Effects of organic amendments on soil carbon content and microbial ...

Archives of Agronomy and Soil Science April 2005; 51(2): 163 – 170

Effects of organic amendments on soil carbon content and microbial biomass – results of the long-term box plot experiment in Grossbeeren (Einfluss organischer Du¨ngung auf den Gehalt des Bodens an Kohlenstoff und mikrobieller Biomasse – Ergebnisse des Kastenparzellen-Dauerversuchs in Grossbeeren)

¨ RG RU ¨ HLMANN & SILKE RUPPEL JO Department of Plant Nutrition, Institute of Vegetable and Ornamental Crops Grossbeeren, Germany (Received 9 August 2004; accepted 1 November 2004)

Abstract The Box Plot Experiment in Grossbeeren was set up in 1972 to investigate diverse fertilization strategies within an irrigated vegetable crop rotation system for three different soils. Here we report on the longterm effects of applying different organic amendments and mineral N fertilizer levels to soils on the content of: (1) microbially decomposable carbon (Cdec); and (2) microbial biomass carbon (Cmic). We determined the Cdec content of soils that were covered with a vegetable crop rotation, and established that the differences between treatments with and without organic amendments corresponded very well to those found under arable crop rotations. Under the given experimental conditions, leaving the crop residues on the field generated an optimum level of soil organic matter content. When we compared the Cdec content of the soils after applying different organic amendments as based on the C input, we found them to be similar. 10 t ha 7 1 yr 7 1 farmyard manure (FYM) has been reported to be sufficient to generate an optimum level of organic matter in arable soils. Here we show that this effect can also be transferable to other organic amendments if the C input is used as the reference base. Regarding Cmic content, we obtained a linear relationship for the differences of Cdec between treated plots which were influenced by different C input and the controls. This relationship did not differ with soil type. Therefore, we assumed that Cdec may be regarded as a permanently present substrate for the nutrition of microorganisms regardless of soil type.

Keywords: Carbon content, long-term experiment, microbial biomass, organic amendment, vegetable crops

Correspondence: J. Ru¨hlmann, Institute of Vegetable and Ornamental Crops Grossbeeren, Theodor-Echtermeyer-Weg 1, D-14979 Grossbeeren, Germany. E-mail: [email protected] ISSN 0365-0340 print/ISSN 1476-3567 online # 2005 Taylor & Francis Group Ltd DOI: 10.1080/03650340400026651

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J. Ru¨hlmann & S. Ruppel

Introduction The application of organic materials to soils affects a large number of chemical, physical, and biological soil properties. These properties include the humus (carbon) content and the microbial biomass. Changes in the humus content of soils occur very slowly, whereas microbial soil parameters can differ significantly from site typical values after application of easily decomposable organic materials, like green manure. However under long-term conditions, the site characteristic level of microbial biomass content becomes related to texture and humus content of soils. To date, the majority of investigations assessing soil carbon and microbial biomass contents were performed in systems with arable crops. Therefore, our aim was to evaluate corresponding results from the long-term Box Plot Experiment in Grossbeeren with an irrigated vegetable crop rotation system and to continue the work started by Baumann and Eich (1982), Ellmer et al. (1999a,b), and Richter et al. (1999). The Box Plot Experiment in Grossbeeren differs from many other long-term experiments. In particular our setup has established different fertilization strategies under the same climatic conditions, but for three different soil types (Paschold 1975; Ru¨hlmann 2003).

Material and methods Experimental setup The Box Plot Experiment in Grossbeeren located south of Berlin, Germany, was established in 1972. The single plots consist of quadratic boxes with a surface of 2 m2 and a depth of 75 cm. The upper 50 cm is filled with soil; the lower 25 cm comprises a sandy drainage layer. A detailed description of the experimental design is provided in Paschold (1975). Three soils all of different origin comprise separate blocks of plots in this experiment. (1) (2) (3)

Origin Großbeeren (area: Nuthe hollow, south of Berlin, Federal State: Brandenburg): Arenic-Luvisol, less silty sand, 5.5% clay (silty sand). Origin Golzow (area: Oderbruch, at the German-Polish border, Federal State: Brandenburg): Gleyic-Fluvisol, heavy sandy loam, 27.5% clay (sandy loam). Origin Wanzleben (area: Magdeburger Bo¨rde, Federal State: Sachsen-Anhalt) LuvicPhaeozem, medium clayey silt, 17.2% clay (clayey silt).

