## 5 Discussion
### Relative Agronomic Effectiveness  
Figure 7 summarizes all previously presented data by showing the calculated relative agronomic effectiveness for the fertilizer materials, where it was possible to calculate AAE. Figure 6: Residual soil properties after fertilization with kitchen waste (KW) after 4 subsequent harvests compared to mineral fertilizer (MF) and organic fertilizer (CMG). Standard errors included, insignificant if not visible. RAE is actually the AAE related to the AAE of the reference mineral fertilizer. The RAE based on the utilization of N (RAE(N)) was calculated and presented for each subsequent harvest and also as a total value after adding all the harvest data (total N). N-utilization-based RAE(N) better characterizes the fertilizer material as it also contains the dry matter yield when calculating the total N-utilisation per area. In general, RAE differed for the materials across time of growth; however, in most of the cases, DKW ST-dig reached the highest values: 88.3%, 147.9%, and 88% after months 1, 2, and cumulative. Then, DKW 1 EM ST and DKW 2 EM showed similar values: 60.1%, 120.6%, 180.4% (DKW 1 EM ST), and 58.4%, 127.4%, and 215.7% (DKW 2 EM) for three subsequent months, meaning that twice the dose addition of EMs provided similar agronomic effects in terms of N use. The weakest RAE was noticed for either only thermally treated kitchen waste (DKW ST) or only microbially treated kitchen waste (KW 1 EM), where the final RAE after 120 days was about 48.6%. However, these materials performed quite well only after month 2 and 3 (RAE equalled 95.6-210.8%) exceeding (after month 3) or remaining similar values to others (after month 2). In absolute terms, taking into account the whole growth period, the dominating processes that decided about the highest agronomic performance of kitchen waste were anaerobic digestion, coupling EM addition with sterilization, twice EM addition, sterilization solely, and EM addition solely. Optionally mixing processed kitchen waste with commercial organic fertilizers like cow manure granulated could be a good idea to alter the agronomic effectiveness. Figure 7: Comparison of RAE for the kitchen waste for each of the 3 harvests and the cumulative N-based RAE after 120 days of growth. The results above are partially in line with the previous authors' works [52] when they concluded that in the warm season, in comparison to effective microorganism-incubated kitchen waste (KW 1 EM), its anaerobic digestion (KW-dig) improved the relative agronomic effectiveness twice after 30 days of growth (82% versus 43%). However, the total effectiveness for anaerobically digested kitchen waste (KW-dig) versus pelleted and effective microorganism-incubated kitchen waste (KW 1 EM) was 32% versus 27%. This is quite comparable to the results in the current study. When it comes to the external literature, many works addressed the processed kitchen waste and its valorization towards organic fertilizers [53; 54; 55; 56; 57; 58; 59; 60]; however, none of them used the same set of technologies applied on ryegrass. The theory behind better agronomic performance of digestates vs. undigested feedbacks is as follows: application of biogas digestate, containing mainly ammonium nitrate, typically has a pH of about 5-6. This ammonium nitrate will be immediately available to plants, allowing 'just-in-time' application. The remaining solvated ammonium hydroxide (NH4 OH) will be nitrified by soil bacteria to form nitrate (NO3-) and volatile nitrous oxide (N2O), but with less emissions because the ammonium concentration is reduced. Excess nitrate will still be lost either by denitrification (right) or by leaching to groundwater. Denitrification adds to the undesirable (N2O) loss, but the acidic conditions may reduce the action of the denitrification bacteria, thus reducing N2O emissions.