The Effect Of Fertilization On Soil Mobile Colloids

Soil fertility is central to the development of modern agriculture and sustainable utilization of soil resources, which is closely related to the content of soil organic matter (SOM). As the most active component of soils, soil mobile colloids have an important influence on the stability and accumulation of SOM. The objectives of this study were1) to investigate the relationship between noncrystalline nanominerals in soil mobile colloids and the content of SOM by studying soils from long-term location experiment, short-term location experiment, natural and farmland, using the combination of solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD) spectroscopy and high resolution transmission electron microscopy (HRTEM) and2) to explore the mechanism of SOM sequestration. The main conclusions are listed as follows.1) After20years fertilization in the long-term location experiment in Hunan Province, the soil pH followed the order:HNPKS<HNPK<HN<HCK<HMNPK<HM, suggesting that organic fertilization could improve the soil pH, while chemical fertilization decreased the soil pH. Meanwhile, the content of SOM from all the six treatments increased, with the highest in HM treatment, followed by HMNPK, showing that organic fertilization (including HM and HMNPK) was the main strategy to improve soil fertility for red soil. Compared to the original soil, contents of total nitrogen in HCK, HN, HNPK, HNPKS four treatments were reduced, while increased in HM and HMNPK. It was found that contents of total nitrogen and organic matter from topsoil were correlation significantly (p<0.001). Contents of available phosphorus in HCK and HN treatments decreased mostly, while in HM and HMNPK increased mostly, followed by HNPK. Contents of potassium in soil were related to the amount of potash fertilizer inputted in soil.2) The basic characteristics of the soil among different fertilizer treatments from short-term location experiment had no significant difference (p>0.05). After agricultural production activities, the soil quantity of granite parent material declined, while it was improved in Quaternary red clay farmland soil.3) The content of noncrystalline Al nanominerals in the soil was determined by acid oxalic acid and sodium pyrophosphate extraction method. It was found that the content of noncrystalline Al nanominerals in the soil was positively correlated with soil organic matter content (r2=0.9018).4) The results from XRD, NMR and HRTEM showed that soil mobile colloids from both HM and HMNPK treatment in the long-term location experiment in Hunan Province contained a large amount of noncrystalline nanominerals, suggesting that organic fertilizer could promote the transformation of crystalline minerals to noncrystalline nanominerals. Main elements in noncrystalline nanominerals were Si and Al. Thereof, the chemical shifts of Si and AL were located at91ppm(Q4(6A1)) and lppm (ⅣAl), respectively. However, crystalline minerals were predominant in Fe, with a small amount of Si and Al. In crystalline minerals, the chemical shift of Si was located at-100～-110ppm, belonging to feldspathic silicon.5) In the shor-term location experiment, soil mobile colloids in Jintan were presented in CK and MNPK treatments except for NPK treatment. However, soil mobile colloids in Zhangjiagang could not markedly indicated the existence of crystal mineral to noncrystalline nanominerals.6) As for farmland soils from Granite and Quaternary red clay, crystalline Fe minerals were dominant, while noncrystalline Al nanominerals were minor. When compared with the natural soil and the farmland soil from granite parent material, it was found that agricultural production activities activated Fe element and then gradually reduced its content. However, the difference of Al and Fe was minor between the natural soil and the farmland soil of Quaternary red clay parent material. Interestingly, Contrast to the natural soil and farmland soil of Purple sandstone and shale parent material, human activities transferred soil crystal mineral to noncrystalline nanominerals.