RESUMO
Management systems to improve soil quality are essential for agricultural and environmental sustainability. We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF). In addition, we examined their relationship to chemical, physical and biological soil quality indicators, as well as to maize yield. The study was conducted on a long-term experiment (18 years) in southern Brazil involving two different systems [no tillage (NT) and conventional tillage (CT)], two cropping systems [black oat/maize (O/M) and black oat + vetch/maize + cowpea (OV/MC)] and two nitrogen fertilizer rates for maize (0 and 180 kg ha1). Based on the three indices, the best managements for soil quality comprised NT (50-212 % better than CT), legume cover crops (10-47 % better than O/M) and N fertilization (8-33 % better than no fertilizer). All three indices proved accurate to assess the impact of soil management systems, especially SR-LF, which showed increased sensitivity and close relationships with chemical, physical and biological soil quality indicators. On the other hand, a poor relationship was observed between soil C indices and maize yield, which was improved only by legume cover crops and N fertilization. The results showed that the association of no-till system to an abundant supply of crop residues is key to ensure high soil quality and crop yields in humid subtropical regions.(AU)
Assuntos
Química do Solo , Qualidade do Solo , Critérios de Qualidade do Solo , 24444 , Conservação de Terras/métodosRESUMO
Management systems to improve soil quality are essential for agricultural and environmental sustainability. We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF). In addition, we examined their relationship to chemical, physical and biological soil quality indicators, as well as to maize yield. The study was conducted on a long-term experiment (18 years) in southern Brazil involving two different systems [no tillage (NT) and conventional tillage (CT)], two cropping systems [black oat/maize (O/M) and black oat + vetch/maize + cowpea (OV/MC)] and two nitrogen fertilizer rates for maize (0 and 180 kg ha1). Based on the three indices, the best managements for soil quality comprised NT (50-212 % better than CT), legume cover crops (10-47 % better than O/M) and N fertilization (8-33 % better than no fertilizer). All three indices proved accurate to assess the impact of soil management systems, especially SR-LF, which showed increased sensitivity and close relationships with chemical, physical and biological soil quality indicators. On the other hand, a poor relationship was observed between soil C indices and maize yield, which was improved only by legume cover crops and N fertilization. The results showed that the association of no-till system to an abundant supply of crop residues is key to ensure high soil quality and crop yields in humid subtropical regions.
Assuntos
Critérios de Qualidade do Solo , 24444 , Qualidade do Solo , Química do Solo , Conservação de Terras/métodosRESUMO
This study aimed to evaluate the effect of forestation with leguminous Acacia mearnsii De Wild in native grasslands on the soil greenhouse (GHG) fluxes and their main driving factors. The experiment was conducted in the Brazilian Pampa over the period of one year in a six-year-old Acacia plantation, evaluating four treatments: Acacia (AM), Acacia with litter periodically removed (A-l), Acacia after harvest (AH) and native grassland (NG) (reference treatment). Air samples were obtained by the static chamber method, and gas concentrations were evaluated by gas chromatography. Soil and climate factors were monitored. The accumulated fluxes of methane (CH4) and nitrous oxide (N2O) were statistically similar between the soils in the AM and NG treatments, which tended to oxidize CH4 (-1445 and -1752 g C-CH4 ha(-1) yr(-1), respectively) and had low emission of N2O (242 and 316 g N-N2O ha(-1) yr(-1)), most likely influenced by the low water-filled pore space and the low content of mineral N in the soil. However, the soil in the AH treatment presented higher emissions of both gases, totaling 1889 g C-CH4 ha(-1) yr(-1) and 1250 g N-N2O ha(-1) yr(-1). Afforestation neither significantly affected the total organic C stocks nor their lability, keeping the C management index for the forested area similar to that in the NG treatment. The conversion from grassland to Acacia forest represents an effective option for mitigating the net reduction in greenhouse gas emissions, which is basically determined by C accumulation in biomass and wood products.
