The main objective of this study was to analyze variable rate seeding (VRS) methods and critically evaluate their suitability and effectiveness for the challenges under field conditions. A search was performed using scientific databases and portals by identifying for analysis and evaluation 92 VRS methodologies, their impact and economic benefits depending on the main parameters of the soil and environment. The results of the review identified that VRS could adapt the appropriate seeding rate for each field zone, which was based on site-specific data layers of soil texture, ECa, pH and yield maps. Then, remotely detected images or other data which identify yield-limiting factors were identified. The site-specific sowing method (with a variable sowing rate for each field area) allows the optimization of crop density to obtain the best agronomic and economic results. Various proximal and remote sensor systems, contact and contactless equipment, mapping and VRS modeling technologies are currently used to determine soil and crop variability. VRS depends on the field characteristics’ sowing equipment capabilities, the planned harvest, soil productivity and machine technology interactions with the environment. When forecasting the effective payback of a VRS over the desired period, the farm size should on average be at least 150 ha. In future studies, to achieve the best solutions and optimal methods, it is important to test, evaluate and put into practice the latest methodologies on farms, to perform complex assessments of changes in sensor, soil, plant and environmental parameters.

A crucial factor that determines the development of production and consumption markets for biofuels is the choice of raw materials that can ensure the highest possible production efficiency, the lowest cost and the smallest emission of harmful substances to the atmosphere during all production stages. Considerations underlying the development of biofuel production have been discussed as well as the theoretical mechanisms linking the generation of biofuels to the level of production and the variability of prices of agricultural raw products. The aim of this study has been to identify the scale at which energy raw materials originating from agriculture are used for liquid biofuels production and to explore their impact on food security. The study used public statistical data (OECD-FAO and IndexMundi). The time span of the analysis was from 2005 to 2018. First-generation biofuels based on food raw materials (cereal grains, root crops, sugarcane and vegetable oils) are becoming increasingly competitive with food production recent years have been a period of the dynamic growth in production of liquid biofuels. In 2018, the global production of these substances reached 167.9 billion litres (bioethanol and biodiesel together), consuming 16.1% of maize grain, 1.7% of wheat grain, 3.3% of grain of other feed grains and 13.5% of vegetable oil.

Reducing the overuse of mineral fertilizers in crop production is a key factor related to healthier soil, healthier food, and more economical, efficient, and cleaner agricultural production. The aim of this study was to investigate and to compare the effects of fixed and variable rate fertilization with fertilizer consumption, energy consumption, and environmental impact. A 4-year experimental field study using crop rotation of four plants (spring barley, winter oilseed rape, winter wheat, and faba bean) was performed. Fertilization with phosphorus and potassium at a variable rate were performed and applied based on the soil properties analyzed before the start of the research and completion of the fertilization maps. Nitrogen fertilization was performed by additional fertilization using a proximal N-sensor, which gives the accurate nitrogen uptake in plants in real-time. This was followed by a comparative evaluation analysis of variables and conventional fixed-rate fertilization methods to assess fertilizer consumption, energy consumption, environmental impact, and economic efficiency. The results of the study showed that an application of a variable fertilization rate can reduce the total amount of nitrogen, phosphorus, and potassium fertilizers by 24.9%, energy consumption by 3463.1 kg ha⁻¹, and emissions of greenhouse gases (GHG) by 341.5 kg CO_2eq ha⁻¹ compared to fixed fertilization rate. The method of fertilization with a variable application rate reduced the costs of fertilization, and at the same time, the costs of the total plant production by €168.0 ha⁻¹, on average.

Three coarse herbaceous energy plants—such as Miscanthus (Miscanthus sinensis), sida (Sida hermaphrodita Rusby) and cup plant (Silphium perfoliatum L.)—were grown and investigated in the experimental fields of Vytautas Magnus University Agriculture Academy, and the technical means of plant processing and utilization for solid biofuel were investigated. The physical–mechanical properties and quality indicators (moisture content, biometrical properties, density, and resistance to compression) of coarse stem herbaceous plants milled and compressed into 6 mm diameter pellets were investigated. The moisture content of the tested pellets was sufficiently low and ranged from 8.7% to 9.6%. The highest density was that of sida pellets (1072.3 ± 43.4 kg m⁻³ DM), and the lowest density was that of Miscanthus pellets (713.5 ± 67.1 kg m⁻³ DM). In order to evaluate the influence of moisture content on the properties of biofuel pressed into pellets, the density and the destructive compressive force of the different-moisture pellets were investigated and their change in the range of 5–15% pellet moisture content was evaluated. Criterion k was calculated to determine the effect of moisture on the pellet quality indicators (density, destructive compressive force, and lower heating value), and the following results were obtained: the highest influence of moisture on density was observed in sida (k = 34.280), on destructive compressive force in Miscanthus (k = 14.5), and on the lower heating value, also in Miscanthus (k = 0.198). After a comprehensive investigation and evaluation of these properties, an empirical model suitable for practical use was developed and prepared. Emissions of harmful gases, such as carbon monoxide, carbon dioxide, and nitrogen oxides, were determined when various coarse stem herbaceous energy plants were burned. The determined emissions of harmful gases into the environment did not exceed the permissible values.

Granular organic fertilizers have been increasingly used in agriculture due to the longer delivery of nutrients to plants and the milder impact on the environment. The aim of this study was to determine the energy, environmental and economic efficiency of granular and non-granular organic fertilizers. Four technological scenarios of organic fertilizer use were used for comparative assessment: (1) manure fertilization (16.0 t ha⁻¹), (2) manure fertilization (30.0 t ha⁻¹), (3) manure pellet fertilization (2.0 t ha⁻¹), and (4) fertilization with meat and bone meal pellets (0.7 t ha⁻¹). Experimental studies using the mass flow method of laser spectroscopy were performed to evaluate the comparative environmental impact of granular and non-granular organic fertilizers. Economic assessment was performed for mechanized technological operations of loading, transportation and distribution of organic fertilizers, estimating the price of aggregates used and fuel consumed, the costs of individual technological operations and other indirect costs. The results showed that for mechanized technological operations, when fertilizing with granular organic manure and meat and bone meal fertilizer, energy consumption is 3.2 to 4.0 times lower compared to fertilization with manure. The average ammonia (NH₃) emissions from granular organic fertilizers were found to be six times lower than from non-granular organic fertilizers. The lowest costs for mechanized works were incurred when using meat and bone meal pellets, the highest economic benefits of organic fertilizers by elements was when using manure 30 t ha⁻¹, and the highest costs for organic fertilizers were incurred when using manure pellets.