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Influence of organic and mineral fertilisation on organic matter fractions of a Brazilian Acrisol under maize/common bean intercrop.


In Brazil, intercropping or mixed cropping is the predominant system among most smallholdings (< 10 ha). The preference for intercropping, compared to sole cropping, is because of lower pest/disease infestation and more efficient soil use. Maize and common beans are largely produced in intercrop systems of smallholdings, and although not commercially relevant it has remarkable social impact (Yokoyama and Stone 2000). Over 59% of the Brazilian maize farms produce the cereal to be used by the farmer, but it corresponds to only ~24.9% of the national maize production. Approximately 14% of the labour involved in the annual crop production is linked to maize production. Similarly, in Minas Gerais State, the largest common bean producer in Brazil, > 290 000 small farmers participate in the production of common beans.

Subsistence smallholdings are generally characterised as a low input small farm, in which the use of mineral fertilisers is very limited due to their high costs. Thus, the use of organic, on-farm produced fertilisers (e.g. composts) is a viable and recommended alternative for smallholdings, particularly in intercrop systems. Additionally, the roots of intercrops freely intermingle, leading to a complementary and more efficient use of nutrients, especially nitrogen (Natarajan and Wiley 1980).

Performance evaluation of different crop systems has been improved by physical fractionation of soil organic matter (SOM), which yields SOM pools that differ in turnover times, and certain pools are more sensitive to changes caused by soil cultivation than total soil organic carbon or soil humic substances (Leite et al. 2003). Physical fractionation of SOM, such as density and particle-size fractionation, has been useful to quantify more labile pools of SOM (i.e. free-light fraction or particulate organic matter) (Christensen 2000; Freixo et al. 2002). Fractions of SOM are key to improve the modelling of biological processes (Sohi et al. 2001).

Soil microbial biomass commonly quantified by fumigation extraction procedure (Vance et al. 1987) or irradiation-extraction method (Islam and Weil 1998) is also considered in studies of SOM dynamics (Graham et al. 2002; Balota et al. 2004). The living organic matter is highly sensitive to changes in soil such as fertiliser addition and edapho-climatic conditions. Although comprising <4% of the total soil organic carbon, the living organic matter plays an important role in the soil functioning as it promotes nutrient cycling (Theng et al. 1989).

In Brazil most studies on SOM dynamics are on grain crops or pasture systems typical of medium- to large-size farms (Tarre et al. 2001; Freixo et al. 2002). However, little is known about the effects of the addition of mineral and organic composts on SOM dynamics under multiple cropping systems. Hence, the objective of this study was to determine the changes in total soil carbon and nitrogen stocks and in soil carbon pools due to long-term addition of mineral fertiliser and compost to a Ferric Acrisol under maize/common bean intercrop in south-eastern Brazil.

Materials and methods

Site and soil description

The study area (Coimbra, State of Minas Gerais, 20[degrees]45'S, 42[degrees]51'W) was naturally covered by an Atlantic Forest (AF), which was converted to agriculture in 1930, lasting for 54 years with subsistence intercropping of maize (Zea mays L.) and common beans (Phaseolus vulgaris) by local farmers.

The mean annual temperature is 19[degrees]C and average rainfall is 1400mm, and roughly two-thirds of this rain falls in the warmer season of the year from October to April. The soil type at the site is a Ferric Acrisol (Chromosol, Australian Soil Classification; Argissolo Vermelho-Amarelo, Brazilian Soil Classification) showing the following chemical and physical characteristics at 0-0.20 m depth in 1984: pH([H.sub.2]O) 5.9; traces of [Al.sup.3+]; 2.6 [cmol.sub.c] [Ca.sup.2+]/[dm.sup.3]; 1.7 [cmol.sub.c] [Mg.sup.2+]/[dm.sup.3]; 11 mg available P/[dm.sup.3]; 58 mg K/[dm.sup.3]; 46 Mg/ha of the total soil carbon stock. Coarse sand, fine sand, silt, and clay were 80, 60, 160, and 700 g/kg, respectively. Soil bulk density was 1.1 Mg/[m.sup.3].

Experimental site

The experiment was initiated in November 1984 and the treatments were:

(1) Control plot (0): Continuation of the intercrop system started in 1930 with no mineral fertiliser, nor compost added to the soil;

(2) Soil fertilised with 10 kg N/ha, 15 kg P/ha, and 17 kg K/ha (MF1);

(3) Soil fertilised with 20 kg N/ha, 30 kg P/ha, and 34 kg K/ha (MF2).

The soil was annually disc-ploughed at 0.20 m and twice lightly disc harrowed using a tractor. The mineral fertiliser was manually added alone or combined with organic compost, which consisted of residues of soybean, maize and common-bean plants mixed with animal manure. The organic compost properties were 380 g water/kg, density 0.36 g/[cm.sup.3], 0.7 dag P/kg, 2.8 dag K/kg, 1.0 dag Ca/Kg, 0.4 dag Mg/kg, 3.2 dag N/kg, and C : N ratio 5. The organic compost was yearly applied at 40 [m.sup.3]/ha (OC) shortly before sowing time and it was partially air-dried to enable manual application.

Plots (0, MF1, MF2, OC, MF1 + OC, and MF2 + OC) were 8 m by 8 m arranged in a complete randomised block design with 4 replications.

Sixteen years (1984-2000) of chemical fertiliser application at sowing time totalled 160 kg N/ha, 245 kg P/ha, and 265 kg K/ha for MF1 treatment, and 320 kg N/ha, 490 kg P/ha, and 530 kg K/ha for MF2 treatment. Topdressing was annually applied to MF1 (20 kg N/ha) and MF2 (40 kg N/ha) 35 days after sowing.

As a reference, soil samples were collected from an area under secondary AF, adjacent to the experiment (100 m away), on the same soil type. At the middleslope, 4 areas (4 m by 4 m) were placed along a 100-m transect in which soil samples were collected.

Carbon and nitrogen inputs

Estimates of C and N input to the soil by maize residues were based on grain yields reported by Maia (1999) assuming that all residues contained 50% C and 2% N. As suggested by Oelbermann et al. (2004), the inputs of belowground residues (dead roots and root exudates) were estimated assuming a shoot/root ratio of maize of 6 : 1.

