Development and infiltration performance of corn straw composite infiltration irrigation pipe

Straw subsurface irrigation (SSI) is an innovative technology based on the combination of straw returning and subsurface drip irrigation. Straw composite infiltration irrigation pipe, which formed from crop straw and soil mixture by extrusion, was used to replace the capillary of subsurface drip irrigation for irrigation. It can help to solve the problems of subsurface drip irrigation to a certain extent, such as the emergence of water shortage, emitter blocking and capillary recycling as well as straw returning. The research and development of straw composite infiltration irrigation pipe that meet the irrigation requirements was related to the success of SSI technology. In the current study, the straw composite pipe (SCP) was produced with corn stalk as the main material by using a self-made straw composite pipe forming machine, orthogonal test of straw composite pipe (SCP) was performed with three-factor and three-levels. The straw content, initial water content and spiral shaft speed were taken as scientific parameters to study the factors affecting the formation and water infiltration properties of SCP. The three levels of straw mass content were 5%, 7%, and 9%, respectively. While, the three levels of initial mass water content were 20%, 22%, and 24%, and the three levels of the spiral shaft speed were 50, 62, and 74 r/min. Effects of straw content, initial water content and spiral shaft speed on the bulk density, permeability rate and water infiltration uniformity coefficient of SCP were analyzed. The results showed that: 1) The bulk density of SCP was in between 1.278-1.355 g/cm3, and the main factor affecting the bulk density of SCP was straw content. With the increasing of straw content, the bulk density of SCP was reduced. The best combination to the formation of SCP was 5% straw content, 22% initial water content, and 62 r/min spiral shaft rotation speed, the corresponding bulk density of SCP was 1.355 g/cm3; 2) The free water outlet rate of the SCP was between 0.76-1.40 L/(m•h) at 0.25 m working pressure, which meets the requirement of commonly micro-irrigation emitters flow rate. Water infiltration rate was mainly influenced by straw content. When the straw content was 9%, the initial water content was 24%, and the spiral shaft rotation speed was 50 r/min, per unit length of SCP had the largest free water outlet rate; 3) Under the condition of free flow, the uniformity coefficient of water permeability for SCP was between 0.13 and 0.35 with low working pressure. The optimal combination was 5% of straw content, 24% of water content and 50 r/min of the spiral shaft rotation speed, but it still could not meet the irrigation requirements; 4) It took into consideration of the formation, water infiltration and water uniformity of SCP, the best characters of SCP was 5% of straw content, 24% of water content and 50 r/min of spiral shaft rotation speed. The conclusions have a certain reference value for the research and development of SCP, which would be beneficial to promote the utilization of straw resources and the development of field water-saving technology.usions have a certain reference value for the research and development of SCP, which would be beneficial to promote the utilization of straw resources and the development of field water-saving technology.