Retention of nutrients by peats and wood wastes

Scientia Horticulturae, 12 (1980) 203--209

203

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

RETENTION OF NUTRIENTS BY PEATS AND WOOD WASTES

M. PRASAD Horticultural Research Centre, Research Division, Ministry of Agriculture and Fisheries, Levin (New Zealand) (Accepted for publication 22 August 1979)

ABSTRACT Prasad, M., 1980. Retention of nutrients by peats and wood wastes. Scientia Hortic., 12: 203--209. The retention and release of major nutrients by New Zealand peats and wood wastes was studied over 24 weeks in an incubation experiment. Irish sphagnum peat was included for comparison. The treatments consisted of fertilized and unfertilized materials. The samples were extracted with water using a 1 : 1.5 (v/v) ratio. Retention of N was low for all peats, but noticeably high for bark and wood shavings after 3 weeks. At 24 weeks, t h e peats retained less than 20%, while the wood wastes retained 35--68% of the applied N. There was little or no release of N by any material. Retention of P was also low for N.Z. peats (except Cambridge), although not as low as for Irish peat, but again high for bark and wood slavings. Retention of K was higher for peats than for wood wastes. Wood wastes contain more water-soluble K than peat.

INTRODUCTION There are numerous materials being used in soil-lessmixes by nurserymen world-wide (Bunt, 1975). Although the main ingredient in soil-lessmixes is usually peat, there is n o w increased interestin substitutingw o o d wastes for peat both in N e w Zealand and elsewhere (e.g.Cotter, 1974; Brown and Pokorny, 1975; Maas and Adamson, 1975; Verdonck et al.,1976; Still,1977; K.H. Marcussen, 1978, personal communication). Information on retention of nutrients by these materials is scarce. Irish sphagnum peat is very susceptible to leaching of P and, to a lesserextent, of K and N, but other peats are less susceptible to P-leaching, e.g. fen peats (Prasad and Woods, 1971). Fine bark has a tendency to retain more K than sand (Brown and Pokorny, 1977). Microbial growth fixes a great deal of N when w o o d wastes are mixed with soil (Allison, 1973) and cause N deficiency in crops (Stillet al.,1972; Cappaert et al.,1974, Glover and Pokorny, 1974). However, information on fixation of N by wood wastes used in soil-lessmedia is meagre. Information on retention of nutrients by compost ingredients is needed, not only to determine f e r t i l i z e r f o r m u l a t i o n f o r soil-less m i x e s , b u t also f o r p l a n n i n g l i q u i d - f e e d p r o g r a m m e s f o r p l a n t s g r o w i n g in t h e s e m a t e r i a l s . C o n s e q u e n t l y , i n c u b a t i o n e x p e r i m e n t s w e r e c o n d u c t e d t o d e t e r m i n e t h e d e g r e e o f N-, P- a n d K - r e t e n t i o n

204 by New Zealand peats from 3 localities and by wood wastes, such as bark, sawdust and wood shavings. Irish sphagnum peat was included for comparative purposes. MATERIALS AND METHODS

Seven materials which could be used as basic or secondary constituents of soil-less compost were incubated with and without added nutrients for subsequent water extraction and estimation of the amounts of nutrients retained or released. The method does not differentiate between biological, chemical or physical fixation or release of nutrients, pH,nutrient composition and particle size are given in Table I. Forty ml of the materials were moistened to a moisture content equivalent to pF 1.5 and incubated at 20°C in 100-ml beakers. The beakers were covered with perforated polythene to allow for aeration. Reagent grade NH4NO3, KH2PO4 and K2SO4 were added in solution form to give a rate of 14.6 mg N, 2.0 mg P and 12.2 ng K per beaker. An untreated set of media control was also made up. There were 2 replicates per sampling-date for each treatment. Distilled water was added fortnightly to restore the moisture levels. Samples were taken at ca. 4 h after N, P and K additions and again after 3, 6, 12 and 24 weeks. At each sampling~late the samples were extracted in a conical flask with 60 ml of H20 on a shaker (180 shakes/rain for 0.25 h (Sonneveld et al., 1974), and total N (Bremner, 1965), P and K were determined.

TABLE I pH, nutrient composition and particle size (see notes) of the peats and wood wastes Materials

Irish peat Hauraki peat

Wyndham peat Cambridge peat Bark I Sawdust = (3 months) Sawdust = (12 months) Wood shavingss

pH ( I : 2 H,O)

Total (%)

Total (ragI-I)

N

P

K

Ca

Mg

Fe

Zn

Mn

Cu

3.84 3.87 3.86 3.81 4.75

1.29 1.22 1.10 1.42 0.17

0.029 0.039 0.053 0.027 0.023

0.015 0.025 0.115 0.016 0.102

0.200 0.138 0.269 0.076 0.250

0.171 0.182 0.212 0 079 0.021

462 1190 3720 986 812

7.5 7~0 11.5 6.0 15.5

18 35 55 14 64

4.9 4.4 4.6 6.8 7.7

5.28

0.07

0.018

0.051

0.065

0.024

137

7.7

41

4.4

4.83 5.15

0.17 0.05

0.024 0.035

0.082 n.L 4

0.095 n~L

0.032 n~L

312 n.zL

17.0 ~a.