Soil sampling and soil carbon pools analysis

Soil samples were collected in April 2000 after maize harvest from 4 blocks at 0-0.10 and 0.10-0.20 m depths using a hand auger. Nine subsamples were collected from each plot. From the forest site, 15 subsamples were taken from each of the 4 areas placed along the 100-m transect and at the same depths. The samples were passed through a 2-mm sieve and a 100-g aliquot of each sample was separated, placed in plastic bags, and stored in refrigerator at 4-8[degrees]C for later determination of microbial biomass. The remaining soil samples were air-dried.

Soil samples were ground and passed through a 0.21-mm sieve to determine total organic carbon (TOC) by wet combustion using a mixture of potassium dichromate and sulfuric acid under heating (Yeomans and Bremner 1988). Extraction and fractionation of soil humic substances (humic acids, fulvic acids, and humin) were carried out using the method recommended by the International Humic Substances Society (IHSS), as described by Swift (1996). The carbon content of humic acid (HAF), fulvic acid (FAF) and humin (HUM) fractions was measured by the dichromate oxidation method (Yeomans and Bremner 1988). The labile organic carbon ([C.sub.L]) was quantified by wet oxidation with KMn[O.sub.4] (33 mol/L) as described by Blair et al. (1995) and modified for tropical soils by Shang and Tiessen (1997). The non-labile carbon ([C.sub.NL]) equivalent to non-oxidised C by KMn[O.sub.4] was calculated by difference ([C.sub.NL] = TOC - [C.sub.L]). Based on the difference between the TOC olAF and the TOC of the cultivated systems, a carbon pool index (CPI) was calculated as CPI = TOC cultivated/TOC AF. According to changes in the proportion Of [C.sub.L] (i.e. L = [C.sub.L]/[C.sub.NL]) in the soil, a lability index (LI) was calculated as LI = L cultivated/L reference. These 2 indices were used to calculate the carbon management index (CMI) by the following formula: CMI = CPI x LI x 100 (Blair et al. 1995).

Total nitrogen (TN) was measured in the soil samples by the Kjeldhal method (Bremner 1996). The microbial biomass carbon ([C.sub.MIC]) was isolated by the irradiation-extraction method using microwave (Islam and Well 1998) and 0.5 mol/L of [K.sub.2]S[O.sub.4] as extractant. The [C.sub.MIC] content was determined by wet combustion (Yeomans and Bremner 1988). The conversion factor (Kc) used to convert the flow of C for [C.sub.MIC] was 0.33 (Spading and West 1988). The [C.sub.MIC]/TOC ratio or microbial quotient was calculated to indicate C inputs and the change of organic substrates for [C.sub.MIC] (Spading 1992). The free light fraction (FLF) was separated from the soil by flotation in NaI solution (SG = 1.8 [+ or -] 0.01) as proposed by Freixo et al. (2002). The siphoned FLF was dried at 80[degrees]C for 72 h, and the total carbon of the FLF ([C.sub.LF]) was determined by dry combustion in a Perkin Elmer 2400 CHNS/O Analyser.

The values of soil bulk density determined by the core method were used to compute the stocks of TOC, nitrogen (TN), and soil carbon pools on a unit area basis to all depths (Carter et al. 1998). Changes in soil carbon stocks of plot experiment were estimated at 0-0.20 m depth.

Statistical analyses

Significant differences in TOC, TN, and soil carbon pools among different amounts of mineral and organic composts combined or alone were identified using ANOVA F-test at P = 0.05 and P = 0.01, with 4 field replications.

Analysis of variance and F-test were performed using SAS (1999) to assess treatment effects on TOC, TN, and carbon pools. Significance was reported at P = 0.01 and 0.05 from each depth separately. Comparisons between cultivated and non-cultivated sites must be viewed with care because the secondary Atlantic Forest was not part of the experimental design in 1984 and sampling collection was performed differently.

Results and discussion


Previous studies on soil C stocks have emphasised the need to correct for the changes in bulk density induced by cultivation or traction of agricultural machinery (Ellert et al. 2002; Sisti et al. 2004). In this study, the values of soil bulk density varied between 1.05 and 1.07Mg/[m.sup.3] at 0-0.10m, and between 0.99 and 1.05 Mg/[m.sup.3] at 0.10-0.20m (Table 1). The differences in terms of soil mass would be 10 and 30 kg soil/ha at 0-0.10 and 0.10-0.20m, respectively. Thus, in this study, the results are presented on the basis of actual sampling depth.

Carbon and nitrogen inputs from maize cropped soil

Estimated carbon and nitrogen inputs by maize biomass increased as mineral fertiliser and organic compost were applied together. Average yearly inputs varied between 3.83 (control) and 9.84 (MF2 +OC) MgC/ha and 0.15 (control), and 0.39 (MF2+OC) MgN/ha (Table 2). The largest C and N inputs shown by soils under mineral and organic compost were also reflected in the largest values of total soil C and N (Table 3). Kanchikerimath and Singh (2001) reported similar results for soils of a long-term in the semi-arid region in India. However, care must be taken to assume that crop residues alone will aggrade soil organic matter. Compared to systems amended with compost, Fortuna et al. (2003) found that it would take several years to achieve changes in the dynamics of soil organic matter pools.

Total stocks of soil carbon and nitrogen

Soils under AF contained larger amounts of TOC and TN than the cultivated plots. Considering 0-0.20m soil depth (0-0.10m+0.10-0.20m), TOC stocks decreased 29, 31, 33, 26, 27, and 24% for 0, MF1, MF2, OC, MF1 +OC and MF2 + OC, respectively (Table 3). Similarly to TOC, TN varied between 35% (MF2) and 12% (MF2+OC) indicating lower losses in soils in which organic compost was applied. Decreases in TOC and TN after the conversion of forest to agriculture have been reported for Brazilian ecosystems (Leite et al. 2003; Zinn et al. 2005), and in this particular study lower amounts of C and N could also be due to monocropping with lower input of plant residues and intensive soil ploughing and harrowing. On the other hand, using as a reference TOC stocks at the beginning of the experiment (46 Mg C/ha), the application of organic compost caused an increase on TOC stocks at 0-0.20 m depth (Table 3).

