Urea has served as the primary nitrogenous fertilizer globally since the early 1950s. It is widely recognized as the most concentrated nitrogen source, containing approximately 46% nitrogen. Presently, around 220 million t/year of urea compounds are manufactured globally to fit the requirements of the agricultural sector. However, a significant drawback of this is that approximately 30–35% of the urea used in soil can be lost to the environment because of its limited effectiveness. Enhancing the efficiency of urea utilization can be achieved by regulating the release of urea-nitrogen in the soil. Numerous researchers have reported that the use of slow or controlled fertilizers can regulate the release and accumulation of nitrogen in the soil. Moreover, the augmentation of soil nitrogen levels can be accomplished by using the slow or controlled release of urea fertilizers. The regulation of the release process can play a vital role in the peril of N loss. This can be effectively alleviated by delaying the release of nitrogen in ammonium form configuration for several days. This delay functions to diminish nitrogen losses, which are caused by the rapid hydrolysis of urea, and loss by leaching or volatilization. Therefore, this review aims to comprehensively explore the use of conventional urea and various materials employed for modifying urea. It will explain the distinctions among modification processes and their respective mechanisms. This review will also discuss the pros and cons of applying slow- and controlled-release nitrogen, the impact of modified urea compounds on crop productivity, and nitrogen use efficiency (NUE).

Ammonium carbonates are a group of fertilizer materials that include ammonium bicarbonate, ammonium carbonate hydrate, and ammonium carbamate. They can be synthesized from diverse nutrient-bearing liquid waste streams but are unstable in a moist environment. While extensively utilized several decades ago, their use gradually decreased in favor of large-scale, facility-synthesized urea fertilizers. The emergence of sustainable agriculture, however, necessitates the recovery and reuse of nutrients using conventional feedstocks, such as natural gas and air-derived nitrogen, and nutrient-containing biogenic waste streams. To this extent, anaerobic digestion liquid presents a convenient source of solid nitrogen and carbon to produce solid fertilizers, since no significant chemical transformations are needed as nitrogen is already present as an ammonium ion. This review describes detailed examples of such feedstocks and the methods required to concentrate and crystallize solid ammonium carbonates. The technologies currently proposed or utilized to stabilize ammonium carbonate materials in the environment are described in detail. Finally, the agricultural efficiency of these materials as nitrogen and carbon source is also described.

Green synthesis methods of silver nanoparticles have gained great attention because they offer sustainable, eco-friendly, and less-toxic alternatives to traditional methods. This study sheds light on the green synthesis of chitosan silver nanoparticle composites, providing a comparative evaluation of microwave-assisted (M1) and a one-pot (M2) reduction methods. The morphological, crystallinity, and structural uniformity characteristics were evaluated by UV-Visible, Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) with employing image processing pipeline based on deep learning model for segmentation and particles size estimation. The UV-visible spectrum exhibited independent SPR peaks ranging from 400 to 450 nm for all samples; however, microwave assisted-synthesis possessed narrower and more intense peaks indicative of better crystallinity and mono-dispersity. SEM depicted smaller, more uniformly dispersed particles for microwave-assisted (M1), while deep learning segmentation showed lower particle size variability (σ ≈ 24–43 nm), compared to polydisperse (σ ≈ 16–59 nm) in M2 samples. XRD showed crystalline face-centered cubic (FCC) silver with dominant peaks in M1 samples, whereas M2 had broader, less intense peaks with amorphous features. Raman vibrations revealed more structural order and homogenous capping in M1 than M2. Therefore, microwave-assisted (M1) showed better control on nucleation, particle size, crystallinity, and homogeneity due to a faster and uniform energy distribution. The future research would focus on the antimicrobial evaluation of such nanoparticles in agronomy.

Extensive application of mineral fertilizers resulted in high soil acidity, which is one of the major problems for crop production and soil degradation. Industrial solid waste, such as lime kiln dust and wood ash, can be used as alternative liming materials to benefit sustainable agricultural development. In this work, pelletized lime kiln dust with and without wood ash was utilized as liming material and the results of the three-year field study were compared with conventional mineral-based liming materials. It was determined that pelletized lime kiln dust satisfies the requirements posed by the recent European Union regulations to qualify as liming materials. The application of 2000 kg/ha Ca equivalent pelletized lime kiln dust increased soil pH_KCl by ~0.55 pH units. Moreover, pelletized lime kiln dust significantly increased spring wheat grain yields ranging from 33.6% to 40.4%, depending on the pellet size. The usage of these liming materials not only increased crop yield but also decreased heavy metal concentration in soil. Due to high alkalinity, carbonate content, easy handling, and the transportation of pelletized lime kiln dust with and without wood ash, the materials have the potential to be used in agriculture as liming materials to reduce soil acidification and increase crop productivity or be used as soil amendments.

The use of major nutrient-containing solid residuals, such as recycled solid waste materials, has a strong potential in closing the broken nutrient cycles. In this work, biofuel ash (BA) combined with green waste compost (GWC) was used as a nutrient source to improve soil properties and enhance wheat and triticale yields. The main goal was to obtain the nutrient and heavy metal release dynamics and ascertain whether GWC together with BA can potentially be used for concurrent bioremediation to mitigate any negative solid waste effects on the environment. Both BA and GWC were applied in the first year of study. No fertilization was performed in the second year of the study. The results obtained in this work showed the highest spring wheat yield when the GWC (20 t ha⁻¹) and BA (4.5 t ha⁻¹) mixture was used. After the first harvest, the increase in the mobile forms of all measured nutrients was detected in the soil with complex composted materials (GWC + BA). The content of heavy metals (Cd, Zn, and Cr) in the soil increased significantly with BA and all GWC + BA mixtures. In both experiment years, the application of BA together with GWC resulted in fewer heavy metals transferred to the crops than with BA alone.