Productive and Environmental Consequences of Sixteen Years of Unbalanced Fertilization with Nitrogen and Phosphorus—Trials in Poland with Oilseed Rape, Wheat, Maize and Barley

Two factorial field experiments were carried out between 2003 and 2018 in the Experimental Stations in Eastern and Western Poland using four crop rotations with winter oilseed rape, winter wheat, maize and spring barley. The initial value of phosphorus (P) in Grabow soil was 69.8 mg P·kg−1 soil and in Baborowko soil it was 111.3 mg P·kg−1 soil (Egner-Riehm Double-Lactate DL). P fertilizer was added annually at 39 kg P·ha−1 under winter oilseed rape, 35 kg P·ha−1 under maize and 31 kg P·ha−1 under wheat and barley using superphosphate and nitrogen (N), which was added at five levels (40–250 kg N·ha−1) per year as ammonium nitrate in addition to controls with no added fertilizer. Through the several years of the experiment, P fertilizer had no effect on crop N use efficiency (NUE) nor crop productivity. There was significant soil p mining particularly in the high-N fertilizer trials causing a reduction in the content of available soil p by up to 35%. This work recommends that, based on soil P analysis, P fertilizer should not be added to high-P soils. This practice may continue uninterrupted for several years (16 in this case) until the excess soil P has been reduced. This mechanism of removal of “legacy” P from soil has major implications in reducing runoff P into the Baltic Sea drainage area and other water bodies.