5Hillard J B. Effects of limestone and phosphorus on nutriefit availability and coastal bermudagrass yield on Ultisol[J] Com'- munications in Soil Science and Plant Analysis, 1992, 23 (12) :175 -188.
6Mitchell R B R A, Masters S S Waller. Big bluestem produc tion and forage quality responses to burning date and fertilizer in tall grass prairie[J]. Journal of Production Agriculture, 1994,7(3):355 -359.
7Binnie R C D M B. Chestnutt effect of regrowth interval on thp productivity of swards defoliated by cutting and grazing [J]. Grass and Forage Science,1991,46(4):343-350.
8West N E. Biodiversity of ranglands[J]. Journal of Range land Management, 1993,48 : 2-13.