Percorrer por autor "Santos, H."
A mostrar 1 - 3 de 3
Resultados por página
Opções de ordenação
- Evaluation of slow release nitrogen fertilization for tall cabbage grown in autumnPublication . Santos, H.; Rodrigues, M.A.; Dias, L.G.; Arrobas, MargaridaTall cabbage (Brassica oleracea, var. costata, cv. Penca de Mirandela) is very popular in Portugal. It forms part of the traditional Christmas Eve dinner every year. The nurseries are prepared in the middle of summer and the young plants transplanted late in August. The highest growth rates of this vegetable as well as the highest demands for nitrogen (N) occur in October and early November, a typical rainy period where there is a high risk of nitrate leaching. Therefore, the use of slow release N fertilisers may be a viable option as a sound N fertilization strategy for this production system. The objectives of the research were to examine the effect on crop yield of three materials that delay N availability to plants and also to monitor when N becomes available lo the crop. Results of a pot experiment are presented where tail cabbage was grown in the autumn as a main crop and Italian ryegrass (Lolium multiflorum L.) was sown in spring in-order to evaluate the residual effect of fertilisers.
- Fatty acid characterization of cyanobacterial strains isolated from Vela lake and Mondego river rice fields (central-western, Portugal)Publication . Galhano, Victor; Santos, H.; Geraldes, Ana Maria; Figueiredo, Daniela R.; Crespí, António; Gomes-Laranjo, José; Peixoto, Francisco P.t is know that particular groups of cyanobacteria are characterized by particular lipid patterns that can be used as their biological markers. The present study examined the fatty acid composition of nostocacean heterocystous cyanobacterial strains isolated from Central-western Portuguese freshwater shallow water bodies, namely Vela Lake and rice fields from Mondego River Basin. Morphological characterization showed that strains from Vela Lake belonged to Aphanizomenon gracile (strains uADFA16 and uADFA18), Aphanizomenon flos-aquae (strain uADFA15) and Anabaena cf. solitaria (strain uADFA14) species, whereas rice field strains belonged to Anabaena cylindrica (strain uTAD_A212) and Nostoc muscorum (strain uTAD_N213). generally, biochemical characterization inferred from lipid analysis showed that the predominant fatty acid methyl esters (FAMEs) in the lipids of the strains were palmitic, oleic and α-linolenic, with trace amounts of myristic and C20 polyunsaturated FAMEs. Palmitic acid contente in uADFA16 was 2.4 and 2.6 times higher than in uTAD_A212 and uTAD_N213, respectively. Surprisingly, the two Aph. gracile strains had different FAME composition and the high concentration of myristic acid in uADFA14 could be indicative of some hepatoxicity. The comparison of quantitative and qualitative FAME composition of the strains isolated from the two different habitats could explain the close chemotaxonomic relationship between the strains uTAD_A212 and uTAD_N213, both isolated from rice paddies. The same approach could be applied to the strains uADFA14 and uADFA18 isolated from the Vela Lake ecosystem. Principal component statistical analysis of variability of fatty acids belonging to the six genera is reported. To our knowledge, there is almost no information about lipid composition in freshwater cyanobacterial species living in different habitats in Portugal. Therefore, this limnological study is a contribution to our investigation on diazotrophic cyanobacteria in the framework of a comprehensive colaboration program concerning the taxonomy, phylogenetic relationships and toxicological effects of pesticides and other xenobiotics on freshwater cyanobacteria.
- Slow-release N fertilisers are not an alternative to urea for fertilisation of autumn-grown tall cabbagePublication . Rodrigues, M.A.; Santos, H.; Ruivo, Sérgio; Arrobas, MargaridaTall cabbage (Brassica oleracea var. costata, cv. Penca de Mirandela) is grown in Portugal during autumn and winter months when heavy rains can be expected. In this agrosystem the management of N is a considerable challenge due to the risk of nitrate leaching. Field experiments with tall cabbage and rye were carried out during the growing seasons of 2007/2008 and 2008/2009. The experimental design included three fertilisers that delay N availability by different mechanisms [Floranid permanent, containing isobutylidene diurea (IBDU); Basacote, a polymer-coated fertiliser; and Entec 26, containing 3,4-dimethylpyrazole phosphate (DMPP) as nitrification inhibitor], two urea treatments (total N applied basally; and divided into two equal rates in preplant and topdress application), and a zero N control. The fertilisers were applied at a rate of 120 kg N ha−1. A pot experiment with tall cabbage followed by ryegrass grown in the same pots was carried out in 2007/2008. The fertiliser treatments were essentially the same and a rate of 2.94 g N/pot was applied. Dry matter yield, plant N concentration, plant N recovery and indices of N-use efficiency were compared among the fertiliser treatments. In the pot experiment, soil nitrate concentration was also monitored by using anion exchange membranes inserted directly into the soil. Urea produced mean DM yields statistically higher than control in all crops and in both field and pot experiments and years. No significant differences in DM yield were usually found among fertilised treatments. Basacote produced DM yields often not significantly different from that of control. In the field experiment of tall cabbage, plants recovered 20 and 50% of the amount of N applied, respectively in Basacote and in the other fertilised plots. In the pot experiment, tall cabbage + ryegrass recovered 49.6 and ≈100% of N applied, respectively in Basacote and in the other fertilised plots. From the strictly agronomic point of view, none of the slow-release N materials provided advantages over urea to be advised for this agrosystem, considering also their high cost.