EFFECTS OF AZOLLA BIOMASS GROWTH ON FLOOD WATER TEMPERATURE AND PH, TILLERING AND YIELD OF PADDY RICE

Abstract

Azolla is a floating pteridophyte, which forms an association with an endosymbiont, the nitrogen-fixing cyanobacterium Anabaena azollae. In Mwea Irrigation Scheme paddies, Azolla biomass coverage ranges from 25 to 50 % with a high biomass growth rate and this has caused a challenge in its management. Knowledge on the effect of Azolla biomass on rice tillering, root development and grain yield are important in order to exploit its potential benefits in Mwea Irrigation Scheme, where nearly 60 % of the total rice in Kenya is produced. The effect of Azolla on tillering, plant biomass, adventitious roots development, basal internode growth and yield of rice, was studied during 2015/2016 short and long rains. Azolla was inoculated in 30 cm x 30 cm plastic pots planted with rice variety Basmati 370. Controls where no Azolla was inoculated were included. Tiller number, plant height, flood water temperature and pH were determined at 21, 32, 42, 60 and 75 days after transplanting (DAT). At 120 DAT, grain yield and yield components were determined. Length of basal node and adventitious root were measured and dry biomass weights of, root and above ground biomass determined. Water temperature in Azolla inoculated pots were significantly lower than in controls by 0.8 °C and 1.3 °C in the second and first seasons respectively with a daily fluctuation of 2 °C. The pH of flood water in potted rice inoculated with Azolla was significantly lower than in control.  Azolla inoculated potted rice had significantly higher number of tillers/m2, spikelets per panicle-1, panicle size m-2, 1000 grain weight and plant biomass than in non-inoculated controls. Adventitious roots were significantly longer and more per unit area in all treatments than in controls. The basal stem node length was significantly shorter while root biomass was less for the Azolla inoculated potted rice than in controls.  In all treatments, Azolla doubled its biomass within an average of 5 days.