Concept:Continuous tillage repeatedly disturbs the soil and destroys its natural aggregates.
Explanation:Each tillage operation breaks soil clods and aggregates.
This exposes organic matter to rapid decomposition.
The soil loses its stable crumb structure.
Frequent disturbance also compacts the subsoil and reduces pore spaces.
As a result, the soil becomes weak and prone to crusting.
Therefore, the main effect of continuous tillage is the physical breakdown of soil structure.
It does not increase infiltration or reduce runoff because those benefits require good structure.
It also does not improve soil texture because texture is a permanent soil property.
Answer:C. break down of soil structure