Emissão de gases de efeito estufa e estoque de carbono no solo em função do manejo e correção de acidez
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Data
2016-02-12
Autores
Janegitz, Moniki Campos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Uma opção viável para mitigação de gases de efeito estufa, na agricultura, é aumentar o aporte orgânico no sistema, através de plantas. A prática da calagem em solos ácidos é indispensável para a melhoria da acidez e contribui para o aumento de produção de grãos e biomassa; por outro lado, resulta em emissão de carbono para a atmosfera. O uso do calcário ou silicato associado ao gesso pode ser eficiente em melhorar o balanço de carbono no sistema, quando comparado apenas com a aplicação isolada desses corretivos, por proporcionar maior crescimento radicular. Assim, o presente trabalho teve como objetivo avaliar a emissão de gases de efeito estufa, bem como alterações no estoque de carbono no perfil do solo, em função da correção da acidez. O experimento foi conduzido em Botucatu, SP, na Fazenda Experimental Lageado, em duas áreas pareadas, uma em semeadura direta e outra em sistema convencional de cultivo, tendo como cultura de verão a soja, seguida de safrinha com milho + braquiária (Urochloa ruziziensis cv. Comum), no primeiro ano, e milheto + braquiária, no segundo ano. Os tratamentos foram: testemunha, calcário, silicato, gesso + calcário, gesso + silicato. Amostras de solo deformadas e indeformadas foram coletadas até 1m de profundidade antes da aplicação dos tratamentos e na semeadura da soja, em novembro, para o cálculo de balanço de carbono no sistema. No primeiro ano, o solo foi coletado apenas de 0 - 0,6m. Foi determinada a fertilidade do solo, teor de carbono e fracionamento físico da matéria orgânica e densidade do solo. O aporte e a persistência de palha sobre o solo foram avaliados periodicamente. Foi realizada diagnose foliar, quantificação radicular, produção de grãos e teor de carbono nos grãos e raiz. As amostragens de gases para a determinação dos fluxos do CO2, N2O e CH4 provenientes do solo foram realizadas após a aplicação dos tratamentos, no primeiro ano, após a semeadura da soja, nas duas safras, e em março do segundo (após semeadura do milho + braquiária) e terceiro anos (após a semeadura do milheto + braquiária) totalizando 80 amostragens, em 22 meses de experimentação. A partir dos dados de estoques de carbono (via aporte de resíduos e solo) e emissão de C-CO2, foi calculado o índice de conservação de carbono. Os dados de N2O e CH4 foram transformados em C-CO2 equivalente segundo o IPCC. A emissão média anual de C-CO2 foi de 7,8 Mg ha-1. Os corretivos foram igualmente eficientes na correção de acidez do solo. Os sistemas de cultivo influenciaram a fertilidade do solo, estoque de carbono, frações de carbono no solo e emissão de gases de efeito estufa. A semeadura direta colaborou para a melhoria do ambiente solo-planta. O uso do calcário, associado ou não ao gesso, aumentou a emissão inicial de CO2 do solo, enquanto a emissão de N2O foi diminuída, na presença de silicato. Para o CH4, ocorreu influxo do gás no solo, sem diferença entre tratamentos para ambos os sistemas de manejo de cultivo, aos 35 dias após a aplicação dos corretivos, sem presença de planta. Conclui-se que o uso de corretivos de acidez do solo não aumenta a emissão de CO2 da biosfera para a atmosfera em relação à testemunha, na avaliação final dos 22 meses de experimentação. A emissão de gases em função da correção de acidez do solo é inicial, e se estabiliza ao longo do tempo, mostrando que o uso do calcário, ainda que possa emitir CO2 para a atmosfera, através de sua reação, causa efeito priming no solo. A emissão acumulada de C-CO2 foi similar nos dois sistemas de cultivo (convencional e direto). O estudo a partir de emissões de gases de efeito estufa, apenas, não permite analisar o sistema de manejo de solo. A adoção da semeadura direta ainda é a principal prática de manejo conservacionista a ser considerada com efeitos diretos no aumento de carbono no sistema. Por outro lado, além da semeadura direta, o uso de calcário associado ao gesso melhora positivamente o índice de conservação de carbono no solo. O uso de gesso melhora as propriedades químicas, aumenta o aporte de C, o estoque de carbono no solo e, consequentemente, pode ser uma prática promissora, favorecendo a mitigação de C da atmosfera para a biosfera, além de promover aumentos de produtividade da soja.
