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Soil organisms in organic and conventional systems SOIL ORGANISMS IN ORGANIC AND CONVENTIONAL
CROPPING SYSTEMS
Wagner Bettiol1,2*; Raquel Ghini1,2; José Abrahão Haddad Galvão1; Marcos Antônio VieiraLigo1; Jeferson Luiz de Carvalho Mineiro1 1Embrapa Meio Ambiente, C.P. 69 - CEP: 13820-000 - Jaguariúna, SP. 2CNPq Fellow.
*Corresponding author <[email protected]> ABSTRACT: Despite the recent interest in organic agriculture, little research has been carried out in this area.
Thus, the objective of this study was to compare, in a dystrophic Ultisol, the effects of organic and conventionalagricultures on soil organism populations, for the tomato (Lycopersicum esculentum) and corn (Zea mays)crops. In general, it was found that fungus, bacterium and actinomycet populations counted by the number ofcolonies in the media, were similar for the two cropping systems. CO evolution during the cropping season was higher, up to the double for the organic agriculture system as compared to the conventional. The numberof earthworms was about ten times higher in the organic system. There was no difference in the decompositionrate of organic matter of the two systems. In general, the number of microartropods was always higher in theorganic plots in relation to the conventional ones, reflectining on the Shannon index diversity. The higherinsect population belonged to the Collembola order, and in the case of mites, to the superfamily Oribatuloidea.
Individuals of the groups Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura and Symphyla were occasionallycollected in similar number in both cropping systems.
Key words: soil microorganisms, organic agriculture, microartropods, cropping systems, environmental impacts ORGANISMOS DO SOLO EM SISTEMAS DE CULTIVO
ORGÂNICO E CONVENCIONAL
RESUMO: Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisadisponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitosde sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e domilho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantespara os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada nosistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistemaorgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas.
De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que nosistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações deinsetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamíliaOribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foramocasionalmente coletados e de forma similar entre os sistemas.
Palavras-chave: microbiota do solo, agricultura orgânica, microartrópodos, sistemas de cultivo, impacto ambiental INTRODUCTION
the use of highly soluble fertilizers, pesticides and growthregulators must be excluded in this system (Paschoal, Contamination of the water-soil-plant system with 1995). Not only does the system have to satisfy the need pesticides and fertilizers, in addition to breaking up the for reducing the environmental negative-impact problems soil structure due to inadequate use of machinery and caused by intensive agriculture, it must also be implements, is one of the main problems caused by economically competitive. In comparing the organic and intensive agriculture. The implementation of integrated the conventional cropping systems, an important step is cropping systems and the reduction of the external to establish which social, economic and ecological factors energy requirements have been suggested to minimize influence the production systems the most. Besides, a these problems. The organic cropping system is defined knowledge of those factors allows for a better as a production system that is sustainable in time and understanding of how the production systems are space, by means of management and protection of the natural resources, without the use of chemicals that are With respect to the biological activity, in studies aggressive to humans and to the environment, retaining to compare the conventional, integrated and organic fertility increases, soil life and biological diversity. Thus, cropping systems, Bokhorst (1989) found that the number Scientia Agricola, v.59, n.3, p.565-572, jul./set. 2002
of worms in a soil planted with sugar beets was five times before liming: pH (CaCl ) 4.4; OM 0.6%; P (resin) 1 µg higher in the organic system than in other systems, and cm-3; K 0.5; Ca 7; Mg 7; H + Al 28; CEC 43 and S 15 that the percentage of wheat and potato roots infected mmol dm-3 of soil; and V 35%. The studies were with arbuscular mycorrhizae was twice as high in the conducted from January 1993 to September 1995.
organic as compared to the conventional and integrated The experiment was set up as randomized blocks systems. Gliessman et al. (1990, 1996), working with with six replicates, and plots measuring 25 x 17 m. Tomato similar objectives, compared conventional and organic planting pits were spaced 0.5 m apart with 1.20 m between strawberry cropping systems in areas where farmers rows. Each plot was split in two halves, the first 12.5 x 17 became organic producers, and verified an increase in m-half being planted with the variety Débora and the other the number of plants infected with mycorrhizae. Swezey planted with the variety Santa Clara. Therefore, each of et al. (1994) found higher microbial biomass in the soil the twelve rows contained 17 planting pits for each variety.
