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Leaching Studies in Lysimeter Units.
Ryan, Michael Fanning, A.
Ryan, Michael
Fanning, A.
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1999-09-01
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Ryan, M., Fanning, A., Leaching Studies in Lysimeter Units, End of Project Reports, Teagasc, 1999.
Abstract
Lysimeter studies have shown the adverse effect of Fallow soil in
releasing NO3-N to soil drainage water. A soil at Johnstown
Castle under Fallow management gave mean NO3-N drainage
water concentrations >MAC (maximum admissible concentration,
11.3 mg/l) in the 10
th
, 11
th
, 12
th
and 13
th
years of cultivation. In
the 14
t h
year this changed as the Fallow treatment showed a
mean value <MAC, indicating reduced N mineralisation.
However, 7 of that year's 13 water samples were > MAC.
On the same soil, barley receiving 120 kg N/ha fertiliser N,
showed variable results - soil drainage water concentrations
were <MAC in one year but >MAC in another year; the mean
values were < the Guide Level (MAC÷2) in both years. When the
fertiliser input was raised to 180 kg N/ha, MAC was breached in
both sampling years and the mean value was > the Guide Level.
Winter wheat receiving 150 kg N/ha as fertiliser had all soil
drainage water concentrations <MAC in one year but two
samples breached MAC in another year. The mean values were
< the Guide Level in both years. On application of 200 kg N/ha,
MAC was breached in both years and mean annual NO3- N
concentrations were < the Guide Level or > the Guide Level,
depending on drainage water volume.
These results apply to a soil in cultivation since 1985 having
reduced organic N reserves. Higher NO3-N concentrations in soil
drainage water would be expected with similar soils recently
changed from grass to arable farming.
On grassed lysimeters (Johnstown Castle soil), that had been
growing barley for 10 years, a combination of 300 kg/ha
fertiliser N with 126 kg/ha cattle slurry N, applied in December
or February and the same amount of fertiliser N plus 120 kg/ha
pig slurry N, applied in December or February gave soil drainage
water samples that only breached MAC once in 12 samplings per
treatment. The mean NO3-N concentrations were < the Guide
Level. A slightly lower mean N (118 kg/ha) input via the slurries plus the same amount of fertiliser N gave lower NO 3- N
concentrations for all treatments except the pig slurry (+
fertiliser) applied in November. This treatment breached MAC
twice and resulted in a mean NO3-N concentration > the Guide
Level.
Cultivating the soil, in order to re-sow grass, produced a large
release of organic N via mineralisation and this combined with a
small fertiliser N input (50 kg/ha) gave very high concentrations
of NO3-N in the drainage water. A delay in sowing from June to
the end of September exacerbated this problem.
The final phase of experimentation showed very low levels of NO3-
N in the drainage water which was primarily induced by
decreasing fertiliser N input to 200 kg/ha and slurry N input to
50 kg/ha.
Five soils, representative of major Irish soils, were subjected to
lysimeter trials in a similar manner under grass. In the first
experiment the soils received 300 kg/ha fertiliser N plus
approximately 120 kg N/ha as pig or cattle slurry.
In Years 1, 2, when mean values were pooled over treatments,
MAC was breached 2, 3 times by Clonroche; 5, 3 times by Elton,
1, 2 times by Oakpark; 5 times and once by Rathangan soil
drainage water. Applying cattle or pig slurry in December with
fertiliser N, applied during the growing season, gave the highest
number of water samples in breach of MAC.
Reducing the fertiliser N to 200 kg/ha and the slurry N to 51
kg/ha drastically lowered the NO3-N concentrations in the
drainage water to sustainable levels. Cultivation followed by
Fallow for 3 months prior to sowing grass gave very high NO3-N
concentrations in all soil drainage waters.
Due to recycling of N via animal excreta, greater leaching of NO3-
N is likely to occur on grazed grass receiving identical N inputs.