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Description
Introduction
According to FAO, the total fertilizer nutrient demand was 185,063 million tons in 2016, and this demand was forecasted to grow to reach 200,919 million tons in 2022 (FAO, 2022), leading to the search for new sources of fertilizers. On the other hand, rational use of fertilizers is necessary, since long-term fertilization can deeply affect the physiochemical and biological soil properties. In addition, the incomplete capture and poor conversion of fertilizer could also cause water pollution and global warming through gas emissions (Masclaux-Daubresse at al., 2010). Therefore, it is crucial to evaluate the effectiveness of new fertilizers, not only considering the productivity of the crops but also studying their effect on soil properties and the environment.
Materials and methods
Laboratory incubation under controlled temperature (25ºC) and soil moisture conditions (De Soto et al., 2023) was used in the evaluation of several materials from two wastewater treatment plants (WWTPs) in Navarre (Spain) as fertilizers in soils with different pH values (8.16 and 6.05). The characterization of the samples was carried out at the beginning of the trial and at 3, 6, and 9 weeks. All samples were analyzed in triplicate.
Results
The electrical conductivity increased in all experiments, since the amendments provide soluble salts to the soil. However, there was a decrease in pH values after the soil incubation.
It was observed an increase in available P (Olsen) and organic matter values after the incubation experiment. Finally, in relation to N, it was observed an initial NH4+ release and a latter nitrification during the incubation.
Discussion
The electrical conductivity increase was due to the amendments providing soluble salts to the soil. This parameter should be controlled in the case of continued applications of the amendments, since it can cause problems in the growth of crops (Porta-Casanellas et al., 2011).
The observed evolution of the total and mineral N can be explained by a stimulation of biological activity in soils (Bernhard, 2010). In relation to these results, there was a decrease in pH values after the soil incubation, very likely due to the nitrification process. This decrease in time could be a long-term problem (especially in soils with low carbonate content), since soil acidification can cause, among other problems, the dissolution and loss of soil inorganic C (Raza et al., 2020).
The initial increase in Olsen P observed was proportional to the dose in both soils. However, the experiment with acidic soil showed higher values of available P, because pH is a key factor in the evolution of P in soils. In relation to organic matter, the application of the products tested produced an increase in organic matter and contributed to the maintenance of soil moisture.
Conclusions
The studied materials from the WWTPs can be seen as potential fertilizers for agricultural soils and can promote circular economy opportunities for the wastewater industry. However, the application of these materials in agricultural soils should be further investigated before becoming common practice due to the observed gains in electrical conductivity and decreases in soil pH values due to the nitrification process.
References
Bernhard, A. The Nitrogen Cycle: Processes, Players, and Human Impact. Nat. Educ. Knowl. 2010, 3, 25.
de Soto, I.S.; Itarte, M.; Virto, I.; López, A.; Gómez, J.; Enrique, A. Evaluation of the Use of a Material with Struvite from a Wastewater Treatment Plant as N Fertilizer in Acid and Basic Agricultural Soils. Agriculture 2023, 13, 999.
FAO-UNESCO. World Fertilizer Outlook and Trends to 2022, World Fertilizer Trends and Outlook to 2022; Food and Agriculture Organization of the United Nations: Rome, Italy, 2019.
Masclaux-Daubresse, C.; Daniel-Vedele, F.; Dechorgnat, J.; Chardon, F.; Gaufichon, L.; Suzuki, A. Nitrogen Uptake, Assimilation and Remobilization in Plants: Challenges for Sustainable and Productive Agriculture. Ann. Bot. 2010, 105, 1141–1157.
Porta-Casanellas, J.; López-Acevedo Reguerín, M.; Poch Claret, R.M. Introducción a La Edafología Uso y Protección de Suelos, 2a ed.; Mundi-Prensa: Madrid, Spain, 2011; ISBN 978-84-8476-405-2.
Raza, S.; Miao, N.; Wang, P.; Ju, X.; Chen, Z.; Zhou, J.; Kuzyakov, Y. Dramatic Loss of Inorganic Carbon by Nitrogen-Induced Soil Acidification in Chinese Croplands. Glob. Chang. Biol. 2020, 26, 3738–3751.
| Keywords | Acid and basic agricultural soil; incubation soil experiment; circular economy opportunities; wastewater treatment plants; fertilizer |
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