Response of rice algal assemblage to fertilizer and chemical application: implications for the early algal bloom management

Authors: OHADI, SARA - University Of California, Davis; GODDAR, AMAR - University Of California, Davis; Madsen, John; AL-KHATIB, KASSIM - University Of California, Davis

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2021
Publication Date: 3/13/2021
Citation: Ohadi, S., Goddar, A., Madsen, J.D., Al-Khatib, K. 2021. Response of rice algal assemblage to fertilizer and chemical application: implications for the early algal bloom management. Crop Protection. 11(3):542. https://doi.org/10.3390/agronomy11030542.
DOI: https://doi.org/10.3390/agronomy11030542

Interpretive Summary: The addition of either nitrogen or phosphorus resulted in increased algal biomass in test containers. Chelated copper formulations were more effective than the standard elemental copper currently used, and Algimycin was more effective than those other algaecides. Two pre-emergent herbicides (oxyfluorfen and oxidaizon) were also able to control algae, but are not currently labeled for that application.

Technical Abstract: California water-seeded rice has been challenged with the rapid growth of nuisance algae in the beginning of the season. Rice seedlings entangled into the algal mat may not be established causing empty patches in the field. Two separate studies were conducted to 1) evaluate the effect of nutrients amount (nitrogen and phosphorous) on algae growth, and 2) test various chemical options for controlling algae. Both studies utilized 19-liter buckets inoculated with algae collected from a rice field. In the nutrient evaluation study, combination of nitrogen (0, 60, 120, 180, 240 and 300 kg ha-1) and phosphorous (0, 20, 40, 60, 80 and 100 kg ha-1) rates were applied into the buckets while in the second experiment nine chemicals with different mode of actions or copper formulations (four formulations) were tested. These studies were completely randomized design with three replicates and repeated two times. The result from the nutrient evaluation study showed that nitrogen and phosphorous can independently cause algae growth as reflected in the fresh and dry biomass. Moreover, low rates of either nitrogen or phosphorus lead to rapid increase of algae biomass and water chlorophyll a content whereas the growth of algae declined at higher rates of applied fertilizer. Among tested chemicals in the second experiment, the chelated formulation of copper (Algimycin PWF) controlled algae (85%) better than the ethanol amine formulations (Cutrine-ultra and Cutrine-Plus) and elemental copper (crystalline copper sulfate). Protox herbicides (oxyflourfen and oxidaizon) were able to control algae up to 70%. Hydrogen peroxide controlled algae by 50% and its efficacy dropped dramatically five days after treatment (DAT). Zinc sulfate was only effective at 1 DAT and algae recovered rapidly after that. Combining fertilizer management practices with chemical options will enable us toward an integrative approach for early algal bloom in the rice cropping system.