No abstract

Drought is a complex natural disaster phenomenon. It is of great significance to analyze the occurrence and development of drought events for drought prevention. In this study, two drought characteristic variables (the drought duration and severity) were extracted by using the Theory of Runs based on four drought indexes (i.e., the percentage of precipitation anomaly, the standardized precipitation index, the standardized precipitation evapotranspiration index and the improved comprehensive meteorological drought index). The joint distribution model of drought characteristic variables was built based on four types of Archimedean copulas. The joint cumulative probability and the joint return period of drought events were analyzed and the relationship between the drought characteristics and the actual crop drought reduction area was also studied. The results showed that: (1) The area of the slight drought and the extreme drought were both the zonal increasing distribution from northeast to southwest in Yunnan Province from 1960 to 2015. The area of the high frequency middle drought was mainly distributed in Huize and Zhanyi in Northeast Yunnan, Kunming in Central Yunnan and some areas of Southwest Yunnan, whereas the severe drought was mainly occurred in Deqin, Gongshan and Zhongdian in Northwest Yunnan; (2) The drought duration and severity were fitted the Weibull and Gamma distribution, respectively and the Frank copula function was the optimal joint distribution function. The Drought events were mostly short duration and high severity, long duration and low severity and short duration and low severity. The joint cumulative probability and joint return period were increased with the increase of drought duration and severity; (3) The error range between the theoretical return period and the actual was 0.1–0.4 a. The year of the agricultural disaster can be accurately reflected by the combined return period in Yunnan Province. The research can provide guidelines for the agricultural management in the drought area.

In order to clarify the response characteristics of tillering and nitrogen (N) uptake and utilization under micro-nano bubble aeration irrigation and nitrogen fertilizer level, the nitrogen uptake and utilization characteristics, tillering and yield of early rice under different irrigation methods and nitrogen levels were investigated. The results showed that micro-nano bubble aerated irrigation and nitrogen fertilizer have substantial influence on tillering of early rice, and the effect of N fertilizer was greater than the effect of oxygen. Nitrogen accumulation increased by 6.75–10.79% in micro-nano bubble aerated irrigation treatment compared with the conventional irrigation. The application of N in treatment of micro-nano bubble aerated irrigation and 160 kg N/ha fertilizer used (W₁N₁) was 90% of the treatment of micro-nano bubble aerated irrigation and 180 kg N/ha fertilizer used (W₁N₂), while the yield decreased by only 0.31%. The study indicated that the adoption of an appropriate deficit N rate combine with micro-nano bubble aerated irrigation can be an effective means to reduce non-beneficial N consumption, achieve higher crop yield and N utilization efficiency.