and in arbuscular mycorrhizae in the organic system than The edging between plots was 10 m wide and was planted in the conventional, in an area being changed from with sorghum. Two tomato plants were transplanted per conventional into an organic apple growing area. All these pit. The tomato crop was conducted using the stake studies emphasize the biological elasticity in the organic system, with one or two stems/plant. The number of stems systems as a fundamental characteristic, influencing the was determined based on the successful establishment of the seedlings. Furrow irrigation and plant pruning were With regard to soil organisms, Brussaard et al.
(1988, 1990) verified that the total biomass of soil The entire area received 4.2 t ha-1 lime and 2 kg organisms was higher for the integrated than for the per meter, 110 and 12 days before planting, respectively.
conventional cropping system, with figures averaging 907 Fertilization in the organic system employed 2.5 L of kg C ha-1 and 690 kg C ha-1, respectively. Of these organic compost (pH=6.4; C=29.6%; N=1.6%; P O =1.8; biomasses, bacteria accounted for over 90%, fungi K O=0.17% and U=25.3%) plus 130 g of single represented approximately 5% and protozoa were less superphosphate/pit; additionally, 2.5 L of organic than 2% of the total biomass. El Titi & Ipach (1989) studied compost, 60 g of single superphosphate, and 60 g of the effect of a cropping system with low input rate index dolomitic lime/pit were applied as sidedressing; plants as well as the conventional system on the soil fauna were sprayed twice a week with biofertilizer (Bettiol et al., components and observed there were smaller populations 1997), at concentrations of 5 or 10%. In the conventional of nematodes pathogenic to plants, higher worm biomass, system, fertilization consisted of 200 g 4-14-8 (NPK)/pit and larger populations of collembolans and Mesostigmata and, after planting, a sidedressing application of 30 g N, mites in the system with low input index. Collembola is a 33 g K and 10.5 g P/pit; 52 days after planting and microarthropod related to the soil’s capacity to suppress beyond, plants were sprayed once a week with foliar Rhizoctonia solani (Lartey et al., 1994). Rickerl et al. (1989) fertilizer [5-8-0,5 (NCaB)] at a rate of 3 mL L-1.
found that populations of this organism were 29% larger In the conventional system, 0.15g/pit of active in soils under minimum tillage as compared to soils under ingredient of the insecticide carbofuram were applied conventional tillage. Ladd et al. (1994) verified that the C before planting. According to the procedures utilized by biomass of microbial populations was greater in soils under conventional local growers, a blend of insecticides, crop rotation than in soils under continuous monoculture; fungicides and miticides was sprayed twice a week, after greater in soils where plant residues were incorporated or planting. Active ingredients of fungicides sprayed during remained on the soil surface than where they were the crop cycle were metalaxyl, mancozeb, chlorothalonil, removed; and smaller in a nitrogen-fertilized soil than in copper oxychloride, kasugamycine, cuprous oxide, methyl non-fertilized ones. This information is important because thyophanate, iprodione, benomyl, cymoxamil, maneb and these are characteristics that contribute to soil biological monohydrate zinc sulphate, at the rates recommended equilibrium, nutrient mineralization and suppressive by the manufacturers. Insecticides used were capacity toward plant pathogens, among others, making deltamethrin, permethrin, methomyl, methamidophos, the system less dependent on external input.
acephate, avermectin and cartap, also at the The objective of this work was to evaluate the influence of the organic and the conventional cropping Extracts of black pepper, Eucalyptus, garlic and systems, for tomato and corn, on the community of soil fern; Bordeaux mixture, and biofertilizer were applied twice a week (Bettiol et al., 1997; Abreu Junior, 1998) tocontrol diseases and pests in the organic system. These MATERIAL E METHODS
applications were performed according to the programadopted by organic producers in the region.
