Species-rich hay meadows are usually managed extensively to maintain their biodiversity, with the harvested biomass traditionally being fed to ruminants for milk or meat production. The quality of the biomass is, however, variable, difficult to predict and often does not fulfil today’s requirements. This study established a field trial at two species-rich hay meadows to investigate the combined effect of fertilisation (none, phosphorus and potassium (PK), nitrogen, phosphorus and potassium (NPK)) and date of first cut (at different phenological stages) on biomass quality and quantity. In addition, the most suitable uses of the biomass were explored, including the alternatives biogas and combustion. After four years of the field trial, the stage of maturity at the time of first cut had a greater influence than extensive fertilisation on biomass quality. Dry matter yield (DMY) of the first cut was about 40%–60% of annual DMY (53.99 ± 12.51 dt ha−1 a−1) depending on site, fertilisation and harvest time. Fertilisation had a stronger effect than harvest time on DMY and annual methane yield. In most cases, there was no significant difference in chemical composition between biomass harvested at the end of the grass-flowering stage and at the seed-ripening stage. Thus, a late cut for hay proved to be the most flexible option.

The nitrogen (N) dilution curve is a useful tool for farmers to assess the effectiveness of fertilizer application. The N dilution curve describes the decrease in plant N as biomass increases. This concept has not yet been tested for its applicability and robustness under different cutting regimes in grasslands. We conducted a principal components analysis on biomass yield and N concentration data to discern relationships among experimental, climatic, and management factors. Next, two N dilution curve parameters were calibrated for different cutting frequencies. We compared N uptake using four different methods utilizing calibrated N dilution curves, a reference curve, and different cutting regimes representing different physiological ages of the crops at cutting. Our results show that excluding cutting frequency information overestimates values of N uptake. Calibration of the N dilution curve according to cutting frequency improves N uptake estimates relative to observed values. Therefore, N uptake is better estimated using both the N dilution curve and the cutting regime information.

No abstract

Biogas production is a key renewable energy pathway for a more sustainable future bioeconomy. However, there is a crucial trade-off between biomass productivity and social-ecological sustainability of available biogas cropping systems. Permanent grassland has been frequently promoted as a promising perennial cropping system for biomass production. Three- and four-cut regimes are usually the highest-yielding and thus preferable for biogas production. A three-year field trial in southwest Germany investigated biomass yield and biochemical composition of mesotrophic Arrhenatheretum grassland under three cutting regimes (two-, three- and four-cut). For the three-cut regime, a preliminary biogas batch test was conducted. The three-cut regime had the highest annual accumulated dry matter yield (11.8–14.8 Mg ha−1), an average specific methane yield of 0.289 m3N kg−1 volatile solids−1 and an accumulated annual methane yield of 3167–3893 m³N ha−1. The four-cut regime performed least favorably due to a lower dry matter yield than the three-cut regime, the highest ash content and the highest nitrogen content. Thus, the three-cut regime promises the best yield performance, whereas the two-cut regime can potentially provide more ecosystem services such as biodiversity conservation and wild-game protection. Consequently, the two-cut regime could help improve the social-ecological sustainability of biogas crop cultivation.

Legumes in grassland can increase locally grown protein in fodder while reducing the nitrogen (N)-fertilizer requirements. Although the benefits of forage legumes are known, there was a decline in their use in the past due to inexpensive N-fertilizer, soya products from abroad, and variable legume persistence. In recent years, mounting environmental concern has sparked new interest in legumes. To quantify the effect of legume reseeding and N-application on permanent grassland on crude protein (CP) and dry matter yield (DM), a multifactorial trial was set up. Factors considered were clover species (red clover, white clover), N-application rate (0–170 kg N ha−1), N-fertilizer type (mineral-N, organic-N), and cutting management (3, 5-cut). Legume percentages were scored, and DM- and CP-yield was measured for three years. Crude-protein gains after legume reseeding were considerable and between 2.5–3.4 after red clover and 0.4–1.7 t CP ha−1 3 years−1 after white clover-reseeding even when compared to the control-high-N treatment. Legume percentages were negatively correlated to N-rates down to rates as low as 42 or 85 kg N ha−1 for a three- or five-cut management, respectively. Nitrogen-applications increased the yield (DM, CP) of control plots, whereas for legume-reseeded plots yield remained unchanged or was reduced. Differences due to N-fertilizer type were small or non-existent. Reseeding of clover was shown to be a viable method to increase crude protein in permanent grassland for about three years (red clover) and possibly beyond (white clover).