# Anaerobic Digestate from Biogas Plants--Nuisance Waste or Valuable Product?
## 3 Results and Discussion
### Apparent Macronutrients and Heavy Metals Recovery  
The apparent macronutrients recovery (ANR) by plants from the tested products were dependent on their form and the type of nutrients (Figure 3). Highest ANR values were determined on objects fertilized with LFs. This results from the fact that this digestate fraction primarily contains soluble forms of nutrients readily available for plants. For the majority of macronutrients, ANR on these objects considerably exceeded 100%. This points to intensive uptake of nutrients from the soil resources by a greater mass of plants than that obtained on the control object. High ANR values were also recorded on objects fertilized with DGs (approximately 100% or higher). It can therefore be concluded that the fertilizer  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Intercept** & **Slope** & \(p\)**-Value** & \(\mathbf{R^{2}}\) \\ \hline N-NH\({}_{4}\) dose on N content & **16.10** & **1.71** & **0.01** & **12.1** \\ P dose on P content & **1.84** & **2.16** & **0.00** & **45.5** \\ K dose on K content & **15.18** & **7.98** & **0.00** & **30.3** \\ Mg dose on Mg content & 0.89 & 0.29 & 0.09 & 4.2 \\ Ca dose on Ca content & **2.45** & **-2.01** & **0.01** & **11.1** \\ Zn dose on Zn content & **18.80** & **-0.20** & **0.01** & **14.4** \\ Cu dose on Cu content & **2.33** & **0.07** & **0.00** & **18.1** \\ Mn dose on Mn content & 54.59 & \(-\)0.57 & 0.08 & 5.1 \\ \hline \hline \end{tabular} Boldface types indicate statistically significant correlations (\(p<0.05\)).  
\end{table}
Table 7: Results of linear regression analyses describing the relationship between nutrient contents in maize and nutrient dose in different forms of digestate.  
use of DGs and LFs will not be associated with a leaching of nutrients to the environment. However, results from this pot experiment in field trials require further validation in field experiments.  
Considerably lower ANR was recorded on objects fertilized with pellets, i.e., PDGs and PSFs, particularly in reference to Ca and Mg. On these objects, the highest values were reached by apparent potassium recovery (approximately 90%). This was similar to that obtained on objects fertilized with DGs. Apparent N recovery reached 73.3% and 53.4%, respectively, for PDG and PSF treatments. This suggests that maize uses nitrogen contained in these products very efficiently. [PERSON] et al. [47] obtained only 30 to 35% of apparent nitrogen recovery of urine-N in grass cultivation. P recovery form fertilizers is usually low. It is one of the causes of its accumulation in the soil and run-off, or leaching of P from the soil to surface waterbodies. In the conducted experiment, very high values of apparent P recovery from PDGs (45%) and PSFs (40%) were obtained. In studies conducted by [PERSON] et al. [48], apparent P recovery was lower than in our research, reaching approximately 23%.  
Apparent Zn and Cu recovery from different forms of digestate was very low (Figure 4). Only on objects fertilized with LFs did the A_H_MsR value exceeded 10%. Only apparent Mn recovery was high, particularly on objects fertilized with LFs and DGs.  
Figure 4: Apparent heavy metals recovery (A_H_MsR) from different forms of digestate. The standard deviation within each treatment (\(n\) = 3) is indicated by the line extending the column. Values followed by the same letters in the column (separately for HMs) are not statistically different (\(p\) < 0.05).  
Figure 3: Apparent macronutrients recovery (ANR) from different forms of digestate. The standard deviation within each treatment (\(n\) = 3) is indicated by the line extending the column. Values followed by the same letters in the column (separately for nutrients) are not statistically different (\(p\) < 0.05).