# Phosphorus Distribution in Soils from Australian Dairy and Beef Rearing Pastoral Systems
## 4 Discussion
### Influence of Management Practices
#### 4.2.1 Fertiliser Variations
Site W5 also had the lowest WEP and CCEP concentrations of all sampled sites. Fertiliser application differences are also notable when interpreting the NMR spectra for this site. Even with the recent inorganic fertiliser addition prior to sampling, the proportion of orthophosphate averaged 9.8% less than other Ferrosol sites. However, this site had the highest proportion of pyrophosphate at 3.1% of all the sites in the Warragul area. Thus, indicating that the retention of P as pyrophosphate and other insoluble inorganic/organic P may account for the low WEP and CCEP concentrations obtained for this soil sample. As with the Warragul sites fertiliser management variations were also evident for the Maffra sites. Site M2 received a P fertiliser application 15 d closer to sampling in comparison with M5 (45 d compared to 60 d). Slightly higher P fertiliser application rates (possibly over an extended period) at site M2 may be reflected in the measured soil P concentrations, particularly total P concentrations (2381 mg P kg\({}^{-1}\) for site M2 and 1775 mg P kg\({}^{-1}\) for site M5). Despite fertiliser additions (13.2 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\), 60 d),site M5 was one of three (also sites M3 and M4) sample locations which had a lower proportion of orthophosphate than the combination of monoester P, diester P and pyrophosphate. The low proportion of orthophosphate at site M5 is an interesting observation due to the relatively recent fertiliser application to the site (60 d). In fact, this results is more reflective of other Maffra soil types which had not received P fertiliser input for an extended period (>730 d). The low proportion of orthophosphate may also be due to insufficient elapsed time to allow fertiliser P to be solubilised and incorporated into the soil structure. The NMR results for site M5 also do not reflect what was found for WEP (48.4 mg P kg\({}^{-1}\)) and CCEP (46.2 mg P kg\({}^{-1}\)) analysis. This was the highest CCEP concentration and second highest WEP concentration measured across all sites. The CCEP and WEP measurements are often associated with \"available\" P measurement and this would be expected to indicate an increased presence of inorganic orthophosphate. These results appeared to be more reflective of the recent fertiliser additions for the Maffra area as site M2 (WEP 53.0 mg P kg\({}^{-1}\) and CCEP 40.2 mg P kg\({}^{-1}\)) produced similar results for recent fertiliser addition. An interesting comparison can be made between sites M6 and M7. Both of these sites are located on the Macalister Research Farm, a dairy farm situated in the MID of south-east Victoria. Each of the irrigation bays measured were a vertic, mesonatric grey Sodosol [39]. Site M6 (graded) was laser graded six years prior to sampling which involved disk ploughing followed by minor cutting and filling. The top soil was retained within the irrigation bay. Site M7 (established) had not been significantly altered through cultivation (>20 years prior). Each of these sites received identical P fertiliser application (15.4 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\)) and timing (130 d) for the two years preceding soil sampling. Even after a six year period from the laser grading, there still appears to be a significant difference between the graded and established sites. This was reflected in both soil P measurements and organic P composition. All soil P concentrations for the 20 mm depth were higher in the established bay (site M6), particularly the environmental P tests (total P 15% greater; Colwell P 4%; Olsen P 6%; WEP 49%; CCEP 74%). This was not completely unexpected. Surface soil and accumulated P is redistributed throughout the soil profile due to laser-grading process. A possible explanation for P being held in a more available form is that the mixing of the soil profile may, in turn, expose fresh P adsorption sites within the soil. With more adsorption sites exposed, graded bays could have a greater capacity to convert newly adsorbed P from the available form to occluded P over time.