Title : Effects of the levels of soil water deficit, duration of soil water shortage on different rice cultivars
The main factors affecting the drought of rice include the levels of water deficit in paddy soil, the duration of soil water shortage, and the drought resistance of rice varieties. In order to clarify the effects of the above drought factors on the growth characteristics and yield traits of rice, and the stable yield mechanism for it, the pot experiment with 3 factors (2 drought resistant rice varieties× 4 soil water deficit levels ×3 soil water shortage duration times) were implemented during the rice growing season in 2017, Among them, 2 varieties were adopted as: C1 (Nanjing 9108) and C2 (Huaidao 5#); 4 soil water deficit levels were treated as: T1 (light drought with mild soil water shortage at soil relative humidity 90% + 5%, LD), T2 (medium drought with medium soil water shortage at soil relative humidity 80% + 5%, MD), T3 ( severe drought with soil relatively heavy water shortage at soil relative humidity maintained at 70% + 5%,SD), and T4 (extreme drought with soil severe water shortage at soil relative humidity of 60% + 5%, ED); 3 soil water shortage duration treatment, respectively: W1 (drought 10d), W2 (drought 20d), and W3 (drought 30d). A total of treatments were 24 with 5 repeated. The growth characteristics (rice plant height, tiller number, ear number, stem weight, dry weight of leaf, dry weight of ear, and SPAD value of chlorophyll content) and yield traits (grain number per spike, empty shrunken rate, and 1000 grain weight) were measured by sampling at different growth stages. The water deficit levels effect, times effect, and variety effect of rice drought were preliminarily analyzed. The results showed that: 1. With the increasing of soil water deficit levels and the increase of soil water shortage duration, the index of growth characteristics and yield traits of rice decreased obviously. 2. In general, the effects of soil water shortage duration on rice were generally greater than that of soil water deficit levles; 3. The SPAD values for various cultivars had a general response to only under the severe drought and extreme drought with the longer soil water shortage duration, and that of under the mild drought and moderate drought treatment in short soil water shortage were not obvious. 4. Compared with C1 (Nanjing 9108), C2 (Huaidao 5#) in the mild drought with short soil water shortage duration had a better stable yield effect, while there was no significant different from C1 (Nanjing 9108) on the stable yield effects for the long duration of the severe drought.