Effect of Various Rates of P from Alternative and Traditional Sources on Butterhead Lettuce (Lactuca sativa L.) Grown on Peat Substrate

Previous research indicated the potential use of struvite (STR) as an alternative source of phosphorus (P) in crop production. A greenhouse experiment was conducted to evaluate the effect of STR and triple superphosphate (TSP) on the growth and chemical composition of butterhead lettuce grown on peat substrate over a three-month period (May–July). Both alternative (STR) and conventional (TSP) fertilizers were applied at three rates: (1) recommended rate based on the elemental content of substrate and crop nutritional need; (2) reduced rate (50% lower than recommended); and (3) increased rate (50% higher than recommended). Unfertilized (control) plants were also grown in the pot experiment. As expected, fertilizer application tended to increase the content of heavy metals in the substrate. Thus, an increase in Zn, Pb, and Cu content in peat substrate was found following STR amendments. However, compared with unfertilized plants, the applied rates of the STR and TSP fertilizers did not increase the content of Cd and Cu in the plant leaf, while Hg content was below the detection limit. In addition, Zn content in the plant leaf significantly decreased following STR and TSP applications. In comparison to unfertilized plants, both alternative and conventional fertilizers increased the content of P and nitrate nitrogen (N-NO3−) in the plant leaf while their effect on Mg content was negligible. The increased rate of STR was the best fertilizer treatment because it produced the largest number of leaves, which were also characterized by the highest P content. Our findings showed that STR was an effective source of P in butterhead lettuce cultivation without adverse effects on heavy metal accumulation.

Isosmotic Macrocation Variation Modulates Mineral Efficiency, Morpho-Physiological Traits, and Functional Properties in Hydroponically Grown Lettuce Varieties (Lactuca sativa L.)

The management of mineral elements in agriculture is important for their nutritional role for plants and dietary value for humans, sparking interest in strategies that can increase mineral use efficiency and accumulation in plant food. In this work, we evaluated the effects of the isosmotic variations of the concentration on three macrocations (K, Ca, and Mg) in lettuce (Lactuca sativa L.). Our aim was to improve the nutritional components of this valuable dietary source of minerals. Using a full factorial design, we analyzed mineral utilization efficiency (UtE), leaf morphology, gas exchange parameters, phenolic profiles (through ultra-high performance liquid chromatography coupled to a quadrupole-time-of-flight (UHPLC-QTOF) mass spectrometry), and enzymatic activities in two phytochemically diverse butterhead lettuce varieties (red or green). Plants were fed in hydroponics with three nutrient solutions (NSs) with different ratios of K, Ca, and Mg. The variation of these minerals in the edible product was associated with alterations of the morphology and physiology of the leaves, and of the quality and functional properties of lettuce, with a trade-off between total accumulation and mineral UtE. Moreover, in non-limiting conditions of nutrient availability, significant mineral interactions were also present. The flexibility of the plant response to the different ratios of macrocations, and the observed large intraspecific variation, were adequate to provide mineral-specific phytochemical profiles to the edible product. Specifically, the full-red lettuce provided more interesting results in regard to the compositional and functional attributes of the leaves.

Comparative Assessment of Hydroponic Lettuce Production Either under Artificial Lighting, or in a Mediterranean Greenhouse during Wintertime

Butterhead lettuce was grown hydroponically in a vertical farm under high (HLI) and low (LLI) light intensity (310, and 188 μmol m−2 s−1, respectively) and compared to hydroponically grown lettuce in a greenhouse (GT) during wintertime in Athens, Greece (144 μmol m−2 s−1). The highest plant biomass was recorded in the HLI treatment, whereas LLI and GT produced similar plant biomass. However, the LLI produced vortex-like plants, which were non-marketable, while the plants in the GT were normal-shaped and saleable. Net photosynthesis was highest in the HLI and higher in the LLI than in the GT, thereby indicating that light intensity was the dominant factor affecting photosynthetic performance. Nevertheless, the unsatisfactory performance of the LLI is ascribed, not only to reduced light intensity, but also to reduced light uniformity as the LED lamps were closer to the plants than in the HLI. Furthermore, the large solar irradiance variability in the GT resulted in substantially higher adaptation to the increased light intensity compared to LLI, as indicated by chlorophyll fluorescence measurements. Light intensity and photoperiod are believed to be the primary reasons for increased nitrate content in the GT than in the vertical farming treatments.

