Resumen: El trabajo tuvo como objetivo estudiar el efecto de la plantación forestal sobre la cobertura del suelo, los tipos productivos y el valor pastoral del estrato herbáceo. El estudio se realizó en tres localidades, en 18 transectas ubicadas en la entre fila, callejones cortafuego y campo natural, localizando 30 marcos de 0,25 m2 en cada una. Se determinó la cobertura de 172 especies y utilizando la clasificación de tipos productivos se estimó el valor pastoral corregido por cobertura vegetal. Las comunidades desarrolladas bajo plantaciones forestales presentaron menor cobertura vegetal. El valor pastoral de las comunidades desarrolladas en callejones cortafuego y plantaciones de Pinus taeda y Eucalyptus grandis fueron inferiores al resto de las situaciones.

Summary: The objective of the work was to study the effect of forest plantation on the soil cover, the productive types and the pastoral value of the herbaceous stratum. The study was carried out in three locations, in 18 transects located in the row between, short fire alleys and natural grassland, locating 30 frames of 0.25 m2 in each. The coverage of 172 species was determined and, using the classification of productive types, the pastoral value corrected for vegetation cover was estimated. The communities developed under forest plantations had lower vegetation cover. The pastoral value of the communities developed in alleys of fire cutting and plantations of Pinus taeda and Eucalyptus grandis were inferior to the rest of the situations.

Resumen: La agricultura ha experimentado un fuerte proceso de cambios que han significado un aumento de las problemáticas sanitarias causadas por patógenos necrotróficos. Diversos trabajos muestran que manejando microorganismos benéfi-cos es posible reducir el impacto de las enfermedades. En base a esto, el objetivo de este trabajo fue determinar el efecto de los cultivos sobre la población de Trichoderma spp. en suelo y en rastrojo, en un sistema agrícola sin laboreo. El monitoreo de la población de Trichoderma spp. se realizó en un experimento con cuatro secuencias de cultivos. Se realizaron muestreos de rastrojo y suelo en primavera y otoño, durante tres años consecutivos. La densidad poblacional de Trichoderma spp. fue determinada mediante el método de dilución y recuento en placa. A su vez, se determinaron las propiedades químicas del suelo de cada tratamiento. Los resultados mostraron que el rastrojo de cebada presentó mayor densidad poblacional de Trichoderma spp. que el rastrojo de otras especies. Las distintas secuencias de cultivo afectaron significativamente la densidad poblacional de este hongo en el suelo. Sin embargo no tuvieron efecto sobre las propiedades químicas del suelo, ni hubo una asociación entre estas y la población de Trichoderma spp. Estos resultados establecen la posibilidad de manejar la población nativa de Trichoderma spp. mediante la elección de los componentes de las secuencias de cultivos, y permiten identificar ambientes más propicios para mantener altas poblaciones de Trichoderma. La identificación de ambientes que favorecen altas poblaciones de Trichoderma podría indicar situaciones más favorables para eventuales inoculaciones del antagonista.

Summary: Agriculture has experienced a strong process of changes that have led to an increase in crop diseases caused by necrotrophic pathogens. Several studies demonstrated that by managing beneficial microorganisms, it is possible to reduce the impact of plant diseases. Based on this, the objective of this study was to determine the effect of field crops on the population of Trichoderma spp. in soil and straw in a no-till cropping system. The population of Trichoderma spp. was monitored in an experiment with four different crop sequences. Samples of soil and crop debris were collected in spring and fall, over three consecutive years. The population density of Trichoderma spp. was determined by dilutions with plate counts method. In addition, soil chemical properties were determined for each treatment. Barley debris showed the highest population density of Trichoderma spp. in relation to other crop debris. Different cropping sequences significantly affected the population density of this fungus in the soil. However, they had no effect on the soil chemical properties, and no association was found between these variables and the population of Trichoderma spp. These results confirm the possibility to handle the native population of Trichoderma spp. through the components of the crop sequences and indicate that conducive environment may support higher populations of Trichoderma. The identification of those environments enhancing Trichoderma could indicate better conditions where inoculations of this antagonist might have higher chances of success.

