| Popis: |
Grain sorghum is an important staple food crop for smallholder farmers in Uganda, but the yields remain low due to the decline in soil fertility, particularly nitrogen (N) and phosphorus (P). A study was conducted on an Acric Ferralsol and Calcic Andosol in contrasting agro-ecological zones (AEZs) of Uganda to evaluate the value of soil organic carbon (SOC) as a proxy of soil fertility status in influencing N fertilizer responses. Sorghum yield response trials to N fertilizer were installed in each AEZ during the growing seasons of 2010–2011. Phosphorus and potassium (K) fertilizers were applied to alleviate nutrient limitations. All experiments were laid in fields of variable fertility categorized into low, medium and high SOC. Substantial yield gains to applied N were observed in medium to high SOC fields. Grain yields were considerably more responsive to increase in SOC and N fertilizer in an Acric Ferralsol, averaging 297% yield gain, than in the Calcic Andosol with 165% yield gain. Application of N fertilizer to soils with relatively high SOC content and fertility bears better yield benefits than the low SOC counterparts. Acric Ferralsol with SOC > 1.7% and Calcic Andosols with SOC of 1.2–1.9% registered highest yield responses to N, suggesting existence of critical SOC ranges for increased N use efficiency in sorghum. |
