Balance sheet method assessment for nitrogen fertilization in winter wheat: II. alternative strategies using the CropSyst simulation model

It is important, both for farmer profit and for the environment, to correctly dose fertilizer nitrogen (N) for winter wheat growth. Balance-sheet methods are often used to calculate the recommended dose of N fertilizer. Other methods are based on the dynamic simulation of cropping systems. Aim of the work was to evaluate the balance-sheet method set up by the Region Emilia-Romagna (DPI), by comparing it with the cropping systems simulation model CropSyst (CS), and with an approach based on fixed supplies of N (T). A 3-year trial was structured as a series of N fertility regimes at 3 sites (Papiano di Marsciano, Ravenna, San Pancrazio). The N-regimes were generated at each site-year as separate trials in which 3 N rates were applied: N1 (DPI), N2 (DPI+50 kg ha-1 N at spike initiation), N3 (DPI + 50 kg ha-1 N at early booting). Above ground biomass and soil data (NO3-N and water) were sampled and used to calibrate CS. Doses of fertilizer N were calculated by both DPI and CS for winter wheat included in three typical rotations for Central and Northern Italy. Both these methods and method T were simulated at each site over 50 years, by using daily generated weather data. The long-term simulation allowed evaluating such alternative fertilization strategies. DPI and CS estimated comparable crop yields and N leached amounts, and both resulted better than T. Minor risk of leaching emerged for all N doses. The N2 and N3 rates allowed slightly higher crop yields than N1