In agricultural activities, there is an increasing need for organic fertilizers to use nature-friendly materials used to fertilize the soil. Farmers have been using granular organic fertilizers made from composted or dried manure of cattle, poultry, pigs, ash, bone meal, and other materials for some time, but the quantities of these organic fertilizers are not large. Biochar is also being intensively studied as a material to improve soil quality and plant growth and reduce greenhouse gas emissions from soil. The suitability of cattle manure compost, poultry manure, biochar, and their combinations for granular fertilizers was analyzed in this work. The preparation of biochar for granulation may have differences compared to other organic materials due to the moisture content, fractional composition, bulk density, and other parameters of the granulated material, so this work examines the physical–mechanical and chemical properties of cattle and poultry manure and biochar raw material and the final granulated product. Research has found that the fractional composition of raw materials under investigation manure and biochar was up to 2 mm. The moisture content of the studied raw material varied from 8.97% in the case of poultry manure to 25.11% in the case of cattle manure compost. The lowest moisture content was obtained due to additional drying. The addition of biochar reduces the granule density in investigated cases. Poultry manure granules were the most mechanically stable, with a semi-static stability of 382.6 ± 78.08 N. After the addition of biochar, weaker binding properties were determined in the experimental granules. Analysis of the composition of elements shows that these granules can be used for fertilization or soil improvement. High concentrations of nitrogen (N), phosphorus (P), and potassium (K) were detected in the granules. The obtained results showed that it is appropriate to enrich the manure granules with biochar.

Due to the continuous creation of organic granular fertilizers of the new composition, there is a lack of knowledge about their properties and the influence of the norm on spreading efficiency. To increase the efficiency of the use of granular organic fertilizers, their spreading aims are to properly choose the most rational spreading parameters and fertilizer norms, considering the characteristics of the fertilizer. To determine this quickly and with lower costs, various theoretical models and computer programs are used to study the dynamics of fertilizer spreading. The purpose of this work was to perform theoretical and experimental comparative studies of the influence of the characteristics and dosage norms of granular fertilizers of poultry manure on the spreading efficiency. During the research, the physical properties of granular poultry manure fertilizers were determined, which have an impact on the quality of spreading. Experimental studies of fertilizer spreading were carried out using two centrifugal spreaders with the same parameters (Amazone ZA-M-1001 (spreading dosage norm, 200 kg ha⁻¹ and 400 kg ha⁻¹; driving speed, 10 km h⁻¹) and ZA-M-1201 (spreading dosage norm, 600 kg ha⁻¹, 800 kg ha⁻¹, and 1000 kg ha⁻¹; driving speed, 5 km h⁻¹)). Before the fertilizer was spread, measurements were made of the flow rate of the spreadable fertilizer through one bunker shutter. Fertilizer application simulations were performed using the discrete element simulation program EDEM. Research has shown that spreading the studied granular fertilizers at the dosage norm of 600 and 800 kg ha⁻¹ allows for the future expansion of the limits of spreading research using a spreading simulation. The most important directions of research would be the research of the spreader vanes’ shape, length, and rational settings positions, using the standard commonly used centrifugal spreader, after making small modifications of the spreader, to achieve that the spreader could spread larger norms of fertilizer or drive faster during spreading.

Continuous efforts are being made to improve fertilizer efficiency by improving fertilizer technology, quality, and application rates. Granular organic fertilizers are more difficult to achieve uniform application because their physical–mechanical properties differ significantly from mineral fertilizers. The properties of granular organic fertilizers can best be determined experimentally. However, these studies are often quite complex. Modern engineering modeling software makes it possible to model the properties of granular fertilizers and their dispersion. This study deals with the theoretical and experimental verification of the physical–mechanical properties of organic bone meal granular fertilizer. For the verification of selected properties of bone meal granules, the following studies were carried out on the granules: determination of poured bulk density, static and dynamic angles of repose, static and dynamic friction coefficients of granule surface, etc. The results showed that for modeling fertilizer properties, it is sufficient to carry out a static compression test to determine the modulus of elasticity and a friction test between granules and the contacting surface to determine the static and dynamic friction coefficients. The remaining properties of the granules can be modeled and calibrated with the DEM software Altair EDEM 2023.