Increased nitrogen availability in soil after repeated compost applications: Use of the PASTIS model to separate short and long-term effects

Regular application of composts on cropped soils has been shown to restore soil organic matter contents. The effect of repeated applications of three urban composts on the nitrogen (N) dynamics in a cropped loamy soil was compared to farmyard manure application and a control receiving no amendment. Each amendment application brought on average 250-400 kg ha−1 of total N. After five applications, total organic N increased in amended soils from 9 to 27% compared to control and the increase of soil organic N corresponded to 32-79% of total N brought by the amendments. The PASTIS model was used to describe the N balance in the soil-plant system during the 2 years after a sixth amendment application and provided correct predictions of N dynamics in cropped plots. The N availability increased in all treatments receiving organic amendments. The N availability in the soils amended with urban composts or manure was predominantly driven by the biodegradability of the organic amendments, their mineral N content and by the cropping conditions. Composts with high biodegradability exhibited higher proportion of N recovery by plants (21% for the municipal solid waste compost) during the year following their application, while more stabilised composts (biowaste compost, co-compost of sludge and green wastes) increased the N availability mainly through the increase of soil organic N content and mineralisation after several compost applications (6-8% of the soil organic N increase). Mature composts behaved comparably to FYM, except that for FYM very little N from the last application was available. Regular compost applications equivalent to 200 kg N ha−1 every other year could increase N availability for crops of 50-70 kg N ha−1 over the 2 years of the crop rotation. However, the most stabilised composts led to a higher crop N recovery but also to potential higher amounts of leached N compared to less mature composts.