Browsing Journal of Range Management, Volume 46, Number 5 (September 1993) by Subjects
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Effect of N-P-K fertilization on yield and tiller density of creeping bluestemForage 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, nom-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.
Old World bluestem response to fire and nitrogen fertilizersOld World bluestem (Bothriochloa ischaemum L.) is being extensively established on marginal farmland in the Southern Plains. This 4-year field study in western Oklahoma developed guidelines for burning and N fertilization of Old World bluestem on calcareous and noncalcareous soils. Plots were on 'lron Master' Old World bluestem on a calcareous soil (Quinlan loam, shallow Typic Ustochrepts) and a noncalcareous soil (Carey loam, Typic Argiustolls). On each soil 4 blocks were split (spring burned, unburned) and N treatments (none, urea, ammonium nitrate) and time of N application (early, late) were randomly assigned within each burn treatment. Burning decreased (P<0.01) herbage yields by 6 to 30% per year. Nitrogen fertilizer broadcast at the rate of 50 kg N ha-1 increased herbage production about threefold. Ammonium nitrate fertilization resulted in 20% more herbage production than urea fertilization 1 year, and in equal production 2 years. The 4th year, application of ammonium nitrate in early April increased production by 20% compared to early April application of urea, urea was as effective as ammonium nitrate when either was applied in late April. Burning or calcareous soil had no adverse influence on the effectiveness of urea as compared to ammonium nitrate. Management implications for western Oklahoma and adjacent areas include: burn Old World bluestem only when necessary to remove substantial amounts of standing dead herbage, and broadcast urea 3 to 4 weeks after grass initiates growth when seasonal rains are more likely to move the urea into the soil, thereby decreasing potential for N loss by volatilization.