Resumen: El objetivo del trabajo fue calibrar y validar el modelo WinIsareg para soja en el litoral del Uruguay. El modelo estima las necesidades de agua de los cultivos bajo diferentes condiciones hídricas, mediante la simulación del balance hídrico (BH) de suelos. La información de suelo, cultivo, y clima, utilizada en la evaluación del modelo fue obtenida durante las temporadas 2011 y 2013. La evaluación consistió en ajustar los coeficientes de cultivo (Kc) y los factores de agotamiento de agua disponible sin estrés («p») para las fases de desarrollo (inicial, media y final) de soja, de forma tal de minimizar las diferencias entre los valores observados y simulados del contenido de agua del suelo. El Kc inicial ajustado fue 0,35, el Kc medio 1,18 y el Kc final 0,75. Los «p» ajustados fueron de 0,4 para las fases germinación y R1-R6 y de 0,6 para el resto del ciclo. Los Kc y «p» obtenidos permitieron lograr una elevada concordancia entre los valores simulados y observados del contenido hídrico del suelo para la calibración y la validación con diferentes situaciones de disponibilidad hídrica. El coeficiente de regresión (b) entre valores observados y simulados fue cercano a 1, las estimaciones del error absoluto (AAE) y raíz cuadrada media del error (RCME) fueron menores a 5 %, el coeficiente de Willmott «d» y la eficiencia (EF) cercanos a 1 y el coeficiente de determinación (R2) mayor a 0,8. El resultado de los indicadores estadísticos permite afirmar con certeza el buen funcionamiento del modelo WinIsareg en soja para el litoral del país.

Summary: This study was aimed to calibrate and validate the WinIsareg model for soybeans in the west area of Uruguay. This model estimating the crop water requirements under different moisture conditions by simulating a soil water balance (BH). The soilsclimate-crop information was obtained during the 2011 and 2013 seasons. The assessment consisted in searching the cultivation coefficients (Kc) and the no-stress available water depletion factors («p») relative to the initial, mid and end season crop development stages in order to minimize the differences between the observed soil water content values. The best adjusted Kc values were 0.35, 1.18 and 0.75 for initial, mid and end season, respectively. The adjusted “p” value was 0.4 in germination and in R1-R6 phases, while it was 0.6 for the rest of the cycle. The Kc and «p» obtained allowed achieving a high concordance between the simulated and observed values of the water content of the soil for calibration and validation with different situations of water availability. The regression coefficient (b) was very close to 1. The mean absolute error and root mean square error were less than 5 %, the Willmott coefficient and the efficiency (EF) were also close to 1, while the determination coefficient (R2) was higher than 0.8. These results allow to affirm with certainty the proper simulation of WinIsareg model in soybeans in the west area of the country.

Resumen: Este trabajo tuvo como objetivo caracterizar la composición específica, la riqueza, equidad y diversidad de comunidades de sotobosque, callejones cortafuego y campo natural. El estudio se realizó en tres localidades, en 18 transectas con direcciones N-S y E-O ubicadas en la entrefila, callejones cortafuego y campo natural, localizando 30 marcos de 0,25 m2 en cada una. Fueron relevadas 172 especies clasificadas por familia y género, y se calculó para la vegetación de cada sitio la riqueza, equidad y diversidad. Vegetaciones desarrolladas en ambientes con mayor interferencia del dosel arbóreo presentaron menor número de familias, géneros y especies. Los valores de riqueza y diversidad disminuyeron ante aumentos de la interferencia del dosel arbóreo y la mayor equidad se asoció a ambientes más sombreados. Plantaciones forestales comerciales de E. grandis y P. taeda con orientación E-O presentaron comunidades de sotobosque con menor riqueza y diversidad especifica. Al aumentar la intensidad del disturbio producido por los rodales se generaron comunidades con los mayores niveles de equidad.

