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.