Bacteria are useful in a number of ways in agriculture. Bacteria are part of the top layer of soil and they impart fertility to the soil. Some bacteria, known as leguminous bacteria, are capable of fixing nitrogen in the soil. Other soil bacteria participate in the nitrogen cycle to convert this fixed atmospheric nitrogen to other useful forms. They also participate in the formation of the humus layer. Bacteria also ensure consistent supply of nutrients to the plants. Provision of nitrogen and phosphorous by microbes simply means fewer requirements of nitrogenous and phosphatic fertilizers and hence cost savings to the farmers and lesser chemical addition to the environment. Some microorganisms also confer protection against pathogens and thus reduce the fungicide requirements. They also enhance stress tolerance in the plants.