Forage production in silvopastoral systems of the Flooding Pampa is based on cool season grasses with a relatively asynchronous phenology regarding their accompanying deciduous trees. However, the productivity of cool season grasses in these systems is usually low. The hypothesis of this work is that the low productivity of cool season grasses is caused by tree litter constraining plant recruitment. Emergence and establishment (reproductive propagation), and tillering (vegetative propagation) patterns of tall fescue, a cool season grass in the region, were studied in two pairs of adjacent non-afforested and afforested poplar stands (tree age 26-28 years, tree density 453-797 plants ha -1 ). Observational and manipulative (i.e. addition of seeds, leaf litter removal) experiments indicated that the recruitment of tall fescue plants is strongly limited by the fall of poplar leaves over emerged seedlings, during autumn. Results suggest that any management practice capable of removing poplar litter, either through grazing or machinery, could neutralize this limitation enhancing the herbaceous primary production of the system.

In managed rangelands periods of low primary productivity determine troughs of forage availability, constraining animal production yearround. Although alternative tools to increase forage availability during critical seasons exists, most of them are unaffordable and short-lived in marginal areas. We explore the potential benefits of deciduous tree plantations favoring winter forage productivity by comparing aboveground net primary productivity (ANPP) patterns in herbaceous understory to tree plantations and natural grasslands in the Pampas (Argentina). These temperate subhumid grasslands are characterized by the coexistence of winter species, mainly C3 grasses of the native genera Stipa, Piptochaetium, and Bromus and the exotic genera Lolium and Festuca) and summer species (mainly C4 grasses of the native genera Paspalum, Bothriochloa, and Stenotaphrum) that replace each other throughout the seasons, with domination of the latter. We hypothesize that the natural decoupling of growing seasons between winter deciduous trees and winter grasses could provide the basis for the sustainable promotion of winter forage. We measured ANPP on two 23-year-old Populus deltoides plantations and their understory and compared them with adjacent open grasslands. Afforested stands had 55-75% higher annual ANPP than their non-afforested neighbors, with trees contributing *70% to total ANPP. Herbaceous canopies beneath plantations achieved about half of the ANPP observed in nonafforested situations with a contrasting seasonal distribution associated with shifts from C4 to C3 grass dominance. Winter ANPP, the most critical source of forage in these grazing systems, was similar or higher in the herbaceous understory of tree plantations to that on their non-afforested counterparts, suggesting that mixed systems involving deciduous trees and understory pastures are a valid and viable option in the region.

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La extensión agropecuaria implica un proceso complejo de interacción entre la educación e investigación agropecuaria y los productores. El proyecto de extensión MAS-PASTO de la Facultad de Agronomía de la Universidad de Buenos Aires (FAUBA), es un proyecto basado en la discusión participativa de conocimientos entre docentes-investigadores, productores y profesionales. El taller 2020 (virtual) tuvo como objetivo que productores, que habían participado en talleres anteriores del grupo (presenciales), afiancen los conocimientos a través de la práctica en establecimientos propios. Para esto cada productor trabajó en alguno de los siguientes ejes temáticos: 1) siembra de pasturas y verdeos; 2) manejo y mejoramiento de pastizales naturales y 3) diseño de circuitos forrajeros. Todos los productores abordaron el cálculo de la producción de carne para sus establecimientos, independientemente del eje temático elegido. Durante 6 meses, se realizó un trabajo conjunto entre productores, docentes y un joven profesional agrónomo. Se trabajó individualmente sobre la aplicación del tema elegido y, al finalizar el trabajo individual, se llevó adelante una jornada conjunta de intercambio donde cada productor presentó a sus pares en forma virtual el trabajo realizado, sus dificultades y resultados obtenidos. El taller se evaluó mediante encuestas a los participantes y la elaboración de un análisis FODA. Los resultados mostraron que el taller permitió a los productores practicar los conceptos presentados previamente e incorporarlos al manejo de sus establecimientos. A su vez, permitió consolidar un método efectivo y replicable para la generación y transferencia de tecnologías de procesos desde la FAUBA hacia el sector productivo.