Quantifying soil carbon stocks and humification through spectroscopic methods: A scoping assessment in EMBU-Kenya

Abstract

A B S T R A C TA soil carbon assessment was performed comparing agricultural cropping systems with natural vegetation along a sampling transect spanning different agro-ecologies on the eastern foot slopes of Mount Kenya in Embu county, 125 km from Nairobi, Kenya. The aim was to determine differences in soil carbon stocks and carbon recalcitrance and relate these to soil textural class, altitude, climatic parameters and land use. Soils from main agricultural systems as tea, coffee and maize-based intercropping, as well as from natural vegetation cover were sampled in triplicates, in five layers from 0 to 30 cm in depth and processed for total carbon analysis. The whole soil samples were also analysed using Laser-Induced Fluorescence Spectroscopy (LIFS) to assess carbon humification. Prototype portable equipment intended for future in situ analysis was used in the lab to ascertain the structure of the most recalcitrant and stable carbon present in different agro-ecosystems. In addition, Near Infrared Spectroscopy (NIRS) was tested for the quantitative analysis of soil carbon, showing that it is a reproducible and low-cost method that provided satisfactory results under the processing conditions of the samples. Results showed wide variation in the level and quality of carbon stored in the soils, depending on soil texture, land use, elevation, climate, agricultural practices and land use history. Considering the heterogeneous nature of sampled soils and the performance of NIRS and LIFS, these results can be used as a basis for the development of fully portable systems able to provide rapid, clean and potentially cost-effective relevant information for soil management.

Chemical characteristics of soil organic matter from integrated agricultural systems in southeastern Brazil

“…The amount of carbon in SOM is higher in the surface layer (0-20 cm; Figure 2a) for all study sites. This is expected as these layers receive a continuous input of recently produced (fresh) organic matter from vegetation and animals (S a et al, 2017;Segnini et al, 2019;Veloso et al, 2019). With increasing depth up to 100 cm, a higher amount of carbon is accumulated in the soils of the integrated agricultural areas than in the native forest reference area.…”

“…Improved soil fertility leads to more productive croplands, pasturelands and planted forest areas. This generates higher biomass production and increases SOM content, even compared to areas with natural vegetation (Lal, 2004(Lal, , 2019Segnini et al, 2019). Therefore, soil conservation management is a critical aspect of maintaining a high production capacity while avoiding degradative processes common to the tropics.…”

Ensemble Modeling on Near-Infrared Spectra as Rapid Tool for Assessment of Soil Health Indicators for Sustainable Food Production Systems

“…In sub-Saharan Africa, 62% of the rural population depends on agriculture as the main source of their livelihoods, and hence there is a close link between agriculture and soil health [1]. Agricultural sustainability necessitates a good understanding of soil characteristics which can inform farmers in making farming decisions and improve the practices that enhance soil quality [1,2].…”

“…In sub-Saharan Africa, 62% of the rural population depends on agriculture as the main source of their livelihoods, and hence there is a close link between agriculture and soil health [1]. Agricultural sustainability necessitates a good understanding of soil characteristics which can inform farmers in making farming decisions and improve the practices that enhance soil quality [1,2]. Both the physical and chemical properties of soil have been used extensively to monitor soil health characteristics [3,4]; while these properties are important for farm productivity, they vary within fields and with land-use types [2,5].…”

“…Near-infrared absorption bands are overtones and combinations of fundamental vibrations of XH bonding, where X can be carbon, nitrogen, oxygen, or sulfur [10]. Near-infrared spectroscopy has the advantage of being rapid, non-destructive, inexpensive, precise, and can be used to estimate waterbearing minerals, such as clay minerals and organic matter, carbon and nitrogen, and cation exchange capacity [3], as well as micro-nutrients and exchangeable cations in soil samples [1,7,11]. Additionally, the technique has been applied in precision soil management as well as regular soil analysis [12].…”