Projected Elevated [CO2] and Warming Result in Overestimation of SPAD-Based Rice Leaf Nitrogen Status for Nitrogen Management

Nitrogen (N) has a unique place in agricultural systems with large requirements. To achieve optimal nitrogen management that meets the needs of agricultural systems without causing potential environmental risks, it is of great significance to increase N use efficiency (NUE) in agricultural systems. A chlorophyll meter, for example, the SPAD-502, can provide a simple, nondestructive, and quick method for monitoring leaf N status and NUE. However, the SPAD-based crop leaf’s N status varies greatly due to environmental factors such as CO2 concentration ([CO2]) or temperature variations. In this study, we conducted [CO2] (ambient and enriched up to 500 μmol moL1) and temperature (ambient and increased by 1.5~2.0 °C) controlled experiments from 2015 to 2017 and in 2020 in two Free-Air CO2 Enrichment (FACE) sites. Leaf characters (SPAD readings, chlorophyll a + b, N content, etc.) of seven rice cultivars were measured in this four year experiment. Here, we provide evidence that SPAD readings are significantly linearly correlated with rice leaf chlorophyll a + b content (chl a + b) and N content, while the relationships are profoundly affected by elevated [CO2] and warming. Under elevated [CO2] treatment (E), the relationship between chl a + b content and N content remains unchanged, but SPAD readings and chl a + b content show a significant difference to those under ambient (A) treatment, which distorts the SPAD-based N monitoring. Under warming (T), and combined elevated [CO2] and warming (ET) treatments, both of the relationships between SPAD and leaf a + b content and between leaf a + b content and N content show a significant difference to those under A treatment. To deal with this issue under the background of global climate change dominated by warming and elevated [CO2] in the future, we need to increase the SPAD reading’s threshold value by at least 5% to adjust for applying N fertilizer within the rice cropping system by mid-century.

Beneficial microorganisms enhance the growth of basil (Ocimum basilicum L.) under greenhouse conditions

The integration of healthy management alternatives continues to be a challenge in the organic production of aromatic and medicinal plants, including of basil (Ocimum basilicum L.). The objective of this work was to evaluate the effects of three beneficial microorganisms (1) Trichoderma harzianum (TH), (2) Bacillus subtilis (BS), (3) Glomus cubense (GC) and their combinations on the growth of basil. A completely randomised design was used with a control and seven treatments with six repetitions. The control (1) was with no microorganism inoculation and the seven treatments were inoculations with the single or the combined microorganisms as follows: (2) TH, (3) BS, (4) GC, (5) TH+BS, (6) TH+GC, (7) BS+GC and (8) TH+BS+GC. Three harvests of fresh biomass were made and a number of growth variables were recorded: fresh and dry biomass, leaf area, number of commercial stems, stem length and thickness, Leaf length and width, relative chlorophyll concentration (SPAD readings) and the levels of N, P, K, Ca and Mg. Overall growth increased by 58% with TH+GC compared with the control and by 55% compared with the single inoculations (TH, BS and GC) and with the triple inoculation (TH+BS+GC). A growth increase of 51% was obtained with BS+GC compared with the control and of 38% compared with the other treatments. These results indicate co-inoculation of TH+GC or of BS+GC are useful alternative managements to increase greenhouse production of basil.

Recommended nitrogen rates and the verification of effects based on leaf SPAD readings of rice

Modern rice production systems need a reliable, easy-to-use, efficient, and environmentally-friendly method to determine plant nitrogen (N) status , predict grain yield, and optimize N management. We conducted field experiments to determine the influence of different N rates on Soil Plant Analysis Development (SPAD) readings of rice leaves. We also performed field validations to evaluate the grain yield and N use efficiency under recommended N rates. Our results showed that leaf SPAD readings increased as N rates increased. We applied the recommended N based on the relationships between the N rates and leaf SPAD readings at the tillering and booting stages. The recommended N decreased N rates and improved N use efficiency without sacrificing grain yield. When compared to farmer practices (FP), the recommended N rates of optimization (OPT) decreased by 5.8% and 10.0%, respectively. In comparison with FP, the N agronomic efficiency of OPT increased by 5.8 and 10.0% while the partial factor productivity of N increased by 6.0 and 14.2%, respectively. The SPAD meter may be a reliable tool to analyze the N in rice, estimate real-time N fertilization, and improve N use efficiency.

