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V. Assessment of Limiting Factors

V. Assessment of Limiting Factors

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Pinus radiata



FORESTS



323



largely but not entirely gone into nutrient surveys of either existing

stands or unplanted sites. This has been with the practical end of providing a guide to planting and fertilizer procedures. In the short term,

it is the relationship between the abnormal or unthrifty tree and the

normal tree which has been examined to find what improvements can

be made. Details on nutrition as such and on the interaction between

the soil and the tree should be first worked out on normal trees.

Over a series of years, Will and his co-workers in New Zealand have

investigated various aspects of nutrient distribution of P . radiata on

pumice soils, and these studies are of value in establishing the status

of normal trees.



A. FOLIAR

ANALYSIS

The mineral nutrient content of trees has been investigated for

nearly a century, and the use of analysis of plant tissue as a diagnostic

technique for evaluating site fertility continues to be discussed and

reviewed (e.g., Viro, 1961; Tamm, 1964).

Work on tissue analysis of P. radiata under forest conditions has been

restricted to foliar analysis except for that of Will (1962), who suggested

the use of wood for phosphorus and later showed (Will, 1965) that both

wood and bark analysis were promising for detecting deficiencies. The

total amount of work done has been rather limited, perhaps as a result

of the large variation within the species including differences in the

number of whorls from tree to tree as discussed under Section 111.

Even though a deficiency may be sufficiently obvious for it to be

recognized from its symptoms, this should be checked by analysis before

undertaking field experimentation. This checking both confirms the diagnosis and indicates whether a second nutrient is involved in deficient or

excessive amounts.

1 . Requirements for Foliar Analysis

The technique of foliar analysis requires that there should be a significant relationship between growth and the foliar nutrient content

when the supply of the nutrient to the tree is progressively restricted.

The measure of growth may be a total over the life of the tree, e.g.,

height, or better still an increment over the current or the previous

growing season. The foliar nutrient contcnt has been measured in various

ways in pines-for example, as weight of nutrient per needle in the wet

or dry state or as percentage of the oven dry material. The last of these

has been used extensively for P . radiata and will be considered here.

Further requirements are: (1) to have an estimate of errors within

and between trees and between forests; ( 2 ) to sample from material of



324



M. RAUPACH



uniform physiological age; ( 3 ) to choose a sample position in the tree

and a time of sampling which are as sensitive as possible with respect

to growth changes; and ( 4 ) to continue to sample for a number of years

over as wide a range of ages, tree quality classes, and site variation as

possible in order to arrive at critical nutrient levels having taken account

of season, age, and tree size.

These requirements are necessary to enable comparisons to be made

and to remove as many of the uncertainties as possible from the interpretation of the results in terms of tree behavior and nutritional

requirement. Tamm (1984) gives a detailed and critical discussion on

these points.

2. Errors and Critical Levels



Will (1957) indicated the distribution of six nutrients in the crowns

of four trees by sampling various portions of the crown and taking

needles of differing age. Each tree was, however, sampled at a digerent

time from December through September. The levels obtained were

greater than those formerly found by Askew (1937) on a similar volcanic

soil except for calcium, which was about the same. The ranges of Will's

results as percentage oven dry weight were as follows:

phosphorus

nitrogen

potassium

calcium

magnesium

sodium



0.106-0.284

0 37-1.14

0.65-1.08

0.040-0.680

0.066-0.216

0.013-0.135



The calcium, sodium and phosphorus levels increased with needle age,

but magnesium and nitrogen tended to decrease. The results for calcium,

potassium, and phosphorus increased toward the base of the crown.

