J. Marques da Silva

Soil apparent electrical conductivity and geographically weighted regression for mapping soil

To resolve the spatial variation in soil properties intensively is expensive, but such knowledge is essential to manage the soil better and to achieve greater economic and environmental benefits. The objective of this study was to determine whether the soil apparent electrical conductivity (ECa), alone or combined with other variables, is a useful alternative for providing detailed information on the soil in the Extremadura region of Spain. Apparent soil electrical conductivity was measured and geographically weighted regression was used to characterize the spatial variation in soil properties, which in turn can be used for soil management. This study shows that soil cation exchange capacity, calcium content, clay percentage and pH have a relatively strong spatial correlation with ECa in the soil of the study area.

Evaluation of spatial and temporal variability of pasture based on topography and the quality of the rainy season

Yield and botanical composition of a given dry-land pasture are heavily influenced by rainfall distribution, and vary according to topography. Through analyzing these parameters, it is possible to identify patterns of spatial distribution, related to topographic characteristics, which can be used to improve spatial management of pasture. The main objective of this project was to assess the role of rainfall, temperature and topography in the spatial and temporal variability of pasture and establish models for predicting the spatial distribution and yield of certain plant species, based on its topographic characteristics. This study was carried out over three years, 2004 to 2006, in a dry-land pasture located in Southern Portugal. The data obtained were analyzed as a function of distance to flow lines and the results demonstrate that certain topographical characteristics, associated with agronomic information, can be very useful in explaining the spatial and temporal variability of yield and the botanical composition of the pasture. The slope of the linear regression of the variables mentioned can be used to estimate the spatial variation of yield and the botanical composition as a function of distance to flow lines. The regression coefficient can be estimated from the annual rainfall, given the strong correlation between the two.

Description standards of primary tillage implements.

Recent research has shown that different types of tillage implements have a different impact on soil translocation. Tillage experiment descriptions in the bibliography are usually incomplete in their description of the implements and the experimental tillage conditions, which makes some difference if one wants to compare different experiments through time and space. The aim of this paper is to present a diagnostic of the problem, showing the importance of describing the implements and at the same time to present a proposal for a standard description of mouldboards, disc harrows and cultivators that should be taken into account when tillage experiments are carried out.

Tree influence on soil and pasture: contribution of proximal sensing to pasture productivity and quality estimation in montado ecosystems

ABSTRACT Montado is a silvo-pastoral ecosystem of the Mediterranean region, a mixed system of trees and pasture, subject to animal grazing. Farmers need information on pasture production and quality in order to assess the direct effect of tree presence on the productivity of their pastoral system, and to devise management that balances farm production and profitability with sustainable soil management. The main objectives of this work were (1) to evaluate tree influence on soil and pasture parameters and (2) to evaluate the use of proximal sensing techniques that have potential for monitoring aspects related to spatial and temporal variability of pasture productivity and quality in montado ecosystems. Both objectives can support the decision-making process of the farmer. The study field is located in Mitra farm, in Southern Portugal. During October 2015, 24 geo-referenced composite soil samples (12 under tree canopy and 12 outside tree canopy) were collected from the 0.0–0.3 m soil layer. The soil samples were analysed for texture (sand, silt, and clay content), moisture content, pH, organic matter, total nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and manganese (Mn). The evolution of the pasture was recorded in the 24 sampling points at five monitoring dates: at the end of autumn (December 2015), at the end of winter (March 2016), and then monthly during spring 2016 (April, May, and June). The following pasture parameters were measured: normalized difference vegetation index (NDVI), capacitance, temperature, green and dry matter, ash, crude protein (CP), and neutral detergent fibre. Soil under tree canopy had significantly higher levels of organic matter, N, P, K, and Mg, and better pasture quality while the pasture productivity was higher outside tree canopy. The correlation between pasture direct measurements and sensor parameters was more consistent between capacitance and pasture productivity and between NDVI and CP. The use of fast and efficient tools associated with geo-referenced systems can greatly simplify the pasture monitoring process, which is the basis for estimating feed availability in the field. The knowledge of biomass quality and quantity is fundamental to support decision-making regarding animal stocking rates and rotation among grazing parcels.

