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Summary of our research
In Africa, rice accounts for approximately 30% of cereal consumption and is the second most important cereal crop after maize. Rice consumption is increasing across Africa, making increased rice production critically important for reducing hunger. Sub-Saharan Africa consists largely of semi-arid regions where, unlike Japan's flooded paddy fields, rice is primarily grown in rainfed conditions (rainfed lowland or upland rice cultivation) across extensive cultivated areas. To increase rice production, proper management of fertilizers and water resources for upland rice is essential. A research group conducted upland rice cultivation trials over two years in semi-arid Kenya and discovered that maximum yield was achieved with 7.5 kg of nitrogen fertilizer per 10a (0.1 hectare), while increasing nitrogen fertilizer to 15 kg actually decreased yield. Even more surprising, contrary to the general belief that combining nitrogen fertilizer with irrigation increases yield, they demonstrated that "high nitrogen × irrigation" actually promotes yield reduction and elucidated the underlying mechanisms.
These new findings challenge the conventional wisdom that the combination of fertilizer and irrigation produces synergistic effects. The results of this research were published online in the international academic journal Field Crops Research on June 6, 2025.
Researcher information
SEKIYA Nobuhito
Graduate School of Bioresources Professor
Specialized area：
Crop Science
Current research field：
Sustainable Rice Production (Organic Rice Farming)
KONDO Makoto
Graduate School of Bioresources Associate Professor
Specialized area：
Animal Science
Current research field：
Nutritive evaluation of ruminant feed