Physical Properties of Granular Organic-based Fertilisers, Part 2:: Dynamic Properties Related to Water

Organic-based fertilisers are granular fertilisers that make use of the synergy between the mineral and organic components. The physical properties of organic-based fertilisers are relatively unknown. The main objective of this research was to compare the physical properties of bulk-blended organic-based (BOF) and compound organic-based fertilisers (COF) with those of mineral fertilisers (MF). New and modified methods were used to measure their atmospheric moisture sorption, capillary rise, slaking and dissolution in water over time. Air moisture sorption by fertilisers increased quadratically with time and with relative humidity. At 82% relative humidity, major changes in fertiliser behaviour occurred. The processes varied among fertilisers. Water sorption from the atmosphere was affected by bulk density as well as by the organic matter (OM), initial moisture, and P contents. The water sorption rate over time during capillary rise took the form of an inverse power function and increased as OM content increased. Some fertilisers were highly affected by tensions while others were only slightly affected, indicating differential rates of release under field conditions. During submersion in water, COF granules dissolved, swelled and slaked to different extents and their diameter decreased quadratically over time. The loss of mass during submersion was affected by OM and nitrogen contents as well as by the initial granule size. Differences between fertilisers were mostly related to the organic matter type and content. Examples of uses and applications of dynamic properties are given for different situations: fast or slow release; dry to wet conditions; and application at the soil surface or incorporation in the soil.