Description

White Guinea yam (hereafter referred to as yam) is a major crop widely cultivated in the Guinea savanna region of West Africa, requiring 8 to 10 months from planting to harvest. The timing of the rainy season’s onset and end is crucial for shoot growth and tuber enlargement. However, climate change is expected to shorten the rainy season in this region, potentially reducing yam yields by 33% by 2050. Adjusting the planting time of yam seed tubers has been proposed as a promising adaptation strategy, but its effectiveness remains unclear. Typically, yam is planted about one month after the rainy season starts to avoid drought stress during early growth. If climate change delays the onset of rainfall, postponing the planting period may cause the crop’s late growth stages to coincide with the dry season, exposing it to drought stress and reducing yields. While Dioscorea alata (water yam) initiates tuber bulking based on photoperiod rather than planting date, little is known about the photoperiodic response of White Guinea yam. This study evaluates the impact of planting time on yam yield through on-farm trials in Nigeria, the world’s largest yam-producing country.

Field trials examined three planting dates: early planting (at the beginning of the rainy season), normal planting (one month later), and late planting (two months later). The results showed that early planting led to harvest occurring about 90 days earlier than normal planting, with a 21% yield increase (Fig. 1). Tuber enlargement was determined by the number of days after planting rather than by calendar date, with minimal influence from photoperiod. Earlier planting advanced tuber bulking, allowing completion within the rainy season when soil moisture was sufficient (Fig. 2). The relatively low rainfall at the beginning of the rainy season had little effect on shoot growth or yield. In contrast, delayed planting caused tuber bulking to overlap with the dry season, significantly reducing yield due to drought stress. These findings highlight the risks associated with late planting under shifting rainfall patterns.

This study provides essential insights for optimizing yam cultivation systems under future climate conditions. Early planting can increase yield and mitigate the negative effects of rainfall variability, but some varieties exhibit unstable sprouting, necessitating the development of improved varieties and cultivation techniques. Additionally, extremely low rainfall at the beginning of the rainy season may delay shoot growth, increasing production risks. Further research is needed to refine planting strategies that ensure stable yields in response to changing climatic conditions.

Figure, table