Barley straw decomposition and S immobilization

SoilBiel.Biochem.Vol. 29, No. 2, pp. 109-114,1997 0 1997ElsevierScienceLtd. All rights reserved Printed in Great Britain PII: !%038-0717(97)00001-1 0038-0717/97517.00+ 0.00

BARLEY STRAW DECOMPOSITION IMMOBILIZATION

AND S

S. J. CHAPMAN h4acaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, U.K. (Accepted 24 October 1996) Summary-Sulphur deficiencies have become increasingly recognized in both soils and crops. The return of plant residues low in S to low S soils may lead to decomposition processes being limited by S availability. In ;a laboratory incubation, barley straw that was low in S was added to four low S soils, with or without added sulphate-S. Straw samples with varying concentrations of S were also added to one of the soils. Decomposition was monitored as CO2 production, and S immobilization was measured by the change in phosphate-extractable-S. Decomposition was limited by S in al1 four soils, but this was dependent on the straw S content. With sufficient S, approximately 40% of the straw C was respired over 25 da:ys at 25”C, but this was up to 30% less where S was limiting. Mineralization occurred at a straw S content of 0.15% irrespective of any S addition. At 0.11% S, there was a balance where decomposition was not retarded in the absente of added S, but immobilization occurred if S was added. However, at 0.07 and 0.04% S, there was increased immobilization, and decomposition was retarded if S was not added. The critical S content for immobilization was estimated to be 0.13% or a C-to-S ratio in the residue of 340. For potential limitation of residue decomposition, the S content would have to be slightly less than this with a C-to-S ratio in the range 400-650 (0.1 l-O.O7% S). In S-deficient areas and depending upon the soil, the incorporation of plant residues low in S may lead to reduced plant growth

and retarded residue decomposition. 0 1997 Elsevier Science Ltd

INTRODUCTION

The incidences of sulphur deficiency in soils and crops have become increasingly recognized both in the U.K. and elsewhere (Syers et al., 1987; Schnug, 1991; McCrath and Zhao, 1995) and are likely to increase as a result of decreased atmospheric inputs. It is important to consider how S deficiency may affect organic matter decomposition, soil microbial activity and nutrient turnover, as wel1 as assessing the implications for plant production. A cycle of events may be envisaged where a soil low in S leads to the growth of S-deficient plants, the subsequent return to the soil of residues low in S, S immobilization during residue decomposition and hence further reductions in soil S. This effect is most commonly seen in nitrogen deficiency following the addition of straw Ito soil (Allison, 1973) but may potentially occur for S also. This possibility is increased, given the increased tendency for residues such as straw to be incorporated into soil as an alternative to burning (Lynch et al., 1980). Decreased organic: matter turnover as a result of S limitation has been suggested by Rasmussen and Rohde (1988) who, in a long-term experiment, found that plots rsceiving N as NHdNOs had more soil C than plots receiving N as (NH&SO+ Conrad (1950) reported how milo plant yield in a pot experiment was reduced by S deficiency caused by the addition of torn starch. Stewart and

Whitfield (1965) also in a pot experiment, found that the yield of winter wheat was reduced following the addition of straw residues. This was despite the fact that the straw contained 0.12% S. Stewart et al. (1966a) later showed that, for their soil, the straw S content had to be over 0.15% for maximum straw decomposition and to avoid depressed plant growth. In a field experiment, White (1984) found a positive correlation between incorporated stubble S content and subsequent barley growth up to a stubble S content of 0.15%. In a previous set of experiments (Chapman, 1997), 1 investigated the effect of S limitation on the decomposition of glucose, starch and cellulose using several S-deficient soils. Here, 1 report on the decomposition of barley straw in four of these soils and on the effect of different straw S contents on C mineralization and S immobilization in one soil.

MATERIALSAND METHODS Straw decomposition

Straw decomposition was measured by soil respiration following the addition of straw to soil, using methods similar to those described in Chapman (1997). Briefly, two sets of 20 g (fresh wt) of soil were thoroughly mixed with 375 mg of hammermilled barley straw in 120-ml soil jars. A sulphurfree nutrient solution (1.2 ml, -S), containing

110

S. J. Chapman Table 1. Properties

Soil

1. 2. 3. 4.

Texture

Bailiesland Conveth Mains Unthank Fordoun Mains

“Water-holding

Initial moisture content (%)

Loamy sand Sandy-silt loam Sandy loam Sandy-silt loam

of the soils used WHC’ (g g-’ soil)

1.3 ll.6 12.1 17.8

pH (CKIZ)

0.434 0.515 0.451 0.614

Total C (%)

5.4 6.4 4.8 5.5

1.3 1.7 2.3 3.3

capacity.

