitrogen content in soil in the vegetation period was observed at the beginning of stem elongation with a tendency to decrease. A significant impact (p is less than 0.05) of nitrogen fertilizer application was noted on the mineral nitrogen content in soil layer 0-0.20 m deep in both trial years. The increasing doses of nitrogen fertilizer raised the amount of mineral N in the soil profile. The significant impact (p is less than 0.001) of nitrogen application and year conditions was observed on grain yield. Close positive correlation significant at 99% probability level was observed between the grain protein content and nitrogen concentration mostly in all soil layers, but it was not found between the grain yield and nitrogen content.