The N-P-K soil nutrient balance of portuguese cropland in the 1950s: the transition from organic to chemical fertilization

Agricultural nutrient balances have been receiving increasing attention in both historical and nutrient management research. The main objectives of this study were to further develop balance methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from cropland topsoil for average conditions in the period 1951–56. We found a consistent deficit in N, both for nationwide (−2.1 kg.ha−1.yr−1) and arable crops (−1.6 kg.ha−1.yr−1) estimates, that was rectified in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2–4.6 kg.ha−1.yr−1 and 1.0–3.0 kg.ha−1.yr−1, respectively). We observed that the 1950s is the very moment of inflection from an agriculture fertilized predominantly through reused N in biomass (livestock excretions plus marine, plant and human waste sources) to one where chemical fertilizers prevailed. It is suggested that N deficiency played an important role in this transitioninfo:eu-repo/semantics/publishedVersio

Driving competitive and facilitative interactions in oak dehesas through management practices

Email: [email protected] audienceDehesas are extant multi-purpose agroforestry systems that consist of a mosaic of widely-spaced scattered oaks (Quercus ilex L.) combined with crops, pasture or shrubs. We aimed to clarify the role of trees in dehesas of CW Spain focussed on the analysis of tree-understorey interactions. Spatial variability of resources (light, soil moisture and fertility), microclimate, fine roots of both herbaceous plants and trees and forage yield was measured. Additionally, we compared the nutritional and physiological status, growth and acorn production of oaks in cropped (fodder crop), grazed (native grasses) and encroached (woody understorey) dehesa plots. Significant light interception by trees was limited to the close vicinity of the trees, with very low reduction away from them. Both microclimate and soil fertility improved significantly in the trees vicinity, irrespective of soil management. Soil moisture varied very few with distance from the trees, as a result of the extended root system of oaks. Root systems of trees and herbs did not overlap to a great extent. Crop production was higher beneath trees than beyond the trees in unfertilised plots and foliar nutrient content of oaks did not increase significantly with crop fertilisation, indicating that trees and crops hardly compete for nutrients. Moreover, trees benefited from the crop or pasture management: trees featured a significantly improved nutritional and physiological status, a faster growth and a higher fruit productivity than trees growing in encroached or forest plot

Multiple resistances against diseases and insects in a breeding population of Pinus pinaster

Peer reviewe

Atacados por todos los flancos: defensas cruzadas de los pinos frente a sus múltiples enemigos

Trabajo presentado como póster al Congreso forestal “Bosques de futuro” celebrado en Orense entre el 25 y el 26 de mayo de 2011Las plantas se defienden de sus enemigos con distintas defensas mecánicas y químicas cuya maximización simultánea podría estar comprometida. En especies de vida larga y de gran tamaño, como los pinos, la teoría predice que la evolución favorece defensas de tipo generalista, eficaces frente a un amplio abanico de enemigos, que actúan de forma cuantitativa reduciendo la palatabilidad de los tejidos, y con ello la eficacia biológica de sus enemigos. En la literatura, sin embargo, no existen evidencias de esta supuesta resistencia cruzada. En esta comunicación integramos los resultados de distintos experimentos independientes realizados con el mismo material genético para determinar si existe correlación genética positiva en la resistencia a distintas plagas y enfermedades, y si ésta está relacionada con caracteres cuantitativos de defensa y con otros caracteres fenotípicos, como la productividad o el esfuerzo reproductor. El trabajo se centra en una submuestra de la población de mejora del programa de mejora genética de Pinus pinaster de Galicia-Costa. El material consiste en 39 familias de medios hermanos de árboles sobresalientes seleccionados en la región de procedencia Galicia-Costa, que se encuentran representados en los huertos semilleros clonales de primera generación del programa. En esta comunicación hemos recopilado la información de distintos experimentos de campo y de invernadero destinados a evaluar la variación genética en resistencia a distintas patologías. Los patógenos considerados son Fusarium circinatum, F. oxysporum y Armillaria ostoyae, y los insectos evaluados son Thaumetopoea pithyocampa, Hylobious abietis y Dioryctria sylvestrella; todos ellos causan importantes daños a las masas de P. pinaster en la zona. Los caracteres de defensa examinados son los niveles constitutivos e inducidos del contenido en diterpenos en el tallo, y de fenoles totales y taninos condensados en las hojas. El peso del piñón, el crecimiento temprano, la producción de conos y la morfología de raíces también se han tenido en cuenta en el estudio. Las relaciones entre parámetros se evaluaron mediante correlación de Pearson entre los valores de mejora de la resistencia a cada patógeno estimados independientemente en cada experimento. También se utilizó un análisis de componentes principales para reducir la dimensionalidad de los datos, e intentar agrupar e identificar síndromes defensivos contra los que los pinos usan los mismos mecanismos de defensa. Los resultados no respaldan nuestra hipótesis inicial, y la ausencia de resistencia cruzada o crossresistance parece la norma en esta especie. Aunque algunas correlaciones positivas revelan un papel relevante de algunos de los caracteres de defensa evaluados protegiendo a las plántulas frente a determinados patógenos o plagas, las defensas químicas analizadas no pueden catalogarse como defensas generalistas eficaces frente a todos los enemigos. Así, la combinación de múltiples caracteres de defensa parece esencial para hacer frente al gran abanico de enemigos de este pino.Financiado por el Ministerio de Ciencia e InnovaciónPeer Reviewe

