# Mechanical Activation of Smectine-Based Nanocomposites for Creation of Smart Fertilizers
## 4 Discussion  
### Nanocomposites Made up of Smectite and Urea Mixture  
The creation of clay-based smart fertilizer is performed using different approaches, including milling [24; 33; 34; 41], aqueous suspension technique [29], premixing the components, followed by extrusion and drying [52; 54], mixing of bentonite and liquefied urea [55], and using irradiation method [35]. The previous mechanochemical activation tests were conducted with a mixture of smectite and urea in a 2:3 ratio [36]. It led to the creation of composites with different forms of nitrogen. This research focuses on new ratios of substances in composite products and an optimal activation time in planetary milling and on the variable rates of release of nitrogen depending on the interrelationship between smectite and urea in the composites. Three types of interrelationships between smectite and urea, which were observed by morphology and structure of composites (Figures 1-5), are as follows: (i) nitrogen intercalations in the interlayer space of smectite, (ii) nitrogen absorption into the micropores of smectites, and (iii) adsorption of nitrogen as films covering micro-aggregates of smectite.  
The planetary milling activation of a smectite and urea mixture in a ratio of 3:2 leads to the formation of controlled release fertilizer nanocomposites. The intercalated urea increases from 17.0 to 18.4% as the grinding time is increased from 3 min to 11 min. The external coating of micro-aggregates thickens by 20.4-21.0% as the duration of milling increases (Figure 2C).  
The shift of the basal reflection to higher d-values with increased activation duration corresponds to increased nitrogen in the interlayer mineral space (Figure 1). The shift of 001 reflection indicates the replacement of solvating cations by urea in activated composites  
Figure 7: Histograms showing the % increase of (**A**)—germination rate, (**B**)—seeding height, and (**C**)—dry weight of oat (_Avenue sativa_). Note that urea and composites are equally effective fertilizers for plant growth. Further note that the composite S3N2 pm11 is the most effective for plant growth as it records the maximum increase of all three parameters. The statistical significance of every parameter indicates at the \(p=0.05\) level. Bars represent standard deviation.  
(Figures 1 and 3), recorded by the absence of the weight loss of solvating water from smectite. Composites are characterized by the shift of the basal reflection from 14.3 to 17.3 A, indicating the presence of nitrogen within the smectite structure. The nitrogen remains absorbed within the isometric microcrystallites (up to 80 nm long) within the smectite (Figure 3).  
The intensity of NH\({}_{2}\) at 1155 cm\({}^{-1}\) increased by enhanced operation time, related to the adsorption of nitrogen on smectite flakes (Figure 4). The NH\({}_{2}\) peak changed from 3485 cm\({}^{-1}\) to 3440 cm\({}^{-1}\) with increased activation time, suggesting intercalation of nitrogen molecules. The shifts of NH\({}_{2}\) and NH peaks indicate the gradual intercalation of these molecules into the interlayer space of smectite (Figure 4) with increasing activation time.