Summary: The objective of this work was to characterize the specific composition, richness, equity, and diversity of the scrubland communities, fire-break roads and natural grassland surfaces. The study was done in three points, in 18 transects (direction N-S and E-W) located within the forest stands, fire-break roads and natural grassland, localizing 30 frames of 0,25 m2 each. Were surveyed 172 species classified by family and gender, and calculated richness, equity, and calculated diversity for the vegetation of each site. Vegetation communities developed in environments where the forest stands do interfere show lower values in the number of families, gender, and species. Values of richness and diversity decreased with increases in tree canopy interference, and greater equity was associated with more shaded environments. Commercial forest plantations of E. grandis and P. taeda, E-W oriented, gave scrubland communities with low richness and specific diversity. By increasing the intensity of the disturbance produced by the stands, communities with the highest levels of equity were generated.

RESUMO O objetivo deste trabalho foi avaliar o efeito de diferentes intensidades de pastejo sob a produção de forragem e o desempenho animal de novilhos superprecoces mantidos sob pastejo contínuo em sistema integrado de produção agropecuária. Os tratamentos consistiram das alturas de manejo de pasto de 10; 20; 30 e 40 cm; e de um tratamento sem pastejo. Os pastos eram constituídos de aveia-preta (Avena strigosa Schreb.) e azevém anual (Lolium multiflorum Lam.) em sucessão a cultura da soja (Glycine max (L.) Merr.). As variáveis massa de forragem, oferta de forragem e palhada residual se ajustaram de forma positiva e linear ao incremento da altura do pasto (P≤0,0001). O desempenho individual de novilhos apresentou resposta quadrática (P = 0,0017) e foi otimizado com o incremento na altura do pasto até valores próximos a 30 cm, com ganho de peso por animal de aproximadamente 1,0 kg dia-1. O mesmo foi observado para o peso vivo ao abate e as características de carcaça (P≤0,0305). Os resultados sugerem que alturas próximas a 30 cm permitem maiores ganhos individuais, devido ao aumento da quantidade de forragem disponível por animal e a melhor qualidade da forragem consumida, não havendo comprometimento da palhada residual destinada à cultura subsequente.

ABSTRACT The aim of this study was to evaluate the effects of different grazing intensities on forage production and animal performance of yearling steers kept under permanent grazing in an integrated crop-livestock system. The treatments consisted of areas with sward heights of 10; 20; 30 and 40 cm, and one treatment with no grazing. The pastures were of bristle oat (Avena strigosa Schreb.) and annual ryegrass (Lolium multiflorum Lam.) following soybean (Glycine max (L.) Merr.). The variables forage mass, forage allowance and residual straw showed a positive and linear fit to the increasing sward height (P≤0.0001). Average daily gain of steers displayed a quadratic response (P = 0.0017), being optimal with increases in grazing height up to values of near 30 cm, showing a weight gain per animal of approximately 1.0 kg day-1. A similar response was seen for live weight at slaughter and carcass characteristics (P≤0.0305). The results suggest that sward heights close to 30 cm provide greater individual gains, due to the increase in forage available to each animal and the better quality of the consumed forage without compromising the residual straw destined for the following crop.

Una manera de aumentar el rendimiento y calidad de forraje de las pasturas nativas es a través de la inclusión de leguminosas en el tapiz. Para un establecimiento apropiado de las mismas es necesario contar con una disponibilidad adecuada de fósforo (P) en el suelo. Dados los niveles deficientes de este nutriente en muchos suelos, es necesario su aporte a través de la fertilización. El objetivo del presente estudio fue evaluar el efecto del P aplicado a la siembra en varias dosis sobre el contenido de P y nitrógeno (N) de Lotus tenuis Waldst. & Kit ex. Willd. (lotus de los bajos) y Trifolium repens L. (trébol blanco), en un Gleysol Lúvico Melánico Típico del Departamento de Cerro Largo, Uruguay. Se evaluaron cuatro niveles de P (0, 21,8, 43,6 y 65,4 kg de P.ha-1) aplicados al voleo en la siembra, como superfosfato triple (0-46-0). El diseño experimental fue de bloques al azar, con ocho repeticiones. A los 120 días post-siembra se recolectaron 10 plantas/parcela/especie, para determinar el peso seco de las partes aéreas y raíz y su contenido de P y N. La concentración de P en la materia seca aumentó con la dosis de P para ambas especies, en tanto que el contenido de N mostró diferencias significativas solo en T. repens.

