Effect Of Drip Tape Disposition Pattern Under Plastic Mulch On Cotton Growth, Water And Nitrogen Transport Of Rootzone

The technique of drip irrigation with plastic film mulch, or called the mulched drip irrigation is a combination of drip irrigation and plastic techniques, which is characterized by irrigational water saving, crop being premature and its output increasing, soil temperature increasing, and preservation of soil moisture. This irrigation technique has been used for many kinds of economic value crops over the world, but the water-saving mechanism for the mulched drip irrigation and the efficient use of fertilizers has not been studied thoroughly. Experiments had been carried out in field, to plant cotton with coupling effect of water and fertilizer under different drip irrigation tape disposition pattern to systematically and comprehensively study the problems about the water and nitrogen transport characteristics soil wetting pattern with the point source drip irrigation, the water and nitrogen transport characteristics under different drip irrigation tape disposition pattern, cotton yield, water use efficiency and soil temperature with coupling effect of water and fertilizer under mulched different numbers. By testing, observing, analyzing, and studying these problems, the results are obtained as follow.The wetting front will become circular in the surface of soil. It is obvious that vertical wetting front is bigger than horizontal as the same drop end flow and the irrigation volume. The horizontal radius and the vertical depth will increase with continuous water application. The wet speed of the horizontal direction and vertical were reduced greatly as some minutes later. The horizontal infiltration rate become high with the soil bulk density increase, and the horizontal wetting front was remarkable power function with time. The speeds of horizontal wetting front become low gradually while there different soil bulk density but the vertical fronts tend to high. In addition, NH4+-N and NO3- -N were affected by change of drop end flow and irrigation volume. As the irrigation volume was increased, the spread distance of NH4+-N was enlarged and NH4+-N concentration in the wetting zone was enhanced, and NH4+-N concentration in the horizontal direction was enhanced along with irrigation volume was increased. The increase of drop end flow influenced NH4+-N in the biggest spread distance. After dripped, NO3- -N concentration in wetting soil was increased along with drop end flow and irrigation volume were increased, little effect on NO3- -N concentration as found a radius of 16cm around point source, much NO3- -N concentration at the boundary of the wetting volume.The amount water added and the way of supplying water and fertilizer were two key important factors to affect the movement,transformation, and leach of urea-N in soil. With the drip irrigation, the fact that soil saturation pond is limited by plastic film to expand around, results in that soil water content beneath film in far more higher than that outside of the film, and the soil beneath the film is wetted in border strip. The results show that soil NO3- -N transport characteristic is similar with the soil water, influenced by the convection-dispersion equation. Distribution range of NO3- -N is similar with the soil wetted volume, its transport characteristics holds coherence with soil water, but distribution of NO3- -N has its own characteristic. Nitrate accumulated at the lateral boundary of the wetted volume, but no significant accumulation was found at the vertical boundary.Results showed that compared with"2 pipes 4 lines", water use efficiency being improved under"1 pipe 4 lines"but seed cotton yield not being significantly reduced."1 pipe 4 lines"could completely satisfy the requirement of cotton in each growth period for soil moisture. It suggested that"1 pipe 4 lines"is a practiced irrigation method which should be researched and applied in cotton producing of arid areas.The experiment for the changes of soil temperature in cotton rhizosphere indicated that film mulching could obviously increase soil temperature and form soil temperature gradients which made film mulching capable of moving soil moisture upward. During one day of cotton growth or cotton growth the temperatures of central positions below mulching film were remarkably higher than those of the lateral positions below mulching film and the temperatures in shallow soil layers increased quickly with a wide range. The perk temperatures in different soil layers appeared late as the temperature measuring positions went downward. The temperature varying ranges and measuring depths could be fitted into an exponential function in which they matched each other best at 14:00.