Impacts of tillage on soil properties and interactions with drainage when reseeding permanent pasture

Grassland reseeding typically requires intensive tillage. This disrupts soil nutrient dynamics, especially under varying drainage condition. This study evaluated the combined effects of tillage legacy, drainage, and soil depth on key soil properties within a long term grassland experiment. Treatments compared two no tillage durations (five years of no-tillage, 5YNT; thirty years of no-tillage, 30YNT), two drainage systems (drained and undrained), and two depths (0–10 cm and 10–30 cm) following reseeding. Total carbon (TC), total nitrogen (TN), total phosphorus (TP), and pH were measured. Significant three way interactions were detected for all variables. At 0–10 cm, undrained 30YNT plots exhibited 69% greater TC and 66.9% higher TP than the lowest values recorded in 5YNT × drained combinations at 10–30 cm. TN followed a similar pattern, with substantial enrichment under long term no tillage. Reseeding reduced TC, TN, and TP within five years, particularly in surface soils, with the largest proportional losses in undrained plots where nutrient concentrations had been high prior to tillage. Findings highlight the importance of conserving long term no tillage systems to enhance nutrient retention and promote sustainable grassland productivity. Conventional tillage of nutrient rich pastures should be avoided to prevent major nutrient losses.