Soil Organic Carbon Stratification Research Articles

Soil carbon storage and stratification under different tillage/residue-management practices in double rice cropping system

The importance of soil organic carbon (SOC) sequestration in agricultural soils as climate-change-mitigating strategy has become an area of focus by the scientific community in relation to soil management. This study was conducted to determine the temporal effect of different tillage systems and residue management on distribution, storage and stratification of SOC, and the yield of rice under double rice (Oryza sativa L.) cropping system in the southern China. A tillage experiment was conducted in the southern China during 2005–2011, including plow tillage with residue removed (PT0), plow tillage with residue retention (PT), rotary tillage with residue retention (RT), and no-till with residue retention on the surface (NT). The soil samples were obtained at the harvesting of late rice in October of 2005, 2007 and 2011. Multiple-year residue return application significantly increased rice yields for the two rice-cropping systems; yields of early and late rice were higher under RT than those under other tillage systems in both years in 2011. Compared with PT0, SOC stocks were increased in soil under NT at 0–5, 5–10, 10–20, and 20–30 cm depths by 33.8, 4.1, 6.6, and 53.3%, respectively, in 2011. SOC stocks under RT were higher than these under other tillage treatments at 0–30 cm depth. SOC stocks in soil under PT were higher than those under PT0 in the 0–5 and 20–30 cm soil layers. Therefore, crop residues played an important role in SOC management, and improvement of soil quality. In the 0–20 cm layer, the stratification ratio (SR) of SOC followed the order NT>RT>PT>PT0; when the 0–30 cm layer was considered, NT also had the highest SR of SOC, but the SR of SOC under PT was higher than that under RT with a multiple-year tillage practice. Therefore, the notion that conservation tillage lead to higher SOC stocks and soil quality than plowed systems requires cautious scrutiny. Nevertheless, some benefits associated with RT system present a greater potential for its adoption in view of the multiple-year environmental sustainability under double rice cropping system in the southern China.

Soil organic carbon in some land uses of Costa Rica

The native vegetation in the Tropics is increasingly replaced by crops, pastures, tree plantations, or settlements with contradictory effects on soil organic carbon (SOC). Therefore, the general objective was to estimate the SOC stock depth distribution to 100-cm depth in soils of Costa Rica and to assess their theoretical carbon (C) sink capacity by different management practices. A study was established in three ecoregions of Costa Rica: the Isthmian-Atlantic Moist Forest (AM), the Pacific Dry Forest (PD), and the Montane Forest (MO) ecoregions. Within each ecoregion, three agricultural land uses and a mature forest were sampled to 100-cm depth. The SOC stock in 0–100 cm depth was 114–150 Mg C ha−1 for AM, 76–165 Mg C ha−1 for PD, and 166–246 Mg C ha−1 for MO. Land use had only weak effects on SOC concentrations and stocks except at PD where both were lower for soils under mango (Mangifera indica) and pasture. This may indicate soil degradation which was also supported by data on SOC stratification. However, it was generally unclear whether differences among land uses within each ecoregion already existed particularly at deeper depths before land-use change, and whether the sampling approach was sufficient to investigate them. Nevertheless, about 26–71% of Costa Rica's total C emissions may be offset by SOC sequestration in agricultural and forest soils. However, ecoregion-specific practices must be implemented to realize this potential.

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

AbstractSoil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.

Changes in soil organic carbon and nitrogen as affected by tillage and residue management under wheat–maize cropping system in the North China Plain

