Response of rice to phosphogypsum application rates in salt-affected paddy soil of the Kyzylorda Region, Kazakhstan

Salt-affected soils are a major constraint to rice production in the arid irrigated environments of Central Asia, including the Kyzylorda region of Kazakhstan. This study assessed the agronomic response of rice to different phosphogypsum (PG) application rates under local paddy-field conditions. A field experiment was conducted during the 2025 growing season under a uniform nitrogen background of N120, with four treatments: 0, 2.5, 5.0, and 7.5 t PG ha⁻¹. Plant density, plant survival until harvest, grain yield, and major yield components were evaluated. The experimental soil was heavy-textured and alkaline, while the irrigation environment was salt-affected. Phosphogypsum application improved all measured agronomic traits relative to the untreated control. Plant density increased from 240 ± 8.5 plants m⁻² in the control to 255 ± 7.2, 268 ± 6.9, and 271 ± 7.8 plants m⁻² at 2.5, 5.0, and 7.5 t PG ha⁻¹, respectively. Plant survival rose from 89.4% in the control to 91.8%, 94.2%, and 96.3% with increasing PG rate. Grain yield increased from 4.28 ± 0.21 t ha⁻¹ in the control to 4.55 ± 0.18, 4.79 ± 0.15, and 4.84 ± 0.17 t ha⁻¹ at 2.5, 5.0, and 7.5 t PG ha⁻¹, respectively. Productive stems, plant height, grains per main panicle, grain weight per panicle, and 1000-grain weight also increased progressively with phosphogypsum application. The highest numerical values for grain yield and all yield components were obtained at 7.5 t ha⁻¹, although the gain over 5.0 t ha⁻¹ was relatively small. These results indicate that phosphogypsum is an effective amendment for improving rice productivity in salt-affected irrigated soils of the Kyzylorda region. Within the tested range, 7.5 t ha⁻¹ provided the strongest agronomic response, while the limited yield increment beyond 5.0 t ha⁻¹ suggests diminishing return at the highest application rate.