One way of increasing forage yield and quality of natural pastures is through the inclusion of legumes in the grass cover. In order to achieve an appropriate crop establishment it is necessary to have an adequate availability of phosphorus (P) in the soil. Given the poor levels of this nutrient in many soils, it is necessary to fertilize. The objective of this study was to evaluate the effect of P fertilization at various doses on the content of P and nitrogen (N) in Lotus tenuis Waldst. & Kit ex. Willd. (lotus from the lowlands) and Trifolium repens L. (white clover) in a smectitic, fine, thermic Oxiaquic vertic argiudoll at Cerro Largo, Uruguay. The treatments were four phosphorus levels (0, 21,8, 43,6 and 65,4 kg P ha-1) broadcasted at seeding as triple superphosphate (0-46-0). The experimental design was randomized blocks, with eight repetitions. At 120 days post seeding, 10 plants/plot/specie were collected to determine the aerial part and root dry weight, and P and N content. P concentration in dry matter increased with P doses for both species, while N concentration showed significant differences only in T. repens.

RESUMOEm Sistemas Integrados de Produção Agropecuária, a presença dos animais em pastejo pode provocar alterações na produção das culturas subsequentes. Com o objetivo de verificar como diferentes manejos do pasto poderiam afetar o cultivo de soja, a 9ª fase de lavoura em rotação pecuária/lavoura foi avaliada. Os tratamentos foram intensidades de pastejo (10; 20; 30; 40 cm de altura do pasto), aplicados desde 2001, em pasto misto de aveia e azevém anual, além de área sem pastejo utilizada como testemunha. O delineamento experimental foi de blocos ao acaso, com três repetições. Houve diferença na população inicial de plantas e na massa do nódulo (P<0,05), porém, o número e a massa de nódulos por planta foi semelhante (P>0,05). O rendimento de soja foi diferente entre os tratamentos, porém, não houve diferença entre áreas pastejadas e não pastejadas. Houve diferença para cobertura e frequência de espécies indesejáveis entre tratamentos (P>0,05). Em conclusão, diferentes intensidades de pastejo afetam os parâmetros de rendimento e desenvolvimento da soja, mas apenas a intensidade de pastejo de 10 cm pode comprometer a safra de soja subsequente.

ABSTRACTGrazing livestock in integrated crop-livestock systems can cause impacts in the subsequent crop cycle. Aiming to investigate how grazing could affect soybean, the 9th crop cycle of a pasture/soybean rotation was assessed. Treatments were grazing intensities (10, 20, 30 and 40 cm of sward height) applied since 2001 in a mixed of oat and annual ryegrass; and an additional no grazing area as control. Treatments were arranged in a completely randomized block design with three replicates. Grazing affected soybean population and the mass of individual nodules (P<0.05), while the number and mass of nodules per plant were similar (P>0.05). Soybean yield showed differences among treatments, but no difference was found between grazed and non-grazed areas. Grazing intensities impact the coverage and frequency of weeds (P>0.05). In conclusion, grazing intensity impacts different parameters of soybean yield and development, but only the grazing intensity of 10 cm can jeopardize the succeeding soybean crop.

