干旱对夏玉米根冠及产量影响试验

为揭示干旱对夏玉米根冠生长及产量形成的影响，2013—2015年在山东夏津、山西运城和河北固城开展夏玉米水分胁迫控制试验，研究不同干旱条件下玉米根冠及产量的变化，厘定干旱敏感时段及临界阈值。结果表明:同一干旱程度，影响玉米地上干物重、产量的关键时段为拔节-抽雄期，抽雄期最敏感，影响根系、根冠比的关键时段为出苗-拔节期，拔节期最敏感。不同干旱程度，在快速失墒阶段，不同生育时段的地上干物重、根干重、根冠比均呈下降趋势，分别较对照减少11.7%~67.8%，35.2%~85.8%和15%~62%；干旱维持阶段与快速失墒阶段相比，地上干物重呈持续下降趋势，较对照减少24.3%~89.7%，根干重、根冠比呈上升趋势或无明显差异，分别较对照减少9.7%~80.8%，9.6%~62%。出苗-拔节期，土壤相对湿度60%~62%为玉米地上部生长及形成合理根冠比的临界阈值；出苗-七叶期，土壤相对湿度51%~60%利于根系生长。土壤相对湿度62%为影响玉米产量的临界阈值，土壤相对湿度31%~40%，出现在拔节、抽雄等敏感期，玉米减产七成以上。土壤相对湿度50%~60%持续时间少于8 d，复水后根冠可迅速恢复生长，但对产量仍有一定程度的影响，减产1.4%~6.6%。

Experiments of Water Stress on Root/Shoot Growth and Yield of Summer Maize

Drought is one of the most important meteorological disasters affecting the growth and production of maize. Dynamic changes and cumulative effect of the drought are closely related to the degree of drought, duration, and growth stages. In order to investigate effects of drought stress on maize, artificial control experiments are carried out in Yuncheng of Shanxi, Xiajin of Shandong and Gucheng of Hebei from 2013 to 2015, in which relative soil moistures are 31%-40%, 41%-50%, 51%-60%, 61%-70% and CK (71%-100%), and the growth stages are seedling-jointing, jointing-tasseling, tasseling-maturity and jointing-maturity. The root/shoot growth and yield of maize are analyzed at different drought levels, effects of rapid water consuming stage and drought maintenance stage under different drought degrees are also analyzed. The growth stage and critical thresholds sensitive to drought stress are determined. Results show that with equivalent drought level, jointing to tasseling stage is the key growth stage affecting the shoot and yield, and the tasseling stage is sensitive to drought stress. The key growth stage of root and root/shoot ratio is from emergence to jointing stage, especially the jointing stage. Under different drought degree, the dry weight of the shoot and root and root/shoot ratio all show down trend at the rapid water consuming stage, which are respectively reduced by 11.7%-67.8%, 35.2%-85.8% and 15%-62% compared to control experiments. At the drought maintenance stage, the dry weight of the shoot is in reduced by 24.3%-89.7%, but the root dry weight and the root/shoot ratio are less sensitive, which respectively decreases by 9.7%-80.8% and 9.6%-62% compared to control experiments. Regression models for drought level and yield reduction rate are established respectively for two drought stages, and are above at 0.05 significant level. The effect of the drought maintenance stage is slightly greater than that of rapid water consuming stage. At the emergence-jointing stage, the relative soil moisture is 60%-62%, which is the critical threshold for the growth of shoot and formation of a reasonable root/shoot ratio. The relative soil moisture is 51%-60% from the emergence to seven-leaf stage, which is conducive to root growth. The relative soil moisture value of 62% is a critical threshold, below which the yield will be influenced by drought. When the relative soil moisture is 31%-40% during the sensitive stage of jointing, tasseling, the yield reduction is more than 70%. When the relative soil moisture is 50%-60% and the duration is less than 8 days, the growth of root and shoot can be restored after rehydration, but the yield is reduced by 1.4%-6.6%. Results can provide basis for rational irrigation and drought dynamic assessment.