Binggeli P., Blackstock P. and McGill C. (2000) Potassium deficiency in conifers on former
agricultural land. Quart. J. For. 94, 229-231
ABSTRACT
Conifers on former agricultural sites in Ireland exhibited potassium deficiency (yellowing, needle loss and
reduced growth increment) within two years of planting. This deficiency appeared to be related to
previous land-use of these lowland peats and may be prevented with the application of potassium at the
time of planting.
INTRODUCTION
In plants potassium is the second most important mineral nutrient after nitrogen. Deficiency of
potassium may lead to reduced growth rates, impaired lignification of vascular bundles, higher
susceptibility to fungal attacks (Marschner 1986) and either higher or lower susceptibility to frost damage
(Jalkanen et al. 1998; Marschner 1986).
Typically in young conifers potassium deficiency takes the form of the yellowing of terminal needles and
in severe cases the whole shoot is affected and may even result in a loss of apical dominance (Taylor
1991). Shoot tip necrosis has been observed in a number of Picea spp. (e.g. van den Driessche &
Ponsford 1995). With age the yellowing only affects older foliage, but in cases of severe deficiency shoot
death also occur. Potassium deficiency causes important diameter growth reduction and also affect
height growth, although this is less marked than in the case of either nitrogen or phosphorus deficiency
(Taylor 1991).
Symptoms indicating potassium deficiency have been observed in the past two years in conifer
plantations, managed by the Western Forestry Co-Operative, in the centre of Ireland within two to three
years of planting. These plantations have been established on previously improved lowland peat soils.
Norway Spruce is often planted instead of Sitka spruce on these sites, as they are susceptible to frost. In
most of these sites there is a history of fairly intensive agricultural production, including hay, silage and
grazing. This paper reports on the findings of an investigation on the occurrence and causes of foliage
yellowing, early needle loss and poor growth increment in the Irish Midlands and makes silvicultural
recommendations.
METHODS
Evidence for poor growth first became apparent in early 1998 and in late 1998 bulk needle samples were
collected at six sites in Co Roscommon (Ballaghaderreen, Ballybane, Ballyglass, Castleplunkett, Cloonfad
and Cloonisisclin). These were analysed for levels of nitrogen, phosphorus and potassium by Coillte
Research Laboratory (Bray, Republic of Ireland).
A field assessment of damage and site conditions was carried out in early April 1999 at three of these
sites (Cloonfad, ....). At each site a qualitative assessment of tree health, soil characteristics and
vegetation (with special emphasis on indicator species) was made. At Cloonfad, a 1994 plantation, the
tree crop in one of the plantations was investigated in more detail. The 1998 height increment growth
was measured along two transects and the percentage needle loss on the main stem for the shoots
produced in 1998, 1997 and 1996 was estimated.
RESULTS
Site description and field observations
All sites examined during the survey consisted of former grassland growing on fen peat. The land-use
history was broadly similar with the fields having been fertilised on a yearly basis and used for hay,
silage and grazing. These fields were well looked after and were reasonably productive. The soils were
dark, homogenous peat and, in some cases, overlaid clay.
Ground vegetation consisted of patches of lush coarse grasses with meadow-sweet (Filipendula ulmaria)
and flag iris (Iris pseudacorus) in places, and scattered Juncus. The complete absence of heather species
indicated a relatively high pH on these sites. Dandelion, Taraxacum officinale, does not grow on sites
deficient in potassium (Tilman et al. 1999) and was absent from the sites surveyed.
The young conifer trees were stunted and generally less than one meter high (range 20 cm to 1.6 m).
The variation in height and yearly increment growth was very patchy. Most trees exhibited chlorosis of
their needles, with some degree of shoot tip necrosis and needle loss very conspicuous. The incidence of
these symptoms was similar to that of variation in height, that is it was very patchy and in groups of 6 to
20 trees.
At Cloonfad the observed yellowing and stunted growth was affected by catena position and mirrored
associated soil and vegetation changes. Upslope, as the soil became more mineral the trees showed less
symptoms. Shelter was another factor which somewhat promoted growth rates but did not appear to
affect yellowing. Norway spruce appeared to be more susceptible to dieback than Sitka spruce and this
was very noticeable when these two species were growing in adjacent fields.
Foliar analysis
The chemical composition of leaves of Sitka spruce, Norway spruce, Lodgepole pine and Scots pine taken
from these sites is given in Table 1. They show that leaves were clearly deficient in potassium with levels
mainly between 0.27 and 0.33%. Levels of nitrogen and phosphorus were mostly satisfactory. Even
where potassium levels were marginal (such as in Site 5b) Norway spruce showed symptoms of
deficiency whereas an adjacent plantation of Sitka spruce had yet to exhibit any deficiency.
Table 1: Chemical composition of Sitka spruce, Norway spruce, Lodgepole pine and Scots pine needles
and deficient and optimal foliar nutrient concentrations (from Taylor 1991) (figures in italic indicate
marginal levels and in bold deficient or severely deficient as stated in Coillte reports; Sampling sites: 1 =
Ballaghaderreen, 2 = Ballybane, 3 = Ballyglass, 4 = Castleplunkett, 5 = Cloonfad and 6 = Cloonisisclin,
Def = Deficient, Opt = Optimal).
