High Nitrogen Fertilization Modulates Morpho-Physiological Responses, Yield, and Water Productivity of Lowland Rice under Deficit Irrigation

A Novel Nutrient- and Antioxidant-Based Formulation Can Sustain Tomato Production under Full Watering and Drought Stress in Saline Soil

As a result of the climate changes that are getting worse nowadays, drought stress (DS) is a major obstacle during crop life stages, which ultimately reduces tomato crop yields. So, there is a need to adopt modern approaches like a novel nutrient- and antioxidant-based formulation (NABF) for boosting tomato crop productivity. NABF consists of antioxidants (i.e., citric acid, salicylic acid, ascorbic acid, glutathione, and EDTA) and nutrients making it a fruitful growth stimulator against environmental stressors. As a first report, this study was scheduled to investigate the foliar application of NABF on growth and production traits, physio-biochemical attributes, water use efficiency (WUE), and nutritional, hormonal, and antioxidative status of tomato plants cultivated under full watering (100% of ETc) and DS (80 or 60% of ETc). Stressed tomato plants treated with NABF had higher DS tolerance through improved traits of photosynthetic efficiency, leaf integrity, various nutrients (i.e., copper, zinc, manganese, calcium, potassium, phosphorus, and nitrogen), and hormonal contents. These positives were a result of lower levels of oxidative stress biomarkers as a result of enhanced osmoprotectants (soluble sugars, proline, and soluble protein), and non-enzymatic and enzymatic antioxidant activities. Growth, yield, and fruit quality traits, as well as WUE, were improved. Full watering with application of 2.5 g NABF L-1 collected 121 t tomato fruits per hectare as the best treatment. Under moderate DS (80% of ETc), NABF application increased fruit yield by 10.3%, while, under severe DS (40% of ETc), the same fruit yield was obtained compared to full irrigation without NABF. Therefore, the application of 60% ETc × NABF was explored to not only give a similar yield with higher quality compared to 100% ETc without NABF as well as increase WUE.

Exogenous Selenium Improves Physio-Biochemical and Performance of Drought-Stressed Phaseolus vulgaris Seeded in Saline Soil

Water and salt stresses are among the most important global problems that limit the growth and production of several crops. The current study aims at the possibility of mitigating the effect of deficit irrigation of common bean plants growing in saline lands by foliar spraying with selenium via the assessment of growth, productivity, physiological, and biochemical measurements. In our study, two field-based trials were conducted in 2017 and 2018 to examine the influence of three selenium (Se) concentrations (0 (Se0), 25 (Se25), and 50 mg L−1 (Se50)) on common bean plants grown under full irrigation (I100 = 100% of the crop evapotranspiration; ETc) and deficit irrigation (I80 = 80% of ETc, and I60 = 60% of ETc). Bean plants exposed to water stress led to a notable reduction in growth, yield, water productivity (WP), water status, SPAD value, and chlorophyll a fluorescence features (Fv/Fm and PI). However, foliar spraying of selenium at 25 or 50 mg L−1 on stressed bean plants attenuated the harmful effects of water stress. The findings suggest that foliage application of 25 or 50 mg L−1 selenium to common bean plants grown under I80 resulted in a higher membrane stability index, relative water content, SPAD chlorophyll index, and better efficiency of photosystem II (Fv/Fm, and PI). Water deficit at 20% increased the WP by 17%; however, supplementation of 25 or 50 mg L−1 selenium mediated further increases in WP up to 26%. Exogenous application of selenium (25 mg L−1 or 50 mg L−1) to water-stressed bean plants elevated the plant defense system component, given that it increased the free proline, ascorbic acid, and glutathione levels, as well as antioxidant enzymes (SOD, APX, GPX, and CAT). It was concluded that the application of higher levels (25 or/and 50 mg L−1) of Se improves plant water status as well as the growth and yield of common beans cultivated in saline soil.

