6/19/2023 0 Comments Linear regression igor pro![]() An unintended consequence of P use in agriculture has been increased P loss to waterways, removing natural limitations to algal growth in the Peel Inlet and Harvey estuarine system ( Kinhill Engineers 1988). To overcome P deficiency, superphosphate application, particularly in the period 1945–1975 became an integral part of farming practice ( Birch 1982 Yeates 1993) in the Peel–Harvey coastal catchment. Soils in south-west Western Australia (SWWA) were deficient in phosphorus (P) when land clearing for agriculture commenced in the 1800s. Landholder practices need to be analysed in detail to confirm if this accumulation occurs everywhere or is only confined to actively farmed land. Thirteen percent of samples had P content in excess of agronomic requirements in 1983, rising slowly to 69% in 2018. Soil P stocks increased since clearing compared with uncleared soils (1221 kg ha –1 m –1 and 285–694 kg ha –1 m –1, respectively). Management of P in sandy soil near the estuary is a high priority as is P stratification in highly P retentive soil. Strong P stratification in the soil is evident, particularly topsoil sandy soils are saturated to depth and clay soils show signs of P saturation in the topsoil. Soil P content was high, with 70% of samples with Colwell P content in excess of agronomic requirements Production is more likely limited by low soil pH (CaCl2) and low K (92% and 67% of paddocks respectively). This paper draws on and undertakes a meta-analysis of 20 200 surface (0–10 cm) and profile (to 100 cm depth) soil samples collected in the period 1983–2018. The catchment’s soils are naturally infertile, but P application has increased P fertility. Phosphorus (P) discharge from agricultural activities is the main source of poor water quality. The Peel–Harvey estuarine system in Western Australia's south-west is affected by poor water quality, algal blooms, and fish kills.
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