DRY-MATTER PRODUCTION AND NUTRIENT CYCLING IN AGROFORESTRY SYSTEMS OFMANDARINE GROWN IN ASSOCIATION WITH ALBIZIA AND MIXED TREE SPECIES

A study on dry matter production and nutrient cycling in agroforestry systems of mandarin grown in association with N-2-fixing Albizia and m ixed tree species (non-N-2-fixing) was carried out in the Sikkim Himal aya. A site with Albizia was referred as Albizia-mandarin stand and th e other site with mixed tree species as mandarin stand. The stand tota l biomass, net primary productivity and mandarin fruit production was higher under the influence of Albizia. Agronomic yield of crops remain ed nearly the same in both the stands. Nitrogen and phosphorus concent rations of different components of Albizia were higher than those of m ixed tree species, whereas their back translocation from leaf to branc h before abscission was lower in Albizia. The mandarin-based agrofores try is a highly nutrient-exhaustive system evaluated in terms of nutri ent exit through the removal of agronomic yield. This system, under th e influence of Albizia, was more productive with faster rates of nutri ent cycling. Nutrient use efficiency increased under the influence of Albizia, in contrary to the hypothesis that efficiency should decrease with increasing rate of uptake. The poor nutrient conservation of Alb izia, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faste r cycling of nutrients. Albizia should be utilised more extensively in the management of mandarin-based agroforestry systems.