Please note that the soil classification is according to World Reference Base for Soil Resources (WRB, 1998) and soil texture is as defined by Bodenkundliche Kartieranleitung KA4 (AG Boden, 1994). The vegetable species grown within an irrigated crop rotation were white cabbage (Brassica oleracea L. var. capitata f. alba), carrot (Daucus carota L.), cucumber (Cucumis sativus L.), leek (Allium porrum L.), and celery (Apium graveolens L. var. rapaceum Mill.). The work presented here is based on the results of the 6th rotation (25th – 29th experimental year). A list of selected treatments is provided in Table I. For the 6th rotation, the application of the organic amendments corresponded to the following mean annual C inputs: 24 t ha 7 1 FYM = 2.250 t C ha 7 1, CR = 0.655/ 1.070/1.150 t C ha 7 1 on silty sand/sandy loam/clayey silt and for the combination CR + FYM = 3.170/3.630/3.850 t C ha 7 1 on silty sand/sandy loam/clayey silt respectively.

Effects of organic amendments on soil properties

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Table I. Description of treatments (CON = control, CR = crop residues, FYM = farmyard manure). Number of treatment

Organic amendment

Mineral N level

1 2 4 8 5 6 9 10

CON FYM CR CR + FYM CON FYM CON FYM

N0 N0 N0 N0 N1 N1 N2 N2

Mineral N fertilizer was applied as calcium ammonium nitrate on three N levels (N0/N1/ N2) corresponding to 0/110/225 kg N ha 7 1 yr 7 1 respectively. All treatments were replicated in quadruplicate. The crops were irrigated with a mean amount of irrigation water of about 175 mm yr 7 1 and the mean sum of precipitation amounted to 527 mm yr 7 1 for the investigated experimental period. A detailed site description with additional information about soils, weather, experimental design, and factors, as well as treatments tested in the experiment were given by Ru¨hlmann (2003). Chemical and biological analyses Samples of the top soil layer 0 – 25 cm were used to estimate total carbon and microbial biomass. The total carbon content in plants, soils, and organic amendments was analyzed using the CNS-Analyzer VARIO EL (Elementar Hanau). The soil samples used to measure basal respiration and microbial biomass were sieved 5 2 mm and stored between sampling and analysis at 7 208C. The basal respiration, i.e., the CO2 exhalation of soil samples without glucose addition, was measured within the first 16 h of incubation at 20 + 18C. The microbial biomass (Cmic) was estimated according to Anderson and Domsch (1978) via substrate-induced CO2 respiration (SIR) by automatic infrared gas analysis (Heinemeyer et al. 1989). Therefore, glucose (2 g kg 7 1 soil) was applied, and the samples were incubated at 20 + 18C. The continuous gas flow was analyzed at hourly intervals. To overcome discrepancies due to differences of the bulk density of soils, the Cmic content was expressed as mg Cmic per cm 7 3 dry soil instead of mg g 7 1. Results The soils of the Box Plot Experiment did not contain carbonate. Therefore, the measured total carbon content corresponded to the content of total organic carbon (TOC). Because changes in TOC content of soils resulting from management conditions affect primarily their microbial decomposable proportion (Cdec), the following results were based on the Cdec content of soils. The Cdec content was calculated from the difference between TOC and the texture-dependent inert TOC content (Ci) (Franko, 1997). All Cdec and Ci contents are given in % dry soil. The Ci contents of silty sand, sandy loam, and clayey silt were calculated to be 0.24, 0.95, and 0.72% respectively, using the regression model of Ko¨rschens (1980), and 0.32, 0.93, and 0.75% using the approach of Ru¨hlmann et al. (1997).

