SUMMARYThe soil CO 2 emission has high spatial variability because it depends strongly on soil properties. The purpose of this study was to (i) characterize the spatial variability of soil respiration and related properties, (ii) evaluate the accuracy of results of the ordinary kriging method and sequential Gaussian simulation, and (iii) evaluate the uncertainty in predicting the spatial variability of soil CO 2 emission and other properties using sequential Gaussian simulations. The study was conducted in a sugarcane area, using a regular sampling grid with 141 points, where soil CO 2 emission, soil temperature, air-filled pore space, soil organic matter and soil bulk density were evaluated. All variables showed spatial dependence structure. The soil CO 2 emission was positively correlated with organic matter (r = 0.25, p < 0.05) and air-filled pore space (r = 0.27, p < 0.01) and negatively with soil bulk density (r = -0.41, p < 0.01). However, when the estimated spatial values were considered, the air-filled pore space was the variable mainly responsible for the spatial characteristics of soil respiration, with a correlation of 0.26 (p < 0.01). For all variables, individual simulations represented the cumulative distribution functions and variograms better than ordinary kriging and E-type estimates. The greatest uncertainties in predicting soil CO 2 emission were associated with areas with the highest estimated values, which produced estimates from 0.18 to 1.85 t CO 2 ha -1 , according to the different scenarios considered. The knowledge of the uncertainties generated by the different scenarios can be used in inventories (r = 0,25, p < 0,05) e a porosidade livre de água (r = 0,27, p <0,01) e negativa com a densidade do solo (r = -0,41, p < 0,01)

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Soil CO 2 emission (FCO2) is governed by the inherent properties of the soil, such as bulk density (BD). Mapping of FCO2 allows the evaluation and identification of areas with different accumulation potential of carbon. However, FCO2 mapping over larger areas is not feasible due to the period required for evaluation. This study aimed to assess the quality of FCO2 spatial estimates using values of BD as secondary information. FCO2 and BD were evaluated on a regular sampling grid of 60 m × 60 m comprising 141 points, which was established on a sugarcane area. Four scenarios were defined according to the proportion of the number of sampling points of FCO2 to those of BD. For these scenarios, 67 (F67), 87 (F87), 107 (F107) and 127 (F127) FCO2 sampling points were used in addition to 127 BD sampling points used as supplementary information. The use of additional information from the BD provided an increase in the accuracy of the estimates only in the F107, F67 and F87 scenarios, respectively. The F87 scenario, with the approximate ratio between the FCO2 and BD of 1.00:1.50, presented the best relative improvement in the quality of estimates, thereby indicating that the BD should be sampled at a density 1.5 time greater than that applied for the FCO2. This procedure avoided problems related to the high temporal variability associated with FCO2, which enabled the mapping of this variable to be elaborated in large areas.

R E S U M OO preparo mecânico do solo é uma das práticas agrícolas que contribuem para o aumento da perda de carbono via emissão de CO 2 do solo (FCO 2 ). Com este trabalho objetivou-se investigar o efeito de três sistemas de preparo do solo na FCO 2 , temperatura e umidade do solo em área de reforma da cultura de cana-de-açúcar. A área experimental foi constituída de três parcelas, cada uma recebendo um dos preparos do solo: preparo convencional (PC), subsolagem convencional (SC) e subsolagem localizada (SL). A FCO 2 , temperatura e a umidade do solo foram avaliadas durante o período total de 17 dias. A FCO 2 foi maior no preparo PC (0,75 g CO 2 m -2 h -1 ). A temperatura do solo não diferiu (p > 0,05) entre as subsolagens: SL (26,2 ºC) e SC (25,9 ºC). A umidade do solo foi maior na SL (24%), seguida pela SC (21,8%) e preparo PC (18,3%). Apenas no preparo PC foi observada correlação significativa (r = -0,71; p < 0,05) entre FCO 2 e a temperatura do solo. O preparo PC apresentou emissão total (2.864,3 kg CO 2 ha -1 ), superior às emissões nas subsolagens: SC (1.970,9 kg CO 2 ha -1 ) e SL (1.707,7 kg CO 2 ha -1 ). A conversão do sistema de preparo PC para a SL diminuiu as emissões de CO 2 do solo, reduzindo a contribuição da agricultura para o aumento dos gases de efeito estufa na atmosfera.Soil tillage and emission of CO 2 , soil temperature and soil moisture in a sugarcane area A B S T R A C TSoil tillage is one of the agricultural practices that may contribute to increase the loss of carbon through emission of CO 2 (FCO 2 ). The aim of this study was to investigate the effect of three soil tillage systems on FCO 2 , soil temperature and soil moisture in a sugarcane area under reform. The experimental area consisted of three tillage plots: conventional tillage (CT), conventional subsoiling (CS), and localized subsoiling (LS). FCO 2 , soil temperature and soil moisture were measured over a period of 17 days. FCO 2 showed the highest value in CT (0.75 g CO 2 m -2 h -1 ). Soil temperature presented no significant difference (p > 0.05) between LS (26.2 °C) and CS (25.9 °C). Soil moisture was higher in LS (24%), followed by CS (21.8%) and CT (18.3%). A significant correlation (r= -0.71; p < 0.05) between FCO 2 and soil temperature was observed only in CT. The conventional tillage presented a total emission (2,864.3 kg CO 2 ha -1 ) higher than the emissions observed in CS (1,970.9 kg CO 2 ha -1 ) and LS (1,707.7 kg CO 2 ha -1 ). The conversion from CT to LS decreased soil CO 2 emissions, reducing the contribution of agriculture in increasing the concentration of greenhouse gases in the atmosphere. Palavras-chave:respiração do solo subsolagem cana-de-açúcar gases do efeito estufa

