High sensitivity to climate change has been demonstrated in global maize production, especially the extreme high temperature and drought events. At present, the interactive effects of those extreme event stresses on maize growth at the grain filling stage are less well studied. In this study, a two-year field experiment was conducted to evaluate the compound effects of three stressors (high temperature, drought, and stress duration) at the filling phase on phenological period, grain filling rate, yield component, and yield of summer maize. The precipitation and temperature were controlled by using a rain-shelter systems and a warming system with infrared radiation lamps in field plots. The results indicated the significant influences of high temperature, drought stress, and the interaction on the growth and yield of summer maize. Under the individual factor of drought, compared to normal irrigation (NI), the significant decrease in grain-filling rate for mild drought (LD) and severe drought (SD) were 70.7% and 60.6%, respectively, while the decrease in grain yield for LD and SD were 80.1% and 93.6%, respectively. Under the individual factor of temperature, the consequences on grain-filling rate and grain yield were more severe at high temperature (temperature increase by 4.5 °C) than low temperature (temperature increase by 2.3 °C). The compound of high temperature and drought indicated that the grain yield increase by the compound effects of 3 °C for 5 days under normal irrigation (NIT₃D₅) and the compound effects of 3 °C for 7 days under mild drought (LDT₃D7) were 3.5% and 10.9%, respectively, compared to without temperature stress. The grain yields were reduced by the other compound effects. The preferential temperature (temperature increase by 2.3 °C) promoted maize growth under normal irrigation and mild drought, while high temperature (temperature increase by 4.5 °C) significantly inhibited maize growth under normal irrigation and heavy drought. The warming climate is favorable to maize production within certain limits, and will provide a scientific basis for agricultural disaster prevention and mitigation.

In order to deeply understand the effect mechanism of rapid drought stress on the physiological and biochemical properties of crop leaves and determine drought thresholds, the potted spring wheat under two water treatments, adequate water supply and continuous drought stress, was researched. In the early stage of drought, the parameters of leaves decreased in the order of stomatal conductance (g_s), intercellular CO₂ concentration (C_i), maximum electron transfer rate (J_max), mesophyll conductance (g_m), photosynthetic rate (P_n,) leaf water content (LWC), triose phosphate utilization rate (TPU), transpiration rate (T_r), and maximum carboxylation rate (V_cmax). Photosynthesis was dominated by stomatal limitation and also limited by carboxylation and mesophyll limitation. The carboxylation limitation was mainly caused by the reduction of electron transport capacity. In the late stage of drought, stomatal limitation first decreased, and then mesophyll limitation decreased. During extreme drought, carboxylation limitation also decreased. With the decrease of relative soil moisture (RSM), except for C_i, which first decreased and then increased, other physicochemical parameters of leaves all showed an S-shaped, decreasing trend. Mild and severe drought thresholds were determined to be 56.6% and 43.6% of the RSM, respectively, according to the curve’s inflection point, corresponding to 16.6% and about 52.2% of the average initial decrease amplitude among all parameters. This will provide a reference for monitoring as well as an early warning of rapid drought in spring wheat.

Agricultural drought definition focuses on the effect of water deficit during the crop growth period on the final crop yield. However, it is difficult to quantify the dynamic process for agricultural drought precisely during the crop growing season and then relate its impact to the final crop yield. This study was conducted to quantify agricultural drought severity for spring wheat (Triticum aestivum L.) at the jointing stage based on the response of leaf physiological parameters to progressive soil drying. The leaf potential and gas exchange parameters were observed daily using a DewPoint Potential Meter (WP4) and portable photosynthetic apparatus (LI-6400) at the jointing stage of spring wheat for two different water treatments: well water supply and natural drought, respectively. The results showed that the leaf photosynthetic features’ response to available soil water could be classified into five main stages, as the available soil water thresholds were at 0.41, 0.2, 0.12, and 0.04, respectively. We defined those five stages as no agricultural drought, mild agricultural drought, moderate agricultural drought, severe agricultural drought, and extremely severe agricultural drought based on the different mechanisms of the net photosynthesis rate’s response to progressive soil drying. The parameters of three stomatal conductance models, i.e., Ball–Berry, Leuning, and Medlyn, had two apparently different groups of values divided by moderate agricultural drought. This study combined atmosphere–soil–crop as a unit to quantify agricultural drought severity during the crop growth period could be used to model crop growth and development under water deficit conditions and calculate agricultural drought indices in drought research and management.

Agricultural drought often refers to water deficit in soil caused by a shortage of precipitation during a specific period in crop growing season, thus leading to final crop production failure. However, soil water content during planting may be related to the final yield of crop. Therefore, the soil water content at planting could have a great impact on determining whether agricultural drought occurs during crop growth and development. In the current study, we used soil water content at planting at 0–50 cm depth, the spring wheat (Triticum aestivum L.) yield from 1987 to 2011, and precipitation from 1971 to 2011 at Dingxi, Gansu Province, China, intending to quantify the influence of soil water content at planting on determining agricultural drought for rainfed spring wheat. The response of spring wheat yield to growing season precipitation comprised two different linear relationships defined by whether the soil water content at planting was greater or less than 100 mm. With the identical amount of soil water content at planting and precipitation during main growth period, a higher soil water content at planting resulted in a greater spring wheat yield. Soil water content at planting was more effective than growing season precipitation for increasing spring wheat yield. According to the probability distributions of soil water content during planting and growing season precipitation, we concluded that 28.6% of the years studued involved agricultural drought for rainfed spring wheat in the Dingxi of Gansu province, China. This analysis, which quantified the relative importance of soil water content at planting (29.97 kg ha⁻¹ per mm) and during growing season precipitation (12.21 kg ha⁻¹ per mm) to determine yield and agricultural drought occurrence for spring wheat, suggests that improving the amount of soil water storage before crop planting is an important way to deal with agricultural drought.