The importance of soil organic carbon (SOC) and nitrogen (N) sequestration in agricultural soils as climate-change-mitigating strategy has received robust attention worldwide in relation to soil management. This study was conducted to determine the temporal effects of different tillage systems and residue management on distribution, storage and stratification of SOC and N under wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping systems in the North China Plain (NCP). Four tillage systems for winter wheat established in 2001 were: moldboard plow tillage with maize residues removed (PT0), moldboard plow tillage with maize residues incorporated (PT), rotary tillage with maize residues incorporated (RT), and no-till with maize residues retained on the soil surface (NT). Compared with PT0 and PT, significantly higher SOC and N concentrations were observed in the surface layer (0–10cm depth) under NT and RT. In 2004, the SOC stocks were lower (P<0.05) under NT and RT than under PT and PT0, however, the opposite trend was observed in 2012. Compared with 2001, the net profile (0–30cm) SOC sequestration rate was 10.60, 13.95, 13.65, and 14.92Mgha−1 in 2012 under PT0, PT, RT, and NT, respectively. As for SOC stocks in the 0–50cm profile, no significant differences (P<0.05) were observed among NT, RT, and PT. The trends in N stocks in profile (0–30, 0–50cm depth) were NT>RT>PT>PT0 in both years. Compared with other treatments, SOC and N stocks were the lowest (P<0.05) under PT0. Therefore, crop residues play an important role in SOC and N management, and improvement of soil quality. The higher SOC stratification was observed under NT and RT than under PT and PT0, whereas the C:N ratio was higher (P<0.05) under PT and PT0 than under NT and RT systems. Therefore, the notion that NT leads to higher SOC stocks than plowed systems requires cautious scrutiny. Nonetheless, some benefits associated with NT present a greater potential for its adoption in view of the long-term environmental sustainability under wheat–maize double-cropping system in the NCP.

Soil carbon stratification affected by long-term tillage and cropping systems in southern Brazil

Continuous residue inputs when associated with minimum soil disturbance gradually promote the stratification of soil organic carbon (SOC) in the soil profile. In temperate soils, this characteristic has been used as an indicator of quality of soil management. However, few studies have been conducted with this indicator in tropical and subtropical climates or with the main soil orders in these areas. To fill this gap, this study was carried out in a subtropical climate with two of the major Brazilian soil orders, Oxisol and Alfisol, that together account for 63% of Brazilian agricultural soils. This study tested the hypothesis that the CSR is affected by soil order and climate type. The main treatments were soil tillage and different cropping systems in two long-term experiments carried out in the State of Rio Grande do Sul, Brazil. The first experiment, established in 1985, was conducted over a clayey Hapludox (Oxisol) soil. The main plots were treated with one of two tillage systems (conventional tillage – CT; and no-tillage – NT). The subplots were treated with one of three cropping systems: (a) continuous crop succession (R0) – wheat (Triticum aestivum L.)/soybean (Glycine max L. Merrill); (b) winter crop rotation (R1)–wheat/soybean/black oat (Avena strigosa Schreber)/soybean; (c) summer and winter crop rotation (R2) – wheat/soybean/black oat/soybean/black oat+common vetch (Vicia sativa L. Walp)/maize (Zea mays L.)/forage radish (Raphanus sativus var. oleiferus Metzg.). The second experiment was established in 1991 over a sandy loam distrophic Paleudalf (Alfisol) soil. Five cropping systems were analyzed under no-till: (a) maize+jack beans (Canavalia ensiformis DC)/soybean (M/JB); (b) maize/fallow/soybean (M/F); (c) maize/ryegrass (Lolium multiflorum Lam.)+common vetch/soybean (M/R); (d) maize+velvet beans (Stizolobium cinereum Piper and Tracy)/soybean (M/VB); and (e) maize/radish oil/soybean (M/FR). The carbon stratification ratio (CSR) was assessed in the 19th and 22nd experimental years for Oxisol and in the 10th and 17th years for Alfisol. This index was calculated through the ratio of SOC stocks in the 0–0.05 and 0.05–0.15m soil layers. The CPI was determined through the ratio of SOC stocks in the 0–0.15m soil layer in a given treatment compared with native vegetation. Regardless of the soil order, SOC was influenced by C input and the tillage system; there was a positive linear relationship between CSR and CPI. The relationship between the CSR and the carbon pool index (CPI) was used to infer the quality of soil management. Higher CSR and CPI indices were found under treatments with minimum soil disturbance and intensive crop rotation. Lower CSR and CPI values were associated with frequent mobilization and lower crop diversity. These CSR indices sensitively distinguished the intensity of tillage (NT replacing CT) and cropping systems (cover crops replacing winter fallow or crop succession). The CSR values in subtropical soils investigated were lower than those reported for temperate soils. The soil order affected the critical CSR value being lower in the Oxisol than in the Alfisol. Our findings recommend accept our hypothesis that the CSR is affected by climate and soil order.

