These materials do not have plant material as their origin, but in many respects they may be similar to organic materials as mulches.
Using inert materials sharply limits evaporation of water from the soil surface and overly wet conditions could develop in heavy, poorly drained soils. Mulching with inert materials helps maintain good structure on the soil surface by protecting the soil from the dispersing action of water from rain or irrigation. Cultivation, of course, is unnecessary when inert mulches are used. The soil temperature under inert mulches is more uniform than it would be if no mulch were applied. When clear or translucent plastic materials are used, the soil warms rapidly. Such materials may raise the temperature higher than opaque materials.
Limestone or acid-derived gravel affect soil acidity but there are no other chemical effects.
The fairly uniform moisture and temperature under the mulch are conducive to development of various micro- organisms in the soil. This could be favorable or undesirable, depending on the nature of the effect of the organism. As the temperature increases, organic matter decomposes more rapidly, releasing nitrogen that is available for plants. Soil granulation could be promoted, but disease-causing organisms would also flourish. Weeds or weed seeds are not introduced with inert mulches.