Search Results (8)

Monitoring invasive plant species is a crucial task to assess their presence in affected ecosystems. However, it is a laborious and complex task as it requires vast surface areas, with difficult access, to be surveyed. Remotely sensed data can be a great contribution to such operations, especially for clearly visible and predominant species. In the scope of this study, water hyacinth (Eichhornia crassipes) was monitored in the Lower Mondego region (Portugal). For this purpose, Sentinel-2 satellite data were explored enabling us to follow spatial patterns in three water channels from 2018 to 2021. By applying a straightforward and effective methodology, it was possible to estimate areas that could contain water hyacinth and to obtain the total surface area occupied by this invasive species. The normalized difference vegetation index (NDVI) was used for this purpose. It was verified that the occupation of this invasive species over the study area exponentially increases from May to October. However, this increase was not verified in 2021, which could be a consequence of the adopted mitigation measures. To provide the results of this study, the methodology was applied through a semi-automatic geographic information system (GIS) application. This tool enables researchers and ecologists to apply the same approach in monitoring water hyacinth or any other invasive plant species in similar or different contexts. This methodology proved to be more effective than machine learning approaches when applied to multispectral data acquired with an unmanned aerial vehicle. In fact, a global accuracy greater than 97% was achieved using the NDVI-based approach, versus 93% when using the machine learning approach (above 93%). Full article

Salinization is a major soil degradation threat in irrigated lands worldwide. In Portugal, it affects several pockets of irrigated agricultural areas, but the spatial distribution and intensity of soil salinity are not well known. Unlike conventional approaches to appraise soil salinity, remote sensing multispectral data have great potential for detecting, monitoring, and investigating soil salinity problems in agricultural areas. This study explores the assessment of soil salinity in irrigated rice cultivation fields using two types of multispectral-based indices calculated from Sentinel-2 satellite imagery: (i) vegetation indices (Normalized Difference Vegetation Index, Green Normalized Difference Vegetation Index, Generalized Difference Vegetation Index and Soil Adjusted Vegetation Index), to monitor the indirect effect of salinity on rice growth; and (ii) salinity indicators, namely those based on visible and near-infrared bands (Normalized Difference Salinity Index) and on shortwave infrared bands (Salinity Index ASTER). The data are for the Lower Mondego Valley (Central Portugal) and the period 2017–2018. Results revealed that salinity indices can be used for mapping soil salinity and constitute a valuable soil salinity assessment tool in rice cultivation areas affected by salinity issues. As there is less reported inventorying of spatial extent of such degradation in irrigated agricultural areas of Portugal, this innovative approach allowed by remote sensing technology can add to understanding the spatial extent of such areas and undertaking more such studies spatially and temporally. Full article

Rice irrigation by continuous flooding is highly water demanding in comparison with most methods applied in the irrigation of other crops, due to a significant deep percolation and surface drainage of paddies. The pollution of water resources and methane emissions are other environmental problems of rice agroecosystems, which require effective agronomic changes to safeguard its sustainable production. To contribute to this solution, an experimental study of alternate wetting and drying flooding (AWD) was carried out in the Center of Portugal in farmer’s paddies, using the methodology of field irrigation evaluation. The AWD results showed that there is a relevant potential to save about 10% of irrigation water with a reduced yield impact, allowing an additional period of about 10 to 29 days of dry soil. The guidelines to promote the on-farm scale AWD automation were outlined, integrating multiple data sources, to get a safe control of soil water and crop productivity. The conclusions point out the advantages of a significant change in the irrigation procedures, the use of water level sensors to assess the right irrigation scheduling to manage the soil deficit and the mild crop stress during the dry periods, and the development of paddy irrigation supplies, to allow a safe and smart AWD. Full article

