Farm studies highlight effects of Nitrates Directive on Irish farmland
TEAGASC is evaluating the regulations imposed on farmers as a result of the Nitrates Directive with the Agricultural Catchments Programme (ACP).
Six catchments of contrasting soil type and farming enterprises have been selected across Ireland, two of which are in Co Wexford. Each is around 10km2 in size; one a tillage area on free-draining soil and the other a grassland (mostly dairying) location on heavy soil. Close to 40 farmers farm in each catchment.
Intensive soil analysis was undertaken by the ACP last year. Areas of around five acres were individually sampled and tested for pH, phosphorus (P) and potassium (K). A repeat survey will be carried out in two years' time to show any trends in soil fertility that may be a result of the Nitrates Directive rules.
Some farms in the catchment areas have historical soil results from REPS. Analysis from five such farms are compared below.
There was a three-year gap between sampling. Changes in soil fertility do show some trends. However, as only five farms are examined, it would be unwise to assume the changes here are applicable to other farms of a similar nature. Changes in soil fertility will depend on several factors, from soil type to farm system.
- A suckler and sheep farm on free-draining soil had a more significant fall in K than P, at 24pc and 3pc respectively, on average from nine samples compared. Seven soils had a lower K concentration, five of which fell by more than 50mg/l. Only two soils had a significant reduction in P concentration.
- A tillage and sheep farm on free-draining soil had a reduction in soil P (-12pc) and K (-7pc). Of the eight samples compared, there was a reduction in both P and K on five. Averaging soil results on this farm is misleading as the P index did not change for any fields sampled, remaining at index 2 (low) or index 1 (very low), and the K index changed in all fields bar one, between index 1 (high) and index 2 (medium).
- There were only four soils compared on a tillage farm on free-draining soil. This farm had a significant increase in P on all fields, moving up from index 2 (low) to index 3 (medium) in 75pc of them. Again, the K concentration reduced significantly on the majority of soils, falling from index 4 (high) to index 3 (medium) on three of the samples, and remaining at index 3 (medium) on one.
- The dairy farm (spring calving, heavy soils) had the highest number of samples -- 11. There was very little change in P where all initially had a P index 2 (low). Only one of the soils changed index, falling from low to very low with a reduction in concentration of 1.1mg/l. The K concentration fell in nine of the samples, but it only resulted in a change of index in three fields.
- The cattle farm (weanling to beef on heavy soil) had five samples and showed a slight increase in P on four of them. All these soils were initially P index 2 (low) and the largest increase was 1.7mg/l. Four of the soils showed a fall in K levels, with only two being of significance, falling by 50mg/l and 33mg/l.
- Potassium levels are quicker to change than phosphorus, and have, on average, fallen across all farms. This would correspond to the fall in chemical K usage identified in the Irish Fertiliser Use Survey (2004-2008).
- Lighter soils are more likely to show a reduction in K where fertiliser applications do not replace off-takes.
- The current application rate of K on tillage farms is replacing a smaller portion of the off-take than on livestock farms.
We only know these trends as a result of soil analysis, and the message to be taken from the examples above is that the only sure way of knowing soil fertility and required fertiliser is by taking a soil sample.