Soil sampling based on disturbed and undisturbed sampling

CO 2 was measured by gas chromatography on a Shimadzu GC-17A equipment. During incubation, no vial showed a variation in sample weight greater than 1%. The vial atmosphere was sampled 1 day after the beginning of incubation (day 0), then every 3 days until day 13, then every 7 days until day 27, on day 42 then every month until day 520. To evaluate a possible influence of the time between sampling and incubation, incubations of aliquot of the same sample were initiated on the sampling day ( tВ =В 0) and 3, 6, 9 and 12 days after sampling ( tВ =В 3, 6, 9 and 12, respectively). For the Bh horizons, composite samples were made over the Bh upper 50В cm for the Cubate soil and the Bh upper 200В cm for the UaupГ©s soils. For the Cubate P and the UaupГ©s A horizons, composite samples were made over the entire horizon thickness. It had a surficial 20-cm thick A horizon overlying a 30-cm thick transitional A-E horizon the E and Bh horizons were 660- and more than 310-cm thick, respectively. In the UaupГ©s area, the soil was situated on a gentle slope inclined toward the river, the vegetation was an evergreen forest of Campinarana Florestada type. It had a surficial 50-cm thick organo-mineral P horizon overlying a 10-cm thick organo-mineral A horizon the E and Bh horizons were 80- and 520-cm thick, respectively. In the Cubate area, the soil was situated in a slightly depressed area subject to frequent surface waterlogging the vegetation was an evergreen forest of Campinarana type. In both areas, the soils developed on sandy continental sediments. Samples were taken from representative podzol soils in two remote areas of the Upper Rio Negro basin, state of Amazonas, Brazil, near the banks of the Cubate and UaupГ©s rivers at 00В° 35вЂІ 48.6вЂІ'N, 67В° 53вЂІ 37.2вЂІ' W and 00В° 10вЂІ 11.2вЂІ' N, 67В° 48вЂІ 56.3вЂІ' W, respectively. In this context, we evaluated a method that allows samples from topsoil or from deeper horizons to be brought back from places located several travel days away from the laboratory, without the need to dry them.

The question raised is then that of the effect of transport time on the mineralization results, do we lose a significant part of very labile organic matter in a few days? Reaching such places requires several days of travel in difficult conditions which do not always allow the transport and installation of heavy instrumentation, or which are incompatible with an extended stay on site necessary for in situ measurements. Many large soil carbon pools around the world are in areas that are difficult to access, as tropical and boreal large forests. This consideration brings up another problem. Recent studies have shown that ex-situ measurement of soil respiration with pre-dried and disturbed samples can give questionable results. Drying the samples or bringing them to field capacity will therefore be a radical ecological change for the existing microbial communities, which could alter the respiration rates. Many soils having a high organic carbon content, however, remain usually all along the year waterlogged or at a moisture level closer to saturation than to field capacity. Such a procedure is well-adapted to agricultural soils that frequently reach field capacity in place. Before incubated, the soil sample is initially dried, sieved and subsequently wetted until reaching the field capacity, or directly conducted to field capacity moisture without drying. A classical method, widely used for agricultural soils, was described by Paul etВ al. Soil microbial respiration rate can be determined in situ, using respiration chambers placed on the topsoil, or in the laboratory by measuring the CO 2 production of a sample placed in incubation chamber. The measurement of soil heterotrophic respiration is of great importance for many purposes and especially for determining the carbon balance of soils in the context of climate change. For each condition, there is an optimum moisture that maximizes respiration: a too high moisture can limit O 2 diffusion and, if below ideal, the access of heterotrophic organisms to soil organic carbon (SOC) becomes restricted. Amongst the main factors that may affect the respiration rate are soil structure, substrate quality and availability, temperature, soil moisture and porosity. The soil heterotrophic respiration is an extremely variable parameter, difficult to quantify. The part not derived from root respiration, called soil heterotrophic respiration, is an indicator of microbial activity which regulates the turnover of organic matter (OM) in the soil. Soil organic carbon mineralization rates are usually evaluated using soil respiration, positively correlated to soil carbon and to microbial biomass and consisting of the sum of radicular and microbial respiration.

Soil sampling based on disturbed and undisturbed sampling