- Email: [email protected]
Mineralization-immobilization of nitrogen in soil amended with low C:N ratio plant residues with different particle sizes
Soil Biol. Biochem.Vol. 26, No. 4, pp. 519-521,1994 Copyright 0 1994 ElsevierScienceLtd Printed in Great Britain. All rights reserved 0038-0717/94
$6.00 + 0.00
SHORT COMMUNICATION MINERALIZATION-IMMOBILIZATION OF NITROGEN SOIL AMENDED WITH LOW C:N RATIO PLANT RESIDUES WITH DIFFERENT PARTICLE SIZES
IN
E. S. JENSEN Plant Biology Section, Environmental Science and Technology Department, Rise National Laboratory, DK-4000, Roskilde, Denmark (Accepted 21 September 1993)
Controversy still exists regarding the effect of plant residue particle size on the rate of residue decomposition and mineralization-immobilization turnover (MIT) of N in the soil. It has been suggested that small particles may decompose faster than larger particles, because the increased surface area and greater dispersion in soil will increase the susceptibility to microbial attack, especially if residues are not readily penetrated by fungi and bacteria (Allison, 1973; Sims and Frederick, 1970; Amato et al., 1984). On the other hand, the microbial biomass and products formed during the initial decomposition of small particles may be better protected against further decomposition, due to a more intimate mixing of the substrate with the mineral soil (Stickler and Frederick, 1959; van Schreven, 1964). The effect of plant residue particle size on MIT may thus be an interaction between soil clay and silt contend, secondary metabolic products, plant residue chemical composition, period of decomposition and soil fauna1 activity. In field experiments, Jensen (1994 this issue, pp. 455-464) observed that the initial decline in organic pea residue r5N was slower in an experiment using residues with a small particle size, and the immobilization of residue and soil N in the microbial biomass was faster, than in an experiment with larger residue particles. I report here the results of a laboratory incubation experiment, which was designed to test these effects of pea residue particle size on the MIT during early stages of decomposition. A sandy loam soil from the plough-layer at the Rise experimental field (Jensen, 1994) containing 11.4% clay, 1.1% C and 0.13% N, and a pH (H,O) of 6.9 was used in the experiment. The soil was air-dried, sieved (5 mm), and conditioned for 4 weeks at 55% WHC and 20°C. Portions of this soil, corresponding to 70 g dry wt were amended with pea residues (5 mg g-t dry soil) either ground (1 mm) or cut into 10 mm pieces, and placed in 250 ml polyethylene bottles. The control soil was unamended. Each treatment had 12 replicates. Pea residues, produced as described bv Jensen (1994), consisted of leaf and stem material and had 2.29% N. 44.5% C (C:N: 19.4) and 0.935 atom% 15Nexcess. The residue C and N input to the soil corresponded to 2.2 mg C and 106 pg N g-r dry soil. The soil was kept at 20°C for 90 days in a temperature chamber, and the water content was adjusted weekly to 55% WHC. The CO, evolution from soils, receiving the same treatments as stated above, was determined by placing bottles with soil (23 g dry wt) in 2 1.glass jars, which could be closed airtight. A CO, trap and a vial with 50ml of water to prevent the soil in drying up were also placed in each jar. The CO,-trap consisted of a 50 ml vial containing 5 ml of 1 N
KOH. The traps were changed every 10 days. The atmosphere of jars was renewed when traps were exchanged. Three replicate jars were used per treatment. Total CO,-C in traps was determined by titrating with 0.25 N HCl after adding 5 ml of 35% BaCl, to precipitate carbonates. and _ nhenoloh_ talein was used ah the indicator. After 0, 10, 30 and 90 days, triplicate bottles of each treatment were analysed for NO; -N, NH,+ -N. total N and 15N enrichment. Inorganic N was extracted with 2~ KC1 (soil : KC1 = 1: 10) and NH,+ -N and NO; -N determined on an autoanalyxer (Jensen, 1994). The rsN enrichment of the inorganic N pool and the total N and lSN enrichment in air-dried and ground soils were determined using a N-analyzer coupled to an isotope ratio mass spectrometer (Jensen, 1991). The CO* evolution was significantly (P < 0.001) higher from soil amended with lOmm-size pea residue particles than from soil receiving 1 mm-size residue particles during the initial 30 days of decomposition [Fig. l(a)]. Sims and Frederick (1970) and Nyhan (1975) found that the CO, evolution decreased and the amount of residue C remaining in the soil increased with increasing particle size. However, they used high C:N ratio residues and possibly the decomposition of the larger residue particles was more reduced by N deficiency than the small particles. In my study the C : N ratio of residues was relatively low, and the decomposition was probably not N-limited. The evolution of COr was higher from soil amended with the large particles than from soil amended with the small particles. This may be due to better protection by clay minerals of the microbial biomass and metabolites formed after amending with small particles. After 30 days of decomposition, the CO, evolution was not significantly influenced by residue particle size. Ladd (1981) found no significant effect of particle size on the amount of wheat r&due i4C (C:N = 18) remaining in the soil after 4-53 weeks incubation. van Schreven (1964) observed an effect of grinding residues on the CO, evolution during the first weeks of decomposition. In my experiment accumulated CO,-C evolved from residue amended soils after 30 days of decomposition, indicated that 39 and 44% of the residue C input had been evolved as CO* from the 1 and 1Omm particle sizes, respectively. After 90 days of decomposition 52% of the residue C had been evolved with both particle sixes [Fig. l(a)]. The net immobilization of N in soil after 10 days of decomposition was significantly greater (P > 0.01) with the small residue particle size than with the large [Fig. l(b)], and
