| The rapid development of agriculture in China has been accompanied by an increase in the use of chemical fertilizers. China’s extensive use of chemical fertilizers has brought along with it many ecological and environmental problems, and the low availability of chemical fertilizers in soil has caused increasingly prominent pollution problems.Straw is an important source of biomass in agricultural production systems and contains large amounts of organic matter, nitrogen, phosphorous, potassium and micronutrients. The effective use of straw resources can play an important role in improving agricultural sustainability and productivity.Straw returning can take nutrients needed by plants present in straw and return them to the soil, thereby reducing soil nutrient depletion. This is an effective method for the direct use of straw. At present, there has been extensive research in China concerning the application of straw returning methods. However, there is a lack of research concerning the effect of different fertilization methods on forms of nitrogen and phosphorous in the soil as well as their effect on corn growth.This study focuses on arable land in the Liao River source region. Through characterization of straw properties,adsorption and leaching experiment of straw modified soil, potted experiments, and field experiments, we studied the effects of crushed straw, decomposition straw, 0.5%, 1.0%, and 2.0% straw charcoal(% charcoal/soil) on corn growth and forms of nitrogen and phosphorous in the soil under both traditional and soil testing fertilization methods.(1) SEM showed that crushed straw has a relatively coarse surface with distinctly visible fibers, while the surface of composted straw is relatively regular and ordered, and the surface of the straw charcoals is coarse with ablated pores. IR spectrometry showed that crushed straw, decomposted straw, and straw charcoal all contain phenolic hydroxyl groups, hydroxyl groups, and phosphorous-containing functional groups.(2) In adsorption simulation experiments, the addition of differently processed straws to soil showed different effects on ammonium absorption rates and amounts in the following order: straw charcoal > crushed straw > decomposition straw. As for the effect on phosphate effects and amounts, straw charcoal > crushed straw. The Freundlich model can better describe the thermodynamics of ammonium and phosphate adsorption, and adsorption dynamics all conform to pseudo-second order kinetic models.(3) The results of leaching simulation experiments showed that soils treated with differently processed straws lose nitrate more easily than ammonium through leaching, and the changes in soluble phosphorous are relatively small. The ability of differently processed straws to control the leaching of nitrogen and phosphorous from the soil are as follows: straw charcoal > crushed straw > decomposition straw. Treatment with straw charcoal can improve the ability of soils to adsorb nitrogen and phosphorous, thereby reducing nitrogen and phosphorous leaching.(4) Potted and field experiments show that in comparison to traditional fertilization methods and soil testing fertilization methods, processing with straw charcoal can increase soil levels of ammonium, nitrate, available nitrogen, and total nitrogen. This effect increased with increasing amounts of straw charcoal, with the effect of 2.0% straw charcoal being the highest. Decomposition straw and crushed straw did not have an obvious effect on ammonium, nitrate, available nitrogen, and total nitrogen levels. Differently processed straws were able to increase levels of soluble phosphorous and available nitrogen in the soil, but total soil phosphorous decreased. Field studies showed that under traditional fertilization methods, available nitrogen, ammonium, and nitrate content in the 0-20 cm soil layer was higher in fall than in spring. Under different soil fertilization methods, the 0-40 cm soil layer had more available nitrogen, ammonium, and nitrate content in mid-spring than in fall. Under soil testing fertilization methods, total nitrogen content in soil was high in 0-0.25 mm particles and total phosphorous content in soil was high in 0.25-0.5 mm and 0.5-1 mm particles.(5) Under different fertilization methods, the effects of differently processed straws on maize height, from greatest to least, were as follows: 2.0% straw charcoal > 1.0% straw charcoal > 0.5% straw charcoal > decomposition straw > crushed straw; straw charcoals were all able to increase corn leaf width. Potted experiments using traditional fertilization methods and soil testing fertilization methods showed a 4-8% improvement in kernel weight per ear and the analagous field experiments showed a 5-7% improvement. Straw charcoals were all able to improve corn productivity(p< 0.05).In summary, under soil testing fertilization methods, straw charcoal had a positive effect on maize growth and reduced nitrogen and phosphorous leaching from soil. This also revealed a mechanism by which straw charcoal can affect the distribution of nitrogen and phosphorous forms in the soil. The results of this study have significant implications for the proper use of fertilization methods and the effective control of non-point source pollution in the Liao River source region. |