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For the 6th rotation (25th – 29th experimental year), a summary of mean Cdec contents for the three different soils is provided in Table II. After comparing the three soils, it became clear that the silty sand was generally characterized by lower Cdec contents than the sandy loam and the clayey silt. Regarding the controls and the treatments with FMY application, the mineral N fertilization (N1 and N2) led, when compared to N0, to an increase in the Cdec content of the silty sand of up to about 0.05%. The corresponding differences of sandy loam and clayey silt amounted to up to around 0.1%. In contrast to the small effect of the mineral N fertilization, the application of organic materials led to significant changes of the Cdec contents. We calculated the difference of the Cdec content between the treatments with organic amendments and the corresponding control on the same mineral N level, and as shown in Figure 1, these differences were mainly induced by the C quantities applied by organic amendments. Thus the low C inputs by CR with 0.655, 1.070, and 1.150 t C ha 7 1 on silty sand, sandy loam, and clayey silt, respectively, led to an increase of Cdec content of between 0.12 and 0.14%. The mean annual FYM application of 2.25 t C ha 7 1 produced differences in Cdec content of between 0.24 and 0.28%, 0.21 and 0.25% as well as 0.28 and 0.31% on silty sand, sandy loam, and clayey silt respectively. The highest differences were revealed for the treatments with combined application of FYM + CR with 0.38 to 0.46%, corresponding to the highest C inputs of 3.170 to 3.850 t C ha 7 1. With regard to the microbial biomass, the following mean Cmic contents of the soils were estimated averaged over the 6th rotation period (25th – 29th experimental year) (Table III). Similar to the Cdec contents, a comparison of the three soils highlighted that the silty sand was prevalently characterized by the lowest Cmic contents. Again, fertilizing mineral N led, compared to organic amendments, to smaller differences of the Cmic contents in relation to those treatments with application of organic amendments. In contrast to the organic amendments which are only temporarily present in the soil, the Cdec content, i.e., the microbially decomposable proportion of the soil organic matter, may be regarded as a substrate permanently present for the nutrition of microorganisms. Therefore the Cmic content was related to the differences of Cdec (Figure 2) which were a result of the different C input as depicted in Figure 1. We found that the relationship between Cmic and Cdec was linear (Figure 2), and there were no significant differences between the three soil types.

Table II. Cdec content of soils (average of 6th rotation) (CON = control, CR = crop residues, FYM = farmyard manure). Cdec content (%) Number of treatment

Organic amendment

Mineral N level

1 2 4 8 5 6 9 10


N0 N0 N0 N0 N1 N1 N2 N2

Silty sand

Sandy loam

Clayey silt

0.20 0.48 0.32 0.59 0.23 0.48 0.26 0.52

0.37 0.62 0.51 0.76 0.43 0.69 0.48 0.69

0.50 0.81 0.63 0.96 0.60 0.88 0.62 0.92


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Figure 1. Differences of the Cdec content of soils between the treatments with organic amendments and the control as affected by C input and soil type.

Table III. Cmic content of soils (average of 6th rotation) (CON = control, CR = crop residues, FYM = farmyard manure). Cmic content (mg cm 7 3) Number of treatment

Organic amendment

Mineral N level

1 2 4 8 5 6 9 10


N0 N0 N0 N0 N1 N1 N2 N2

Silty sand

Sandy loam

Clayey silt

80.3 121.0 109.4 171.8 94.4 126.2 104.9 134.9

98.8 120.3 118.3 164.5 95.0 133.5 105.9 124.2

103.9 141.4 124.9 174.3 115.5 164.5 124.6 136.4

Discussion The Cdec contents were estimated to vary between 0.2 and 0.6% (Table II). This range is, as according to Ko¨rschens (1997), typical for many arable soils subject to common management practices and the climatic conditions of Central Europe. Therefore, this range can be interpreted as an optimum level of soil organic matter allowing high level plant biomass

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Figure 2. Cmic content of soils in relation to the differences of the Cdec content between the treatments with organic amendments and the control.

production combined with tolerable nutrient losses to the environment. However in our case, the retention of the crop residues alone was observed to be sufficient to enrich the upper bound of this optimum level both on sandy loam and on clayey silt. This may be related to the high yield potential in this experiment as reported by Ru¨hlmann (2003). The amount of FYM fresh matter necessary to realize the optimum level of Cdec content in arable soils was previously estimated to be about 10 t ha 7 1 yr 7 1 (Ko¨rschens & Schulz, 1999; Ko¨rschens, 2002). This amount of FYM corresponds to 800 – 1000 kg C depending on its quality and is in good accord with the mean annual C input by crop residues as mentioned above. Both this finding as well as the linear relationship between the C input by organic amendments and the Cdec content (Figure 1) indicate that the amount of 10 t FYM, as reported to be sufficient to generate an optimum level of organic matter in arable soils, could be transferred to other organic amendments applied to soils grown with vegetables if the C input is used as the reference base. Due to the linear relationship, as seen in Figure 1, as well as the additive effect seen in the CR + FYM treatment, a similar microbial efficiency during the transformation of the different organic amendments was assumed. Previously this microbial efficiency has been estimated to be 0.658 – 0.699 for shoots of different vegetable crops (Klimanek, 1997) and 0.6 for FYM (Franko, 1997). In strong contrast to previous reports, in our study, equal C input to different textured soils led to similar differences of the Cdec content between treatments with and without organic amendments (Figure 1). As expected, these differences were slightly lower on the coarser textured silty sand than on sandy loam and clayey silt. This observation may be explained by the relation between the processes of accumulation and decomposition of soil organic matter. Moreover these processes can be assumed not to be equilibrated at least in the finer textured sandy loam and clayey silt. However in the future, we expect a further differentiation of the Cdec content between treatments with and without organic amendments as it may take 50 years or more to obtain such an equilibrium. Hence, later we want to report on C dynamics of


