Mechanism And Simulation Of Soil Water And Heat Transport In Potato Field Under Drip Irrigation With Plastic-film Mulch

The solar and thermal resources are rich for potato production,while the water resources are extremely scarce in Northwest China.Both water and heat stress can affect potato yield and quality.Drip irrigation and plastic-film mulch can save water,increase yield,and improve potato quality by providing favorable water and heat conditions for potato growth.The study on mechanism and simulation of soil water and heat transport in potato field under drip irrigation with plastic-film mulch will provide scientific basis for the design and management of drip irrigation system.Field experiments were conducted at Shiyanghe Experimental Station,China Agricultural University,Wuwei,Gansu Province,China using plastic-film mulch and drip irrigation to explore the effects of three typical plastic-film mulches(transparent plastic-film mulch,TMP2;non-mulched check,NMP2;black plastic-film mulch,BMP2)and three wetted soil percentages(35%,TMP1;55%,TMP2;75%,TMP3)on water and heat transport and potato growth under surface drip irrigation with plastic-film mulch in 2014 and 2015.The HYDRUS-2D code was applied to simulate soil water and heat transport.Moreover,a model was developed to simulate water and heat transport in potato field under drip irrigation with plastic-film mulch.The main results are as follow:(1)The effects of different plastic-film mulches on heat transport and potato growth were obtained.The BMP2 treatment had higher net solar radiation than TMP2 treatment.During vegetative growth,the maximum mulch surface temperature in BMP2 treatment was 3.0 and 3.9? greater than in TMP2 treatment in 2014 and 2015,respectively.The difference in net solar radiation,soil heat flux,and temperature among different treatments diminished with plant canopy enlargement.The plant height in BMP2 treatment was greater than TMP2 treatment.The above-ground radiative and thermal conditions might be the main factor that affected the plant heights during vegetative growth.Although the potato yield of TMP2 treatment was almost the same with BMP2 treatment,BMP2 treatment had 9%and 8%higher evapotranspiration than TMP2 treatment in 2014 and 2015,respectively.(2)The effects of different plastic-film mulches and wetted soil percentages on soil water distribution and potato growth were obtained.The soil water content was higher in the mulched treatments than in the non-mulched treatment at 0-10 cm soil depth.As the plant canopy increased,the differences diminished.The soil water fluctuations in the top of the bed with black plastic mulch were greater than with transparent plastic mulch.The water content in the subsoil of TMP1 treatment decreased with the potato growth.The TMP1 treatment had more root than TMP2 and TMP3 treatments.The TMP1 treatment had the highest water use efficiency,17%and 25%higher than the TMP3 treatment in 2014 and 2015,respectively.The 35%wetted soil percentage irrigation regime combined with transparent plastic mulch was favorable for potato production in Northwest China.(3)The HYDRUS-2D code was applied to simulate soil water and heat transport under different wetted soil percentages.Soil water contents were simulated by HYDRUS-2D with three simulation approaches:simulation with soil hydraulic parameters estimated from measured soil textural information(SSTI),measured soil water retention curve(SSWRC),and inverse model(SInverse).The performance of SInverse was the best,especially at 0-10 cm soil depth.The simulation results of soil temperature with thermal parameters estimated by inverse model were satisfactory with RMSE ranged from 1.0 to 2.5 ? at 10-50 cm soil depth(except at 20 cm soil depth in TMP2 treatment).(4)A model was developed to simulate heat transport in potato field under drip irrigation with plastic-film mulch.The canopy coverage degree and the transmissivity of photosynthetically active radiation were used in the model to consider the canopy growth and the process of radiation transport.After calibration and validation,the model can be used to simulate the daily and season variations of temperature,soil heat flux,and net solar radiation.The most important parameter affecting diural canopy temperature in BMP2 and TMP2 treatments,obtained by the global sensitivity analysis,was mean stomatal resistence.