Soil aggregation and organic carbon protection in a no-tillage chronosequence under Mediterranean conditions

Low-intensity soil management systems like no-tillage (NT) are being increasingly accepted as an essential part of sustainable farming systems. The objective of this work was to study the effects of NT maintenance over time on soil aggregation and soil organic carbon (SOC) protection on a semiarid Mediterranean agroecosystem. A NT chronosequence was established with five phases: (i) conventional tillage (CT); (ii) NT for 1year (NT-1); (iii) NT for 4years (NT-4); (iv) NT for 11years (NT-11) and (v) NT for 20years (NT-20). N fertilization was based on pig slurry for the whole experimental area. Soil samples were collected from four depths (i.e., 0–5, 5–10, 10–20, 20–30cm). Dry and water-stable aggregates, SOC concentration and C concentration of water-stable aggregates were measured. SOC concentration reached its maximum value after 11years under NT. However, the differences between NT phases were only found in the 0–5cm soil depth. In soil surface (i.e., 0–5cm), water-stable large macroaggregates (2–8mm) were 0.02, 0.12, 0.32 and 0.31gg−1 dry soil for the NT-1, NT-4, NT-11 and NT-20 phases, respectively. C concentration of microaggregates increased in relation with the number of years under NT. SOC and water-stable macroaggregate stratification were greatest with the increase in the years under NT, emphasizing the close relationship between SOC and aggregation. In Mediterranean semiarid agroecosystems, the increase in the proportion of stable macroaggregates and the enrichment of C concentration within microaggregates are two main mechanisms of SOC protection when NT is maintained over time.

Effect of conservation tillage on soil quality in the piedmont plain of Mount Taihang

保护性耕作被认为是华北平原农业可持续发展的重要措施, 但目前缺乏这些措施对土壤质量影响的系统报道。本研究以长期定位试验为基础, 探讨了太行山前平原两熟制高产农田不同耕作措施对麦田土壤质量的影响。试验始于2001 年, 设置翻耕玉米秸秆不还田(非保护性耕作对照, CK)、翻耕玉米秸秆粉碎还田(CT)、旋耕玉米秸秆粉碎还田(RT)和免耕玉米秸秆直立还田(NT)4 个处理。2007 年冬小麦收获后分层测定土壤有机碳(soil organic carbon, SOC)含量、容重(<i>ρ</i>_<i>b</i>)、水稳性团聚体、水分特征曲线、饱和导水率(<i>K</i>_s)和微生物量碳氮。2008 年测定了剖面SOC 含量、<i>ρ</i>_<i>b</i> 和蚯蚓数量。结果表明, 连续多年保护性耕作后土壤剖面的SOC 储量无显著变化, 但保护性耕作(RT 和NT)下SOC 的层化比率(1.74~2.04)显著高于翻耕处理(CK 和CT, 1.37~1.45); 保护性耕作显著提高了表层微生物量碳、氮含量以及单位面积土壤中的蚯蚓数量。NT 处理导致耕层(0~20 cm)土壤<i>ρ</i>_<i>b</i> 增加, 但提高了土壤团聚体的稳定性。CK 和CT 处理显著增加了0~5 cm 土层裂隙(>500 μm)和传输孔隙(500~50 μm)的比例, 而NT 处理则增加储水孔隙(50~0.5 μm)的含量。另外, 保护性耕作提高了土壤的<i>K</i>_s、田间持水量和有效水含量。对土壤质量指标<i>S</i> 的分析结果表明, 实施保护性耕作后, 太行山前平原地区土壤质量总体上得到改善。

Impact of ridge tillage on soil organic carbon and selected physical properties of a clay loam in southwestern Ontario

Ridge tillage (RT) creates a distinctly different soil environment relative to no-tillage (NT) and mouldboard plow tillage (MP), which may in turn affect soil properties. In this study, the impacts of long-term (29 years) RT on soil organic carbon (SOC), water content, bulk density and penetration resistance were compared with NT and MP tillage on a clay loam soil under a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation. The ridges in RT were formed at 76-cm spacing and corn was planted in the center of the ridges whereas soybean was planted in the shoulders of the ridges at 38-cm spacing. Soil samples were collected from the ridge crest (i.e. corn row), from the two ridge shoulder positions and from the interrow (furrow) positions of the ridges to evaluate both the spatial and profile distributions of the selected soil properties under RT relative to NT and MP. Ridge tillage produced low SOC in the interrows, high SOC in the crests and medium SOC in the shoulders relative to MP and NT. Soil water content was higher in the interrows than in the crests of the ridges, while soil penetration resistance followed the reverse trend. No-tillage resulted in a distinct SOC stratification with significantly higher SOC in surface soil and slightly lower SOC in subsurface soil while a uniform distribution of SOC was observed in the plow layer of MP soil. Hence, RT produced different SOC, water content, bulk density and penetration resistance distributions than NT and MP. Twenty-nine years of RT management resulted in improved soil physical conditions in the plow layer for crop root growth relative to NT and greater SOC stocks within the plow layer compared to MP.

