How can humans make soil unproductive?

Answer 1

BY using it too intensively. Soil is a slow accumulation of plant matter, organic material. When farming a considerable portion of the plant matter is remove so people can eat the part of the plant they want. Usually the part of the plant they want is the seed as in wheat, rice, corn, or the seed and its protective nutrient rich covering, as in apples, Pears, plums, fruits in general. Nuts, of course too. So, by removing the nutrient rich part of the plant matter the soil gets depleted. IN tropical areas soil depletion is oddly fast, one or two harvests, it enough to leave the soil nearly barren. In cooler climates, and less wet climates, the accumulation is thicker and richer, the soil can be used more times before damaging it. Still, without fertilizers most fields lay fallow (allowed to rest and recuperate, often with planting nitrogen fixing legumes) once every three to 7 years.

Human behavior causes floods mostly by one of 2 methods. The first one is simply by trying to control where and how rivers flow. SOmetimes the flooding in controlled, forming reservoirs, but just as often flooding occurs unplanned some place else.

The other method of provoking flooding is by removing lots of vegetation from an area, allowing the water to run off quickly. Farmland replacing forests is an example of this. Uncultivated forests are capable of handling huge amounts of water, just because a given area of land has so much more tonnage of plants and trees to take up water and retain it as plant matter, or release it back into the air as plants "breathe." Most agricultural products reduce severely the total amount of plant matter on the land. IN some areas this lack of "breathing" lets the water table rise, reducing the amount of available "cushioning" a lower water table provides and so flooding occurs more quickly with less rain.

Many small local floods are caused just by having to much land area covered by pavement, houses, building in general, and with bad planning the rain water directed into too small an area to absorb it.