Maize, a major food source for the world’s tropical regions, is often impaired by droughts under a changing climate, which creates the importance of making efforts to improve the tolerance characteristics of maize under field conditions. The experiment was conducted during the dry season of the 2020–2021 period to investigate the stimulatory effects of plant growth regulator (PGR) ethephon (2-chloroethylphosphonic acid) on the morpho-physio-biochemical traits of maize and to identify suitable application approaches for efficient production under water stress. The factorial randomized complete block design was followed for the present experiment. Ethephon was applied at the vegetative 6 leaves (V6) and/or 10 leaves (V10) stages. Seven application approaches (doses in g a.i. ha⁻¹) of ethephon, i.e., 281 at the V6 stage (E1), 281 at the V6 stage + 281 at the V10 stage (E2), 281 at the V10 stage (E3), 562 at the V6 stage (E4), 562 at the V6 stage + 562 at the V10 stage (E5), 562 at the V10 stage (E6), and no ethephon (E7), were used for maize production. Another factor was that three water levels were used, i.e., well-watered conditions (watering every week) (W1), short water stress (no watering during 48–69 days after planting) (W2), and prolonged water stress (no watering during 48–83 days after planting) (W3). Water stress negatively affected most of the morpho-physiological traits, and in W2 and W3 conditions, the grain yield was significantly lower, i.e., 4.82 and 4.27 t ha⁻¹, respectively, compared to W1 (5.71 t ha⁻¹). The plant height and leaf area index at the reproductive milk stage of maize (R3) were significantly reduced by all approaches of ethephon application compared to no ethephon. However, across the water levels, E3 performed better and produced a higher grain yield (5.11 t ha⁻¹), which was mostly seen by a higher 100-grain weight (24.52 g) and a slightly higher grain number per plant (356.12). It was also positively supported by most of the physiological and biochemical traits, as they were especially higher in the relative growth rate (25.73 mg plant⁻¹ day⁻¹), net assimilation rate (0.79 mg cm⁻² day⁻¹) at V6-R3, heat use efficiency (3.39 kg ha⁻¹ °C days⁻¹), electrolyte leakage (5.69%), and proline (28.78 µmol g⁻¹ FW). These traits, under prolonged stress, also gave the maximum drought tolerance index by E3, i.e., the relative growth rate (1.00) and net assimilation rate (1.00) at V6 to R3, heat use efficiency (1.06), relative water content (1.00), electrolyte leakage (1.65), proline (1.88), 100-grain weight (1.01), grain yield (1.11), and water productivity (1.53). A path analysis showed that the shoot weight at R3 (1.00), the stem diameter at the R3 stage (1.00), net assimilation rate (0.95), relative water content (0.95), 100-grain weight (0.90), grain number (0.76), proline (0.75), SPAD value (0.71), and total soluble sugar (0.57) were highly positive, and electrolyte leakage (−0.84) was negatively correlated with the grain yield under prolonged water stress. The maximum positive direct effect on the grain yield was found in the shoot weight (1.05), net assimilation rate (0.68), leaf area index at R3 (0.45), SPAD (0.22), and electrolyte leakage (0.21). The ethephon application as the E3 approach was more efficient in both short and prolonged stress, especially under prolonged stress, as it showed a higher energy use efficiency (1.55) and less CO₂-eq emission (3603.69) compared to the other approaches of ethephon. The subsequent efficient ethephon approaches were E1 under short water stress, E6 under prolonged water stress, where E5 performed minimally, and no application of ethephon, which exhibited the worst efficiency under water stress.

Zinc (Zn) fertilization is widely used in maize (Zea mays L.) production to alleviate Zn deficiency and improve biomass and grain yield. However, limited research exists on Zn management in maize cultivated in high-pH paddy soils following rice-based systems, where altered soil chemistry may affect Zn availability and plant uptake. This study aimed to evaluate the effects of Zn application rates on growth, yield, and Zn uptake in two hybrid maize varieties under such conditions. Field experiments were conducted during the 2019 and 2020 dry seasons in Phetchabun Province, Thailand, using a randomized complete block design with a 4 × 2 factorial arrangement and four replications. Treatments included four Zn rates (0, 5, 10, and 20.6 kg of Zn/ha), applied as Zn sulfate monohydrate (ZnSO₄·H₂O, 36% Zn) by soil banding at the V6 stage, and two hybrid varieties, Suwan 5731 (SW5731) and Suwan 5819 (SW5819). In 2019, significant Zn × variety interactions were observed for biomass, crop growth rate (CGR), and grain yield. SW5819 at 10 kg of Zn/ha produced the highest biomass (31.6 t/ha) and CGR (25.6 g/m²/day), increasing by 15.3% and 39.1%, respectively, compared to its own no Zn treatment. In contrast, 20.6 kg of Zn/ha reduced SW5819 biomass by 6.6% and 13.1% relative to SW5731 and its own no-Zn treatment, respectively. Grain yield in SW5819 peaked at 14.7 t/ha under 5 and 10 kg of Zn/ha, significantly higher than SW5731 under 0 and 5 kg of Zn/ha by 16.7%, while SW5731 showed no significant response. In SW5819, shoot and grain Zn uptake significantly increased under 5 and 10 kg of Zn/ha by up to 36.8% and 33.3%, respectively, compared to no Zn treatment. The lowest shoot Zn uptake was found in SW5819 under 20.6 kg of Zn/ha (264.1 ± 43.9 g/ha), which was lower than all its Zn treatments and all SW5731 treatments, showing a reduction of 19.4–43.6%. Zn application improved soil Zn availability, and Zn partitioning among plant organs varied with Zn rate and season. A moderate Zn rate (10 kg of Zn/ha) optimized maize performance under high-pH, rice-based conditions, emphasizing the need for variety-specific Zn management.