Values of TOC were higher (P < 0.05) in MF2 + OC (25.02 and 23.86 MgC/ha) than in MF2 (23.07 and 20.17 Mg/ha) at 0-0.10 and 0.10-0.20m soil depth, respectively (Table 3). Stocks of soil nitrogen (TN) followed similar pattern only for 0-0.10 m soil layer (M F2 + OC 2.15 Mg/ha; MF2 1.73 Mg/ha). At 0.10-0.20m soil depth, with the application of compost, all soils showed higher carbon and nitrogen stocks (P < 0.05) than those soils that received only mineral fertilizer, or control soils. The magnitude of the differences at 0-0.10 m depth was not large, but the application of organic compost did cause an increase on TOC and TN. Among the main effects, compost had the largest impact on TOC and TN (Table 4). In Brazil, the addition of organic fertiliser to acid soils leads to an increase on soil organic matter in which the effect may not be significant with only one application, in a study about the effect of 40 years of farmyard manure, mineral, and mixed fertilisations on soil organic properties of a Fluvi-ealcaric Cambisol from north-eastern Italy, Nardi et al. (2004) also reported a larger influence of the organic treatment alone on total organic carbon than mineral fertiliser alone or mixed with farmyard manure. In contrast to the control treatment or the treatment in which only mineral fertiliser was applied and carbon input was only due to plant residues, the treatments with the application of organic compost received compost with diverse biochemical composition. In a study comparing different plant residues, Drinkwater et al. (1998) reported that large amounts of soil carbon from compost have larger residence time probably due to its partial decomposition or recalcitrant material.

Stocks of C in different pools

Cultivated soils showed lower [C.sub.MIC] than forest soil. At 0-0.10 m depth, compared with the forest soil, the decreases of [C.sub.MIC] were 55% (0), 41% (MF 1), 51% (MF2), 60% (Of), 55% (MF 1 + Of), and 52% (MF2 + OC), and at 0.104).20 m, the decreases were 51% (control), 40% (MF1), 38% (MF2), 54% (OC), 43% (MF1 +OC), and 46% (MF2 + OC) (Table 3). Similar losses were also reported by Rosa et al. (2003) on similar studies in the same biome. However, the magnitude of the losses in our study was smaller because of higher clay content (differences of 300 g clay/kg).

The stocks of [C.sub.MIC] were influenced by the application of compost and mineral fertiliser alone (Table 4), but under the experimental condition the effects were not strong enough to cause significant differences among treatments. These results are in contrast to other studies in which the microbial biomass and activity are higher with the application of organic compost (Graham et al. 2002). In the present study the lack of [C.sub.MIC] differences among treatments could be due to sampling undertaken soon after incorporation of plant residues. Also, the microwave irradiation technique used to measure soil microbial biomass, despite being a non-toxic treatment, may contain an appreciable portion of nonbiomass compounds that may lead to inaccuracies (Wang et al. 2001).

The stocks of [C.sub.LF] in soils under AF, similarly to TOC and [C.sub.MIC], were larger than those for cultivated soils. At 0-0.10m, the decreases were 89% (0), 88% (MFI), 87% (MF2), 81% (OC), 84% (MFI +OC), and 83% (MF2+OC). At 0.10-0.20 m, the decreases were 77% (control), 76% (MFI), 74% (MF2), 62% (OC), 65% (MF1 + OC), and 64% (MF2 + OC) (Table 3). Roscoe and Buurman (2003) reported similar results on acidic soil of the Brazilian Savannah (Cerrados). In forest soils there appear to be high amounts of particulate organic matter, plant residues, and root exudates that may result in high values for [C.sub.LF].

Values of [C.sub.LF] were higher (P < 0.05) with the application of organic compost than with the application of mineral fertiliser alone and the control treatment. At [C.sub.LF]).10 and 0.10-0.20 m depths, the largest stocks of [C.sub.LF] were found with the application of organic compost (2.14 and 1.87 Mg/ha) and the lowest in the control treatment (1.31 and 1.14 Mg/ha), respectively (Table 3). Similar results were reported by Wu et al. (2004) on Chinese loess soils with the application of 75 Mg compost/ha.year for 20 years resulting in the largest stocks of [C.sub.LF] (3.8 Mg/ha).

After conversion of forest into agriculture, C inputs are diminished while decomposition rate increases, thus leading to significant C decreases of the light fraction. Similar to reports by Freixo et al. (2002) and Leite et al. (2003), in this study the [C.sub.LF] pool was also more sensitive to changes in soil management than TOC and [C.sub.MIC] However, our results show that [C.sub.L], followed by TN, were the most sensitive variables to compost application at all depths, and among the main effects, compost alone showed significant influence on most of the measured soil variables (Table 4).

Soils under AF showed also higher [C.sub.MIC]/TOC ratio than cultivated soils at both 0-0.10m (2.57%) and 0.10-0.20m (2.36%). The highest [C.sub.MIC]/TOC ratios were shown by MF1 (2.31%) and MF2 (1.99%), and the lowest by OC (1.49% at 0-0.10m; 1.32% at 0.10-0.20 m) (Table 5). The [C.sub.MIC]/TOC ratio in different studies varies from 0.27 to 7.0% (Anderson and Domsch 1989) due to differences in soil types, soil management, vegetation cover, sampling time, and analytical procedure. Considering a [C.sub.MIC]/TOC ratio of 2.2% as soil organic matter in equilibrium (Jenkinson and Ladd 1981), only MFI and AF soils show soil organic matter in equilibrium with decomposition rate.

The values of [C.sub.LF]/TOC in the soils under AF were also higher than those for cultivated plots at all depths. Among the cultivated plots, soils that have received compost (OC soils) showed the highest values of [C.sub.LF]/TOC at both 0-0.10 m (8.76%) and 0.10-0.20m (8.11%). The lowest [C.sub.LF]/TOC ratio was found in the control soil (5.57% at 0-0.10m and 5.13% at 0.10-.20m). Soils that received no compost showed the highest [C.sub.MIC]/[C.sub.LF] ratio, considered indicators of substrate quality added to maintain microbial biomass (Table 5). This could be due to the low amounts of [C.sub.LF] in soils with only mineral fertiliser. However, low [C.sub.MIC]/[C.sub.LF] ratio was also found in soils under AF and with the application of organic compost (Table 5).

