Silicon supplied via foliar application and root to attenuate potassium deficiency in common bean plants

Potassium (K) deficiency affects physiological performance and decreases vegetative growth in common bean plants. Although silicon (Si) supplied via nutrient solution or foliar application may alleviate nutritional stress, research on the bean crop is incipient. Thus, two experiments were carried out: initially, a test was performed to determine the best source and foliar concentration of silicon. Subsequently, the chosen Si source was supplied in nutrient solution via roots or foliar application to verify whether Si supply forms are efficient in alleviating the effects of K deficiency. For these purposes, a completely randomized 2 × 3 factorial design was used, with two levels of K: deficient (0.2 mmol L−1 of K) and sufficient (6 mmol L−1 of K); and Si: in nutrient solution via roots (2 mmol L−1 of Si) or foliar application (5.4 mmol L−1 of Si) and control (0 mmol L−1 of Si). Our findings revealed that Si supplied via foliar spraying using the source of sodium silicate and stabilized potassium at a concentration of 5.4 mmol L−1 was agronomically viable for the cultivation of bean plant. K deficiency, when not supplied with silicon, compromised plant growth. Moreover, root-and-foliar-applied Si attenuated the effects of K deficiency as it increased chlorophylls and carotenoids content, photosynthetic activity, water use efficiency and vegetative growth. For the first time, the role of Si to mitigate K deficiency in the bean crop was evidenced, with a view to further research on plants that do not accumulate this beneficial element.

Foliar and Root Applications of Vegetal-Derived Protein Hydrolysates Differentially Enhance the Yield and Qualitative Attributes of Two Lettuce Cultivars Grown in Floating System

Lettuce (Lactuca sativa L.) is a leafy vegetable cultivated widely for its fast and year-round production and its beneficial phytochemical content, which may be boosted further by plant biostimulants that are considered eco-sustainable means for enhancing horticultural crop production. A greenhouse experiment was carried out to evaluate the yield and qualitative parameters of two differently pigmented lettuce cultivars grown in a floating raft system either untreated or treated (leaf, root or leaf/root application) with vegetal protein hydrolysates (PHs). For foliar application (F), lettuce plants were sprayed at a dose of 3 mL L−1, whereas for root application, 0.15 (T1) or 0.3 (T2) mL L−1 was applied to the nutrient solution alone or in combination with foliar spray (T1 + F and T2 + F) with the same foliar concentration. Bio-morphometric and production data were collected after harvest. Physiological and plant nutrition assays included leaf gas exchange, leaf fluorescence, SPAD index, mineral content, carotenoids, total phenols, total ascorbic acid content and antioxidant activities. Cultivar-specific reactions to biostimulant application were noted: whilst the green pigmented cultivar thrived under nutrient solution applications and recorded higher yield by 82.7% (T1) or (T1 + F) and 71.7% (T2), the red cultivar thrived under combined treatments, yielding 55.4% (T2 + F) higher than control and providing the most concentrated phytochemical content. These latter treatments also engendered the highest SPAD index, Fv/Fm ratio, CO2 assimilation, stomatal conductance and transpiration. In addition, the T2 + F treatment boosted ‘Canasta’ hydrophilic antioxidant activity (21.9%) and total ascorbic acid (5.6-fold). Nutrient solution treatments alone proved advantageous when compared to foliar treatments, while mixed treatments proved genotype-specific. New research on genotype specificity of biostimulant effects is warranted for future use, in order to rationalize biostimulant application modes and dosages.

Changes in melon plant phytochemistry impair Aphis gossypii growth and weight under elevated CO2

Elevated CO2 (eCO2) modifies plant primary and secondary metabolism that subsequently impacts herbivore insect performance due to changes in its nutritional requirements. This laboratory study evaluated interactions between Aphis gossypii Glover (Hemiptera: Aphididae) and melon (Cucumis melo L., Cucurbitaceae), previously acclimated two or six weeks to different CO2 levels, eCO2 (700 ppm) or ambient CO2 (400 ppm). Under eCO2, melon plants decreased nitrogen foliar concentration and increased carbon to nitrogen ratio, independently of acclimation period, significantly reducing the content of some amino acids (alanine, asparagine, glycine, isoleucine, lysine, serine, threonine, and valine) and increasing the carbohydrate (sucrose) content in melon leaves. The dilution in some essential amino acids for aphid nutrition could have aggravated the reduction in A. gossypii population growth reared on melon previously acclimated two weeks to eCO2, as well as the loss of aphid body mass from two successive generations of A. gossypii reared under eCO2 on plants previously acclimated two or six weeks to eCO2. The response to eCO2 of phloem feeders, such as aphids, is actually variable, but this study highlights a negative response of A. gossypii to this climate change driver. Potential implications on control of this pest in a global change scenario are discussed.