Assuntos
Acacia , Florestas , Pradaria , Poluentes Atmosféricos/análise , Poluição do Ar/prevenção & controle , Brasil , Meio Ambiente , Agricultura Florestal/métodos , Efeito Estufa , Metano/análise , Óxido Nitroso/análise , Solo/químicaRESUMO
O trabalho objetivou identificar os principais atributos químicos de solo que limitam o crescimento do Eucalyptus saligna em plantios sem calagem na região Sudoeste do Rio Grande do Sul, bem como determinar os valores críticos de cada fator. O estudo foi realizado em povoamentos florestais de dois Latossolos Vermelhos e um Neossolo Quartzarênico da região. Foram realizadas análises químicas do solo e, através de correlações (P 0,05) entre estes e variáveis de crescimento das plantas, verificou-se que os atributos que mais limitaram o crescimento das plantas foram a saturação por Al, a saturação por bases e o teor de Mg trocável, com decréscimo de até 50% nos parâmetros de crescimento. As correlações com os atributos químicos da camada subsuperficial de solo (20-40cm) foram mais significativas do que na camada superficial (0-20cm). Os níveis críticos médios para obtenção de 80% do rendimento relativo no crescimento em diâmetro e em volume de plantas foram de 79% para saturação por Al, 8,3% para saturação por bases e 0,3 cmolc dm-3 para o teor de Mg trocável. Os resultados indicam que a calagem não deve ser suprimida dos plantios de eucalipto em solos ácidos do Pampa gaúcho, mas a quantidade necessária de calagem para esta cultura parece ser menor do que a atualmente recomendada.
The study aimed to identify the main soil chemical attributes that constrains the Eucalyptus saligna growth in no-limed plantations at the southwestern region of Rio Grande do Sul state, as well as to determine the threshold values of each attribute. Forest plantations from two Oxisols and one Quartzipsamment were evaluated. Correlation analysis (P 0.05) between soil chemical attributes and plant growth variables indicated that the most constraining soil attributes were the Al saturation, bases saturation and exchangeable Mg content, whose decrease in plant growth was up to 50%. Subsurface soil attributes (20-40cm depth) had closer relation with plant growth than surface soil ones (0-20cm). The average threshold values for achieving 80% of the relative yield capacity in diameter growth of trunks and in volume were 79% for Al saturation, 8.3% for bases saturation and 0.3 cmolc dm-3 for exchangeable Mg. The results evidenced that liming should not be suppressed in eucalypt plantations on acid soils at south Brazilian Pampa and that the required amount of lime seem to be smaller than that currently recommended.
Assuntos
Eucalyptus/crescimento & desenvolvimento , Pradaria , Química do Solo , Solos ArenososRESUMO
O trabalho objetivou identificar os principais atributos químicos de solo que limitam o crescimento do Eucalyptus saligna em plantios sem calagem na região Sudoeste do Rio Grande do Sul, bem como determinar os valores críticos de cada fator. O estudo foi realizado em povoamentos florestais de dois Latossolos Vermelhos e um Neossolo Quartzarênico da região. Foram realizadas análises químicas do solo e, através de correlações (P 0,05) entre estes e variáveis de crescimento das plantas, verificou-se que os atributos que mais limitaram o crescimento das plantas foram a saturação por Al, a saturação por bases e o teor de Mg trocável, com decréscimo de até 50% nos parâmetros de crescimento. As correlações com os atributos químicos da camada subsuperficial de solo (20-40cm) foram mais significativas do que na camada superficial (0-20cm). Os níveis críticos médios para obtenção de 80% do rendimento relativo no crescimento em diâmetro e em volume de plantas foram de 79% para saturação por Al, 8,3% para saturação por bases e 0,3 cmolc dm-3 para o teor de Mg trocável. Os resultados indicam que a calagem não deve ser suprimida dos plantios de eucalipto em solos ácidos do Pampa gaúcho, mas a quantidade necessária de calagem para esta cultura parece ser menor do que a atualmente recomendada.(AU)
