Comeback on the cards for phosphorus?

Phosphorus (P) use on Irish farms has declined in the past decade due to high costs; low grain and meat prices; nitrates regulations; and agri-environmental schemes.

The Agricultural Catchments Programme (ACP) focuses on sustainable P use and how it is needed to sustain and achieve high-agricultural output on Irish farms. The ACP has worked with 320 farmers over nine years through advisory and research.

The programme was established in 2009 to evaluate the environmental and economic effectiveness of the Nitrates Action Programme (NAP) measures in areas (catchments) representing the main land type and medium and high intensity agricultural production systems of Ireland.

Work in the catchments and on farms is focused on improving soil fertility, farming in a sustainable manner and maintaining high water quality.

Importance of P

P is crucial in stimulating early plant development. P is particularly important in arable cropping systems, where P is removed with the crop. However, P use needs to be monitored as high P concentrations in water can lead to eutrophication of waterways.

Measurements

Soil sampling is carried out every two years in the catchments area to measure soil fertility. This allows nutrient management plans to be formulated. Water quality and rainfall is also measured.

Results from Castledockerell and Dunleer

Speaking at last week’s scientific meeting of the Fertilizer Association of Ireland, Teagasc’s Noeleen McDonald presented data from the Castledockerell and Dunleer catchments between 2010 and 2014.

  • She stated that 60% of soils were in index one and two for soil P;
  • P inputs increased over the study period, resulting in positive field P balances;
  • The area in catchments with high P status and higher P loss risk potential declined in Castledockerell, but increased in Dunleer over the study period;
  • Average P balances increased in Castledockerell with increasing mineral P applications. These P fertiliser inputs did not fulfill the P build-up requirements;
  • Average P balances increased in Dunleer due to inputs from organic sources.

Results from the study also showed that soil type affected P loss. Castledockerell soil was less likely to lose soil P than soils in Dunleer, as it can store and buffer the P.

P losses to water are also affected by weather, hydrology and point sources.