Phenology of Four Varieties of Gooseberry (Physalis peruviana L.) in Greenhouses and Hydroponics for its Commercial Production in Mexico

Objective: To measure the phenology, morphology and development of four varieties ofPhysalis peruviana L. under greenhouse and hydroponics conditions, by effect of the ionicstrength of the Steiner nutrient solution for cultivation in Mexico.Design/Methodology/Approach: The research was conducted under a completelyrandom design with factorial arrangement, the treatments evaluated resulted from thecombination of the levels of the variety factor (Colombia, Sacha, Chiclayo and Modified)with the levels of the ionic strength of the Steiner nutrient solution (50, 100 and 150%),and the experimental unit was a potted plant. For phenology each phase was recorded inthe plants, SPAD readings were taken in the vegetative stage, for diameter and heightseveral samples were taken, and pH and electrical conductivity were accomplished onstems and petioles of shoots of each treatment. An analysis of variance and thecomparison of means per Tukey (p ? 0.05) were implemented with the SAS 9.2 program.Results: The varieties under study showed differences in the time of occurrence of thephenological stages. SPAD readings, basal diameter, pH and electrical conductivity in sapwere affected by each factor except for the interaction. Meanwhile, plant height wassignificantly affected in the first 24 days after transplant (dat) by the combination of thetwo factors. Study Limitations/Implications: The results obtained are limited to the varieties, theenvironmental conditions, and the time when the varieties were evaluated.Conclusions: The phenology of each variety was not expressed at the same time in anyconcentration, as an early variety was given to Chiclayo, Colombia and Sacha, which arevarieties that in the concentrations 50 and 150% of the nutrient solution started harvestingat 99 dat.

Evaluation of staygreen sunflower lines and their hybrids for yield under drought conditions

The experimental material for the present study comprised of 28 inbred lines (including two checks) which were developed by mutation and hybridization among the lines from AICRP trials MARS, UAS, Dharwad and on the basis of SPAD readings and stay green nature, they were considered as drought tolerant lines. These lines were used for the present experiment and were evaluated under both normal and moisture stress condition in rain out shelter to study their root characteristics. Among 28 inbreds evaluated, eight inbred lines i.e. DSR-13, DSR-19, DSR-23, DSR-24, DSR-37, DSR-66, DSR-107 and DSR-132 were identified as drought tolerant nature which exhibited least reduction in their yield under moisture stress condition. Simultaneously hybridization programme was also initiated during summer 2018 using these 28 inbred lines as testers (males) and 5 CMS lines as female lines in Line × Tester fashion. Among 140 hybrids developed, only 40 F1 hybrid combinations were further analyzed for heterosis and combining ability studies along with four checks RHA 6D-1, RHA 95C-1, KBSH-53 and Cauvery Champ. Most of the hybrid combinations showed significant negative heterosis for flowering indicating earliness, and also all the combinations showed a positive heterosis for plant height indicating tallness dominant over dwarf checks. The combinations CMS 7-1-1 A × DSR-37 (624 kg/ha), CMS-853A × DSR-19 (624 kg/ha), and CMS-853A × DSR-23 (619 kg/ha) exhibited significant maximum heterosis for seed yield (kg ha−1) over the checks KBSH-53 (496.50 kg/ha) and Cauvery Champ (486.50 kg/ha) showing maximum seed yield per hectare.

