By Dennis S. Ashilenje, Abdelaziz Hirich, Krishna P. Devkota, Ayyoub Taousse, and Abdelaziz Nilahyane
Researchers examined the influence of irrigated grass and alfalfa established in arid locations with a range of soil salinity to determine their influence on C mineralization and accumulation. Overall, blue panicum grass-alfalfa mixtures could trigger C mineralization and support C stabilization suggesting a balance between microbial energy needs and nutrient cycling in these saline soils.
Arid soils have low organic matter with drastically limited crop nutrient reserves. These soils have worse tendencies to salinize and deteriorate microbial habitats and crop growth. Crop losses to salinity can be up to 70-100% except for salt-tolerant species (Ashilenje et al., 2022a, Ashilenje et al., 2023). These crops can revitalize soil microbial activities, stimulate nutrient cycling, and enhance soil health. This is the case for blue panicum grass (Panicum antidotale Retz) demonstrated to be able to exclude sodium (Na+) from its roots (El Mouttaqi et al., 2023). But alfalfa (Medicago sativa) is pertinent to dryland forage production, particularly in the desert conditions of southern Morocco. In a recent synthesis, researchers observed that although alfalfa has low salinity tolerance in general, this classification may be challenged by the ubiquity of alfalfa varieties sharing saline niches with salt-tolerant grasses (Ashilenje et al., 2022b). This raises the question if blue panicum grass can reduce salinity and sequester carbon (C) in a shared soil habitat that allows alfalfa to accrue nitrogen (N) and support microbial activities. The aim of this study was to determine the influence of blue panicum grass – alfalfa crop mixtures on C mineralization and buildup in aridsaline soils of Southern Morocco.
Study description
The study included four treatments with blue panicum grass (BP) and alfalfa (ALF) monocrops or in mixtures of 50%ALF – 50%BP and 70%ALF – 30%BP. These were randomized complete block experimental designs established at sites near Laâyoune, Morocco with low (ECe = 9 dS m-1), moderate (ECe = 25 dS m-1) and severe (ECe = 54 dS m-1) salinity. Crops were irrigated but without mineral N except that applied to a previous barley crop. Soil C mineralization was measured at weekly intervals from December 2021 to March 2022 and August to November 2022. Carbon mineralization is the rate at which organic matter is degraded to humus and in the process some C is lost as CO2. This was detected with an EGM-5 CO2 gas analyzer and the rate of CO2-C flux was determined as a linear change in CO2 flux over a duration of 3 minutes (Parkinson, 1981). The remaining C is stabilized by forming aggregates with mineral components of soil. A net stabilization compared to mineralization contributes to soil C accumulation. Soil organic matter (SOM) was evaluated two years after crop establishment at a depth of 15 cm. SOM was estimated as 1.72 times the concentration of soil organic C represented by the concentration of chromate remaining after the oxidization of organic matter. Data was subjected to ANOVA to detect for significant site by treatment interactions directing an enhancement in C mineralization and accumulation.
Cropping mix, soil salinity and carbon
Treatment had significant influence (p = 0.03) on C mineralization across sites. The mixture with 30% blue panicum grass and 70% alfalfa tended to stimulate greater (p < 0.05) cumulative-C mineralization at moderate and high salinity than the blue panicum grass monocrop (Fig. 1). In the case of soils with low salinity, cumulative C mineralization did not vary significantly (p < 0.05) in response to the cropping systems.
Blue panicum grass growth dominated as salinity intensified and vice versa for alfalfa. The grass roots may be more recalcitrant thus more limiting in their supply of substrate available as a source of energy for soil microbes. But dominance of alfalfa may encourage preferential legume root biomass with a more easily mineralizable N pool used as an alternative source of assimilates for microbes.
The average active C measured in March and November 2022, responded significantly (p = 0.03) to the joint effect of varying salinity and cropping system (Fig. 2). Active C was greatest in soils beneath alfalfa with low salinity and under the blue panicum grass monocrop in severely saline soils. In both these sites, the mixture with 30% blue panicum grass and 70% alfalfa came second in magnitude of soil active C. Conversely, this mixture generated the least active C in moderately saline soils that extended to 15 cm. This soil often remained filled with saline water after rainfall and irrigation. There was no significant influence of the treatments (p = 0.2) on SOM, which ranged between 1.3-2.3%, although in some cases it exceeded the background levels (<1.3%).
Conclusions
This study concludes that blue panicum grass alfalfa mixtures in seeding ratios of 30:70% can trigger soil C mineralization conducive to C stabilization in arid-saline soils, which suggests a beneficial balance between microbial activities, nutrient cycling, and C stabilization. Additionally, the role of blue panicum grass in alleviating salinity in mixed stands may be surpassed by favorable mineralization of the organic pool of mineral elements originating from better quality alfalfa root residues.
Acknowledgement
This research was funded by OCP Phosboucraa Foundation, Grant Number FPB_SPA002_2020. We thank Mohammed Belcaid and Driss Zouine for logistics.
Dr. Ashilenje (e-mail: Dennis.Ashilenje@um6p.ma) is Assistant Professor, African Sustainable Agriculture Research Institute (ASARI), Mohammed VI Polytechnic University (UM6P), Laâyoune, Morocco. Dr. Hirich is Professor, ASARI – UM6P. Dr. Devkota is Senior Scientist, International Center for Agricultural Research in the Dry Areas (ICARDA), Rabat, Mr. Taousse is Research Technician, ASARI. Dr. Nilahyane is Assistant Professor, ASARI – UM6P.
Cite this article
Ashilenje, D.S., Hirich, A., Devkota, K.P., Taousse, A., Nilahyane, A. 2024. Carbon Stabilization in the Arid-Saline Soil Environment of Southern Morocco, Growing Africa 3(1), 10-11. https://doi.org/10.55693/ga31.JJZN3441
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