519
Short Communication
520
after 30 days, net immobilization was still observed with the small particle size, whereas in the large particle size treatment, net mineralization was observed. After 90 days, net mineralization was observed with both particle sizes, but it was greatest with the large particle size [Fig. l(b)]. These results are in agreement with the effect of residue particle size on the net mineralization of N observed by Stickler and Frederick (1959) van Schreven (1964), Sims and Frederick (1970) and Vigil ef al. (1991) using either low or high C:N ratio residues.
80
0
I I I I I b) Total inorganic N
I
I
I
I
I
I
30
10
I
90
I I I I I c) Net mineralization
I
I Residue N
I 0
10
I
I
I
I
I
___- - *
I
30 INCUBATION TIME (days)
I
I 90
The use of “N-labeled residues made it possible to separate the overall net mineralization into the net mineralization of labeled residue N and the net mineralization (immobilization) of soil N [Fig. I(c)]. The net mineralization of residue 15N from IOmm residues was significantly (P c 0.01) greater than from 1 mm residues during the 90 days of decomposition. After 90 days 21 and 26% of the residue isN were present in the inorganic soil N pool in soil amended with 1 and 10 mm residues, respectively. The total recovery of labeled N at 90 days was not significantly different between the two treatments, 101 + 4% ( f SD), indicating that no gaseous losses of labeled N occurred during the incubation. This implies that 79 and 74% of the rsN were still present in organic form 90 days after incorporation of 1 and 10 mm pea residue particles, respectively. This is in contrast to Amato et al. (1984), who found that after 140 days of decomposition significantly more 15Nremained in soil in organic forms after intact low C: N ratio residues compared to ground. Amendment with residues caused net immobilization of non-labeled soil N in more than 30 days [Fig. I(c)]. The net immobilization of non-labeled soil N was increased more by small than large particles, but after 90 days particle size had no significant effect. The average immobilization of non-labeled soil N during the initial 10 days of decomposition was 2.0 and 3.5 pg N mg-’ residue for the 10 and 1 mm residues, respectively. The results of the present investigations and previous findings can be summarized as follows. The decomposition of plant residues, microbial biomass and metabolites formed during the early decomposition of materials of low C:N ratios is slower with small, than with coarse, residues probably due to a better protection of the residues and biomass by clay minerals. During initial decomposition of high C:N ratio residue, the decomposition of larger sized residue may be N-limited, resulting in a slower rate of decomposition compared to smaller residues. More residue N remained in organic forms during early stages of decomposition in the soil amended with the smaller particles. Furthermore, the immobilization of soil N was greater with small than with large particles. This may be due to a more intimate mixing with soil, resulting in stabilization of the organic residue-derived N after contact with clay and other particles. The greater immobilization of N with small residues may also be due to a larger proportion of the residue C being available to the microbial biomass from small than from large residues. This is because a greater proportion of the available C is protected by lignin in the larger particles. The plant residue particle size appears to be an important factor in the initial residue decomposition and MIT in soil. The potential for manipulating crop residues (e.g. by reducing particle size) in order to conserve N in agroecosystems, especially during initial decomposition in the autumn, should be studied in more detail. Acknowledgemenfs--I thank Merete Brink Jensen for excellent technical assistance, Drs K. E. Giller, A. J. Andersen and L. H. Sorensen for useful comments and suggestions, and Lis Petersen for typing the manuscript. REFERENCES
Fig. 1. Influence of size of pea residue particles on C and N mineralization in soil. (a) Cumulative CO, evolution from soil; 0, control soil; 0, soil amended with residues ground to pass 1 mm; 0, soil amended with residues cut into 10 mm pieces. Mean CV.s on the cumulative CO, evolution in the control, 1 and 10mm residue particle size treatments were 18, I and 4%, respectively. (b) Total inorganic N pool. (c) Net mineralization of iSN-labeled residue N (---) and non-labeled soil N (-). Bars indicate LSD,,,,, which are only presented where the effect of particle size is significant.
