GRAZING DATE AND FREQUENCY-EFFECTS ON PRAIRIE SANDREED AND SAND BLUESTEM

A 5 year study was conducted during 1988-1992 to quantify the effects of grazing date and frequency on total organic reserves of prairie san dreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem (Andr opogon hallii Hack.), Treatments consisted of mid-month grazing period s in (1) June, (2) July, (3) August, (4) October, (5) June and July, ( 6) June and August, (7) July and August, or (8) June, July, and August , Seasonal stocking rates were equal among treatments and divided equa lly over multiple grazing periods, Grazing treatments were applied to the same pastures during 4 consecutive years with yearling cattle and 4-7 day grazing periods, Mean tiller weight of etiolated initial-sprin g growth was used to estimate total organic reserves in the fifth year , Dormant season grazing in October was not different from 4 years of rest for either species, Total organic reserves in prairie sandreed de creased when paddocks were grazed in June or July regardless of the nu mber of grazing periods per treatment, Reserves in sand bluestem were maintained by grazing once in June or August, Rotationally grazing pas tures 2 or more times during June-August is least likely to maintain o r increase total organic reserves in either species, Multiple grazing periods initiated in June reduced reserves by about 38% in prairie san dreed and 30% in sand bluestem, When stocking rates are similar to thi s study, deferment periods should be longer than 60 days after grazing in June to avoid measurable reductions in total organic reserves in b oth species, Periodic deferment of grazing until mid-August or later w ill be required to maintain simultaneously high levels of reserves in prairie sandreed and sand bluestem.