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Humic Acid-based Soil Conditioners for Soil Cultivation in Arid and Semiarid Climates -
Potential for the Economization of Water and Fertilizers

Nicole Merkl1, Vera Hoogen1, Heiner Hoogen1, Oliver Bens2

1Hoogen Bodensanierung GmbH, Senftenberg, Germany
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2Chair of Soil Protection and Recultivation, Brandenburgische Technische Universität Cottbus, Germany


Humic acids are natural occurring macro-molecules that fulfill important functions in soil, as e.g. they store water and nutrients in a plant availably form and thus allow healthy plant growth. Therefore, they are particularly of interest for plant cultivation under extreme climatic and edaphic conditions, i.e. in the case of desert landscapes, extreme drought and nutrient deficiency. Humic acids can technically be extracted from fresh or carbonized organic material as e.g. lignites.
To verify the benefit of the application of humic acids as a soil conditioner in arid and semiarid regions, an extensive field experiment was installed in the botanical garden of the emirate Sharjah (U.A.E.) by the company Hoogen in cooperation with the municipality of Sharjah. The experiment was evaluated in cooperation with the Brandenburg University of Technology Cottbus.
The experimental plots were installed (I) on bare desert soil and (II) on an area where red desert sand and compost of city waste were previously applied in a layer of 20 cm. A liquid humic acid product was applied in various concentrations prior to the planting of Oklahoma grass (Paspalum vaginatum). Additionally, a number of commercially available soil conditioners, partly based on humic acids, and several grass varieties were tested. Combinations of different soil conditioners were also evaluated.
After 3 and 24 months the trial was evaluated for plant biomass of shoot and root, macro- and micro-nutrients in soil and macro-nutrients in plant (shoot and root). So far, the results for the first evaluation are available.
Under nutrient deficient conditions, many of the soil conditioners resulted in a reduced shoot growth, probably due to the fixation of the remaining nutrients by the conditioners. Contrarily, the root biomass increased in some cases, indicating a flux of carbon to the root, a process that occurs when soil-derived resources such as water and nutrients decrease. In soil treated with city waste, the soil conditioners caused an increased shoot growth and an decreased root growth, resulting in a higher shoot : root ratio than the control. This indicates a better nutrient and water supply, which allows the plants to favor shoot growth.
After 3 months no significant difference between nutrient concentrations in soil could be observed. However, significant results are expected for the second evaluation after 24 months.
Ongoing experiments clarify the benefit of soil conditioners under reduced irrigation. First results show that under the use of liquid humic acids irrigation can be reduced by 50% without affecting plant growth or vitality.
The results of the experiment serve as a basis for the development of new soil conditioners and cultivation methods for arid and semiarid landscapes with the objective to save irrigation water and fertilizers.