Dissolution rates of mineral nitrogen fertilisers : effects of moisture and precipitation
Hygroscopicity and deliquescence refer to the ability of a solid to absorb air moisture in which it dissolves and have long been recognised as properties having negative impacts on the product quality of explosives, pharmaceuticals, and fertilisers. Contrastingly, this thesis reconsiders and reap...
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| Formato: | H3 |
| Lenguaje: | Inglés sueco |
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SLU/Dept. of Soil and Environment
2018
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| Materias: |
| Sumario: | Hygroscopicity and deliquescence refer to the ability of a solid to absorb air moisture in
which it dissolves and have long been recognised as properties having negative impacts on
the product quality of explosives, pharmaceuticals, and fertilisers. Contrastingly, this thesis
reconsiders and reappraises the hygroscopic effects of common mineral fertilisers, proposing
hygroscopicity to beneficially enable quick dissolution under humid air conditions in absence
of precipitation. Although precision fertilisation has improved, little is known about
the dissolution dynamics of mineral nitrogen fertilisers in the field when exposed to either
moist air or precipitation. In this thesis, dissolution rates of fertilisers based on ammonium
nitrate (Axan™) and calcium nitrate (Kalksalpeter™), and of comparable pure salts, were
recorded in a hygroscopicity test (≥90 % relative humidity at 25°C). Furthermore, dissolution
rates of the fertilisers were also studied in a rain simulation (moderate intensity). In the
hygroscopicity test, the pure reference salts had a higher hygroscopicity and shorter dissolution
time relative the fertiliser products. The ammonium nitrate-based fertiliser and the
pure ammonium nitrate salt moreover had higher dissolution rates (completely dissolved
after 5.0 and 2.3 hours) compared to the corresponding calcium nitrate fertiliser and salt
(21.1 and 4.3 hours respectively). All compounds tested dissolved within 24 hours. Endothermic
properties, i.e. heat uptake during dissolution, seemed strongly correlated to the hygroscopic
rates recorded. According to a thermodynamic calculation made, strongly endothermic
salts had higher hygroscopicity compared to those with moderate or weak endothermic
properties. In the rain simulation, the ammonium nitrate and calcium nitrate-based
fertilisers required 5 and 6.5 mm of simulated precipitation, respectively. However, a theoretic
estimation suggested less water to be sufficient at optimal application. For highly soluble
fertilisers, the time during which the fertiliser is exposed to water may be more important
from a dissolution point of view than the solubility. Considering the dissolution rates
of fertilisers reported in this work, regardless if driven by hygroscopicity or precipitation,
the limiting factor in the fertilisation system does not seem to be the dissolution but the
dilution to concentrations non-toxic for crops. Future research should focus on the transport
of dissolved nitrogen in the soil, at different soil moisture levels. Thereby, the time for a dry
solid fertiliser to dissolve and reach the root zone of a crop could be better predicted. |
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