Allison F. E. (1973) Soil Organic Matter and Its Role in Crop Production. Elsevier, Amsterdam. Amato M., Jackson R. B., Butler J. H. A. and Ladd J. N. (1984) Decomposition of plant material in Australian soils. II. Residual organic 14Cand 15Nfrom legume plant parts decomposing under field and laboratory conditions. Australian Journal of Soil Research 22, 33 l-34
1.
Jensen E. S. (1991) Evaluation of automated analysis of 15N and total N in plant material and soil. Plant and Soil 133, 83-92.
Short Communication Jensen E. S. (1994) Dynamics of mature pea residue nitrogen turnover in unplanted soil under field conditions. Soil Biology & Biochemistry 26, 455464. Ladd J. N. (1981) The use of “N in following organic matter turnover, with special reference to rotation systems. PIant and Soil 58,401-411. Nyhan J. W. (1975) Decomposition of carbon-14 labelled -plant materials in a grassland soil under field conditions. Soil Science Societv of America Proceedinas 39. 643-648. van Schreven D. A. (1964) A comparison beiween the effect of fresh and dried organic materials added to soil on carbon an nitrogen mineralization. Plant and Soil 20, 149-165.
521
Sims J. L. and Frederick L. R. (1970) Nitrogen immobilization and decomposition of corn residue in soil and sand as affected by residue particle size. Soil Science 109, 355-36 1. Stickler F. C. and Frederick L. R. (1959) Residue particle size as a factor in nitrate release from legume tops and roots. Agronomy Jaurnai 51, 271-274. Vigil M. F., Schepers J. S. and Doran J. W. (1991) Mineralization-immobilization of N in soils amended with corn residues of various particle sizes. In Agronomy Absfracfs, 1991 Annual Meetings, p. 279. American Society of Agronomy, Madison, Wisconsin.
$6.00 + 0.00
SHORT COMMUNICATION MINERALIZATION-IMMOBILIZATION OF NITROGEN SOIL AMENDED WITH LOW C:N RATIO PLANT RESIDUES WITH DIFFERENT PARTICLE SIZES
IN
E. S. JENSEN Plant Biology Section, Environmental Science and Technology Department, Rise National Laboratory, DK-4000, Roskilde, Denmark (Accepted 21 September 1993)
Controversy still exists regarding the effect of plant residue particle size on the rate of residue decomposition and mineralization-immobilization turnover (MIT) of N in the soil. It has been suggested that small particles may decompose faster than larger particles, because the increased surface area and greater dispersion in soil will increase the susceptibility to microbial attack, especially if residues are not readily penetrated by fungi and bacteria (Allison, 1973; Sims and Frederick, 1970; Amato et al., 1984). On the other hand, the microbial biomass and products formed during the initial decomposition of small particles may be better protected against further decomposition, due to a more intimate mixing of the substrate with the mineral soil (Stickler and Frederick, 1959; van Schreven, 1964). The effect of plant residue particle size on MIT may thus be an interaction between soil clay and silt contend, secondary metabolic products, plant residue chemical composition, period of decomposition and soil fauna1 activity. In field experiments, Jensen (1994 this issue, pp. 455-464) observed that the initial decline in organic pea residue r5N was slower in an experiment using residues with a small particle size, and the immobilization of residue and soil N in the microbial biomass was faster, than in an experiment with larger residue particles. I report here the results of a laboratory incubation experiment, which was designed to test these effects of pea residue particle size on the MIT during early stages of decomposition. A sandy loam soil from the plough-layer at the Rise experimental field (Jensen, 1994) containing 11.4% clay, 1.1% C and 0.13% N, and a pH (H,O) of 6.9 was used in the experiment. The soil was air-dried, sieved (5 mm), and conditioned for 4 weeks at 55% WHC and 20°C. Portions of this soil, corresponding to 70 g dry wt were amended with pea residues (5 mg g-t dry soil) either ground (1 mm) or cut into 10 mm