Management impacts on soil organic matter of tropical soils.

Increased soil organic matter (SOM) improves the cation exchange capacity of tropical weathered soils, and liming is required to achieve high yields in these soils. Despite a decrease in SOM in the short term, liming may increase SOM with time by improving cation chemical bonds with soil colloids. Soil C may also be increased in high dry matter input cropping systems. We evaluated C changes in a Typic Rhodudalf as affected by four production systems with increasing residue inputs, with or without limestone or silicate. Soil use intensification by increasing the number of species in rotation as well as acidity remediation resulted in higher plant residue production. Introducing a green manure or a second crop in the system increased plant residue by 89% over fallow, but when a forage crop was used, plant residues more than doubled. Soil acidity amelioration increased plant residue deposition by 21% over the control. The introduction of a forage crop increased labile SOM and C contents in the particulate fraction, and lime or silicate application led to increases in the more stable SOM fraction. High amounts of plant residues (>70 Mg ha?1 in 5 yr) are effective in raising soil labile C, but the alleviation of soil acidity results in increased soil stable C irrespective of crop rotations in tropical weathered soils, and in this case plant residue deposition can be lower. Lime and silicate are equally effective in alleviating soil acidity and increasing soil C, probably due to the formation of cation bridges with soil colloids

Balanço de potássio no sistema plantio direto em razão da adubação potássica na sucessão milheto-soja.

Trabalho publicado também nos Resumos do CONGRESSO BRASILEIRO DE SOJA, 6., 2012, Cuiabá

COSMOS: the COsmic-ray Soil Moisture Observing System

The newly-developed cosmic-ray method for measuring area-average soil moisture at the hectometer horizontal scale is being implemented in the COsmic-ray Soil Moisture Observing System (or the COSMOS). The stationary cosmic-ray soil moisture probe measures the neutrons that are generated by cosmic rays within air and soil and other materials, moderated by mainly hydrogen atoms located primarily in soil water, and emitted to the atmosphere where they mix instantaneously at a scale of hundreds of meters and whose density is inversely correlated with soil moisture. The COSMOS has already deployed more than 50 of the eventual 500 cosmic-ray probes, distributed mainly in the USA, each generating a time series of average soil moisture over its horizontal footprint, with similar networks coming into existence around the world. This paper is written to serve a community need to better understand this novel method and the COSMOS project. We describe the cosmic-ray soil moisture measurement method, the instrument and its calibration, the design, data processing and dissemination used in the COSMOS project, and give example time series of soil moisture obtained from COSMOS probes

Consequence of clear-cutting and drought on deep soil CO2 and N2O profile concentrations and surface fluxes in Brazilian eucalypt plantations

The major factors driving greenhouse gas effluxes from forest soils (substrate supply, temperature, water content) vary with soil depth. Our study aimed to assess the consequences of drought on the temporal variability of CO2 and N2O fluxes throughout very deep soil profiles in Eucalyptus grandis plantations at the end of the rotation and the first 16 months after clear-cut, in coppice. Two treatments were compared: one with 37% of throughfall excluded by plastic sheets (TE), and one without rain exclusion (WE). Every two weeks for 19 months, soil CO2 and N2O surface fluxes were measured using the closed-chamber method and the profile concentrations were measured at 7 depths in the soil down to 15.5m from in each treatment. CO2 and N2O concentrations measured in treatment TE were on average 17.3 and 5.8% lower than in treatment WE, respectively, throughout the soil profile. Across the two treatments, CO2 concentrations increased from 4102 ±2310 ppm at 10cm deep to 14480±2854 ppm at 15.5m and N2O concentrations remained roughly constant down to 15.5m. Improving our understanding of the spatiotemporal dynamics of gas concentrations in deep soil layers is an important issue for the management of tropical planted forests in the context of climate change. (Résumé d'auteur