Effect of different soil types and season on the vegetative propagation of <i>Pterocarpus</i> species in the humid tropic of south eastern Nigeria

Abstract

In addition to the use of Pterocarpus species as a major source of vegetable and fodder, the recent decline in timber sources has led to logging of Pterocarpus species for timber production. Increase in the use of Pterocarpus species for timber production has led to drastic decline in their population. Consequently, a decline in the availability of the vegetable has resulted to the increase in the cost of the Pterocarpus species vegetable. Thus, there is a need for understanding the factors that may be influencing the propagation and growth of Pterocarpus species.This study was carried out to assess the effect of soil types and season on the rooting ability of stem cuttings of Pterocarpus tree species. Five-centimeter-long leafy stem cuttings of near uniform diameter were collected randomly from healthy parent trees of the selected Pterocarpus tree species (P. mildbraedii, P. santalinoides and P. soyauxii). The cuttings were collected in the morning using secateurs and cutlass, and then placed in humid plastic bags to minimize heat stress till they were planted. A 3 x 2 factorial experiment in RCBD with ten replicates was used to assess the rooting ability and growth pattern of the stem cuttings. From this study, it was observed that season and soil type played important roles in the rooting percentage of the three plants studied. From this study, it was observed that most growth parameters were better on clay soil during the dry season except for the shoot length of P. mildbraedii and the leaf area of P. soyauxii cuttings planted on loamy soil. The plant species type, soil type and the treatment interactions had significant effect (P≤0.001) on leaf number, shoot length, leaf length, root length and shoot fresh weight. It was also observed that clay soil supported growth of the three Pterocarpus species studied over the loamy soil during the rainy season study with the exception of P. santalinoides which recorded higher values for leaf number (24), shoot length (5.19cm) and leaf area of P. mildbraedii (4.45cm) on loamy soil. In conclusion, the growth performances of the three plant species studied were observed to be higher on clay soil than on loamy soil, especially during the rainy season. This could be because of the natural ability of the soil to retain water whereas; the cases when the loamy soil did better could be attributed to the abundant availability of soil nutrients. It is recommended from the success of this research that clay soil should be used as a growth medium for the vegetative propagation of the selected Pterocarpus species studied. This will help in the multiplication of Pterocarpus species from cuttings since the seeds are either seasonal or scarce. Also, this could improve the multiplication and development of Pterocarpus species plantation in the humid tropics like in Nigeria.

Keywords: Pterocarpus species, Clay, Loamy soil, Seasons, Plant growth parameters