An increase in the amount of concentrate feed offered to livestock is a key factor behind declining water quality in NI, a senior DAERA official has said.
Speaking at a conference in Belfast, Brian Ervine from DAERA described phosphorus as “the problem nutrient” for local lakes and rivers.
He showed trends in phosphorus surplus, which is the amount of phosphorus that comes on to farms through feed and fertiliser, minus the amount that leaves through milk, livestock and grain sales.
“The phosphorus surplus of NI agriculture has gone up because the industry has intensified by importing more concentrate feed,” Ervine said.
DAERA figures indicate that average phosphorus surplus on NI farms stood at 10.8kg/ha last year.
“Around 5kg [per hectare] is a more sustainable position for agricultural systems,” Ervine said.
The figures are backed up by initial results from the Soil Nutrient Health Scheme, where 45% of fields in the first zone of the soil-sampling project were above optimal levels for phosphorus.
Excessive phosphorus in agricultural soils can enter waterways through surface run-off, especially at times of high rainfall, and this has been a long-standing environmental issue in NI.
Average phosphorus levels in NI rivers did fall sharply in the mid-2000s, when the first Nitrates Action Programme was rolled out.
This programme included the introduction of the closed period for slurry spreading, as well as grant schemes for improved slurry storage on farms.
However, Ervine presented figures on Monday which showed that average phosphorus levels in NI rivers bottomed out in 2012 and have generally been on an upward trend since.
“Phosphorus went down, but then it started to go up again and we are back to where we started,” he said.
Official statistics from DAERA show that since 2009 the amount of concentrate feed delivered to NI farms increased by 30%, or 600,000t, to stand at 2.6m tonnes last year.
Cattle feed makes up 52% of the total concentrate used on NI farms and the amount of cattle feed delivered last year was 307,000t higher than 2009 levels.
Over the same period, annual deliveries of poultry and pig feed are up by 182,000t and 127,000t, respectively.
“Intensive systems are where our phosphorus surplus has come from through imports. It’s not just poultry and pig systems, which actually aren’t that large. Cattle is the main livestock system in NI, whether it’s dairy or beef, and that has moved to intensification,” Ervine said.
Excessive phosphorus levels in waterways were a key issue behind the growth of blue-green algae in Lough Neagh over the summer.
Ervine acknowledged that other contributing factors were also at play, such as warmer water temperatures and the presence of Zebra mussels, which affect water clarity.
However, he maintained that surplus phosphorus was an important reason for the algal blooms, and a large proportion of the excess nutrients in waterways originate from farms.
“In Lough Neagh, if the nutrients weren’t there, then the algae wouldn’t be there,” he said.