Nitrogen (N) management remains a global challenge for the sustainability of diversified farming systems. Field crops are often over-supplied with nitrogen by farmers aiming to high productivity. Although the increase of nitrogen rates leads in many instances to high yields, degree of effectiveness for nitrogen use remains low. Urease and nitrification inhibitors are technologies which have been present in the fertilizers market at least 50 years. Inhibitors exploitation ensures long-term nitrogen release and improved N-uptake by plants and N-storage in seeds and silage. Avail of inhibitors, such as the decline of nitrogen leaching in form of NO₃⁻, reduction of emissions in NH₃ form, and rise of yield, are some of the desirable attributes that are derived from their integration in fertilization schedules. This review reports the evaluation of applied nitrogen, with inhibitors, and field crops based on nitrogen indices. The examined N-indicators include Nitrogen use efficiency (NUE), Nitrogen Utilization Efficiency (NUtE,) Nitrogen Agronomic Efficiency (NAE), Nitrogen Harvest Index (NHI), and N uptake. This review gathered all, to the best of our knowledge, available data regarding the utilization of nitrification and urease inhibitors under an exclusively agronomic perspective. Either dual or single use of nitrification and urease inhibitors has been reported to significantly increase yield components and promote nitrogen uptake. To conclude, the assessment of N-related indices is vital to promoting sustainability in diversified farming systems, while the integration of inhibitors in national N fertilizations schemes may contribute to system profitability through enhancement of N-supply to crops.

Trichoderma harzianum, as a natural endophytic biocontrol agent, can ameliorate plant development, nutrient uptake, and resistance to biotic and abiotic stresses. This study aimed to investigate the effect of Trichoderma harzianum inoculation on agronomical and quality characteristics of two monoecious hemp (Cannabis sativa L.) varieties, Fedora 17 and Felina. A greenhouse pot experiment was conducted in a completely randomized design of two treatments of Trichoderma harzianum with a low and high dose of the fungus (T1 and T2). The significance of differences between treatments was estimated by using a Fisher’s test with a significance level p = 0.05. The root density of both varieties was significantly affected by treatments, and higher values were recorded in Fedora 17 (2.32 mm cm⁻³). The Arbuscular Mycorrhizal Fungi (AMF) colonization of the root system and the soil emission of CO₂ were higher after the inoculation of Trichoderma harzianum. The highest values of plant height and dry weight were noticed for T2, especially in variety Felina. Trichoderma harzianum positively influenced characteristics of inflorescences such as their number, fresh weight moisture, and compactness in both varieties, while the dry weight, length, and dry yield of inflorescences were not improved. Finally, the fertigation of Trichoderma harzianum in hemp plants was beneficial by increasing the cannabidiol (CBD) content, especially in T2 treatment (4 × 10¹² CFU kg⁻¹).

Field experiments were conducted during 2019 in two different locations in Greece (Athens and Farsala) to evaluate the effect of urea and urea fertilization with inhibitors on the agronomic yield and quality characteristics of two cannabis varieties (Cannabis sativa L.), “Uso31”and “Fedora 17”. The experimental design was split-plot with four different fertilization treatments—control, Urea (U), urea with Urease Inhibitor (UI), and urea with Nitrification Inhibitor (NI) and urease inhibitor (UI). The significance of differences between treatments was estimated by using Tukey’s test with a significance level of p = 0.05. The plant height was significantly affected by the different fertilizations and different varieties as well as by the two locations. The maximum plant height was 197 cm for “Fedora 17”in Farsala. The seed yield was higher forthe urea with inhibitors treatment in both varieties. The Cannabidiol (CBD) content was significantly affected by the fertilization—it was higher in urea with inhibitors in “Uso31”and “Fedora 17” treatments. The lowest CBD content value was 1.29% (control) and the highest was 1.69% (urea NI + UI). In conclusion, in both varieties, it seems that urea with inhibitors has a positive effect on their growth, as well as on the increase in cannabidiol (CBD) content.

Quinoa (Chenopodium quinoa Willd.) crop under Mediterranean conditions: a review

While processing tomato cultivation (Solanum lycopersicum L.) is considered one of the most important industrial crops in Greece, a waste known as tomato pomace is growing significantly high. Notably, the tomato pomace presents enormous opportunities for the creations of organic fertilizers. The aim of this study was to investigate the use of tomato pomace as a fertilizer in the same crop. A field experiment was established at the Agricultural University of Athens during 2018 and 2019 in a randomized complete design with five treatments (control, inorganic NPK (NPK), Tomato pomace and Biocycle Humus Soil (Tp and BHS), Tomato pomace and Farmyard manure (Tp and FYM), and Tomato pomace and Compost (Tp and CM). Physical soil properties such as soil porosity and penetration resistance were improved by the application of organic blends. Additionally, soil nitrogen content ranged from 0.10% (control and NPK) to 0.13% (Tp and FYM). A significant increase of yield was noticed under organic fertilization where the highest yield of 8.00 tn ha⁻¹ was recorded in Tp and BHS (2018). Lycopene content was significantly affected by fertilization and its highest values were 87.25 (Tp and BHS; 2018), and 88.82 mg kg⁻¹ fresh (Tp and FYM; 2019). Regarding fruit firmness, the three organic blends did not have statistically significant difference. In addition, the Total Soluble Solids (TSS) was significantly affected by the fertilization and the maximum value was 4.80 ◦Brix (Tp and CM; 2018). In brief, tomato pomace blended with organic fertilizers was yielded considerable since it improved soil quality and increased yield.

Pomace from tomato paste is produced in great amounts after tomato processing industries in Greece. The aim of this study is to evaluate tomato pomace as fertilizer in sweet maize cultivation. Two-year experiments were set up in West Greece under organic cultivations. The experiments followed a randomized complete block design, with four treatments, with which were different fertilizer applications (control, Tomato pomace, Tomato pomace & inorganic fertilizer (NPK), Tomato pomace & manure) in three replications. The root density, root surface, and symbiotic of arbuscular mycorrhizal fungi (AMF) were statistically affected by fertilization for both years, and the combination of Tomato pomace (Tp) and manure gave the highest values. Organic carbon (C) was significantly affected by year and fertilization, as well as the total nitrogen (N) was significantly affected by fertilization. Soil porosity under tomato pomace and mix of tomato pomace and inorganic fertilizer do not show statistically significant differences. The highest values for plant growth and leaf area index were under the combination of tomato pomace and manure. The yield was statistically affected by fertilization and year. Therefore, tomato mixtures with manure as well as compost had the most positive results in almost all parameters of the studies.