Effects of Azolla and inorganic nitrogen application on growth and yield of rice in mwea irrigation scheme

Use of inorganic fertilizers constitutes 20% of the rice production cost in Mwea. Azolla fern, which grows in Mwea Irrigation paddies, has the potential to supplement the nitrogen requirement, thus reducing the fertilizer costs. A field experiment was conducted in Mwea Irrigation Scheme during 2015 long and short rains to determine the effect of Azolla incorporation and inorganic nitrogen on growth and yield of rice. The treatments comprised three nitrogen fertilizer levels (0, 30 and 60kg N ha-1) and three Azolla biomass levels (0, 7.5 and 15tons ha-1) laid out in a randomized complete block design with a split-plot arrangement. Data on plant height and number of tillers per plant were collected at 21, 35, 45, and 65 and 75 days after transplanting rice while yield and yield components were determined at 120 days after transplanting rice. Soil was analysed for N, P and K, before and after termination of the experiment. Data were subjected to analysis of variance using SAS and means separated using the least significant difference test at p ≤ 0.05. Azolla incorporation significantly increased residual soil phosphorus, grain weight, % grain filling and grain yield. Inorganic nitrogen significantly increased plant height, tiller numbers, neck node, and panicle length, number of panicle m-2 and grain yield. Grain yield increase from Azolla treatment ranged from 5 to 42% compared to that of inorganic nitrogen which ranged from 18 to 36%. Application of 15t ha-1 of Azolla biomass recorded the highest yield, however, it was not significantly different from that of 7.5t ha-1.