Haplic Acrisol Research Articles

The pH buffering capacity of Acrisols under cassava production in Southeastern Vietnam, Chau Thanh district

AbstractThis study examined the pH buffering capacity (pHBC) of haplic Acrisols under intensive cassava production in an upland area of Southeastern Vietnam where accelerated soil acidification has occurred. Soil samples (0–20, 20–40 and 40–60 cm) were taken at 12 sites under cassava and three sites under secondary dipterocarp forest as reference. The pH buffer curves were linear in the pHH2O range from 3.97 to 5.24, corresponding to a pHCaCl2 range from 3.74 to 5.20. Soil pHBC were low (1.16 ± 0.13 cmol/kg/pH) and correlated significantly with pH, Aluminium (Al) and Al‐related components. The results suggested that exchange acidity contributes significantly to soil's buffering capacity in acidic soils with low organic carbon. It also pointed to the possibility of using indicators of acidity to estimate soil pHBC. The low pHBC indicated a high risk for further acidification and also pointed to the possibility of using lime to remediate soils. Either acid buffering capacity or lime buffering capacity not pHBC in general should be considered, respectively, in acidification and liming studies. Factors and processes involved in soil acidification and liming need to be addressed as a background for soil remediation in the study area.

Biological nitrogen fixation and soil N2O emissions from legume residues in an Acrisol in SE Brazil

Information is lacking concerning the contribution of green manure legumes to N2O emissions from tropical soils. In a three-year field study, we measured the N accumulation and the N2 fixation by three green manure legumes and the effects of their residues on N2O production from a tropical soil (Haplic Acrisol) under an organic farming system. The legumes were jack bean (Canavalia ensiformis L.), velvet bean [Mucuna pruriens (L.) DC] and sunn hemp (Crotalaria juncea L.), which were mown at the late pod-filling stage. The N accumulation in residues varied substantially among the legume types and the growing seasons (78–422 kg ha−1). The contribution of N2 fixation to legume residues, expressed as the proportion of N in plant derived from air (%Ndfa), was relatively low in the first year (23–36%) and increased significantly in the following two years (46–85%). The highest amount of N2 fixed was in the residues of jack bean, reaching 360 kg N ha−1. The residue of this legume and that of velvet bean caused the highest mean annual soil N2O emissions (3.78 and 3.29 kg N2O-N ha−1, respectively). The mean percentage of N lost as N2O derived from residues was not significantly affected by legume type, ranging from 0.58% (sunn hemp) to 0.72% (velvet bean). These percentages were below the default IPCC emission factor of 1% for N additions from plant residue or from synthetic fertilizers. We also showed that N in legume residues derived from BNF offers an important environmental advantage over synthetic N fertilizers owing to the avoidance of GHG emissions (360–944 CO2-equivalent ha−1 yr−1) during Haber-Bosch process and also during transportation and application in the fields. The three green manure legumes provided significant higher cash crop (squash) yield compared to maize, indicating the direct economic benefit of BNF for organic farming. More field studies are needed to assess the dynamics of gaseous N losses from plant residues in other tropical biomes.

Aggregate stability affects carbon sequestration potential of different tropical soils

Aggregate stability and carbon (C) sequestration in soils are closely related phenomena. However, high aggregate stability does not always ensure high carbon sequestration to some soil types since other binding agents could dominate other than carbon. Thus, this study aimed to determine the relationship between aggregate stability and carbon sequestration of different tropical soils which basically differ in geology, genesis, and possibly in their dominant aggregating agents. The study selected four representative soil types (Haplic Acrisol, Calcaric Cambisol, Silic Andosol and Haplic Ferralsol) found in Leyte and Samar that were characterized by previous workers. Soil Organic Carbon (SOC) and Aggregate Stability (AS) in dry and wet conditions were quantified using standard procedures. Some pertinent secondary data were also recorded as reference for each soil type. Results revealed that only Silic Andosol showed positive significant correlation (0.93) between aggregate stability and soil organic carbon (SOC). The other soil types showed weak and negative correlation between aggregate stability and SOC; however, their stability revealed a strong positive relationship with inorganic binding agents. Therefore, each soil type reflects a different relationship between aggregate stability in wet condition and SOC and that the variations could be attributed to the differences in the morpho-physical and geochemical nature of the soils. Moreover, SOC is found to greatly influence the aggregate stability in Silic Andosol, thus the soil carbon sequestration potential of this soil type is generally related to its aggregate stability. However, in other soil types like Haplic Acrisol, Calcaric Cambisol, and Haplic Ferralsol, other binding agents like Calcium (Ca) and iron oxides dominate and control the formation and stability of aggregates rather than SOC.