Survival time analysis of Pinus pinaster inoculated with Armillaria ostoyae: genetic variation and relevance of seed and root traits

Results of a greenhouse Armillaria ostoyae inoculation experiment, designed for screening resistant Pinus pinaster genotypes and for exploring the role of different phenotypic traits in seedling susceptibility, are reported. The experiment included 39 open-pollinated pine families that comprised a random subset of the breeding population of P. pinaster in Galicia (NW Spain). We employed a non-parametric survival-time analysis to analyze patterns of survival times during 14 months after inoculation with a local A. ostoyae strain. Results indicate (i) a significant correlation between seed weight and tree susceptibility, with seedlings originating from large seeds being more susceptible, (ii) a positive family mean correlation between secondary root weight and size and median life expectancy, and (iii) genetic variation of tree tolerance to A. ostoyae, with some families surviving significantly longer than others. Less susceptible families could be used in breeding programmes or directly in forest plantations to reduce the losses caused by A. ostoyae. Large within-family variation in tolerance to the disease was also observed, suggesting that non additive genetic variance was also important. Although being infected, 32 out of the 1200 inoculated trees survived the fungus infection. These tolerant genotypes comprise an attractive collection to further investigate genetic, phenotypic and environmental factors affecting pine susceptibility to Armillaria root rot.This work was supported by the projects RTA2007-100 and PSE310000 from Ministerio de Ciencia y Tecnología. L. Sampedro was supported by a Doc-INIA grant.MCYTINIAPeer reviewe

Changes in limiting resources determine spatio-temporal variability in tree–grass interactions

Changing biotic and abiotic stress mediate in plant-plant interactions resulting in positive to neutral or negative effects, and these effects can change with gradients of stress or through plant dynamics. Here we studied the variability in annual grass production and composition induced by gradients of intercepted light by trees in years of contrasting precipitation in Mediterranean holm oak open woodlands. Although trees reduce the light radiance received by the pasture community, the presence of trees generally had a positive effect on pasture production in average climatic years where soil fertility was low. However, the interaction changed with increasing abiotic water stress. In a dry year, the increase in fertility could not be utilized and the effect of the crown was neutral. The effect of shade turned out to be beneficial for growth, contrary to the situation in an average climatic year. Light insolation was positive for legume biomass. There was high variability in functional components over the course of the growing period and from 1 year to another. Under low levels of other biotic stresses such as livestock grazing or root competition, the limiting factor among light, soil moisture or soil nutrients may determine whether facilitation or competition occurs. © 2009 Springer Science+Business Media B.V