ICN03, KHPPO~ and trace elements, was added to one set, such that the soils were amended with (g-’ fresh wt) 150 pg N, 15 pg P and 437 pg K. The second set of soils were given the same nutrient solution, als0 containing K2S04 (1.2 ml, + S) to give S at 15 pg g-’ fresh wt soil. Distilled water was added to bring the moisture content up to 55% of the water-holding capacity (Table 1). Each treatment was set up in triplicate. The soil jars were placed in sealed 800-ml Kilner jars and incubated at 25°C for 3 weeks. Headspace CO2 was measured by gas chromatography. In the first experiment, barley straw having 0.079% S was added to four low S soils: Bailiesland, Conveth Mains, Unthank and Fordoun Mains (soils 1-4; see Chapman (1997) for further details). In the second experiment, four samples of barley straw having a range of S contents (see Table 3) were added to Bailiesland soil. At the end of the incubation period in the second experiment, phosphate-extractable-S in the soil was determined by X-ray fluorescente spectroscopy (Chapman, 1987). Total straw S and straw S04-S were determined as described by Scott et al. (1984).

Data treatment

The respiration curves were fitted to a number of standard functions as described by Chapman (1997). The functions used were an exponential model (exp), a combined linear and exponential model (lexp) and a double exponential model (dexp). These models were fitted to the data for each of the replicate jars so as to give replicate parameter values which then could be used to calculate the maximum slope and final value (Table 2). These derived data were analysed using ANOVA, and differences between the treatments were compared using the protected LSD (least significant differente) test. The curve-fitting and ANOVA were performed using GENSTAT (Rel. 2.2, Rothamsted Experimental Station).

RESULTS

Carbon mineralization from the straw added to the four soils, measured as soil respiration, followed an exponential curve, except that for soil 3 there was a strong linear component, and for soil 4 a

Table 2. Models used to fit the C mineralization

data

Model

Equation

Maximum

slope

Final value

Exponential (exp) Linear-exponential (lexp) Double exponential (dexp)

I’ = A + BR‘ I’ = A + BR” + Cx y = A + BR’ + CS‘

BLo&R BLo&R + C BROLog,R + C@Lo&S, $o;($G(-(Lo&siLoaR)

A A* A

yhere C/B)/

A. B, C, R and S are parameter values. *Ignoring the linear part of the function.

Table 3. Derived values of the maximum slape (respiration rate) and predicted final value (total carbon respired as a percentage of carbon added) from the curves tîtted to the soil respiration data following the addition of barley straw containing different contents of S to four S-deficient soils, with or without additional sulphur Soil

Soil SOa - S (pg PK’)

1 2 3 4 SE”

1 1

1 1 SE

?? ,***Significantly

3.1 2.2 4.7 3.1 0.24 3.1 3.1 3.1 3.1

Total straw s (%)

Model

Ma$num slape (-“SC g dry wt daI$)

0.079 0.079 0.079 0.079

exP exp lexp dexp

307 465 430 360

0.041 0.068 0.111 0.148 0.0021

lexp dexp dexp dexp

1110 168 202 205

_y

285 447 486 359

3700 2700 2320 3630

1042’ 232* 205 207

1720 2960 4750 5020

25.5

different from -S at P < 0.05 and P < 0.001, respectively. “Pooled standard error.

23.0

Final palue C g- dry wt) +s 3540 4170”’ 3610*** 4410* 268 1950 4220* 4220 5170 517

Straw decomposition and S immobilization

111

soil 1 3600

3600

2400

2400

0

1

5

10

15

20

0

25

soil 3

6

10

15

20

25

5

10

15

20

25

sol1 4

3600

2400

.a 8 a

1200 W

0

5

10

15

20

00

25

Time Fig. 1. Respiration in four S-deficient soils (l-4), measured as CO+I, following the addition of barley straw, with (m) or without (0) additional sulphur, added as K$Od.