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

AbstractSoil gross nitrogen (N) transformations are crucial for assessing forest N status. Although there is evidence suggesting that the N cycle is open in the karst forest, southwest China, process‐based investigation of gross soil N transformations is limited. In the current study, gross soil N transformations were investigated using 15N isotope dilution and 15N tracer techniques in a typical karst forest with calcareous soil (Calcareous lithosols) in comparison with an adjacent nonkarst forest with red soil (Haplic acrisol).The gross rates of N mineralization, nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and nitrate immobilization were significantly greater in the karst forest. Ammonium immobilization was comparable to gross N mineralization, so that ammonium could be efficiently conserved in the nonkarst forest. Meanwhile, the produced nitrate was mostly retained via DNRA and nitrate immobilization. This resulted in a negligible net nitrate production in the nonkarst forest. In contrast, ammonium immobilization rate only accounted for half of gross N mineralization rate in the karst forest. The nitrate retention capacity is relatively low, with 41.6 ± 4.2% of the produced nitrate being retained via DNRA and nitrate immobilization. Due to relatively low nitrate retention capacity, nitrate was accumulated in the karst forest soil. Our results indicate that the nonkarst forest with red soil holds a very conservative N cycle, but the N cycle in the karst forest is leaky.

Adsorption and risk of phosphorus loss in soils in Amazonia

Low availability of phosphorus in Amazonian soils is the result of both naturally occurring low levels and adsorption processes in the soil. These factors encourage the use of intensive phosphate fertilizations to increase productivity, which, in turn, increases P saturation and contamination risk. This study was designed to determine the adsorption capacity, as well as the risk of P loss and contamination of water bodies by P in Amazonian soils. Eleven soils located in zones free from any alteration were selected in order to set parameters for natural conditions for the local soils. Adsorption experiments were carried out in CaCl2 solution 0.01 mol L−1, containing 0 to 200 mg L−1 of P in the form of KH2PO4. The phosphorus sorption index (PSI) was determined, and soluble and available forms of P were extracted in water, Mehlich-1, Olsen, and CaCl2 solutions. The phosphorus saturation degree (PSD) was obtained by extraction with acid solution of ammonium oxalate. PSI was lower in the soil GL (Eutric Gleysol) and higher for NT (Rhodic Nitisol), while the maximum adsorption capacity (Smax) was lower in the soil AR (Ferralic Arenosol) and higher in AC1 (Haplic Acrisol 1). The PSD was higher in AT (Hortic Anthrosol) which also showed higher values of soluble and available P, while lower saturation values were observed in FR2 (Xanthic Ferralsol), FR4 (Rhodic Ferralsol), Haplic Acrisol 2, and Eutric Gleysol (< 5%). These soils presented low to medium maximum adsorption capacity and low P saturation; however, Ferralic Arenosol soil showed a high risk of P loss, making P management very difficult. Similarly, Hortic Anthrosol showed high susceptibility to P loss.

Characteristics of soil acidification of haplic Acrisols on ancient alluvial deposits under intensive cassava cultivation in Chau Thanh district, Tay Ninh province

Characteristics of soil acidification of haplic Acrisols on ancient alluvial deposits under intensive cassava cultivation in Chau Thanh district, Tay Ninh province

Data mining methods applied to map soil units on tropical hillslopes in Rio de Janeiro, Brazil

