## 3 Results and Discussion
### Total Soil Phosphorus (P) Content
Rationale fertilisation (right form, right rate, right time, right method) should cover the nutritional needs of crop plants and prevent the decrease of soil P reserves [43]. The application of P-fertilisers in our studies generally provides good protection of soil P stocks against their depletion through crop uptake or leaching. A decrease in total P content despite fertilisation was noted only in experiment IV (except for AB\({}_{g}Bm\) at a P dose of 35.2 kg/ha). An increase in total P content was found in experiment II under \(-\)PP where PR and A\({}_{g}Bm\) were applied at P doses of 35.2 kg/ha, and in experiment III when SP and A\({}_{g}Af\) were applied at P doses of 26.4 and 35.2 kg/ha and AB\({}_{g}Af\) at a P dose of 35.2 kg/ha. In other cases, no differences in relation to the initial state were proven. It is known that due to the high P fixing capacity of most soils and the low P use efficiency (around 10-15%) of most crops, surplus P input from fertilisers tends to accumulate in soils [44]. This accumulation is known as 'legacy P' and is calculated as the difference between inputs and outputs [45]. These stocks can be used by the plants, provided that they are activated. According to [PERSON] et al. [40], 'legacy P' represents a significant potential secondary P source that could substitute manufactured fertilisers, at least in part. Moreover, [PERSON] et al. [46] suggested that the accumulated (surplus) P in agricultural soils is sufficient to sustain crop yields worldwide for about 100 years, if it were available. In our studies, no significant differences in soil P content after the application of traditional and recycling fertilisers were found when they were applied at the same P doses (Table 6). In experiment II, regardless of plant protection treatments, the total soil P content increased with the increase in the P dose applied in fertilisers, while in other experiments only an increasing tendency was noted. These results seem to confirm the thesis that the fertiliser type can be much less substantial than the P amount applied [42]. In three other European long-term field experiments, where the annual P dose ranged between 23 and 35 kg/ha (and did not exceed the doses used in our experiments), the soil P content did not increase significantly [47]. We reported elsewhere that the increase in fertiliser doses up to 26.4 and 35.2 kg P/ha was usually already statistically ineffective [48]. Those findings, together with the tendency to accumulate unused P in soil, as discussed here, should provide a basis for a rational P-fertiliser dosage. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**P-Fertiliser**} & \multirow{2}{*}{**P Dose (kg/ha)**} & \multirow{2}{*}{**Plant Protection**} & \multicolumn{2}{c}{**P Content (g/kg)**} \\ \cline{5-5}  & & & & **Start** & **End** \\ \hline V & No P & 0 & \(+\)PP & 0.622 & 0.540 b  \\  & SP & 17.6 & & 0.604 & 0.591 ab \\  & & 26.4 & & 0.613 & 0.603 a  \\  & 35.2 & & 0.602 & 0.613 a  \\  & AH\({}_{g}\) & 17.6 & & 0.611 & 0.604 a  \\  & 26.4 & & 0.605 & 0.613 a  \\  & 35.2 & & 0.611 & 0.626 a  \\  & AH\({}_{g}Bm\) & 17.6 & & 0.599 & 0.597 a  \\  & 26.4 & & 0.608 & 0.611 a  \\  & 35.2 & & 0.592 & 0.621 a  \\ \hline \hline \end{tabular}  
* \({}^{1}\) different letters indicate significant differences at \(p<0.05\): small letters—for P fertiliser treatments in each experiment separately, capital letters—for plant protection treatments in experiment II; arrows indicate significant increase or decrease in relation to the starting state; +applied, \(-\)not applied.  
\end{table} 
Table 6: _Cont._  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**P-Fertiliser**} & \multirow{2}{*}{\ \begin{tabular}{c} **P Dose** \\ **(kg/ha)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Plant** \\ **Protection** \\ \end{tabular}