Soil Aggregation in Relation to Organic Amendment: a Synthesis

Soil aggregation, a key aspect of soil physical health, is a crucial component of agroecosystem sustainability as it affects numerous soil processes and agroecosystem productivity. Application of organic amendment (OA) plays a vital role in improving soil aggregation. In this review, we provide a comprehensive synthesis and a critical assessment of the current state of knowledge in soil aggregation in relation to OA. We first highlight factors (such as soil texture and clay mineralogy, source and type of OA, OA application rate and frequency, and OA application mode) determining the effect of OA on soil aggregation. Secondly, we review how OA regulates soil aggregation and point out that OA improves soil aggregation mainly via: (i) increasing soil organic carbon (SOC) content where OA acts as an external source of SOC, (ii) promoting soil biotic activity where OA acts as a substrate for microbes, and (iii) increasing soil hydrophobicity, thus reducing aggregate turnover. Finally, we draw reader’s attention to the complex linkages between OA quality and soil aggregation. The OA quality defined by 13C-NMR spectroscopy in terms of organic C type can explain variable effects of OA on soil aggregation better than C/N and lignin/N ratio indices. Considering organic C types, OA rich in carbohydrate C fractions tends to induce rapid but short- and medium-term effects on soil aggregation, while OA riched in aromatic C fractions barely affects soil aggregation. We conclude that soil structure can be significantly modified through better agronomic practices of OA application which will enhance soil aggregation, reduce soil erosion, and subsequently increase overall productivity.