Some critical question for grassland farming in northern China

The central point of grassland farming is animal production by grazing and/or feeding. Animal growth is a natural dynamics, which was affected annually by the quality and quantity of forage and environment. Therefore, annual dynamics in the producing process of animal has great significance in animal and grassland management. Lots of factors should be considered, such as three action factors in grazing: intensity, frequency and timing, and four behavior factors in grazing: physical damage, trampling, unbalanced nutrition and saliva. In the case, optimizing feeding on grassland by grazing and/or by supplement is an active strategy and method for grassland management. As grassland resource has spatial and temporal meaning, and forage quality was associated with seasons, optimizing feeding is to keep the balance of the animal growth and timedependent quality of forage. Important problems in grassland farming in northern China is as follows:1）Grass performance to gazing and/or cutting, which is basis for understanding grassland healthy existence and /or degradation in grazing reaction. 2）Dynamics of net grassland production and nutritional process of forage, which is central factors for determining grazing feeding. 3）Rational grazing, i.e., adaptive intensity and frequency of grazing, which is ensuring for grassland management and for animal production. 4）Optimizing feeding on grassland, which is an active action for grassland management and for animal production.