Coating of sepiolite-chitosan nanocomposites onto urea increases nitrogen availability and its use efficiency in maize

To improve the use efficiency of fertilizer and to reduce the rate of nitrogen release, a coated urea was prepared using clay-polymer nanocomposites (CPU). Sepiolite and chitosan were used to form nanocomposites with different clay mineral/polymer ratios. The nanocomposites and CPUs were characterized using several techniques including Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) specific surface area measurement. The FTIR examination revealed functional groups related to chitosan that interacted with sepiolite. The nitrogen release of CPUs was examined in the sand column showing that 75% of nitrogen content of CPU samples released in about 25 d, much longer than that of urea (3 d) and the rate of release of nitrogen was reduced by increasing the proportion of sepiolite in the clay/polymer nanocomposites. The release mechanism of CPUs was evaluated and the results showed the mechanism was not Fickian diffusion but anomalous diffusion. The nutrient use efficiency of CPUs was studied under greenhouse conditions using Zea mays (corn) as the test plant and a significant efficiency improvement was observed. The results showed that the CPUs with slow-release properties could be considered as efficient N fertilizers in agricultural and horticultural applications.