Rethinking the Plant Economics Spectrum for Annuals: A Multi-Species Study

The plant economics spectrum hypothesizes a correlation among resource-use related traits along one single axis, which determines species’ growth rates and their ecological filtering along resource gradients. This concept has been mostly investigated and shown in perennial species, but has rarely been tested in annual species. Annuals evade unfavorable seasons as seeds and thus may underlie different constraints, with consequences for interspecific trait-trait, trait-growth, and trait-environment relations. To test the hypotheses of the plant economics spectrum in annual species, we measured twelve resource-use related leaf and root traits in 30 winter annuals from Israel under controlled conditions. Traits and their coordinations were related to species’ growth rates (for 19 species) and their distribution along a steep rainfall gradient. Contrary to the hypotheses of the plant economics spectrum, in the investigated annuals traits were correlated along two independent axes, one of structural traits and one of carbon gain traits. Consequently, species’ growth rates were related to carbon gain traits, but independent from structural traits. Species’ distribution along the rainfall gradient was unexpectedly neither associated with species’ scores along the axes of carbon gain or structural traits nor with growth rate. Nevertheless, root traits were related with species’ distribution, indicating that they are relevant for species’ filtering along rainfall gradients in winter annuals. Overall, our results showed that the functional constraints hypothesized by the plant economics spectrum do not apply to winter annuals, leading to unexpected trait-growth and trait-rainfall relations. Our study thus cautions to generalize trait-based concepts and findings between life-history strategies. To predict responses to global change, trait-based concepts should be explicitly tested for different species groups.

39 Management of cereal-grain forages for yield and quality

Cereal-grains have a long history of providing quality forage for livestock operations. Our objective is to review the existing literature and describe the principle factors controlling the yield and quality of cereal-grain forages. Generally, cereal-grain forage production can occur via management scenarios that include: 1) winter-annuals planted during fall and then grazed or harvested the following spring; 2) cereals not requiring vernalization planted during early spring and harvested during late-spring or summer; and 3) cereals not requiring vernalization planted during late-summer and harvested before winter. Winter-annuals planted during fall also are used extensively for fall grazing, particularly for backgrounding stocker cattle. The requirement for vernalization before plants elongate and produce viable seed plays a large role in synchronizing management strategies with producer goals. For example, maximization of fall growth can be attained by choosing a species or cultivar that does not require vernalization and will elongate, but this choice will likely eliminate winter survival and subsequent spring forage production. Ambient temperature during plant maturation affects lignin formation positively; therefore, forages grown during cooler fall temperatures will typically exhibit greater NDF digestibility than those maturing during summer. Most nutritional characteristics are influenced heavily by two competing processes that include the normal negative maturation effects that reduce the quality of most forages. However, this process is juxtaposed against the physiological process of grain fill, which can dilute concentrations of forage fiber components, increase energy density, and improve DM digestibility at advanced plant-growth stages. Digestibility of NDF declines with plant maturity, and generally is not affected by grain fill. A boot-stage harvest for silage often exhibits the most favorable nutritional characteristics for lactating dairy cows; however, producers making this management choice will need to accept a substantial yield penalty compared with a commonly recommended harvest at soft-dough stage, which would likely maximize yield.

143 Economics of cool-season annuals or reduced labor supplementation systems for wintering cowcalf pairs

Cattle producers typically feed hay and supplement for a 90 to 120 day window to maintain cows during the winter in Alabama. A 75-day trial evaluated the use of three systems (n = 3 replications per system): 1) rotationally grazed-winter annuals (GWA) on a 14-day rotation, 2) free-choice whole cottonseed (WCS) and bermudagrass hay, or 3) 50% soybean hulls and 50% corn gluten feed (SH:CGF) fed on alternate days at up to 1% BW daily and free-choice bermudagrass hay. GWA had the greatest Total Cost Per Pair Per Day (TCPD) for the 75 day grazing system at $6.58, followed by WCS at $4.73 and SH:CGF at $4.86. Initial and final cow BCS was not different among treatments (P = 0.1558). Cow ADG was greater (P = 0.0370) on GWA than SH:CGF and WCS (0.9, 0.2, and 0.2 kg, respectively), and calf ADG followed a similar pattern (1.5, 1.2, and 1.1 kg/day for GWA, WCS, and SH:CGF, respectively). WCS and SH:CGF were static across trial when only days of trial are considered, but TCPPD decreased linearly (R=.9723) as days on grazing increase. GWA becomes the low cost feed option (with WCS and SH:CGF inputs remaining constant) if trial days were extended to 119 days. This project demonstrates that GWA produces greater animal performance than other project diets, but requires additional grazing days (>119) to be the least cost feeding option.

139 Evaluation of cool-season annuals or reduced labor supplementation systems for wintering cowcalf pairs

Cattle producers typically feed hay and supplement for a 90- to 120-d window to maintain cows during the winter in Alabama. Relying on stored feeds can increase management system costs and labor needs. The objective of this demonstration project was to compare alternative, reduced labor management systems commonly used by producers in the region for diet quality and animal performance responses. A 75-day trial evaluated the use of three systems (n = 3 replications per system): 1) rotationally grazed-winter annuals (GWA) on a 14-day rotation, 2) free-choice whole cottonseed (WCS) and bermudagrass hay, or 3) 50% soybean hulls and 50% corn gluten feed (SH:CGF) fed on alternate days at up to 1% BW daily and free-choice bermudagrass hay. GWA had the greatest diet digestibility (P < 0.0001), and SH:CGF and WCS were not different from one another (88.7%, 64.3%, and 64.6%, respectively). Diet CP values differed (P < 0.0001) for WGA (21.5%), SH:CGF (13.1%), and WCS (11.2%), respectively. Initial and final cow BCS was not different among treatments (P = 0.1558). Cow ADG was greater (P = 0.0370) on GWA than SH:CGF and WCS (0.9, 0.2, and 0.2 kg, respectively), and calf ADG followed a similar pattern (1.5, 1.2, and 1.1 kg/day for GWA, WCS, and SH:CGF, respectively). This project demonstrates that winter annuals provided 75 days of high-quality winter grazing and resulted in greater animal performance than the other diets. However, all diets provided reduced labor options to maintain cows throughout the winter.