Seasonal variation of the rhizosphere soil aggregation in an Oxisol

Abstract

Soil aggregation is a key process that results in soil structure formation and stabilization and controls several soil functions. The root system and its mycorrhiza symbiosis contribution to aggregate stabilization have been widely studied. However, only a few studies have considered a large variety of cropping systems under different seasons within tropical environments. Our goal was to better understand the response of aggregate stability in the rhizosphere (RS) and bulk soil (BS) to six cropping systems in an Oxisol, in the summer and winter seasons. Readily-dispersible clay and mechanically-dispersible clay were evaluated as aggregate stability indicators. RS and BS were also characterized for soil physical (i.e., water content), chemical (i.e., soil organic carbon, K, P, Ca, Mg, Al, potential acidity), and physicochemical (i.e., pH, ΔpH, and point of zero charge) properties. Dispersible clay was approximately 1.2 times lower (p < 0.05) within the RS than in the BS, which suggests that the crop root systems increased aggregate stability, but their influence on soil aggregation differed among cropping systems. Aggregate stability was approximately 3 times higher (p < 0.05) in the winter compared to the summer season. In general, RS had better chemical and physicochemical soil parameters than BS. Winter season also showed better chemical and physicochemical parameter values. Overall, these results reflect (i) the positive root system influence of the winter crops on soil structure stability, (ii) the negative response of soil structure stability to the addition of high doses of chemical fertilizers to soybean and maize (cash crops) in the summer season, (iii) the minimal influence of soybean and maize root system on formation and stabilization of the aggregates in the summer season, and (iv) the different weather condition in the summer and winter seasons. Thus, better erosion control practices and crops that promote soil aggregation should be adopted in the summer season. Finally, attention should also be given to the root exudates and their relationship with soil, as they can either increase or decrease soil aggregation.