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- The combined effects of salts and calcium on growth and mineral accumulation of Tetragonia tetragonioides - A salt removing speciesPublication . Neves, Alcinda; Miguel, Maria Graça; Marques, C.; Panagopoulos, Thomas; Beltrão, JoséHigh soil salinity levels have drastic effects on the growth and yield of horticultural crops. Salination may be controlled by environmentally safe and clean techniques as the use of salt removing species. Tetragonia tetragonioides, a wild halophytic species has been studied for this purpose. It was studied the effect of high salt concentrations on growth and mineral composition and the influence of high calcium concentration on plant response. Plants were grown in 5 litters in randomized pots and were daily irrigated. The NaCl concentration of the irrigation solution ranged from 0 up to 200 mM. Additionally, the irrigation solution provided plants with two calcium concentrations: 2 and 10 mM of CaCl2. T. tetragonioides present high ability for sodium and chloride leaf accumulation. Besides that, the species provide more advantages: 1) high biomass production potential; 2) several harvests during the year (summer and winter); 3) high content of minerals; 4) horticultural importance, as a leaf vegetable crop; 6) easy multiplication (seed propagation) and easy crop management; 7) tolerance to drought and warm conditions; 8) soil erosion control due to its excellent soil covering. The obtained results suggest that plants supplemented with the high calcium level had longer stems than plants in the low calcium level, accumulated greater amounts of calcium at high salinity levels and present similar leaves dry matter.
- Analysis of spatial interpolation for optimising management of a salinized field cultivated with lettucePublication . Panagopoulos, Thomas; Jesus, J.; Antunes, Maria Dulce; Beltrão, JoséThe lack of randomisation in irrigation experiments is usually a disadvantage. The introduction of spatial variable experimental design offers a convenient tool to help solving this problem. In order to understand the variation of some soil physical and chemical properties in an experimental block and its effect on lettuce (Lactuca sauna L.) production, graphical interpretation of those soil properties was done with the use of geostatistics in a geographic information system (GIS). In this work three techniques of geostatistics were used for the creation of several maps of soil properties in an experimental plot cultivated with lettuce. Lettuces were evaluated for individual weight and diameter at the end of the cropping season. The soil properties studied were: total mineral nitrogen, phosphorus, potassium, pH, electric conductivity and saturated soil hydraulic conductivity. The techniques used were: ordinary kriging, inverse distance and Thiessen polygon. Cross validation used to compare the prediction performances of the three geostatistical interpolation algorithms determined that kriging was the best technique for each soil property. Prior to the creation of the maps, semivariograms were produced for each soil property. The maps resulting from the interpolation techniques were introduced in a GIS and their values reclassified. After that, spatial modelling was used to develop a final overlay map from all the information of the analysed soil properties simulating a "lettuce production capability map". This final map was created with the objective to determine which areas in the plot had optimal conditions for lettuce development. It was concluded that the plot did not had an optimal area for lettuce production. Localized problems with soil properties were found that could be solved with simple geographically restricted amendment treatments. Final lettuce yield had high correlation (r(2) = 0.83) with the lettuce capability map derived. (c) 2005 Elsevier B.V. All rights reserved.