El embalse de Salto Grande, formado en 1979 al finalizar la construcción de la represa homónima, ocupa la última porción del curso medio del río Uruguay. Estas obras determinaron la inundación de numerosas hectáreas en los departamentos de Artigas y Salto en Uruguay y en Entre Ríos, Argentina, con destrucción de bosques ribereños e isleños de elevada diversidad. A más de tres décadas de este disturbio ha sido posible observar regeneración natural de fajas boscosas sobre sus riberas. La composición florística y los caracteres de la vegetación de estos bosques han sido estudiados mediante recorridas exhaustivas y muestreos en 16 lugares a orillas del embalse, realizándose análisis estadísticos de los datos. En toda el área se contabilizaron 100 especies leñosas: 83 nativas y 17 exóticas pertenecientes a 34 familias. No obstante, el número de especies registradas en cada local es mucho menor, con mínimos de 10, 12, 17 especies por recorrida; dos, siete, nueve especies por muestreo en algunos bosquecitos; y un máximo de 48 y 33 especies (por recorrida y muestreo respectivamente) en el local más norteño. En las comunidades del embalse estudiadas se repiten y son predominantes Erythrina crista-galli, Vachellia caven (Acacia caven), Sesbania virgata, Sebastiania schottiana, Terminalia australis y otras, reconocidas como especies pioneras o sucesionales tempranas. La familia dominante es Fabaceae. En islas próximas a Bella Unión, al norte del embalse se conserva la vegetación de selva con pocas alteraciones, constituyendo fuentes de propágulos.

The reservoir of Salto Grande, formed in 1979 when the building of the homonymous dam was completed, covers the last stretch of the middle section of the Uruguay river. These works caused the flooding of numerous hectares in the departments of Salto and Artigas in Uruguay, and in the province of Entre Ríos in Argentina, destroying woods of great diversity on the riverside and on the islands. After more than three decades of this disruption, it has been possible to observe natural regeneration of wooded strips on the banks. The composition of the flora and the characters of the vegetation in these woods have been thoroughly studied on rounds of observation and samplings performed on 16 places on the banks of the reservoir and statistical analysis of the data have been done. One hundred woody species have been counted all over the area: 83 native ones and 17 exotic ones belonging to 34 families. Nevertheless, the number of species listed in each location is much less, with a minimum of 10, 12, 17 species per observation round; two, seven, nine species per sampling in some small woods; and a maximum of 48 and 33 species (per round and per sampling, respectively) in the most northern location. In the communities of the reservoir which were studied Erythrina crista-galli, Vachellia caven (Acacia caven), Sesbania virgata, Sebastiania schottiana, Terminalia australis and others recognized as pioneers or early successional species are recurrent and predominant. The predominant family is Fabaceae. On the islands near Bella Unión, to the north of the reservoir, the forest vegetation remains with few alterations, thus being a source of propagules

El trabajo se realizó en la Facultad de Agronomía, ubicada en Paysandú, Uruguay (32º 23’57,86" latitud sur y 58º 02' 42,48" longitud oeste, 61 msnm). El objetivo fue estudiar la respuesta en la producción invernal de un campo natural bajo diferentes dosis de fertilización nitrogenada y ofertas de forraje. El experimento fue conducido en un diseño experimental central compuesto rotacional de precisión uniforme, con dos factores a cinco niveles cada uno: nitrógeno (N) = 0, 44, 150, 256, 300 kg/ha de N y ofertas de forraje (OF) = 4,0; 5,5; 9,0; 12,5 y 14,0 kg MS/100 de peso vivo (PV), distribuidos en dos bloques. Los resultados obtenidos permiten establecer la clara interacción entre el efecto de la fertilización nitrogenada, la intensidad del pastoreo y la composición botánica de la pastura, determinando resultados distintos según los niveles de cada factor utilizado. Existió una marcada repuesta del número de macollos de Bromus auleticus al aumentar la OF de forraje independientemente del nivel de N, que sugiere su baja tolerancia al aumento en la intensidad de pastoreo. Se destaca la capacidad pionera de colonizar ambientes pobres que presentó Stipa setigera, que permitiría la recuperación temprana de ambientes altamente disturbados, posibilitando el incremento de la productividad del sistema

