Influence of continuous sugarcane cropping on the micromorphological properties of yellow latosols in Alagoas state, Brazil

The effects of continuous sugarcane cropping on the properties of a clayey Yellow Latosol were studied in the region of the Low Coastal Tablelands of Alagoas State, Brazil. Four sites were selected at Caeté mill, São Miguel dos Campos, AL, involving a native forest (Tn) and sugarcane fields cultivated for periods of two (T2), eighteen (T18) and twenty-five (T25) years. The soils were morphologically characterized and undisturbed samples of the A, AB, and BA horizons of each profile were collected for micromorphological analysis. The results showed that agricultural use promoted morphological changes with the development of an Ap horizon with loss of original structure. After an evident negative impact on physical properties after the first crop (profile T2), management practices promoted a partial increase in the macroporosity of the surface horizon after 18 and 25 years. Besides the development of compaction in the Ap and AB horizon with cultivation, a natural pedogenetic dense layer was observed in the BA horizon. This densification is increased with agricultural use, due to the filling of pores with illuvial clay. Total porosity measurements obtained by image analysis of thin sections revealed decreasing porosity at the surface horizon with the first cultivation. This reduction, however, did not increase with continuous cropping. The image analysis also showed that the natural porosity of the BA horizon is very small even in the profile under native forest, indicating pedogenic origin of the densification of this horizon. Although clay coatings were not observed in the field, micromorphology showed pedofeatures with clay coatings in peds and filling of pores with illuvial clay. This observation and the significant increase of the textural gradient all suggest a tendency to the formation of an argillic horizon with time.

Clayey Yellow Latosol; physical properties; cropping time; densification; cohesion; compactness

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