Measurements by Hall and Raupach (1963) on 8-year-old trees on a

potassium-deficient podzolic soil near Traralgon, Victoria, were made

on needles collected in March. The needles were from each of six random

trees in plots with and without added potassium fertilizer and represented samples from the highest laterals with each of one, two, and three

ages of needles as well as from the middle and lowest laterals with three

ages. Each age was sampled, giving 144 lots of needles which were

analyzed for nitrogen, phosphorus, and potassium; the wet weight of u)

needles was recorded. The results are summarized in Table I, significant

differences between treated and untreated plots being indicated. The

results for all three elements tend to decrease with increasing needle age

and with distance down from the top of the tree. The range of nitrogen

and of potassium contents was lower than found by Will, but it was



TABLE I

Values of Nitrogen, Phosphorus, and Potassium (Mean Percent) in Needles of Varying Age from Various Positions in the Crown

of 8-Year-Old Pinus radiata for Control and Fertilized Treeso

Age of needles

Approximate



6 months



height above

ground (feet)



Treatment



26



0

+Kb

0



21

16

13

10



+Kb

0

fKb

0

+Kb

0



+Kb

b

c



12-18 months



N



P



K



N



1.82

1.74

1.80

1.67*

1.59

1.55

1.49

1.34*

1.28

1.10*



0.256

0.220*”

0.206

0.157*

0.150

0.138

0.131

0.123

0.118

0.117



0.274

0.467***

0.247

0.361***

0.213

0.284***

0.204

0.248*

0.218

0.242



-



1.45

1.53

1.38

1.46

1.28

1.28

1.14

1.08



24-30 months



P



K



N



P



K



0.161

0.130*

0.118

0.111

0.090

0.093



0.204

0.317***

0.178

0.243**

0.150

0.203**

0.140

0.167



1.07

1.08

0.94

1.07*

0.92

0.94



-



-



0.080

0.086



-



0.097

0.091

0.075

0.085

0.070

0.076



Least significant differences a t P < 0.05 for % N = 0.12, % P = 0.023 and % K = 0.037.

Potassium chloride, 3 ounces per tree.

*, **, and ***: differences between treatments of 0 and +K significant a t P < 0.05, 0.01, and 0.001, respectively.



0.142

0.199**

0.113

0.173***

0.111

0.145*



2



$

a



g

B



w

M



a,



TABLE I1

Mean Percentages of Nitrogen, Phosphorus, and Potassium in Trees with Differing Numbers of Whorls in the Current Season’s Growth

Number of whorls

in current year’s

growth



N



P



K



N



P



K



N



P



K



N



P



I(



4

3

2

1



1.32

1.37

1.40

1.38



0.326

0,330

0.312

0.202



1.13

1.20

1.23

1.04



1.35

1.46

1.55

-



0.237

0.228

0.197

-



1.01

1.09

1.10



1.46

1.57



0.193

0.173



1.08

1.00

-



1.55

-



0.166



0.97



-



-



First (top) whorl



Second whorl



Third whorl



-



-



-



Fourth whorl



-



-



-



Pinus radiata



327



FORESTS



about the same for phosphorus. Although the nitrogen and phosphorus

percentages differed little in the two older age groups, the wet needle

weight was significantly higher for the treated trees; however, these

percentages differed more frequently in the younger needles, where the

weights were found not to alter. Annual height increments were greater

for the treated trees. Evidently the increased growth of the treated trees

produced a greater number of similarly sized needles in the youngest

group and, together with larger needles in the older age groups, diluted

the nitrogen and phosphorus in the young needles; even so their levels

were still sufficient.

Further results on differences within trees are given in Table I1 for

6-year-old trees from Mount Burr, South Australia (Raupach, unpublished work). Needles from the terminal 6 inches of laterals were analyzed from trees with one, two, three, and four whorls in the current

season’s growth from spring to autumn. The use of measures of needle

size as covariates failed to reduce sampling variations. Estimates of the

components of variance giving rise to differences between whorls and

between trees and excluding other errors are given in Table 111. For

TABLE I11

Estimates of Components of Variance between Whorls and between Trees

Component of

variance due to



Degrees of

freedom



Percent



Whorls

Trees



6

15



0.0026

0.0044



Percent

P



N

~



Percent

K

~~



0.00183

0.00057



~



0.0022

0.0073



phosphorus, most of the error is between whorls. In any case the errors

are such that it is essential to sample a number of trees and take care to

sample from a uniform whorl for the most reliable data. To these variances would have to be added a further term due to errors from other

causes; an estimate of variance for this further term (with 31 degrees of

freedom) from the data used to obtain Table I1 is percent N, 0.0159;

percent P, 0.00229; percent K, 0.0060.

