Modelling the impact of urban compost application on nitrogen dynamics in a cultivated soil

The need of realistic site specific and local studies still exists for developing sustainable urban compostapplication practices, to provide adequate nitrogen for crop growth, and minimise leaching of nitrogen into groundwater.This research aimed at evaluating the effect of repeated application of three urban composts on the dynamics of nitrogen(N) in a cultivated loamy soil and to compare these treatments with farmyard manure application and with a controltreatment without any amendment application. The dynamics of nitrogen was evaluated by sampling destructively the soiland by measuring its mineral nitrogen content. The deterministic model PASTIS, which accounts for and links transportprocesses in soil, crop nutrient uptake and carbon and nitrogen transformations in soil, was used to describe and predictnitrogen balance in a soil-plant system.Experimental results showed that accumulation of mineral N were significantly higher in the amended treatments than inthe control treatment due the mineralization of organic N brought by the amendments. PASTIS gave correct predictionsof nitrogen dynamics in bare and cultivated plots. Furthermore, simulations showed that nitrogen availability of urbancomposts, from previous and last applications, was predominantly driven by: (1) the quality of organic matter ofamendment (2) mineral-nitrogen content and (3) cropping conditions. Composts with high biodegradability presentedhigher nitrogen release the year following their application, while more stable composts with low biodegradabilityallowed availability of N after several years of compost application. Soil mineral content had increased in all treatmentsthat received organic amendment which increased N plant uptake from 60 to 118 Kg N.ha-1 during two years compared tosoil without amendment. Simulated N fluxes showed that application of organic amendments increased nitrogen leachingfrom 6 to 17 Kg N. ha-1 for two years compare to control treatments with 30% of the leaching that occurred during thefirst winter period following amendment application when the soil was kept bared and 40 % of the losses occurred during the dormancy period of winter wheat