Changes in rice tillage systems have been taking place in the sense of seeking alternatives to reduce environmental impacts and promote improved yield. Direct-seeded rice technology reduces water consumption and methane emissions. However, in this cropping system, the natural effect of flooding on soil pH is lost because the area is maintained unflooded after seedling emergence until the crop reaches tillering stage. Consequently, it is unclear whether acidity in the topsoil and subsoil within this period affects nutrient availability and rice grain yield. Our study evaluated the effects of dolomitic lime and phosphogypsum applications on soil chemical attributes, plant nutrition, and grain yield in direct-seeded flooded rice. Two field experiments were conducted under different conditions of soil acidity. The main trial was conducted during three consecutive growing seasons from 2013 to 2016. A complementary trial was conducted in 2017 for only one rice harvest, in order to investigate the short-term effects of lime and phosphogypsum application. For both experiments, lime was incorporated into the topsoil at 0, 0.5-, 1-, and 1.5-times the recommended rate for flooded rice, according to SMP buffer method, and phosphogypsum was applied to the soil surface at 0, 2, 4, and 6 Mg ha⁻¹. Liming alleviated topsoil acidity, causing an increase in soil pH and the exchangeable Ca²⁺ and Mg²⁺ contents, and a reduction in exchangeable Al³⁺ content. An increase in soil exchangeable Ca²⁺ content and a decrease in soil exchangeable Al⁺³ content also occurred at 0.20–0.40 m depth at 35 months after liming. Despite alleviating the soil acidity, lime application did not improve the rice grain yield. Phosphogypsum application increased Ca²⁺ and SO₄-S availability throughout the soil profile (0–0.60 m), as well as the phosphorus, potassium, calcium, and sulfur levels of rice flag leaves and the grain yield. A promising short-term effect on rice yield was obtained, as well as a residual effect that lasted for at least three years after phosphogypsum addition. Overall, a phosphogypsum rate of ∼4 Mg ha⁻¹ increased rice yield by 10–11%. Although a possible involvement in acid-subsoil amelioration on rice yield response to phosphogypsum is difficult to exclude entirely, it is more probable that yield benefits imparted by phosphogypsum resulted from increased SO₄–S availability throughout the soil profile. We conclude that, although liming is of no advantage, the use of phosphogypsum improves the performance of direct-seeded rice.

Changes in rice tillage systems have been taking place in the sense of seeking alternatives to reduce environmental impacts and promote improved yield. Direct-seeded rice technology reduces water consumption and methane emissions. However, in this cropping system, the natural effect of flooding on soil pH is lost because the area is maintained unflooded after seedling emergence until the crop reaches tillering stage. Consequently, it is unclear whether acidity in the topsoil and subsoil within this period affects nutrient availability and rice grain yield. Our study evaluated the effects of dolomitic lime and phosphogypsum applications on soil chemical attributes, plant nutrition, and grain yield in direct-seeded flooded rice. Two field experiments were conducted under different conditions of soil acidity. The main trial was conducted during three consecutive growing seasons from 2013 to 2016. A complementary trial was conducted in 2017 for only one rice harvest, in order to investigate the short-term effects of lime and phosphogypsum application. For both experiments, lime was incorporated into the topsoil at 0, 0.5-, 1-, and 1.5-times the recommended rate for flooded rice, according to SMP buffer method, and phosphogypsum was applied to the soil surface at 0, 2, 4, and 6 Mg ha^-1。石灰降低了表土的酸度，导致土壤pH值增加以及可交换的Ca ²⁺和Mg ²⁺含量增加，而可交换的Al ³⁺含量降低。撒石灰后35个月，土壤中可交换的Ca ²⁺含量增加，而土壤可交换的Al ⁺³含量也发生在0.20–0.40 m深度处。尽管减轻了土壤的酸度，但石灰的施用并未提高稻米的产量。施用磷石膏可增加Ca ²⁺和SO _4的含量整个土壤剖面（0–0.60 m）中-S的有效性，以及水稻旗叶的磷，钾，钙和硫水平以及谷物的产量。获得了对水稻产量的有希望的短期影响，以及在添加磷石膏后至少持续了三年的残留影响。总体而言，磷石膏的使用率约为4 Mg ha ^-1，可使稻米产量提高10-11％。尽管很难完全排除酸性土壤改良对水稻对磷石膏的产量响应的影响，但更有可能的是，磷石膏赋予的增产效益是由于整个土壤剖面中SO ₄ -S利用率的提高而引起的。我们得出的结论是，尽管撒石灰没有优势，但使用磷石膏可以改善直播稻的性能。