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Last week, we reported that fertiliser use jumped 10% year on year for the 12-month period 31 September 2017 to 1 October 2018.
Now on the face of it, this sounds like a significant increase. So was it? Given the year that was – remember we had the beast from the east, prolonged drought in the east, more maize and beet grown and a lot more forage and catch crops grown, so was there really more fertiliser used or was it sold and is still on farms?
Also, while it might be 10% more compared with 2017, how does it compare to the 20-year usage figure?
For reporting purposes, the Department’s year runs from 1 October to 30 September. During this period, nitrogen increased by 10.6% from 369,089t to 408,495t during the 12 months to October 2018. Phosphorus use increased to 46,387t (up 10.7%), while potassium use reached 120,267t – an increase of 10.6%.
Background
It is important to put these figures into context. Nitrogen use peaked in 1999 at 442,916t and dipped in 2011 when the figure fell to 295,795t (Figure 1). Phosphorus use dipped to a record low in 2008/9 when milk prices and weather combined to make that a year to forget.
However, phosphorus use was on the decline before that and stayed at relatively low levels until 2016/17 when it exceeded 40,000t for the year.
Potassium also dipped significantly to a record low of 52,000t in 2008 and has more than doubled since to exceed 120,000t in the 2017/18 year.
So what drove the increase in usage? We have to be careful as 2016/17 was a brilliant year for grass and growing conditions were such that grass was growing exceptionally well as weather patterns suited perfectly.
In the east of the country a drought took hold from June onwards, meaning there was little or no point in spreading fertiliser for a good period of the summer
The year just gone was another exceptional year but for a lot of different reasons.
An exceptionally cold and late spring saw grassland farmers grow little or no grass in February, March and April compared to the normal. Fertiliser or no fertiliser, soil temperatures were so low that growth was non-existent.
In the east of the country a drought took hold from June onwards, meaning there was little or no point in spreading fertiliser for a good period of the summer.
In the west of the country, it was in general a very good year as the low rainfall allowed grazing and cutting in places that had not been cut for a long time.
When the rain finally arrived in September in the east, there was a late push and extension to fertiliser spreading, which definitely would have pushed up usage in September compared with the year before.
As the drought became apparent and a forage shortage loomed there was significantly higher maize and beet planting.
The maize area doubled and there were 23,000ha of forage crops sown mostly on tillage ground that had been harvested for winter cereals.
On top of all this, there has been an ongoing campaign by Teagasc and all advisers to use more lime, phosphorus and potassium on an ongoing basis to grow and manage grassland better.
Soil fertility results are still well below optimum for large parts of the country.
The fruit of this work is the fact that more nitrogen, phosphorus and potassium are being spread.
Soil fertility had been in decline since the mid-noughties, linked closely with lower lime and lower compound fertiliser use.
Over the last decade in particular, a worrying trend of continuous mining of the native fertility of some soils may have eroded their grass and crop production potential.
This limited their ability to maximise grass as our main fodder source and to maximise the yield potential from new cereal varieties.
However, the Teagasc soils database now indicates large improvements in soil pH levels and early signs of improvements in both soil P and K levels on farms, although the rates of these improvements are enterprise-specific.
In 2017 and 2018, a total of about 90,000 soil samples were analysed by Teagasc and this large database of soil analysis results has been shown to generally reflect national soil fertility trends.
Over this period, 49% of soil samples came from dairy farms, 44% from drystock farms and 7% from tillage farms. Notably, in 2018, the number of soil samples taken on dairy farms increased by 29% compared with the previous five-year average.
Across all farm enterprises, the only soil fertility indicator showing significant positive signs of improvement was soil pH.
Increased research and advisory emphasis on the importance and benefits of lime application to our naturally acidic soils since 2013 has helped to raise awareness among farmers.
This is reflected by current national lime use (over one million tonnes), which had increased by on average 211,000t per year since 2013 compared with the previous five years.
The optimum soil pH for grassland mineral soils is 6.3 and from 2014 to 2016, on average 37% of soils tested were in this range whereas in 2017 to 2018, on average 54% of soils had optimum pH levels.
When soils from tillage farms were examined separately, the improvements in soil pH were greater, with up to 83% of samples having optimum soil pH in 2017 to 2018. This large improvement in soil pH will have significant positive effects on nutrient uptake efficiency from applied fertiliser and organic manures and also on the longevity of reseeded grassland swards and, in particular, the maintenance of clover.
Soil pH levels on dairy farms have shown improvements since 2015 and increased annual lime applications have contributed to a dramatic change in soil pH status over the last five years with 64% soils below optimum pH in 2014 to 2015 and just 39% in 2017 to 2018.
Examining soil P and K levels across all farming systems, just 38% and 45% soil samples, respectively, had sufficient P and K for optimal grass and crop production (= index 3).
The 2018 soil results show some positive signs but a large proportion of soil samples still have low fertility (ie index 1 and 2) with 59% low in P and 50% low in K.
These results show very little difference between grassland enterprise (dairy v drystock) in terms of soil P and K fertility levels with 40% and 50% of soils with sufficient P and K (= index 3), respectively.
Increased N-P-K compound fertiliser use on grassland farms over the last four to five years has not yet been reflected in soil P, which is naturally slow to respond. However, it appears that soil K levels are beginning to respond positively with a reduction of 10% in low K soils in 2018.
This is a positive result as it indicates a halt to steady decline in soil K, some of which may have been a result of increased grass utilisation and the removal of high-quality baled silage from paddocks being routinely grazed. These paddocks need to have adequate K fertiliser returned to balance the high K offtake.
The samples from tillage farms show a slow but steady improvement in both soil P and K levels over the past four years, with approximately 46% and 57% of soils with sufficient P and K for crop production (= index 3), respectively.
These positive trends in national soil fertility represent a foundation to build on.
While they represent a snapshot at national scale, the real focus is needed at farm, and even field, scale to develop a balanced fertiliser programme and to utilise organic manures resources where they are most beneficial on low soil P and K soils. Soil fertility is a cornerstone of our grass-based animal production systems and critical for enhancing crop yields and quality into the future.
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