Zero tillage normally increases organic matter, especially if summer fallow has been eliminated. The active fraction of OM, which is either alive or rapidly decomposing, greatly increases with no-till practices. In some soils OM does not increase much, even after successive years of no-till. No-till improves soil structure. This results when OM combines with soil mineral particles to form aggregates.
Conventional tillage destroys soil aggregates.
One advantage of the aggregates formed in no-till soils is the large network of pores which form between them. This network serves as a subway system for the movement of nutrients, air and water to crop roots. Like aggregates, these pores are destroyed by tillage. No-tilling allows this layer to build up to useful levels. This duff layer suppresses weeds and reduces evaporation.