The experiment was carried out in Jaguariúna, Weed control was carried out by mechanical SP, Brasil, latitude 22° 41' S, longitude 47° W Gr., and weeding and with the herbicide glyphosate (directed an altitude of 570 m, on a dystrophic Ultisol, with the spray) on post-planting in the conventional system, and following chemical properties of the 0-0.2 m topsoil layer, with mechanical weeding in the organic system.
Scientia Agricola, v.59, n.3, p.565-572, jul./set. 2002
Soil organisms in organic and conventional systems After harvesting the tomato the area was planted animals to leave the soil. Samples remained in the extractor with ‘BR 201’ corn; sowing occurred 178 days after for 72 hours. An alcohol:glycerin (1:1) aqueous solution was planting the tomatoes. The organic system plots received used for specimen preservation. After extraction, the animals an application of 4 m3 of organic compost and single were counted and separated into groups with the use of a superphosphate at the rate of 20 g per meter; in addition, stereoscopic microscope. Mites and other smaller animals the biofertilizer was sprayed at 10% as sidedressing. In were fixed on permanent slides for identification. Data were the conventional system fertilization consisted of 500 kg expressed as number of individuals per 785 cm3 soil.
ha-1 of the 4-14-8 NPK rate applied pre-planting and 15 g Shannon’s diversity index (Shannon & Weaver, 1949) was m-1 urea as sidedressing. Weed control used the herbicide calculated for a better understanding of the variations in the paraquat (directed spray) in the conventional system, and mechanical weeding was used in the organic.
Organic matter decomposition rate estimate: The After harvesting the corn, ‘Débora’ tomatoes were decomposition rate was estimated via loss of organic again cultivated, as previously described. Transplantation content from leaf litter confined in nylon bags, 20 x 20 was made 401 days after the initial tomato planting.
cm, with a 1 mm mesh, where 10 g of elephant grassdried at 60°C for three days. The field-collected samples, Soil Microorganisms
were collected every 20 days and transported to the A sample composed of 20 sub-samples of soil laboratory, dried at 105°C for 24 hours and ashed at taken at the planting row from the 0-7 cm-depth layer was 600°C for 4 hours. The loss of organic matter estimate obtained for each plot. Samples were placed in plastic was calculated using the equation described by Santos bags and immediately transported to the laboratory.
& Whitford (1981), which corrects for the adhesion of soil Assessments were performed within 24 hours after Evaluation of earthworms in the soil: The first Populations of fungi, bacteria and actinomycetes: evaluation was carried out 81 days before the first The populations of fungi, bacteria and actinomycetes were planting, i.e., before plowing and liming. A hand excavator quantified through the serial-dilution method, followed by was used to collect samples; two samples were collected plating in culture medium. Martin’s culture medium (Tuite, from each plot, up to a depth of 20 cm, with 20 cm 1969) added of 100 mg mL-1 streptomycine was used for diameter. Shortly after planting the tomatoes, and 90 days fungi; for bacteria, the agar nutrient medium added of later, samples were taken at about 40 cm depth, with a nistatin (42 mg L-1) was used; for the actinomycetes, the diameter of 10 cm. Three samples were collected from alkalized agar-water medium was utilized. Aliquots (0.1 the compost: one from the pile surface; another at a layer mL) from three dilutions, for each soil sample, were up to 35 cm, and the third at a depth of 90 cm. The worm transferred to the culture media in three replications.
populations were determined 370, 407, and 471 days Assessments were performed by counting the number of colonies per Petri dish and expressed as colony-formingunits/g of dry soil (CFU g-1 dry soil).
RESULTS AND DISCUSSION
Total respiratory activity: Total microbial respiration was evaluated according the method described by Grisi (1978). Soil samples (200 g) were actinomycetes were similar for the two cropping systems incubated for 10, 20, and 30 days within tightly sealed over the entire period of study, with populations of fungi containers holding 10 mL of a 0.5 mol L-1 (10 mL) KOH varying from 104 to 105, whereas populations of bacteria and solution. At 10-day intervals, the solution was substituted actinomycetes varied from 105 to 107 CFU g-1 dry soil (Figure and titrated with 0.1 mol L-1 of HCl. Incubation was 1). Similar results were obtained by Castro et al. (1993), conducted in the dark, at 25°C. This parameter was when several types of soybean management were expressed as g CO (g dry soil-1) (day-1). Since the more compared, and by Cattelan & Vidor (1990) on soils substantial changes happened in the first days, only cultivated with different crop rotation systems. Grigorova & readings up to the tenth day were used to determine Norris (1990) justified not adopting this method for mean values. For the statistical analysis, data were evaluating soil microorganisms, because only a small transformed into square root (x + 0.5) and subjected to fraction of microbial biomass could be cultivated on a analysis of variance and Duncan’s mean comparison test.
