# Phosphorus Distribution in Soils from Australian Dairy and Beef Rearing Pastoral Systems
## 4 Discussion
### Influence of Management Practices
#### 4.2.2 Moisture Variations  
Moisture is a factor which may impact on soil P speciation and organic P composition. Moisture has been shown to increase organic P forms in soil [23]. For example, an increase in diester P and,indeed, other organic P components have been linked to increased moisture and acidic pH [23]. This may be due to lower decomposition rates and/or decreased microbial biomass. However, another study has shown a positive correlation with increased microbial populations for pasture based soils [23; 48]. Hence, the influences of microbial populations are still debatable due to variable results related to the heterogeneity of diester P [23; 53].  
Investigation of moisture inputs received by sampled sites showed a stark difference between the rainfall averages of the Maffra (582 mm) and the Warragul areas (1021 mm). Even though the Maffra area received only 57% of the average rainfall of Warragul, this is somewhat offset if not surpassed, due to all sites in the Maffra area receiving boarder-check (flood) irrigation as part of the MID. The timing of the irrigation applications may also be important as the irrigation season of the MID occurs annually between 15 August and 15 May, encompassing the Australian summer. Sampling for the Maffra area occurred during April 2007 and was towards the end of the regular irrigation season. Without intensive monitoring of moisture inputs at each individual site it is difficult to estimate the impact of soil hydration on the final results. This intensive and costly monitoring is outside the scope of the present study. Even so, there may be some correlation between the irrigated system (Maffra), with a relatively constant water supply, and the rain-fed system (Warragul). As moisture is known to increase soil organic P [23] this may account for the much higher organic P (combined monester P and diester P) proportions found in sites in the Maffra area, averaging 37.5% compared with those in the Warragul area which averaged 31.1%.  
Soil moisture may have also been a factor affecting sites within a sampled area. The Dermosols of sites W1 and W2 are located on a flood plain area and, as such, would be subjected to saturation and flooding during different seasonal events. However, this possibility was not deemed sufficient to class the soil as a hydrosol for the purpose of this study. Nevertheless, moisture may be considered an important factor for the organic P composition of soil from sites W1 and W2. In wetland soils, organic P has been shown to be predominant [54; 55]. This may also account for the large difference in organic P concentration (combined monoester P and diester P) obtained for soil from Dermosol sites W1 and W2 (32.9% and 31.6%) compared to those from Ferrosol sites W3 and W4 (21.3% and 24.9%) under the same farm management. However, it is important to note that prior to sampling, both Warragul and Maffra areas were subjected to extended drought conditions (>3 years). For the period between 2002 and 2006 inclusive, the Warragul and Maffra areas received approximately 79% (ranging between 68% and 93%) and 78% (ranging between 61% and 90%) of the long term (>100 years) average rainfall respectively [56]. Hence, it is unlikely that the Dermosol sites W1 and W2 were subject to normal soil flooding and saturation processes throughout the extended dry period. Nevertheless, the generally higher moisture content at these sites over an extended period may be sufficient to enable formation of higher organic P concentration than in the Ferrosol sites.