Efficient detection and monitoring procedures of invasive plant species are required. It is of crucial importance to deal with such plants in aquatic ecosystems, since they can affect biodiversity and, ultimately, ecosystem function and services. In this study, it is intended to detect water hyacinth (Eichhornia crassipes) using multispectral data with different spatial resolutions. For this purpose, high-resolution data (<0.1 m) acquired from an unmanned aerial vehicle (UAV) and coarse-resolution data (10 m) from Sentinel-2 MSI were used. Three areas with a high incidence of water hyacinth located in the Lower Mondego region (Portugal) were surveyed. Different classifiers were used to perform a pixel-based detection of this invasive species in both datasets. From the different classifiers used, the results were achieved by the random forest classifiers stand-out (overall accuracy (OA): 0.94). On the other hand, support vector machine performed worst (OA: 0.87), followed by Gaussian naive Bayes (OA: 0.88), k-nearest neighbours (OA: 0.90), and artificial neural networks (OA: 0.91). The higher spatial resolution from UAV-based data enabled us to detect small amounts of water hyacinth, which could not be detected in Sentinel-2 data. However, and despite the coarser resolution, satellite data analysis enabled us to identify water hyacinth coverage, compared well with a UAV-based survey. Combining both datasets and even considering the different resolutions, it was possible to observe the temporal and spatial evolution of water hyacinth. This approach proved to be an effective way to assess the effects of the mitigation/control measures taken in the study areas. Thus, this approach can be applied to detect invasive species in aquatic environments and to monitor their changes over time. Full article

As surface irrigation systems are one of the most used water management techniques in the world, often working with high water losses, there is an urgency to their improvement. Modern methods that provide water savings and labour reduction require adequate design, management knowledge, and technical decision support. This study aims to improve water saving techniques for on-farm systems through an example of the decision-aid process being applied as a methodology based on the field experimentation and modelling of modern surface irrigation technologies in the Hetao (China) and Lower Mondego (Portugal) case studies. The performance indicators of irrigation water productivity (IWP) and the economic water productivity ratio (EWPR) were applied to compare the performance of several project solutions. The results obtained include a complete description of the latest irrigation solutions at the level basin, graded border, and graded furrows, which are adaptable to those case studies. The results revealed the benefits of a level-basin solution. For example, in Hetao, replacing the traditional system with a 100 m or 200 m long level basin, resulted in an increase in IWP by 40% and 3%, respectively, and in EWPR by 23% and 67%, respectively. The effect of a longer basin enables the reduction in operative costs, with a slight increase in distribution uniformity. In Lower Mondego, the IWP increased by 65% and the EWPR increased by 82%, by adopting graded furrows with 1.0‰ slopes and 200 m lengths. The main drivers of development of these surface irrigation systems were determined, namely, the runoff reuse and the system design and management. The issue that the local markets with equipment and consulting services should be available for farmers is also relevant to the development. It was proven that the effectiveness of modern surface water systems must adapt the solutions of the projects to the local characteristics of plot size and slope, soil type, and water supply. Full article

The new technologies of surface irrigation require the adoption of effective Laser-controlled precision land levelling (PLL) to reach the high irrigation performance standards, with significant benefits on water saving, salinity control, crop productivity, and farmer’s income. This study aimed to assess the performance and the impacts of PLL on surface irrigation systems, focusing the maize crop on the irrigation districts Hetao (China) and Lower-Mondego (Portugal). The experimental study at field scale assessed the PLL and evaluated the on-farm irrigation under precise levelled fields and well management practices. PLL operators have been inquired to improve the knowledge about hiring services. The design of surface irrigation scenarios allowed to explain the effects of field size and slope on irrigation and land levelling performance. The best practice to manage the PLL maintenance is an important issue to guarantee a high effectiveness of irrigation performance. The optimization of PLL appeals the application of best soil tillage practices and the monitoring of soil surface elevations with newest information technologies. Efficient operational guidelines to support the PLL planning, schedule, and operation, well trained operators and carefully adjusted equipment, are key factors to the improvement. Full article

