At urban locations certain challenges are concentrated: organic waste production, the need for waste treatment, energy demand, food demand, the need for circular economy and limited area for food production. Based on these factors the project presented here developed a novel technological approach for processing organic waste into new food. In this system, organic waste is converted into biogas and digester residue. The digester residue is being used successfully as a stand-alone fertilizer as well as main substrate component for vegetables and mushrooms for the first time - a "digeponics" system - in a closed new low energy greenhouse system with dynamic soap bubble insulation. Biogas production provides energy for the process and CO2 for the greenhouse. With very limited land use highly efficient resource recycling was established at pilot scale. In the research project it was proven that a low energy dynamic bubble insulated greenhouse can be operated continuously with 80% energy demand reduction compared to conventional greenhouses. Commercial crop yields were achieved based on fertilization with digestate; in individual cases they were even higher than the control yields of vegetables such as tomatoes, cucumber and lettuce among others. For the first time an efficient direct use of digestate as substrate and fertilizer has been developed and demonstrated.

Drought stress is one of the many factors that lead to decreased yield in both quality and quantity. One method to improve plant resistance to this stress is application of biostimulants. The most widely used biostimulants are protein hydrolysates, containing sea algae extract and humus compounds. In the present study, the influence of the amino acids as well as combination of amino acids with Ascophyllum nodosum filtrate on broccoli (Brassica oleracea var. italica) plants cvs. 'Agassi' and 'Tiburon' was investigated. The plants were watered with Ascophyllum nodosum filtrate three days before planting and sprayed three times with amino acids two, four and six weeks after planting. The present results show that biostimulants have a significant effect on both gas exchange and transpiration rate both prior to the application of stress, under drought stress and after re-watering. Biostimulant treatment led to an increase of drought tolerance in both studied cultivars but the final effect depended on cultivar. 'Tiburon' cultivar turned out to be more tolerant to drought stress than 'Agassi'. The application of biostimulants resulted in an increase of photosynthetic rate, stomatal conductance, internal CO 2 concentration and transpiration rate in 'Agassi' cultivar under drought stress. This effect was not observed in 'Tiburon'. The chlorophyll content was higher under drought stress as compared to the value prior to stress in both cultivars.

Magnesium (Mg) serves specific physiological functions in plants, as it participates in 250÷400 processes and may not be replaced by other elements, even those exhibiting similar physicochemical properties, such as Co 2+ , Mn 2+ or Ni 2+ . The aim of the conducted studies was to optimize magnesium nutrition of onion (Allium cepa L.), through the evaluation of yielding of plants, and to determine its effect on contents of the following elements in leaves and bulbs: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg). Magnesium was applied in the quick-acting form, MgSO4·7H2O, based on the chemical analyses of soil, in doses corresponding to 50, 100, 150 and 200 mg Mg·dm -3 soil. The other nutrients were supplemented to standard levels recommended for the cultivation of onion, amounting to (in mg·dm -3 soil) 150 N, 80 P and 200 K. Magnesium nutrition was found to have a positive effect on yielding of onion and its quality. Significantly the highest total yield (4.85 kg·m -2 ) and merchantable yield (4.78 kg·m -2 ) were obtained when applying Mg-100, which amounted to an increase by 38% and 45% in comparison with the control combination. Plant nutrition with magnesium in case of leaves significantly affected an improvement of their nutrient status for nitrogen, deterioration of calcium nutrition, while in case of leaves and bulbs that of potassium. Analyzed levels of magnesium nutrition had a significant effect on nutrient status of leaves and bulbs for this nutrient. Leaves accumulated more nitrogen, potassium, calcium and magnesium than bulbs. Controlled magnesium nutrition of plants is an effective method of biofortification of onion with this nutrient.

Effect of Temperature on the Yield and Quality of Broccoli Heads The effect of temperature on the yield and quality of broccoli heads was determined. The study involved three cultivars: Cruiser, Skiff and Fiesta. The seedlings were planted on five different dates in 1995 and 1996, nine in 1997 and eight in 1998. The length of time from planting to the first harvest for all the 27 cultivation periods was divided into three equal parts determining in this way three phases of growth. The time of harvest was defined as the fourth phase. Temperatures on a scale from 0°C to 40°C were divided into five-degree ranges. Then, for the four growth phases, correlations were determined between the number of hours at a temperature in the five-degree ranges and the total yield, the percentage of loose heads and the percentages of heads with uneven surface or non-uniform buds. The length of time at a temperature in the range of 15-25°C during the first growth phase after planting and the phase preceding harvest had the greatest influence on total yield. Longer times at temperatures above 20°C contributed to smaller yields. The longer was the length of time at a temperature ranging from 20 to 25°C during the phase preceding harvest and at a temperature ranging from 5 to 15°C during harvest, the lower the percentage of heads with uneven surface was observed. Longer periods with temperatures above 20°C at harvest time contributed to the loosening of heads.

A way to alleviate excessive Mn nutrition of plants is through silicon application. The aim of the present study was to examine the effect of different Si concentrations in a nutrient solution and Si plant spraying treatments (in the form of silica sol) on the yielding and nutritional status of hydroponically grown lettuce under Mn-stress. The experiments were conducted under controlled conditions in a phytotron. The influence of the following Si levels in the nutrient solution (5.5-control; 15.5; 23.25 and 31 mg Si dm-3) and foliar sprays (distilled water; Si solution) were investigated. Silicon supplied through fertigation significantly affected the plant's nutrient status and alleviated the Mn stress, increasing fresh matter production, RWC (Relative Water Content) and the number of leaves per plants, while decreasing the share of dry matter. The Si nutrition did not change the content of Mn in the leaves, but caused a significant increase in N, P, Na, Fe and Si concentrations with a simultaneous decrease of Zn and Cu levels. The content of Ca, Mg and K was relatively stable (except for the treatment with the most intensive Si nutrition). Generally, the concentrations of N, P, K, Ca, Mg, Na and Fe within the tested Si range were higher than in the control, while being lower in the case of Zn and Cu. Overall, the foliar application of Si did not change plant yielding, the number of leaves on plants and most macro-and microelement concentration in leaves, but modified significantly the RWC as well as the Cu and Na content. The dry matter content under Si nutrition was varied. In summary, an effective method to alleviate Mn-stress is to apply silica sol to a nutrient solution used for plant fertigation.