The effects of temperature, water availability and seed burial depth on seed germination and seedling establishment of Calobota sericea (Fabaceae)

Abstract

Calobota sericea is a perennial legume species from South Africa that has the potential to be implemented as a fodder crop in water-limited agro-ecosystems. Apart from dormancy breaking requirements, no information regarding the germination and seedling establishment requirements of C. sericea is currently available. Therefore, the aim of this study was to determine the germination and establishment abilities of C. sericea at different temperatures, water potentials and seed burial depths. In the first trial seeds were incubated at constant temperatures of 5–30 °C at 5 °C increments and in the second trial, seeds were incubated at 20 °C, at water potentials ranging from 0 to −1.0 MPa. The seedling emergence trial consisted of a complete randomised block greenhouse trial where seeds were sown at five burial depths (1–5 cm). Seeds were found to germinate best at temperatures ranging between 10 and 20 °C, but still had a germination percentage greater than 80% at 5 °C. The C. sericea seeds were also found to require a water potential of at least – 0.3 MPa to reach a germination potential of 60%, below which germination was severely impacted. Seedling emergence was found to be highest at burial depths of 2–4 cm. After establishment, seedlings generally displayed a decrease in above ground plant part height with increasing burial depth, but an increase in seedling mass. More resources, in terms of mass, were allocated to early root development as opposed to leaves and stems. Results from the current study therefore suggests that C. sericea seeds can be planted between 2 and 3 cm deep, during winter season, when temperatures are lower, and rainfall more prevalent and less erratic.