Effect of different growing periods on the nutritional composition of cowpea (Vigna unguiculata) leaves

Introduction: The nutritional composition of plant tissues is influenced by climatic conditions during their growth and development. Climate influences the growth rate, chemical composition and yield of crops. This study was conducted to evaluate the effect of growing periods on the nutritional composition of six cowpea varieties; Kenyan local variety (KLV), Indonesian local variety (ILV), Malaysian local variety (MLV), Japanese local variety (JLV) and two Kenyan varieties (K80 and KenKunde). Methodology: The seeds were grown in an experimental glasshouse under three varying growing periods in 2015 and 2016, respectively. The effect of growing condition on moisture, protein, potassium, calcium, magnesium, manganese, iron and zinc content was assessed. Results: Moisture content varied from 67.9% to 78.0% and 81.1% to 88.8% in 2015 and 2016, respectively; while protein contents ranged from 7.3% to 14.6% and 18. 4% to 30.4% in 2015 and 2016, respectively. In 2015, there was a significant increase in moisture content, protein, K, Ca, Mg and Mn in KLV as temperature increased. This trend was different for ILV and MLV, which showed significant differences across growing periods with the June growing period showing the highest moisture, protein, K, Mg and Mn contents. In 2016, protein, Ca and Mg contents increased in response to increasing temperature across the growing periods. KLV and Kenkunde exhibited higher concentrations of most components. Conclusion: There were significant differences among varieties and across growing periods in nutrient content implying both variety and climatic conditions affect nutritional composition.