科研之友
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摘要
monthly measurements of the grass height, total above-ground biomass and the proportions of live and dead biomass, specific leaf area (sla) and leaf area index (lai) were made in one cattle ranch at the fazenda nossa senhora (fns) (february of 1999 to january of 2005) and also in rolim de moura (rdm) (february to march of 1999) in rondˋnia state. the predominant grass species is urochloa brizantha (hochst. ex a. rich) r. d. webster (covering 99% of the area in fns and 76% in rdm), with minor patches of urochloa humidicula. this pasture was regularly grazed. the average grass height was 0.16 m but monthly value varied between 0.09 m after intensive grazing in the dry season to 0.32 m in a wet season without grazing. the lai, total biomass, dead plant material, live above-ground plant material and sla average 2,5 m2 m-2, 2202 kg ha-1, 2916 kg ha-1 and 19 m2 kg-1 respectively. the monthly average above-ground biomass showed little seasonal variation, but annual averages ranged from 4224 kg ha-1 in 2002 to 6667 kg ha-1 in 2003. live biomass was significantly higher during the wet season than during the dry season (3229 versus 2529 kg ha-1) whereas dead biomass was higher during the dry season than during the wet season (2542 versus 1894 kg ha-1). the groundwater levels changes from -3.1 m to -6.5 m during the wet and dry seasons, respectively. the annual average of sla was 16.3 m2 kg-1 in 1999 and 20.4 m2 kg-1 in 2001. and for lai was 1.5 in 2000 to 2.8 in 2003. the albedo changes from 0.18 down to 0.16 at higher values of lai.
