The effect of crop-pasture rotations on the C, N and S contents of soil aggregates and structural stability in a volcanic soil of south-central Chile

Abstract

The effects of six crop-pasture rotations were evaluated on properties of soil aggregates in a volcanic soil (Humic Haploxerand) of south-central Chile. Rotations that included intensive cropping without pastures, and crops with short- or long-term pastures were maintained for 12 years after which soil samples were taken at 0–5 and 5–10 cm depths for analysis of the C, N and S contents in the different grades of water-stable aggregates. The mean weight diameter of the aggregates was also determined as an indicator of structural stability. The results showed that the rotations which included long-term pastures of alfalfa (Medicago sativa L.) or white clover (Trifolium repens L.) had higher contents of C, N and S in soil and there was a higher concentration of these elements in macro-aggregates (>0.5 mm) than in micro-aggregates (<0.5 mm). Additionally, the rotations with pastures also produced greater structural stability of the soil aggregates. Consequently, crop rotations that included pastures, particularly those of longer duration, improved the soil and were therefore a more sustainable use of the soil resource compared to the more intensive rotations. Additionally, there was evidence of hierarchical organization of the soil structure, which is a previously non-described feature of volcanic soils.

Keywords:

• Andisol
• annual crops
• pastures

Acknowledgements

This research was funded by the Chilean Institute for Agricultural Investigations (CRI-INIA) and the Soils Department, Faculty of Agronomy of the University of Concepción, Chile, and was part of a project for a doctoral thesis of the Environmental Science Programme (EULA) of the University of Concepción. The authors sincerely thank Pablo Undurraga, Research Agronomist, for assistance in laboratory analysis of soil samples.