UPTAKE AND EXPENSE OF NITROGEN, PHOSPHORUS AND POTASSIUM IN GRAIN SORGHUM DEPENDS ON NITROGEN FERTILIZATION
The uptake and expense of nitrogen, phosphorus and potassium in grain sorghum was studied in a field experiment during the period 2017-2018. Hybrid EC Alize was grown under non-irrigated conditions. The applied nitrogen fertilization was in rates 0, 60, 120, 180, 240 and 300 kg N.ha-1. It was established that application of N240 and N300 let to high average uptake of nitrogen (212.0 kg N.ha-1) and phosphorus (125.2 kg P2O5.ha-1) in maturity. The higher removal of 159.9 kg K2O.ha-1 on average was observed at N180 rate. The expense of nitrogen for production of 1 t of grain increased in parallel with the nitrogen fertilization. The highest nitrogen expense of 39.7 - 45.3 kg N.t-1 grain was established when sorghum received 300 kg N.ha-1 and it exceeded the control by 38.8 in 2017 and by 53.6% in 2018. Sorghum plants used 15.5 - 16.6 kg P2O5 an average to form 1 t of
grain and nitrogen fertilization in rates N60-N300 slightly affected the phosphorus expense. Nitrogen fertilization proven increased the expense of potassium for production of 1 t of grain compared to N0 control plants. The increase was by 8.3 -20.0% in 2017 and by 8.0 - 34.0% in 2018. Sorghum plants expensed 23.2 - 24.2 kg K2O on average to form 1 t of grain at nitrogen rates N180-N300. The strong positive correlation was established between nitrogen fertilization with N uptake (0.966**) and N expense (0.997**) and K uptake (0.820*) and K expense (0.870*).