The research was conducted at the School of Agronomy, located in Paysandú, Uruguay (32º 23’57,86" South and 58º 02' 42,48" West 61 msnm). The aim was to study the response in winter production of a native pasture to different levels of nitrogen fertilization and herbage allowance. The experiment was led in an experimental central compound rotational design of uniform precision, with two factors with five levels each: nitrogen (N) (0, 44, 150, 256, 300 kg/ha of N) and herbage allowance (HA) (4,0; 5,5; 9,0; 12,5 and 14,0 kg MS/100 kg of live weight LW), distributed in two blocks. The results obtained show a clear interaction between the nitrogen fertilization, grazing intensity and pasture botanical composition, determining distinct results depending on the levels of each factor used. There was a strong response in the number of tillers of Bromus auleticus when increasing the HA regardless of the level of N, suggesting their low tolerance to increased grazing intensity. It highlights the pioneering capacity to colonize poor environments Stipa setigera presented, that would allow early recovery of highly disturbed environments, enabling increased system productivity

Para comprender mejor las consecuencias de la aplicación de diferentes intensidades de pastoreo, se desarrollaron funciones de respuesta de la producción y composición del forraje de una pastura de Lolium perenne a ofertas de forraje (OF) y se analizaron en forma multivariada las características estructurales. Las OF evaluadas fueron 2,0- 4,5-7,0 y 9,5 kg MS/100 kg de peso vivo animal/día. Las relaciones entre producción de forraje y utilización relativa del forraje con las OF fueron lineales: producción de forraje (kg MS/ha) = 3619+1078OF (P<0,0038; r²=0,74); utilización del forraje (porcentaje) = 88,8-3,86OF (P<0,0066; r²=0,69), no detectándose diferencias en el forraje desaparecido. La relación de la OF de la biomasa aérea pre pastoreo y la altura del follaje para todo el período fue: biomasa aérea (kg MS/ha) = -758+237x, (P<0,0001; r²=0,79) siendo x = altura (cm). La biomasa de láminas prepastoreo fue afectada linealmente (P<0,01; r²=0,70) por la biomasa de láminas verdes remanentes del pastoreo anterior y por la densidad de macollos (P<0,0001; r²=0,67). El análisis de componentes principales indicó que bajo esas condiciones, únicamente la mayor OF evaluada mantenía los valores de las variables relativamente altos, sugiriendo así una mayor productividad y estabilidad de la pastura bajo este manejo. Las relaciones obtenidas se consideran útiles para el manejo de las pasturas, a pesar de que las condiciones ambientales variaron durante el período de medición, la frecuencia del pastoreo fue mayor a la recomendada y algunos macollos pasaron al estado reproductivo

For a better understanding of the consequences of the application of different grazing intensities, functions of response of composition and forage production of a pasture of Lolium perenne under different grazing herbage allowance levels (OF) were developed, and their structural characteristics were analysed with a multivariate method. The OF evaluated were 2.0- 4.5-7.0 and 9.5 DM kg/100 kg of animal liveweight/day. The relationships between forage production and relative forage utilization with the OF were lineal: forage production (DM kg/ha)=3619+1078OF, (P<0.0038; r²=0.74); forage utilization (percentage )=88.8-3.86OF, (P<0.0066; r²=0.69), but no differences were detected in the disappeared forage. The relationship between pre-graze aerial biomass and foliage height (cm) for the entire period was: aerial biomass (DM kg/ha) = -758 + 237x (P<0.0001; r² = 0.79), for x=height (cm). The pre-graze green leaves biomass was lineally affected (P<0.01; r²=0.70) ) by the remainder green leaves biomass post-graze and by tillers density (P<0.0001; r²=0.67). Principal component analysis indicated that, under these conditions, only the biggest OF evaluated maintained the values of variables relatively high, suggesting a highest pasture productivity and stability under these treatments. The relationships achieved are useful for pasture management, although the environmental conditions changed during the experimental period, the grazing frequency was higher than the recommended and some tillers began to reproductive state

