Effects of inorganic nutrient P and N application on Azolla biomass growth and nutrient uptake

Rice farmers in Mwea Irrigation Scheme routinely apply P and N fertilizers which affect water nutrient levels. A study was conducted to establish the effects of nutrient N and P application on Azolla biomass accumulation. The study was conducted in a batch culture experiment, using 5g of fresh Azolla biomass samples from each of the six major paddy schemes namely: Mwea, Ahero, West Kano, Bunyala, TARDA, and Taveta. Treatments consisted of 0 and 3mg P l-1 and 0 and 200mg N l-1, laid out in a randomized complete block design replicated three times. Azolla samples were grown in batch culture plastic pots of 8.4 x 10-3m3 for 10 days using canal water, which was replenished every three days. Fresh Azolla biomass weight was recorded at 0, 5 and 10 days after inoculation. Data was subjected to analysis of variance using SAS statistical package version 9.1 and means separated using the least significant difference test (p≤0.05). The pH levels in irrigation water averaged 7.2 while N, P and K levels were 20.2, 11.6 and 15ppm respectively. Tissue N and K for Azolla accession averaged 4.2% and 1.6% respectively. Biomass accumulation and doubling time of Azolla were significantly affected by exogenous P and N nutrient application. Doubling time ranged from 5.5 days to 6.7. Application N and P significantly reduced Azolla biomass accumulation and increased biomass doubling time.