Effects of long-term mineral fertilization on silage maize monoculture yield, phosphorus uptake and its dynamic in soil

A long-term continuous silage maize (Zea mays L.) monoculture experiment (1993-2019) was conducted at Cerveny Ujezd in the Czech Republic to assess the effects of different mineral fertilizers on phosphorus transformations and balance. An unfertilized control (C) was compared with i) ammonium sulfate (AS), ii) urea ammonium nitrate (UAN), iii) UAN + triple superphosphate and potassium chloride (UAN+PK), and iv) UAN + triple superphosphate and magnesium sulfate (UAN+PMg), respectively. The dry aboveground biomass yield (BY), P uptake by plants, bioavailable and stable soil P forms, soil P-sorption characteristics, as well as simple P-balance, sustainability yield index (SYI), and agronomic efficiency (AE) were evaluated. Maize P uptake, content, BY, AE, SYI, and P utilization over the 27 years increased in the order of UAN+PK > UAN+PMg > UAN > AS > C treatments. P uptake was positively correlated with bioavailable soil P and BY. AS and UAN only fertilizing caused a more negative P balance (on average -621 kg P ha(-1) 27 yrs(-1)) as compared to the control (-483 kg P ha(-1) 27 yrs(-1)). The bioavailable Al and Fe forms strongly influenced the soil P sorption parameters. As example, phosphorus sorption index increased to 137% for C, averagely to 183% for AS and UAN fertilizing treatments, and 124% for P fertilizing treatments in the year 2019 as compared to 1997 (=100%). Generally, almost all indices show that N only fertilizing (AS and UAN) significantly decreases the bioavailable and even the stable inorganic P forms and has a negative influence on P sorption parameters and thus, overall P-sustainability. The effect of this fertilizing system was even more negative than in the unfertilized control, due to the higher yield and P uptake in AS and UAN treatments. Although soil P was not a limiting nutrient for plant growth, it is possible to expect its direct influence on BY in AS and UAN treatments in the near future.