Additional results for phosphorus are available from older trees

(Raupach, 1967), and these together with partial regressions of growth

increment on foliar nitrogen and phosphorus are given in Table IV.

A further study was made on needles from branches corresponding

to the height of 21 feet in Table I, i.e., the topmost laterals with two

ages of needles. Six trees were sampled at each of the two age groups

over a period from March in one year to February in the next year.

Newly developing spring needles were also collected in December and

February, giving a third age group. The means of the percentage nitro-



TABLE IV

Mean Percentages of Phosphorus from Four Sampling Positions of Older Trees together with Variance Estimates of within and between

Tree Deviations, Regressions of Volume Increment (AV, in Cubic Feet) on Percent Phosphorus and Nitrogen and the Multiple

Correlation Coefficient R for Some of the Positionsa

Phosphorus (percent)

Variance

Sampling

position



Ti

T2



L

Ned



Mean

0.135

0.107

0.075

0.074



Between trees

0.001609

0.001326

0.000335

0.000135



K



Within trees

0.000162

-



Regressionb



+ 0.0942% N - 0.149

AV = 4.480***% P + 0.283*% N - 0.469



R



AV = 1.900***%P



+ O . 8104



A V = 6.188***%P+0.381*%N -0.671



_+0.8397

+ O . 7899



The variances within and between trees have 30 and 25 degrees of freedom, respectively. The sampling positions were: TI, the top

foot and Tz,the second foot of the leading shoot; L, the tip foot from a lateral one-third of the way down the crown; Ned, a general

sample of needles from all over the tree.

*** Significant a t P < 0.001; * Significant at P < 0.05.



%?

C



+d



k-



id



Pinus radiata



329



FORESTS



gen, phosphorus, and potassium varied with time, as shown in Fig. 8;

although studies on a number of forests are necessary to see how widely

these findings hold, it would appear that no time is ideal for sampling

the current season’s growth for phosphorus, the percentage of which

fell rapidly with time until the following year’s growth was well under

way. For potassium and nitrogen, sampling the current season’s needles

in autumn and in autumn or winter, respectively, would seem satisfactory. As it is not usually convenient to collect needles at different times

of the year for several nutrients, individual laboratories use their own

procedures and should work out errors for these.

Needleso-lyeors old



x



Needles I-2years old



Needles 2-3years old



02r

1.8



[



c



c

0



z

a



-



t



v)



a



L



r

0



n

v)



0



r



a



0

A



J



A



O



Months



D



F



A



J



A



O



Months



D



F



A



J



A



O



Monjhs



D



F



FIG.8. Nitrogen, phosphorus, and potassium contents of needles of growth from

the current season and aged one and two years. The needles are from the same location on the trees. A sampling of new season’s needles in December causes the age of

the needles collected previously to fall by one year, but the lines drawn are for the

same lots of needles,



Thus differences within the tree are large if needles of different age

or position in the crown are sampled at different times of the season;

these can be made as constant as practicable and the sampling position

as sensitive as possible to growth measures by careful choice and definition. Work in progress on a number of forests in southern Australia has

used needles from the tip 6 inches of a lateral ( a ) one-third of the way

down the crown and ( b ) from the second whorl from the top of the tree

provided that it has developed in the current season; otherwise the first

whorl is taken. Samples have been taken in March. Of these ( b ) is preferred. Samples from at least six trees are collected from each location

and analyzed either singly or in composites of three to keep a check on

between-tree variations which appear rather similar from forest to forest.



330



M. RAUPACH



The between-tree standard deviation for foliar nitrogen and potassium

is about 15 percent of the critical level; for phosphorus in position ( b )

it is higher.

Critical levels for nitrogen, phosphorus, potassium, and magnesium

have been quoted by Will (1961) on the basis of agreement between

the results of glasshouse work with perlite and water cultures with cases

of known deficiencies in nurseries and forests. These levels are about

0.1 percent for phosphorus, 0.7 to 1.1 percent for potassium, and, if

chlorosis was absent, 1.6 percent for nitrogen and 0.08 to 0.11 percent

for magnesium. More recently Will (1965) has given a critical level of

0.11 percent for phosphorus based on the results from 11 New Zealand

forests. Below this level tree vigor was restricted. WilI adopted the following sampling procedure as standard. Full-length needles were collected from the current season’s growth in December from shoots in the

upper third of the green crown on young trees and a little above the

mid-point of the crown on older trees more than 30 feet high.