double exponential gave a better fit (Fig. 1, Table 3). The maximum slope (respiration rate) occurred early on in the incubation, and there was no effect of added S on this in any of the sok The effects of added S were only apparent from day 7 onwards in soils 2-4 resulting in significant differences in the final values for th.e percentage of straw C respired. Even with added S, the final value was, at most, 45%, presumably because, over the time course of the incubation, lignin and lignin-protected cellulose would not have been appreciably decomposed (Cheshire et al., 1979). The response of the four soils to S addition did not relate to the phosphateextractable S valnes (mainly sulphate, though with a minor fraction of organic S), except that soil 2, with the lowest extractable S, gave the most response. It is not clear as to why soil 1 did not show any response to S addition, in contrast to soils 2-4, when the same sol11had shown a good response following the addition of starch (Chapman, 1997). Where barley straw with different S contents was added to soil 1, significant increases in C mineralization as a result asf S addition were seen at the two lowest straw S contents (Fig. 2, Table 3). The pattern of respiration for the straw having 0.041% S was rather different from the other straws, with the maximum respiration rate being five times that of the other straws. This was probably a result of the

severe S deficiency delaying the maturity of the straw (Platou and Irish, 1982), such that more easily-decomposed fractions remained in the straw. Though the addition of S neither increased the maximum slope nor the final value (the slope was, in fact, slightly decreased, Table 3), there was a significant (t-test, P < 0.005)increase in the linear component of the lexp model fitted (parameter C, Table 2) from 47.6 (SE 0.9) to 82.9 (SE 1.4) pg C g-’ dry wt soil d-‘. For the straw with 0.068% S, there was a significant increase in both the maximum rate of respiration and in the final value. There was no effect of added S with the 0.111 and 0.148% S straws in agreement with the earlier result for soil 1 with the 0.079% S straw. The amounts of sulphate-S remaining in soil 1 after incubation with the straw confirmed the S limiting conditions for the samples with 0.041 and 0.068% S with no S addition. Here, the final soil extractable S remained very low, at less than 4 pg g-’ dry weight soil (Table 4). A smal1 part of this S may have been organic since the actual analysis was of total S in a phosphate extract, but if the remainder was mainly sulphate, it was presumably unavailable to the microbial biomass (see also Hunt et al., 1986). The amounts of soil SOd-S immobilized, particularly where there was added sulphate, decreased with increasing straw S. There was appar-

112

S. J. Chapman

0.066% s = .I

3600

3600 -

2400

2400 -

1200

1200 -

8 E .o, g

0-I 0

3600

1

5

10

15

20

0

25

0.111% s

5

10

15

20

25

_ 0.146% S 3600 -

2400

2400 -

1200 -

0

0: 0

5

10

15

20

25

I

I

I

I

I

5

10

15

20

25

Time Fig. 2. Respiration in one S-deficient soil (soil l), measured as C02-C, following the addition of barley straw samples containing increasing amounts of total S, with (m) or without (0) additional sulphur, added as K2S04. ent mineralization at al1 but the lowest leve1 of straw S with no added sulphate, although it was only significant (i.e. greater than zero) at the highest content of straw S. Mineralization also occurred from the latter straw with added sulphate. However, this mineralization does not take account of the S04-S present in the straw, and if this is included, then there was immobilization in both the presence and absente of sulphate addition. The apparent mineralization of soil S actually comes from the remainder of the straw SO4-S that has not been immobilized to organic S. Table 4 also shows the final straw C-to-S ratio, which includes both

straw decomposition products and the microbial biomass associated with the decomposing straw. This ratio was calculated from the amount of straw C remaining in the soil (i.e. not released as CO*) and the final amount of S in the straw (i.e. organic S originally in the straw plus that immobilized). Where there was adequate S for decomposition, either present in the straw initially or added subsequently, the final C-to-S ratio was reduced to below 210-250, but where S was stil1 limiting, the C-to-S ratio was at or above 480. The straw with 0.111% S and no added S gave a final C-to-S ratio of 270 and was probably close to the limiting case.

Table 4. Sulphate-S balance and change in straw C-to-S ratio during the decomposition of barley straw having different amounts of S in a low S soil, with or without added S Total straw S(%)

0.041 0.068 0.111 0.148 SE

Straw soqs

1.5 3.1 8.6 15.2 0.44

Final soil so,-s (pg g-’ dry weight soil) -S

+s

2.1 3.6 4.3 6.9

6.8 9.1 15.7 23.4 0.42

Immobilized soil so,-S”

Initial straw Cto-Sb ratio

+s

-S

0.4 -0.4 -1.2 -3.8

12.2 9.4 3.4 -4.4

1070 650 400 300

0.48

“Calculated as the differente between final soil S04-S and initial soil SOd-S (-S: 3.1 pg g-‘; + S: 19.1 pg g-‘). ?aking straw C as 44%. ‘Sec text for method of calculation.