Spad index for diagnosis of nitrogen status in ‘Esmeralda’ peach

The objective of this research was to evaluate the technical feasibility of SPAD index in the diagnosis of N status in ‘Esmeralda’ peach. The field trial, with five N rates applied to the soil (0, 40, 80, 120 and 160 kg ha-1 of N as urea form) was conducted in a randomized block design with four replications. During the years 2014, 2015, 2016 and 2017, SPAD readings were carried out with a Minolta SPAD-502 chlorophyll meter, in the leaf middle part, in 40 leaves per plot. The leaf N content determination was performed in CHN-S Elemental Analyzer. SPAD index and leaf N content increased in a linear way in response to increasing N rates applied in soil. There was a positive linear correlation between SPAD index and N concentration in leaves (0.652; 0.756; 0.762 and 0.767, p<0.05). SPAD index can be used for nutritional N diagnosis purpose in peach when readings are taken between the 13th and 15th weeks after full bloom. In the range between 39 and 49, the SPAD index indicates the leaf N content is included in “normal” class (33 – 45 g kg-1) of agronomic interpretation for the States of Rio Grande do Sul and Santa Catarina, Brazil.

impact of cultivar and irrigation on yield, leaf surface temperature and SPAD readings of chili pepper

Paprika is an extremely popular and widespread plant species in Hungary. Chili peppers belongs to paprika and it can be consumed fresh or processed. The production of peppers began with the cultivation and control of some parameters for good results of paprika production. The aim of this article is to compare the water supply of four chili pepper hybrids ("Habanero", "Hetényi Parázs", "Unikal" and "Unijol") by means of investigation on open field and to examine how different temperatures and water stress factors influence the yield of chili peppers. The experiment area consisted of four different hybrids in three different irrigation treatments (control, deficit- and regular irrigation). The chlorophyll content was estimated with SPAD and the leaf surface temperature with Raytek MX4 TD. Our research concluded that deficit irrigation produced the highest yields for all cultivars and the lowest yields for the highest water supply.

Effect of moisture stress on physiological mechanisms in drought tolerance in selected genotypes of groundnut (Arachis hypogaea L.)

Eight groundnut genotypes of including four released and pre-released genotypes were evaluated for moisture stress at pegging (M2) and pod development (M3) stage stress situations with control (M1) during post-rainy season (Nov-April), 2018-19 at University of Agricultural Sciences, Dharwad and Karnataka, India. The drought stress was imposed by with holding irrigation at 40-80 DAS (M2) and 80 DAS-harvest (M3). Observations were recorded for physiological parameters like leaf area, SPAD readings, chlorophyll content, stomatal frequency, photosynthetic rate and pod yield per plant. Among the selected genotypes, GPBD-4, Dh-257 and Dh-256 are considered as drought tolerant genotypes at both the stress levels based on lesser reduction in leaf area, optimum chlorophyll content and photosynthetic rate, less leaf folding and by these adaptations recorded reduced reduction in pod yield over control. Genotypes, Dh-86 and TMV-2 affected severely by drought at both the stages. But higher effect was observed under pod developmental stage stress.

Correlation analysis of the SPAD readings and yield of sweet potato (Ipomoea batatas L.) under different agrotechnical conditions

We studied the effect of planting method (flat and ridge planting) and row spacing (0.75-1.0 m) on the yield and SPAD readings of sweet potato (Ásotthalmi 12 variety) in a small-plot field experiment in 2017 and 2018. The experiment was set up in lattice design with 4 replications. The SPAD readings of sweet potato were measured four (2017) and three (2018) times during vegetation period (by Konica Minolta 502). A high yield level was reached both in 2017 (23.23-50.69 t ha-1 marketable yield) and 2018 (33.26-47.34 t ha-1) due to the effects of the favourable soil (chernozem), the near-optimal agrotechnical background, irrigation and the warmer-than-average vegetation period. In both years, higher yields were obtained with flat planting and 0.75 m row spacing. The proportion of non-marketable tubers was between 9.97-15.57% in 2017 and 8.65-11.01% in 2018. The SPADmax values were measured in July (39.61-50.31 in 2017) and in August (49.90-55.33 in 2018). Strong correlation observed among SPAD readings, the whole yield and the marketable yield in both years (r = 0.632*, r = -0.664* and r = 0.709**, respectively). Also, a strong correlation was observed between the planting method and the obtained SPAD readings (r = -0.847**, -0.682* in 2017 and r = -0.634*, -0.488 in 2018, respectively), while there was no correlation between row spacing and SPAD readings (r = -0.006NS-0.190NS). Crop year had a strong effect on SPAD readings (r = 0.639**-0.871**).