Preparation of polyacrylamide/montmorillonite infiltrating irrigation material and field test of its water conducting performance

Abstract: Based on the characteristics of micro water requirement of psammophytes, a kind of infiltrating irrigation composite material was prepared by using Polyacrylamide (PAM) and Montmorillonite (MMT). An infiltrating irrigation system was then designed based on the composite material. The film-forming properties of the composite water conducting materials with different proportions of PAM and MMT were observed and analyzed by using a scanning electron microscope, and water absorption performance and water release performance of the material were tested in air and sand. The composite water conducting materials were made into an infiltrating irrigation emitter, and the water conductivity of the infiltrating irrigation head was studied. On this basis, an infiltration irrigation system was designed, and then water transmission performance of the infiltration irrigation system was studied. A field test of infiltrating irrigation system in Ulan Buhe desert was carried out. The self-regulation mechanism of composite material was analyzed by X-ray diffraction, infrared spectrum analyzer and scanning electron microscope. The results showed that the best mass ratio of PAM to MMT was 0.25. The material had good coating uniformity on the fiber surface. The water absorption test showed that, in the first 40 min, the water absorption increased rapidly. From 40 to 120 min, the water absorption continued to increase, but the water absorption rate began to decrease gradually. After 120 min, the water absorption amount changed little, and the water absorption rate almost dropped to 0. The water absorption amount was 30.2 g/g at 150 min. In air, the composite released water rapidly in the first 50 minutes, and then kept stable until 140 minutes, reaching 24.2 g/g. The water release rate in dry sand was slightly higher than it in air. The water release reached 28.5 g/g. The water conducting test of infiltrating irrigation emitter showed that the soil moisture content was 13% after the water diversion was stable, indicating that the soil moisture content could meet the growth needs of Cistanche deserticola. The water conducting tests of infiltrating irrigation showed that the effluent rate of irrigating system gradually decreased within 24 h, and the initial effluent rate reached 52 mL/h, and then decreased rapidly to 21 mL/h at 6 h. The effluent rate began to slow down and tend to be stable, and the effluent rate was 7 mL/h at 24 h. The water conducting curve of infiltrating irrigation system within 7 days showed that the water conducting rate was 420 mL/d on the first day, and then kept stable at about 160 mL/ d. In the three dry and wet cycles, the water conductivity of the infiltrating irrigation system was 420 mL/d in the first day, and 165 mL/h in the second to third day. The results showed that when the external soil moisture was low, the hydraulic conductivity of the infiltrating irrigation system was faster (about 420 mL/d), and with the water conduction, the external soil moisture gradually increased, and the water conducting rate of the infiltrating irrigation system decreased and remained stable. When the soil moisture decreased again, the water conductivity of the infiltrating irrigation system would increase again. So the dry and wet alternating test showed that it could self-regulate the water conducting rate according to the soil moisture, and the inoculation rate of Cistanche deserticola improved from 23% to 86%. The infrared spectrum analysis results showed that the lamellar structure of MMT had not been destroyed, and PAM was connected to MMT by intercalation effect. X-ray diffractometer analysis results showed that the laminar spacing of MMT increased from 1.21 to 1.45 nm after intercalation reactions. The microscopic analysis showed that the water conducting materials mainly relied on the interaction between PAM and MMT to transfer water. When the soil moisture was low, the moisture content of the water conducting materials near the soil side decreased and was in a relatively dry state, and the MMT particles aggregated to form a rapid water conducting channel. When the external soil moisture was high, the moisture content of the water conducting material near the soil side was also high, and it was in the state of water absorption and swelling. The water conducting channel of montmorillonite was cut off, and the water conducting rate dropped rapidly so as to realize the self-regulation of the water conducting rate of the composite material. The results could provide information for the application of seepage irrigation materials.