The FAF was the only humic substance to be significantly influenced by the treatments, and the application of organic compost alone had the largest impact on FAF (Table 4).

Apart from MF2 soils, soils with no application of organic compost showed the highest (P<0.05) stocks of FAF at 0-0.10m (Table 3). On the other hand, at 0.10-0.20m the stocks of FAF were higher (P < 0.05) under MF1 soils than MFI + OC soils. Organic fertilisation of soils affected the stocks of the HAF, although only the MF2 + OC soil (3.93 Mg/ha) showed higher values than MF2 treatment (2.91 Mg/ha) at 0-0.10 m. The stocks for both FAF and HAF of forest soils were higher than in cultivated soils. At 0-.20 m, the diminution varied from 8.07% (MF2) to 23.1% (MF2 + OC) for FAF stocks and from 1.85% (MF2 + OC) to 29.1% (control) for HAF stocks (Table 3). Similar decreases were reported by Islam and Weil (2000) at 0-0.15m in an Orthi-Ferric Acrisol in Bangladesh, but with a much higher magnitude for both FAF (77-156%) and HAF (30-79%) stocks. For the HUM fraction the diminutions in relation to AF soil were 19.8% (OC) and 33.4% (MF2). The largest amounts of TOC were presented in the humin fraction and varied from 49.73% (MF2 + OC) to (59.74% (OC) at 0-0.10m and from 54.8% (MFI + OC) to 60.9% (MFI) at 0.10-0.20 m (Table 6).

Soils with the application of organic compost showed higher stocks of labile organic carbon ([C.sub.L]) than those with the application of mineral fertiliser alone or the control treatment. The largest stocks of [C.sub.L] were found in MF2 + OC soils (1.79Mg[C.sub.L]/ha at 0-0.10m; 1.54Mg[C.sub.L]/ha at 0.10-0.20m) (Table 3). High amounts of labile organic carbon indicate that the soil shows good quality only if this fraction is able to provide plant nutrients and interfere with soil aggregate stability (Whitbread et al. 1998). The stocks Of [C.sub.L] in the forest soil were the highest. At 04). 10 m depth, the decrease due to cultivation was 48% for soils with no compost and 20% for soils with the application of organic compost. These results are lower than those reported by Whitbread et al. (2003) for lowland rice in Australia (79%) and for a wheat-legume system in Thailand (90%). The decrease in labile organic carbon is generally associated with aggregate disruption and greater organic matter oxidation after forest conversion into conventional agriculture with ploughing and several harrowings. At 0.10-0.20 m depth, however, only those soils with no application of organic compost showed a decrease in [C.sub.L] (13%) (Table 3). The diminution of [C.sub.L] was more significant than observed for TOC and [C.sub.NL]. Also, among all measured variables, [C.sub.L] was the most influenced by the application of compost, especially at 0-0.10 m (Table 4). However, the use of [C.sub.L] as an early warning indicator of soil organic matter changes cannot be generalised for all agroecosystems as, compared to [C.sub.LF], it does not provide sensible results for situations where organic carbon is increasing, such as under pasture (Skjemstad et al. 2006). Additionally, Mendham et al. (2002) reported that [C.sub.L] poorly related to the labile carbon fraction in similar soils. The 3 soil organic variables most influenced by the application of compost were [C.sub.L], TN, and [C.sub.LF] at both depths and this could be due to the high amounts of fresh residues leading to changes in [C.sub.L] and [C.sub.LF] and low C : N ratio that influenced TN. Fortuna et al. (2003), in a study about the effects of crop rotations and compost applications on soil-C sequestration and decomposition, found that the majority of compost application to the soil entered the particulate organic matter fraction. Among the soil organic variables, [C.sub.L], due to its relative tedious laboratory procedure would be the only technique to suffer from being widely used.

The CMI was largest in those soils with the application of organic compost and varied from 61 (0) to 106 (MF2+OC) at 0-0.20m (Table 7). Values of CMi <100 show negative impact of management practices on the stocks of soil carbon and hence on soil quality (Blair et al. 1995). To recommend CMI as an index requires more studies in more environments. In our case the positive impact indicated by CMI depended on the soil depth in which the index was applied. This needs more Clarification to separate soil management from laboratory procedure factors.


Conversion of Atlantic Forest into agroecosystems led to soil organic degradation and the use of compost alone aggraded SOM pools, except the fulvic acid fraction.

Compost alone showed the largest impact on soil organic variables and labile carbon followed by total nitrogen and light-fraction carbon were the most sensitive soil organic variables to compost application.

Manuscript received 23 March 2006, accepted 5 December 2006


Anderson TH, Domsch KH (1989) Ratios of microbial biomass carbon to total organic carbon in arable soils. Soil Biology and Biochemistry 21, 471-479. doi: 10.1016/0038-0717(89)90117-X

Balota EL, Colozi-Filho A, Andrade DS, Dick RP (2004) Long-term tillage and crop rotation effects on microbial biomass and C and N mineralization in a Brazilian Oxisol. Soil and Tillage Research 77, 137-145. doi: 10.1016/j.still.2003.12.003

Blair GJ, Lefroy RDB, Lisle L (1995) Soil carbon fractions based on their degree of oxidation, and development of a carbon management index for agricultural systems. Australian Journal of Agricultural Research 46, 1459-1466. doi: 10.1071/AR9951459

Bremner JM (1996) Nitrogen total. In 'Methods of soil analysis. Part 3'. (Ed. DL Sparks) pp. 1085 1121. (American Society of Agronomy: Madison, WI)

Carter MR, Gregorich EG, Angers DA, Donald RG, Bolinder MA (1998) Organic C and N storage, and organic fractions, in adjacent cultivated and forested soils of eastern Canada. Soil and Tillage Research 47, 253-261. doi: 10.1016/S0167-1987(98)00114-7

Christensen BT (2000) 'Organic matter in soil-structure, function and turnover.' DIAS Report No. 30. (Plant Production: Tjele)

Drinkwater LE, Wagoner P, Sarrantonio M (1998) Legume-based cropping systems have reduced carbon and nitrogen losses. Nature 396, 262-265. doi: 10.1038/24376

Ellert BH, Janzen HH, Entz T (2002) Assessment of a method to measure temporal change in soil carbon storage. Soil Science Society of America Journal 66, 1687-1695.