Changes in nutrient concentration and oxidative metabolism in pecan leaflets at different doses of zinc

Zinc deficiency limits pecan nut production. The objective of this study was to evaluate changes in nutrient concentration and oxidative metabolism in pecan leaflets in response to the application at different doses of zinc. The foliar concentration of nutrients, leaflet area, total chlorophyll, dry weight (leaflets and root), superoxide dismutase (SOD), hydrogen peroxide, catalase (CAT), guaiacol peroxidase (GP) and antioxidant capacity were evaluated. Statistical analysis indicates that the application of 200 µmol Zn²⁺ affected the foliar concentration of N-total (24.50 ± 2.51 g/kg), P (10.34 ± 2.53 g/kg), Fe²⁺ (153.33 ± 6.27 mg/kg) and Zn²⁺ (42.00 ± 2.84 mg/kg), showing a greater area of the leaflet, total chlorophyll content and dry weight (leaflets and root). Plants treated with 50 µmol Zn²⁺ showed a higher level of SOD activity (1.38 ± 0.016 units/min/g), GP (5.56 ± 0.229 nmol glutathione/min/g), and the production of hydrogen peroxide, without exceeding the control. On the other hand, Zn treatments caused a significant decrease in CAT activity. Zn is an essential micronutrient for the growth and development of pecan, which promotes the accumulation of other nutrients. Therefore, its absence affects the generation of oxidative stress with the subsequent activation of the antioxidant defense enzyme system.

Does the application of growth bioregulators improve the foliar concentration of nutrients, non-structural carbohydrates and yield in pecan?

ABSTRACT Carya illinoinensis (Wangenh.) K. Koch. is a deciduous fruit species with high economic impact and nutritional value that exhibits alternate bearing behavior. In this study, the concentration of foliar nutrients, non-structural carbohydrates and yield were evaluated in cultivar Western Schley pecan in response to the foliar application of gibberellic acid (50 mg L-1 GA3), prohexadione calcium (500 mg L-1 PCa) and thidiazuron (10 mg L-1 TDZ).The statistical analysis reveals that between agricultural cycles, the treatments showed no variation in the foliar concentration of nitrogen total (N-total), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), copper (Cu), manganese (Mn) and non-structural carbohydrates (fructose, glucose, sucrose and starch). However, the application of PCa showed no significant effect on the concentration of phosphorus (P) (1.5 and 1.9 g kg-1). On the other hand, the concentration of zinc (Zn) (27.0-60.1 mg kg-1) showed a significant difference between years, with no effect due to the application of growth bioregulators. The trees treated with GA3 minimized alternate bearing by presenting similar values (12.4 and 15.3 kg tree-1) of yield. Likewise, the applied treatments did not affect the nut weight per kilogram (kg) (5.5-6.8 g) and kernel percentage (56.5-60.8). These data provide a new perspective on the complex nature of alternate bearing production in cultivar Western Schley pecan and are interpreted to indicate that alternate production could be regulated by carbohydrate reserve, nutrient concentration, and gibberellins.

Eco-Physiological Responses of Black Chokeberries as Affected by Applications of Oil Cake

This study was carried out to examine the optimum amount of oil cake necessary for the desired nutritional status of “Nero” black chokeberry (Aronia melanocarpa (Michx.) Elliot) in an experimental field plot between the years 2018 and 2019. The treatments included 0% (0.0 kg/ha), 25% (4.4 kg/ha), 50% (8.8 kg/ha), 75% (13.1 kg/ha), and 100% (17.5 kg/ha) of a recommended amount of oil cake. The pH in the plots with 8.8, 13.1, and 17.5 kg per ha applied ranged between 7.0 and 7.3, and these values were lower than the values observed on the plots with 0.0 and 4.4 kg per ha applied at the end of July in the years 2018 and 2019, with the concentrations of soil NO3-N and NH4-N remaining low in the off-season. The foliar concentration of total-nitrogen (T-N) was higher for the plants treated with all the oil cake treatments in 2018 and with the oil cake of 17.5 kg/ha in 2019 compared to that of 0.0 kg/ha. The foliar soil plant analysis development values for June and August increased on the bushes treated with 13.1 and 17.5 kg per ha in both the years of 2018 and 2019. The cane diameter, canopy width, and total dry weight were significantly increased by bushes treated with 8.8, 13.1, and 17.5 kg per ha in both years. The fruit yield, harvest index, and percentage of T-N partitioning into fruit were maximized by the treatment with 13.1 kg per ha. An amount of 75% of the recommend application for young black chokeberry may be the prominent application rate in terms of maximized fruit productivity while balancing with the demands of vegetative growth in order to reset the recommended amount of fertilizer.

