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Microclimate near the ground strongly influences soil temperature and soil water regimes. Compared with open field, shade and shelter from vegetation canopy covers modify the microclimate, the surface energy balance and the type and growth of understorey vegetation, hence altering microclimate dependent soil and vegetation processes. These processes affect C and N cycles and the use of natural resources as light and water, being of great importance for ecosystem dynamics and sustainability.
Within
this context, the aims were
(i) to understand both the differentiation of microclimate near the ground and
the soil energy balance (including the soil heat flux) induced by changes in
radiation, temperature, water and wind regimes in forest plantations,
agroforestry systems of wide-spaced trees and crops;
(ii) to study the consequences of this differentiation on soil and vegetation
processes, namely the effects of soil temperature and water on the rates of seed
germination, early root development and soil organic matter mineralization.
These analyzes were further extended to vegetation development and growth in
relation to temperature, soil water availability and intercepted solar radiation
in temperate and tropical dry land ecosystems.
Integrated with other projects of the Centro de Pedologia (SUSTAINFOR Group), the results provided a deeper insight into the functioning of the physical environment of those ecosystems and on their ability to use natural resources in a sustainable way, helping to cope with local consequences of global climate changes. In addition, the research provided a framework for post graduation formation within the Centre.
In evergreen oak woodland (“montado”) and wetland pastures with ash trees (“lameiro”), individual trees intercept solar radiation differently at different compass directions. Daily and seasonal variations of soil and air temperature are smaller under the canopy than in the open. Due to canopy interception, rainfall under the trees is reduced, but the ash tree funnelling ratio is about one. Soil water content is similar near the trees and in the open. Dominant grass species are different under the tree-modified microclimate, but their growth is similar.
Evaluated by leaf area, chlorophyll and nutrient contents, tree growth in eucalyptus plantation is enhanced with the addition of harvest residues and N fertilizer, compared to any of them alone and to understorey cultivated legumes.
Sunflower stands sown at different densities in soils with very different water contents have different surface rugosities and exchange rates of heat and water between soil and atmosphere, and produce very different leaf areas and biomass.
Intercepted solar radiation and surface albedo change along the crop cycle, but radiation use efficiency for biomass is similar for all conditions. Crop phenology is similarly determined by temperature in all conditions.
As temperature is the major controller of rates of biological processes, a thermal gradient plate was developed and is being used to establish the relationships with rates of seed germination and early root development for pasture species.
Strong radiative night cooling induces cold damage in crops and orchards, despite the soil heat flux during the night to warm up the surface. Based on the surface energy balance, a model to predict minimum temperature is available, allowing for procedures to be taken to mitigate the cold effects.
Furthermore, temperature data and available soil water were used to define the growing seasons in Angola Republic.
Despite the development of soil science, the current knowledge on the soils of Portugal is yet scarce, and in many instances it is not sufficient to optimise the use and management of natural resources, sustain ecosystem functions, and control environmental quality. The research planned for this group intended to fill some of the existing knowledge gaps, providing information on the evolution, constitution and behaviour of soils from Portugal, namely those with stagnic features occurring in Southern Portugal and in volcanic areas (Andisols) from the Azores, and also on soils affected by mining activities.
The
research undertook pursued
a) Stagnic Luvisols: the understanding of the relationships between soil
properties, geology-lithology and landscape through the study of soil
toposequences and detailed physical, chemical and mineralogical characterisation;
b) assessment of the behaviour of these soils facing water quality, as well as
the risks and suitable technology for their use;
c) Andisols: assessment of charge variation and ability to retain cations and
anions (specially
P) and development of collaborative studies on the constitution,
characterisation and classification of thesesoils;
d) soils affected by mining activities: evaluation of contamination, degradation
and contaminants bioavailability (heavy and trace metals) and prediction of
element solubility from its total and labile pools according to soil chemical
properties, and determination of the proper methodology to evaluate and test
their availability.
At
the end of the period, group research objectives begun to move to
(i) Ferralsols from Angola Republic through the assessment of factors
determining the content of extractable Al and the total reserve in bases, and
(ii) to the assessment of factors determining the occurrence of podzolization
process and spatial distribution of Podzols in Portugal.
Study of Stagnic Luvisols showed that their properties and spatial distribution are related to the morpho-lithological environment, and that their poor drainage and high compaction are related with structure instability and dispersibility.
This is mainly ascribed to their low OM contents and to high exchangeable Na levels in B-horizons, the role of exchangeable Mg being not as marked as found for similar soils. Dilute soil solutions were found to increase soil dispersivity and use of irrigation water with appropriate electrolyte concentration is required for sustainable soil use.
Research on Andisols contributed to their characterization and classification and to a better understanding of their electrochemical characteristics and ionic sorption-desorption features; on the Andisols from Azores, a deeper knowledge on its P sorption-desorption ability at field conditions (which concern their fertility management and soil & water protection from detrimental fertilization effects) was achieved.
Integrated geochemical, isotopic and biochemical studies confirmed the mobilization of Pb from abandoned massive sulphide mines in the Iberian Pyrite Belt as the main source of anthropogenic pollution in the Lower Guadiana Basin (soils, waters and biota). Yield and quality (U content) decrease were observed for vegetables irrigated with a low quality water (salinity and high U content) growing in soils contaminated by U.
