Previous tests have shown that nitrogen applied to California's annual rangeland increases the length of the grazing season by increasing the growth of grass during the winter. However, recent studies at the Hopland Field Station covering a two-year period indicate that growth rate of the common annual grass, soft chess (Bromus mollis), increased very little when the average soil temperature dropped below 45°F. Grass fertilized with nitrogen showed the greatest increase in growth compared with unfertilized grass when the average soil temperature was between 47° and 55°F. When the temperature went above 55°F, the difference between growth of fertilized and unfertilized grass decreased.