selective medium. However, Cattelan & Vidor (1990) Soil microarthropods: Collecting was made with a demonstrated the effectiveness of the method in studies with Uhland-type, stainless steel auger 5 cm in diameter and 10 different cropping systems. In spite of a similar behavior in cm in height, totaling four samples per plot. Samples were regard to microbial populations, starting 145 days after placed in plastic bags and taken to the laboratory. Collecting planting the tomatoes, the bacteria populations (Figure 1 C) was between 8:00 and 10:30 h, 82 days before and 325 were higher in the organic system as compared to the days after the first tomato seeding, for a total of 16 conventional. This could be due to soil plant cover, like evaluations. Extraction was according to Tullgren’s modified Cattelan & Vidor (1990) who found a smaller bacterial method, which uses heat and desiccation to force the population on naked as compared to cultivated soil.
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Soil total respiratory activity continued higher in the organic system during the crop cycles, showing in some evaluations twice as much as the evolution observed in the conventional system (Figure 2). Differences were found during the intermediate period, that is, between 142 and 400 days after planting. There were no statistical Log10 CFU/g of soil 4,2
differences between treatments at the initial periods or at the end. The higher respiratory rate in the organic system could be due to the addition of an exogenous source of organic matter to the soil and the consequent stimulationof heterotrophic microorganisms (Lambais, 1997).
Observed organic matter decomposition rates ranged from 15 to 45% of organic carbon loss in a 20-day period. Rodrigues et al. (1997) observed, in corn cultivatedduring the summer, values reaching 70% of carbon loss Log10 CFU/g of soil
in a period of 30 days. There was no difference among results from the organic and the conventional systems (Figure 3). However, regardless of the system, there was an influence of time on the organic matter decomposition rate was, although no interaction between time and the treatments was found. This suggests that variations found during the study period could be related to the humidity and temperature fluctuations that occur in the field, thus Log10 CFU/g of soil
providing no evidence that the adopted management forms The CO release method used in this study to Days after planting
evaluate respiratory activity favors the microorganism Figure 1 - Dynamic population of fungi, bacteria and actinomycetes population, since soil manipulation can eliminate the in soil from organic (- - -) and conventional ( ) cropping majority of the microarthropod community. Several systems for tomato and corn. CFU: Colony Forming Units.
A=Fungi; B=Actinomycetes; C=Bacteria. The data authors have, in microcosmos studies, demonstrated the represent the mean of six replicates. The bars indicate role microarthropods in soil organic matter decomposition process. A low fungivore density (Collembola) has astimulating effect on microbial respiration, whereas high densities inhibited microorganism respiration Barsdate et al, 1974; Hanlon & Anderson, 1979).
Mites and insects, belonging to various families, were the two main groups of arthropods found in the soil in 1993 and 1994 (Tables 1 and 2). In general, rates and numbers of individuals from these groups were higher in the organic cropping system, reflecting on Shannon’s diversity indices, which were higher in the organic system on all sampling dates (Figure 4), but not on the soil organic matter decomposition (Figure 3).
