Artur Kowalski

Application of microbial biostimulants can reduce the need for applying mineral fertilisers, particularly those with limited availability or high environmental impact, like phosphate fertilisers. A consortium of bacterial strains able of solubilizing phosphorous (P) was applied together with reduced P fertilization (60% of standard dose) carried out with either a complex fertilizer (CF) or simple P fertilizer (SF) and compared to standard fertilization rates. Trials with field grown cucumber plants were carried out for four years. The application of the microbial inoculum with reduced dose of both fertilizers did not negatively impact on plant physiological parameters and on yield. The evaluation of the inoculation impact on soil microbial activity, carried out on plants grown in rhizoboxes, showed that the aforementioned inoculation, combined with reduced doses of both fertilizers, significantly increased microbial activity in the rhizosphere compared to fertilizers applied at full doses without inoculation. The results suggest that the integration of microbial biostimulants to a reduced mineral fertilization is a strategy that can be applied also in the long term, leading to a significant reduction in the use of mineral fertilizers and a positive economic and environmental impact.

In addition to its obvious benefits, mineral fertilisation also poses a number of threats to the environment. A four-year study was conducted to verify the possibility of integrating the application of a bacterial consortium to reduce the dose of mineral phosphorus (P) fertilisers in field-grown tomato crops without negative effects on yield. The combination of the microbial consortium with a 60% dose of both simple and complex P fertilisers did not show statistical differences in crop productivity and fruit quality compared to the full dose fertilisation each year, even when considering the cumulative yield. This was paralleled by a similar level of leaf chlorophyll index. Plants grown in rhizoboxes showed that the inoculation favoured, in the case of the complex fertiliser, a modification of the root system architecture, though not confirmed statistically. In the case of this kind of fertiliser, the inoculation induced a significant increase in the rhizospheric bacterial metabolic activity, which could be partly accounted for by the agronomic performance. However, this was not paralleled by a modification of the metabolic biodiversity of the bacterial population. The study demonstrated that, for highly demanding crops such as tomato, a valid agrononomic target for the application of microbial-based products integrated into a reduced mineral P fertilisation strategy could reach crop productivity not different from that obtained without them. Such a strategy could favour the adoption of an integrated nutrient management strategy by farmers, with positive impacts also on the environment.

In this study, the effect of different photosynthetic photon flux density (PPFD) provided by LEDs (Light Emitting Diodes) and photoperiod on biomass production, morphological traits, photosynthetic performance, sensory attributes, and image texture parameters of indoor cultivated romaine lettuce was evaluated. Two cultivars of lettuce Lactuca sativa var. longifolium namely ‘Casual’ (Syngenta)—midi romaine lettuce with medium-compact heads—and ‘Elizium’ (Enza Zaden)—a mini type (Little Gem) with compact heavy heads—were used. PPFD of 160 and 240 µmol m⁻² s⁻¹ and photoperiod of 16 and 20 h were applied, and Daily Light Integral (DLI) values were 9.2, 11.5, 13.8, and 17.3 mol m⁻² day⁻¹. The experiment lasted 30 days in the Indoor Controlled Environment Agriculture facility. DLI equal to 17.3 mol m⁻² per day for cv. ‘Casual’ and 11.5–17.3 mol m⁻² per day for cv. ‘Elizium’ allowed to obtain a very high fresh weight, 350 and 240 g, respectively, within 30 days of cultivation in an indoor plant production facility. The application of the lowest PPFD 160 µmol m⁻² s⁻¹ and 16 h photoperiod (9.2 mol m⁻² per day DLI) resulted in the lowest fresh weight, the number of leaves and head circumference. The level of nitrate, even at the lowest DLI, was below the limit imposed by European Community Regulation. The cv. ‘Elizium’ lettuce grown at PPFD 240 µmol m⁻² s⁻¹ and 16 h photoperiod had the highest overall sensory quality. The cv. ‘Casual’ lettuce grown at PPFD 160 µmol m⁻² s⁻¹ and 20 h photoperiod had the lowest sensory quality. The samples subjected to different photoperiod and PPFD were also successively distinguished in an objective and non-destructive way using image features and machine learning algorithms. The average accuracy for the leaf samples of cv. ‘Casual’ lettuce reached 98.75% and for cv. ‘Elizium’ cultivar—86.25%. The obtained relationship between DLI and yield, as well as the quality of romaine lettuce, can be used in practice to improve romaine lettuce production in an Indoor Controlled Environment.

The study examined the influence of light quality on the growth and nutritional status of romaine lettuce grown in deep water culture with a floating raft system using two different nutrient solutions. Four spectra of LED light were used with different ratios of R, G, and B lights (80:10:10, 70:10:20, 60:10:30, and 70:18:12). Two nutrient solutions with a low (A) and moderately high (B) nutrient content were used. Regardless of the nutrient solution, the RGB 70:18:12 light promoted the production of leaf biomass as well as inhibited the accumulation of K and Mg in the leaves. Moreover, those plants were characterized by a low Nitrogen Balance Index (NBI) and a high flavonol index. In the last week of cultivation, there was a strong decrease in K, P, and nitrates in the nutrient solution, and an increase in Ca. In the final stage of growth, symptoms of withering of the tips of young leaves (tipburn) were observed on the plants. The most damage was observed on the plants growing under 70:10:20, 70:18:12, and with the higher concentration of minerals in the solution (B).

