Fire changes the larger aggregate size classes in slash-and-burn agricultural systems

Abstract

The slash-and-burn agricultural system is one of the oldest types of no-tillage soil management. However, farmers using fire may cause unintentional damage to soil structure in the slash-and-burn system. Herein, it is assumed that larger soil aggregates (≥2.0mm to<8.0mm) are the most affected by fire, with direct impacts to their structural stability. An experimental fire was carried out, and the rainfall simulation approach for a period of 30min with a rainfall intensity of 58mmh−1 was used to assess the effects of fire on soil aggregate stability. The macro-aggregate stability was evaluated for the test plot as well as an undisturbed soil sample using two aggregate sizes: 2–4mm and 4–8mm. The fire temperature measured at the soil surface was very high (673±93°C). Consequently, the soil structural stability under the slash-and-burn agricultural system rose significantly. Larger aggregates of ≥2.0mm or ≥4.0mm size indicated a clear influence of fire on soil physical properties. The fire temperature dramatically changed the distribution of the aggregates of ≥4mm, since aggregates of this size were more frequent (51%) and stronger compared to unburned soil. The methodology is critical to detect the changes in the physical properties of aggregates affected by fire. Aggregate stability methods using a single sieve of ≥0.25mm over rainfall simulation, but without consideration of the completely fragmented particles remaining in the sieve, were not able to detect the aggregation changes.