A soil survey is the main source of soil spatial information and is very useful in supporting land use decisions, especially for agronomic purposes. However, the continuity of soil surveying in Brazil has been compromised due the minimal amount of government investment in the sector. The goal of this study was to evaluate the performance of three data mining methods—decision trees (DT), random forest (RF), and artificial neural networks (ANN)—with R software to predict soil map units from the Guapi-Macacu watershed in Rio de Janeiro State, Brazil. Terrain attributes derived from a digital elevation model (DEM), remote sensing data (Landsat 5), and a geology map were used as predictors. Evaluation of the models' performance was based on statistical indices obtained from a confusion matrix by using validation samples. Furthermore, a comparison was performed to analyze the agreement between the maps created from the models and from a conventional soil map (legacy data); sampling locations were not used as input data in the training process. The results indicated better performance from the RF model compared with the DT and ANN models. The accuracy was calculated through validation samples indicating values in the Kappa index corresponding to 0.76 (RF), 0.72 (ANN) and 0.66 (DT). A comparison between the maps obtained from the models and the conventional soil map exhibited better agreement with the RF model (68.7%), followed by the ANN (62.8%), and DT (62.3%) models. The classification accuracy, obtained through comparisons with sampling locations, exhibited correct classification of 57.6% in the RF model, 56.8% in the DT, and 56.1% in the ANN model; the conventional soil map had 69.7% correct classification. In general, most of the confusion between soil map units was observed in Haplic Gleysols, Haplic Acrisols (Clayic) and Fluvisols. In terms of covariates importance, in general, the terrain attributes derived from the DEM had more influence as predictor covariates than the indices obtained from the Landsat data. The application of data mining can improve the methods applied to soil map units, thereby contributing to increasing information related to soil-landscape relationships and enhancing the products of soil surveys.

Mapping of natural gamma radiation (NGR) dose rate distribution in tin mining areas of Jos Plateau, Nigeria

An extensive study was conducted to measure the natural gamma radiation (NGR) dose rates for the tin mining areas of Jos Plateau with an objective to establish a reference data record on the levels and distribution of natural background gamma radiation. The measurement was carried out using a portable NaI(Tl) scintillation survey meter. The results obtained, varied significantly for different soil types and for geological features of the study area. NGR dose rates values ranged between 40 nGy h−1 measured on Ferric Luvisols–Ferric Luvisols (S13) soil type, underlain by geological formation G7 (sandstone, clay and shale) and 1265 nGy h−1 recorded on, Haplic Acrisols (S27), underlain by geological formation G8 (Younger granites) with overall mean value of 250 nGy h−1. This is by a factor of four higher than the reported world average value of 59 nGy h−1. Mean indoor and outdoor annual effective dose for the public was estimated to be 1.2 and 0.31 mSv/y, respectively. An isodose map for the distribution and exposure rate due to natural sources radiation for the study area was also plotted using ArcGis software. The data here presented can use to prepare a national radiological map for the country.

Influence of Crust Formation on Soil Porosity under Tillage Systems and Simulated Rainfall

Surface crusts, formed by raindrop impact, degrade the soil surface structure causing changes in porosity. An experiment was conducted with the objective of evaluating the influence of the formation of a crusting layer on the porosity (percentage of area, shape and size) of a Haplic Acrisol under three tillage systems, and simulated rainfall. The tillage systems were: conventional tillage (CT), reduced tillage (RT) and no-tillage (NT). Each tillage system was submitted to different levels of simulated rainfall (0, 27, 54 and 80 mm) at an intensity of 80 mm·h−1. Undisturbed soil samples were collected and resin impregnated for image analysis in two layers: layer 1 (0–1 cm) and layer 2 (1–2 cm). Image analysis was used to obtain the pore area percentage, pore shape and size. The degradation of the soil surface and change in porosity, caused by rainfall, occurred differently in the tillage systems. In the CT and RT systems, the most pronounced pore changes caused by rainfall occurred in layer 1, but in the NT system, this change occurred in layer 2. The rainfall caused change of pore area percentage in the CT and RT systems, with reduction of complex and an increase of rounded pores. The NT system showed greater occurrence of the rounded pores (vesicles), originated by processes of wetting below the residue cover, and by alternating periods of wetting and drying. In this study, the changes in porosity were attributed to two main factors: (1) to the effect of the raindrop directly on the soil surface (for CT and RT tillage systems) and (2) water transfer processes in the soil surface (for NT systems).

