Effect of organic amendments on nitrate leaching mitigation in a sandy loam soil of Shkodra district, Albania

European lacustrine systems are frequently exposed to nitrate (NO3) pollution causing eutrophication processes. An example of these lakes is Shkodra Lake, a large, shallow lake shared by Albania and Montenegro, in the Balkans Peninsula. Shkodra Lake is a natural sink that collects NO3- from agricultural activities, widely diffused in the surrounding area. The additions of wheat straw and biochar have been suggested to increase soil NO3- retention of agricultural lands. To better understand the role of these two organic soil amendments in mitigating NO3- leaching from arable lands, a pot experiment using a representative sandy loam soil of the Skodra Lake basin was performed. More specifically, a greenhouse experiment with Lolium multiflorum L. and Zea mays L., was carried out for three months, to evaluate the concentrations of NO3--N in leachate and the cumulative leaching losses of NO3--N, after wheat straw (10 Mg ha(-1)) and biochar (10 Mg ha(-1)) soil addition, under the same rate of NPK fertiliser (300 kg ha(-1)). The effect of the two organic amendments on nitrate retention, was evaluated according to two methods: i) Soil NO3--N leaching with distilled water; and ii) Soil NO3--N extraction with 2M KCl. The leached NO3--N and the Potentially Leachable NO3--N (2M KCl extraction) were respectively determined. N uptake by plants, as well as the Nitrogen Use Efficiency were also calculated. A retention effect on nitrate was found in Lolium multiflorum L. and wheat straw treatments compared to control, by reducing leached NO3--N almost to 35%. In SBFL (soil+biochar+fertiliser+ Lolium) treatment, biochar effectively reduced the total amount of nitrate in leachate of 27% and 26% compared to SFL (soil+fertiliser+Lolium) and SSFL (soil+straw+fertiliser+Lolium) treatments, respectively. The potentially leachable NO3--N was two to four times higher than the leached NO3--N. The amount of potentially leachable NO3--N per hectare ranged from 220 in SL (soil+Lolium) treatment, to 500 kg ha(-1) in SFL. N plant uptake values ranged from 18.16 mg kg(-1) in the non-fertilised treatment to 58.06 mg kg(-1) soil in SSFM (soil+straw+fertiliser+maize) treatment. The NUE showed a similar trend (from 0 in the non-fer-tilised treatment to 47.9 % in SSFM). Results indicated a mitigating action of biochar on leaching of NO3--N (leached up to 100 kg ha(-1)), despite the retention effect of the two different amendments applied.