Economically viable options to mitigate emissions of greenhouse gases include increasing the stocks of croplands. The use of liming acid soils is essential to correct soil acidity and contributes to high production resulting in carbon emission in the atmosphere. The use of lime or silicate application with gypsum may improve the balance of soil carbon through increased root growth compared to the use of lime only. The main objective of this work is to study changes in the carbon storage in the soil profile as well as changes in carbon emission affected by soil acidity amelioration. The experiment was carried out in an Oxisol in Botucatu, São Paulo at the Lageado Experimental Farm under no tillage and another in a conventional system area. Crop cultivation was soybean in the summer and corn+Urucloa in the winter in the first year, and millet+Urocloa in second year cultivation. The experimental design was a randomized block with five treatments and four replications. The treatments were: control, lime, silicate, gypsum+ lime and gypsum+ silicate. Deformed and under formed soil samples of both experimental areas were taken at a depth of one meter before treatment applications and in soybean sown in November. In the first year, soil samples were collected at depths from 0 to 0.6 m. Soil fertility, carbon content, organic matter physical fractionation and bulk density were evaluated. Contribution and the persistence of the amount of straw produced in each crop and input of carbon was also evaluated. Leaf analysis, root quantification, grain yield and carbon content in the grains and roots were also analyzed. CO2, CH4 and N2O fluxes were determined from the soil using static chambers and were measured after the treatment applications, soybean planting in the summer and winter crops, in March 2013 and 2014 under corn+Urochloa and millet+Urochloa. Gas fluxes were measured for 22 months, totaling 80 sampling periods. We evaluated the CO2-C/[residue- C+soil-C]; the carbon emission quotient was proposed as C retention index (CRI), in which low values indicate a high capacity of the management system to store C in the soil. According to the IPCC in CO2- equivalent factors, nitrogen oxide and the methane emission should be adjusted. The annual average emission was 7,8 Mg ha-1of C-CO2- equivalent. Soil amendments were equally efficient in soil acidity amelioration. Cultivation systems influenced the soil fertility, carbon stock, carbon fractions in soil and greenhouse gases. Conservation systems, such as no till, contributed to the improvement of the soil-plant environment compared to the conventional system. The lime use associated or not with gypsum increased the initial CO2 emission, while N2O emission was decreased in the presence of silicate. For CH4 inflow into the ground, no difference between treatments was observed after 35 days of treatment applications, with no plants in the soil. However, we concluded that soil acidity amelioration did not increase the C-CO2 equivalent emission from biosphere to atmosphere compared to the treatment control after 22 months of trial. Data on lime-contributed to atmospheric CO2 and the effect stabilized over time. Limed treatments increased soil organic carbon confirming priming effect of liming. Accumulated C-CO2 emission was similar by the both soil management systems. It is not possible to analyze the soil tillage system with a study on greenhouse gas emissions only. Regarding adopting no-till, it is still the main conservation management practice having direct effects on the carbon mitigation in the system. Chemical soil characteristics were influenced with gypsum use as soil carbon stock and soybean yields also increased with this treatment.
Economically viable options to mitigate emissions of greenhouse gases include increasing the stocks of croplands. The use of liming acid soils is essential to correct soil acidity and contributes to high production resulting in carbon emission in the atmosphere. The use of lime or silicate application with gypsum may improve the balance of soil carbon through increased root growth compared to the use of lime only. The main objective of this work is to study changes in the carbon storage in the soil profile as well as changes in carbon emission affected by soil acidity amelioration. The experiment was carried out in an Oxisol in Botucatu, São Paulo at the Lageado Experimental Farm under no tillage and another in a conventional system area. Crop cultivation was soybean in the summer and corn+Urucloa in the winter in the first year, and millet+Urocloa in second year cultivation. The experimental design was a randomized block with five treatments and four replications. The treatments were: control, lime, silicate, gypsum+ lime and gypsum+ silicate. Deformed and under formed soil samples of both experimental areas were taken at a depth of one meter before treatment applications and in soybean sown in November. In the first year, soil samples were collected at depths from 0 to 0.6 m. Soil fertility, carbon content, organic matter physical fractionation and bulk density were evaluated. Contribution and the persistence of the amount of straw produced in each crop and input of carbon was also evaluated. Leaf analysis, root quantification, grain yield and carbon content in the grains and roots were also analyzed. CO2, CH4 and N2O fluxes were determined from the soil using static chambers and were measured after the treatment applications, soybean planting in the summer and winter crops, in March 2013 and 2014 under corn+Urochloa and millet+Urochloa. Gas fluxes were measured for 22 months, totaling 80 sampling periods. We evaluated the CO2-C/[residue- C+soil-C]; the carbon emission quotient was proposed as C retention index (CRI), in which low values indicate a high capacity of the management system to store C in the soil. According to the IPCC in CO2- equivalent factors, nitrogen oxide and the methane emission should be adjusted. The annual average emission was 7,8 Mg ha-1of C-CO2- equivalent. Soil amendments were equally efficient in soil acidity amelioration. Cultivation systems influenced the soil fertility, carbon stock, carbon fractions in soil and greenhouse gases. Conservation systems, such as no till, contributed to the improvement of the soil-plant environment compared to the conventional system. The lime use associated or not with gypsum increased the initial CO2 emission, while N2O emission was decreased in the presence of silicate. For CH4 inflow into the ground, no difference between treatments was observed after 35 days of treatment applications, with no plants in the soil. However, we concluded that soil acidity amelioration did not increase the C-CO2 equivalent emission from biosphere to atmosphere compared to the treatment control after 22 months of trial. Data on lime-contributed to atmospheric CO2 and the effect stabilized over time. Limed treatments increased soil organic carbon confirming priming effect of liming. Accumulated C-CO2 emission was similar by the both soil management systems. It is not possible to analyze the soil tillage system with a study on greenhouse gas emissions only. Regarding adopting no-till, it is still the main conservation management practice having direct effects on the carbon mitigation in the system. Chemical soil characteristics were influenced with gypsum use as soil carbon stock and soybean yields also increased with this treatment.
Descrição
Palavras-chave
Calagem, Estoque de carbono, Emissão de CO2, Gesso, Aquecimento global, Liming, Carbon stock, CO2 emission, Gypsum, Global warming