Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: Aquatic and Riparian Weed Management to Protect U.S. Water Resources in the Far West United States

Location: Exotic and Invasive Weeds Research

Title: Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications

Authors
item Spencer, David
item Linquist, Bruce -

Submitted to: Paddy and Water Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 25, 2013
Publication Date: January 24, 2014
Citation: Spencer, D.F., Linquist, B.A. 2014. Reducing rice field algae and cyanobacteria abundance by altering phosphorus fertilizer applications. Paddy and Water Environment. 12:147-154.

Interpretive Summary: In California’s water seeded rice fields abundant algal growth can be a problem during rice establishment. We set up experiments to evaluate the effects of phosphorus fertilizer management on algal growth in rice fields. In two field-scale experiments, the effects of surface, incorporated, and delayed fertilizer applications were tested. In addition, the effects of phosphorus application timing on rice yields was measured in two smaller enclosure experiments. Results indicate that higher levels of phosphorus fertilizer were associated with increased algal growth. Rice fields which received conventional surface applied P fertilizer had 4 to 8 times more algal/cyanobacterial biomass and 3 to 11 times higher concentrations of soluble reactive phosphate (SRP) than those in which the P fertilizer was incorporated or delayed by 30 days. In the enclosure experiments, weight of algae per square yard and water concentrations of dissolved phosphorus were also significantly greater in enclosures that received the phosphorus fertilizer. Delaying the application by up to 28 days after seeding did not affect rice yields. Reducing dissolved phosphorus concentrations in rice field water will result in reduced algal growth. This can be accomplished by either incorporating P fertilizer into the soil or by delaying its application until rice plants are well above the water’s surface. Reduced algal growth also means that it will not be necessary to apply copper sulfate to kill the algae.

Technical Abstract: In California’s water seeded rice systems algal/cyanobacterial biomass can be a problem during rice establishment. Algal/cyanobacterial growth may be stimulated by phosphorus (P) additions in freshwater habitats, so we set up experiments to evaluate the effects of fertilizer P management on algal/cyanobacterial growth in rice fields. In two field scale experiments surface, incorporated, and delayed P applications were evaluated. In addition, the effects of P application timing on algal/cyanobacterial biomass and rice yields were evaluated in two smaller enclosure experiments. Results indicate that higher levels of P fertilizer were associated with increased algal/cyanobacteria biomass. Rice fields which received conventional surface applied P fertilizer had 4 to 8 times more algal/cyanobacterial biomass and 3 to 11 times higher concentrations of soluble reactive phosphate (SRP) than those in which the P fertilizer was incorporated or delayed by 30 days. Nutrient limitation experiments using the cyanobacterium, Nostoc spongiaeforme, and water from the P incorporated fields and fields where P application was delayed indicate that water from these fields would be described as P-limiting for N. spongiaeforme. While water from the surface applied fields was not P limited. In the enclosure experiments, algal/cyanobacterial biomass and water SRP concentrations were also significantly greater in enclosures that received the P fertilizer. Delaying the application by up to 28 days after seeding did not reduce rice yields. These results agree with previous reports on the relationship between rice field algae and SRP concentration in rice field water samples. The management implication of these findings is that reducing SRP concentrations in rice field water will result in reduced algal/cyanobacterial biomass. This reduction can be accomplished by either incorporating P fertilizer into the soil or by delaying its application until rice plants are well above the water’s surface.

Last Modified: 10/24/2014
Footer Content Back to Top of Page