Crop rotation
Sustainability may also involve crop rotation. Crop rotation and cover crops prevent soil erosion, by protecting topsoil from wind and water. Effective crop rotation can reduce pest pressure on crops and replenish soil nutrients. This reduces the need for fertilizers and pesticides. Increasing the diversity of crops by introducing new genetic resources can increase yields. Perennial crops reduce the need for tillage and thus help mitigate soil erosion, and may sometimes tolerate drought better, increase water quality and help increase soil organic matter. There are research programs attempting to develop perennial substitutes for existing annual crops, such as replacing wheat with the wild grass "Thinopyrum intermedium", or possible experimental hybrids of it and wheat.