In this study, the impacts of groundwater level on nitrate nitrogen accumulation in the vadose zone of a cotton field were investigated. Experiments were conducted in a cotton field at the CAS Ecological Agricultural Experiment Station in Nanpi from 2008 to 2010. A vertical observation well was drilled, and time-domain reflectometry probes and soil solution extractors were installed every 50 cm in the walls of the well to a depth of 5 m. The soil water content was monitored, and soil solution samples were obtained and analyzed every six days throughout the growing seasons during the three studied years. Additionally, a water consumption experiment was conducted, and the topsoil water content and leaf area index were measured in the cotton field. The resulting data were used to estimate parameters for use in a soil hydraulic and nitrate nitrogen movement model, and cotton evapotranspiration was calculated using the Penman–Monteith method. Groundwater level increases and decreases of ±4 m were simulated during a ten-year period using HYDRUS-1D. The results showed significant nitrate nitrogen accumulation in the vadose zone when the groundwater level remained unchanged or decreased, with increased accumulation as the groundwater depth increased. Additionally, increased precipitation and a deeper groundwater level resulted in greater nitrate nitrogen leaching in the cotton root zone. Therefore, irrigation and fertilization strategies should be adjusted based on precipitation conditions and groundwater depth.

Biochar is generally available to absorb nitrogen, phosphorus and other pollutants to improve water quality. However, the feasibility of biochar in improving water quality deterioration after straw returning is still unclear. In this study, pot experiments were conducted to evaluate the effects of straw decomposition on total phosphorus (TP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N) and potassium permanganate index (CODMn) under CK (no straw returning), ST (straw of 7 t/hm² returning) and SC (straw of 7 t/hm² and biochar of 20 t/hm² returning) conditions. Results showed that straw returning could significantly increase the nitrogen and phosphorus contents in field water. After adding biochar, there were significant differences in TP, NH₄⁺-N, NO₃⁻-N and CODMn both in surface water and 0–10 cm soil water in SC treatment compared to ST treatment. The concentration of TP, NH₄⁺-N, NO₃⁻-N and CODMn in surface water under SC treatment were always lower than that under ST treatment, and the maximum concentration could decrease by 52.29%, 39.67%, 35.23% and 44.50%, respectively. In 0–10 cm soil water, the concentration of TP, NO₃⁻-N and CODMn under SC treatment was always significantly higher than that under ST treatment, and the NH₄⁺-N concentration in SC treatment was gradually higher than that under ST treatment at the middle-late observation period. Results indicate that straw returning combined with biochar can effectively decrease the nitrogen concentration, phosphorus concentration and organic pollutants in surface water, inhibit the diffusion of non-point source pollutant, and reduce the risk of water pollution caused by straw returning.

The zero-inertia model is widely used for simulating surface flow in irrigation systems. This model is accurate when inflow discharge is constant. However, simulation of irrigation systems with rapidly varied inflow discharge is needed due to the development of real time control irrigation technology. Hence, the objective of this study is to validate the zero-inertia model with rapidly varied inflow discharge. For this purpose, twenty-three border irrigation tests at a range of inflow changes on different field slopes and roughness coefficients were conducted. Then, the sensitivity analyses of bed slope, infiltration parameters, and roughness coefficient were examined. The results indicate that the zero-inertia model predictions are in good agreement with field data in both advance/recession times and flow depths. The infiltration parameters were the most sensitive input variable of the zero-inertia model. The input variables have a more considerable impact on the recession phase than the advance phase. Keywords: zero-inertia model, rapidly varied inflow, border irrigation, sensitivity analysis DOI: 10.25165/j.ijabe.20201302.5228 Citation: Liu K H, Jiao X Y, Li J, An Y H, Guo W H, Salahou M K, et al. Performance of a zero-inertia model for irrigation with rapidly varied inflow discharges. Int J Agric & Biol Eng, 2020; 13(2): 175–181.

Surface irrigation under different irrigation techniques is evaluated in this research, based on water applying method, water infiltration depth, and irrigation water use efficiency. For that purpose, field experiments were conducted using cotton grown in silt loam soil at Wuqiao Eco-Agricultural Experimental Station in 2015 season. To evaluate the infiltration and distribution under conventional continuous inflow in comparison to increased discharge and decreased discharge irrigation in blockedend furrows, nine irrigation treatments were applied. They are known as continuous flow irrigation (CFI), decreased discharge irrigation (DDI) and increased discharge irrigation (IDI). In DDI and IDI irrigation treatments, the inflow should be varied before the completion of the advance phase and cut off time in all treatments when the advance wave reaches the end of the field. The infiltration depth in cm was functioned to opportunity time () in minute for the double ring infiltrometer as: 381. 0 51. 0   Z .The average application efficiency of DDI irrigation is higher than that of CFI and IDI irrigation treatments. Decreased discharge in DDI irrigation treatment when the position of the advancing wave front reaches 0.75 of the furrow's length can potentially save water and irrigation time compared with other irrigation treatments.