Organic farmers usually do not have the opportunity to address the actual symptoms of deficiency through the foliar application of synthetic fertilization, therefore, the main treatment is realized by green manure crop cultivation and application of organic fertilizers. The aim of this long-term experiment was to compare two different production systems with and without livestock in terms of organic farming, and a control variant with no fertilization was also included (treatment 1). The production system without animal husbandry was based on solely the application of renewable external resources (compost or digestate) (treatment 2) and the same fertilization with the addition of auxiliary substances (AS) (treatment 3). The production system with animal husbandry included utilization of fertilizers produced on the farm (fermented urine or manure) using solely farm fertilizers (treatment 4) and in addition with AS (treatment 5). Each treatment had three replications. This work describes the average yields from four experimental years and five experimental localities. Winter wheat, potatoes, winter wheat spelt and legume-cereal mix with corn were used and examined as model crops during the first four years of this long-term research. The highest average yield of winter wheat grain and potato tubers during the first two years of the experiment were obtained after the treatments 2 (7.1 t/ha grain, 33,9 t/ha tubers) and 3 (7.0 t/ha grain, 34,1 t/ha tubers). The several times higher nitrogen content in applied digestate and compost in comparison with fermented urine and manure was probably the reason for such results. On the contrary, the results obtained from the third (spelt) and fourth (LCM and corn) experimental years favored treatment 4 (5,5 t/ha grain, 4,6 cereal unit/ha) and 5 (5,4 t/ha grain, 4,7 cereal unit/ha) from the long-term point of view. After four experimental years, the presented results supported the application of farm fertilizers as a preferable option. The treatments with additional application of AS did not provide a higher yield, therefore, such an application seems unnecessary.

Nitrogen fertilization cannot be used by actual needs of plants during vegetation in organic farming. The proper crop rotation and harmonic nutrition are necessary for good and quality products. The methods of treatment are mainly realized by cultivation of green manure crop and fertilizing by organic fertilizers. The aim of the long-term experiment was to evaluate the effect of different localities and different organic fertilizers on crop yield in organic farming. Variants of fertilization included in the experiment are: 1. Unfertilized control, 2. Green manure, 3. Green manure + renewable external sources, 4. Green manure + renewable external sources + auxiliary substances, 5. Green manure + farm fertilizers, 6. Green manure + farm fertilizers + auxiliary substances. The experiment started by sowing of winter wheat so green manure crop was not grown in the first experimental year. The highest yield of winter wheat grain coming from the first year of the experiment was observed on the variant with renewable external sources (digestate). Average grain yield on this variant was about 7.12 t/ha (up to 0.74 t/ha increased than the unfertilized control). Average yield of potatoes from the second year of the experiment was the highest after combination with green manure + renewable external sources (compost + digestate) + auxiliary substances. This variant achieved yield about 34.08 t/ha, which is increased by 9.35 t/ha compared to the control variant. Results from this two-year experiment showed that the most suitable combination of fertilization with or without green manure crop is compost + digestate. These results were probably caused by higher content of nitrogen in organic fertilizers (compost + digestate) used in this variant compared to other variants. Statistical difference of achieved yields was observed between each experimental station in both experimental years.

Nitrogen fertilization of plants during the vegetation is very problematic in terms of organic farming. The balanced crop rotation and versatile nutrition are essential for maintaining good yields and high‑quality products. The application of organic fertilizers and incorporation of green manure crops are one of the best options for achieving optimal results in organic farming. The goal of this long‑term research was to examine the effect of several different organic fertilizers and divergent experimental stations on crop yield in conditions of organic farming. a total of 6 variants of fertilization were evaluated in this experiment: 1. unfertilized, 2. green manure (GM), 3. GM + renewable external sources, 4. GM + renewable external sources + biostimulants, 5. GM + farm fertilizers, 6. GM + farm fertilizers + biostimulants. The winter wheat was sown at the start of the experiment in autumn of 2014. Therefore, green manure was not cultivated in the first experimental year. The results from the first year of this experiment showed, that the variant with renewable external resource (digestate) provided the highest yield. The average yield of wheat grain on this variant was about 7.12 t/ha, which is increased by 0.74 t/ha in comparison with unfertilized control variant. The potatoes were used as a model crop in second year of the experiment. The highest yield of potatoes coming from the second experimental year was observed on the combination of green manure + renewable external sources (compost and digestate) + biostimulants. The average yield of potatoes on this variant was about 34.08 t/ha. The yield of potatoes observed on the unfertilized variant was lower by 9.35 t/ha. The content of nitrogen in organic fertilizers (compost and digestate) was higher in comparison with other organic fertilizers used in the experiment, which probably caused these results. The winter wheat spelt was used as a model crop in the third year of the experiment. The application of organic fertilizers was completely omitted in this year. The highest average yield of spelt (5.5 t/ha) was observed on the variant called green manure + farm fertilizers. The average yield achieved on the unfertilized variant was lower by 0.7 t/ha. The result from this three experimental years point out the similarity between farming with and without animal husbandry in organic farming. The statistical differences between experimental stations were observed in experimental years.