Optimizing Nitrogen Fertilizer and Seed Rate to the Growth, Yield and Yield Attributes of Rain-Fed Lowland Shaga Rice in Northwestern Ethiopia

Abstract

Achieving high yields and quality rice while minimizing environmental impact is crucial for rice production in Ethiopia. However, the absence of specific recommendations for nitrogen (N) fertilizer and seeding rates limits productivity. This study aimed to optimize N fertilizer and seeding rates to enhance the growth and yield of Shaga rice. A factorial combination of three N rates (184, 276, and 368 kg ha⁻¹) and seed rates (60, 80, and 100 kg ha⁻¹) was conducted using a randomized complete block design with three replications. Results indicated that the interaction between N rates and seed rates significantly affected partial factor productivity of nitrogen (PFPn), grain yield, leaf area index, filled spikelets, number of spikelets per panicle, and biomass accumulation. The application of N at a rate of 184 kg ha⁻¹ resulted in a 49.2% increase in grain yield. In contrast, higher N rates (368 kg ha⁻¹) led to a decrease in PFPn to 8.4%. Specifically, the combination of an N rate of 184 kg ha⁻¹ with a seed rate of 100 kg ha⁻¹ yielded 6.7 t ha⁻¹ in Fogera, while applying 276 kg N/ha with a seed rate of 60 kg ha⁻¹ produced 6.2 t ha⁻¹ in North Achefer. Additionally, high N doses delayed physiological maturity and reduced PFPn. Economic analysis revealed that the combinations of N at 184 kg ha⁻¹ with a seed rate of 100 kg ha⁻¹, along with N at 276 kg ha⁻¹ with a seed rate of 60 kg ha⁻¹, yielded the highest net income returns of 151,456 and 137,811 Birr per hectare in Fogera and North Achefer, respectively. These combinations are recommended as optimal strategies for maximizing profitability in rice production in the two areas.