A Novel Phosphogypsum Application Recommendation Method under Continuous No-Till Management in Brazil

Phosphogypsum (PG) is used in tropical and subtropical agriculture when subsoil acidity is an important yield-limiting factor. However, the conditions that increase crop yield under PG application in continuous no-till systems remain unclear. In addition, the methods used in Brazil to estimate the PG requirements are sometimes imprecise. Thus, to develop an accurate method for establishing PG recommendation, a dataset from experiments performed in southern Brazil and selected published papers involving PG application on various Oxisols under continuous no-till was analyzed by computational techniques of data mining using the M5-Rules algorithm to create regression models. Experimental areas consisted of annual crops managed under a long-term (>= 10 yr) no-till system. These included maize (Zea mays L.), soybean [Glycine max (L.) Merr.], wheat (Triticum aestivum L.), and barley (Hordeum distichum L.). Results allowed the proposal of a new method for establishing the PG requirement to increase Ca2+ saturation to 60% in the effective cation exchange capacity (ECEC) at the 20- to 40-cm soil layer when this is lower than 54% using the following equation: PG (Mg ha(-1)) = (0.6 x ECEC - exchangeable Ca2+ content in cmol(c) dm(-3)) x 6.4. The PG rates indicated by this method agreed with those leading to the maximum economic yields obtained in most studies conducted on continuous no-till soils in Brazil. The proposed method might be efficiently used when subsoil acidity is an important growth-limiting factor.