Structure and function of Populus deltoides agroforestry systems in eastern India:: 2.: Nutrient dynamics

Nutrient concentrations in plant and soil and their rates of cycling in poplar (Populus deltoides)-based agroforestry systems were studied at Pusa, Bihar, India. The nutrient concentrations in the standing biomass of the crop were more than those in tree, whereas the nutrient contents showed the reverse trend. Soil, litter and vegetation accounted for 80.3-99.5, 0.1-5.0 and 0.4-14.7%, respectively, of the total nutrients in the system. Considerable reduction (40-54%) in concentration of nutrients in leaves occurred during senescence. The uptake of nutrients by vegetation, and also by different components with and without adjustment for internal recycling, were calculated separately. Annual transfer of litter nutrient to the soil by vegetation was 37.3-146.2 N, 5.6-17.9 P and 25.0-66.3 K kg ha(-1) year(-1) in young (3-year-old) and mature (9-year-old) plantations. Turnover rate and time for different nutrients ranged between 0.86-0.99 year(-1) and 1.01-1.16 years, respectively. Compartmental models for nutrient dynamics have been developed to represent the distribution of nutrient contents and net annual fluxes within the system. This study shows that the poplar-based agroforestry system can be sustainable in terms of soil nutrient status.