Plants depend upon the soil ecosystem making nutrients available within soil water. Humus is different from decomposing soil organic matter. Rotating crops adds nutrients to the soil. Hydroponics refers to the technique of growing plants without soil. Vegetation plays a major role in determining the composition of the soil. Citrus plants are also sensitive to excessive salt in the soil. There is also concern over soil erosion. Cuttings are particularly susceptible to rot in moist soil. Vegetation acts as an interface between the atmosphere and the soil. Effects occur to agricultural lands which have certain types of soil contamination. Triclosan favors anaerobic conditions which is typical in soil and sediment. The bacterial spores which cause it are common in both soil and water. Agriculture thrives with much wheat farming on the rich soil. They also sowed vegetables in the fertile soil. This feature is slight or absent in trees that grow in rocky soil or gravel.