Soil organic matter humification under different tillage managements evaluated by Laser Induced Fluorescence (LIF) and C/N ratio

AbstractIn this work is presented the use of the C/N ratio and the Laser Induced Fluorescence (LIF) spectroscopy for determining the humification of soil organic matter (SOM) in an Oxisol under three different long-term tillage managements (no-tillage (NT), reduced tillage (RT) and conventional tillage (CT)). Humification of SOM was evaluated in the soil and its fractions (clay<2μm, silt 2–20μm, sand 20–1000μm). The obtained results show that lower SOM humification was observed in soil under NT, mainly at the surface (0–5cm). In CT, SOM humification values maintained constant for all investigated depths (0–5, 5–10, 10–15 and 15–20cm). Also, clay was the soil fraction that exhibited the lesser humification of SOM. Based on the obtained results it can be said that NT favors the accumulation of SOM on its surface, increasing aggregate stability and presenting samples with lower humification indexes. These results indicate a larger availability of nutrients for the plants in this management

Optical And Esr Study Of Er3+ In Linbo3

We report laser-excited optical transitions between the 4S3/2 and 4I15/2 multiplets of Er3+ as an impurity in the LiNbO3 host, together with the optical-absorption spectra at liquid-helium and liquid-nitrogen temperatures. The optical data allow us to determine the crystal-field splittings of those levels and the spin-Hamiltonian parameters for the 4I15/2 lower multiplet. The observed electron-spin resonance and the angular variation of this spectrum agree with the parameters obtained by optical techniques. Both techniques show that only one of the three possible trigonal sites in LiNbO3 is occupied by Er3+ within the experimental sensitivity, in agreement with recent x-ray standing-wave measurements. © 1995 The American Physical Society.5153206320

Soil carbon stocks and stability across an altitudinal gradient in southern Peru

Carbon accumulation and sequestration in Andean soils are scarcely documented. Carbon contents, carbon stocks, and stability were determined in five Peruvian agroecologies, along a 1,000 km (621 mi) transect covering the arid Pacific coast, the Andean high plateau, and the tropical highland rainforest in the eastern flank of the Andes. It was hypothesized that the carbon stocks and stability varied with land use and altitudinal gradient. Results showed that the soils in the tropical highland rainforest site presented the higher (p > 0.05) carbon contents (134 g kg−1 [13.4%]). Coffee plantations in the tropical highland rainforest and alfalfa under irrigation in the dry valleys presented larger (p > 0.05) carbon stocks (83 Mg ha−1 [37 tn ac−1]) than primary rainforests. The dry lowlands showed the lowest carbon contents (51 g kg−1 [5.1%]) and carbon stocks (40 Mg ha−1 [18 tn ac−1]). Soil organic carbon increased with elevation in the arid environments. In the high plateau potato systems, low carbon contents (68 g kg−1 [6.8%]) and carbon stocks (47 Mg ha−1 [21 tn ac−1]) were found. The soils in both the tropical highland rainforest and the dry valleys presented lower humification index, when compared to other agroecologies. Humification increased with soil depth due to the presence of recalcitrant carbon, while at the surface the presence of labile carbon dominates as a result of a constant input of plant residues. Results suggest that diversified production systems with crops and livestock are more stable for carbon stocks, which might be essential to help farmers adapting to the effects of climate change. Therefore, viable land uses, from the carbon economy perspective, must be promoted to support sustainable agricultural practices for most important ecological conditions