A Biopolymer Coating Strategy for the Slow Release of Urea from Urea Fertiliser

Abstract

Due to the rapid dissolution of urea fertilisers in water, leaching and evaporation from the soil cause approximately 70 % of the urea to be lost to the atmosphere and groundwater without being used by plants. It is known that a significant portion of urea fertiliser is released into the atmosphere as ammonia gas, and into groundwater as nitrate and nitrite, resulting in nitrogen losses. To mitigate these losses, various studies have been conducted on coating urea fertiliser with different materials. Biopolymers, in addition to providing controlled release, also act as soil conditioners by increasing the water-holding capacity of the soil and providing necessary moisture to plants during dry periods. In this study, three different types of biopolymers – chitosan, pectin, and xanthan gum – at two different concentrations (1 % and 3 %), were used to coat urea fertiliser aiming for controlled release. Biopolymer solutions and their cross-linkers were prepared, and the urea fertiliser was coated using a laboratory-scale coating drum. The chemical structure of the coated urea fertiliser was determined using Fourier-Transform Infrared Spectroscopy, and its morphology was examined with a Scanning Electron Microscope. The water-holding capacity in the soil and the ammonia released into the atmosphere were also analysed. The results indicated that the most effective biopolymer coating type for the slow-release mechanism of urea was pectin at a 1 % coating ratio on the fertiliser granules. The concentration of ammonia released from the soil and the water-holding capacity of the soil treated with biopolymer-coated urea fertiliser were tested through various experiments, and the results were analysed statistically. According to the statistical analysis, the 1 % pectin-coated urea fertiliser yielded the best results in both experiments, with an ammonia release value of 246.66 ppm and an evaporation rate of 67.84 % at the end of 30 days.Zbog visoke topljivosti urea gnojiva u vodi, oko 70 % uree biva neiskorišteno od strane biljaka bilo da odlazi u atmosferu (isparavanje) ili podzemne vode (ispiranje tla). Značajan dio uree iz gnojiva otpušta se u atmosferu kao amonijak, dok se u podzemne vode prenosi kao nitrat i nitrit. S ciljem smanjenja tih gubitaka, provedena su brojna istraživanja vezana uz oblaganje gnojiva na bazi uree različitim materijalima. Biopolimeri, osim što omogućuju kontrolirano otpuštanje, oplemenjuju tlo povećavajući njegov kapacitet zadržavanja vode i osiguravajući biljkama prijeko potrebnu vlagu tijekom sušnih razdoblja. U ovom istraživanju, s ciljem postizanja kontroliranog otpuštanja, za oblaganje uree upotrijebljena su tri biopolimera: kitozan, pektin i ksantan guma, u udjelima 1 i 3 %. U tu svrhu pripremljene su biopolimerne otopine i aditivi za poprečno umrežavanje te je gnojivo na bazi uree obloženo pomoću bubnja za oblaganje. Infracrvenom spektroskopijom s Fourierovom transformacijom analizirana je kemijska struktura obloženog gnojiva, dok je morfologija ispitana pretražnom elektronskom mikroskopijom. Analizirani su i kapacitet zadržavanja vode u tlu te količina amonijaka otpuštenog u atmosferu. Količina amonijaka oslobođena iz tla i kapacitet zadržavanja vode u tlu tretiranom gnojivom na bazi uree obloženim biopolimerom ispitani su raznim eksperimentima, a rezultati su podvrgnuti statističkoj analizi. Rezultati su pokazali da je oblaganje granula gnojiva biopolimerom pektinom u udjelu od 1 % najdjelotvornije s 246,66 ppm oslobođenog amonijaka i stopom isparavanja od 67,84 % nakon 30 dana.