Establishment yield and nutrient composition of four legumes as influenced by age of growth in a cool tropical climate at Jos, Plateau State, Nigeria

An experiment was conducted with 2 temperate (Trifolium pratense and T. repens) and 2 tropical (Stylosanthes guianensis and Centrosema molle syn. C. pubescens) forage legumes in an elevated tropical environment of Jos, Nigeria to determine the influence of age of growth on forage yield and nutrient concentrations in the establishment year. The experiment was a 4 harvest times (9, 13, 17 and 21 weeks after sowing; WAS) × 4 legume species (2 temperate and 2 tropical) factorial treatment arrangement in a randomized complete block design with 4 replications, conducted in the growing seasons of 2015 and again 2016. In 2015, S. guianensis produced highest (P<0.05) dry matter yield (8.2 t DM/ha), while T. pratense produced the highest yield (3.6 t DM/ha) in 2016. In both years leaf:stem ratio decreased significantly with age. In 2016 crude protein (CP) concentration declined in all species as age at harvest increased (P<0.05), while at any given age highest CP concentration occurred in T. repens and lowest in S. guianensis (P<0.05). At any age, concentration of calcium followed the pattern T. pratense>T. repens>C. molle>S. guianensis (P<0.05), while phosphorus concentration in forage declined with age at harvest with significant (P<0.05) differences only for tropical legumes. The detergent fiber concentrations (NDF and ADF) were higher in S. guianensis (P<0.05) at any harvest stage. Non-linear regression analysis suggested that these forage legumes, when planted in early June in this environment, could be harvested at the optimum stages of 15, 16, 18 and 21 WAS for T. pratense, T. repens, S. guianensis and C. molle, respectively. However, more studies, especially with earlier planting dates, need to be conducted on the temperate legumes to determine their full yield potential in this environment, especially over a wider range of seasonal conditions.