Impact of reduced tillage on soil organic carbon and nutrient budgets under organic farming

AbstractNo-tillage (NT) and reduced tillage (RT) systems are well-known management tools for reducing soil erosion and improving soil fertility. NT and RT may improve the environmental and economic performance of organic farming, but they are still not common practice among organic farmers. This paper presents the effects of tillage [RT versus conventional tillage (CT)], fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators such as soil organic carbon (Corg), microbial biomass and microbial activity, soil nutrients and nutrient budgets in an organic farming system during the first six-year crop rotation period of a long-term experiment on a clayey soil in a temperate climate. RT caused stratification of soil organic carbon (Corg), microbial properties and soil nutrients in the soil profile. Under RT, Corg in the 0–10 cm soil layer increased from 2.19 to 2.61% (w/w) from 2002 to 2008, whereas it remained constant under CT. In both tillage treatments, Corg remained constant in the 10–20 cm soil depth. Microbial biomass C increased by 37% under RT in the 0–10 cm soil depth and microbial activity [dehydrogenase activity (DHA)] was enhanced by 57%. Soil microbial biomass C and DHA in the 10–20 cm soil depth were also higher under RT (+10 and +17%, respectively). Soluble soil P and K were 72 and 40%, respectively, higher in 0–10 cm soil depth under RT when compared with CT. Fertilization showed no effects on the measured soil properties. Biodynamic preparations increased solely the Cmic-to-Nmic (soil microbial biomass C to soil microbial biomass N) ratio by 7% in the 0–10 cm soil depth. Nutrient budgets for P were balanced in all treatments, but N and K exports were higher under RT compared to CT. We conclude that RT is a suitable method for increasing indicators of soil fertility in organic farming systems. The combined effects of RT and an organic farming system with a diverse, ley-based crop rotation and organic fertilization merit further promotion and it may be considered for supporting actions by the agricultural policy schemes.

The effect of reduced tillage agriculture on carbon dynamics in silt loam soils

Reduced tillage (RT) agriculture is an effective measure to reduce soil loss from soils susceptible to erosion in the short-term and is claimed to increase the soil organic carbon (SOC) stock. The change in distribution and total SOC stock in the 0–60 cm layer, the stratification of microbial biomass carbon (MB-C) content in the 0–40 cm layer and the carbon (C) mineralization in the upper 0–5 cm layer in silt loam soils in Western Europe with different periods of RT agriculture were evaluated. Ten fields at seven locations, representing the important RT types and maintained for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. RT agriculture resulted in a higher stratification of SOC in the soil profile than CT agriculture. However, the total SOC stock in the 0–60 cm layer was not changed, even after 20 of years RT agriculture. The MB-C was significantly higher in the 0–10 cm layer under RT agriculture, even after only 5 years, compared to CT agriculture. The higher SOC and MB-C content in the upper 0–5 cm layer of RT fields resulted in a higher C mineralization rate in undisturbed soil in the laboratory. Simulating ploughing by disturbing the soil resulted in inconsistent changes (both lower and higher) of C mineralization rates. A crop rotation with root crops, with heavy soil disturbance every 2 or 3 years at harvest, possibly limited the anticipated positive effect of RT agriculture in our research.

Impacts of long-term and recently imposed tillage practices on the vertical distribution of soil organic carbon