Final straw C-to-SC ratio -S

+s

690 480 270 210

250 230 220 220

Straw decomposition DISCUSSION

Although Stotzky and Norman (1961) suggested that the S content of most plant materials was sufficient to prevent S: limitation during decomposition, the above results confirm those of Stewart et al. (1966a) in showing that the decomposition of straw can be limited by S. Maftoun and Banihashemi (1981) similarly fcund that the addition of sulphateS stimulated the decomposition of wheat straw but not of alfalfa. Thsrse results are also to be expected from the S requirements for cellulose decomposition where the critical C-to-S ratio, the ratio above which C mineralization would be limited by S, is in the range 300-490 (Stewart et al., 1966b; Chapman, 1997). The critical C-to-S ratio for plant residues, as opposed to pure carbon compounds, is usually defined slightly differently as the C-to-S ratio below which no immobilization would occur during decomposition in soil. This is usually considered to be in the short- to medium term since, ultimately, al1 the S in plant residues would be mineralized, given sufficient time. The residue C-to-S ratio above which decomposition is potentially limited by S may not necessarily be identical with that above which immobilization occurs. The microbial population decomposing certain residues may have sufficient S not to be limited in degradative ability and not immobilize it :From the soil and yet wil1 immobilize it from the soil if excess S is provided. This is illustrated by the 0.111% S straw which did not show any response to S during decomposition (Fig. 2) and which, in the absente of added S, did not immobilize any soil S, but showed immobilization when excs:ss S was added (Table 4). Immobilization therefore may depend not only on the residue C-to-S ratio but also on the supply of sulphate-S. The critical C-ILO-S ratio for immobilization by barley straw lies somewhere in the range of 300400, which is in broad agreement with a number of studies using other plant residues. These have been extracted from the literature and are summarized in Table 5. These generally show, at the lower end of the range, the highest value examined at which mineralization occurred and, at the upper end of the range, the lowest value examined at which immobilization occurred. Interpolating the values in Table 4, with S added, to the point of zero immobilization returns a C-to-S ratio value of 340, or 0.13% S. Interpolating the data of Stewart et al. (1966a) also gives 0.13% S. A. value around 340 would agree with most of the rl:sults in Table 5. The exception is that of Wu et al. (1993) who found immobilization by barley straw with a C-to-S ratio of 206. Lefroy et al. (1994), using 35S-labelled rite straw, indicated a critical S leve1 for mineralization of less than 0.086% S (or a C-,to-S ratio of 512, taking straw C as 44%). However, although this indicates mineralization of straw 35;S,it does not show net mineraliz-

and

S immobilization

113

Table 5. Studies giving a critical C-lo-S ratio (x) above which S immobilization may be expected during the decomposition of plant materials in soil Plant residue

Critical

C-to-S ratio

Range of plant materials Wheat straw

200 < .Y < 420

Wheat straw Cotton and torn residues Sorghum residues Wheat straw

270 < x < 370 148 < .Y < 406

Refuse compost and wheat straw-corn straw mixture Rape and barley straw Barley straw

100 < x < 404

‘1 < 350

s < 1000 .r < 899

Reference (Barrow,

1960)

(Stewart and Whitfield, 1965) (Stewart er rrl., 1966a) (Nelson. 1973) (White, 1984) (Castellano and Dick, 1988) (Gallardolara er al., 1990)

64 < I < 206

(Wu et 01.. 1993)

300 < x < 400

This study

ation since an equal or greater amount of 32S may have been simultaneously immobilized. The critical C-to-S ratio for the limitation of straw C mineralization is probably greater than 340 and within the range 400-650 (0.11 l-0.068% S, Table 4), in agreement with the value of 490 estimated for cellulose (Chapman, 1997). Straw with a C-to-S ratio of 550 (0.079% S) was limited by S during decomposition in three soils but not in a fourth. Whether decomposition wil1 be limited by S content in the field wil1 depend upon the soil and, in particular, on the amount of sulphate-S available for immobilization. For example, the incorporation of 8 t ha-’ straw having 0.06% S to plough depth in a soil able to supply 2 pg S g-’ soil would result in complete immobilization of the available S and severe limitations on plant growth. Incorporation of 12 t ha-’ would lead to straw decomposition being limited by S. Poor incorporation or surface straw applications would be even more likely to show retarded decomposition. The effects of straw incorporation on the yield of cereals as a result of S deficiency have been noted in both pot (Stewart and Whitfield, 1965) and field (White, 1984) experiments, and with the increasing incidences of S deficiency, these effects may become increasingly observed. Acknowledgements-The author is grateful to the late Cordon Sharp who supplied the straw samples for the second experiment. This-werk was supported with funding from the Scottish Office Agriculture, Environment and Fisheries Department.

