ChileanJAR

A method to esti mate, with cuttings, growth and productivity of a pasture when grazed is proposed. During the growing season, with series of data starting at different cutting dates, dry matter accumulation is measured periodically. The function y = A/(1 + be^-ax) is adjusted with the least square method, where A is the maximum accumulated dry matter in each series, x is the time expressed in number of days trom the start of regrowth, and a and b arethe coefficients obtained from the adjustment. Growth rate is calculed from the derivative dy/dx of the function with respect to time. Since there are differences in the starting date of each series, daily dry matter increase, for a given total dry matter accumulation, can be determined for different dates. Date from phalaris (1980 end 1981) and fescue (1981), in the Biobío Andes Foot-hills, and from the mixtures white dover + grasses and su b-clover + fescue (1981), in the Arauco Province,are presented. The results show high determination coefficients and significant regressions at the 5% level, for alI series (except one), and at 1%, for most of them. The maximum growth rates occured between October 15 and November 25, ranging between 60 and 200 kg D.M./ha/day and were dependent on the year, type of pesture, zone, and amount of actual photosynthesizing material.