Low efficiency of conventional fertilizer (quick release fertilizer) application in agricultural sectors has caused environmental pollution and health problems. A method to overcome the drawback of the conventional fertilizer is by controlled release fertilizer (CRF) preparation. CRF is expected to be able to fulfil the nutrient demand of targeted plants. The objective of this research is to prepare CRF by coating NPK fertilizer with multilayer chitosan-polyanion using alginate, pectin, and sodium tripolyphosphate (TPP). In addition, the effect of the layer arrangement modification of material on the rate of nitrogen release was also studied. The mechanical strength of coated fertilizer was analysed by compressive stress test and the properties of the fertilizer coating was observed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The nitrogen release study shows that multilayer of chitosan-alginate (CA)5, chitosan-pectin (CP)5, and chitosan-TPP (CT)5 as coating material was able to increase the compressive stress and decrease the nitrogen release of coated fertilizer. These results are supported by the FTIR analysis which exhibits the formation of ionic interaction between amine group of chitosan and carboxyl group of alginate in chitosan-alginate (CA)5 layer, carboxyl group of pectin in chitosan-pectin (CP)5 layer, and phosphate of TPP in chitosan-TPP (CT)5 layer. On the other hand, the modification of the arrangement of chitosan-alginate layers showed that the fertilizer with the alternating layer arrangement (CA)5 was able to optimally increase the compressive strength. The mathematical model for the nitrogen release of coated fertilizer is also prepared and simulated with the MATLAB software. The simulation results showed that the nitrogen release of coated fertilizer followed the proposed diffusion mechanism. The obtained diffusivity coefficient value in the layer of chitosan-alginate (CA)5 is 2.0933 × 10−6 cm2/s, 2.5606 × 10−6 cm2/s in chitosan-TPP (CT)5 layer, and 3.7256 × 10−6 cm2/s in chitosan-pectin (CP)5 layer.
The wide use of conventional release fertilizer (quick release fertilizer, QRF) which has low nutrient uptake efficiency due to the high solubility has been a major challenge to the agriculture sector. The purpose of fertilizer application is to optimize nutrient intake of the plant and to increase crop yields. Unfortunately, the application of QRF is difficult to meet the target due to excessive nitrogen loss [
One of the potential materials that can be used as coating in CRF production is chitosan. Chitosan is available abundantly in nature and also has the ability to form film that does not soluble in water. With its biodegradability, chitosan tends to be an eco-friendly polymer [
This study is aimed at preparing CRF coated by multilayer of chitosan-polyanion as a barrier film that can retain the fertilizer nutrients such as nitrogen, phosphorus, and potassium. The layer arrangement modification of chitosan-alginate will be carried out to obtain the best layer which can retain the nutrient longer. The coating process was conducted with layer by layer spray drying technique under continuous dry air flow. Also, the kinetics of nitrogen release was also studied by using the diffusion model approach.
Multicomponent (nitrogen, phosphate, potassium) commercial fertilizer (NPK granules) obtained from Pupuk Indonesia Holding Company was used in this study. Local Indonesian chitosan powder (>90% degree of deacetylation, 10–500 cps viscosity, <1.5% ash content, <0.5% protein content) was purchased from PT Biotech Surindo (Cirebon, Indonesia). Glacial acetic acid (Merck, Germany) was used as the solvent, and alginate, citrus pectin, and sodium tripolyphosphate from Sigma-Aldrich (USA) were used as polyanion.
The experiment was conducted based on the previous method with some modification [
Sample identifications.
Sample ID | Preparation method |
---|---|
TC | Uncoated fertilizer |
C10 | 10 layers of chitosan-coated fertilizer (CCCCCCCCCC) |
(CP)5 | Coated fertilizer with 5 layers of chitosan and 5 layers of pectin with alternating arrangement (CPCPCPCPCP) |
(CT)5 | Coated fertilizer with 5 layers of chitosan and 5 layers of TPP with alternating arrangement (CTCTCTCTCT) |
(CA)5 | Coated fertilizer with 5 layers of chitosan and 5 layers of alginate with alternating arrangement (CACACACACA) |
(C2A2)2C2 | Coated fertilizer with 6 layers of chitosan and 4 layers of alginate with arrangement (CCAACCAACC) |
C3A4C3 | Coated fertilizer with 6 layers of chitosan and 4 layers of alginate with arrangement (CCCAAAACCC) |
The mechanical strength of coated fertilizer was tested with LLOYD INSTRUMENTS LTD Version 4.0-LR Series Mark IV. The surface of coated fertilizer was analysed with scanning electron microscopy (SEM). The coating layer was characterized by SIMADZU Fourier transform infrared (FTIR) spectroscopy. Meanwhile, the nitrogen release was observed by placing 1 g of fertilizer in a beaker glass filled with 100 mL of demineralized water, and it was sealed with parafilm. The amount of coating agent which is attached in the fertilizer was determined by the gravimetric method. The amount of released nitrogen from CRF granule into the water was analyzed by the Kjehdahl method. The kinetics of fertilizer nutrient release was evaluated by using a diffusion model approach using MATLAB to obtain the diffusion coefficient of the formed layer.