Fortuna A, Harwood RR, Paul EA (2003) The effects of compost and crop rotations on carbon turnover and the particulate organic matter traction. Soil Science 168, 434-444. doi: 10.1097/00010694-200306000-00005

Freixo AA, Machado PLOA, Santos HP, Silva CA, Fadigas FS (2002) Soil organic carbon and fractions of a Rhodic Ferralsol under the influence of tillage and crop rotation systems in southern Brazil. Soil and Tillage Research 64, 221-230. doi: 10.1016/S0167-1987(01)00262-8

Graham MH, Haynes R J, Meyer JH (2002) Soil organic matter content and quality: effects of fertilizer applications, burning and trash retention on a long-term sugarcane experiment in South Africa. Soil Biology and Biochemistry 34, 93-102. doi: 10.1016/S0038-0717(01)00160-2

Islam KR, Weil RR (1998) Microwave irradiation of soil for routine measurement of microbial biomass carbon. Biology and Fertility of Soils 27, 408-416. doi: 10.1007/s003740050451

Islam KR, Weil RR (2000) Land use effects on soil quality in a tropical forest ecosystem of Bangladesh. Agriculture, Ecosystems and Environment 79, 9-16. doi: 10.1016/S0167-8809(99)00145-0

Jenkinson DS, Ladd JN (1981) Microbial biomass in soils: measurement and turnover. In 'Soil biochemistry'. (Eds EA Paul, JN Ladd) pp. 415-417. (Marcel Dekker: New York)

Kanchikerimath M, Singh D (2001) Soil organic matter and biological properties after 26 years of maize wheat-cowpea cropping as affected by manure and fertilization in a Cambissol in semiarid region of India. Agriculture, Ecosystems and Environment 86, 155-162. doi: 10.1016/S0167-8809(00)00280-2

Leite LFC, Mendonca ES, Machado PLOA, Matos ES (2003) Total C and N storage and organic C pools of a Red-Yellow Podzolic under conventional and no tillage at the Atlantic Forest Zone, Southeastern Brazil. Australian Journal of Soil Research 41, 717-730. doi: 10.1071/SR02037

Maia CE (1999) Reserva e disponibilidade de nitrogenio pela adicao continuada de adubacao organica e da mineral na cultura do milho em um Podzolico Vermelho-Amarelo Cambico. MSc thesis, Vicosa, Universidade Federal de Vicosa.

Mendham DS, O'Connell AMO, Grove TS (2002) Organic matter characteristics under native forest, long-term pasture, and recent conversion to Eucalyptus plantations in Western Australia: microbial biomass, soil respiration, and permanganate oxidation. Australian Journal of Soil Research 40, 859-872. doi: 10.1071/SR01092

Nardi S, Morari F, Berti A, Tosoni M, Giardini L (2004) Soil organic matter properties after 40 years of different use of organic and mineral fertilizers. European Journal of Agronomy 21, 357-367. doi: 10.1016/j.eja.2003.10.006

Natarajan M, Wiley RW (1980) Sorghum-pigeonpea intercropping and the effects of plant population density--2: resource use. Journal of Agricultural Science 95, 59-55.

Oelbermann M, Voroney RP, Gordon AM (2004) Carbon sequestration in tropical and temperate agroforestry systems: a review with examples from Costa Rica and Southern Canada. Agriculture, Ecosystems and Environment 104, 359-377. doi: 10.1016/j.agee.2004.04.001

Rosa MEC, Olszevski N, Mendonca ES, Costa LM, Correia JR (2003) Formas de carbono em Latossolo Vermelho Eutroferrico sob plantio direto no sistema biogeografico do Cerrado. Revista Brasileira Ciencia Solo 27, 911-923.

Roscoe R, Buurman P (2003) Tillage effects on soil organic matter in density fractions of a Cerrado Oxisol. Soil and Tillage Research 70, 107-119. doi: 10.1016/S0167-1987(02)00160-5

SAS (1999) 'User's guide: basic and statistic.' (SAS: Cary, NC)

Shang C, Tiessen H (1997) Organic matter lability in a tropical oxisol: evidence from shifting cultivation, chemical oxidation, particle size, density, and magnetic fractionations. Soil Science 162, 795-807. doi: 10.1097/00010694-199711000-00004

Sisti CPJ, Santos HP, Kochhann R, Alves B JR, Urquiaga S, Boddey RM (2004) Change in carbon and nitrogen stocks in soil under 13 years of conventional or zero tillage in southern Brazil. Soil and Tillage Research 76, 39-58. doi: 10.1016/j.still.2003.08.007

Skjemstad JO, Swift RS, McGowan JA (2006) Comparison of the particulate organic carbon and permanganate oxidation methods for estimating labile soil organic carbon. Australian Journal of Soil Research 44, 255-263. doi: 10.1071/SR05124

Sohi S, Mahieu N, Arah JRM, Polwson DSP, Madari B, Gaunt JL (2001) A procedure for isolating soil organic matter fractions suitable for modeling. Soil Science Society of America Journal 65, 1121-1128.

Sparling GP (1992) Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter. Australian Journal of Soil Research 30, 195-207. doi: 10.1071/SR9920195

Sparling GP, West AW (1988) A direct extraction method to estimate soil microbial C:Calibration in situ using microbial respiration and [sup.14]C labelled cells. Soil Biology and Biochemistry 20, 337-343. doi: 10.1016/0038-0717(88)90014-4

Swift RS (1996) Organic matter characterisation. In 'Methods of soil analysis'. (Eds DL Sparks, AL Page, PA Helmke, RH Loeppert, PN Soltanpour, MA Tabatabai, CT Johnston, ME Summer) pp. 1011-1020. (Soil Science Society of America/American Society of Agronomy: Madison, WI)

Tarre R, Macedo R, Cantarutt RB, Rezende CdeP, Pereira JM, Ferreira E, Alves B JR, Urquiaga S, Boddey RM (2001) The effect of the presence of a forage legume on nitrogen and carbon levels in soils under Brachiaria pastures in the Atlantic forest region of the South of Bahia, Brazil. Plant and Soil 234, 15-26.

