Impacts of mechanized forest management on physical properties of clayey- sandy Oxisols

A mecanização do sistema de produção florestal contribui para obtenção de alta produtividade. Contudo, as práticas de manejo mecanizado promovem alterações edáficas, sobretudo sobre as propriedades físicas do solo, as quais precisam ser avaliadas para assegurar a sustentabilidade da atividade florestal a médio e longo- prazos. Objetivou-se avaliar os efeitos cumulativos do conjunto de operações florestais mecanizadas (colheita e preparo do solo) e sua atenuação por resíduos em superfície sobre as propriedades físicas do solo. O estudo foi realizado em fazenda da Klabin S/A em Telêmaco Borba - PR, Brasil, em área dominada por Latossolos Vermelhos distróficos argilo-arenosos. Os tratamentos consistiram de dois sistemas de colheita (harvester + forwarder - HF e feller + skidder - FS) em conjunto com a renovação do plantio (R), seguido do manejo de resíduos culturais em que 100%, 50% e 0% do total de resíduos produzidos na colheita foram mantidos, sendo seguido de preparo de solo, ou, então, pela condução do plantio colhido (C). Determinaram- se de forma sistemática em campo a resistência do solo à penetração (RP) (0-0,60m) e umidade gravimétrica do solo (U am ). Transectos de amostragem foram alocados perpendicularmente às linhas de plantio coletando-se amostras indeformadas em pontos equidistantes demarcados a cada 0,50 m. Densidade do solo (Ds), porosidade (macro, micro e total), resistência do solo à penetração (RP) e umidade na capacidade de campo (θ cc ) foram determinadas nas amostras coletadas nas camadas 0-0,10; 0,10-0,20; 0,20-0,40 e 0,40-0,60 m, enquanto a permeabilidade do solo ao ar (K a ), condutividade hidráulica em solo saturado (K s ), pressão de pré-consolidação (σp) e o grau de compactação (GC) foram nas camadas 0-0,30 e 0,30-0,60 m. Intervalos de confiança e correlações foram calculados considerando probabilidades de até 0,10 e 0,05, respectivamente. O comportamento geoespacial da RP foi avaliado por meio de análise geoestatística. A RP não apresentou dependência espacial nas camadas 0-0,20 e 0,40 m, sendo que, nas camadas 0,40-0,60 m, constatou-se dependência espacial fraca, para HF R e FS R . Esses resultados estão relacionados ao efeito do preparo de solo sobre o comportamento geoespacial da RP. Nas áreas de renovação, as médias (0-0,60 m) de Ds foram significativamente menores em HF R 0 (1,21 kg dm -3 ) e FS R 0 (1,24 kg dm -3 ) em relação à HF R 100 (1,40 kg dm -3 ). Nesse caso, o maior volume de resíduos em HF R 100 contribuiu com esse resultado. Nas áreas de condução dos plantios, a média (0-0,60m) de Ds em HF C (1,30 kg dm -3 ) foi significativamente menor em relação a FS C (1,46 kg dm -3 ). Esse resultado está associado ao menor volume de resíduos sobre a superfície do solo durante a colheita em FS C . Não foram constatadas diferenças significativas para as médias de RP em HF R e FS R . Porém, as médias (0-0,60 m) em HF C (1,23 MPa) foram significativamente menores que em FS C (2,00 MPa). Em poucas situações foram constatadas diferenças significativas para as médias de porosidade (macro, micro e total), K s , K a , GC e σp, contudo o comportamento geral dessas variáveis estiveram associados às alterações na Ds e, em análise conjunta, indicaram que os diferentes tipos de manejo adotados promoveram alterações na estrutura do solo, percebidas no curto prazo. Nas presentes condições, as maiores quantidades de resíduos sobre a superfície do solo atenuaram os efeitos degradantes do tráfego na colheita sobre a estrutura do solo e, em contrapartida, em áreas de renovação do plantio, as maiores quantidades de resíduos prejudicaram o resultado final do preparo de solo.The mechanization of forest production system contributes to the achievement of high yield. However, the mechanized management practices promote edaphic changes, especially on the physical properties of the soil, which need to be evaluated to ensure the sustainability of the forestry activity within medium and long-term. The objective of this study was to evaluate the cumulative effects of mechanized forest operations (harvesting and soil tillage) and their attenuation by surface residues deposition on soil physical properties. The study was carried out on a Klabin S/A farm in Telêmaco Borba - PR, Brazil, in an area predominantly covered by Oxisols, with clayey-sand texture. Treatments consisted in two harvesting systems (harvester + forwarder - HF and feller + skidder - FS) with the forest renewal (R), followed by the management of cultural residues, in which 100%, 50% and 0% of the total residues produced at harvest were maintained, followed by soil tillage, or then by mantaining the harvested crop (C). The soil penetration resistance (PR) (0-0.60 m) in the field and soil moisture (U am ) were systematically determined. Sampling transects were allocated perpendicularly to the plant lines and samples were collected at equidistant points in intervals of 0.50 m. Bulk density (Sd), porosity (macro, micro and total), soil resistance to penetration (PR) and soil water content at field capacity (θ cc ) were determined in the samples collected in the layers 0-0.10; 0.10-0.20; 0.20- 0.40 e 0.40-0.60 m, while soil air permeability (K a ), soil saturated hydraulic conductivity (K s ), pre-consolidation pressure (σp) and compaction level (GC) were obtained for 0-0.30 and 0.30-0.60 m layers. Confidence intervals and correlations were calculated considering probabilities of 0.10 and 0.05, respectively. The geospatial behavior of RP was evaluated through geostatistical analysis. The PR did not present spatial dependence in the 0-0.20 and 0.20-0.40 m layers, and within layers 0-0.40-0.60 m, weak spatial dependence was observed for HF R and FS R . These results are related to effect of the soil tillage on the geospatial behavior of PR. In the plantation renewing areas, the average (0-0.60 m) of Sd were significantly lower in HF R 0 (1.21kg dm -3 ) and FS R 0 (1.24 kg dm -3 ) than in HF R 100 (1.40 kg dm -3 ). In this case, the higher volume of residues in HF R 100 contributed the most to this result. In areas maintaining forest, the average (0-0.60 m) of Sd in HF C (1.30 kg dm -3 ) was significantly lower in relation to FS C (1.46 kg dm -3 ). This result is associated to the lower volume of residue on the soil surface during FS C harvesting. No significant difference was reported for the means of PR in HF R and FS R . However, the averages (0-0.60 m) of PR in HF C (1.23 MPa) were significantly lower than in FS C (2.00 MPa). In few situations, significant differences were observed for the porosity (micro, macro, and total), Ks, Ka, GC and σp means, however, the general behavior of these variables was associated with changes in Sd and, in a joint analysis, indicated that the different types of management adopted promoted changes in soil structure, perceived in the short-term. Under these conditions, the higher level of residue on soil surface attenuated the degrading effects of harvest traffic on soil structure. On the other hand, in areas of forest renewal, the higher level of residue impaired the final result of soil tillage