REFERENCES F. E. (1973) Soil Organic Matter and its Role in Crop Production. Elsevier, Amsterdam. Barrow N. J. (1960) A comparison of the mineralization of nitrogen and of sulphur from decomposing organic materials. Australian Journal of Agricultural Research 11,960-969. Castellano S. D. and Dick R. P. (1988) Distribution of sulfur fractions in soil as influenced by management of Allison

114 organic

S. J. Chapman Soil 1403-1407.

residues.

Journal52,

Science

Society

of

America,

Chapman S. J. (1987) Microbial sulphur in some Scottish soils. Soil Biology & Biochemistry 19, 301-305. Chapman, S. J. (1997) Carbon substrate mineralization and sulphur limitation in soil. Soil Biology di Biochemistry 29,

115-122.

Cheshire M. -V., Sparling G. P. and Inkson R. H. E. (1979) The decomnosition of straw in soil. In Straw Deca; and its Effect on Disposal and Vtilization, ed. Crossbard, E., pp: 65-71. WiÏey, Chichester. Conrad J. P. (1950) Sulfur fertilization in California and some related\ factors. Soil Science 70, 43-54. Gallardolara F., Navarro A. and Nogales R. (1990) Extractable sulfate in 2 soils of contrasting pH affected by applied town refuse compost and agricultural wastes. Biological Wastes 33, 39-5

1.

Hunt H. W., Stewart J. W. B. and Cole C. V. (1986) Concepts of sulfur, carbon and nitrogen transformations in soil: Evaluation by simulation modeling. Biogeochemistry 2, 163-177.

Lefroy R. D. B., Chaitep W. and Blair G. J. (1994) Release of sulfur from rite residues under flooded and non-flooded soil-conditions. Australian Journal of Agricultural Research 45, 657-667.

Lynch J. M., Ellis F. B., Harper S. H. T. and Christian D. Cl. (1980) The effect of straw on the establishment and growth of winter cereals. Agriculture and Environment 5, 321-328.

McGrath S. P. and Zhao F. J. (1995) A risk assessment of sulphur deficiency in cereals using soil and atmospheric deposition data. Soil Vse and Management 11, 110-114. Maftoun M. and Banihashemi Z. (1981) Effects of added sulfur, aluminum sulfate and ferrous sulfate on CO2 evolution, microbial-population and nitrification in alfalfa-amended and straw-amended soil. Agrochimica 25, 3 18-326.

Nelson L. E. (1973) The effect of crop residues on the growth of turnips and their recovery of sulphur from soils. Soit Science 115, 447-454.

J. S. and Irish R. (1982) The Fourth Nutrient. The Sulphur Institute, Washington.

Platou

Major

Rasmussen P. E. and Rohde C. R. (1988) Long-term tillage and nitrogen-fertilization effects on organic nitrogen and carbon in a semiarid soil. Soil Science Society of America Journal52, 1114-1117. Schnug E. (1991) Sulphur nutritional status of European crops and consequences for agriculture. Sulphur in Agriculture 15, 7-12.

Scott N. M., Dyson P. W., Ross J. and Sharp G. S. (1984) The effect of sulphur on the yield and chemical composition of winter barley. Journal of Agricultural Science 103, 699-702.

Stewart B. A., Porter L. K. and Viets F. G. (1966a) Effect of sulfur content of straws on rates of decomposition and plant growth. Soil Science Society of America Proceedings 30, 355-358.

Stewart B. A., Porter L. K. and Viets F. G. (1966b) Sulfur requirements for decomposition of cellulose and glucose in soil. Soil Science Society of America Proceedings 30, 453456.

Stewart B. A. and Whitfield C. J. (1965) Effects of crop residue, soil temperature, and sulfur on the growth of winter wheat. Soil Science Society of America Proceedings 29, 752-755.

Stotzky G. and Norman A. G. (1961) Factors limiting microbial activities in soil 11. The effect of sulfur. Archiv für Mikrobiologie 40, 370-382.

Syers J. K., Curtin D. and Skinner R. J. (1987) Soil and fertiliser sulphur in U.K. agriculture. Proceedings of the Fertiliser Society 264, 1-43.

White P. J. (1984) Effects of crop residue incorporation on soil properties and growth of subsequent crops. Australian Journal of Experimental Animal Husbandry 24, 219-235.

Agriculture

and

Wu J., O’Donnell A. G. and Syers J. K. (1993) Microbial growth and sulphur immobilization following the incorporation of plant residues into soil. Soil Biology & Biochemistry 25, 1567-1573.