A major portion of maize is produced under rainfed conditions in the tropics with relatively poor yield because of the unpredictable and irregular distribution of seasonal rainfall, as well as a decline in pre-rainy season rainfall due to climate change, so identification of sustainable production options is utmost needed. Thus, the present studies were conducted in a greenhouse (GH) to ascertain the water stress-tolerant traits of maize and at the field level in the tropical environment of Thailand to see the stimulating possibility of the ascertained traits in a locally popular cultivar using ethephon. Depending on tolerance level, three maize genotypes (Suwan 2301 > Suwan 4452 > S 7328) were tested under different water conditions—well-watered, short-term, and long-term water stress—in the GH. At the field level, the locally popular maize cultivar Suwan 5819 was examined with six ethephon levels (doses in g a.i. ha⁻¹ of ethephon, i.e., T1, 281 at V6 stage; T2, 281 at V6 + 281 at V10 stage; T3, 281 at V10 stage; T4, 562 at V6 stage; T5, 562 at V6 + 562 at V10 stage; T6, 562 at V10 stage) against no ethephon application (T0) under rainfed conditions. Maize suffered from the scarcity of sufficient rainfall during 26–39 days after planting (DAP) and 43–63 DAP in the field. The yield index (YI) was identified from biplot analysis as one of the suitable standards for drought tolerance checks for maize at GH as well as at field level in the tropics. The YI value of observed agro-physio-biochemical traits of maize in GH showed that relative water content (RWC, 1.23), stem base diameter (SBD, 1.21), total soluble sugar (TSS, 1.15), proline (Pr, 1.13), aboveground plant biomass (APB, 1.13), root weight (RW, 1.13), relative growth rate (RGR, 1.15), specific leaf weight (SLW, 1.12), and net assimilation rate (NAR, 1.08) were the most desirable. Efforts were made to stimulate these traits under water stress at the field level. Ethephon application as T1 helped to gain higher kernel yield (KY) (5.26 t ha⁻¹) with the support of higher RWC (90.38%), proline (24.79 µmol g⁻¹ FW), TSS (1629 mg g⁻¹ FW), SBD (24.49 mm), APB (271.34 g plant⁻¹), SLW (51.71 g m⁻²), RGR (25.26 mg plant⁻¹ day⁻¹), and NAR (0.91 mg cm⁻² day⁻¹) compared to others, especially no ethephon application. Furthermore, the attributes SLW, SBD, Pr, heat utilization efficiency (HUE), 100-kernel weight, TSS, electrolyte leakage, and lodging percentage showed a substantial direct effect and significant correlation with KY. Aside from higher KY, ethephon application as T1 tactics resulted in higher values of energy efficiency (1.66), HUE (2.99 kg ha⁻¹ °C days⁻¹), gross margin (682.02 USD ha⁻¹), MBCR (3.32), and C absorption (6.19 t C ha⁻¹), indicating that this practice may be a good option for maize sustainable production under rainfed conditions.

Zinc (Zn) is often of deficient in paddy soils, and optimizing its application is crucial for improving maize productivity in intensive rice–maize cropping systems. This study aimed to develop practical Zn fertilizer strategies suitable for paddy soils with varying pH levels, thereby improving nutrient management and understanding of soil microbial responses. Field experiments were conducted during the 2020–2021 dry seasons at three sites: Chon Daen (pH 5.8), Noen Maprang (pH 6.7), and Lom Sak (pH 7.8). A two-factorial randomized complete block design with four replications was used, including four ZnSO₄·H₂O rates (0, 1.5, 3, and 6 times the DTPA-extractable Zn in soil) and two hybrid maize varieties, Suwan 5731 and Suwan 5819. Results showed that at Chon Daen, Zn application significantly enhanced shoot Zn uptake and soil Zn concentration, with SW5819 exhibiting greater Zn efficiency and biomass production. At Noen Maprang, Zn application did not significantly affect dry matter, while, at Lom Sak, Zn responses were moderate, though SW5819 maintained better growth and Zn uptake. Across sites, maize Zn efficiency was highest under acidic conditions and in SW5819. Soil microbial communities remained largely unaffected by Zn fertilization and were primarily influenced by soil pH, with Proteobacteria, Crenarchaeota, and Ascomycota dominating bacterial, archaeal, and fungal groups, respectively. These findings support the feasibility of Zn fertilization strategies to enhance both crop productivity and nutritional quality without altering the microbial community composition.