Residual effects of acidity amendments and phosphorus sources on sunflower growth and soil chemical attributes

Abstract

ABSTRACT Sunflower cultivation has expanded in recent years; however, phosphorus deficiency and soil acidity constrain crop productivity. This study evaluated sunflower development and soil chemical properties of an Ultisol in northwest Paraná State, Brazil, under the residual effects of phosphorus sources and acidity amendments. The experiment followed a randomized block design in a factorial arrangement, combining nine phosphorus sources: control without phosphorus (T1), hen manure (T2), carbonized rice chaff (T3), soil remineralizer (T4), thermophosphate with micronutrients (T5), magnesium thermophosphate (T6), single superphosphate (T7), triple superphosphate (T8), and potassium thermophosphate with micronutrients (T9), with two acidity amendments (lime and calcium–magnesium silicate), with six replicates. Plant growth, yield components, and root development were assessed, and soil samples were analyzed for pH, available phosphorus, and exchangeable aluminum. Among phosphorus sources, carbonized rice chaff promoted the greatest increases in growth and yield. Liming increased crop yield, whereas acidity amendments did not differ in their isolated effects on soil pH and aluminum; however, significant interactions with phosphorus sources were observed for phosphorus availability. The combined use of lime and organic phosphorus sources, particularly carbonized rice chaff, represents a viable strategy to improve sunflower yield and root development in acid soils of northwest Paraná.