Theng KG, Tate KR, Sollins P, Moris N, Nalini N, Tate RL II (1989) Constituents of organic matter in temperate and tropical soils. In 'Dynamics of soil organic matter in tropical ecosystems'. (Eds DC Coleman, JM Oades, G Uehara) pp. 5 32. (NifTAL Project-Department of Agronomy and Soil Science, University of Hawaii: Honolulu)

Vance ED, Brookes PC, Jenkinson DS (1987) An extraction method for measuring soil microbial biomass C. Soil Biology and Biochemistry 19, 703 707. doi: 10.1016/0038-0717(87)90052-6

Wang W, Dalai RC, Moody PW (2001) Evaluation of the microwave irradiation method for measuring soil microbial biomass. Soil Science Society of America Journal 65, 1697-1703.

Whitbread A, Lefroy RDB, Blair GJ (1998) A survey of the impact of cropping on soil physical and chemical properties in north-western New South Wales. Australian Journal of Soil Research 36, 669-681. doi: 10.1071/S97031

Whitbread A, Blair G, Yothin K, Lefroy R, Naklang K (2003) Managing crop residues, fertilizers and leaf litters to improve soil C, nutrient balances, and the grain yield of rice and wheat cropping systems in Thailand and Australia. Agriculture, Ecosystems and Environment 100, 251-263. doi: 10.1016/S0167-8809(03)00189-0

Wu T, Schorneau JJ, Fengmin L, Quian P, Malhi SS, Shi Y, Xu F (2004) Influence of cultivation and fertilization on total organic carbon and carbon fractions in soils from the Loess Plateau of China. Soil and Tillage Research 77, 59-68. doi: 10.1016/j .still .2003.10.002

Yeomans JC, Bremner JM (1988) A rapid and precise method for routine determination of organic carbon in soil. Communications in Soil Science and Plant Analysis 19, 1467-1476.

Yokoyama LP, Stone LF (2000) 'Cultura do feijoeiro no Brasil--Caracteristicas da producao.' (Embrapa Arroz e Feijao: Santo Antonio de Goias, Brazil)

Zinn YL, Lal R, Resck VS (2005) Changes in soil organic carbon stocks under agriculture in Brazil. Soil and Tillage Research 84, 28-40. doi: 10.1016/j.still.2004.08.007

L. F. C. Leite (A,D), E. S. Mendonca (B), and P. L. O. A. Machado (C)

(A) Embrapa Middle-North, Caixa Postal 01, Teresina 64006-220, PI, Brazil.

(B) Departamento de Solos, Universidade Federal de Vicosa, 36571-000 Vicosa, MG, Brazil.

(C) Embrapa Rice and Beans, Caixa Postal 179, 75375-000 Santo Antonio de Goias, GO, Brazil.

(D) Corresponding author. Email:
Table 1. Soil bulk density of a Ferric Acrisol in the 0-0.10 and
0.10-0.20m layers as affected by different fertiliser treatments in an

Within a column, means followed by the same letters are not
different by F-test at P = 0.05. AF Atlantic Forest; 0, control; MFI,
mineral fertilisation, 10 kg N/ha, 15 kg P/ha, and l7 kg K/ha; MF2,
mineral fertilisation, 20 kg N/ha, 30 kg P/ha, and 34 kg K/ha; OC,
organic compost, 40 [m.sup.3]/ha

 Bulk density (Mg/[m.sup.3])
Treatment 0-0.10 m 0.10-0.20 m

Control 1.07a 1.04a
MFI 1.06a 0.99a
MF2 1.06a 1.01a
0C 1.05a 1.04a
MFI + OC 1.05a 1.05a
MF2 + OC 1.05a 1.04a

Table 2. Grain yield and estimated annual carbon (C) and nitrogen
(N) inputs (Mg/ha) to the soil from maize cropped in southern Brazil

0, Control; MF1, mineral fertilisation, 10kg N/ha, 15kg P/ha, and
17 kg K/ha; MF2, mineral fertilisation, 20 kg N/ha, 30 kg P/ha, and
34 kg K/ha; OC, organic compost, 40 [m.sup.3]/ha

 Grain Shoots (A) Roots (A) Total
Treatment yield C N C N C N

Control 2.92 3.29 0.13 0.55 0.02 3.83 0.15
MFI 4.52 5.09 0.20 0.85 0.03 5.93 0.24
MF2 5.85 6.58 0.26 1.10 0.04 7.68 0.31
OC 6.09 6.85 0.27 1.14 0.05 7.99 0.32
MF1 + OC 7.18 8.08 0.32 1.35 0.05 9.42 0.38
MF2 + OC 7.50 8.44 0.34 1.41 0.06 9.84 0.39

(A) Considering a C and N content of 50% and 2%, respectively, in the
plant tissues.

Table 3. Stocks of carbon and nitrogen, and carbon pools of a Ferric
Acrisol at 0-0.10 and 0.10-0.20m layers as affected by different
fertiliser treatments in an intercrop

For each pool, means within columns followed by the same letters are
not different by F-test at P=0.05. AF: Atlantic Forest; 0, control;
MF1, mineral fertilisation, 10 kg N/ha, 15 kg P/ha, and 17 kg K/ha;
MF2, mineral fertilisation, 20 kg N/ha, 30 kg P/ha, and 34 kg K/ha; OC,
organic compost, 40 [m.sup.3];/ha

 Mineral fertilisation
compost 0 1 2 Mean

 Total organic carbon (TOC, Mg C/ha)
AF 35.00 [+ or] 5.29
0 23.43a 22.90a 23.07b 23.13
OC 24.40a 24.39a 25.02a 24.60
Mean 23.91 23.64 24.04 --

 Total nitrogen (TN, Mg N/ha)
AF 2.59 [+ or] 0.41
0 1.73a 1.77a 1.73b 1.74
OC 1.94a 1.95a 2.15a 2.01
Mean 1.83 1.86 1.94 --

