Loading...
4 results
Search Results
Now showing 1 - 4 of 4
- Linear relationship of a soil total water potential function and relative yield—A technique to control salinity and water stress on golf courses and other irrigated fieldsPublication . Beltrão, José; Bekmirzaev, Gulom; Ben Asher, Jiftah; Costa, Manuel; Panagopoulos, ThomasA simple empirical approach is proposed for the determination of crop relative yield (%) through the soil total water potential (kPa). Recurring to decimal logarithms, from analytical exponential expressions, a linear simple relationship of soil total water potential Ψt (matric Ψm + potential Ψo) function and crop relative yield was studied and developed. The combination of the salinity model, the soil water retention model and the matric potential approach were used to reach this objective. The representation of turfgrass crop relative yield (%) versus a function of soil total water potential f(Ψt) values was shown through a log-normal graph (y = a + mx); the log scale axis “y” (ordinates) defines relative yield Yr, being two the origin ordinate “a” and “m” the slope; the normal decimal scale axis “x” (abscissa) is the function of soil total water potential f(Ψt). Hence, it is possible, using only two experimental points, to define a simple linear relation between a function of soil total water potential and crop relative yield, for a soil matric potential value lower than −20 kPa. This approach was first tested on golf courses (perennial turfgrass fields), but it was further decided to extend it to other annual crop fields, focused on the model generalization. The experimental plots were established, respectively, in Algarve, Alentejo and Oeiras (Portugal) and in the North Negev (Israel). Sprinkler and trickle irrigation systems, under randomized blocks and/or water and salt gradient techniques, were used for water application with a precise irrigation water and salt distribution. Results indicated that there is a high agreement between the experimental and the prediction values (R2 = 0.92). Moreover, the precision of this very simple and easy tool applied to turfgrass fields and other irrigated soils, including their crop yields, under several different sites and climatic conditions, can contribute to its generalization.
- 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.
- Crop response to combined availability of soil water and its salinity level: theory, experiments and validation on golf coursesPublication . Ben-Asher, Jiftah; Beltrão, José; Bekmirzaev, Gulom; Panagopoulos, ThomasThe phenomenological expression showing crop yield to be directly dependent on water deficiency, under saline conditions, has encouraged a continued focus on salinity as a viable approach to increase crop yields. This work reassesses crop response to availability of saline soil water ASW in two stages (A) Develop a simple approach suggesting that permanent wilting point (WP) increases under high saline soil water tension and relative yield of Lettuce (Lactuca sativa L., var longifolia Lam., cv. Nevada) and maize (Zea mays L., cv. Jubilee sweet) decrease. (B) Using a deterministic numerical soil water model to validate the theory on Bermuda grass of golf courses. The experimental plots were established in the North Negev, Israel (Sweet corn) and the Algarve, Portugal (Lettuce and Bermuda grass covering the golf courses). Sprinkler irrigation and line source techniques were used for water application, creating a saline gradient under a precise irrigation water distribution. Two salinity empirical models were tested (Mass and Hoffman MH and van Genuchten–Gupta vGG). Their empirical models were modified and instead of soil electrical conductivity of irrigation water (ECe) we used wilting point (WP) and RASW to follow the changes in relative yield. The validation was conducted with theoretical soil plant atmosphere water (SPAW) to predict the results on golf courses. It is concluded that an alternative S-shaped response model provides better fit to our experimental data sets. Modified MH model (Yr = Y/Ymax = a ∗ (ASW–threshold’s constant) revealed that a single dimensionless curve could be used to express yield—salinity interference when represented by varying ASW. The vGG model: vGG can represent salt tolerance of most crops, by using varying wilting point of average root zone salinity, at which the yield has declined by 50%. The abscissa of both models was based on WP rather than the standard soil electrical conductivity (ECw). The correlation between the experimental data and WP or relative available soil water (RASW) was acceptable and, therefore, their usefulness for prediction of relative yield is acceptable as well. The objectives of this study were: 1. To develop a simple model describing the effect of salinity through soil water availability on crop production; 2. To replace the standard varying soil electrical conductivity ECe used by MH and vGG models by two soil parameters (at wilting point- θwp and at field capacity θfc) in order to describe the relationship between them and relative yield. 3. Validate the new model with respect to independent salinity on Golf courses and a mathematical deterministic model.
- 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.