Soil Chemical Properties, Enzyme Activity and Soybean and Corn Yields in a Tropical Soil Under No-till Amended with Lime and Phosphogypsum

Coupled lime and phosphogypsum (PG) application is widely used in no-tillage system (NTS) areas to ameliorate the soil fertility along the soil profile. In the present study, we evaluated the effects of broadcast lime and phosphogypsum (PG) application over soil chemical properties, soil enzyme activity and crop production of a no-tillage system (NTS) area under crop rotation for 15 years. We analyzed soil samples collected 16 months after last amendments' application. The following attributes were determined: pH, soil organic carbon (SOC), calcium (Ca), magnesium (Mg), potassium (K) and sulfur (S) up to 150 cm, and soil enzyme activity (ss-glucosidase and arylsulfatase) up to 60 cm as a function of four treatments: control (no amendments), lime (6.3 Mg ha(-1)), PG (10 Mg ha(-1)) and lime + PG. We compared the results to soil samples from a native forest (NF) site and evaluated soybean and corn production as well as S levels in their index leaves during two growing seasons. SOC contents were higher for NF samples for soil samples collected on the first 20 cm. The soil pH increased until 40 cm in limed treatments. PG alone decreased exchangeable K and Mg contents in the uppermost layer when compared to control. ss-glucosidase activity decreased with depth for all treatments and NF and it was increased with amendments ' application. Arylsulfatase activity increased in lime treatments and decreased with the application of PG alone when compared to control. The joint application lime and PG provided best results in achivieng optimal nutrients levels and amelioriation of soil chemical propoerties, which resulted in the highest soil enzyme activity and crop grain yields.