Grain nitrogen content and productivity of rice and maize under variable doses of fertilizer nitrogen

The rice-maize system is a dominant cropping system of south Asia and consumes a considerable amount of fertilizer. The indiscriminate use of fertilizer particularly nitrogen (N) is degrading the soil health and polluting the environment. Lower N-use efficiency is a major problem and needs to be improved for higher yield, lower cost of cultivation and better environment. The grain quality is also altered by the N-application as N is a major constituent of protein. Studies on the effect of N-application on grain N-content is still lacking. We hypothesised that optimization of N application would result in economising N dose, improving yield and NUE and improving grain quality. Under that context, a field experiment was conducted with different doses of fertilizer N for rice and maize. Fertilizer N was applied at the rate of 0, 40, 80, 120, 160, 200 and 240 kg ha^-1 (N0-N240). An increase in grain yield was observed up to 80 and 160 kg ha^-1 for rice and maize, respectively. The N content of grain increased with N rates and a significant increase was noted in N200 (1.42%) being at par with N240 (1.49%) but significantly higher than others by 13-32%. With an increase of each kilogram of N, the grain N content increased by 14 and 20 μg (microgram) for rice and maize, respectively. The leaf N content registered a decreasing trend with the progress of the crop growth for both rice and maize. The agronomic efficiency (AE) of N initially increased with an increase in the rate of fertilizer N followed by a decrease with higher doses of N. Unlike the AE, the partial factor productivity (PFP) of N decreased gradually with an increase in the rate of fertilizer N. The chlorophyll content of flag leaves also registered an increasing trend with an increasing rate of fertilizer N. On the surface soil (0-15 cm), the treatments which received lower (N0, N40) and higher (N240) fertilizer N recorded a comparatively higher total soil N than other treatments. The mean NUE was 0.42 and 0.75 for rice and maize, respectively. The study suggests an economic fertilizer N rate of 165 and 167 kg N ha^-1, for rice and maize, respectively. It also concludes that the grain N content can be altered by N-application rates though more research is needed.

Soil application of effective microorganisms and nitrogen alleviates salt stress in hot pepper (Capsicum annum L.) plants

The application of effective microorganisms (EMs) and/or nitrogen (N) have a stimulating effect on plants against abiotic stress conditions. The aim of the present study was to determine the impact of the co-application of EMs and N on growth, physio-biochemical attributes, anatomical structures, nutrients acquisition, capsaicin, protein, and osmoprotectant contents, as well as the antioxidative defense system of hot pepper (Capsicum annum L.) plants. In the field trials, EMs were not applied (EMs^-) or applied (EMs⁺) along with three N rates of 120, 150, and 180 kg unit N ha^-1 (designated as N₁₂₀, N₁₅₀, and N₁₈₀, respectively) to hot pepper plants grown in saline soils (9.6 dS m^-1). The application of EMs and/or high N levels attenuated the salt-induced damages to hot pepper growth and yield. The application of EMs⁺ with either N₁₅₀ or N₁₈₀ increased the number, average weight and yield of fruits by 14.4 or 17.0%, 20.8 or 20.8% and 28.4 or 27.5%, respectively, compared to hot pepper plants treated with the recommended dose (EMs^- × N₁₅₀). When EMs⁺ was individually applied or combined with either N₁₅₀ or N₁₈₀, increased accumulation of capsaicin were observed by 16.7 or 20.8%, protein by 12.5 or 16.7%, proline by 19.0 or 14.3%, and total soluble sugars by 3.7 or 7.4%, respectively, in comparison with those treated with the integrative EMs^- × N₁₅₀. In addition, the non-enzymatic contents (ascorbate, and glutathione) and enzymatic activities (catalase, superoxide dismutase, and glutathione reductase) of the antioxidant defense systems significantly increased in hot pepper plants treated with EMs⁺ alone or combined with N₁₅₀ or N₁₈₀ under salt stress conditions. Higher accumulation of nutrients (N, P, K⁺, and Ca²⁺) along with reduced Na⁺ acquisition was also evidenced in response to EMs⁺ or/and high N levels. Most anatomical features of stems and leaves recovered in hot pepper plants grown in saline soils and supplied with EMs⁺ and N. The application of EMs and N is undoubtedly opening new sustainable approaches toward enhancing abiotic stress tolerance in crops (e.g. hot pepper).