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This study aimed to characterize soil carbon dioxide (CO 2) emission associated with soil pore distribution in an Oxisol and Ultisol under chiseling in the planting row and in total area for sugarcane (Saccharum officinarum) cultivation. The experimental design was a large paired-plot design. Treatments consisted of chiseling in the planting row (CPR) and chiseling in total area (CTA) in an Oxisol and Ultisol. Soil CO 2 emission, soil temperature, and soil moisture were assessed over 12 days in the Oxisol and 11 days in the Ultisol at a depth of 0-0.10 m. Organic carbon associated with minerals (OCAM) and particulate organic carbon (POC) were also assessed. OCAM, pore class C2 (0.05 ≤ ɸ < 0.1 mm), soil moisture, and soil temperature explained 72 and 53% of the variability of soil CO 2 emission in CPR and CTA, respectively. In the Ultisol, pore class C1 (ɸ ≥ 0.1 mm) and OCAM explained 82% of the variability of soil CO 2 emission in CPR. In CTA, soil moisture, OCAM, and POC explained 67% of the variability of soil CO 2 emission. In the Oxisol, CPR and CTA affected soil structure, causing changes in both soil porosity and soil CO 2 emission. In the Oxisol, the lowest average value of soil CO 2 emission (2.8 μmol m −2 s −1) was observed in CPR whereas its highest value (3.4 μmol m −2 s −1) was observed in CTA. In the Ultisol, soil tillage (CPR and CTA) did not affect soil CO 2 emission. These results indicate that the intensity of soil tillage in more clayey textured soils favors soil CO 2 emission possibly due to a higher carbon availability for microbial activity when compared to more sandy textured soils. A less intensive soil tillage can be considered as an efficient strategy to reduce soil CO 2 emission and hence soil organic carbon losses. Thus, this management strategy proved to be efficient in terms of mitigating greenhouse gas emissions, reducing the contribution of agriculture to global climate change.

Core Ideas Spatial distribution P. brachyurus nematode is influenced by soil chemical properties. In sites with low fertility the plants become more susceptible to nematode attack. In sites concentrating greater amount Mg are favorable to greater number of nematode. The economic damage to Brazilian soybean [Glycine max (L.) Merr.] production attributed to Pratylenchus brachyurus has increased in recent years. The objective of this study was to determine the influence of soil properties on nematode variability in a soybean crop. Soil and root samples (0–0.20 m) were collected from 142 points in an area that was 180 by 180 m. Root samples were analyzed for nematodes, and soil samples were analyzed for chemical attributes. The data were analyzed using principal component analysis and geostatistics. The spatial variability maps of the attributes S, Ca, Mg, K, sum of bases, base saturation index, and cation exchange capacity were aligned with the water runoff direction. Soil organic matter and K were associated with very low number of nematodes in the root (NNR) (NNR ≤ 3614), low (3614 < NNR ≤ 10,496), and moderate (10,496 < NNR ≤ 21,248). On the other hand, the regions with high Mg, S, and soybean productivity were associated with regions with high (21,248 < NNR ≤ 43,648) and very high (NNR > 43,648) NNR. The findings indicated that soil chemical characteristics influence the population dynamics of the root‐lesion nematode P. brachyurus.