Currently the productivity of some European cropping systems is maintained artificially by increasing production factors like mineral fertilizers or pesticides in order to mask the loss of productivity resulting from soil quality degradation. Green manures are known as a good alternative to the use of mineral fertilizers and pesticides. They are an important source of nitrogen and reduce significantly weed invasion. Nevertheless, the literature providing a precise quantification of total nutrients available for plants after incorporation of leguminous species cultivated in Portugal is scarce. This lake of knowledge’s makes farmers worried about hypothetic productivity loss, making them to use excessive complementary amounts of mineral fertilizer. Providing farmers with tools to calculated accurately the reduction of mineral fertilizer will increase their gain and avoid environmental pollution by nutrients lixiviation. Under the scope the international H2020 SoilCare project, a study was conducted during the winter and spring of 2018–2019 at Baixo Mondego valley in Central Portugal, where the main land use is the monoculture of irrigated corn. The nutrient uptake was determined for 5 species of legumes: pre-inoculated Pea (Pisum sativum L.); Yellow Lupin (Lupinus luteus), Red Clover (Trifolium pratense); Balansa Clover (Trifolium michelianum); Arrowleaf Clover (Trifolium vesiculosum) and a control (natural vegetation). For each treatment, we determined total dry matter yield for leguminous and weeds, macronutrients uptake (N and P Total, K, Na, Ca, Mg, S) and micronutrients uptake (Cu, Zn, Fe, Mn). Combining soil analyses, theoretical main crop needs in nutrients (short cycle grain maize) and mineralization rates, we calculated the precise amendment needed to obtain the expected yield of maize in what concerns the macronutrient. The production of total dry matter (leguminous and weeds) was very similar for the 5 treatments e.g., about 7 ton/ha. Nevertheless, considering leguminous production, the higher dry matter yields was obtain for the Arrowleaf Clover and the lower for the Red Clover respectively 5.5 and 3.5 ton/ha. The Macronutrient content (N,P,K) of the leguminous ranged between 22.9 and 28.0 g/kg for N, 2.4 and 3.1 g/kg for P and 12.1 and 31.5 g/kg for K. The Yellow Lupin presented the higher values of N, the clovers the higher values of P and K. The total quantity of macronutrients incorporated in the soil was in average 152 kg/ha for N, 20 kg/ha for P and 170 kg/ha for K with the higher quantities for Arrowleaf Clover. We considered a mineralization coefficient of 0.5 for N and 0.6 for P during the first year and a nutrient extraction of 280 kg/ha of N, 50 kg/ha of P and 245 kg/ha of K, for a production yield of 12 t/ha of corn grain. After correction of plant needs following the soil analyses results, we determinate an optimized fertilization rate of 180-40-0, were the green manure supplies about 35%, 25% and 100% of the NPK extraction of the grain maize. Full article

Rice is a historically important crop in Portugal. This crop development and production strongly depend on atmospheric conditions in the growing season. Given the strong dependence of climatic conditions, climate change may pose a significant risk for future rice production. In the present study, a high spatial resolution bioclimatic characterization over the main rice producing region in Portugal was performed for the recent past (1950–2000) and for the future (2041–2060) under four different anthropogenic forcing scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). This zoning is performed by using eight bioclimatic indices, based on temperature and precipitation, using a very high resolution gridded dataset (Worldclim). For the future period, an 11-member global climate model ensemble was used, also taking into account model/scenario uncertainties and bias. Additionally, a new index was developed to incorporate the main features of temperature and precipitation at each rice field level. Under recent past climates, a clear north–south gradient in temperature and precipitation is apparent, with the regions of Tejo and Sado presenting higher temperatures and lower precipitation than the Mondego and Vouga regions. Additionally, there is a coastal–inland effect due to the Atlantic Ocean influence. Under anthropogenic climate change, all indices point to annual higher temperatures and lower precipitations across all rice producing regions, accompanied by increased seasonality. Furthermore, the rise of summertime temperatures may substantially increase water demands, which, when unmitigated, may bring physiological problems in the crop development. We conclude that climate change may negatively impact the viability of rice production in Portugal, particularly taking into account the national grown varieties. Thus, adequate and timely planning of suitable adaptation measures are needed to ensure the sustainability of this historically important food sector. Full article