Integrating Azolla with Reduced Nitrogen Fertilizer Improves Weed Suppression, Productivity and Profitability of Lowland Rice Systems

Daudi Katigula Kasabuku; Mawazo Jamson Shitindi; Said Hussein Marzouk; Eliakira Kisetu Nassary

doi:10.66132/ngas020202

Authors

Daudi Katigula Kasabuku Sokoine University of Agriculture https://orcid.org/0009-0009-3530-0007
Mawazo Jamson Shitindi Sokoine University of Agriculture https://orcid.org/0000-0002-5579-902X
Said Hussein Marzouk Ministry of Education and Vocational Training https://orcid.org/0000-0001-5525-2270
Eliakira Kisetu Nassary Sokoine University of Agriculture https://orcid.org/0000-0002-7327-4366

DOI:

https://doi.org/10.66132/ngas020202

Keywords:

Azolla pinnata, Biological nitrogen fixation, Integrated nutrient management, Lowland rice, Nitrogen use efficiency, Weed suppression

Abstract

Sustainable rice production in sub-Saharan Africa is increasingly threatened by declining soil fertility, high nitrogen fertilizer costs, and severe weed infestation, which together limit productivity and farmer profitability. While mineral nitrogen fertilizer remains essential for yield improvement, its inefficient use increases production costs and environmental risks. Biological alternatives such as Azolla pinnata offer potential for supplementing nitrogen while simultaneously suppressing weeds; however, quantitative field evidence on its capacity to reduce nitrogen requirements while improving agronomic and economic performance in East African irrigated rice systems remains limited. This study aimed to evaluate whether Azolla integration can reduce nitrogen fertilizer requirements while improving weed suppression, grain yield, and economic returns in lowland irrigated rice systems. A randomized complete block design with eight treatments and four replications was conducted over two cropping seasons. Results showed that Azolla application significantly reduced weed density by up to 84% compared to the unfertilized control. The combined application of Azolla with 40 kg N ha⁻¹ produced the highest grain yield (3.7 t ha⁻¹), representing a 68% increase over the control, while also achieving the highest net economic benefit (981.5 USD ha⁻¹) and benefit–cost ratio (2.36). Higher nitrogen rates without Azolla did not produce additional economic advantages, highlighting the importance of integrated nutrient management. The study demonstrates that Azolla integration with moderate nitrogen rates improves nitrogen use efficiency, weed control, yield stability, and farm profitability. Adoption of Azolla with 40–80 kg N ha⁻¹ is therefore recommended as a climate-smart and cost-effective nutrient management strategy for sustainable intensification of irrigated rice systems. This study was conducted over two seasons at a single irrigation scheme; therefore, further multi-location and long-term studies are needed to confirm the stability of these findings under diverse agroecological conditions.

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