Influence of pruning frequency of Albizia lebbeck, Gliricidia sepium and Leucaena leucocephala on nodulation and potential nitrogen fixation

The influence of four pruning frequencies on biomass, nodulation and N2 fixation was investigated on Albizia lebbeck, Gliricidia sepium and Leucaena leucocephala grown in the screenhouse for 16 months, using acetylene reduction and 15N dilution methods. Frequent prunings at 4-month intervals had no deleterious effect on symbiotic N2 fixation, which increased in Gliricidia and Leucaena in particular. Nodulation and nitrogenase activity varied inconsistently within species, and were not influenced by pruning frequency. Cumulative assessment of pruning effect showed higher biomass, N yield and N2-fixing capacity of the woody species than at last harvest, and appeared to have more practical relevance. Across species, cumulative total dry matter, N yields, and both percentage and absolute amount of N2 derived from atmosphere increased with pruning frequency, except when trees were pruned 3 times. Of the three species, G. sepium had the lowest biomass production, N2 fixation and N accumulation