# Phosphorus Distribution in Soils from Australian Dairy and Beef Rearing Pastoral Systems
## 4 Discussion
### Influence of Management Practices  
#### 4.2.1 Fertiliser Variations  
The impact of different management practices applied to the sampling sites were also investigated. An important feature of site W7 is that it had not received any fertiliser P applications for a minimum of two years prior to sampling. Thus, a combination of soil type (the only grey sandy loam Dermosol) and fertiliser application is likely to be the cause of the difference between site W7 and the other sites. The lack of fertiliser inputs to site W7 is clearly reflected in the total P (1103 mg P kg\({}^{-1}\)), extracted total P (836 mg P kg\({}^{-1}\)) and orthophosphate portion (52.2%) measurements, each the lowest among the Warragul sites. The lower orthophosphate in this soil, in turn, increased the relative proportions of other soil P types, with W7 having the highest proportion of monoester P (39.6%) and the second highest proportion of pyrophosphate (2.6%) (Table 4). This view is well supported by the scatter plots in Figure 4.  
The apparent increase in orthophosphate concentrations due to fertiliser application is not unexpected. In fact the purpose of any type of fertiliser P application is to increase available P for pasture production and all fertiliser P inputs for the sampled site were inorganic blends. Depending on soil texture, fertilisers additions have also been found to increase soil organic P, especially monoester P [23; 52]. Sites M1 to M4 also had similar soil characteristics, but received different fertiliser P inputs over different periods. Site M1 had 11.8 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\) applied approximately 365 d prior to sampling, whereas 14.5 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\) was applied approximately 45 d pre-sampling to site M2 (Table 1). Site M2 also had an extra 14.5 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\) addition around 400 d before sampling. The extra and more recent fertiliser additions appears to be reflected in the soil P concentrations (total P and orthophosphate portion). All measured P concentrations were higher at site M2 than at site M1, including total P (23% higher), Colwell P (41%), Olsen P (73%), WEP (80%) and CCEP (24%). The CCEP concentrations appears to be most affected by the recent fertiliser additions. Although the fertiliser additions are not enough to fully account for differences between P capacity measurements (namely total P and Colwell P), they may also be indicative of different long term management strategies between the sites. Interestingly, these differences were also reflected by three of the different proportions in the four \({}^{31}\)P NMR chemical regions. Corresponding signal proportions for sites M1 and M2 were orthophosphate (66.4% and 64.3%), monoester P (28.2% and 29.1%), diester P (2.0% and 2.5%) and pyrophosphate (3.3% and 4.1%). Only the orthophosphate proportion of the soil from site M2 was lower than that obtained from site M1. Although the difference is small (2.1%) and could be insignificant, it may also indicate that soil from site M2 contained higher proportion of structurally bound (reserve) P, as reflected by its higher Colwell P value (Table 2). The results reported for the Ferrosol site W5 must also be viewed carefully. Although this site received a fertiliser addition close (45 d) to the time of sampling the total P input was relatively minor, equivalent to 3.7 kg\(\cdot\) P\(\cdot\) ha\({}^{-1}\). This application was the only fertiliser P application for at least a three year period prior to sampling. The apparent lack of fertiliser input was obvious with all soil P measurements lower at site W5 compared with soil from other Ferrosol sites (W3 and W4). The difference is particularly noticeable when comparing the agronomic soil P test results of the Colwell and Olsen P values. The average concentrations (sites W3 and W4) of 432 mg P kg\({}^{-1}\) (Colwell P) and 107 mg P kg\({}^{-1}\) (Olsen P) were clearly higher than those found for site W5 (Colwell P 126 mg P kg\({}^{-1}\) and Olsen P 36 mg P kg\({}^{-1}\)).