The effect of nitrogen fertilization in rates 0, 60, 120, 180, 240 and 300 kg N.ha-1 on the mineral balances of nitrogen, phosphorus and potassium was studied in the experimental field of Agricultural University of Plovdiv, Bulgaria in 2017-2018 under non-irrigated conditions in grain sorghum hybrid EC Alize. Total nitrogen as NH4NO3 was applied as pre-sowing fertilization on the background P50K50 fertilization as triple superphosphate and potassium chloride, respectively. The experimental design consisted of a randomized, complete block design with four replications. The size of individual trial plots was 20 m2. It was found that the grain removed 112.6 kg N.ha-1, 51.1 kg P2O5.ha-1 and 23.7 kg K2O.ha-1 on average in 2017. In the wet vegetation of 2018, the average quantities of nutrients were higher by 20.4%, 12.5% and 49.4%, respectively for nitrogen, phosphorus and potassium. Nitrogen fertilization proven increased the accumulated nitrogen and potassium in the sorghum grain and it slightly affected the grain phosphorus export. The grain nitrogen removal increased in parallel with the applied nitrogen up to N180 in 2017, and up to N240 in experimental 2018. The most potassium of the grain 27.6 - 43.5 kg K2O.ha-1 was taken up when sorghum was fertilized with N180 and N240. The high N300 rate significantly decreased accumulated potassium in the grain, compared to the variants fertilized with N120-240. Without nitrogen fertilization sorghum grain annually removed 90.6 – 98.4 kg N.ha-1. The mineral balance of nitrogen was a negative when sorghum received 60 - 120 kg N.ha-1 and the soil contained less than 40 mg Nmin.kg-1 soil. The phosphorus mineral balance changed from -10.9 kg P2O5.ha-1 at N120 rate up to 2.1 kg P2O5.ha-1 at the N0 control. Under P50K50 background fertilization the mineral balance of phosphorus was a negative in all nitrogen fertilized variants in 2018, and it was a negative at fertilization rates 60, 120 and 180 kg of N.ha-1 in 2017. The mineral balance of potassium was a positive at all studied nitrogen levels N0 – N300. After sorghum harvesting, 14.4 - 27.2 kg K2O.ha-1 on average remained in the soil.

mineral balance, fertilization, grain sorghum

field crops and pastures

Presentation: poster