Site
Sitka spruce
Nitrogen (%)
Phosphorus (%)
Potassium (%)
Norway Spruce
Nitrogen (%)
Phosphorus (%)
Potassium (%)
Lodgepole pine
Nitrogen (%)
Phosphorus (%)
Potassium (%)
Scots pine
Nitrogen (%)
Phosphorus (%)
Potassium (%)
1
2
0.73
0.10
0.44
0.56
0.09
0.51
1.89
0.30
0.25
3
4
1.72
0.24
0.27
1.39
0.16
0.55
1.92
0.24
0.27
1.45
0.15
0.27
1.98
0.19
0.44
5a
5b
5c
6
1.52
0.28
0.33
2.01
0.30
0.33
2.18
0.24
0.52
1.95
0.30
0.34
Def
Opt
<1.2
<0.14
<0.5
>1.5
>0.18
>0.7
<1.2
<0.14
<0.5
>1.5
>0.18
>0.7
<1.2
<0.14
<0.5
>1.5
>0.18
>0.7
<1.2
<0.14
<0.5
>1.5
>0.18
>0.7
Growth increment and needle loss
At Cloonfad there were no significant differences between the two transects although trees in the
transect closest to the hillside (and more sheltered) had a slightly greater 1998 increment growth than
the more exposed transect (27.1±12.3 cm vs. 19.4±9.5 cm). Overall, in 1998 the saplings grew by
22.6±11.3 cm (range 4 to 50 cm) and the needle loss on the 1998, 1997 and 1996 portions of the main
stem were, respectively, 22%, 57% and 82%. There was much variation in needle loss regardless of
stem age, with one individual having lost 98% of its needles, whereas another had lost just 6% of its
needles. With one exception the needle loss increased with the age of the stem. 1998 increment growth
was significantly correlated with cumulated needle loss (ANOVA P < 0.05). Only one individual suffered
from leader death.
DISCUSSION
Potassium deficiency has been associated with air pollution and soil acidification in continental Europe
(Thelin et al. 1998), but it is generally not recognised as a problem in plantations in the British Isles
(Innes 1995). Yet the foliar analysis, yellowing and needle loss of conifers from the Irish Midlands clearly
show that potassium deficiency can be a problem. The observed symptoms did, however, differ slightly
from those commonly reported, as shoot death was nearly absent.
Potassium deficiency on fertile, former agricultural, land does need to be investigated in more detail,
however, the reasons for its occurrence in the Irish Midlands may be explained by recent investigations
elsewhere. Over the past 25 years soil potassium levels have declined significantly under grassland in
northern England (Skinner & Todd 1998) and there are clear indications that heavy nitrogen fertilisation
enhances potassium deficiency in conifers on potassium deficient sites (e.g. van den Driessche &
Ponsford 1995). Prior to their conversion to plantation forestry in the 1990s the studied sites were
improved for agriculture in the 1970s and 80s and have, over the past two decades, received yearly
fertilisation carried out to promote grass growth. This fertiliser programme and cropping pattern appears
to have acerbated potassium deficiency on these lowland peat sites, with their already low levels of soil
potassium.
The symptoms of potassium deficiency are readily identifiable and the fertility of sites suffering from this
deficiency may be redressed by the application of muriate potash. Application of muriate potash, rather
than potassium sulphate, on the grounds of much reduced costs, is to be favoured, although it increases
the risk of fertiliser scorch (Proe 1994). It is recommended that, on lowland, apparently fertile, pastures
on peat that are free of dandelions, potassium should be applied at the time planting in order to reduce
costs.
REFERENCES
Driessche, R. van den & Ponsford, D. (1995) Nitrogen induced potassium-deficiency in white spruce
(Picea glauca) and Engelmann spruce (Picea engelmannii) seedlings. Can. J. Forest Res. 25, 1445-1454.
Innes, J.L. (1995) Influence of air-pollution on the foliar nutrition of conifers in Great Britain. Envir. Poll.
88, 183-192.
Jalkanen, R.E., Redfern, D.B. & Sheppard, L.J. (1998) Nutrient deficits increase frost hardiness in Sitka
spruce (Picea sitchensis) needles. Forest Ecol. Mgmt 107, 191-201.
Marschner, H. (1986) Mineral nutrition of higher plants, 2nd edn. Academic Press, London.
Proe, M.F. (1994) Plant nutrition. For. Commn Bull. 111, 37-65.
Taylor, C.M.A. (1991) Forest fertilisation in Britain. For. Commn Bull. 95, 1-45.
Thelin, G., Rosengren Brinck, U., Nihlgard, B. & Barkman, A. (1998) Trends in needle and soil chemistry
of Norway spruce and Scots pine stands in South Sweden 1985-1994. Envir. Poll. 99, 149-158.
Tilman, E.A., Tilman, D., Crawley, M.J. & Johnston, A.E. (1999) Biological weed control via nutrient
competition: Potassium limitation of dandelions. Ecol. Appl. 9, 103-111.
Skinner, R.J. & Todd, R.J. (1998) Twenty-five years of monitoring pH and nutrient status of soils in
England and Wales. Soil Use Mgmt 14, 162-169.