Measures of Canopy Structure from Low-Cost UAS for Monitoring Crop Nutrient Status

Deriving crop information from remotely sensed data is an important strategy for precision agriculture. Small unmanned aerial systems (UAS) have emerged in recent years as a versatile remote sensing tool that can provide precisely-timed, fine-grained data for informing management responses to intra-field crop variability (e.g., nutrient status and pest damage). UAS sensors with high spectral resolution used to compute informative vegetation indices, however, are practically limited by high cost and data dimensionality. This research extends spectral analysis for remote crop monitoring to investigate the relationship between crop health and 3D canopy structure using low-cost UAS equipped with consumer-grade RGB cameras. We used flue-cured tobacco as a case study due to its known sensitivity to fertility variation and nutrient-specific symptomology. Fertilizer treatments were applied to induce plant health variability in a 0.5 ha field of flue-cured tobacco. Multi-view stereo images from three UAS surveys collected during crop development were processed into orthoimages used to compute a visible band spectral index and photogrammetric point clouds using Structure from Motion (SfM). Plant structural metrics were then computed from detailed high resolution canopy surface models (0.05 m resolution) interpolated from the photogrammetric point clouds. The UAS surveys were complimented by nutrient status measurements obtained from plant tissues. The relationships between foliar nitrogen (N), phosphorus (P), potassium (K), and boron (B) concentrations and the UAS-derived metrics were assessed using multiple linear regression. Symptoms of N and K deficiencies were well captured and differentiated by the structural metrics. The strongest relationship observed was between canopy shape and N foliar concentration (adj. r2 = 0.59, increasing to adj. r2 = 0.81 when combined with the spectral index). B foliar concentration was consistently better predicted by canopy structure with a maximum adj. r2 = 0.41 observed at the latest growth stage surveyed. Overall, combining information about canopy structure and spectral reflectance increased model fit for all measured nutrients compared to spectral alone. These results suggest that an important relationship exists between relative canopy shape and crop health that can be leveraged to improve the usefulness of low cost UAS for precision agriculture.

Relationship between soil fertility and plantain nutrition in Cundinamarca (Colombia) with the incidence of two bacterial diseases

The bacteriosis and moko of plantain are ones of the most important phytosanitary problems in the production of musaceae in Colombia. To contribute to the management of these diseases in the department of Cundinamarca, soils and foliar tissues were analyzed, as well as the symptoms of the diseases in 149 farms of producers in the municipalities of Chaguani, La Palma, La Vega, and Viota (Cundinamarca). A descriptive analysis of the chemical properties of soils and foliar concentration of nutrients was carried out; the Student-Welch t-test was applied (P<0.05); the distribution patterns of the diseases were represented cartographically. According to the results obtained, the sampled soils are not saline, they have extreme to strong acidity, low effective cation exchange capacity and low fertility; meanwhile plants show a deficit of elements such as nitrogen, phosphorus, sulfur, copper, zinc, and boron. Considering the total number of farms evaluated, the incidence of bacteriosis and moko disease was reported in 63 and 14% at the departmental level, respectively. A higher concentration of sulfur and zinc was observed in farm soils free of both diseases. Finally, plants reported as free of bacteriosis showed a higher concentration of potassium and lower concentrations of calcium and manganese; while plants reported as free of moko disease showed higher concentrations of nitrogen, sodium, and copper, and a lower concentration of calcium. The results obtained contribute to the planning of large-scale management strategies, in order to reduce the risk of dissemination of diseases of economic importance for plantain crop.

Repaid Identification and Prediction of Cadmium–Lead Cross-Stress of Different Stress Levels in Rice Canopy Based on Visible and Near-Infrared Spectroscopy

Accurate detection of cadmium (Cd) and lead (Pb)-induced cross-stress on crops is essential for agricultural, ecological environment, and food security. The feasibility to diagnose and predict Cd–Pb cross-stress in agricultural soil was explored by measuring the visible and near-infrared reflectance of rice leaves. In this study, two models were developed—namely a diagnostic model and a prediction model. The diagnostic model was established based on visible and near-infrared reflectance spectroscopy (VNIRS) datasets with Support Vector Machine (SVM), followed by leave-one-out cross-validation (LOOCV). A partial least-squares (PLS) regression, as the prediction model was employed to predict the foliar concentration of Cd and Pb contents. To accurately calibrate the two models, a rigorous greenhouse experiment was designed and implemented, with 4 levels of treatments on each of the Cd and Pb stress on rice. Results show that with the appropriate pre-processing, the diagnostic model can identify 79% of Cd and 85% of Pb stress of any levels. The significant bands that have been used mainly distributed between 681–776 nm and 1224–1349 nm for Cd stress and 712–784 nm for Pb stress. The prediction model can estimate Cd with coefficient of determination of 0.7, but failed to predict Pb accurately. The results illustrated the feasibility to diagnose Cd stress accurately by measuring the visible and near-infrared reflectance of rice canopy in a cross-contamination soil environment. This study serves as one step forward to heavy metal pollutant detection in a farmland environment.