PERFORMANCE OF BIODEGRADABLE FLOATING DIRECT COVERS IN THE FIELD PRODUCTION OF BUTTERHEAD LETTUCE DURING SPRING AND AUTUMN TRIALS

Non-degradable polypropylene nonwovens are difficult to dispose and their utilization represents high economic costs. This study was conducted on lettuce cultivated during the spring and autumn seasons in the southern part of Poland to test biodegradable nonwovens as plant covers. Several nonwovens were developed from aliphatic-aromatic copolyesters (ACC), one without modifiers (SB48/11) and three with the addition of fatty acid dimers: two commercial variants (SB20/13, SB21/13) and one made from plant biomass (SB28/13). Nonwoven polypropylene (PP) fleece was included as a control cover. One week after covering with SB48/11, stomatal conductance (gs) increased in lettuce plants in parallel with higher transpiration rate (E) and sub-stomatal CO2 concentration (Ci) relative to the control, but differences in these parameters evened out in mature plants. In the spring, degradable covers with their higher mass per unit area, caused a decrease in marketable yield of lettuce compared to the control PP, resulting mainly from the deterioration of plant quality and lower mean weight per head. In the autumn season, yield was statistically not different between treatments. Yield of spring lettuces was 78% higher compared to the autumn cultivation period. Plants grown under SB20/13 had the lowest dry weight and L-ascorbic acid, while plants under SB21/13 had the highest dry weight and L-ascorbic acid content. Plants under SB28/13 had higher chlorophyll a content. Generally, no effect of covers was noted for carotenoid concentrations. The content of dry weight, L-ascorbic acid, and carotenoids were higher in plants harvested in spring, while no effects of crop season on chlorophyll level were observed. All tested biodegradable nonwovens are a potential substitute for standard polypropylene in autumn trials, but for spring covering unit weight of these materials should be reduced.

Nanoparticles of cerium, iron, and silicon oxides change the metabolism of phenols and flavonoids in butterhead lettuce and sweet pepper seedlings

The aim of the study was to determine the effects of CeO2, Fe2O3, and SiO2 nanoparticles on the metabolism of phenols and flavonoids and the antioxidant status of butterhead lettuce...

Exploring the Potential of Lettuce (Lactuca sativa L.) as an Early Crop in Florida’s Sandy Soils

Lettuce (Lactuca sativa L.) is planted in Florida starting late fall at the end of September and continuing through the last harvest in May. In recent years, the season has shortened because of warm temperatures and weather-related events, such as rainfall at the beginning and the end of the season. During the transition between summer production in the Western U.S. lettuce season and the beginning of Florida’s winter production, there may be shortages of lettuce and other leafy vegetables in U.S. East Coast markets. In this research, we evaluated a set of lettuce breeding lines and cultivars in both sand and muck soils and a subset of romaine lettuces to determine whether lettuce planted in Florida’s sandy soils could help meet the supply shortage in the delay between the Western and Eastern U.S. lettuce seasons. Significant genetic variation and genotype × environment (G×E) interactions were observed among lettuce genotypes when planted in both sand and muck soils, suggesting that lettuce cultivars should be adapted and bred specifically for sandy soils. Romaine and butterhead lettuce lines produced higher yield in sandy soils; a particular romaine breeding line (BG18-0588) had good yield and less heat-related disorders when planted in warmer temperatures. Producing lettuce in sandy soils may have a higher production cost because of additional specific practices such as transplant production, plastic mulch, and fertigation, but these costs may be offset by increased productivity due to better weed control and nutrient timing. However, a future analysis should be conducted to elucidate the economic feasibility of producing lettuce in sandy soils.