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

Abstract

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

Mismatch between a science-based decision tool and its use: The case of the balance-sheet method for nitrogen fertilization in France

“…This argument was along the same lines as what we found in the Nitrate Group reports. Furthermore Shanahan et al [27] emphasized that averages did not overcome farmers' difficulties in fixing an accurate and realistic target yield, similar to what we demonstrated with the way farmers fixed their target yield. Forty years after the implementation of the balance-sheet method, despite many proposals to improve the estimation of the target yield, issues have not changed.…”

“…In France, since Meynard et al [23] first showed that it was a major source of error in N rate estimation, many paths have been provided to rationalize the estimation of crop N requirements. For instance, Meynard and Limaux [24] or Limaux [12] suggested focusing on targeted grain numbers per square meter or crop growth, which is better correlated to wheat N requirements; it was also proposed to use dynamic simulation models to estimate crop requirements [24][25][26]. The current proposal is to make an average.…”