 Microbial biomass carbon
 ([C.sub.MIC], Mg/ha)
AF 0.90 [+ or] 0.19
0 0.40a 0.53a 0.44a 0.46
OC 0.36a 0.40a 0.44a 0.40
Mean 0.38 0.46 0.44 --

 Light fraction carbon
 ([C.sub.LF], Mg/ha)
AF 11.74 [+ or] 0.31
0 1.31b 1.40b 1.47b 1.39
0C 2.14a 1.81a 1.92a 1.96
Mean 1.85 1.60 1.69 --

 Fulvic acids fraction (FAF Mg/ha)
AF 3.80 [+ or] 0.56
0 3.63a 3.58a 3.59a 3.60
OC 3.066 2.90b 3.59a 3.18
Mean 3.34 3.24 3.59 3.18

 Humic acids fraction (HAF Mg/ha)
AF 3.70 [+ or] 0.39
0 2.70a 2.94a 2.91a 2.85
OC 3.09a 2.70a 3.93a 3.24
Mean 2.89 2.82 3.42 --

 Humin fraction (HUM, Mg/ha)
AF 18.10 [+ or] 2.10
0 12.67a 13.27a 11.98a 12.64
OC 14.58a 13.84a 12.44a 13.62
Mean 13.62 13.55 12.21 --

 Labile carbon ([C.sub.L], Mg/ha)
AF 2.10 [+ or] 0.02
0 0.92b 1.21b 1.11b 1.08
OC 1.73a 1.56a 1.79a 1.69
Mean 1.32 1.38 1.45 --

 Non-labile carbon ([C.sub.NL], Mg/ha)
AF 32.90 [+ or] 2.42
0 22.51b 21.68b 21.96b 22.05
OC 22.67a 22.83a 23.23a 22.91
Mean 22.59 22.25 22.59 --

 Mineral fertilisation
compost 0 1 2 Mean

 Total organic carbon (TOC, Mg C/ha)
AF 27.21 [+ or] 2.00
0 22.19a 21.00a 20.17b 21.12
OC 23.03a 22.63a 23.86a 23.17
Mean 22.61 21.81 22.00 --

 Total nitrogen (TN, Mg N/ha)
AF 2.19 [+ or] 0.16
0 1.58b 1.53b 1.47b 1.53
OC 1.76a 1.84a 2.12a 1.90
Mean 1.67 1.67 1.79 --

 Microbial biomass carbon
 ([C.sub.MIC], Mg/ha)
AF 0.65 [+ or] 0.10
0 0.32a 0.39a 0.40a 0.37
OC 0.30a 0.37a 0.35a 0.34
Mean 0.31 0.38 0.38 --

 Light fraction carbon
 ([C.sub.LF, Mg/ha)
AF 5.02 [+ or] 0.57
0 1.15 1.17b 1.31b 1.21
0C 1.87a 1.74a 1.78a 1.80
Mean 1.50 1.45 1.54 --

 Fulvic acids fraction (FAF Mg/ha)
AF 3.65 [+ or] 0.15
0 3.32a 3.44a 3.51a 3.42
OC 2.96a 3.00b 3.17a 3.04
Mean 3.14 3.22 3.34 --

 Humic acids fraction (HAF Mg/ha)
AF 3.15 [+ or] 0.22
0 2.26a 2.66a 2.30a 2.41
OC 3.02a 2.71a 2.95a 2.89
Mean 2.64 2.68 2.62 --

 Humin fraction (HUM, Mg/ha)
AF 15.62 [+ or] 2.35
0 13.20a 12.80a 11.60a 12.53
OC 13.14a 12.40a 13.71a 13.08
Mean 13.17 12.60 12.65 --

 Labile carbon (C.sub.L], Mg/ha)
AF 1.18 [+ or] 0.04
0 1.01b 0.996 1.06b 1.02
OC 1.38a 1.42a 1.54a 1.45
Mean 1.19 1.20 1.30 --

 Non-labile carbon ([C.sub.NL], Mg/ha)
AF 26.08 [+ or] 1.39
0 21.18a 20.01b 19.10b 20.09
OC 21.66a 21.21a 22.32a 21.73
Mean 21.42 20.61 20.71 --

Table 4. Variance analyses of F-statistic for effect on total carbon
and nitrogen and organic carbon pools of a Ferric Acrisol at different

TOC, Total organic carbon; TN, total nitrogen; [C.sub.MIC],
microbial biomass carbon; [C.sub.LF], light fraction carbon; FAF,
fulvic acids fraction; HAF, humic acids fraction; HUM, humin fraction;
[C.sub.L], labile carbon

 [C.sub. [C.sub.
Source of variation TOC TN MIC] LF]
Organic compost 7.17 * 18.28 * 6.60 ** 16.71 *
Mineral fertilisation 0.16 n.s. 0.88 n.s. 4.26 ** 0.28 n.s.
Organic x mineral 0.91 n.s. 2.13 n.s. 2.59 n.s. 0.73 n.s.

Organic compost 4.74 ** 22.60 * 1.22 n.s. 18.92 *
Mineral fertilisation 0.73 n.s. 0.78 n.s. 2.29 n.s. 0.17 n.s.
Organic x mineral 1.23 n.s. 3.95 ** 0.18 n.s. 0.30 n.s.

Source of variation FAF HAF HUM [C.sub.L]

Organic compost 7.99 * 3.92 n.s. 1.16 n.s. 243.04 *
Mineral fertilisation 1.78 n.s. 3.51 n.s. 1.08 n.s. 3.02 n.s.
Organic x mineral 2.73 n.s. 3.73 n.s. 0.12 n.s. 11.13 *

Organic compost 10.89 * 4.11 * 0.23 n.s. 33.05 *
Mineral fertilisation 0.55 n.s. 0.03 n.s. 0.36 n.s. 0.75 n.s.
Organic x mineral 0.05 n.s. 0.91 n.s. 0.98 n.s. 0.23 n.s

n.s. * P < 0.05, ** P < 0.01; n.s., not significant at P = 0.05.

