Nitrogen relationships in Polish cropping systems

Based on FAO data, the paper presents trends in nitrogen (N) input and output in Poland. As N input ( N inp), nitrogen from mineral fertilisers, manure application, biological fixation, and deposition was included. The N outputs ( N out) include the N contained in crop harvest (main products and by-products). The trend analyses were carried out for the period before (1961–1989) and after (1990–2018) the changes in the political and economic systems. Additionally, trends in the nitrogen use efficiency ( NUE) and nitrogen surpluses ( N S) are presented for these periods. In both compared periods, the mean values of N budget indicators in Poland were (kg N∙ha –1 UAA): N inp 120 and 125, N out 61 and 84, N S 60 and 41 and NUE 53 and 67%, respectively. The estimated Y max, which represents the N out value reached at saturating N fertilisation, reached the values of 127 and 263 kg N∙ha –1 UAA in these periods. The difference in these values suggests a significant impact of agronomy improvement on N out in the recent period. The trends of nitrogen within 16 regions in period 2002–2019, based on national data, resulted in a significant variation in N indicators. The values found were in the following ranges (kg N∙ha –1 UAA): N inp 78–167; N out 62–99; N S 15–83 and Y max 139–317. The NUE ranged from 50–81%. The obtained results indicate that in Poland and its regions there is still a need to improve of the nitrogen efficiency.