Potential of Azolla as a Nitrogenous Biofertiliser for Irrigated Rice at the Lower Moshi Irrigation Project, Tanzania

Abstract

A field experiment was conducted at the Lower Moshi Irrigation Project, Tanzania, to quantify the green-manurial potential of Azolla grown as a dual crop with irrigated rice. Azolla alone and in combination with 40 and 80 kg N ha-1 as urea (45%N) was compared with untreated control or, 160 Kg N ha-1 as urea. These treatments were tested on Wahiwahi (indigenous) and IR54 (improved) rice varieties in a split-plot design with 3 replications, in 18 m2 plots each of which received a basal phosphate dose of 20 Kg P ha-1 as Tripe super phospate (TSP). Rice plant height, tiller number, panicles per m2, grains per panicle, grain mass and the ultimate grain yield were the parameters of interest that were used to quantify the potential. Azolla was broadcast in plots flooded with shallow water, left to multiply between rice hills and then manually incorporated into the soil as two successive crops, the second being a regrowth of the first, before the rice canopy prevented further incorporation. At an inoculation rate of 3.0 t ha-1, 19.63 t ha-1 of fresh Azolla was obtained in 15 days. The N yield of Azolla was slightly higher under the indigenous rice variety but, on the overall, one crop of Azolla yielded 26 kg N ha-1. Azolla alone significantly (P=0.05) improved most of the parameters cited above, the improvement being comparable to that obtained with 160 kg N ha-1 as urea or with Azolla supplemented with lower dose of urea. Azolla therefore, demonstrated considerable potential (albeit its diminution by rice canopy) in promoting rice performance under conditions of the Lower Moshi Irrigation Project. Given the low amounts of N accumulated by Azolla, further studies are suggested to identify other possible rice growth-promoting factors in Azolla, and to quantify its full potential under different ecological and cultural conditions.

UNISWA Research Journal of Agriculture, Science and Technology Vol. 4 (2) 2000: pp 190-198