Optimization of the nutrient growing solution and inoculation rate for Azolla mexicana production and use as fertilizer

Abstract

Azolla is a water fern that can be utilized and developed as a soil amendment or fertilizer. Azolla hosts Anabaena cyanobacteria in its vacuoles and benefits from atmospheric N fixation by the Anabaena. The purpose of this study was to enhance Azolla production in natural or artificial ponds for field application. We identified the optimum nutrient concentrations and inoculation rate to maximize growth of Azolla mexicana and measured the nutrient concentrations in A. mexicana for use as fertilizer. A. mexicana was cultivated in nutrient solutions in a greenhouse, and ten individual nutrients were examined at four different concentrations using a randomized complete block design with three replicates. In addition, studies on inoculation rate and combined nutrient solutions were conducted. Azolla growth parameters (biomass, relative growth rate (RGR), doubling time, and percent greenness) and nutrient concentrations were measured. There were no significant differences in Azolla growth parameters among nutrient concentrations with all other nutrients held constant, except for Zn which affected the percent greenness. Inoculation rates of 50 to 100 g m−2 were optimum for 14-day Azolla growing periods in the greenhouse. Azolla nutrient concentrations were influenced by nutrient concentrations in the media. A nutrient solution (Widiastuti2) was developed that resulted in excellent Azolla growth, while also being economical due to its lower nutrient concentrations. If, however, higher Azolla micronutrient concentrations are desired, Widiastuti3 or the original Watanabe solution may also be used.