Growth and yield responses to simulated hail damage in drip-irrigated cotton

The frequent occurrence of hailstorm in Xinjiang affects cotton(Gossypium hirsutum L.)production and causes enormous economic loss.The indeterminate growth habit of cotton allows for varying degrees of recovery and yield when different hail damage levels occur at different stages,which brings inconvenience to agricultural insurance claims and post-damage management.Therefore,this study aimed to elucidate cotton recovery and yield responses to different levels of simulated hail damage at different growth stages.Four levels of hail damage(0,30,60,and 90%)were simulated every 15 d from the five-leaf stage to the boll opening stage in 2018 and 2019,for a total of six times(Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅴ,and Ⅵ).The results showed that seed cotton yield decreased as the damage level increased and yield reduction increased when the damage was applied to older plants(for 30,60 and 90% damage levels,yield reduction was 9-17%,22-37% and 48-71%,respectively).One possible reason was that the leaf area index and leaf area duration of plant canopy decreased after hail damage,resulting in a reduction in the accumulation of above-ground biomass.However,when hail damage occurred before bloom,due to the indeterminate growth habit of cotton,the vegetative organs produced a strong compensation ability that promoted the bud development.The compensation ability of vegetative organs decreased when hail damage occurred after bloom and the recovery time was too short to promote new boll maturity.As the first study to understand the recovery of cotton after hail damage,it analyzed the leaf area index,leaf area duration,above-ground biomass accumulation and yield,rather than the yield alone.The findings are of great importance for cotton production as they inform decisions about post-damage management practices,yield forecasts and insurance compensation.

NUMERICAL SIMULATION STDUY OF HAIL CLOUDPART Ⅱ.MECHANISM OF HALL FORMATION AND HAIL SUPPRESSION WITH SEEDING

A detailed 3-D hail cloud numerical model and parameterization of mierophysieal processes were described in Part Ⅰ(Hong 1999)of this study.In this part,a hail cloud occurring in Xunyi area.Shaanxi Province on July 8,1997 is simulated by the model to analyze mechanisms of hail formation and hail suppression with seeding.The results show that 97% of hail embryos are frozen drops.The seeding experiments with AgI in terms of heights show that if the seeding is made before hail formation,the optimum seeding position is located in the maximum updraft area and its center,i.e.,AgI is seeded in the zone with high water content to be coordinated with maximum zone of the updraft.The seeding makes concentrations of graupel and frozen drop increase and their average mass or size decrease,so that the proportion of conversion from graupel and frozen drop into hail descends greatly,and the mass and concentration of hailstone are decreased to achieve our purpose for hail suppression.