The largest populations of insects were from the Order Collembola, and the number of individuals found in Figure 2 - CO evolution from soil microorganisms of organic- the organic system was three times as high as that in the and conventional systems for tomato and corn crops.
conventional system, during the first nine months (Table Results were obtained though soil incubation at 25°C 1). During the following six months, the number of for 10 days. For each planting time, data followed thesame letter did not differ (Duncan 5%).
collembolans remained 20% higher in the organic croppingsystem than in the conventional (Table 2). These data because these organisms are, for the most part, agree with El Titi & Ipach (1989), who verified larger mycophagous, modifying the community of fungi. Because populations of collembolans for the low-input system than in this work the practices in the organic system stimulated for the conventional. Collembolans contribute to the soil’s the community of collembolans, it can be inferred that abilitity of suppressing plant pathogens such as these organisms are responsible, at least in part, for the Rhizoctonia solani, Fusarium oxysporum f. sp.
suppression ability in soils enriched with organic matter.
vasinfectum, and Pythium (Wiggins & Curl, 1979; Curl et Still, in regard to insects, the number of individuals was al., 1985a, b; Rickerl et al., 1989; Lartey et al., 1994), low for the rest of the orders (Tables 1 and 2).
Scientia Agricola, v.59, n.3, p.565-572, jul./set. 2002
Soil organisms in organic and conventional systems Decomposition rate (%)
1 1 8 - 1 3 9 - 2 3 4 - 2 5 5 - 2 7 0 - 2 9 2 - 4 5 1 - 4 7 1 - 5 0 1 - D a y s a f t e r p l a n t i n g
Figure 3 - Organic matter decomposition rate soil of organic and conventional cropping systems.
Shannon´s diversity index
1 1 8 1 3 9 1 6 7 2 1 4 2 3 4 2 5 5 2 7 0 2 9 2 3 1 2 3 3 2 D a y s a f t e r p la n t in g
Figure 4 - Shannon´s diversity index for soil microarthropods of the organic and conventional cropping systems.
During the first nine months of evaluation (Table populations of collembolans and Gamasida mites in the 1), for both cropping systems, the largest mite population low-input system than in the conventional.
was of the superfamily Oribatuloidea, followed by the Due to the more abundance of microarthropods in the organic system, it was believed that the organic Passalozetoidea, all in the suborder Oribatida and with matter decomposition rate would be higher in this system, similar behavior between cropping systems. In the because these organisms contribute for organic matter suborder Gamasida the most abundant population was degradation and stimulate microbial activity in the soil Laelapidae and in Actinedida the most abundant was (Nosek, 1981). Accordingly, when the presence of Pygmephoridae, both more numerous in the organic Oribatida and Collembola in litterbags incorporated into the system. Populations in the suborders Acaridida and organic and the conventional systems was evaluated, a Ixodida were very small. In the six subsequent months larger number of individuals in the litterbags was found for (Table 2), when only the families of mites were quantified, the organic system (Melo & Ligo, 1999), indicating that this the largest population was of Scheloribatidae followed by system contributes for an increase in biological diversity.
Galumnidae, with similar behavior between the systems.
Since the presence of these organisms in larger numbers The expressive number of individuals in the families was not accompanied by a higher decomposition of Galumnidae and Scheloribatidae for both cropping organic matter, one can say that the differences in systems is due to the characteristic these families exhibit arthropod density found in the soil between the organic toward occupying space in agroecosystems. In the orders and the conventional systems did not reflect on the Actinedida and Gamasida, families Cunaxidae and organic matter decomposition rate, as evaluated by the Laelapidae were the largest, respectively. In general, mite litterbag method. The community of microarthropods in the population densities in the classes Gamasida and soil might have, among other factors, influenced microbial Actinedida were higher in the organic system. The fact activity, since the organic system showed a higher that the Gamasida showed high numbers is possibly due microbial activity potential than the conventional system.
to a large Collembola population, because these The influence of the soil fauna on the organic matter organisms are a source of food for this class of mites. El decomposition rate of forest soils is well documented, but Titi & Ipach (1989) verified the existence of larger this is not true for agricultural ecosystems (Crossley et al., Scientia Agricola, v.59, n.3, p.565-572, jul./set. 2002
Table 1 - Number of soil microarthropods in the tomato organic (O) and conventional (C) cropping systems.
Data expressed in number of individuals per 785 mL soil and represent the mean of six replicates.
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Soil organisms in organic and conventional systems Table 2 - Number of soil microarthropods in the corn organic (O) and conventional (C) cropping systems.
Data expressed in number of individuals per 785 mL soil and represent the mean of six replicates.
Scientia Agricola, v.59, n.3, p.565-572, jul./set. 2002
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