Impact of Folic Acid in Modulating Antioxidant Activity, Osmoprotectants, Anatomical Responses, and Photosynthetic Efficiency of Plectranthus amboinicus Under Salinity Conditions

Salinity is a major threat to the sustainability of agricultural production systems. Salt stress has unfavorable implications on various plant physio-morphological and biochemical reactions, causing osmotic and ionic stress. Exogenously applied folic acid (FA) may at least provide one mechanism to evade the injurious stress effects of saline irrigation water on Plectranthus amboinicus. In this regard, two pot trials were performed during the 2018-2019 and 2019-2020 seasons in an open greenhouse of an experimental farm (29°17'N; 30°53'E) in Fayoum, Egypt. We tested four levels of saline irrigation water (SW): 34, 68, and 102 mM NaCl, plus tap water as the control = 0), combined with FA at three concentrations (25 and 50 μM, plus spray with distilled water as the control = 0). The growth parameters, biochemistry, physiology, elemental leaf status, essential oil content, and anatomical responses were assessed. Salt markedly reduced photosynthetic productivity [Fv/Fm and performance index (PI)], total chlorophyll [soil plant analysis development (SPAD)], and leaf osmoprotectant compounds, i.e., total soluble sugars (TSS), free amino acids, proline, and total phenolics, thus hampering P. amboinicus growth and essential oil yield. However, the addition of FA as a foliar spray to P. amboinicus irrigated with saline water induced increases in Fv/Fm, SPAD, and PI. These were linked with enriched stem anatomical structures, leaf osmoprotectant compounds, and enhanced leaf enzymatic activity, e.g., superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, glutathione, ascorbic acid, and antioxidant content. Under salt stress, supplementation of 25 and 50 μM FA increased the growth and production of essential oil by 27.8 and 55.6%, respectively, compared with no applied FA. The highest growth characteristics and elemental leaf contents were obtained when P. amboinicus was irrigated with 0 mM saline water and treated foliarly with 50 μM of FA compared with non-treated plants. Overall, these data showed that foliar spraying with FA reduces the impact of salt stress on P. amboinicus irrigated with saline water.

Exogenously Applied Proline Enhances Morph-Physiological Responses and Yield of Drought-Stressed Maize Plants Grown Under Different Irrigation Systems

The exogenous application of osmoprotectants [e.g., proline (Pro)] is an important approach for alleviating the adverse effects of abiotic stresses on plants. Field trials were conducted during the summers of 2017 and 2018 to determine the effects of deficit irrigation and exogenous application of Pro on the productivity, morph-physiological responses, and yield of maize grown under two irrigation systems [surface irrigation (SI) and drip irrigation (DI)]. Three deficit irrigation levels (I₁₀₀, I₈₅, and I₇₀, representing 100, 85, and 70% of crop evapotranspiration, respectively) and two concentrations of Pro (Pro₁ = 2 mM and Pro₂ = 4 mM) were used in this study. The plants exposed to drought stress showed a significant reduction in plant height, dry matter, leaf area, chlorophyll content [soil plant analysis development (SPAD)], quantum efficiency of photosystem II [Fv/Fm, Fv/F0, and performance index (PI)], water status [membrane stability index (MSI) and relative water content (RWC)], and grain yield. The DI system increased crop growth and yield and reduced the irrigation water input by 30% compared with the SI system. The growth, water status, and yield of plants significantly decreased with an increase in the water stress levels under the SI system. Under the irrigation systems tested in this study, Pro₁ and Pro₂ increased plant height by 16 and 18%, RWC by 7 and 10%, MSI by 6 and 12%, PI by 6 and 19%, chlorophyll fluorescence by 7 and 11%, relative chlorophyll content by 9 and 14%, and grain yield by 10 and 14%, respectively, compared with Pro₀ control treatment (no Pro). The interaction of Pro₂ at I₁₀₀ irrigation level in DI resulted in the highest grain yield (8.42 t ha^-1). However, under the DI or SI system, exogenously applied Pro₂ at I₈₅ irrigation level may be effective in achieving higher water productivity and yield without exerting any harmful effects on the growth or yield of maize under limited water conditions. Our results demonstrated the importance of the application of Pro as a tolerance inducer of drought stress in maize.

Effects of Water and Nitrogen Management on Water Productivity, Nitrogen Use Efficiency and Leaching Loss in Rice Paddies

