This chapter discusses soil fertility and soil organic matter as the foundation of sustainable agriculture. Shifting cultivation refers to a practice in which farmers burn an area, farm until nutrients decline, and then moves to a new plot, leaving the land to fallow for up to 20 years to restore soil fertility. With growing populations, this long waiting period os not possible, and there has been a reduction of soil fertility. Soil organic matter is a slow ecological variable and is a sustainability indicator, and performs many functions, including providing nutrients, buffering nutrients, and structure, etc. Soilless cultivation replaces these functions by keeping plants continuously in solution. Sandy soils hold less organic matter than clay soils, because clay soil have a texture and a structure effect. There are five soil-forming factors: the first parameter is the parent material, which is the rocks that were formed and broken down; the second is the climate, due to temperature and rainfall; the third are the organisms that are found the soil; the fourth factor is relief, or whether the soil can drain or hold water; and the last is time. A fertile soil supports good plant growth, which is due to the age and degree of weathering of the soil, as well as the past management, what the French call the “memoire de sol,” or the memory of the soil. Soil erosion and lack of care for organic matter make for threats to soil degradation.
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