Table 5. Proportion of the microbial biomass carbon in the total
organic carbon ([C.sub.MIC]/TOC), proportion of the light fraction
carbon in the total organic carbon ([C.sub.LF]/TOC), and proportion of
the microbial biomass carbon in the light fraction carbon ([C.sub.MIC]/
[C.sub.LF]), of a Ferric Acrisol in the 0-0.10, 0.10-0.20, and 0-0.20m
layers, as affected by different fertiliser treatments in an intercrop

AF, Atlantic Forest; 0, control; MFI, mineral fertilisation, 10kgN/ha,
15 kg P/ha, and 17 kg K/ha; MF2, mineral fertilisation, 20 kg N/ha,
30 kg P/ha, and 34 kg K/ha; OC, organic compost, 40 [m.sup.3]/ha

Treatment [C.sub.MIC]/ [C.sub.LF]/ [C.sub.MIC]/
 TOC TOC [C.sub.LF]

AF 2.57 33.54 0.08
0 1.71 5.57 0.31
MF1 2.31 6.11 0.38
MF2 1.90 6.38 0.30
OC 1.49 8.76 0.17
MF1 + OC 1.64 7.40 0.22
MF2 + OC 1.71 7.68 0.22
1.s.d. 0.65 3.27 0.09

AF 2.36 18.47 0.13
0 1.43 5.13 0.28
MF1 1.84 5.58 0.33
MF2 1.99 6.52 0.31
OC 1.32 8.11 0.16
MF1 + OC 1.64 7.71 0.21
MF2 + OC 1.47 7.48 0.19
1.s.d. 0.59 3.10 0.11

AF 2.47 27.77 0.09
0 1.57 5.35 0.29
MF1 2.08 5.86 0.35
MF2 1.95 6.45 0.30
OC 1.41 8.44 0.17
MF1 + OC 1.64 7.55 0.22
MF2 + OC 1.60 7.58 0.21
1.s.d. 0.54 3.13 0.13

Table 6. Proportion of the total fulvic acids (FAF), humic acids
(HAF), and humin (HUM) fractions in relation to the total organic
carbon (TOC) and humic acid and fulvic acid relationship (HAF/FAF) of a
Ferric Acrisol in the 0-0.10, 0.10-0.20, and 0-0.20 m layers, as
affected by different fertiliser treatments in an intercrop

AF, Atlantic Forest; 0, control; MF1, mineral fertilisation, 10kg N/ha,
15 kg P/ha, and 17 kg K/ha; MF2, mineral fertilisation, 20 kg N/ha,
30 kg P/ha, and 34 kg K/ha; OC, organic compost, 40 m;/ha


AF 10.86 10.57 51.71 73.14 0.97
0 15.48 11.58 54.09 81.14 0.75
MF1 15.65 12.84 57.95 86.44 0.82
MF2 15.54 12.60 51.93 80.07 0.81
OC 12.53 12.65 59.74 84.93 1.01
MF1 + OC 11.91 10.99 56.74 79.65 0.92
MF2 + OC 14.34 15.71 49.73 79.78 1.10
1.s.d. 3.61 4.02 5.15 4.12 0.39

AF 13.41 11.58 57.41 82.43 0.97
0 14.95 10.20 59.50 84.66 0.68
MF1 16.37 12.66 60.94 89.97 0.77
MF2 17.40 11.41 57.52 86.33 0.66
OC 12.85 1311 57.03 82.99 1.02
MF1 + OC 13.24 12.00 54.80 80.03 0.91
MF2 + OC 13.30 12.38 57.46 83.14 0.93
1.s.d. 2.95 2.98 4.13 4.98 0.37

AF 12.01 10.96 54.07 77.04 0.92
0 15.22 10.90 56.75 82.87 0.72
MF1 16.00 12.75 59.40 88.14 0.80
MF2 16.42 12.03 54.58 83.03 0.73
OC 12.69 12.88 58.42 83.98 1.02
MF1 + OC 12.55 11.48 55.81 79.83 0.91
MF2 + OC 13.83 14.08 53.51 81.42 1.02
1.s.d. 3.15 3.12 4.55 5.11 0.31

Table 7. Proportion of the labile carbon in the total organic carbon
([C.sub.L]/TOC) and carbon management index (CMI) of a Ferric Acrisol
in the 0-0.10, 0.10-0.20, and 0-0.20m layers, as affected by different
fertiliser treatments in an intercrop system

AF, Atlantic Forest; 0, control; MFI, mineral fertilisation, 10kg N/ha,
15 kg P/ha, and 17 kg K/ha; MF2, mineral fertilisation, 20kg N/ha,
30 kg P/ha, and 34 kg K/ha; OC, organic compost, 40 [m.sup.3];/ha

 [C.sub.L]/ Index
Treatments TOC CPI L LI CMI

AF 6.00 -- 0.06 -- --
0 3.94 0.64 0.04 0.64 41
MF1 5.30 0.62 0.06 0.88 54
MF2 4.82 0.62 0.05 0.79 49
OC 7.09 0.66 0.08 1.19 78
MF1 + OC 6.39 0.66 0.07 1.07 71
MF2 + OC 7.16 0.68 0.08 1.20 82
1.s.d. 2.33 0.08 0.02 0.29 13

AF 4.34 -- 0.04 -- --
0 4.55 1.01 0.05 1.06 107
FM1 4.72 0.93 0.05 1.10 103
FM2 5.27 0.90 0.06 1.24 111
OC 5.98 1.03 6.00 1.41 145
MF1 + OC 6.27 1.00 7.00 1.49 148
MF2 + OC 6.46 1.05 7.00 1.53 161
1.s.d. 2.21 0.09 0.02 0.27 17

 0-0.20 m
AF 5.36 -- 0.06 -- --
0 4.24 0.78 0.04 0.78 61
MF1 5.02 0.74 0.05 0.93 68
MF2 5.03 0.72 0.05 0.93 67
OC 6.55 0.80 0.07 1.23 98
MF1 + OC 6.33 0.79 0.07 1.19 94
MF2 + OC 6.82 0.82 7.00 1.28 106
1.s.d. 2.39 0.11 0.02 0.21 14
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Author:Leite, L.F.C.; Mendonca, E.S.; Machado, P.L.O.A.
Publication:Australian Journal of Soil Research
Geographic Code:3BRAZ
Date:Feb 1, 2007
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