Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to soil to supply one or more plant nutrients essential to the growth of plants. Organic fertilizer is on the rise as people are resorting to environmental friendly (or 'green') products. Although organic fertilizers usually contain a lower concentration of nutrients, this lower concentration avoids complication of nitrogen burn harming the plants. In addition, organic fertilizers such as compost and worm castings break down slowly into complex organic structures (humus) which build the soil's structure and moisture- and nutrient-retaining capabilities.