Produtividade e composição mineral do feijão em resposta às adubações com molibdênio e níquel

RESUMO Níquel e molibdênio são micronutrientes essenciais que apresentam a capacidade de alterar o crescimento e o desenvolvimento do feijoeiro. O objetivo deste trabalho foi avaliar a produtividade, o crescimento e a composição mineral do feijão Ouro Vermelho em resposta às adubações com molibdênio (Mo) e níquel (Ni). O experimento foi conduzido a campo em Argissolo Acinzentado distrófico, no arranjo fatorial 5 x 2, referente a cinco doses de Ni (0; 15; 30; 45 e 60 g ha-1) e duas de Mo (0 e 80 g ha-1), no delineamento em blocos casualizados, com quatro repetições. A aplicação foliar de Ni e Mo foi feita aos 25 dias após a semeadura, por meio de um pulverizador manual. As características avaliadas foram: estande final, altura, produtividade, número de vagens por planta, número de sementes por vagem, massa de 100 sementes e os teores de N, P, K, Fe, Mo, e Ni. Verificou-se que a adubação molíbdica aumentou o teor de N na folha, reduziu o teor de Fe na semente e, em doses elevadas de Ni, reduziu o teor de Ni nas sementes. As doses de Ni, sem aplicação de Mo, aumentaram o teor de N na folha e, na presença do Mo, aumentaram o teor de Fe na semente. Houve aumento do número de grãos por vagem, com a aplicação de Ni, e da massa seca da parte aérea, com a adubação molíbdica. As adubações com 80 g ha-1 de Mo e 60 g ha-1 de Ni aumentaram em 12,71 e 27,5%, respectivamente, a produtividade do feijoeiro.

Effect of Dissolved Organic Matter from Wheat Straw or Swine Manure on the Cu Adsorption in Three Chinese Soils

Batch equilibration experiments were conducted to evaluate the effects of dissolved organic matter (DOM) from wheat straw (DOMw) and swine manure (DOMs) on copper (Cu) adsorption and behavior in Haplic Phaeozems, Haplic Acrisol, and Eutric Fluvisol in China. Results showed that the Cu adsorption isotherms were well fitted with both Langmuir and Freundlich equations. The Cu maximum potential adsorption capacity of the three soils followed the order of Eutric Fluvisol > Haplic Phaeozems > Haplic Acrisol. DOMw and DOMs increased the Cu adsorption capacity in Haplic Phaeozems and Haplic Acrisol, and the promoting role of DOMs on Cu adsorption was obviously higher than that of DOMw. Increasing DOM concentration of DOMw and DOMs promoted the Cu adsorption in Haplic Phaeozems and Haplic Acrisol. However, this promoting effect weakened with increasing DOM concentration. Moreover, DOMw and DOMs inhibited the Cu adsorption in Eutric Fluvisol, and this inhibitory effect significantly increased with increasing DOM concentration. The results may be used to assess the potential environmental contamination of the studied soils and to control the application of organic fertilizers.

Effects of agricultural wastes ash on nutrients concentration and yield of maize (Zea mays l) in Haplic Acrisol of Southeastern Nigeria

Field trials and a pot experiment were conducted during the 2005 and 2006 cropping seasons at Michael Okpara University of Agriculture, Umudike, Nigeria, to assess the effect of various agricultural wastes ash on nutrient concentration, growth and yield of maize in a Haplic Acrisol. The treatments comprised palm bunch ash, kitchen residues ash, cocoa pod husk ash, saw dust ash, calcium carbonate, oyster shell ash and a control. Each of the ash was applied at five levels: 0, 2, 4, 6 and 8 tonnes per hectare. They were replicated three times in a split plot completely randomized design for the pot experiment and randomized completely block design for the field trials. The effects of the treatments were measured on nitrogen, phosphorus, potassium, calcium, and manganese and iron concentration in maize crop. Other plant parameters measured were maize height at 8 weeks after planting, stem diameter, stover weight and grain yield weight in the field trails. The results obtained showed that all the agricultural wastes significantly (P < 0.05) increased the concentrations of nitrogen, phosphorus, potassium and calcium. They also significantly (p<0.05) reduced the concentration of iron and manganese in the plant. The wastes applied significantly increased the plant height at 8 WAP, maize stem diameter, stover weight and grain yield. Among the treatments tested, 6t/ha of cocoa pod husk ash significantly (P<0.05) increased nitrogen concentration in the maize from 0.49 in the control to 5.17%. Plant height, stem diameter and stover weight were also increased by the application of 6t/ha of cocoa pod husk ash. While 4t/ha of kitchen residue ash, 4t/ha of oyster shell ash and 4 t/ha of cocoa pod husk ash significantly (P<0.05) increased the concentration of phosphorus from 1.01% to 4.98%, calcium from 0.4% to 6% and potassium from 0.19% to 0.42% respectively. The soil pH correlated negatively with iron and manganese concentration, positively with phosphorus and calcium concentration. These results show that maize can be grown successfully on Haplic Acrisol of the Southeastern Nigeria using waste from agricultural products. Key words: Agricultural wastes ash, nutrient concentration, growth, grain yield, HaplicAcrisol

