EFFECT OF UREA AND UREA WITH UREASE INHIBITOR ON YIELDS AND NITROGEN AND CADMIUM CONTENT IN POTATOES

Worldwide the urea fertilisers are the fastest growing and most commonly used source of nitrogen in agriculture. The benefits of using urea as a fertiliser are due to its high nitrogen content (approximately 46 % nitrogen), non polarity, high solubility, and low costs for manufacture, storage, and transport. Among the various available mitigation tools, urease inhibitors like NBPT (N-(n-butyl) thiophosphoric triamide) have the highest potential to improve the efficiency of urea by reducing N losses, mainly via ammonia volatilization. In 2011 and 2012 a small-plot experiment was established with the potato 'Karin' variety. The experimental locality was Zabcice, ca 30 km south of Brno, a maize-growing region. Prior to planting both mineral fertilisers (urea and urea with urease inhibitor NBPT - UREA stabil) were applied to the soil surface. During planting these fertilisers were incorporated into the soil. The experiment involved 7 treatments: 54, 72, 90 kgN . ha(-1) as urea, 54, 72, 90 kgN . ha(-1) as UREA stabil and unfertilised control. Each treatment was repeated 4 times. The focus of the experiment was to monitor the effect of two different fertilisers and different N-doses on the yields of potato tubers and content of nitrogen (N) and cadmium (Cd) in tubers and tops (stems + leaves). In 2011 the contents of nitrogen in the tubers fluctuated between 14.3 and 15.6 g . kg(-1) d.m. and in the tops between 29.7 and 40.9 g . kg(-1) d.m. The contents of cadmium in tubers ranged between 0.14 and 0.17 mg . kg(-1) d.m. and in tops between 0.50 and 0.72 mg . kg(-1) d.m. In 2011 the tuber yields fluctuated irregularly, i.e. between 17.0 and 32.9 Mg . ha(-1). In 2012 the nitrogen contents in tubers ranged between 16.0 and 17.3 g . kg(-1) d.m. and in the tops between 23.9 and 36.9 g . kg(-1) d.m. Cadmium contents in tubers fluctuated between 0.13 and 0.20 mg . kg(-1) d.m. and in the tops between 0.35 and 0.64 mg . kg(-1) d.m. In 2012 the tuber yields fluctuated irregularly between 25.2 and 33.9 Mg . ha(-1). Based on the results we can conclude that both fertilisers (urea, UREA stabil) were reflected in the N and Cd contents of the biomass of potatoes irregularly in dependence on the year, rate of fertiliser and analysed plant organ (tubers, tops). In both years the contents of N and Cd were higher in the tops. Tuber yields fluctuated irregularly in dependence on the year and rates of nitrogenous fertilisers.