Effects Of Ridging On Water Heat Transport And Nitrogen Distribution In Paddy Soil

In rice production,soil water and heat conditions are important influencing factors for stable crop yield and high yield,and suitable temperature and soil moisture are necessary conditions for good rice growth.In the context of global warming,the number of high temperature and drought events in the southwest region has increased significantly.Sustained high temperatures affect key reproductive growth processes such as flowering,pollination and fruiting,resulting in a decline in rice yield.At the same time,excessive nitrogen fertilizer application will lead to an increase in nitrogen input in the soil,and the nitrogen balance will be seriously imbalanced.Part of the fertilizer nitrogen that has not been absorbed and utilized by rice is lost in the form of ammonia volatilization and other gaseous forms,and the other part is transported to the deep soil with irrigation water and rainwater in the form of nitrate nitrogen,which not only reduces the utilization rate of nitrogen fertilizer,but also increases the environmental cost of paddy land,and it is of great significance to explore the change law and accumulation of inorganic nitrogen in paddy soil under different farming systems,so as to provide a good soil environment for the growth and development of rice and reduce the risk of environmental pollution.Ridge rice fields change the surface form from flat to ridged by leveling the land,and realize semi-arid cultivation of rice fields.On the one hand,ridge rice fields increase the surface area of the soil,so that part of the soil is in direct contact with the atmosphere and solar radiation,and on the other hand,the rate of material circulation,energy conversion and information transmission is increased.In this study,relying on the long-term rice-field natural no-tillage experimental station of Chongqing Southwest University,three tillage modes were selected as the research objects:ridge cropping(RT),water and drought flat cropping(CT)and winter paddy field(FPF).According to the effects of the three tillage modes on soil temperature,soil moisture content and soil conductivity,the HYDRUS model was used to simulate the hydrothermal transport,and the influence on the nitrogen distribution of paddy soil layers at different depths under the three tillage modes was studied.The main results are as follows:(1)By ridge cropping,the contact area with the outside world can be increased,solar radiation can be better absorbed,and ridge cropping can reduce the salt content of the soil tillage layer,improve the ability of paddy soil moisture retention and salt inhibition,and significantly improve the coupling of 0-20cm soil water,heat and salt.(2)High temperature changed the coupling relationship between water,heat and salt in paddy soil under normal temperature conditions;soil temperature was significantly positively correlated with soil electrical conductivity;soil temperature and soil moisture content were only significantly negatively correlated under normal temperature conditions.Under the condition of high temperature,the water content of ridge-planted paddy field is the highest,and the soil electrical conductivity is the lowest.Ridge-planting can slow down the effect of increasing soil electrical conductivity caused by high temperature.(3)The HYDRUS model was used to simulate the changes of soil moisture and soil temperature in ridge cropping and flat cropping under normal temperature and high temperature environments.The two evaluation indexes of rms error RMSE and coefficient of determination R2 were used to evaluate the fit between the measured value and the simulated value.The results show that the simulated values of soil moisture content and temperature of paddy fields fit well with the measured values,and the HYDRUS model can realize the dynamic simulation of soil moisture content and soil temperature in paddy fields under normal temperature and high temperature environment.(4)In the ridge farming mode,in the environment of alternating dry and wet conditions,redox reactions are frequent.The accumulation of ammonium nitrogen and nitrate nitrogen in the 0-10cm soil layer is the lowest,which are 14.95kg/hm~2 and 17.1kg/hm~2 respectively;the accumulation of ammonium nitrogen and nitrate nitrogen in the 40-50cm soil layer is the highest,respectively45.3kg/hm~2,75.3kg/hm~2.