Effect of different long-term fertilization regimes on the viral community in an agricultural soil of Southern China

Fertilization plays a pivotal role on soil biological process and affects the soil bacterial community, which act as hosts for viruses. The effect of fertilization on soil viral community has not been well explored. In this study, a Haplic Acrisol soil, which is the soil type for 13 provinces in Southern China, was analyzed after 22 years different fertilization regimes for their viral composition. The soil responded to organic fertilizations with an increased amount of soil organic matter (SOM) and pH (increased from 5.7 to 6.6), while with the decreased SOM and pH for chemical fertilization, especially for single nitrogen fertilization. The combined effects of SOM and pH caused by long-term different fertilization regimes on soil viral communities were investigated by direct calculation of virus-like particles (VLPs) through epifluorescence microscopy. The highest VLP abundance (13.1 × 107 per gram dry soil) was detected in soil applied with chemical and organic fertilizers. The viral and bacterial abundances of organic soil were 4 and 5 times higher than those of inorganic soil respectively. Transmission electron microscopy observation revealed a higher frequency of Myoviridae viruses in soil with organic amendments than without organic amendments, and vice versa for Podoviridae viruses. These results demonstrate that organic fertilizer could increase viral abundance and morphological diversity through suppressing soil acidification and improving soil organic matter.

An evaluation of the factors influencing seed oil production in Camellia reticulata L. plants

Camellia seed oil is well known for its industrial uses. However, despite the increasing use of this oil, few studies have investigated which factors impact seed oil production. Thus, the aims of this study are to identify which factors influence the percentage seed oil of Camellia reticulata, a by investigating both seed and environmental variables. Firstly, fruit traits were studied and correlated against percentage seed oil data, and then environmental variables linked to seed oil production were investigated. The first experiments analyzed how well fruit characteristics (size, length, weight, seed number, seed oil) of the Camellia plants predict percentage seed oil. The second experiment modelled the effect of environmental variables (soil, elevation, temperature and rainfall) on seed oil production. The results indicated that the kernel ratio per fruit, seed weight to fruit weight ratio and fruit weight positively influenced percentage seed oil while, when these previous effects are accounted for, the number of seeds reduced percentage seed oil. The environmental model showed that seed oil was influenced most strongly by elevation and soil type, with haplic Acrisols providing the highest seed oil. Thus it is clear that Camellia seed oil is affected by a variety of factors, and these should be taken into account when selecting species and cultivars for the planting of Camellia stands for oil production.

Influence of Copper on Transport and Dissipation of Lambda-Cyhalothrin and Cypermethrin in Soils

Repeated applications of bordeaux mixture (a blend of copper sulfate and calcium hydroxide) and pyrethroid insecticides (Pys) have led to elevated copper (Cu) and Pys concentrations in vineyard surface soils. To understand the potential influence of Cu on the fate of Pys in the soil environment, we selected two Pys, cypermethrin (CPM) and lambda-cyhalothrin (λ-CHT), and two typical Chinese vineyard soils, Haplic Acrisol and Luvic Phaeozem, as experimental samples. The dissipation experiment was conducted at room temperature in the dark, and the transport of both Pys through the soils was investigated using soil thin-layer chromatography. The results showed that the transport of Pys in both soils increased as the Cu2+ concentration increased from 0 to 100 mg L−1, and Pys were more transportable in Haplic Acrisol (HA) than in Luvic Phaeozem (LP) under the same experimental conditions. For CPM, only 100 mg L−1 of Cu2+ significantly (P < 0.05) increased Pys transport through both soils relative to water. Lambda-CHT was significantly (P < 0.05) transported through HA by all the Cu2+ concentrations compared to water, and all but the 1 mg L−1 of Cu2+ significantly (P < 0.05) increased the transport of λ-CHT through LP relative to water. However, the dissipation rates of CPM and λ-CHT decreased with the addition of Cu to soils. Our findings suggest that the risk of groundwater contamination by Pys increases in the soils with elevated Cu concentrations.