A partial study of vertical distribution of conventional no-till seeders and spatial variability of seed depth placement of maize in the Alentejo region, Portugal

Abstract The requirements for a good stand in a no-till field are the same as those for conventional planting as well as added field and machinery management. Among the various factors that contribute towards producing a successful maize crop, seed depth placement is a key determinant. Although most no-till planters on the market work well under good soil and residue conditions, adjustments and even modifications are frequently needed when working with compacted or wet soils or with heavy residues. The main objective of this study, carried out in 2010, 2011 and 2012, was to evaluate the vertical distribution and spatial variability of seed depth placement in a maize crop under no-till conditions, using precision farming technologies and conventional no-till seeders. The results obtained indicate that the seed depth placement was affected by soil moisture content and forward speed. The seed depth placement was negatively correlated with soil resistance and seeding depth had a significant impact on mean emergence time and the percentage of emerged plants. Shallow average depth values and high coefficients of variation suggest a need for improvements in controlling the seeders’ sowing depth mechanism or more accurate calibration by operators in the field.

Stochastic simulation of maize productivity: spatial and temporal uncertainty

There is an emerging interest in evaluating the uncertainty of agricultural production to enable the production process and decision making guidance. The main objective of this work was to estimate the spatial and temporal maize yield uncertainty using stochastic simulation techniques, including Sequential Gaussian Simulation. The results showed: (1) that it is possible to estimate the spatial and temporal dynamics of production based on one year’s data; (2) that the productivity variation in stochastic simulation has a higher amplitude in relation to real production data; (3) that the simulations allow approximate estimation of the productivity multi-year behaviour.

Long-term effect of super phosphate fertilizer on accumulation of soil phosphorus on a pasture

The purpose of the present work was to clarify some aspects of the complexity of phosphorus (P) dynamics under specific soil and climate conditions and a particular type of agro ecosystem: the Mediterranean pasture. The deviation between measured and estimated soil P content was evaluated over 12 years, in a 6 ha permanent bio-diverse pasture field in Southern Portugal. A simple dynamic model found good agreement for estimating the soil P content where P fertilizer had been regularly applied, but was not nearly as effective for the period during which the field did not receive P fertilizer. The dynamic of transformation between diverse P pools in Mediterranean shallow soils make the estimation of P balance very complex and justify more experiments.

Differential vineyard fertilizer management based on nutrient,s spatio-temporal variability

Conventionally, vineyard fertilizer management has been based on information from composite soil samples and no account has been taken of the existing spatial variability in soil fertility. This study presents a quantitative analysis of soil phosphorus (P2O5) and potassium (K2O) content as well as pH carried out in an 80 ha vineyard, during 2011 and 2013 in order to identify their spatial variability and temporal stability. Additionally a quantitative analysis of plant P2O5 and K2O content was carried out in 2013 with the objective of evaluating the spatial variability of plant nutrients.In 2013 a contact sensor was used to survey soil apparent electrical conductivity (ECa) and an active optical sensor was used to measure the plant Normalized Difference Vegetation Index (NDVI). The results showed a low potential for implementing site-specific management of phosphorus fertilizer but an interesting potential for implementing site-specific management of potassium fertilizer and pH correction. The concentration of P2O5 and K2O in the plant showed a CV<30%, with adequate values in almost the entire area of the field, in contrast to the concentration of these main macronutrients in the topsoil. These results show that for differential nutrient management of vineyards, plant nutrient concentration is a more stable tool than soil nutrients concentration. The ECa and the NDVI presented weak correlations with soil and plant concentration of, , respectively, P2O5 and K2O, which shows that further development of vegetation operational sensors is needed to support decision making in the vineyard fertilization management.

Proximal sensing for monitoring the productivity of a permanent Mediterranean pasture: influence of rainfall patterns

Proximal sensing for monitoring the productivity of a permanent Mediterranean pasture: influence of rainfall patterns J Serrano, S Shahidian, J Marques da Silva, F Moral and F Rebollo Departamento de Engenharia Rural, Instituto de Ciências Agrárias e Ambientais Mediterrânicas (ICAAM), Escola de Ciências e Tecnologia, Universidade de Évora, Apartado 94, 7002-554 Évora, Portugal, Departamento de Expresión Gráfica, Universidad de Extremadura, Badajoz, Spain jmrs@uevora.pt

Comparing the DUALEM and VÉRIS sensors for mapping soil properties

The objective of this study was to evaluate two apparent soil electrical conductivity (ECa) sensors (DUALEM 1S and VERIS 3100) for mapping soil property variability in a Mediterranean shallow soil. The ECa data from the top 0–0.30 m soil layer were used. Soil spatial variability of a 6 ha experimental field was characterized by 76 samples geo-referenced with GPS. The results of the DUALEM sensor showed significant correlation coefficients between ECa and the relative field elevation (RFE), bedrock depth, pH, sand, silt and soil moisture content. On the other hand, significant correlation coefficients were found between the ECa measured by VERIS sensor and pH, sand, clay, organic matter and soil moisture content. This paper discusses possible reasons for the somewhat different behaviour of the two sensors.