The aim of this study is to assess the fixation of the major nutrients C, N, P, Ca, Mg, K, Na by algal biomass produced in the rice fields of Thessaloniki plain in Greece under semi-arid Mediterranean conditions and to evaluate the limiting factors for their growth. Measurements were performed in experimental rice-field following the regional conventional practices (C-H treatment): (a) direct sowing, (b) continuous flooding with few intermissions, (c) use of nitrogen fertilizers at 176 kg N ha-1, and (d) application of herbicides (active ingredients benzofenap and clomazone). Herbicides were not applied in a small part of the field isolated by bunds (C-NH treatment) in order to assess possible limiting effects of herbicides on algae growth. Climatic data, measurements of rice crop characteristics and water quality of the ponded water in the C-H part of the experimental field were also obtained in order to assess the limiting effects of light, temperature and nutrients based on a modelling approach. Green algae were found to be dominant in the specific system. Considering the two treatments, the results showed that herbicides did not affect algae growth probably due to the short period of exposure followed by the continuous flooding. Nutrients fixation by algae for C-H followed the order C (52.1 %) > Ca (5.6 %) > K (3.5 %) > N (2.4 %) > Mg (0.3 %) ≈ Na (0.3 %) > P (0.24 %) with a final dry biomass production at 1,118 kg ha-1. Based on the measurements and model simulations the most limiting factors under the regional conventional practices of rice cultivation were the temperature at the initial and final stage of rice growing season, the light when the leaf area index of rice was >2 and phosphorus concentration in the ponded water. The mean algae growth rate during the flooding period was estimated at 8.2 kg ha-1 day-1, while the maximum rate was estimated at 15.9 kg ha-1 day-1 at the initial growth stages of rice before the beginning of intense light limitations from rice crop coverage.
Nutrients fixation by algae and limiting factors of algal growth in flooded rice fields under semi-arid Mediterranean conditions: case study in Thessaloniki plain in Greece
ASCHONITIS, Vasileios;
2013
Abstract
The aim of this study is to assess the fixation of the major nutrients C, N, P, Ca, Mg, K, Na by algal biomass produced in the rice fields of Thessaloniki plain in Greece under semi-arid Mediterranean conditions and to evaluate the limiting factors for their growth. Measurements were performed in experimental rice-field following the regional conventional practices (C-H treatment): (a) direct sowing, (b) continuous flooding with few intermissions, (c) use of nitrogen fertilizers at 176 kg N ha-1, and (d) application of herbicides (active ingredients benzofenap and clomazone). Herbicides were not applied in a small part of the field isolated by bunds (C-NH treatment) in order to assess possible limiting effects of herbicides on algae growth. Climatic data, measurements of rice crop characteristics and water quality of the ponded water in the C-H part of the experimental field were also obtained in order to assess the limiting effects of light, temperature and nutrients based on a modelling approach. Green algae were found to be dominant in the specific system. Considering the two treatments, the results showed that herbicides did not affect algae growth probably due to the short period of exposure followed by the continuous flooding. Nutrients fixation by algae for C-H followed the order C (52.1 %) > Ca (5.6 %) > K (3.5 %) > N (2.4 %) > Mg (0.3 %) ≈ Na (0.3 %) > P (0.24 %) with a final dry biomass production at 1,118 kg ha-1. Based on the measurements and model simulations the most limiting factors under the regional conventional practices of rice cultivation were the temperature at the initial and final stage of rice growing season, the light when the leaf area index of rice was >2 and phosphorus concentration in the ponded water. The mean algae growth rate during the flooding period was estimated at 8.2 kg ha-1 day-1, while the maximum rate was estimated at 15.9 kg ha-1 day-1 at the initial growth stages of rice before the beginning of intense light limitations from rice crop coverage.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