The overseeding of ryegrass (Lolium multiflorum Lam) on sub-tropical native pastures increases the availability and quality of forage in the cold season. However, soil chemical amendment and nitrogen use can affect the floristic composition, with consequences to the primary and secondary production. In a randomized complete block design with three replications, the effect of nitrogen fertilization (40, 90 and 140 kg/ha of nitrogen) on native pasture overseeded with ryegrass in two consecutive years was assessed regarding production and composition of pasture and performance of beef calves. In both years, the forage accumulation rate and forage production responded linearly to the increase in nitrogen rates as a result of increased participation of ryegrass. The lower efficiency of responses in 2008 was due to the increased participation of dead material and the reduction of ryegrass in the forage sward. In 2007 there was an increasing substitution of the participation of native grasses by ryegrass with increasing nitrogen rates. Native legumes and other species were almost not affected by nitrogen fertilization. The average daily weight gain of the animals responded linearly to nitrogen rates in 2007, and quadratically in 2008. The stocking rate and gain per hectare increased linearly in both years, with greater responses in 2007. The production and composition of forage and livestock production are improved by the use of nitrogen, but the efficiency of responses can be affected by sowing date and nitrogen fertilization.

El trabajo se realizó en la Facultad de Agronomía, ubicada en Paysandú, Uruguay, 32º 23’57,86" S y 58º 02' 42,48" O, 61 m s n m. El objetivo fue estudiar la respuesta en la producción invernal de un campo natural bajo diferentes dosis de fertilización nitrogenada y ofertas de forraje. El experimento fue conducido en un diseño experimental central compuesto rotacional de precisión uniforme, con dos factores a cinco niveles cada uno: nitrógeno (N) = 0, 44, 150, 256, 300 kg/ha y ofertas de forraje (OF) = 4,0; 5,5; 9,0; 12,5 y 14,0 kg MS/100 kg de peso vivo (PV), distribuidos en dos bloques. La producción invernal (kg MS/ha) mostró compensación entre factores, siendo máxima con dosis altas de N y baja oferta de forraje, o con baja dosis de N y alta oferta de forraje. La eficiencia de utilización de fertilizante alcanzó un máximo de 16 kg MS/kg N, similar a la lograda con especies cultivadas. La respuesta observada se reflejó en la calidad de la vegetación, estimada a partir de la relación entre la biomasa de especies invernales y estivales (relación I/E), que maximizó a dosis intermedias de N. En consecuencia, la combinación de dosis bajas de nitrógeno (50 kg/ha) con asignaciones intermedias de forraje (8,0% PV), permitió duplicar la producción promedio de las pasturas naturales de similar composición florística de la zona del litoral del Uruguay.

This research was conducted at the Faculty of Agronomy, located in Paysandú, Uruguay, 32º 23’57,86" S y 58º 02' 42,48" O, 61 m s n m. The aim was to study the response in winter production of a native pasture to different levels of nitrogenous fertilizer and herbage allowance. The experiment was led in an experimental central compound rotational design of uniform precision, with two factors with five levels each one: nitrogen (N) (0, 44, 150, 256, 300 kg/ha of N) and herbage allowance (OF) (4,0; 5,5; 9,0; 12,5 and 14,0 kg MS/100 kg of live weight PV), distributed in two blocks. Winter production (MS kg/ha) was the highest with high doses of N and low supply of forage. It was also high under low dose of N and high herbage allowance, revealing some compensation between both factors. The efficiency of fertilizer use peaked at 16 kg MS/kg N, and was similar to the one achieved with cultivated species. The observed response was mirrored in the vegetation quality, estimated from the relation between the biomass of winter and summer species (I/E ratio), which turned out to be the highest with intermediate doses of N. Consecuently, the combination of low levels of N (50 kg/ha) with intermediate herbage allowance (8,0% PV), helped double the average winter production of the native pasture of West Uruguay.