Raupach ( 1967) has given percentages of nitrogen and phosphorus

for good, marginal, and poor growth as greater than 1.4 and 0.14, about

1.2 and 0.12, and less than 1.0 and 0.10, respectively; Hall and Raupacli

(1963) have shown marginal and poor growth below 0.35 and 0.25 percent potassium, respectively.

Results of foliar analysis reported by Humphreys ( 1964), Humphreys

and Lambert (1965), and Gentle et al. (1965) have included calcium,

sodium, aluminum, manganese, and iron in addition to the three elements considered above. Needle samples were taken from the current

season’s growth on the second whorl beneath the leading shoot in May

or early June. For vigorous healthy growth, a level of 0.10 percent

phosphorus was sufficient; foliar aluminum contents were in the range

321 to 1412 parts per million (Humphreys and Truman, 1964).

Some results on trace element contents in green needles and in surface

pine litter have been given by Tiller (1957a); other results on nickel,

copper, molybdenum, zinc, boron, and chromium showed considerable

variation between two different sampling positions within the tree

( Raupach, 1967). Concentrations of nickel, copper, and zinc were found

to be higher at the top of the tree, while the reverse held for boron,

chromium, and molybdenum. The nickel and phosphorus contents of the

needles were related. In New Zealand, Will et al. (1963) have established a critical level for boron of 15 ppm. and found values as low as

7 in affected trees.



3. The Use of Nutrient Ratios

As discussed in Tamm’s (1964) review, ratios of foliar nutrient contents may be of interest, especially N:P or N:K, which would be re-



Pinus radiata



331



FORESTS



stricted to definite limits in living material. Limits for N:P have been

reported by Boszormhyi (1958) to be between 5 and 16 for P. sylvestris.

A maximum of 16 has also been given for good growth of pine and birch

forests on peatland in Finland by Puustjarvi (1962) even in cases where

supplies of both these nutrients were adequate. Richards (1961) found

a decline in the yield of P. taeda for ratios of N : P below 10.4, which is

close to van Goor’s (1953) range of 9.2 to 11.5 for the optimal growth

of Japanese larch (Larix leptolepis) .

Observations from a large number of forests of P. radiutu in southern

Australia, mentioned under Section V, A, 2, and results from glasshouse

trials give a N:P range of 5 to 16. It is reasonable to think of certain

levels of nitrogen and phosphorus below which growth does not occur,

other nutrients being in good supply. These are shown by the broken

lines in Fig. 9. If the above ratios are used, the lines AB and CD in

A



I



0



0.1



0.2



Phosphorus ( percent)



FIG. 9. A representation of nitrogen and phosphorus contents of needles. The

lines AB and C D are drawn for nitrogen to phosphorus ratios of 16 and 5,

respectively.



Fig. 9 would distinguish the region of growth and no growth. For the

sampling procedure ( b ) described in Section V, A, 2 (i.e., the same as

for the second whorl of Table 11) a sloping line or curve BC is also

indicated and, while the line CD is well supported, it is less easy to see

how far BA extends because few of the trees have very high nitrogen

and low phosphorus contents.

B. POT EXPERIMENTS

This valuable means of investigation allows a more effective control

of many of the variables associated with tree growth under forest conditions at the cost of limitations in the extrapolation of the results back

into the field. Used as a “stepping stone” between the laboratory study



332



M. RAUPACH



and the field or in order to answer a specific idea capable of exact definition and control, the technique needs no justification. Experience with

P . radiata has shown that where soils (most often topsoils) are used and

the trees are grown in pots holding 10 kg. or more of soil for periods of

at least two years, the results in terms of foliar nutrient levels and

fertilizer responses are surprisingly close to those found under forest

conditions.



1. Deficiencies and Toxicities in P . radiata

Boron deficiency and toxicity have been demonstrated and described

in water cultures by Ludbrook (1940); zinc, manganese, copper, and

boron deficiency symptoms have been given by Smith and Bayliss

( 1942) and Smith (1943) using the same technique. Purnell (1958) has

presented photographs of calcium, magnesium, phosphorus, potassium,

and nitrogen deficiencies in sand cultures.