Changes in Soil Organic Carbon Fractions in Response to Cover Crops in an Orange Orchard

ABSTRACT: The cultivation of cover crops intercropped with fruit trees is an alternative to maintain mulch cover between plant rows and increase soil organic carbon (C) stocks. The objective of this study was to evaluate changes in soil total organic C content and labile organic matter fractions in response to cover crop cultivation in an orange orchard. The experiment was performed in the state of Bahia, in a citrus orchard with cultivar 'Pera' orange (Citrus sinensis) at a spacing of 6 × 4 m. A randomized complete block design with three replications was used. The following species were used as cover crops: Brachiaria (Brachiaria decumbes) -BRAQ, pearl millet (Pennisetum glaucum) -MIL, jack bean (Canavalia ensiformis) -JB, blend (50 % each) of jack bean + millet (JB/MIL), and spontaneous vegetation (SPV). The cover crops were broadcast-seeded between the rows of orange trees and mechanically mowed after flowering. Soil sampling at depths of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m was performed in small soil trenches. The total soil organic C (SOC) content, light fraction (LF), and the particulate organic C (POC), and oxidizable organic C fractions were estimated. Total soil organic C content was not significantly changed by the cover crops, indicating low sensitivity in reacting to recent changes in soil organic matter due to management practices. Grasses enabled a greater accumulation of SOC stocks in 0.00-0.40 m compared to all other treatments. Jack bean cultivation increased LF and the most labile oxidizable organic C fraction (F1) in the soil surface and the deepest layer tested. Cover crop cultivation increased labile C in the 0.00-0.10 m layer, which can enhance soil microbial activity and nutrient absorption by the citrus trees. The fractions LF and F1 may be suitable indicators for monitoring changes in soil organic matter content due to changes in soil management practices

Changes in Soil Organic Carbon Fractions in Response to Cover Crops in an Orange Orchard

ABSTRACT The cultivation of cover crops intercropped with fruit trees is an alternative to maintain mulch cover between plant rows and increase soil organic carbon (C) stocks. The objective of this study was to evaluate changes in soil total organic C content and labile organic matter fractions in response to cover crop cultivation in an orange orchard. The experiment was performed in the state of Bahia, in a citrus orchard with cultivar ‘Pera’ orange (Citrus sinensis) at a spacing of 6 × 4 m. A randomized complete block design with three replications was used. The following species were used as cover crops: Brachiaria (Brachiaria decumbes) – BRAQ, pearl millet (Pennisetum glaucum) – MIL, jack bean (Canavalia ensiformis) – JB, blend (50 % each) of jack bean + millet (JB/MIL), and spontaneous vegetation (SPV). The cover crops were broadcast-seeded between the rows of orange trees and mechanically mowed after flowering. Soil sampling at depths of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m was performed in small soil trenches. The total soil organic C (SOC) content, light fraction (LF), and the particulate organic C (POC), and oxidizable organic C fractions were estimated. Total soil organic C content was not significantly changed by the cover crops, indicating low sensitivity in reacting to recent changes in soil organic matter due to management practices. Grasses enabled a greater accumulation of SOC stocks in 0.00-0.40 m compared to all other treatments. Jack bean cultivation increased LF and the most labile oxidizable organic C fraction (F1) in the soil surface and the deepest layer tested. Cover crop cultivation increased labile C in the 0.00-0.10 m layer, which can enhance soil microbial activity and nutrient absorption by the citrus trees. The fractions LF and F1 may be suitable indicators for monitoring changes in soil organic matter content due to changes in soil management practices