pieces, and placed in 250 ml polyethylene bottles. The control soil was unamended. Each treatment had 12 replicates. Pea residues, produced as described bv Jensen (1994), consisted of leaf and stem material and had 2.29% N. 44.5% C (C:N: 19.4) and 0.935 atom% 15Nexcess. The residue C and N input to the soil corresponded to 2.2 mg C and 106 pg N g-r dry soil. The soil was kept at 20°C for 90 days in a temperature chamber, and the water content was adjusted weekly to 55% WHC. The CO, evolution from soils, receiving the same treatments as stated above, was determined by placing bottles with soil (23 g dry wt) in 2 1.glass jars, which could be closed airtight. A CO, trap and a vial with 50ml of water to prevent the soil in drying up were also placed in each jar. The CO,-trap consisted of a 50 ml vial containing 5 ml of 1 N
KOH. The traps were changed every 10 days. The atmosphere of jars was renewed when traps were exchanged. Three replicate jars were used per treatment. Total CO,-C in traps was determined by titrating with 0.25 N HCl after adding 5 ml of 35% BaCl, to precipitate carbonates. and _ nhenoloh_ talein was used ah the indicator. After 0, 10, 30 and 90 days, triplicate bottles of each treatment were analysed for NO; -N, NH,+ -N. total N and 15N enrichment. Inorganic N was extracted with 2~ KC1 (soil : KC1 = 1: 10) and NH,+ -N and NO; -N determined on an autoanalyxer (Jensen, 1994). The rsN enrichment of the inorganic N pool and the total N and lSN enrichment in air-dried and ground soils were determined using a N-analyzer coupled to an isotope ratio mass spectrometer (Jensen, 1991). The CO* evolution was significantly (P < 0.001) higher from soil amended with lOmm-size pea residue particles than from soil receiving 1 mm-size residue particles during the initial 30 days of decomposition [Fig. l(a)]. Sims and Frederick (1970) and Nyhan (1975) found that the CO, evolution decreased and the amount of residue C remaining in the soil increased with increasing particle size. However, they used high C:N ratio residues and possibly the decomposition of the larger residue particles was more reduced by N deficiency than the small particles. In my study the C : N ratio of residues was relatively low, and the decomposition was probably not N-limited. The evolution of COr was higher from soil amended with the large particles than from soil amended with the small particles. This may be due to better protection by clay minerals of the microbial biomass and metabolites formed after amending with small particles. After 30 days of decomposition, the CO, evolution was not significantly influenced by residue particle size. Ladd (1981) found no significant effect of particle size on the amount of wheat r&due i4C (C:N = 18) remaining in the soil after 4-53 weeks incubation. van Schreven (1964) observed an effect of grinding residues on the CO, evolution during the first weeks of decomposition. In my experiment accumulated CO,-C evolved from residue amended soils after 30 days of decomposition, indicated that 39 and 44% of the residue C input had been evolved as CO* from the 1 and 1Omm particle sizes, respectively. After 90 days of decomposition 52% of the residue C had been evolved with both particle sixes [Fig. l(a)]. The net immobilization of N in soil after 10 days of decomposition was significantly greater (P > 0.01) with the small residue particle size than with the large [Fig. l(b)], and
519
Short Communication
520
after 30 days, net immobilization was still observed with the small particle size, whereas in the large particle size treatment, net mineralization was observed. After 90 days, net mineralization was observed with both particle sizes, but it was greatest with the large particle size [Fig. l(b)]. These results are in agreement with the effect of residue particle size on the net mineralization of N observed by Stickler and Frederick (1959) van Schreven (1964), Sims and Frederick (1970) and Vigil ef al. (1991) using either low or high C:N ratio residues.
