1,721,059 research outputs found
Closed cycle subirrigation with low concentration nutrient solution can be used for soilless tomato production in saline conditions
No full textClosed cycle soilless techniques can be adopted to minimize water and fertilizer losses in greenhouse cultivation. There is a general lack of information regarding the soilless cultivation of vegetables with
closed cycle subirrigation techniques, specifically when using saline water. In this study, a trough bench subirrigation system (SUB), with two fertilizer concentrations (‘‘100%’’, containing 9.8 mol m-3 N-NO3,
1.6 mol m-3 P-H2PO4, 8.7 mol m-3 K+, 2.8 mol m-3 Ca+, 1.8 mol m-3 Mg+, 4 mol m-3 S-SO4, and ‘‘70%’’, containing 70% of the macronutrient concentration) in the nutrient solution (NS), was compared with open cycle drip-irrigation (DRIP with ‘‘100%’’ NS). For all the three treatments, NS was prepared using rain water (0.05 dS m-1) and adding NaCl (1 g L-1), in order to simulate moderate saline irrigation water.
The effect of the treatments on tomato (Solanum lycopersicum L.) plant growth, yield, fruit quality, water use efficiency (WUE) and fertilizer consumption was evaluated. Substrate and recirculating NS composition were also studied. Subirrigation, regardless of NS concentration, reduced plant height (by 30 cm), leaf area (by 1411 cm2), total fresh and dry weight (by 429 and 48.5 g plant-1, respectively) but not dry matter percentage of the whole plant, with respect to DRIP. Yield was reduced when plants were subirrigated with the higher concentrated NS, but no differences with open cycle DRIP were recorded
when the lower NS concentration was used in SUB. Fruit quality was not affected by irrigation system or NS concentration. The higher WUE was obtained with subirrigation. NaCl accumulated similarly over the
crop cycle in recirculating NS of both SUB treatments and in growing substrates of all the three treatments. Higher salt concentration was found in subirrigated substrates, in particular in the upper
part of the substrate profile. Fertilizers accumulated in the subirrigated substrates when the higher NS concentration was used, but not when the NS concentration was reduced by 30%. The results of this study
indicate that tomato can be grown successfully in a closed cycle subirrigation system, using saline water,
by reducing the fertilizer NS concentration normally used with traditional open cycle systems
Calcium can prevent toxic effects of Na+ on tomato leaf photosynthesis but does not restore growth
No full textThe availability of good-quality irrigation water is decreasing worldwide, and salinity is an increasingly important agricultural problem. To determine whether detrimental effects of NaCl on plant growth and leaf physiology can be minimized by additional Ca2+ supply, tomato (Solanum lycopersicum L.) ‘Supersweet 100’ was grown hydroponically. The basic nutrient solution contained 11.1 mm NO3 − and 2.8 mm Ca2+. Three levels of NaCl (14.1, 44.4, and 70.4 mm) were added to the basic solution to determine Na+ effects on leaf physiology and growth. To determine if Ca2+ could alleviate the toxic effects of Na+, treatments with 10 or 20 mm Ca2+ combined with 44.4 or 70 mm NaCl were included as well. To distinguish between osmotic and ion-specific effects, there were three treatments in which all nutrient concentrations were increased (without NaCl) to obtain electrical conductivity (EC) levels similar to those of the NaCl treatments. Nutrient solutions with 70.4 mm NaCl reduced leaf photosynthesis, chlorophyll content, gas-phase conductance, carboxylation efficiency, and dark-adapted quantum yield. Inclusion of 20 mm Ca2+ prevented these effects of NaCl. NaCl also decreased leaf length and elongation rate. This could not be prevented by adding extra Ca2+ to the solution; reductions in leaf elongation were due to osmotic effects rather than to Na+ specifically. Likewise, plant dry weight was negatively correlated with solution EC, suggesting an osmotic effect. Leaf area development apparently was more important for dry matter accumulation than leaf photosynthesis. Adding 20 mm Ca2+ to the 70 mm NaCl solution reduced the Na+ concentration in the leaf from 79 to 24 mg·g−1
On the relationship between C-band interferometric coherence and crop phenology: Case study of Metaponto plain (Basilicata, Italy)
No full textIn this paper we discuss the use of Sentinel-1 interferometric Synthetic Aperture Radar (SAR) coherence to study the crop phenology. This research activity has been proposed within the project “On Demand Services for Smart Agriculture” (ODESSA)”, funded by the European Regional Development Fund (ERDF), Axis I Research and Innovation, Action 1B.1.2.1
Economic models of social learning
No full textThe theory of rational social learning studies how individual decision makers are influenced by the actions taken by others when information is dispersed. We present and discuss some models of Bayesian social learning which recently appeared in the economics literature. We focus on the problems of information acquisition, stationarity of the environment and endogenous pricing, and we propose some applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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