Actually, there are two questions there.
Trees certainly have their place in the system and specifically in terms of river management when they are next to waterways. We know that developing a riparian strip with trees or shrubs breaks the hydrologic connection between the fields and the waterway, which would have a beneficial effect on the drainage of the land and the retention of nutrients. That has also been demonstrated in some concerted actions taken in watersheds.
In terms of the intercropping and the major crops with trees, I don't think the practice is feasible for everyone. However, it is certain that some areas of agricultural land are particularly vulnerable and perhaps unproductive when they are low-lying or poorly drained. They could certainly be well suited for sylviculture.
We have to have an overall vision for the integrated management of problematic watersheds. The quality of the soil and the water, the performance of the crops and the impact of agricultural activity on water quality downstream are all interrelated.