Zahid Majeed

A comprehensive review on biodegradable polymers and their blends used in controlled-release fertilizer processes

Abstract Biodegradable polymer-coated controlled-release fertilizers (PC-CRFs) are essential means to reduce cost, improve marketability, conserve land fertility, achieve high crop yields and combat climate challenges. It is known that about 15–30% of any fertilizer packed in a PC-CRF does not get released due to the concentration gradient difference across the polymer coatings. To release the trapped fertilizer(s), it is desired that polymer-based coatings should biodegrade after the fertilizer is completely released into the soil. This review has aimed to provide a comprehensive account for various biodegradable polymers/blends derived either from natural or synthetic sources which are cited in the literature for PC-CRFs. In addition, this review covers the discussion on their classification criteria, trends in the processes of fertilizer coatings, methodological issues for their biodegradation assessment, coating attributes that affect the biodegradability and an outlook into their biodegradation kinetic models that involve enzymes and microbial processes. It also concludes that experimental as well as modeling data are insufficient to assess the biodegradation contribution of the overall nutrient release in PC-CRFs.

Lignin reinforcement of urea-crosslinked starch films for reduction of starch biodegradability to improve slow nitrogen release properties under natural aerobic soil condition

Abstract The urea-crosslinked starch (UcS) film has a major drawback of very rapid biodegradability when applied as slow release fertilizer in soil. Lignin reinforcement of the UcS was used to prepare composite films, aimed to reduce the starch biodegradability and slow the release of nitrogen in aerobic soil condition. Study results revealed that mineralization of the composite films was delayed from 6.40 to 13.58% more than UcS film. Inhibition of composite films mixing with soil, the Michaelis-Menten reaction rates for α-amylase were inhibited ~1.72–2.03 times whereas the Michaelis-Menten reaction rates for manganese peroxidase were increased ~1.07–1.41 times compared to UcS film. Saccharides–glucose, maltose and maltotriose demonstrated that their rates of formation (zero-order reaction) and depletion (first-order reaction); both were slowed more in aerobic soil which received the composite films. Increasing of lignin in composite films, the acid to aldehyde ratios of vanillyl and syringyl phenols of the lignin declined from 1.18 to 1.17 (~0.76%) and 1.59–1.56 (~1.78%), respectively. The diffusivity of nitrogen was effectively slowed 0.66–0.94 times by the lignin in composite films and showed a “Fickian diffusion” mechanism (release exponent n=0.095–0.143).

Lignin Loading Effect on Biodegradability and Nitrogen Release Properties of Urea Modified Tapioca Starch in Wet Soil

Plant based biopolymers are abundantly and easily available naturally biodegradable raw materials to prepare slow release nitrogen technologies. To test the lignin loading effect on biodegradability of the slow release fertilizer (SRF) and nitrogen release applications, a pot experiment under real soil conditions was conducted. Lignin at different loading percentages 5%, 10%, 15% and 20% were mixed with urea-modified tapioca starch acting as slow release fertilizer (SRF). Increasing the percentage of lignin to starch reduced the weight loss with improved nitrogen slow release properties in wet soil. Soil microbial biomass was negatively correlated with increase of lignin percentages. Lignin is a low cost biopolymer and can be used to improve starch biodegradation and its slow release nitrogen properties.

Lignin Modified Urea Fertilizer's Biodegradation and Nitrogen Release under Reduced Soil Condition

Lignin is a natural biopolymer easily available in industrial waste and currently being used in slow release matrix improvements. Research work objective is to study the effect of 5% to 20% alkaline kraft lignin (AL) loadings on the biodegradation and nitrogen release in urea modified tapioca starch, acting as biodegradable slow release fertilizer (SRF) under reduced soil condition. Weight loss (%) of SRFs reduced from 76% to 35% with increasing %AL until day 28. Biodegradability (%) of SRFs affectively reduced at low 5-10%AL compared to high 15-20%AL. Nitrogen release was reduced with increasing the %AL in SRFs. Nitrogen release mechanism showed fickian diffusion mechanism (n<0.5) except for 10%AL (0.5<n<1). The lowest diffusion coefficient, 1.71 x 10-8cm2/s was observed in 10%AL. Fourier transformed infrared analysis of the biodegraded SRFs showed anhydroglucose ring asymmetric stretching vibration due to COC and COH (904-1140cm-1), lignins aromatic ring stretching (1451-1500cm-1) and deformation of C-H in lignins guaicyl ring or starch glucose ring (1162 cm-1). Lignin can effectively be used to improve nitrogen slow release and reduce biodegradability of SRFs under reduced soil.

Starch Biodegradation in a Lignin Modified Slow Release Fertilizer: Effect of Thickness

Biopolymers and their modified blends are naturally biodegradable materials being intensively used in control nutrient release formulations. Material biodegradability varies with thickness which further effect natural decay when applied in soil. Preliminary study was conducted for a urea-nitrogen incorporated slow release fertilizer (SRF) prepared with 0.27mm, 0.54mm and 1.03mm thickness. The starch biodegradation was decreased with increased in thickness both in non-sterile flooded soil (NSF) and sterile flooded soil (SF). NSF soil data was corrected with SF soil (as control) showed improved exponential decay constant and half-life estimates compared to NSF soil only. Study concludes that SRF thickness is important parameter increases half-life and reduces starch biodegradability in SRF.

The Potential of Thiosulfinates in Garlic Extract as Urease Bioinhibitor

Research on garlic or scientifically called as Alliumsativum L. has been conducted to ensure its inhibitory effects as potentially safe and biodegradable inhibitor. From previous research, thiosulfinates (TS) contained in garlic extract proved to inhibit platelets aggregation in medical applications. TS are obtained by extracting garlic cloves. In this study, the inhibitory effect is determined by analyzing ammonia (NH3) concentration in enzyme-containing solution and standard urea assay mixtures using UV-Vis spectrophotometer device. The Beer’s law is used to calculate the concentration with an aid of the curve value of standard NH3 calibration graph. Based on previous research, the NH3 concentration is predicted to decrease with amount of enzyme-containing solution and incubation time.