The correct fertilization of vegetable crops is commonly determined on the basis of soil and plant costly destructive analyses, demanding more sustainable non-invasive optical detection. Here, we tested the ability of the combined transmittance/fluorescence leaf clip Dualex device for determining the nitrogen (N) status of cabbage plants. Fully developed leaves from plants grown under different N rates of 0; 100; 200; 300 kg N ha⁻¹ in 2018 and 2019 were measured in the field by the Dualex sensor twice a year in July and October. The chlorophyll (Chl) and nitrogen (nitrogen balance index, NBI) indices and the flavonols (Flav) index of the sensor were positively and negatively correlated to leaf nitrogen, respectively. Merging the two-years data, the NBI versus leaf N correlation was less point dispersed in October than July (R² = 0.76 and 0.64, respectively). NBI was also correlated to cabbage yield, better in July than October. Our results showed that the multiparametric Dualex device can be used as precision agriculture tool for the early prediction of plant N and cabbage yield with economic advantage for the growers and reduced environmental contamination due to nitrate leaching.

BACKGROUND: Accumulation and stability of tomato lycopene markedly depends on the cultivar, plant growing and storage conditions. To estimate lycopene in open‐field cultivated processing and fresh market tomatoes, we used a calibrated spectral reflectance portable sensor.RESULTS: Lycopene accumulation in fruits attached to the plant, starting from the Green ripening stage, followed a sigmoidal function. It was faster and reached higher levels in processing (cv. Calista) than fresh market (cv. Volna) tomatoes (90 and 62 mg kg⁻¹ fresh weight, respectively). During storage at 12, 20 and 25 °C, Red tomatoes retained about 90% of harvest lycopene for three weeks. Pink tomatoes increased lycopene during the first week of storage, but never reached the lycopene values of Red tomatoes ripened on the vine. Storability at 12 °C retaining the highest quality in red tomatoes was limited to 14 and 7 days for Calista and Volna cultivars, respectively.CONCLUSION: Significant differences in lycopene accumulation and stability between processing and fresh market tomatoes were established by examining with time the very same fruits by a non‐destructive optical tool. It can be useful in agronomical and post‐harvest physiological studies and can be of interest for producers oriented to the niche nutraceutical market. © 2018 Society of Chemical Industry

Reflectance spectroscopy represents a useful tool for the non-destructive assessment of tomato lycopene, even in the field. For this reason, a compact, low-cost, LED-based sensor has been developed to measure reflectance in the 400-750 nm spectral range. It was calibrated against wet chemistry and evaluated by Partial Least Squares (PLS) regression analyses. The lycopene prediction models were defined for two open-field cultivated red-tomato varieties: the processing oblong tomatoes of the cv. Calista (average weight: 76 g) and the fresh-consumption round tomatoes of the cv. Volna (average weight: 130 g), over a period of two consecutive years. The lycopene prediction models were dependent on both cultivar and season. The lycopene RMSEP produced by the 2014 single-cultivar calibrations validated on the 2015 samples was large (33 mg kg-1) in the Calista tomatoes and acceptable (9.5 mg kg-1) in the Volna tomatoes. A more general bi-cultivar and bi-year model could still explain almost 80% of the predicted lycopene variance, with a relative error in red tomatoes of less than 20%. In 2016, the in-field applications of the multi-seasonal prediction models, built with the 2014 and 2015 data, showed significant (P<0.001) differences in the average lycopene estimated in the crop on two sampling dates that were 20 days apart: on 19 August and 7 September 2016, the lycopene was 98.9±9.3 and 92.2±10.8 mg kg-1 FW for cv. Calista, and 54.6±13.2 and 60.8±6.8 mg kg-1 FW for cv. Volna. The sensor was also able to monitor the temporal evolution of lycopene accumulation on the very same fruits attached to the plants. These results indicated that a simple, compact reflectance device and PLS analysis could provide adequately precise and robust (through-seasons) models for the non-destructive assessment of lycopene in whole tomatoes. This technique could guarantee tomatoes with the highest nutraceutical value from the production, during storage and distribution, and finally to consumers.

ISHS III International Symposium on Organic Greenhouse Horticulture Effect of organic fertilization on the quality and yield of two radish cultivars in greenhouse organic cultivation

A multiparametric optical sensor was used to nondestructively estimate phytochemical compounds in white cabbage leaves directly in the field. An experimental site of 1980 white cabbages (Brassica oleracea L. var. capitata subvar. alba), under different nitrogen (N) treatments, was mapped by measuring leaf transmittance and chlorophyll fluorescence screening in one leaf/cabbage head. The provided indices of flavonols (FLAV) and chlorophyll (CHL) displayed the opposite response to applied N rates, decreasing and increasing, respectively. The combined nitrogen balance index (NBI = CHL/FLAV) calculated was able to discriminate all of the plots under four N regimens (0, 100, 200, and 400 kg/ha) and was correlated with the leaf N content determined destructively. CHL and FLAV were properly calibrated against chlorophyll (R² = 0.945) and flavonol (R² = 0.932) leaf contents, respectively, by using a homographic fit function. The proposed optical sensing of cabbage crops can be used to estimate the N status of plants and perform precision fertilization to maintain acceptable crop yield levels and, additionally, to rapidly detect health-promoting flavonol antioxidants in Brassica plants.