FORMATION OF SUNFLOWER HEAD PRODUCTIVITY AS AFFECTED BY AMMONIUM SULFATE AND SULFUR BENTONITE APPLICATION ON GRAY FOREST SOILS IN THE REPUBLIC OF TATARSTAN

Abstract

The scientific article studies the effect of ammonium sulfate and sulfur bentonite on the formation of sunflower head productivity in the hybrids Antemis and Terramis on typical gray forest soils of the Republic of Tatarstan. The field experiment was conducted in 2023–2025 at the Agrobiotechnopark of Kazan State Agrarian University. The following treatments were compared: control without fertilizers, background complete mineral nutrition for a planned seed yield of 2.5 t/ha, background nutrition with ammonium sulfate at 100 kg/ha, and background nutrition with sulfur bentonite at 50, 100, and 150 kg/ha. The soil of the experimental site had a nearly neutral reaction, a humus content of 3.0%, a very high supply of available phosphorus, and an increased supply of available potassium. The meteorological conditions during the study years ranged from a dry period in 2023 to excessive moisture in 2025, which made it possible to assess the stability of hybrid responses to fertilization. It was found that sulfur-containing fertilizers noticeably improved the morphological parameters of the sunflower head, increasing the share of productive area, seed filling, the thousand-seed weight, and the seed weight per head. The highest result among the studied treatments was obtained with ammonium sulfate at 100 kg/ha: in the Antemis hybrid, the head diameter was 20.8 cm, the productive area was 315.6 cm², and the seed weight per head was 82.3 g; in Terramis, the corresponding values were 20.5 cm, 302.8 cm², and 75.1 g. Sulfur bentonite showed a dose-dependent effect, with the maximum response among its rates observed at 150 kg/ha. The Antemis hybrid was characterized by a larger head and greater seed weight, while Terramis maintained a positive response to sulfur-containing fertilizers but was inferior in absolute productivity indicators.