Characteristics of termite mounds and associated Acrisols in the coastal savanna zone of Ghana and impact on hydraulic conductivity

Characteristics of termite mounds and associated Rhodic Acrisol and Haplic Acrisol in the coastal savanna zone of Ghana and their impact on hydraulic conductivity were assessed. The texture of the mounds was sandy clay in contrast to the sandy clay loam of the surface soils. Translocation of fine to medium sized soil materials influenced the relatively higher bulk density (>1.60 Mg/m3) and contents of organic carbon, nitrogen and exchangeable bases in the mounds. Kaolinite was the dominant clay mineral with pH values generally below 5.3 in all the soils reflecting the weathered tropical soil environment. Dispersion ratio values, which were 0.5 for the surface soils, indicated greater stability of the mound due to aggregate cementing action by the termites. Estimated mound density was about 120 mounds per ha, which tied in with known groundwater reserves at the study sites. Majority of the mounds exhibited a cone-shaped morphology with heights varying between 3.05-4.00 m in the Rhodic Acrisol and 2.05-4.20 m in the Haplic Acrisol with corresponding estimated total mass of 96,361 kg and 54,910 kg per 1000 m2 land area. These estimates represented a large amount of material relative to the 25,000-26,000 kg of surface soil material within the same unit area. The K in the surface soils ranged from 3.3 x 10-5 to 5.0 x 10-5 m/s while the value for the mound was ≤0.5 x 10-5 m/s. Lower porosity, θ; the effect was more pronounced when the mound was applied on the soil surface. Improvement in water retention and nutrient availability to plants and prevention of leaching to avoid groundwater contamination are some of the positive attributes of this study.

Municipal Household Solid Waste Compost: Effects on Carrot (&lt;i&gt;Daucus carrota&lt;/i&gt;) Yield and Nutrient Content

An experiment was conducted to evaluate the impact of municipal household solid waste compost on N, P and K uptake and yield of carrot (Daucus carrota), using a coastal savanna Haplic Acrisol. Bulked samples of fresh solid waste from 45 households within the Cape Coast Municipality in the Central Region of Ghana with 57 % total mass of organic components were composted using the pit method. Treatments applied were control, single supper phosphate (SSP) at 1.8g pot-1 and sulphate of ammonia (SoA) at 2.0g pot-1, compost at 7.0g pot-1 and 14.0g pot-1, combined application of the 2 rates of compost and mineral fertilizer, and combined application of the 2 rates with 2.0g pot-1 SoA. Each pot contained 7.0 kg of soil. A completely randomized design with four replicates was used. Carrot seeds were sown and nitrogen, phosphorus and potassium concentrations in carrot shoots were determined at six weeks after germination. Combined application of compost and inorganic fertilizer significantly increased N, P, K and ash concentration in the carrot shoot. Compost applied at 14.0g pot-1 in combination with 1.8g pot-1 SSP and 2.0g pot-1 SoA supplied 23 % N, 34 % K and 20 % ash to the carrot shoot, whereas sole application of compost at 14.0g pot-1 contributed 4.9 % N, 7.4 % K and 13.65 % ash respectively to the carrot shoots. Phosphorus content measured in the carrot shoots were however < 2.6 % in all treatments. Carrot yield positively correlated with shoot N, P and K contents (P < 0.01).Keywords: Household solid waste, compost, biodegradable, Haplic Acrisol, Daucus carrota.

Produtividade de soja e milho após coberturas de inverno e descompactação mecânica do solo