60 n.L

5.7 n.a.

140% < 1 ram, 40% 1--6.4 ram, 20% > 6.4 mm. 2 18% < 1 mm, 74% 1--3 ram. s consisted of divers mostly 3--8 m m long all passing 3 ~ sieve. 4 n.a. ffi not available.

2O5 RESULTS AND DISCUSSION

Nitrogen.

There was little difference in the recovery of N when sampled 4 h after application (Fig. 1). After 3 weeks, and on subsequent~sampling dates, however, the increased retention of N by bark, 3-month old sawdust and w o o d shavings was very evident. This trend continued through 6, 12 and 24 weeks. After 24 weeks, only about 32% of the added N was extracted from w o o d shavings, 44% from bark, and 58 and 65% from the 3- and 12-monthold sawdust, respectively. In contrast, over 80% of the added N was recovered from peats. There was little release of N from unfertilized materials except by the more decomposed Cambridge peat with a higher N content, and the Irish peat, but even with these materials the amount released was small in relation to the amount applied in the fertilized treatment (less than 10%, see Table II). These results indicate that N deficiency can occur if plants are grown in u n c o m p o s t e d w o o d y materials having a base dressing and liquid feed programme suitable for peat composts. Given results from other experiments, showing that H20-extractable N from a range of composts was related to -

-

Total applied 243 mg.l-'(in 1:1.5 HIO extraCt) PEATS ... ............................................................ A Wp

_~,,. "

2O(

"1"

2401

~"

200.

C --

160"

Z "

&

~

WOOOWASTES

i~

ID

\,.. .......

......a

~ .~ ~ - ~ .

.........

o

S(12)

120.

80"

3

6

12

24

Time, w e e k s

Fig. 1. Retention of N by peats and wood wastes. Ip, Irish peat; Hp, Hauraki peat;Wp Wyndham peat; Cp, Cambridge peat; B, Bark; S(s), Sawdust (3 months); S(,2) , Sawdust (12 months); Ws, Wood shavings. LSD (95%) to compare one material between samplingdates: Ip, 33; Hp, 24; Wp, 26; Cp, 21; B, 14; S(3), 34; S(12), 11; Ws, 33.

206 plant uptake of N (Prasad, 1979), we can assume that N which is not extracted by H20 would not be available for plants, at least in the short term. The extraction method used here is similar to that used widely in The Netherlands, where it has been shown to reflect the availability of nutrients in composts (Sonneveld et al., 1974}. Higher rates of N in the base dressing, particularly in a form of slow release N or in the liquid feed, would probably offset N deficiency, and preliminary studies at this Centre using ornamental crops in wood wastes confirm this suggestion. The other possibility is to reduce the Nretention by the addition of N and then compost the material to lower the C/N ratio (Cappaert et al., 1974}. Aged sawdust generally retained less N than fresh sawdust, which agrees with the findings of other workers (Still et al., 1972). Wood shavings retained more N than sawdust, possibly due to the higher content of younger woody material which retains N more strongly.

Phosphorus.

The retention of P was lowest in Irish peat (Fig. 2). There was some retention of P by both Hauraki and Wyndham peats, while Cambridge peat retained a considerable amount of P. In these peats, most of the P-retention occurred in the first 3 weeks. The retention of P by bark and wood shavings was considerable and most of it occurred in the first 6 weeks. Retention of P by both types of sawdust was intermediate between peats (with the exception of Cambridge peat), and bark and wood shavings. There was little or no release of P from these unfertilized materials and the amounts extracted at 24 weeks were so low that it would not contribute to P nutrition (see Table II). -

-

Total applied 33 mg.r~(in 1:1,5 H=O extract)

~J

PEATS : e ~-~. . . . . -o-- . . . . . . . . ~ ................ ........... ~ ........................ ~ . . . . . . . . . . . . . . . . . . .

30

o 4~ X

2o

• ,y.,p --OHp ~Wp

\ \\

10

~ . . . . . . . ~. . . . . . . . . . . . . . .

~ ................

vCp

-r C

i

30~\ 20]

0

WOODWASTES "~,~ i° . . . . . . . . . . . . . . . . . . . . . . . . .

3

(~

:~:~--~

12"

S~

24

Time, weeks Fig. 2. Retention of P by peats and wood wastes. Symbols as in Fig. 1. LSD (5%) to compare one material between sampllng-dates. Ip, 2.4; Hp, 2.7; Wp, 3.6; Cp, 4.7; S(3 ), 3.0; S(12), 2.5; We, 3.3.

