De-inking Sludge and Phosphorus Effects on Growth and Symbiotic Dinitrogen
Pakistan Journal of Biological Sciences. 10 (14): 2379-2388.
De-inking Sludge and Phosphorus Effects on Growth and Symbiotic Dinitrogen Fixation in Forage Legumes
Iraj Allahdadi1, Chantal J. Beauchamp2, FranÇois-P. Califour2, H. Khalaj1, M. R. Labafi. H.A1
1 Department of Agronomy and Plant Breeding, Aburaihan Campus, University of Tehran; 2 Departement de phytologie, Faculte des Sciences de 1’Agriculture et de 1’Alimentation, UNiversite Laval, Qubec, Canada
The de-inking process produces a waste by-product, called de-inking paper sludge (DS), that contains paper fibers, clay particles and inks, and high C concentrations combined with low N and P concentrations. The use of high rates of DS to increase the soil organic matter thus requires provision of high rates of N and P for adequate plant growth. Using dinitrogen (N2)-fixing forage legumes is an alternative to N fertilization under such circumstances. In a greenhouse study, DS rates of 0, 50 or 100 Mg ha-1 and five rates of P (40, 80, 120, 160, or 200 kg P2O5 ha-1) were applied on two soil types, a clay loam (Pintendre) and a silty clay loam (St-Augustin). Nitrogen uptake and symbiotic N2 fixation (SNF) were estimated in alfalfa (Medicago sativa L.), sweetclover (Melilotus officinalis L.) and red clover (Trifolium pratense L.); Bromegrass (Bromus inermis L.) and alfalfa ineffective for N2 fixation were used as the reference (non-N2 fixing) crops. Atmospheric N2 fixation was estimated by natural abundance of 15N (d15N). Under controlled conditions, high rates of DS substantially reduced d15N values, particularly with high rates of P. In addition, N uptake of legumes generally increased with increased P concentrations, and it peaked with 120 or 160 kg P2O5 ha-1. Correlated with the trends observed with d15N values, and it peaked with 120 or 160 kg P2O5 ha-1. Our results showed that under high rates of application of DS and adequate P supply, forage legumes fixed more atmospheric N2. d15N can be a good indicator of SNF under the above-mentioned conditions.
Key words: de-inking sludge, symbiotic fixation, forage legumes, Phosphorus availability