Effect of P rates in long-term conservation agriculture trials on the vertical distribution of soil acidity and nutrient availability

Abstract

Few studies are published on the long-term impact of phosphorus (P) rates as triple superphosphate (208 g P kg−1) on the vertical distribution of soil acidity and the availability of macro and micronutrients within conservation systems. This study explores the long-term impacts of increasing P rates on the vertical distribution of soil acidity and Mehlich-3 nutrient availability in long-term trials managed under conservation tillage in North Carolina. In 2022, soil samples were collected from two contrasting long-term trials: one on a sandy, poorly drained Portsmouth soil at Tidewater Research Station (67 years) and another on a well-drained, clay-rich Lloyd soil at Piedmont Research Station (37 years), at depths of 0–5, 5–10, 10–20, and 20–30 cm. In general, the greater crop yield and nutrient removal over the years occurred with higher rates of P, resulting in a decrease in the soil available potassium (K). Historical use of P increased the content of other nutrients that are part of phosphate compounds (i.e., calcium [Ca] and magnesium [Mg]) or are contaminants in these fertilizers (i.e., zinc [Zn] and manganese [Mn]). The distinct trend of sulfur (S) in both locations, where soil available S content increased with P rates at Tidewater and decreased at Piedmont, reflects the complexity of S dynamics in soils with contrasting characteristics. These findings reveal differences between soils and the importance of integrated nutrient management in long-termexperiments to avoid bias in the crop response over the years, especially in fields managed under conservation tillage.