Effect of Some Tree Species in Improving the Soil Chemical Properties and Earthworm Activities of Degraded Tropical Ultisol

Abstract

The effect of some tree species in improving the soil chemical properties and earthworm activities of degraded ultisol were investigated at Umudike, Nigeria. The study was carried out under some indigenous trees canopies such as Cacao, Breadfruit, Avocado pear, and Mango, to investigate the level of soils nutrients and results were compared with the soils of their open adjacent sites which were ten (10m) meters away at 0 – 30 cm soil depth. Generally, soils under tree canopies had higher values of pH, Organic carbon, Organic matter,  Total N, Exchangeable Ca, Exchangeable Mg, Exchangeable K, Exchangeable Na, Effective Cation Exchange Capacity (ECEC), Base saturation and Available Phosphorus than the soils of their adjacent sites. However, soils under the Cacao tree canopy had higher values of nutrient elements than those of Mango, Breadfruit, and Avocado pear at 0−30 cm soil depth. Also, soils under tree canopies gave significantly (P < 0.05) higher mean values of earthworm population and casts than those of their adjacent sites at various soil depths (0 – 30 and 30 – 40 cm). At 0−30 cm soil depth, Cacao (14.00 and 9.00) gave significantly (P < 0.05) higher mean values of earthworm population and casts than Mango (5.00 and 2.33), Breadfruit (9.67 and 6.00) and Avocado pear (8.00 and 4.00) per m², respectively. These were in the following significant decreasing magnitude: Cacao > Breadfruit > Avocado > Mango. Mango gave significantly (P < 0.05) the least mean values of earthworm population and casts. Therefore, trees when used as an alley in farms added more nutrients to the soils via litter. These litters when broken down by the action of earthworms also release the nutrients which would, therefore, support the above-ground vegetation. Therefore, an increase in organic matter values of soils under the tree canopies and leaf litter might have influenced earthworms’ abundance.