我国北方地区,一年生牧草和饲料作物的播种期一般在春季,视其生物学特性而定,喜温作物推迟播期只能收草,种子有时不成熟。但是多年生牧草宜采用夏播,夏播有两个好处。一是在这类地区春季经常是干旱少雨,蒸发量大,不利于种子萌发及保苗,而夏播时正逢雨季来临,温度增高,种子萌发快,易保苗。二是在进行夏播前有一段空隙时间,在此期间可以清除杂草,这可使多年生牧草不会受到杂草的抑制和争夺水分、养 In northern China, annual planting of forage grass and forage crops is generally in spring, depending on their biological characteristics. However, the delayed sowing of hi-temperature crops can only receive grass and the seeds are sometimes immature. However, perennial herbage should be used summer sowing, summer sowing has two advantages. First, in these areas, the spring is often arid and dry, evaporation is large, is not conducive to the seed germination and seedlings, and the summer sowing coincides with the arrival of the rainy season, the temperature increases, the seed germination fast, easy to seedlings. Second, before the summer sowing there is a gap time during which weeds can be cleared, which allows perennial grasses will not be weed suppression and competition for water, raising