Growth and nodulation response of six indigenous trees and two shrubby legumes to phosphorus and nitrogen fertilizers in two soils of Ghana

Fast growth and high N2-fixation make multipurpose trees attractive in agroforestry. We assessed the effects of N and P fertilizer application on nodulation and growth of Millita thonningii native to West Africa and compared its attributes with five known multipurpose leguminous trees Acacia auriculiformis, A. mangium, Albizia lebbeck, Albizia zygia, Leucaena leucocephala, and two shrubby legumes, Cajanus cajan and Crotalaria ochroleuca in Hatso and Toje soils.They all were nodulated without inoculation, with nodulation being higher in Toje soil. Up to 90 kg P ha -1 enhanced nodulation and growth, but further increase to 120 kg P ha -1 caused from 53% to 600% reduction in nodules on M. thonningii and A. zygia , respectively and significant reduction in tree growth. Nitrogen fertilization decreased nodulation in the tree legumes more in the two shrubs and also more when the N fertilizer was combined with 90 kg P ha-1. M. thonningii had highest yield in both un-amended and amended soils, almost 3 and 7 times more than the lowest, A. zygia , in the un-amended Toje and Hatso soils, respectively. M. thonningii used less P for growth, on average 22 and 18 mg P g -1 dry matter in the Toje and Hatso soils, compared to 50 and 39 mg P g -1 for the six trees. Thus M. thonningii with its high yield, nodulation and P use efficiency has great potential in agroforestry.