Study On Salt Characteristics Of Secondary Salinized Soil And Salt Reduction Effect Of Carbon Regulator

The objective of this thesis was to solve the problem of the secondary salinization in greeenhouse vegetable soil.Samples were taken from Yi Jia Kang Ecological Agriculture Co.,Ltd.of Wuxi,followed by analyses of soil properties,and indoor cultivation of Chinese cabbage seedlings,to study the salinity characteristics and feasibility of lowering soil salt concentration using carbon regulator(Straw + Agent).The main results are as following:(1)The greenhouse soil was characterized by eutrophication,high salt concentration,soil acidification,and nutrient imbalance caused by improper fertilization.The soil salt composition was composed mainly of Ca2+ and NO3-,accounting for 55.3%and 58.7%of the total cations and anions,14%and 44%of total salts contents respectively.Soil salinity(conductivity or total salts)had a significant correlation with total nitrogen,nitrate nitrogen,ammonium nitrogen(p<0.01),but no significant correlation with soil available phosphorus,available potassium,or organic matter.The increase of NO3--N is the direct cause of the increase of total salt content in soil,while the overuse organic fertilizers,nitrogen fertilizers,NPK compound fertilizers,and nitrogen-containing water soluble fertilizers is the fundamental reason of secondary salinization.(2)Adding carbon regulator could significantly reduce soil soluble salt.The results showed that,soil conductivity in all treatments with the addition of carbon regulator declined,compared with the control,soils from 32g/kg T4 decreased the most(by 45%)in salt content.Total salt,correlated with soil conductivity,also decreased significantly after carbon regulator treatment.Similarly,total salt content in 32g/kg T4 decreased by 38.10%.NO3-decreased the most among all salt ions,while the other three aions showed an increasing tendency.Ca2+content declined the most among all cations,followed by Mg2+,wlhile K+ content increased,and Na+ increased slightly in treatments with carbon regulator.(3)The addition of carbon regulators showed significant effects on soil organic nitrogen.The results showed that the content of NO3-decreased gradually while the organic nitrogen increased significantly after carbon regulator addition.Soil organic nitrogen in 32g/kg T4 increased by 106%.The contents of ammonia and amino acid nitrogen increased first and then decreased,with the highest content detected in 24g/kg T3 which was 1.4 and 1.72 times of those of CK respectively.T4 decreased slightly,amino sugar nitrogen was not obviously increased,unidentified organic nitrogen increased significantly with the addition of carbon regulating agent,in consistent with the change of total organic nitrogen.(4)Soil physicochemical properties improved significantly after carbon agent addition.The pH value increased,which could improve situation of soil acidification caused by long-term use of nitrogen fertilizer.The field water holding capacity,improve the ventilation,the water retention capacity of the soil,soil nutrient structure,and the overall soil properties.(5)The experiment of Pakchoi with soil pretreated with carbon regulators showed that the addition of carbon regulator could significantly increase germination rate and biomass,promoting the growth and development of roots.The application of carbon regulator in treatment 24g/kg T3 is optimal with the consideration of comprehensive economic benefits.