Cabbage is an annual vegetable crop species cultivated throughout the year. The development of high-yielding cabbage hybrids and the optimization of several agronomic management practices such as fertilization and crop rotation have resulted in increased soil fertility, crop yield and product quality. This study aimed to investigate the effects of the farming system (organic and conventional) and the applied rotation scheme on soil nutrient content, head yield and the nutrient content of cabbage. The preceding crops included either pea (P), faba bean (F) or cabbage (C), and thus, the rotation schemes were P-C, F-C and C-C. Sheep manure was applied in the organic farming system, and the inorganic fertilizer 11-15-15 (N-P₂O₅-K₂O) was applied to the conventionally cultivated plants. The results reveal an interaction between the farming system and the preceding crop for the head yield, with the lowest values (57.00 t ha⁻¹ and 53.87 t ha⁻¹ in 2015/2016 and 2016/2017, respectively) recorded in plots where cabbage was cultivated as a preceding crop under the organic farming system. The N, P and K contents in head tissues were affected only by the farming system, with the greatest values recorded in the conventional farming system. Both factors affected the nutrient content in the soil. Specifically, the highest values of NO₃⁻ and total N content in the soil were recorded in the P-C and F-C rotations, and the K content was higher in the continuous cabbage cropping system (C-C). Moreover, the NO₃⁻, P and K contents in the soils were higher in the conventional farming system compared to the organic system. To conclude, combining inorganic fertilization in a crop rotation scheme with legume species such as pea and faba bean as preceding crops for cabbage can result in increased soil fertility and head yield.

In the current study, the impact of the preceding crops on growth, fresh pod yield, nitrogen fixation efficiency, and nitrogen nutrition of faba bean (Vicia faba L.) was investigated for two years in both organic and conventional crops. As preceding crops served cabbage, pea, and faba bean. The pod number per plant (PN) and the total fresh pod yield (TFPY) were significantly lower with cabbage compared to pea and faba bean as preceding crops in both cropping systems and both experimental years. However, in the organic farming system, pea increased significantly in PN and TFPY compared to faba bean as a preceding crop, while in the conventional system, there was no significant difference between the two legumes. The greater yield performance with the two legumes as preceding crops was associated with higher soil NO₃-N and total-N concentrations at the beginning of the subsequent faba bean crop. The higher soil N availability when the preceding crop was a legume resulted partly from the higher biomass of crop residues left by these crops on the field after harvest, compared to cabbage. However, it was also associated with a more extensive nodulation of the faba bean roots by rhizobia and a higher percentage of N derived from atmosphere (%Ndfa) in their plant tissues, as determined through the natural abundance of the 15N isotope, when the preceding crop was a legume. The cropping system had no impact on pod yield, but organic farming increased the %Ndfa in both years.

Manure is a common source of nitrogen (N) in organic farming. However, manure is not always easily available, while the maximum N amount added as animal manure in organic agriculture is restricted by EU regulations. The present study was designed to test whether green manuring with a warm-season legume and intercropping with a cold-season legume can substitute farm-yard manure or compost as N sources in organic greenhouse tomato crops. To test this hypothesis, a winter-spring (WS) tomato crop was installed in February following the incorporation of crop residues of an autumn-winter (AW) tomato crop intercropped with faba bean, which had been fertilized with cowpea residues as green manure. This treatment, henceforth termed legume treatment (LT), was compared with the use of compost or manure as an N fertilization source in both tomato crops. In addition, a combination of compost and LT was also used as a fourth treatment. The results showed that green manuring with legumes and particularly cowpea can contribute a significant amount of N to the following organic tomato crop, through the biological fixation process. Nevertheless, legumes as green manure, or compost, or their combination cannot efficiently replace farmyard manure as an N fertilization source. Compost exhibited a slow mineralization course.

The use of biostimulants consisting of plant growth-promoting rhizobacteria (PGPR) has been rapidly expanding in horticulture in recent years. In the current study, a novel mix of six Bacillus sp. strains (B. subtilis, B. pumilus, B. megaterium, B. amyloliquefaciens, B. velezensis, B. licheniformis) was tested as a PGPR biostimulant in two experiments with zucchini squash (Cucurbita pepo L.). The first experiment took place in greenhouse soil in winter, while the second experiment was conducted in an open field during summer. In both experiments, seeds of the local landrace “Kompokolokytho” and the commercial hybrid “ARO-800” were either inoculated or non-inoculated with the PGPR biostimulant. The application of the six Bacillus sp. strains increased both the vegetative growth and the yield of zucchini squash, and these effects were associated with significantly higher shoot phosphorus levels in both experiments and both genotypes. Furthermore, at the end of the cultivation, the colony-forming units of Bacillus sp. were appreciably higher in plants originating from inoculated compared to non-inoculated seeds, indicating that the tested mix of Bacillus sp. can be successfully applied through seed inoculation. “ARO-800” produced more vegetative and fruit biomass than “Κompokolokytho” under greenhouse cropping conditions, while in the open field crop, both genotypes performed equally. Presumably, this response occurred because “ARO-800” did not express its full yield potential in the open field due to stress imposed by the high summer temperatures, while the local landrace, which is traditionally grown in open fields, may be more resilient to stress conditions frequently encountered in open fields.

The use of biostimulants consisting of plant growth promoting rhizobacteria (PGPR) is rapidly expanding in horticulture in recent years. In the current study, a novel mix of six Bacillus sp. strains was tested as a PGPR biostimulant in two experiments with zucchini squash (Cucurbita pepo L.) cultivated in the greenhouse soil and in an open field, respectively. In both experiments, seeds of the local landrace ‘Kompokolokytho’ and the commercial hybrid ‘ARO-800’ were either inoculated or non-inoculated with the PGPR biostimulant. The application of the six Bacillus sp. strains increased both the vegetative growth and the yield of zucchini squash, and these effects were associated with significantly higher shoot phosphorus levels in both experiments and both genotypes. Furthermore, at the end of the cultivation, the colony forming units of Bacillus sp. were appreciably higher in plants originating from inoculated compared to non-inoculated seeds, indicating that the tested mix of Bacillus sp can be successfully applied through seed inoculation. ‘ARO-800’ produced more vegetative and fruit biomass than ‘kompokolokytho’ under greenhouse cropping conditions, while in the open-field crop both genotypes performed equally, presumably because the local landrace is traditionally grown in open fields, and thus it is not well adapted to greenhouse cropping.