EFFECT OF N-P-K FERTILIZATION ON YIELD AND TILLER DENSITY OF CREEPING BLUESTEM

Forage quality and quantity from palatable grasses, like creeping bluestem [Schizachyrium scoparium (Michx.) Nash var. polycladus (Schriber & Ball) Bruner (Syn S. stoloniferum Nash.)], are limited, especially in winter when cows graze Florida range. We anticipated that N fertilizer (0, 40, 60, 120 kg ha-1), P (0, 25 kg ha-1) and K (0, 100 kg ha-1) would increase bluestem yield, tiller density, and forage quality. Within sample dates yield and tiller density increased linearly with N rate. For example 31 days after fertilization, intercepts for equations predicting yield were 319 kg ha-1 and 124 m-2 with coefficients of 1.2 and 0.29, respectively, where the independent variable is N rate. Over sample dates yield responses to N rate were quadratic and tiller densities were cubic. Reproductive tiller density was increased by N fertilization (1989 tiller density, no. m-2, = 30 + 0.29N). Neither yield nor tiller density was affected by P fertilizer, but K fertilizer increased reproductive tiller density, hence fall yield. After 3 years of fertilization, N had negative quadratic and negative linear effects on yield and tiller density, respectively. Tissue N concentration in the fall was reduced with N fertilization because of increases in reproductive growth (1988 calendar 145 days postfertilization, g kg-1 = 5.7 - 0.041 N + 0.00031 N2). Fertilization of creeping bluestem is not a recommended practice when bluestem is to be grazed in fall and winter.