Although many studies suggest that no-tillage (NT) increases soil organic carbon (SOC) within the soil profile relative to mouldboard ploughing, other studies indicate that no net change occurs. The latter studies suggest that NT only stratifies the SOC, where a near-surface increase in SOC is offset by a concomitant decrease in the subsurface. We examined the SOC distribution and stocks in a cool, humid Brookston clay (Typic Argiaquoll) soil under four soil management systems with a corn–soybean rotation. The objectives of this study were to compare the profile distribution and total amount of SOC under long-term (21 years) NT and mouldboard plough (MP) tillage with the changes that occur over 8 years when 13-years continuous NT is converted to MP, and when 13-years continuous MP is converted to NT. In the top 5 cm of soil, the long-term NT management accumulated greater SOC compared with the long-term MP treatment. However, this near-surface increase was offset by lower SOC concentrations in the 10–20 cm depth, resulting in similar total amounts of SOC stored in 0–20 cm for both long-term NT and MP. The SOC stratification that existed after 13 years of NT management was eliminated with one mouldboard ploughing operation, however the total SOC content in the plough layer of the new-MP treatment remained relatively constant over the subsequent 8 years. Soil organic carbon stratification was evident in the new no-tillage treatment 3 years after the cessation of tillage. The continuous build-up of SOC in the surface of new-NT soils was associated with no change in the total amount of SOC in the plough layer relative to long-term NT. This implies that the diminution of SOC in the 10–20 cm depth was at the same rate as the accumulation of SOC in the 0–5 cm depth. Although there was no net effect of tillage on total carbon stocks in this fine-textured soil, SOC stratification required several years to build-up after adoption of NT, but only a single year to destroy under MP.

Occasional Tillage of No‐Till Systems: Carbon Dioxide Flux and Changes in Total and Labile Soil Organic Carbon

Soil organic carbon (SOC) accumulation occurs mostly in the top 5 cm of soil with continuous no‐till (NT) while SOC losses often occur at deeper depths. We hypothesize that one‐time tillage conducted once in &gt;10 yr to mix the high SOC surface layer with deeper soil will not result in large SOC losses following tillage with a net positive gain in SOC eventually. Two experiments in long‐term NT fields were installed under rainfed corn (Zea mays L.) or sorghum [Sorghum bicolor (L.) Moench.] rotated with soybean [Glycine max (L.) Merr.] in eastern Nebraska. Tillage treatments were applied in the spring or fall and included: NT, disk, chisel with 10‐cm wide twisted shanks, moldboard plow (MP), and mini‐moldboard plow (miniMP). A portable infrared gas analyzer was used to monitor CO2 flux immediately following tillage. Effect of tillage on profile distribution of total and labile (particulate and oxidizable) SOC was determined. At 24 to 32 mo following tillage, SOC mass was determined for depths of 0 to 5, 5 to 20, and 20 to 30 cm. Some tillage operations effectively redistributed total and labile SOC with little increase in CO2 flux compared with NT. Total and labile SOC concentrations were reduced by 24 to 88% in the 0‐ to 2.5‐cm depth and increased by 13 to 381% for the 5‐ to 10‐cm depth for the various tillage operations. Moldboard plowing caused the greatest redistribution of SOC. On an equivalent soil mass basis, tillage did not cause significant losses of total or labile SOC between tillage and planting of the next crop or by 24 to 32 mo after tillage. Stratification of SOC in long‐term NT soil could be reduced most effectively by means of one‐time MP tillage without increased loss of labile SOC.

Qualidade física do solo em pomar de laranjeira no noroeste do paraná com manejo da cobertura permanente na entrelinha

O tráfego de máquinas e a compactação do solo ocorrem próximo à copa das plantas de citros, aumentando as restrições físicas do solo ao crescimento das raízes. Estratégias de manejo incluem o uso de coberturas permanentes do solo nas entrelinhas de pomares de laranjeira, mas são desconhecidos os seus efeitos na qualidade física do solo. O objetivo deste estudo foi quantificar o impacto de sistemas de manejo com cobertura permanente do solo em alguns indicadores de qualidade física do solo em um pomar de laranjeira. O estudo foi realizado em um experimento de longa duração de laranjeira 'Pêra' sobre limoeiro 'Cravo' com sistemas de cobertura permanente do solo nas entrelinhas, no município de Alto Paraná, noroeste do Paraná, em um Argissolo Vermelho distrófico latossólico, com horizonte superficial de textura arenosa. Os tratamentos de cobertura permanente nas entrelinhas com a gramínea mato-grosso ou batatais (Paspalum notatum) manejada com roçada e a leguminosa amendoim forrageiro (Arachis pintoi) foram comparados ao manejo tradicional, em que a vegetação espontânea foi dessecada com herbicida pós-emergente. O delineamento experimental utilizado foi de bloco ao acaso com três repetições. Em maio de 2003, a amostragem de solo foi realizada sob rodado e entrerrodado das máquinas nas entrelinhas do pomar. As amostras indeformadas de solo obtidas no centro da camada de 0-15 cm de profundidade foram utilizadas para determinação dos seguintes indicadores: conteúdo de água na capacidade de campo, porosidade total do solo e densidade do solo, a partir dos quais foram estimados os indicadores capacidade de aeração do solo e capacidade de armazenamento de água do solo. Amostras de solo deformadas foram coletadas nas camadas de 0-5 e 10-15 cm de profundidade, para determinação dos teores de C orgânico do solo e cálculo da taxa de estratificação de C orgânico do solo. Os indicadores de qualidade do solo, capacidade de armazenamento de água do solo, capacidade de aeração do solo e taxa de estratificação de C orgânico do solo foram eficientes na avaliação de sistemas de manejo de solo em citros. A manutenção da vegetação das entrelinhas vegetadas com a gramínea mato-grosso ou batatais melhora a qualidade física do solo, independentemente das posições rodado e entrerrodado. A qualidade física do solo é afetada negativamente na posição rodado sob o manejo com amendoim forrageiro e nas posições rodado e entrerodado no manejo tradicional da vegetação espontânea com herbicida pós-emergente.