Effective water and nitrogen (N) management strategies are critical for sustainable agricultural development. Lysimeter experiments with two deep percolation rates (low percolation and high percolation, i.e., LP and HP: 3 mm d−1 and 5 mm d−1) and five N application levels (N0~N4: 0, 60, 135, 210 and 285 kg N ha−1) were conducted to investigate the effects of controlled drainage on water productivity (WP) and N use efficiency (NUE) in water-saving irrigated paddy fields. The results demonstrated that NH4+-N and NO3−-N were the major components of total nitrogen (TN) in ponded water and leachate, accounting for more than 77.1% and 83.6% of TN, respectively. The risk of N leaching loss increased significantly under treatment of high percolation rates or high N application levels. High percolation loss required greater irrigation input, thus reducing WP. In addition, N uptake increased with increasing N application, but fertilization applied in excess of crop demand had a negative effect on grain yield. NUE was affected by the amount of N applied and increased with decreasing N levels. Water and N application levels had a significant effect on N uptake of rice, but their interaction on N uptake or NUE was not significant. For the LP and HP regimes, the highest N uptake and WP were obtained with N application levels of 285 kg ha−1 and 210 kg ha−1, respectively. Our overall results suggested that the combination of controlled drainage and water-saving irrigation was a feasible mitigation strategy to reduce N losses through subdrainage percolation and to provide more nutrients available for rice to improve NUE, thus reducing diffuse agricultural pollution. Long-term field trials are necessary to validate the lysimeter results.

Plant Growth-Promoting Rhizobacteria Improve Growth, Morph-Physiological Responses, Water Productivity, and Yield of Rice Plants Under Full and Deficit Drip Irrigation

Inoculating rice plants by plant growth promoting rhizobacteria (PGPR) may be used as a practical and eco-friendly approach to sustain the growth and yield of drought stressed rice plants. The effect of rice inoculation using plant growth hormones was investigated under drip full irrigation (FI; 100% of evapotranspiration (ETc), and deficit irrigation (DI; 80% of ETc) on growth, physiological responses, yields and water productivities under saline soil (ECe = 6.87 dS m^-1) for 2017 and 2018 seasons. Growth (i.e. shoot length and shoot dry weight), leaf photosynthetic pigments (chlorophyll 'a' and chlorophyll 'b' content), air-canopy temperature (Tc-Ta), membrane stability index (MSI%), and relative water content, (RWC%) chlorophyll fluorescence (F_v/F_m) stomatal conductance (gs), total phenols, peroxidase (PO), polyphenol oxidase (PPO), nitrogen contents and water productivities (grain water productivity; G-WP and straw water productivity; S-WP) were positively affected and significantly (p < 0.05) differed in two seasons in response to the applied PGPR treatments. The highest yields (3.35 and 6.7 t ha^-1 for grain and straw yields) as the average for both years were recorded under full irrigation and plants inoculated by PGPR. The results indicated that under water scarcity, application of (I₈₀ + PGPR) treatment was found to be favorable to save 20% of the applied irrigation water, to produce not only the same yields, approximately, but also to save more water as compared to I_100%.

Transcriptomic and Metabolomic Analyses Reveal Key Metabolites, Pathways and Candidate Genes in Sophora davidii (Franch.) Skeels Seedlings Under Drought Stress

Soil aridification and desertification are particularly prominent in China's karst areas, severely limiting crop yields and vegetation restoration. Therefore, it is very important to identify naturally drought-tolerant plant species. Sophora davidii (Franch.) Skeels is resistant to drought and soil infertility, is deeply rooted and is an excellent plant material for soil and water conservation. We studied the transcriptomic and metabolomic changes in S. davidii in response to drought stress (CK, control; LD, mild drought stress; MD, moderate drought stress; and SD, severe drought stress). Sophora davidii grew normally under LD and MD stress but was inhibited under SD stress; the malondialdehyde (MDA), hydrogen peroxide (H₂O₂), soluble sugar, proline, chlorophyll a, chlorophyll b and carotenoid contents and ascorbate peroxidase (APX) activity significantly increased, while the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities and soluble protein content significantly decreased. In the LD/CK, MD/CK and SD/CK comparison groups, there were 318, 734 and 1779 DEGs, respectively, and 100, 168 and 281 differentially accumulated metabolites, respectively. Combined analysis of the transcriptomic and metabolomic data revealed the metabolic regulation of S. davidii in response to drought stress. First, key candidate genes such as PRR7, PRR5, GI, ELF3, PsbQ, PsaK, INV, AMY, E2.4.1.13, E3.2.1.2, NCED, PP2C, PYL, ABF, WRKY33, P5CS, PRODH, AOC3, HPD, GPX, GST, CAT and SOD1 may govern the drought resistance of S. davidii. Second, three metabolites (oxidised glutathione, abscisic acid and phenylalanine) were found to be related to drought tolerance. Third, several key candidate genes and metabolites involved in 10 metabolic pathways were identified, indicating that these metabolic pathways play an important role in the response to drought in S. davidii and possibly other plant species.