Efficiency of Mineral Nitrogen Fertiliser Use and Nitrate Migration in Soil Depending on Long-Term Use of NPK Fertilisers and Their Interactions

The efficiency of mineral nitrogen fertiliser utilisation, accumulation of nitrates in the soil and their leaching was studied in Central Lithuania between 1971 and 2020. The research was carried out based on a multi-factorial scheme design with 45 treatment plots. The design consisted of three designs: a 27-treatment design of 3×3×3, in which three (0, 3 and 6) nitrogen, phosphorus, and potassium fertiliser rates were studied; an 8-treatment design of 2×2×2, in which two (1 and 5) nitrogen, phosphorus, and potassium fertiliser rates were studied, supplemented by the central design treatment 333 (9 treatments in total); and an 8-treatment design of 2×2×2, with two (2 and 4) nitrogen, phosphorus, and potassium fertiliser rates, supplemented by the central design treatment 333 (9 treatments in total). The hundreds indicate nitrogen, the tens indicate phosphorus, and the ones indicate potassium fertiliser rates, where on average over the experimental period 1 rate N = 36, P ₂ O ₅  = 32, K ₂ O = 32 kg ha ^− 1 . The treatments are arranged in two replicates. The specific NPK rates are provided in the results tables, with the following abbreviations: N ₀ , N ₁₀₈ , N ₂₁₆ – 0, 108, and 216 kg ha ^− 1 of nitrogen (N) applied annually, respectively; P ₀ , P ₉₆ , P ₁₉₂ – 0, 96, and 192 kg ha ^− 1 of phosphorus (P ₂ O ₅ ); and K ₀ , K ₉₆ , K ₁₉₂ – 0, 96, and 192 kg ha ^− 1 of potassium (K ₂ O).The findings of the present study demonstrate that, in the presence of low quantities of mobile phosphorus and potassium in the soil, nitrogen accumulation in the yield of agricultural plants depended not only on nitrogen, but also on the fertilisation rates of P ₂ O ₅ and K ₂ O. Agricultural plants best utilised nitrogen from mineral fertilisers (81.0%) as a result of annual fertilisation with 108 kg N, 192 kg P ₂ O _5, and 96 kg K ₂ O ha ^− 1 ; and the worst (19.2%), with heavy fertilisation at the rate of 216 kg N ha ^− 1 , but without phosphorus and potassium fertilisers. NO ₃ ⁻ not taken up by agricultural plants accumulated in the soil and was leached out. A reliable correlation was established between the NO ₃ ⁻ concentration in the soil and the N balance. In addition, the concentration of NO ₃ ⁻ in lysimetric waters was also reliably correlated with the concentration of this element in the soil. Most N leached from the soil of the N ₁₈₀ P ₀ K ₁₈₀ fertilised fields: 30 ± 19 and 107 ± 49 kg ha ^− 1 in the summer-autumn and winter-spring periods, respectively. On the other hand, when agricultural plants were fertilised with two times lower N rates, together with phosphorus and potassium (N ₉₀ P ₉₀ K ₉₀ ), only 8 ± 4 and 29 ± 11 kg ha ^− 1 of N was leached from the soil during the summer-autumn and winter-spring periods, respectively. Therefore, in order to improve the efficiency of nitrogen fertiliser utilisation and reduce water pollution with nitrogen compounds, it is necessary to use nitrogen fertiliser to agricultural plants according to their nutritional needs and to ensure their optimal nutrition with phosphorus and potassium, having determined the amount of these nutritional elements in the soil.