Study On Water Saving Mechanism And Threshold Parameters Of Maize Deficit Compensation Irrigation

Deficit compensation irrigation is one important technology of water saving irrigation,which cause a small reduction in crop production but it can greatly improve the water use efficiency.Among,low irrigation limit and upper irrigation limit are two core parameters in this technology,low irrigation limit represents the degree crop suffered from water deficit,while the upper irrigation limit reflects the effort of the compensation to the crop and size of the irrigation water.On the basis of predecessors' research,this paper selected three low irrigation limits and three upper irrigation limits according to the water deficit degree,then it was divided into nine treatments through permutation and combination.In the canopy,pot experiment was conducted through studying the different irrigation threshold parameters' influence on maize's growth physiological indexes,analyzing its changing rule,then revealing the mechanism of maize water saving,discussing the method of diagnosis on water deficit.The main results are as follows:(1)When low irrigation limit is lower,the maize was suffered from water stress saverely,upper irrigation limit would produce minor volatility about compensation effect;when low irrigation limit is higher,the maize is impervious to water stress,difference upper irrigation limit did not make a big difference.The maize growth could get a large compensating effect after irrigation when low irrigation limit was set to 60%?_f.(2)The water deficit led to increase the leaf-air temperature difference,the leaf-air temperature of 50%?_f low irrigation limit was higher than the 60%?_f and 70%?_f.In sunny daym,the maize leaf temperature and air temperature all changed in a wider range,the leaf-air temperature in sunny dan was higher than in the cloudy and rainy day.The maize stem sap flow velocity(SF)presented a normal pattern of diurnal variation,the mumber and width of the peak was related to weather conditions;there were extremely significant correlation between the maize stem sap flow velocity and solar radiation(Rs),vapor pressure deficit(VPD),air temperature(T)and relative humidity(RH),the sequence was Rs>T>VPD>RH;there were extremely significant correlation between SF and meteorological factors,the theoretical results fit well with model estimated and measured values and it is feasible to prodict SF.The research revealed the change rules of maize stem sap flow velocity and established the estimating model,providing theoretical basis for maize irrigation system.(3)Proline(Pro)and malondialdehyde(MDA)were influenced by water stress apparently,Pro and MDA cumulants and their average value increased with the worse of water stress;in different period,the order of Pro cumulant average is grouting tassiling stage>mature stage>jointing stage,the order of MDA cumulant average is jointing stage>grouting tassiling stage>mature stage;the cumulants of Pro and MDA were interrelated,it is beneficial to decrease the cumulant of MDA,if the Pro can give full play to its osmotic adjustment.The activity of Catalase(CAT)and Peroxidase(POD)was influenced by water stress apparently,and the activity of CAT and POD first increased then decreased with the increasing of water stress;In different growth period,the average values of CAT and POD activity decreased with the increase of lower irrigation limit;The order of maximum value of CAT activity was jointing stage>grouting tasseling stage>mature stage,and the maximum value of POD activity had an opposite change rule to that of CAT activity.(4)Under the condition of deficit compensation irrigation,the total amount of dry matter and grain yield of corn will increase with the increasing of low irrigation limit.Higher upper irrigation limit increased the soil evaporation and crop transpiration,but was not obvious for increasing the dry matter quality and yield of corn,which increased the soil water invalid consumption and reduced the crop water use efficiency.In the early growth period about maize,the maize' s plant was smal and the evaporation was large.With the extension about the growth of corn,crop water use efficiency increased gradually: the mature period > grouting tasseling stage > jointing stage.Under the condition of deficit compensation irrigation,the maize yield increased with the increasing of low irrigation limit and the crop water use efficiency decreased with the increasing of low irrigation limit.The optimal irrigation threshold parameter for maize was 60%?_f and 90%?_f.(5)Maximum daily shrinkage(MDS)and Daily increase(DI)in different treatments were influenced by water deficit apparently,the response of Recovery time(RT)in the three treatments to the soil water content was accordant;the correlation analysis with soil water content showed that MDS and DI were affected greatly and the correlation coefficients with soil water content were smaller;the correlation coefficients of RT and ? were the highest and RT was impacted smaller by different treatments of water dificit,RT could be a superb index to diagnosis the crop water stress.