Decadal-scale litter manipulation alters the biochemical and physical character of tropical forest soil carbon

© 2018 Elsevier Ltd Climate change and rising atmospheric carbon dioxide (CO2) concentrations are likely to alter tropical forest net primary productivity (NPP), potentially affecting soil C storage. We examined biochemical and physical changes in soil C fractions in a humid tropical forest where experimental litter manipulation changed total soil C stocks. We hypothesized that: (1.) low-density soil organic C (SOC) fractions are more responsive to altered litter inputs than mineral-associated SOC, because they cycle relatively rapidly. (2.) Any accumulation of mineral-associated SOC with litter addition is relatively stable (i.e. low leaching potential). (3.) Certain biomolecules, such as waxes (alkyl) and proteins (N-alkyl), form more stable mineral-associations than other biomolecules in strongly weathered soils. A decade of litter addition and removal affected bulk soil C content in the upper 5 cm by +32% and −31%, respectively. Most notably, C concentration in the mineral-associated SOC fraction was greater in litter addition plots relative to controls by 18% and 28% in the dry and wet seasons, respectively, accounting for the majority of greater bulk soil C stock. Radiocarbon and leaching analyses demonstrated that the greater mineral-associated SOC in litter addition plots consisted of new and relatively stable C, with only 3% of mineral-associated SOC leachable in salt solution. Solid-state13C NMR spectroscopy indicated that waxes (alkyl C) and microbial biomass compounds (O-alkyl and N-alkyl C) in mineral-associated SOC are relatively stable, whereas plant-derived compounds (aromatic and phenolic C) are lost from mineral associations on decadal timescales. We conclude that changes in tropical forest NPP will alter the quantity, biochemistry, and stability of C stored in strongly weathered tropical soils

Assessing interrill erosion rate from soil aggregate instability index, rainfall intensity and slope angle on cultivated soils in central Greece

In order to develop anew formula for assessing interrill erosion rate by incorporating the soil aggregate instability index, beta, erosion plots at seven sites in central Greece were used to measure interrill erosion rate under natural rainfall conditions during, a 39-month period. Soils classified as Alfisols, Inceptisols and Entisols with slopes 7-21%. moderately well to excessively drained, clay to loamy textured. were Studied. Runoff and total sediment were collected after each ponding rainfall event. The equation E-i = 0.628 beta S-t(1.3) e(0.6967/30) was finally proposed (R-2 = 0.939. P < 0.001) to describe interrill erosion rate. The term, S-t represents the tangent of the slope angle, and 130 represents the maximum rainfall intensity in 30 min. The addition of the aggregate instability index to improve existing methodologies provide was considered to provide an easy to determine and reliable measure of soil erodibility. Validation with independent data showed that the model predicted interrill erosion well (R-2 = 0.766. P < 0.001). Therefore, the proposed model based on the aggregate instability index, beta, has the potential to improved methodology for assessing interrill erosion rate. (C) 2004 Elsevier B.V. All rights reserved

Effects of Pea Cultivation as Cover Crop on Nitrogen-Use Efficiency and Nitrogen Uptake by Subsequent Maize and Sunflower Crops in a Sandy Soil in Central Greece

The long-term positive effects of cropping systems involving rotation with cover crops on soil properties and the environment are well recognized. The present work concerns a 3-year field experiment focusing on two cropping systems including two energy crops [maize (Zea mays L.) and sunflower (Helianthus annuus L.)] cultivated May-September on an infertile sandy soil, and Pisum sativum cultivated as cover crop after the harvest of the energy crop. Soil samples from two soil layers, 0-20 cm and 20-40 cm deep, were collected at the beginning and end of the experiments; they were analyzed for soil physical and chemical properties such as soil moisture properties, total nitrogen (N), phosphorus (P), potassium (K), pH, organic matter, and organic carbon (C). The results demonstrated the effect of pisum intercropping on the performance of the subsequent energy crop. These results are particularly important for the cultivation of less fertile soils such as sandy soils, which can be put in use for the production of energy crops such as maize and sunflower, which are characterized by high nutrientparticularly Ndemand

Catchment-wide estimate of single storm interrill soil erosion using an aggregate instability index: A model based on geographic information systems

The main objective of this paper is to estimate interrill erosion after rainfall in the basin of Mourganis river (442 km 2; Kalabaka province, Trikala prefecture, Thessaly, Greece). For the estimation of the interrill erosion, the method of Valmis et al. (1988) was used, in combination with Nearing et al. (1989). Input data of the algorithm include the slope angle of the ground surface, the rainfall, the ground cover type, the height of canopy, and the instability of ground of the study area. The spatial data were processed by standard GIS software. Soil samples were collected in the field to calibrate the model. The results comprise soil erosion maps for two specific rainfall scenarios. The first rainfall scenario refers to the most extreme rainfall in this catchment that happened on the 7/21/1959 with 48 mm/h. The second scenario is closer to average as the intensity rainfall is 3. 54 mm/h. The total mass of eroded material ranges from 0. 048 t/ha (assuming mean rainfall intensity) up to 3.5 t/ha (for the extreme scenario). We note that the western part of the Mourgani basin exhibits higher erosion than the eastern part. © 2012 Springer Science+Business Media B.V