The SEM images of C10, (CA)5, (CT)5, and (CP)5 layers are shown in Figure
Scanning electron microscopic of coating layer: (a) C10. (b) (CA)5. (c) (CT)5. (d) (CP)5.
Effect of coating material to the compressive stress of the fertilizer.
Effect of chitosan-polyion multilayer coating on the release of nitrogen.
Compressive stress analysis has been used for investigating the effect of multilayer coating to the mechanical strength of the coated fertilizer. Coated fertilizer that has a good mechanical strength will be more durable during bulk storage time and field application. Figure
Meanwhile, the (CA)5 sample has the highest value of compressive stress. It is supported by the image in Figure
From Figure
FTIR analysis was used to confirm the existing functional groups from each layer composition. As shown in Figure
FTIR (Fourier transform infrared spectroscopy) of coating layer.
Pectin in FTIR spectra (Figure
FTIR spectra shows peaks at 1218 cm−1 and 1147 cm−1 in chitosan-TPP (CT)5 layer. Those peaks are caused by the stretch vibration of P=O, while the peak at 891 cm−1 is caused by asymmetric stretching of P-OP vibration. The 1560 cm−1 in pure chitosan which caused by the N-H bend vibration of amine group shifted to 1634 cm−1 in (CT)5 layer. This shifting shows that ionic interaction also occurs in chitosan-TPP layer which is caused by the interaction between phosphate group in TPP and amine functional group in chitosan [
The result of nitrogen release in water is shown in Figure
The result above is supported by the weight ratio data of coating mass and coated fertilizer mass in Figure
Coating mass after five hours nitrogen release test.
Schematic interaction of (a) chitosan-alginate (CA)5, (b) chitosan-pectin (CP)5, and (c) chitosan-TPP (CT)5.
Figure
From Figure
Chitosan-alginate layer with a different arrangement will affect the layer formation. Consequently, it will also affect the nitrogen release profile. From Figure
Effect of arrangement chitosan-alginate layer to the release of nitrogen.
The coated fertilizer applied to the field is surrounded by water as a diluting agent. It is generally assumed that the water will penetrate through the coated fertilizer and then dissolve the content of nitrogen inside the coating as described by previous research work [
With the initial condition (
MATLAB simulation of nitrogen release.
Calculated diffusion coefficient.
ID | Diffusion coefficient (cm2/s) | Equilibrium constant ( |
SSE (sum of square error) |
---|---|---|---|
C10 | 4.5747 × 10−6 | 0.8350 | 1.5 × 10−3 |
(CA)5 | 2.0933 × 10−6 | 0.8132 | 1.3 × 10−3 |
(CT)5 | 2.5606 × 10−6 | 0.8139 | 1.3 × 10−3 |
(CP)5 | 3.7256 × 10−6 | 0.8397 | 8.4 × 10−4 |
Chitosan-polyanion multilayer such as chitosan-alginate (CA)5, chitosan-pectin (CP)5, and chitosan-TPP (CT)5 was able to form layer as fertilizer granule coating which could increase the mechanical strength and decrease the nitrogen release of coated fertilizer. In addition, the modification of chitosan-alginate arrangement layers such as (CA)5, (C2A2)2C2, and C3A4C3 are also able to reduce the nitrogen release but still inferior than the previous multilayer. The alternating layer (CA)5 exhibits the highest mechanical strength and lowest nitrogen release rate compared to others. Meanwhile, the mechanism of nitrogen release of the coated fertilizer follows the proposed diffusion mechanism. It also complies with the mathematical model with the effective diffusivity values for (CA)5, (CP)5, and (CT)5 layer in the range of 2.0933 × 10−6–4.5747 × 10−6 cm2/s.
The data used to support the findings of this study are included within the article.
The authors declare no conflicts of interest.
The authors acknowledge Mita Putri Indrayanti, Yusrizal Azmi Hafidhuddin, and Daniel Timotius who provided help during the research and preparation of the manuscript. The authors gratefully acknowledge the financial support provided by International Foundation Science (IFS) (grant number J-3-F-6014-1).