Management strategies to improve the nitrogen use efficiency in grasslands and the protein quality in grass silages: Lessons from a practical study on dairy farms in Flanders

Abstract Background Grasslands are the primary source of forage for ruminants. Legal restrictions on nitrogen fertilization force farmers to optimize nitrogen use efficiency (NUE) of grassland and protein quality in grass silage. Methods The present study included grassland data from 10 dairy farms in Flanders. For each grassland field, the presence of clover was determined based on the seed mixture composition. Soil and manure were sampled before the first application and analyzed to determine plant available N content. The annual NUE was calculated for each field possible (n = 28). Prewilted grass samples were taken just before ensiling (n = 65) and grass silage samples (n = 41) were collected from the same fields. Results Clover fields demonstrated improved NUE due to a lower nitrogen input from fertilizers compared to pure grassland fields (75 vs. 265 kg ha−1). The protein quality of the grass silage was positively correlated with the organic matter digestibility, sugar content, and dry matter content of the prewilted grass. Conversely, crude ash content had a negative effect. Conclusions These findings underscore the importance and potential of clover and the practical feasibility of optimizing grassland management to improve both NUE in grasslands and protein quality of the silage.