Study On Spatial Variability Of Soil Nutrients And Heavy Metals In Different Soil Local Types And Fertilization Strategy

In order to explore the spatial variability rule of main soil nutrients and heavy metals in farmland scale and to deepen the study on the technology of precision fertilization based on soils, the paper described two scaled- cultivation districts which represented waist black sand (located in Sanye Village, Zhangdian Town) and waist black clay soil (located in Guan Zhuang Village, Shengao Town) respectively as research objects, took the same experiment in 2004 as a reference, applied the methods of classical statistics, geostatistics and GIS spatial interpolation, and developed soil positioning and sampling in different farmland-scaled cultivation layers (0-20 cm) of different soil local types in 2013 and 2014. We determined the organic matter (OM), total nitrogen (TN), alkali-hydrolyzable nitrogen (AHN), available phosphorous (AP), available potassium (AK), pH and total cadmium, total chromium, total copper, total lead, total zinc content indicators, analyzed soil profile and observed and recorded the shape and quantity of earthworm of fertile fields in different soil local types, developed GIS geographic mapping, grade evaluation of soil nutrients and safety assessment of soil heavy metals, and put forward the strategies of precision fertilization based on soil local types and soil treatments. The main results were as followings:(1) The soil nutrient content of waist black clay soil was significantly higher than that of waist black sand. The content of OM, TN, AHN, AP and AK of waist black clay soil was 1.75, 1.67,1.40,1.67 and 3.71 times of waist black sand respectively, while the difference of pH value wasn’t significant. According to the spatial distribution maps of soil nutrient contour of two soil local types, the contents of soil nutrient of waist black sand were closely related to the pH, the OM, TN and AHN in the area of which pH was between 6.3 and 7.5 were significantly higher than the area of which pH was above 7.5. The fertility of waist black clay soil distributed unevenly. There were obviously high and low fertility areas, and it showed the increasing trend from southwest to northeast. According to the standard of grade evaluation of soil nutrients, the OM, TN, AHN, AP and AK of waist black sand were lack, general, general, general, extremely lack while those of waist black clay soil were extremely rich, rich, rich, extremely rich, rich.(2) The content of total cadmium, total chromium, total copper, total lead and total zinc of waist black clay soil were 1.49,1.54,1.80,1.77,1.26 times of those of waist black sand soil. According to the spatial distribution maps of heavy metals of different soil local types based on GIS spatial interpolation analysis, the distribution of heavy metals in waist black sand soil area had obvious spatial field of peak data, gradually reduced from the high value area in the form of radiation. However, the content distribution of heavy metals of samples in waist black clay soil was not obvious. According to the "Soil Environmental Quality Standard" (GB 15618-2008), high than secondary grade belongs to light pollution, high than primary standard belongs to clean and low than primary standard belongs to cleaner. The total cadmium content of samples in waist black sand soil area all belonged to light pollution; 12.0%,12.0% and 10.0% samples of total chromium, total copper and total lead were belonged to clean the rest samples were cleaner; 2.0% samples of total zinc content were belonged to light pollution,10.0% samples belonged to clean and 88.0% samples belonged to cleaner. The total cadmium content of samples in waist black clay soil area were belonged to light pollution,10.0%,8.0%,8.0% and 10.0% samples of total chromium, total copper, total lead and total zinc were belonged to clean and the rest samples were cleaner.(3) From the survey of soil profile analysis and the number of earthworm, we found that the thickness of plough horizon and subsoil of waist black sand were shallow than waist black clay soil. The colour of Waist black sand had the characteristics of shallow soil color, soft and workable soil and weak performance of preservation of moisture and fertility. We could find a large amount of earthworms which were small and red at the depth of 0-20 cm in waist black sand where the number of earthworms was 290 thousands per hectare and there were also a few earthworms at the depth of 20-40 cm. Nevertheless, waist black clay soil had the characteristics of dark soil, viscosity, weak permeability, slightly thicker topsoil and shallow ground water level. We could find a small amount of earthworms which were big and green at the depth of 0-20 cm where the number of earthworms was 100 thousands per hectare and there were no earthworm at the depth of 20-40 cm.(4) In view of the soil nutrient contents in waist black sand area and waist black clay soil area, most farmers of waist black sand area should apply nitrogen and potassium fertilizer heavily and increase the quantity of phosphatic fertilizer. Besides, they should adjust pH to neutral or acidic on the basis of increasing organic fertilizer application and implementation of straw returned. However, the emphasis of waist black clay soil was improving soil structure to improve the permeability of soil ventilation. We should reduce nitrogen, potassium and phosphatic fertilizer, or apply P and K fertilizer overyear to enhance the fertilizer efficiency. Furthermore, we could find that the two scaled-farmland areas both had the light pollution of total cadmium. To counter the problem, we should apply soil cleaning agent or use phytoremediation to improve the level of soil purification.