207

The higher retention of P by Hauraki, Cambridge and Wyndham peats and bark was correlated with total Fe, and it is possible that as Fe was released some was active in fixing P. However, an appreciable amount of P-retention in the woody materials would be due to exchange sites on the internal surfaces of particles (Brown and Pokorny, 1977). The retention of P was not entirely undesirable, as leaching would be reduced where water-soluble P was being used in the base dressing. However, the retention of P would also suggest that plant availability of P was reduced. In other experiments carried out at Levin, slightly lower P levels have been recorded in a number of plant species (begonia, kalanchoe, gloxinia and ficus) grown in bark in comparison to those grown in peat, even though the P application rate (as Osmocote + Superphosphate) was 15--20% higher. This would indicate that at least part of the P retained in bark is not available for plant growth. - - Water-extractable K was generally higher in woody materials than peats both from fertflised and unfertilised treatments (Table II and Fig. 3). For all materials there was a trend towards higher retention of K over time. After 6 weeks, significantly lower levels of K were extracted than at the start for all materials except wood shavings. In practice, it seems that base dressing could be lower in woody materials than peat, due to higher levels of native K and lower retention. At the same

Potassium.

Total applied 204 mg.I °' (in 1:1"5H20 extract)

160 ¸

PEATS

q i

120 ~ ~ . ~ _ ~

E

_ ~ ....

~

..............

~<~Hp

80.

~

Cp

-r LO

24O: ~~ \

WOODWASTES

200~ ~

~

.- ..........

~ _

"T

..........

CO

E

~i~ .y_~:_+.ew , " "o S(t2)

~

~-A 8

12(>

3

6

12 Time,weeks

24

Fig. 3. Retention of K b y peat and wood wastes. Symbols as in Fig. 1. LSD (5%) to compare one material between sampling-dates. Ip, 11 ; Hp, 11; Wp, 10; Cp, 12; B, 21 ; S(3), 32; S(z2) , 25 ; Ws, 22.

208

TABLE II N, P and K (mg 1-1) in the 1 : 1.5 water extract at the start (0) and at 24 weeks (24) from unfertilised materials Materials

Irish peat Hauraki peat Wyndham peat Cambridge peat Bark Sawdust (3 months) Sawdust (12 months) Wood shavings

N

K

P

0

24

0

24

0

24

10.0 1.2 11.5 3.5 1.1 1.0 1.5 1.0

14.4 2.4 5.9 15.7 0.8 0.8 1.6 1.6

0.3 0.3 0.2 0.1 0.2 0.1 0.1 0.5

1.5 0.2 0.4 0.1 0.4 0.3 0.3 0.9

5.1 5.1 14.4 3.8 15.0 13.2 21.9 12.5

2.2 1.6 15.3 0.9 8.0 10.0 21.8 9.2

time, excessive watering could cause K to be leached easily from the woody materials.

ACKNOWLEDGEMENTS

Appreciation is expressed to Mr. T.M. Spiers and Miss P.M. Jongeneel for carrying out the chemical analyses. REFERENCES Allison, F.E., 1973. Soil Organic Matter and its Role in Crop Production. Elsevier, Amster dam, p. 114. Bremner, J.M., 1965. Inorganic forms of nitrogen. In: C.A. Black, D.D. Evans, J.L. White, L.E. Ensminger and F.G. Clark (Editors), Methods of Soil Analysis, Am. Soc. Agron. Madison, WI, p. 1199. Brown, E.F. and Pokorny, F.A., 1975. Physical and chemical p.roperties of media composed of milled pine bark and sand. J. Am. Soc. Hortic. Sci., 100: 119--121. Brown, E.F. and Pokorny, F.A., 1977. Potassium distribution and retention in pine bark and sand media. HortScience, 12: 343--344. Bunt, A.C., 1975. Modern Potting Compost. Allen and Unwin, 19--40. Cappaert, I., Verdonck, O. and De Boodt, M., 1974. Bark waste as a growing medium for plants. Acta Hortic., 37: 2013--2022. Cotter, D.J., 1974. Yield of successive cropping of t o m a t o in sawdust and bark media. HortScience, 9: 387--388. Glover, G. and Pokorny, F.A., 1974. Early plant growth delay in container media containing bark and sand. Proc. Sci. Nutr. Assoc. Res. Conf., 19: 13--14. Maas, E.F. and Adamson, R.M., 1975. Peat, bark and sawdust mixtures from nursery substrates. Acta Hortic., 50: 147--151. Prasad, M., 1979. Analytical m e t h o d s for soilless composts. In: Development and Use of Soilless Media for Horticulture. Seminar, Hortic. Res. Centre, Levin, 1979: 9.1---9.18.

209 Prasad, M. and Woods, M.J., 1971. Leaching and nutrient uptake of tomatoes in peats. J. Sci. F o o d Agric., 22: 564--568. Sonneveld, C.J., van den Ende, J. and van Dijk, P.A., 1974. Analysis of growing media by means of a 1:1½ volume extract. Commun. Soil Sci. Plant Anal., 5: 183--202. Still, S,M., 1977. Comparison of chrysanthemum growth in pine bark or commercial soilless mixes. HortScience, 12: 573--574. Still, S.M., Gartner, J.B. and Hughes, T., 1972. Effect of sawdust age and N application on chrysanthemums grown on white oak sawdust media. For. Prod. J., 22: 111--114. Verdonck, O., Cappaert, I. and De Boodt, M., 1976. A comparative study between peat, pine leaf-mould and bark compost as a substrate for p o t plants. Acta Hortic., 64: 245--248.