Determining the Optimal NPK Rate for the Growth and Yield of Voandzou (Vigna subterranea (L.) Verdc.) in the Sudanese Zone of Chad

Abstract

Voandzou (Bambara groundnut, Vigna subterranea (L.) Verdc.) is an underutilised legume in Chad, where production remains largely traditional and technical recommendations for mineral fertilisation are limited. This study evaluated graded NPK (15-15-15) rates to identify an appropriate application rate for the local Houlsar ecotype under Sudanese-zone conditions. A Fisher block design comprising four treatments and four replicates was used. The treatments were T1 (0 kg/ha NPK), T2 (50 kg/ha), T3 (100 kg/ha), and T4 (150 kg/ha). Leaf number was assessed at 30 and 45 days after sowing (DAS), and pod number, pod yield, and 1,000-seed weight were measured. Leaf number did not differ significantly among treatments at either assessment. T3 recorded the highest mean leaf number at 30 DAS (33.25 ± 8.70) and 45 DAS (73.40 ± 14.497). T2 produced the highest number of pods per plant (53.00 ± 2.581), whereas T3 recorded the highest pod yield (1.958 ± 0.587 t/ha), followed by T2 (1.846 ± 0.037 t/ha). T2 also produced the highest 1,000-seed weight (0.632 ± 0.038 kg). The unfertilised control and the highest NPK rate generally produced lower yield-related values. Under the conditions of this trial, 50 kg/ha NPK (15-15-15) provided strong yield performance while using less fertiliser than the higher-rate treatments. Further trials are required to confirm the recommendation across seasons and sites.