Doctoral thesis (Dissertations and theses)
Land-use effects on soil quality of agricultural systems in the Central Andes of Bolivia
Coca Salazar, Alejandro Ariel
2021
 

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Keywords :
Soil microbial activity; soil aggregates; chicken manure; Solanum tuberosum; fallow; Eucalyptus globulus
Abstract :
[en] Increasing demands for food of the growing world population has led to agricultural intensification and rapid changes in land use worldwide. Resulting modifications of soil characteristics could have cascading effects on soil functioning and the delivery of ecosystem services (e.g. food production). Maintenance of soil quality, the capacity of a soil to function to sustain biological productivity while maintaining environmental quality, is thus of central importance in order to ensure long-term provision of food, and its evaluation allows to understand the soil responses and to predict potential consequences of land-use changes. Over the last decades, agricultural systems of the Central Andean region of Bolivia have experienced rapid changes of land use and management practices such as shortening of fallow periods, use of chicken manure fertilization to improve soil fertility, and the plantation of Eucalyptus globulus L. on arable soils. So far, the effects of these changes on soil quality have not been assessed. Improving agricultural production while contributing to sustainability of these ecosystems requires soil quality evaluations under the current land uses. This thesis evaluated the effect of fields cultivated with potato, fallow fields (2-6 years old), eucalyptus plantations, and the use of chicken manure for fertilization on soil quality in agricultural ecosystems of the Central Andes. The combined responses of soil physico-chemical properties, soil aggregates, microbial processes, and their interactions were evaluated as indicators of soil quality. Short-term fallowing did not contribute to soil fertility restoration or soil structure improvement, indicating a neutral effect on soil quality compared to fields cultivated with potato. However, fallowing soils lead to reduced net nitrogen transformation rates and lower abundance and activity of ammonia oxidizing bacteria, suggesting sensitivity of these processes to land-use change. Fertilization with chicken manure improved soil quality by increasing labile carbon and nitrogen fractions and microbial activity. Manure also promoted seed germination and plant growth, however, immature manure caused root damage on Avena sativa L. seedlings. Turning manure piles accelerated the composting process and reduced root damage. It is recommended to compost manure for 100 days and to conduct turning events to reduce the risk of manure phytotoxicity. The plantation of eucalyptus promoted organic matter accumulation, and increased the total amount of carbon in different fractions. Soil structure was also improved and contributed to carbon stabilization. These changes are commonly associated with an improvement of soil quality for cultivation, but increased exchangeable Al and potential allelopathic interactions reduced biological soil quality compared to cultivated fields (reduced metabolic potential of soil bacteria, N transformation rates, and increased microbial energy maintenance demands) The plantation of eucalyptus should be avoided in agricultural areas, and careful land-use planning should guide its plantation to avoid negative effects on crops. Under the three land uses, ammonia-oxidizing archaea were dominant nitrifying organisms in terms of abundance and activity, but the contribution of ammonia-oxidizing bacteria to nitrification significantly increased with pH. We have also demonstrated that the activity of ammonia oxidizers should not be inferred from amoA gene abundances alone, but that their nitrification rates should be measured separately to determine their role in the environment. Labile carbon fractions (hot water extractable carbon and microbial biomass carbon) were strongly associated to microbial processes and were sensitive to land-use changes. Moreover, increases in microbial activity (respiration potential and net nitrogen mineralization) were associated to aggregate formation and stability. Labile carbon fractions and microbial processes should be considered for monitoring soil quality in response to land-use change and agricultural practices. This study demonstrated that the short fallow periods did not contribute to soil quality improvement for cultivation compared to fields cultivated with potato. The use of composted chicken manure for fertilizing soils improved to soil quality for agricultural production but the use of immature manure should be avoided to reduce the risk of phytotoxic effects. The introduction of eucalyptus to the Andean agricultural systems reduced soil quality for cultivation compared to fields cultivated with potato. Labile carbon fractions and microbial processes stand out as sensitive and informative soil quality indicators of the early changes occurring in these agricultural systems following land-use change.
Research center :
Laboratory of Plant and Microbial Ecology - InBioS
Disciplines :
Microbiology
Author, co-author :
Coca Salazar, Alejandro Ariel ;  Université de Liège - ULiège > InBioS
Language :
English
Title :
Land-use effects on soil quality of agricultural systems in the Central Andes of Bolivia
Defense date :
07 September 2021
Number of pages :
152
Institution :
ULiège - Université de Liège
Degree :
Grade de Docteur en Sciences
Promotor :
Carnol, Monique  ;  Université de Liège - ULiège > Integrative Biological Sciences (InBioS)
Cornelis, Jean-Thomas ;  Université de Liège - ULiège > Département GxABT > Echanges Eau - Sol - Plantes
President :
Javaux, Emmanuelle  ;  Université de Liège - ULiège > Astrobiology
Secretary :
Van Wesemael, Bas
Jury member :
Cotrufo, Francesca
De Neve, Stefaan
Merckx, Roel
Name of the research project :
Land use effects on soil quality of agricultural systems in the Central Andes of Bolivia
Funders :
Académie de Recherche et d'Enseignement Supérieur (Belgique). Coopération au Développement - ARES. CCD
Available on ORBi :
since 15 September 2021

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