Se evaluó el efecto de intensidades de pastoreo aplicadas como ofertas de forraje (OF) de 2,0 - 4,5 – 7,0 y 9,5 kg MS/100 kg de peso vivo animal, de agosto a noviembre, en la densidad y peso de los macollos de una pastura de Lolium perenne. El diseño fue completamente al azar con dos repeticiones. Las relaciones entre ambas variables y las OF fueron lineales en octubre y noviembre: Densidad de macollos (macollos/m²)=1821+209 OF (P<0,001; r²=0,76), Peso seco del macollo (mg)=19,3+8,1 OF (P<0,0001; r²=0,70), no ocurriendo mecanismos de compensación. Las OF afectaron la persistencia de la pastura, perdiéndose en noviembre 58 plantas/m² por cada 1 % de disminución en la OF (P<0,0001; r²=0,84). Las OF también afectaron el rebrote. La relación entre el peso del macollo remanente y el del rebrote para todo el período fue significativa (P<0,0004; r²=0,66): Peso de macollo (mg) pre-pastoreo=34,61+0,99 x, siendo x=peso de macollo del forraje remanente del pastoreo anterior. Los resultados obtenidos reflejan la complejidad de los procesos, y que en las condiciones de Uruguay la luz no es el principal factor limitante en la productividad de las pasturas, y que la intensidad del pastoreo es una variable importante de manejo.

The effect of intensities of grazing applied as forage offers (OF) - 2,0 - 4,5 - 7,0 and 9,5 kg DM/100 kg of animal liveweight on tillers density and dry weight was evaluated from August to November in a Lolium perenne sward. The design was totally at random with two replicates. The relationships between both variables and the OF were lineal in October and November: Tillers density (tillers/m²)=1821+209 OF (P<0,001; r²=0,76), Tillers dry weight (mg)=19,3+8,1 OF (P<0,0001; r²=0,70). No compensatory mechanisms occurred. Grazing intensity affected the persistence of the pasture. In November, 58 plants/m² got lost for every 1 % decrease in the OF (P<0,0001; r²=0,84). The OF also affected pasture regrowth. The relationship between tiller weight of the remainder pos-graze and tiller weight of the regrowth for the whole period was significant (P<0,0004; r²=0,66): Tillers dry weight (mg) pre-graze=34,61+0,99 x, for x=weight of tiller of the forage remainder of the previous defoliation. The obtained results reflect the complexity of the processes. Under Uruguay´s conditions the light is not the main factor limiting pasture productivity, while defoliation intensity is an important variable.

A taxa de aparecimento de folhas (TAF) e o filocrono são conceitos associados, que exercem forte influência na produção de forragem. O filocrono é o intervalo de tempo entre o aparecimento de duas folhas sucessivas acima do pseudocaule e varia de acordo com alguns fatores ambientais, sendo a temperatura o fator determinante. O experimento foi conduzido em pastagem natural em Eldorado do Sul, RS, com o objetivo de testar a variação no filocrono em diferentes estações do ano, níveis de oferta de forragem (NOF) e posições topográficas (PT). Para a definição do filocrono, foram amostrados perfilhos marcados e estabeleceu-se a relação entre número de folhas produzidas e a soma térmica do período amostral. A soma térmica (em °C) necessária para que a planta emita uma folha é igual a 1/b, sendo b o coeficiente angular verificado na regressão. As retas obtidas para as combinações entre estações, NOF e PT foram comparadas. Em condições de primavera e verão, se obteve filocrono de 156°C para P. notatum e de 238°C para C. selloana, independentemente dos tratamentos avaliados.

Leaf appearance rate and phyllochron are related variables which play a central role in forage production. Phyllochron is the time interval between the appearance of successive leaves and varies according to a number of environmental factors, among which temperature is the most important. The experiment was conducted in natural pasture with the aim of testing phyllochron variation under different seasons, herbage allowances, and topographic positions. Marked tillers were used to define the phyllochron, establishing a relationship between the number of leaves produced against thermal time during the sampling period. The time (expressed in °C) needed for the emergence of a leaf is equal to 1/b, where b is the slope coefficient of the regression. The lines for the season combinations, herbage allowances and topographic positions sampled were compared. Under Spring and Summer conditions, the phyllochrons for P. notatum and C. selloana were 156°C and 238°C respectively, regardless of treatment.