A comparison of nitrogen use efficiency and surplus in two dairy farms typologies

Referring to the Destra Brenta district (Veneto Region, Italy) two farming systems were considered: grassland-hay (H) vs. arable land-silage maize (M). Manure and crop products belonged to an internal flow, thus an annual farm gate balance of nitrogen (N) was carried out to determine the nutrient use efficiency (NUE) and surplus by using data from a survey. Surplus was determined as difference between inputs (I) and outputs (O) and NUE as ratio between O and I. The main I was represented by purchased concentrate, on the contrary fertilizer accounted only for low amounts. Surplus per surface unit was significantly higher in M-farms group than in H one (269 vs. 369 kg N per ha; P<0.01). Surplus referred to unit of fat corrected milk was significantly lower in M-farms (17.6 vs.15.6 kg of N per ton of FCM; P<0.01) leading to an higher N-NUE (0.260 vs. 0.278; P<0.05).