## 3 Results
### Soil Properties  
Overall, after the second crop cycle, the physical and chemical properties of the soils changed significantly compared with the first crop cycle (Table 5). The pH increased from 6.1 to 6.3, the OM from 6.1 to 7.6%, and the total N from 2.7 to 3.2 mg kg\({}^{-1}\). The soil properties that decreased significantly after the second crop cycle were the EC from 0.13 to 0.09 dS m\({}^{-1}\). The soil EC was low (<0.40 dS m\({}^{-1}\), [18]) and was similar in the treatments fertilised with digestates and with the N mineral fertilisation. The exchangeable bases also decreased significantly at the end of the second crop cycle, K\({}^{+}\) from 1.44 to 1.33 cmol\({}_{\rm c}\) kg\({}^{-1}\), Ca\({}^{2+}\) from 7.45 to 5.53 cmol\({}_{\rm c}\) kg\({}^{-1}\) and Na\({}^{+}\) from 0.04 to 0.01 cmol\({}_{\rm c}\) kg\({}^{-1}\).  
Figure 2: Nitrogen partial productivity (NPP, g DMY g\({}^{-1}\) N) and nitrogen agronomic efficiency (NAE, and N\({}_{\rm m}\)AE, g DMY g\({}^{-1}\) N) of (**a**) lettuce and (**b**) kale, and nitrogen recovery efficiency (NRE and N\({}_{\rm m}\)RE, %) of (**c**) lettuce and (**d**) kale. The data are presented as mean \(\pm\) SE (\(n\) = 4). According to [PERSON]’s multiple range test, different letters above the columns indicate statistically significant differences among the treatments for each nitrogen use efficiency indexes (\(p\) < 0.05).  
All soil properties changed significantly regarding the changes between the treatments (\(p<0.001\)). The treatments with the application of digestate at an N rate of 170+85 and 170+170 kg ha\({}^{-1}\) showed the highest values of pH (6.5), and on the contrary, the application of mineral N (Ni85) gives the lowest pH value (5.8). The treatments Ni85, DG-N170+85 and DG-N170+170, showed the highest values of the EC (\(\approx\)0.13 dS m\({}^{-1}\)), and in the other treatments, the EC ranged between 0. 10 and 0.09 dS m\({}^{-1}\). The soil OM showed the highest value (7.7%) in DG-N170 and DG-N170+Ni60 and the lowest in Ni85 (5.6%) and both the control and DG-N85 (6.1%) treatments. The content of total N in the soil was higher in the treatments DG-N170+85 and DG-N170+Ni60 (3.4 mg kg\({}^{-1}\)) and DG-N170+170 (3.3 mg kg\({}^{-1}\)) and showed the lowest content in the Ni85 and control treatments (2.4 and 2.5 mg kg\({}^{-1}\) respectively). The exchangeable bases K\({}^{+}\), Ca\({}^{2+}\), Mg\({}^{2+}\) and Na\({}^{+}\), showed the lowest in the control and Ni85 treatments and the highest in the DG-N170+85 and DG-N170+170. For K\({}^{+}\), the soil content ranged between 1.02 and 1.23 cmol\({}_{\rm c}\) kg\({}^{-1}\) in Ni85 and the control treatments to 1.36 and 1.43 in the DG-N170+170 and DG-N170+85. The Ca\({}^{2+}\) content (cmol\({}_{\rm c}\) kg\({}^{-1}\)) in the soil was 5.99 in the Ni85 and increased to 6.96 (DG-N170+170), 6.87 (DG-N170+Ni25), 6.79 (DG-N85) and 6.76 (DG-N170+85). For the Mg\({}^{2+}\), the lowest soil content (cmol\({}_{\rm c}\) kg\({}^{-1}\)) was observed in the Ni85 treatment (0.84) and the highest soil content in the DG-N170+170 treatment (1.72). Na\({}^{+}\) had the lowest soil content (cmol\({}_{\rm c}\) kg\({}^{-1}\)) in the control (0.02) and the highest in DG-N170+85 and DG-N170+170 (0.034). After the two crop cycles, the amount of soil available P remained high and the crops showed adequate levels of P, in all the treatments. Additionally, the soil content in heavy metals remained low and similar to the control treatment (data not shown).