Study On NPK Distribution Patterns In Purple Soil Under Drip Fertigation

Under the pressure of soil resources shortage and environment deterioration, drip fertigation technology has been accepted by many scholars for its superiority of economy water and fertilization as well as high production and efficiency. It has been widely applied by some areas both domestic and overseas. But the investigation of fertilizer movement and distribution pattern in soil under drip fertigation condition is very restricted especially research data based on soil in the south. Most terrain in southwest of China is hilly country for that agricultural development is seriously limited by seasonal drought. Therefore, spreading drip fertigation technology to southwest has great significance in solving irrigation problem in dry season and increaseing grain production. For purpose of exploring the suitable fertigation mode in this region, purple soil was selected as the study object in this paper. The simulative soil columns in the laboratory were used to investigate the migration behavior of NO3--N, NH4+-N, available phosphate, available potassium, available Ca2+and Mg2+in different soil depth, and the effect of soil texture, fertigation concentration and fertigation method on nutrient distribution pattern were analyzed.The main conclusions were draw as following:(1) NO3--N was easy to transport with water after fertigation, which could almost reach the soil wetting front synchronous. With droplets flow to fertigate, the vertical movement of NO3--N in soil profile was found more distinct than the radial movement; a large number of NO3--N accumulated in the bottom of soil column and it showed significant signs of spreading down sequentially. Migration ability of NO3--N varied from soil textures and the order was sandy loam＞clay loam＞loamy clay. With the fertigation concentration increased, NO3--N content in all soil layer increased and more NO3--N accumulated in deeper soil layer. Intermittent schedule of fertigaiton2h every two days could better achieve economy water and fertilization.(2) Under the condition of drip fertigation, NH4+-N and K+showed the similar distribution regularity that both nutrients mainly gathered in the surface and hard to move to the subsoil layer. Fertigation with NH4+-N, the distribution area in sandy loam was r=0-7cm, d=0-7.5cm, in clay loam and loamy clay was r=0-7cm, d=0-3.5cm respectively. The migration ability showed sandy loam＞clay loam＞loamy clay. NH4+-N content in the soil area of r=3～8cm、d=0～7.5cm in clay loam and loamy clay significantly increased by doubling fertigation concentration, but it had no significant contribution to vertical movement of NH4+-N. Fertigation with potassium, the migration quantity of available potassium in sandy loam and clay loam was significantly greater than that in loamy clay with the radial distance increased from Ocm to4cm. Increasing fertigation concentration induced the greatest increase of adsorption quantity of available potassium in loamy clay around emitter, it could also benefit to the radial movement of available potassium in0～10cm topsoil layer to some extent.(3) Under drip fertigation condition, the transport ability of available phosphate was greater than NH4+-N but less than NO3--N due to the matrix flow and adsorption. With droplets flow fertigation, available phosphate accumulated in soil surface around the emitter and its content decreased with the increase of soil depth and vertical distance. The radial migration distance of available phosphate in three soil was0～10cm and the transportation ability showed sandy loam＞clay loam＞loamy clay. When fertigation concentration was higher, the vertical migration distance of available phosphate was20cm in sandy loam and clay loam,10cm in loamy clay, respectively. As fertigation concentration doubled, content of available phosphate in sandy loam and clay loam with soil area of r=0～8cm, d=0～11.5cm increased by2-3times, and the content of available phosphate in loamy clay of r=0～8cm, d=0-3.5cm also increased2-3times. Fertigation mode had no distinct influence on the distribution of available phosphate.(4) Fertigation with compound fertilizer of PK, available Ca2+and Mg2+transfered along with moisture movement. As the occurrence of drip irrigation, Ca2+and Mg2+formatted a desalination zone of r=0-5cm, d-0-3.5cm, and this area in sandy loam soil slightly extended in vertical direction. Dripping with higher concentration of PK had better effect on leaching of Ca2+and Mg2+in desalination zone.(5) Spreading fertigation in experimental purple soil of southwest, many factors such as soil texture and migration characteristics of nutrients should be considered. For NO3--N, lower concentration and intermittent schedule disposal are preferred, and the distance between emitter is30-50cm; in coarse soil, the fertigation volume should be controlled to maintain capillary ascension of moisture to reduce nutrient loss.(6) Fertigation with ammonium nitrogen and potassium, it’s suggested that burying the emitter around crop root and adopting the subsurface drip irrigation. The design of distance between emitters is based on the root distribution of crop, and making sure that the intensity of emitter is greater than that of NO3--N. Fertigating with lower concentration of fertilizer can not only reduce adsorption of NH4+-N and K+by soil, but also directly provide nutrients to crops. For phosphate, subsurface drip irrigation should be adopted and bury the emitter10cm below the soil surface. The emitter distance should be greater than that of NH4+-N.