## 3 Results and Discussion
### P Content and Accumulation in Plant Biomass  
#### 3.2.1 Wheat Grain and Straw  
Crop plants are the main beneficiaries of soil resources and fertiliser support in an arable field. The range of P content determined in wheat grain and straw in our studies (Table 7) did not differ from the values reported in the literature [49; 50]. The grain contained 5-15 times more P than straw, which is natural for cereals [51]. The wide range of grain P to straw P proportion in our experiments confirms that plants primarily provide P for seeds, and a large part of assimilates are transported from older leaves and stems to the generative parts before harvesting [52; 53]. None of the presented experiments showed a significant effect of the applied fertiliser treatments on the P content in wheat grain and straw. In experiment II, P content in grain increased under +PP, mainly due to reduced competition from weeds [54], but also partly at the cost of straw [53]. Plant protection did not change the effect of fertiliser treatments. The P content in grain and straw in our experiments had a strong positive correlation with the P content in soil (Table 8). It was also claimed by [PERSON] et al. [55] that luxury consumption of P does occur in agronomic species produced on P-enriched soils. A strong positive correlation was found between the P content in wheat grain and straw (Table 9), as was also reported by [PERSON] et al. [56], as well as between P content in grain and in post-harvest residues. Winter wheat (experiments III and IV) showed a noticeably lower P content in grain than spring wheat (experiments I, II and V), which may be linked to a dilution effect [57] due to the higher yield of winter wheat grain (7.07-9.78 t/ha) as compared with spring wheat (4.18-6.70 t/ha). On the basis of research conducted in Sweden, [PERSON] et al. [58] reported the opposite--a higher P content in winter wheat grain than in spring wheat, but also found a negative correlation between grain P content and grain volume. In our research, the dilution effect was observed in all elements of plant biomass (Table 10). Regarding the effect of P fertilisation on the P content in plants, there are divergent opinions in literature: no influence is indicated [59], and an increase in the P content in organs along with the increase in the P dose [60]. The reaction may vary by species [51]. \begin{table}
\begin{tabular}{c c c} \hline
**In** & **P Content** & **P Accumulation** \\ \hline Wheat grain & 0.704 1 & ns \\ Wheat straw & 0.490 & 0.313 \\ Weed & \(-\)0.322 & 0.352 \\ Post-harvest residues & 0.469 & 0.182 \\ \hline \end{tabular}
\end{table} 
Table 8: Relationship between P content and P accumulation in plant biomass parts and total soil P content—simple correlation coefficients. Most of the P uptaken by plants in our experiments was accumulated in wheat grain (Table 7). It is consistent with earlier reports that about 60-85% of aboveground P is stored in cereal grain [61]. P accumulated in straw is usually far lower, mainly due to a low P content [62]. In our research, P accumulation in grains showed greater dependence on grain yield volume than P content in grain, whereas in the case of straw it was primarily a function of P content (Table 11). In all of our experiments, the lowest P accumulation in grain was recorded when no P was applied. It was associated with a lower yield (see correlation coefficient in Table 11) due to lower soil P abundance (Table 6). Regardless of the fertiliser type, increasing the P dose from 17.6 to 26.4 and 35.2 kg/ha did not significantly differentiate the P accumulation in grain, as other studies also pointed out [60]. The relationship between P accumulation in grain and P content in soil has also not been proven (Table 8). Waste-fertilisers not worse than commercial fertilisers guaranteed the P uptake by wheat and P accumulation in its grain and straw (Table 7). Differences in the fertilisers' effect on the P accumulation in wheat grain were shown only in experiment I.