The study aimed to identify the main soil chemical attributes that constrains the Eucalyptus saligna growth in no-limed plantations at the southwestern region of Rio Grande do Sul state, as well as to determine the threshold values of each attribute. Forest plantations from two Oxisols and one Quartzipsamment were evaluated. Correlation analysis (P 0.05) between soil chemical attributes and plant growth variables indicated that the most constraining soil attributes were the Al saturation, bases saturation and exchangeable Mg content, whose decrease in plant growth was up to 50%. Subsurface soil attributes (20-40cm depth) had closer relation with plant growth than surface soil ones (0-20cm). The average threshold values for achieving 80% of the relative yield capacity in diameter growth of trunks and in volume were 79% for Al saturation, 8.3% for bases saturation and 0.3 cmolc dm-3 for exchangeable Mg. The results evidenced that liming should not be suppressed in eucalypt plantations on acid soils at south Brazilian Pampa and that the required amount of lime seem to be smaller than that currently recommended.(AU)
Assuntos
Eucalyptus/crescimento & desenvolvimento , Solos Arenosos , Química do Solo , PradariaRESUMO
The study aimed at to determine the magnitude of the methane (CH(4)) and nitrous oxide (N(2)O) flux rates in soils at Hennequin Point, King George Island, Antarctic, under different slope positions, vegetal covers and presence of skuas, as well as to evaluate the main soil and climate factors that are involved with the flux of such gases. In situ gas sampling (closed chamber method) was performed in four sites along a transect involving a skua nesting field in a moraine with 5% and 100% of surface covered by vegetal, and two poor-drained soils in the toeslope (a bare alluvium soil and a poor-drained moss field with 100% soil cover). Flux rates ranged from -0.86±0.45 to 2.75±1.52 µg N(2)O-N m(-2) h(-1) and -12.26±3.05 to 1.42±1.31 µg CH(4)-C m(-2) h(-1). The soil totally covered by vegetal in the skua field had the largest CH(4) influx rates. However, this benefic effect was counterbalanced by the greatest N(2)O efflux rates from this soil, resulting in the largest contribution to the global warming potential among the soils evaluated. Flux rates were closely related to soil temperature, but no significant relation was observed with mineral N contents and water-filled pore space. In turn, accumulated CH(4) and N(2)O emissions were closely related to the total N and total organic C stocks in the soil. Net CH(4) influx predominated even in the poor-drained soils, suggesting that the coarse soil texture avoided critical anaerobic conditions. No significant changes in flux rates were observed for sampling time along the day.
Assuntos
Metano/análise , Óxido Nitroso/análise , Poluentes do Solo/análise , Poluentes Atmosféricos/análise , Regiões Antárticas , Monitoramento Ambiental , Poluição Ambiental/estatística & dados numéricos , SoloRESUMO
A aplicação de dejeto líquido de suínos em áreas de lavoura e/ou pastagem representa a adição de nutrientes às plantas e também uma alternativa de reciclagem. Contudo, as perdas de nitrogênio e fósforo por escoamento superficial no plantio direto podem diminuir sua eficiência à nutrição de plantas e representar um poluente potencial, comprometendo a qualidade da água no ambiente. Esse trabalho teve por objetivo avaliar a importância do escoamento superficial às perdas de nitrogênio e fósforo aplicados via dejeto líquido de suínos. O trabalho foi conduzido na Universidade Federal de Santa Maria, RS, no período de maio de 2000 a maio de 2002 em Argissolo Vermelho Arênico distrófico. Numa rotação aveia preta/milho/nabo forrageiro, foram estudadas as doses de 0, 20, 40 e 80 m³ ha-1 de dejetos líquidos de suínos, distribuídas a lanço sobre a superfície antes da semeadura de cada espécie da rotação. As concentrações de fósforo disponível e nitrogênio mineral na solução escoada na superfície do solo foram diretamente relacionados com as doses de dejeto aplicadas. As concentrações de nitrogênio e fósforo na solução escoada na superfície do solo, bem como a predominância de amônio ou nitrato, estão diretamente relacionadas ao intervalo entre a aplicação do dejeto e o primeiro escoamento superficial. As perdas de nitrogênio e fósforo por escoamento superficial, expressas em kg ha-1, são pequenas, porém as maiores concentrações observadas nos picos de perdas preocupam com relação à possibilidade de eutroficação de mananciais de água.