Carbon and nitrogen stocks of an Arenosol under irrigated fruit orchards in semiarid Brazil

Soil organic matter accumulation provides benefits to soil productivity and reduces atmospheric carbon concentration. However, little is known about the accumulation of C and N by sandy soils under perennial irrigated crops in semiarid regions. The objective of this study was to evaluate the effect of irrigated fruit orchard cultivation on the stocks of soil organic carbon (SOC) and total nitrogen (N) of an Arenosol/Quartzpsament from Paraipaba-CE, Semiarid Brazil. Soil samples were taken from irrigated orchards of banana (Musa ssp.), cashew (Anacardium ocidentale), guava (Psidium guajava), bullock's heart (Annona reticulata), mango (Mangifera indica), and sapote (Manilkara zapota) in the wetted-bulb and non-irrigated area between the plant rows. Additional samples were collected from adjacent areas under secondary Caatinga forest, and under a 2-year-old deforested area. Sampling depths were: 0-0.1, 0.1-0.2, and 0.2-0.4 m. The highest contents of SOC and N were found in the surface layer. The soil bulk density did not change in depth. The stocks of SOC and total N under secondary forest at 0-0.40 m layer were 27.6 and 2.4 Mg ha-1, respectively. Caatinga Forest conversion into fruit orchard cultivation led to a decrease of 5 to 23% and 4 to 21% on SOC and N stocks, respectively. Compared to other soil uses, sapote and bullock's heart contributed for a lower decrease of SOC and N stocks after deforestation. Guava, bullock's heart, mango and sapote contributed for improving the SOC stratification index.

Variabilidade espacial da resistência do solo à penetração e da taxa de estratificação de carbono orgânico do solo em um Latossolo Vermelho eutroférrico

A compactação e a qualidade do solo são constantemente questionadas para a definição do manejo de solo em plantio direto. Os objetivos deste estudo foram avaliar a variabilidade espacial da resistência do solo à penetração, da densidade do solo e a taxa de estratificação de carbono orgânico do solo em camadas de um Latossolo Vermelho eutroférrico, textura muito argilosa, em áreas contíguas de plantio direto com rotação de culturas e plantio direto com sucessão de culturas associado à escarificação. O estudo foi realizado de maio a junho de 2002, no município de Palotina, região Oeste do Paraná. As amostras para determinação da densidade do solo, da resistência do solo à penetração e do teor de carbono orgânico do solo foram obtidas em 120 pontos, em uma grade de 2 x 5m, na profundidade de 0,40m. Foram feitas três medidas de resistência do solo à penetração, em um período de 10 dias, iniciado depois de cessada a precipitação. A densidade do solo não explicou a dependência espacial da compactação do solo. A resistência do solo à penetração e a taxa de estratificação de carbono orgânico do solo apresentam alcances de 17m. A variação temporal da dependência espacial da resistência do solo à penetração ocorre nas camadas de 0,05-0,20m. As semelhanças da dependência espacial da resistência do solo à penetração e da taxa de estratificação de carbono orgânico do solo, revelaram a importância da qualidade do solo na estabilização espacial e temporal da compactação do solo, expressa pela resistência do solo à penetração em sistemas de plantio direto.

