Hydrological Process And Its Impact Upon Crops In Farmland Vulnerable To Waterlogging

Farmland hydrological processes and crop production are in close contact. In the rainy and low-lying agricultural area, excessive precipitation will not only lead to saturation of agricultural soil water and groundwater level uplift, but also lead to surface and subsurface water-logging hazard of the crop. Eventually, it can lead to the reduction of farm crops and the phenomenon of agricultural production rise and fallen badly. China is one of the countries which occurred surface and subsurface water-logging frequently, and has a different level of water-logging every year. The Jianghan Plain is one of the serious water-logging disaster regions which caused huge losses to agricultural production. Therefore, based on a long series of observation data, researching the farmland hydrological processes and exploring the optimal regulation pattern of cropland water has important scientific significance and practical value for the farmland water management and agricultural disaster prevention and reduction, on the other hand, it has important scientific significance for enrichment and development of hydrology, especially the theoretical system of agricultural hydrology. In accordance with the reality of rainy and waterlogged disaster-prone region, taking the farmland vulnerable to water-logging as the research object, relying on the internal and external school base, selecting two dryland crops(wheat, cotton) widely cultivated in Jianghan Plain to water-logging stress experiment, researching crop growth, yield performance under water-logging combined with different fertilization methods, exploring the optimal regulation pattern of water and fertilization, all is not only beneficial to the sustainable development of agriculture, but provides a theoretical basis and practical basis for agricultural disaster prevention and reduction.Farmland hydrological dynamic is agricultural hydrology and water conservancy research priorities. In shallow groundwater conditions, groundwater, soil water, plant water, atmospheric water is a continuous hydrological process, they together constitute a complete farmland water system. Through the long series matching observation data of the precipitation, soil water and groundwater, adopting the drought and flood index method to divide the level of year, it reveals the dynamic characteristics of the water-logged farmland soil water and groundwater, and analyzes the variation of soil water and groundwater and its response degree to different rainfall combined with the crop production. The results showed that soil water and groundwater depth are very sensitive to precipitation. When rainfall exceeds a certain standard, soil water content significantly is increased and the groundwater level is obviously raised; Because the precipitation exists the inter-annual and seasonal differences so that soil water, groundwater level also showed obvious inter-annual, seasonal differences.Combined with the agricultural production, in the wheat and cotton growing season vulnerable to water-logging stress, it analyzes the problem of the over wet soil and over shallow groundwater depth causing subsurface water-logging stirred by the precipitation. The result shows that lasted longer general continuous precipitation or single heavy rainfall is the motive factor causing the soil water-logging. For different level years, the characteristics of wheat water-logging is that water-logging will absolutely occur in partial flood season, water-logging will occur sometimes in normal season, and water-logging does not occur in partial dry season. In cotton partial dry season, the situation of too wet soil causing water-logging generally doesn’t occur. The subsurface water-logging both in the cotton bud or cotton boll stage will occur in normal season because of the concentrated precipitation’s time, but not serious water-logging. In partial flood season, during the three key growth period of cotton, soil moisture of the cotton fields is too wet, resulting in cotton under long term soil moisture waterlogged stress, and the degree of water-logging reach extreme heavy. Long term water-logging caused serious damage on crop yield. On Agricultural Station,1989-2003wheat (881) yield and the groundwater buried depth of wheat key growth stage of3-5months is correlate analyzed, the results showed that:the yield of wheat and groundwater depth exists significantly positive correlation, groundwater depth is deeper, the higher the yield of wheat.Through the test-pit experiment of the two varieties of wheat in filling stage under the different groundwater depth conditions, study the apparent morphological indicators and physiological growth state indicators of wheat as well as the study of the influences of different buried depth of groundwater on wheat yield factors. The results showed that: wheat chlorophyll content, chlorophyll fluorescence parameters, and the components of wheat production are closely related to groundwater depth. Groundwater depth is more shallow, the faster the negative impact on the leaf color degree; groundwater depth is more shallow, the more severe negative impact on the leaf color degree; When the too shallow groundwater depth causing the crop water-logging, the chlorophyll fluorescence parameters showed specific changes. The initial fluorescence Fo and the maximal photochemical efficiency Fv/Fm were significantly decreased. The groundwater depth has different degrees of damage on wheat yield components of effective panicles number, grains per spike,1000-grain weight. Overall, groundwater depth0cm-30cm is the most serious water level for the wheat subsurface water-logging,30cm-60cm is the second serious degree of water level. Based on the influences of different groundwater buried depth on these indexes, groundwater depth75cm is a reasonable water level in wheat grain filling period. In addition, based on each index of the two varieties of wheat responses to water-logging, Emai23has a better resistance to water-logging than Zhengmai9023. Based on the regional agricultural production, through the pot and test-pit experiment to simulate cotton bud, flower and boll stage under water-logging stress and bud flowering under intermittent water-logging stress, and set the multi-gradient top-dressing method and level after water-logging, from the test results:(1)The leaf color degree is sensitive to water-logging stress, and the decline range and the water-logging level are positively related; Water-logging stress has a long time negative effect on the leaf color degree and it will not restore to control level in the short time. Fertilization has an obvious effect on the recovery of the leaf color degree, as long as adopt timely and appropriate amount topdressing after the general water-logging level, cotton leaves can gradually resume its main physiological function, but for the serious water-logging, need to increase the amount of fertilizer; From the way of the topdressing, waterlogged cotton taking comprehensive nutritional regulation scheme is always better than just fertilization scheme.(2) Chlorophyll fluorescence parameters after water-logging show specific rules, initial fluorescence Fo rise and Fv/Fm decline, both illustrate that moisture stress hurt the PS Ⅱ, reduce the PS Ⅱ primary light energy conversion efficiency, make cotton leaf PS Ⅱ latent activity center is impaired, the primary reaction process of the photosynthesis is inhibited. Topdressing has significant effect on the recovery of the chlorophyll fluorescence parameters, the spraying fertilization combination with hole fertilization are more effective. Therefore, after water-logging, cotton field should promptly drainage and apply fertilizer to reduce the effect water-logging on photochemical efficiency.(3)Cotton red stem and green stem ratio value is sensitive to water-logging, it greatly increased and exceeded the normal ratio of original growth period. Experiment proved that this sensitivity was positively related with the water-logging time and depth. In addition, cotton red stem and green stem ratio value also showed a strong sensitivity for high temperature stress. Therefore, for the farmland vulnerable to water-logging, when the red stem and green stem ratio value shows irregularly, it may mean that the farmland underground water level is higher, the soil is too wet and crop is subject to excessive water stress or high temperature stress, growth is inhibited. At this time, it is necessary to consider the farmland drainage control strategies or through nutrition regulation to make up for the damage on cotton.(4)After water-logging, cotton yield reduction has become an inevitable trend which can be reflected through the reduction of fu peach and autumn peach. Topdressing has a significant effect on the increase of fu peach and autumn peach, but the influences of water-logging stress on the cotton bolls is higher than the influences of the topdressing on the increase of cotton bolls. Topdressing has a certain role on the yield, for the mild water-logging stress, the amount of fertilization has no too big difference, for the severe water-logging stress, fertilization increased40%for cotton production significantly increased yield.