Effect of defoliation patterns and developmental morphology on forage productivity and carbohydrate reserves in WW-B.Dahl Grass [Bothriochloa bladhii (Retz) S.T. Blake]

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Texas Tech University

This study was conducted to develop strategies to improve WW-B Dahl establishment, and increase forage productivity using different management practices. Specific objectives included: 1) to quantify plant morphology in WW-B.Dahl plants at three growth stages; 2) to determine forage yield, quality, and leaf and stem seasonal pattern regrowth in WW-B.Dahl plants under different patterns of defoliation; 3) to evaluate total non-structural carbohydrate (TNC) concentrations and TNC pool sizes under different defoliation intensities; and 4) to evaluate seed and storage times to increase germination of WW-B.Dahl grass. Three hundred sixty WW-B.Dahl phytomers in 19-l pots were used. Pots were irrigated twice each week (1.17 liters wk-1), and maintained under greenhouse conditions at 30.2°C during 153 days in 2006. Experimental treatments were composed for three factors: 1) growth stages (GS): vegetative (V), reproductive (R), and post-reproductive (PR); 2) intensity of defoliation (ID): 0, 45, 65, and 85%; and 3) day after defoliation (DAD): 0, 3, 6, and 9 days. Variables evaluated included developmental morphology through the mean stage count (MSC) index and its variability (SMSC), forage yield (FY) and quality (CP, IVDMD), residual herbage and quality (CP and IVDMD), and TNC reserves (concentration and pool sizes).
Seed germination was evaluated using the ragdoll technique. Sixty treatments were composed by the interaction of age of seed or seed lot, kind of seed [dehulled and hulled], and storage time at 5°C (0, 2, 4, 6, 8, and 10 wk). Analysis of variance including tests for normality and homogeneous variances were performed for defoliation data, TNC reserves, and germination data. Fisher’s LSD tests at P<0.05 level were conducted to test significant differences among treatments means. Tiller variability (SMSC) throughout the growing season and vegetative tillers in late summer should be considered to plan proper grazing management in productive WW-B.Dahl stands. The high regrowth rates in vegetative stage and carbohydrate reserves replenishment (3- to 6-DAD) showed by WW-B.Dahl throughout the growing season highlighted the importance of residual herbage for plant recovery following defoliation. Forage yield, quality, regrowth rates, and carbohydrate reserves replenishment suggested that WW-B.Dahl grass may be properly used (45 to 65%) in V and R stages when a large proportion of vegetative tillers are present. According to the forage quality and carbohydrate reserves results, excellent cattle gains may be obtained in WW-B.Dahl pastures during the growing season, as well quickly plant recovery following defoliation, tiller recruitment, and rapid growth initiation the next growing season. Germination data indicated that stored dehulled seed for 2- to 8-wk at 5°C before seeding may produce better pastures of WW-B.Dahl.

Defoliation, Old world bluestem, Bothriochloa bladhii