80
0
I I I I I b) Total inorganic N
I
I
I
I
I
I
30
10
I
90
I I I I I c) Net mineralization
I
I Residue N
I 0
10
I
I
I
I
I
___- - *
I
30 INCUBATION TIME (days)
I
I 90
The use of “N-labeled residues made it possible to separate the overall net mineralization into the net mineralization of labeled residue N and the net mineralization (immobilization) of soil N [Fig. I(c)]. The net mineralization of residue 15N from IOmm residues was significantly (P c 0.01) greater than from 1 mm residues during the 90 days of decomposition. After 90 days 21 and 26% of the residue isN were present in the inorganic soil N pool in soil amended with 1 and 10 mm residues, respectively. The total recovery of labeled N at 90 days was not significantly different between the two treatments, 101 + 4% ( f SD), indicating that no gaseous losses of labeled N occurred during the incubation. This implies that 79 and 74% of the rsN were still present in organic form 90 days after incorporation of 1 and 10 mm pea residue particles, respectively. This is in contrast to Amato et al. (1984), who found that after 140 days of decomposition significantly more 15Nremained in soil in organic forms after intact low C: N ratio residues compared to ground. Amendment with residues caused net immobilization of non-labeled soil N in more than 30 days [Fig. I(c)]. The net immobilization of non-labeled soil N was increased more by small than large particles, but after 90 days particle size had no significant effect. The average immobilization of non-labeled soil N during the initial 10 days of decomposition was 2.0 and 3.5 pg N mg-’ residue for the 10 and 1 mm residues, respectively. The results of the present investigations and previous findings can be summarized as follows. The decomposition of plant residues, microbial biomass and metabolites formed during the early decomposition of materials of low C:N ratios is slower with small, than with coarse, residues probably due to a better protection of the residues and biomass by clay minerals. During initial decomposition of high C:N ratio residue, the decomposition of larger sized residue may be N-limited, resulting in a slower rate of decomposition compared to smaller residues. More residue N remained in organic forms during early stages of decomposition in the soil amended with the smaller particles. Furthermore, the immobilization of soil N was greater with small than with large particles. This may be due to a more intimate mixing with soil, resulting in stabilization of the organic residue-derived N after contact with clay and other particles. The greater immobilization of N with small residues may also be due to a larger proportion of the residue C being available to the microbial biomass from small than from large residues. This is because a greater proportion of the available C is protected by lignin in the larger particles. The plant residue particle size appears to be an important factor in the initial residue decomposition and MIT in soil. The potential for manipulating crop residues (e.g. by reducing particle size) in order to conserve N in agroecosystems, especially during initial decomposition in the autumn, should be studied in more detail. Acknowledgemenfs--I thank Merete Brink Jensen for excellent technical assistance, Drs K. E. Giller, A. J. Andersen and L. H. Sorensen for useful comments and suggestions, and Lis Petersen for typing the manuscript. REFERENCES
Fig. 1. Influence of size of pea residue particles on C and N mineralization in soil. (a) Cumulative CO, evolution from soil; 0, control soil; 0, soil amended with residues ground to pass 1 mm; 0, soil amended with residues cut into 10 mm pieces. Mean CV.s on the cumulative CO, evolution in the control, 1 and 10mm residue particle size treatments were 18, I and 4%, respectively. (b) Total inorganic N pool. (c) Net mineralization of iSN-labeled residue N (---) and non-labeled soil N (-). Bars indicate LSD,,,,, which are only presented where the effect of particle size is significant.
Allison F. E. (1973) Soil Organic Matter and Its Role in Crop Production. Elsevier, Amsterdam. Amato M., Jackson R. B., Butler J. H. A. and Ladd J. N. (1984) Decomposition of plant material in Australian soils. II. Residual organic 14Cand 15Nfrom legume plant parts decomposing under field and laboratory conditions. Australian Journal of Soil Research 22, 33 l-34
1.
Jensen E. S. (1991) Evaluation of automated analysis of 15N and total N in plant material and soil. Plant and Soil 133, 83-92.
Short Communication Jensen E. S. (1994) Dynamics of mature pea residue nitrogen turnover in unplanted soil under field conditions. Soil Biology & Biochemistry 26, 455464. Ladd J. N. (1981) The use of “N in following organic matter turnover, with special reference to rotation systems. PIant and Soil 58,401-411. Nyhan J. W. (1975) Decomposition of carbon-14 labelled -plant materials in a grassland soil under field conditions. Soil Science Societv of America Proceedinas 39. 643-648. van Schreven D. A. (1964) A comparison beiween the effect of fresh and dried organic materials added to soil on carbon an nitrogen mineralization. Plant and Soil 20, 149-165.
521
Sims J. L. and Frederick L. R. (1970) Nitrogen immobilization and decomposition of corn residue in soil and sand as affected by residue particle size. Soil Science 109, 355-36 1. Stickler F. C. and Frederick L. R. (1959) Residue particle size as a factor in nitrate release from legume tops and roots. Agronomy Jaurnai 51, 271-274. Vigil M. F., Schepers J. S. and Doran J. W. (1991) Mineralization-immobilization of N in soils amended with corn residues of various particle sizes. In Agronomy Absfracfs, 1991 Annual Meetings, p. 279. American Society of Agronomy, Madison, Wisconsin.