## 3 Results and Discussion
### P Content and Accumulation in Plant Biomass
#### 3.2.3 Post-Harvest Residues  
Plant parts remaining in the field after harvesting are incorporated into the soil. P stored in this biomass is then slowly released and gradually used by succeeding plants, avoiding leaching into groundwater and water ecosystems [84].  
The P level in post-harvest residues in our individual experiments (Table 7) was determined by the ratio between the residues of the roots, stubble and weeds. For the latter, the species composition, weed relative height in the wheat canopy and the P content of those weed parts (roots, stems or leaves) that prevailed in the biomass left on the field, are of importance [73]. The values obtained were within the limits considered natural [50]. The P content in post-harvest residues correlated positively with the P content in soil (Table 8), as did the P content in grain and straw (Table 8).  
None of our experiments demonstrated a significant effect of P-fertilisers treatments on the P content in post-harvest residues (Table 7). In experiment II, post-harvest residues showed a higher P content under +PP than under -PP. Herbicide limited the weed growth, along with a great part of their above-ground biomass (green, richer in P [73]), which was located in the zone below the moving level, left in the field and enriched the post-harvest residues. At the same time, in the field under -PP, most of the above-ground weed biomass was removed during harvesting, while the weed parts poorer in P (i.e., the stems and roots) remained in the field. This may explain the negative correlation between the P content in weed biomass and in post-harvest residues (Table 9). Interaction between plant protection and P-fertilisation (experiment II) was not found (Table 7).  
A substantial P amount was accumulated in the post-harvest residues (Table 7). In experiments I-III, this quantity equalled or exceeded the P accumulation in wheat straw. Waste-fertilisers usually resulted in the same P accumulation as traditional fertilisers. Only in experiment I did B\({}_{\text{s}}Bm\) cause higher P accumulation in residues than SP, A + H\({}_{2}\)O and A\({}_{\text{s}}Bm\), but it was equal to PR. B\({}_{\text{s}}Bm\) application induced a greater wheat root biomass [85], which could be attributed to PSM activity [86], however, no parallel effect was observed due to A\({}_{\text{s}}Bm\). In experiments II-V, P-fertilisation treatments did not differentiate the P accumulation in post-harvest residues.  
In experiment II, +PP treatment contributed to a higher P accumulation in post-harvest residues, probably as a result of a higher low height weed proportion in the total residue biomass. This thesis is further enhanced by the fact that the P accumulation in residues depended more strongly on the P content than on the biomass volume (Table 11). +PP against -PP treatment did not change the P-fertilisers' effect on P accumulation in post-harvest residues.  
We have not been successful in finding other studies on the effects of recycled fertilisers or PSM on the P content and P accumulation in post-harvest residues. Partial reference can be made to the studies on the P amount in those plant organs whose remains are components of the post-harvest residues found in wheat straw (see Section 3.2.1), weeds (see Section 3.2.2) and roots. Lower maize root biomass fertilised with SSA in comparison to SP applied at the same dose, and root growth stimulation by seed-inoculated PSM, were reported by [PERSON] et al. [64]. The biomass volume may be an indirect indicator of the P accumulation in the roots. As the post-harvest residues are the natural way of P and the recycling of other nutrients, more research seems to be needed, especially based on field experiments.