The results of Humphreys and Truman (1964) in water culture

showed that increasing amounts of phosphorus were necessary to sustain

the same rate of growth when the trivalent aluminum concentration was

increased; they pointed out that this could be of interest on some lowphosphate soils. Just this situation had been considered earlier for P .

radiata by Kanwar (1959), who offered the same explanation for his

pot results but did not produce any proof.

The composition of nutrient solutions in sand and water cultures has

been examined by Will (1961) with the aim of comparing the composition of the solution for the most satisfactory seedlings with solutions

from soils with vigorous trees. The following quantities (in parts per

million) were obtained in the cultures: nitrogen, 100; phosphorus, 1;

potassium, 10; magnesium, 10. They were of the same order as those in

soil solutions from two sites. These nutrient levels are lower than many

others which have been suggested for pot studies including those of

Travers (1965). Will is correct in stressing the necessity of keeping the

concentration and balance of nutrient solutions as close as possible to

what is found in the soil. The foliage from many of his seedlings, the

oldest of which was eight months, contained N :P ratios outside the portion ABCD of Fig. 9 on occasions when visual symptoms of imbalance

were present, but all were inside this portion of the figure when the

symptoms were absent.



2. Successive Crops

Wollum and Youngberg (1964) examined changes in nitrogen status

on the incorporation of various litter materials and with three different

precrop treatments on pumice and granitic soils of low nitrogen content.



Pinus radiata



FORESTS



333



Whereas Douglas fir (Pseudotsuga menziesii Mirb. ) depressed the

growth of P . radiata, alder (Alnus rubra Bong.) and snow-brush

(Ceanothus velutinus Dougl. ) improved growth and gave higher nitrogen contents.

In relation to studies on nursery exhaustion, Hatch (1961) reported

levels of nitrogen, phosphorus, potassium, calcium, and magnesium in

the needles, roots, and stems of one-year-old seedlings over four

consecutive seasons.



C. FIELDEXPERIMENTS

Brockwell and Ludbrook (1962) in an investigation over 16 years on

the effect of phosphate on soils of low fertility near Moss Vale, New

South Wales, showed that the best responses initially observed on young

trees were maintained as increased growth rates throughout the experiment. No difference was found between the results with rock phosphate

and superphosphate. The work was at the following forests: ( 1 ) Penrose,

( 2 ) Wingello and ( 3 ) Belanglo, the surface soils of which had 70, 1501,

and 100 ppm., respectively, of acid-soluble phosphorus in the depth

0 to 4 inches. They defined the optimum level of soil phosphorus as that

beyond which no additional response could be obtained with fertilizer,

reckoning that each hundredweight over 0 to 4 inches raised the soil

phosphorus by 13.6 parts per million for rock phosphate and 8.1 for

superphosphate. The optimum level was 45 to 55 ppm. for P . taeda and

P . etliottii and 130 to 175 for P . radiata. Humphreys (1964) showed that

the height of 8-year-old trees on three different soil types at Wingello

gave differential responses to superphosphate and limestone (see Table

V ) . One podzolic soil (Nowra grit) reacted to calcium alone, the red

earth to phosphorus alone, and the other podzolic soil (Hawkesbury

sandstone) to both nutrients. Humphreys explained the effect by the

limitation of root development because of low calcium levels and the

inhibition of phosphorus uptake by the accumulation of aluminum at the

root surface. Since calcium is not recycled efficiently, a deficiency in trees

on the podzolic soils would become worse with time. Humphreys found

that in many cases limestone and superphosphate both had to be added;

separate correlations of foliar calcium and phosphorus with height index

at age 20 years were significant.

A further evaluation of Brockwell and Ludbrook's work at Penrose

by Gentle et al. (1965) showed that the added phosphate had not been

removed by leaching from the yellowish brown sandy A horizon (depth

0 to 11 inches) into the B horizon over a period of 14 years. The rock

phosphate was still present in the calcium phosphate fraction, but the

superphosphate was now present mostly as aluminum phosphate with



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