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.

Activated sludge systems designed for enhanced nutrients removal are based on the principle of altering anaerobic and aerobic conditions for growth ofmicroorganisms with a high capacity of phosphorous accumulation. To avoid return of large parts of accumulated phosphorous in the processes of sludge conditioning chemical precipitation is often applied. This can be not be the case, at least for a part, if prior to other processes of sludge handling, the sludge will be disintegrated. It was demonstrated that disintegration of surplus activated sludge permits removal of a substantial part of nutrients in the form of struvite. The effects of sludge disintegration on metals ions release and poly-P destruction were elucidated. Appropriated handling of disintegrated sludge allows for removal of at least 25% of the inflowing phosphorous load without addition of chemicals.