Técnicas de cultivo de arroz irrigado: relação com a qualidade de água, protozoários e diversidade fitoplanctônica

Abstract

O efeito de técnicas de cultivo do arroz irrigado sobre a qualidade da água efluente foi avaliado através de parâmetros físicos, químicos e biológicos. A pesquisa foi desenvolvida na Estação Experimental do Instituto Riograndense do Arroz (IRGA) no município de Cachoeirinha, RS, bacia do Rio Gravataí. Os testes foram realizados com 3 técnicas distintas e usuais de plantio: convencional, pré-germinado e direto. Constatou-se que, nos primeiros 30 dias de irrigação, os parâmetros medidos dentro dos quadros de plantio apresentaram valores superiores aos da entrada; após este período, a situação se inverteu. Com o crescimento, as plantas de arroz funcionaram como um banhado natural, extraindo da água e do solo uma quantidade significativa de nutrientes, não somente durante sua fase inicial, mas, também, durante todo o seu ciclo. Esses nutrientes foram extraídos do meio líquido, melhorando a qualidade ambiental da água efluente. Dentre todas as técnicas de cultivo, o menor impacto sobre a qualidade da água foi apresentado pelo plantio direto.

Qualidade microbiológica da água da cultura do arroz irrigado, no sul do Brasil

“…According to the WHO (1989) recommendations for unrestricted irrigation, the concentration of fecal coliforms should be lower than 1000 UFC/100 mL, and therefore, water used for irrigation that presents values higher than 1000 UFC/100 mL of fecal coliform concentration, may be used only for forage and the cultivation of cereals -such as the rice culture evaluated in this study. The authors Furtado and Luca (2003) proved that the density of total and fecal coliforms in water taken from rivers is greater than that of the irrigation water found in the areas of rice plantation, where the direct planting system was the one which presented the lowest bacterial density. These authors state that in the rice field plots, where the sheet of water is shallow, the solar radiation penetrates strongly into the water and causes an antimicrobial effect, contributing to the reduction of the populations of micro-organisms sensitive to ultraviolet radiation.…”

“…This data presented by other authors bears out the results of the present study as regards the total coliforms found in the five regions of irrigated rice plantations in Rio Grande do Sul all of which may be showing the influence of factors such as the phytosanitary treatments utilized in rice cultivations and the presence of domestic animals in the vicinity of these agricultural areas. There is evidence that plantations of irrigated rice can act as a biological filter, removing nutrients from the eutrofized hydraulic medium for use by the plants and thus reducing the concentration of nutrients in the water draining out of the plantation as compared to what it was at the entry point (Furtado and Luca, 2003). On the other hand, competitors are present in the aquatic environment and the count of these entero-bacterium drops rapidly, presumably because they cannot successfully compete with nutrients containing other bacteria present in the above-mentioned environment (Wcislo and Chrost, 2000).…”

Do phytoplankton and epiphyton communities differ between organic and conventional rice fields?

“…Euglenophyceae and Cryptophyceae increased densities in the phytoplankton community in period 2. Cyanophyta and Euglenophyta showed a positive relationship with these factors in mesocosms, whereas Chlorophyta, Bacillariophyta, Cryptophyta, and Dinophyta showed a decrease in density (Furtado & Luca 2003). Cryptophyceae was the Y functional group; it is tolerant to low luminosity and, therefore, uses the phagotrophic mode to obtain energy (Reynolds et al 2002).…”

“…These planting systems result in different environmental conditions. In the rice paddy water in OF, higher turbidity values were recorded (> 62 NTU) because of the suspension of solids that is promoted by the practice of turning over residual plants (Furtado & Luca 2003). The lower values of pH observed (4.6 -5.8) is because the anaerobic conditions in flooded soil as a result of decomposition process that produces organic acids (Bohnen et al 2005).…”

Ocorrência de Euglenophyceae pigmentadas em rizipiscicultura na Região do Vale do Itajaí, SC, Sul do Brasil

“…Florações desta espécie foram relatadas em ambientes rasos, tanques de peixes ou em cultivo de arroz por Xavier et al (1991), Heckman et al (1993), Pereira et al (2000), Furtado & De Luca (2003), Mainardes-Pinto & Mercante (2003) e Tamanaha (2004, dados não publicados), entre outros autores.…”