Improving soil surface properties: a driving force for conservation tillage under semi-arid conditions

The effect of long term conservation tillage (CT) application on soil organic carbon (SOC) concentration, and on stratification ratios (SR) of SOC, soluble organic carbon (SOCs), microbial biomass carbon (MBC) and protease activity (PA) has been studied. The SR was established dividing values of these variables at 0-5 cm depth by values at 10-25 cm depth. The results were compared with those obtained under traditional tillage (TT). The study was conducted in a wheat-sunflower crop rotation established in 1991 under rainfed conditions in south-west Spain. The results showed here correspond to the years 2001 (sunflower) and 2002 and 2004 (wheat). Despite a slight increase in SOC and the SR of SOC under CT compared to TT, noticeable and significant increases of SR of SOCs, MBC and PA were recorded in CT compared to TT. These increases reveal that the stratification of SOC under CT have consequences on soil functions beyond that of potentially sequestering more C in the soil. CT also improved soil quality by softening the loss of CaCO3, compared to TT.

Duration of tillage management affects carbon and phosphorus stratification in phosphatic Paleudalfs

Surface accumulation of soil organic carbon (SOC) under conservation tillage has significant effects on stratification of other nutrients, on crop productivity and in ameliorating the greenhouse effect via atmospheric CO 2 sequestration. A measure of SOC stratification relative to deeper soil layers has been proposed as a soil quality index. Our objective was to determine the effects of the duration of tillage practices upon the SOC and extractable P distribution with depth in Maury silt loams (Typic Paleudalfs) at similar levels of corn ( Zea mays L.) productivity without P fertilization. Soil samples (0–20.0 cm in 2.5 cm increments) were collected under moldboard tillage (MT), chisel tillage (CT) and no-tillage (NT) and in surrounding tall fescue ( Festuca arundinacea L.) sods selected from three tillage experiments (1–2-, 8- and 29-year durations) in Kentucky. SOC stratification was greater under conservation tillage (CT and NT) and sods than under MT. SOC and soil-test-extractable P stratification were positively related. Increasing the duration under NT caused the thickness of C stratification to increase. In NT soils, C stratification ratio (CSR) approached CSR in the nearby long-term sods with time. Conservation tillage rapidly promoted the occurrence of CSR greater than 2 while MT always resulted in values lower than 2. The rapid initial change in CSR suggests characterization of thin soil layers (i.e. 2.5 cm depth increments) is desirable under conservation tillage.

Eye-dropper technique proves effective method of testing steel

The importance of soil organic carbon (SOC) sequestration in agricultural soils as climate-change-mitigating strategy has become an area of focus by the scientific community in relation to soil management. This study was conducted to determine the temporal effect of different tillage systems and residue management on distribution, storage and stratification of SOC, and the yield of rice under double rice (Oryza sativa L.) cropping system in the southern China. A tillage experiment was conducted in the southern China during 2005–2011, including plow tillage with residue removed (PT0), plow tillage with residue retention (PT), rotary tillage with residue retention (RT), and no-till with residue retention on the surface (NT). The soil samples were obtained at the harvesting of late rice in October of 2005, 2007 and 2011. Multiple-year residue return application significantly increased rice yields for the two rice-cropping systems; yields of early and late rice were higher under RT than those under other tillage systems in both years in 2011. Compared with PT0, SOC stocks were increased in soil under NT at 0–5, 5–10, 10–20, and 20–30 cm depths by 33.8, 4.1, 6.6, and 53.3%, respectively, in 2011. SOC stocks under RT were higher than these under other tillage treatments at 0–30 cm depth. SOC stocks in soil under PT were higher than those under PT0 in the 0–5 and 20–30 cm soil layers. Therefore, crop residues played an important role in SOC management, and improvement of soil quality. In the 0–20 cm layer, the stratification ratio (SR) of SOC followed the order NT>RT>PT>PT0; when the 0–30 cm layer was considered, NT also had the highest SR of SOC, but the SR of SOC under PT was higher than that under RT with a multiple-year tillage practice. Therefore, the notion that conservation tillage lead to higher SOC stocks and soil quality than plowed systems requires cautious scrutiny. Nevertheless, some benefits associated with RT system present a greater potential for its adoption in view of the multiple-year environmental sustainability under double rice cropping system in the southern China.