Studies on some native plants growing in degraded mining soils with high trace metals content (As, Pb, Cu, Zn, Sb) revealed to be of great interest in phytoremediation, specially if amended by organic matter.
Through a protocol established between the Agriculture Ministry and the Portuguese Soil Science Society, members of the group drew up the state-of-the-art of mapping quality and classification of soils in Portugal as well as the guidelines to improve the organization and collection of soil information at national level (www.spcs.pt).
It was aimed to achieve a deep understanding on the environmental impacts and on the potential success of minimum tillage systems in sugar beet culture and to improve adequate agricultural and forest techniques on soil water, nutrients and C management both in sugar beet and eucalyptus. A special attention was given to demonstration activities for the economic players. To attain such goals, for sugar beet it was intended to study and promote the implementation of minimum tillage systems in its production and quality, to evaluate their respective effects on irrigation water management and environmental quality, and to improve knowledge on plant water needs and tolerance, on the influence of soil fragmentation and hydrological regimes in the seeding phase, and on root development limitations due to soils bulk density increase. For eucalyptus, it was planned to study the relationships among productivity, water and nutrients availability and plant spacing, to study the seasonal relationships between nutrient concentration in soil solution and in eucalyptus leaves to better understand processes that influence those dynamics; in order to attain a better understanding on soil surface hydrological characteristics under eucalyptus canopy, underground mass and nutrients were quantified, soil water balance was assessed and surface runoff was modeled.
In sugar-beet crops under irrigation, in Vertisols, Luvisols, Cambisols and Fluvisols, the conservative soil tillage system was compared with the traditional soil tillage system regarding crop productivity, soil physical and chemical condition and amounts of water use and water use efficiency. The conservative soil tillage increased the amount and quality of sugar-beet production and ameliorated soil physical conditions and contributed to increase the amount of organic C, decreasing run-off and soil losses. The conservative soil tillage system also reduced the amount of irrigation water applied to the crop and improved water use efficiency. The application of the conservative soil tillage, through a combination of reduction of production costs and water use and enhancement of soil quality, created conditions for a sustainable crop management and a greater competitiveness of farmers.
Amounts of root mass in eucalyptus and pinus plantations were assessed and related with soil types and productivity; amounts of C in mineral soils and root mass were related to total organic C in the system.
Contribute to establish guidelines for a sustainable management of the Portuguese most important forestry and agro-forestry systems, that is, Eucalyptus globulus plantations, Quercus suber and Quercus rotundifolia stands (oak woodlands). Such a sustainable management aims the enhancement of site productivity and soil quality, the sustainable use of natural resources and the reduction of inputs and negative impacts on the environment.
Specifically it is envisaged to obtain a deeper understanding on the effects of harvest residues management of eucalyptus plantations, regarding tree growth and nutrition status, improvement of soil quality, and the accumulation of organic carbon in the soil; to contribute for the establishment of criteria and indicators of sustainability and soil quality, and to reconcile economical, ecological and environmental issues. Evaluation of carbon and nitrogen mineralization dynamics following clear-felling in different harvest residue management, in the presence or absence of fertilizers, ash or other residues and herbaceous legumes, is therefore required.
In oak woodlands (“montado”) with natural or improved pastures, in Southern Portugal it is aimed to understand how wide spaced trees, affect the spatial pattern of soil physical, chemical and biological properties, contribute to accumulate organic carbon in the soil and thus benefit soil quality, affect the amount, diversity and quality of herbaceous biomass, and how trees create islands of enhanced fertility and contribute to the landscape stability under a climate change scenario.
Moreover, the expected results should allow the design of practical systems for a better management of natural resources, and contribute to reduce threaten of soil and land degradation.
The studies in eucalyptus plantations, carried out in Cambisols with medium fertility, showed that the removal of organic layers and harvest residues, when compared with its maintenance on the soil, did not affect the tree growth and nutrient status, and soil quality (bulk density, compaction, infiltration rate and water conductivity, nutrient availability, amount of organic C) during the first rotation. The amount of understory vegetation was not also affected, but biological diversity was higher with harvest residues maintenance. The maintenance of harvest residues in the site, associated with fertilization, promoted tree growth at low extent, which is ascribed to the strong effect of water availability on the stand productivity. Organic C content in the system is mostly dependent on tree productivity, and its intra annual dynamics is mostly dependent on meteorological conditions. Slash management did not affect amount of soil N mineralization, and the ammonium is largely predominant.
The studies carried out in oak woodlands with natural and improved pastures, showed that the amounts of organic C, N, exchangeable base cations and extractable P and K in soil, were higher beneath tree canopy than in the open, being maximum values observed close close tree trunk. It was observed that bulk density decreases under tree canopy, whilst water infiltration rate increases, but the amount of available water was not affected. Efflux of CO2 from the soil and potential of N mineralization are greater beneath tree canopy, but this is only partially dependent on the greater amount of C and N due to tree presence. These patterns are ascribed to the effect of tree litterfall, tree roots and throughfall and stemflow on soil organic matter and nutrient fluxes. However, understory productivity is not affected by trees. According to this, trees in oak woodlands create islands of enhanced soil quality which contribute to organic C sequestration and to landscape diversity and stability.