Phosphorus transport in subsurface flow from a stony soil under irrigated and non-irrigated lucerne

The extent of phosphorus (P) loss from soils under deep rooting crops such as lucerne is currently unknown. This study used large lysimeters (2.0 by 1.5 m) to quantify the amounts and forms of P in drainage under lucerne from two sites, a non-irrigated dairy system and an irrigated dairy system that also received farm dairy effluent (FDE). Results showed despite greater P inputs to the irrigated compared to the non-irrigated site, there was no difference in total P concentrations in drainage. There were also no differences in the forms of P lost between sites, which were dominated by particulate P (48%-52%). More P was lost from the irrigated (0.262 kg ha(-1)) than the non-irrigated site (0.164 kg ha(-1)). The larger P loss was a result of irrigation producing more drainage (42%) than observed at the non-irrigated site. The amount and forms of P lost from lucerne were similar or lower than losses reported for similar soils under grass/legume-based pasture swards amended with P fertiliser and FDE. Because P leaching was regulated by drainage volume rather than P input, management of irrigation water to reduce drainage from the root zone will likely help minimise P leaching.

Automated summary

Despite greater phosphorus inputs to the irrigated site compared to the non-irrigated site, there was no difference in total phosphorus concentrations in drainage, with particulate phosphorus dominating the forms lost. More phosphorus was lost from the irrigated site due to higher drainage volume caused by irrigation. Management of irrigation water to reduce drainage from the root zone can help minimize phosphorus leaching.