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different fertilized plots of the Box Plot Experiment in Grossbeeren using the C model CANDY (Franko et al., 1997). Plotting the Cmic content of the different soils against the differences of the Cdec content between the treatments with and without organic amendments gave a linear trend with no observable significant differences between the three tested soils (Figure 2). However it seems reasonable to interpret the Cdec content as a substrate permanently present for the nutrition of microorganisms; otherwise differing soil texture would ultimately affect the biological activity of soils, the so-called efficient mineralization time (EMT), due to changed conditions of soil aeration and moisture, as has been previously proposed (Franko & Oelschla¨gel, 1995). Consequently, to obtain a real link between Cmic content and substrate supply (Cdec content), it seems to be necessary to compare these parameters on the biological time base EMT. The results of these investigations will be presented later in context with the proposed C model calculations as mention above. Acknowledgement We thank Ruth Willmott (www.bioscript.de) for editing the manuscript. References AG Boden 1994. Bodenkundliche Kartieranleitung. 4. Aufl., Nachdruck 1996. Schweizerbart’sche Verlagsbuchhandlung. Anderson JPE, Domsch KH. 1978. A physiological method for the quantitative measurement for microbial biomass. Soil Boil Biochem 10:215 – 221. Baumann E, Eich D. 1982. New preliminary reference values of organic matter in plant production. Gartenbau 35:163 – 165. [In German] Ellmer F, Geyer B, Grimm J, Kru¨ck S, Mollenhauer S, Peschke H, Richter K, Ru¨hlmann J, Schmaler K. 1999a. Grundlagen umweltschonender Bodennutzungsstrategien im nordostdeutschen Tiefland. Abschlussbericht des ¨ kologische Hefte der Landwirtschaftlich-Ga¨rtnerischen Fakulta¨t, interdisziplina¨ren DFG-Projektes Ri 640. In: O Kap. 3.1.: Humus- und Stickstoffgehalte sowie bodenbiologische Parameter von Mineralbo¨den, HumboldtUniversita¨t zu Berlin, Heft 11:49 – 60. Ellmer F, Geyer B, Grimm J, Herden S, Mollenhauer S, Peschke H, Richter K, Ru¨hlmann J, Schmaler K. 1999b. Grundlagen umweltschonender Bodennutzungsstrategien im nordostdeutschen Tiefland. Abschlussbericht des ¨ kologische Hefte der Landwirtschaftlich-Ga¨rtnerischen Fakulta¨t, interdisziplina¨ren DFG-Projektes Ri 640. In: O Kap. 3.3.1.: Ertra¨ge der Fruchtarten, Humboldt-Universita¨t zu Berlin, Heft 11:126 – 142. Franko U. 1997. Modelling of soil organic matter. Arch Acker-Pflanzenbau Bodenkd 41:527 – 547. [In German] Franko U, Crocker GJ, Grace PR, Klir J, Ko¨rschens M, Poulton PR, Richter DD. 1997. Simulating trends in soil organic carbon in long-term experiments using the CANDY model. Geoderma 81:109 – 120. Franko U, Oelschla¨gel B. 1995. Effect of climate and texture on the biological activity of soil organic matter turnover. Arch Acker-Pflanzenbau Bodenkd 39:155 – 163.I [In German] Heinemeyer O, Insam H, Kaiser EA, Walenzki G. 1989. Soil microbial biomass and respiration measurements: an automated technique based on infra-red gas analysis. Plant Soil 116:77 – 81. Klimanek E-M. 1997. Importance of crop and root residues of agricultural crops for soil organic matter. Arch AckerPflanzenbau Bodenkd 41:458 – 511. [In German] Ko¨rschens M. 1980. Relation between content of fine grained soil particles, total carbon and total nitrogen content of the soil. Arch Acker-Pflanzenbau Bodenkd 24:585 – 592. [In German] Ko¨rschens M. 1997. Dependence of soil organic matter (SOM) on location and management, and its influence on yield and soil properties. Arch Acker-Pflanzenbau Bodenkd 41:435 – 463. [In German] Ko¨rschens M. 2002. Importance of soil organic matter (SOM) for biomass production and environment (a review). Arch Acker-Pflanzenbau Bodenkd 48:89 – 94. Ko¨rschens M, Schulz E. 1999. Soil organic matter. Dynamics – reproduction – economically and environmentally justified reference values. UFZ-Ber. Nr. 13/99, ISSN 0948-9452. [In German]

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