O objetivo deste trabalho foi avaliar o efeito de coberturas de inverno e da descompactação mecânica do solo sobre o desempenho de soja e milho, em sistema de plantio direto. Foram conduzidos dois experimentos em Eldorado do Sul, RS, sobre Argissolo Vermelho compactado, nas safras 2005/2006 e 2006/2007. No primeiro, o delineamento experimental foi em blocos ao acaso, com parcelas subdivididas. Os tratamentos consistiram de duas profundidades teóricas de atuação da haste sulcadora da semeadora (0,06 e 0,12 m, subparcela) e de três tipos de coberturas do solo no inverno (parcela): pousio, aveia-preta (Avena strigosa) e aveia-preta+ervilhaca (Vicia Sativa). Em 2006, a cobertura aveia-preta+ervilhaca foi substituída por nabo-forrageiro (Raphanus sativus). No segundo experimento, realizado em blocos ao acaso, o solo foi escarificado e os tratamentos consistiram do uso de aveia-preta ou nabo-forrageiro como cobertura de inverno. Os cultivos de cobertura reduziram a compactação superficial do solo (0-0,06 m) em comparação ao pousio e, na safra 2006/2007, sob condições de baixa disponibilidade hídrica, proporcionaram maior produtividade de milho e soja. Isso não se repetiu em 2006/2007, quando a disponibilidade hídrica foi adequada. O aumento da profundidade de atuação das hastes sulcadoras não influenciou a produtividade da soja e do milho. A escarificação reduziu a produtividade da soja e do milho em relação ao SPD contínuo.

Fitomassa e relação C/N em consórcios de sorgo e milho com espécies de cobertura

O objetivo deste trabalho foi quantificar a produtividade de fitomassa, o teor e acúmulo de nitrogênio (N), e a relação carbono/nitrogênio (C/N) de monocultivos de sorgo (Sorghum bicolor) e milho (Zea mays) e de seus consórcios com guandu-anão (Cajanus cajan), crotalária (Crotalaria juncea), tremoço branco (Lupinus albus), girassol (Helianthus annuus) e nabo-forrageiro (Raphanus sativus), manejados em diferentes estádios. O experimento foi conduzido de março a julho de 2008, em Argissolo Vermelho distroférrico de textura média, no sistema plantio direto. O delineamento experimental foi o de blocos completos ao acaso, com quatro repetições, e parcelas subdivididas, constituído pelos tratamentos: monocultivos de sorgo e milho e seus respectivos consórcios com guandu-anão, crotalária, girassol, nabo-forrageiro e tremoço branco, nas parcelas; e épocas de corte, aos 60, 90 e 120 dias após a semeadura nas subparcelas. Consórcios de sorgo e milho com outras espécies superaram expressivamente a produtividade de fitomassa de seus monocultivos que ainda acumularam menos N e apresentaram maiores relações C/N na fitomassa. Para aumentar a produtividade de fitomassa, a melhor época de corte é aos 120 dias após a semeadura das culturas de cobertura. O corte aos 90 dias após a semeadura propicia o maior acúmulo de N e as menores relações C/N.

Spatial changes in soil organic carbon density and storage of cultivated soils in China from 1980 to 2000

We address the spatial changes in organic carbon density and storage in cultivated soils in China from 1980 to 2000 on the basis of measured data from individual studies and those acquired during the second national soil survey in China. The results show a carbon gain in ∼66% of the cultivated area of China as a whole with the increase in soil organic carbon (SOC) density mostly ranging from 10% to 30%. Soil organic carbon density increased in fluvi‐aquic soils (fluvisols, Food and Agriculture Organization (FAO) of the United Nations) in north China, irrigated silting soils (calcaric fluvisols) in northwest China, latosolic red earths (haplic acrisols/alisols), and paddy soils (fluvisols/cambisols) in south China. In contrast, significant decreases are observed in black soils (phaeozems) in northeast China and latosols (haplic acrisols) in southwest China. No significant changes are detected in loessial soils (calcaric regosols) and dark loessial soils (calcisols) in the loess plateau region. The total SOC storage and average density in the upper 20 cm in the late 1990s are estimated to be ∼5.37 Pg C and 2.77 kg/m2, respectively, compared with the values of ∼5.11 Pg C and 2.63 kg/m2 in the early 1980s. This reveals an increase of SOC storage of 0.26 Pg C and suggests an overall carbon sink for cultivated soils in China, which has contributed 2–3% to the global terrestrial ecosystem carbon absorption from 1980 to 2000. Statistical analyses suggest an insignificant contribution to the observed SOC increase from climate change, and we infer that it is mostly attributable to improved agricultural practices. Despite the SOC density increases over 20 years, the SOC density of the cultivated soils in China in the late 1990s is still ∼30% lower compared to their uncultivated counterparts in comparable soil types, suggesting a considerable potential for SOC restoration through improving management practices. Assuming a restoration of ∼50% of the lost SOC in the next 30–50 years, these soils could potentially absorb ∼1.03 Pg C from the atmosphere.