Method for continuously measuring soil infiltrability of plow-cultivated layer and hardpan in farmland

The study on farm land infiltration is of great importance for understanding the impacts of plow-cultivation on soil hydrodynamics, guiding cultivation decision making and irrigation as well as improving ecological environments of farm land. A new method, including the experimental system and the related algorithm procedures was advanced for continuous measurement of soil infiltrability curve of cultivated layer and the hardpan of the farm field. A well-controlled water flow of constant flow rate was applied to the soil surface. The initial very high infiltration rate was estimated from the time-dependent function of the wetted soil surface area. And the latter infiltration process, including the relatively steady infiltration of the cultivated layer and that of the hardpan infiltration is estimated from the difference of applied water flow rate and the out flow rate. An integrated experimental system that completely controlled by a computer was developed, including a computer with the supporting software for process control and data record as well as for infiltration process computation, a Mariotte bottle for water supply of constant flow rate, a specially designed outlet unit for point distribution of water flow at the soil surface, a ring for the soil boundary control, a digital camera for automatic record of the increasing process in the wetted soil surface area as time, two electronic balances for measuring the flow rates both of water supply and drainage. Detailed experimental procedures were presented. Computational algorithms for infiltration rates at various steps were detailed. The demonstrational laboratory experiments were conducted to illustrate the experimental procedures, infiltration estimation methods at different stages, using air-dry silty clay with flow rate of about 2 L/h in 3 replicates. The results from the laboratory simulation experiment indicates that this method is capable of making continuous measurement of the infiltration process of typical farm field, including both of the cultivated layer and the hardpan. The experimental results showed that the advances in wetted soil surface areas as time were well fitted with a exponential function, with determination coefficients (R2) of 0.99. The measured infiltration processes, exclusive of the hardpan infiltration were well fitted by the well-known infiltration models, such as Philip, Horton and Kostiakov models, with determination coefficients (R2) ranging from 0.91 to 0.99. The hardpan infiltration rate was 8.02 mm/h on average. Error analysis based on supplied water and infiltrated water volume indicates this method produces an error of 5.75%. This indicates a well acceptable accuracy. The results verify the measurement method, computational model and the experimental procedures. The method proposed in this study is featured with time and water efficiency and easy for field application. It will supply a useful tool for further research in the direction.