Effects Of Humic Acid,Dicyandiamide And Their Combination On Soil Carbon And Nitrogen Transformation,Crop Yield And Nutrient Utilization

In the current practice of agricultural production,unreasonable fertilizer input has caused problems such as deterioration of soil quality,environmental pollution,and productivity decline,etc.Improving soil quality and nutrient use efficiency by applying soil conditioners and nutrient synergist may be an effective way to solve these problems.With combined of simulation soil incubation and field plot experiment,this paper studied the effects of humic acid and dicyandiamide?DCD?on soil carbon and nitrogen content,maize/wheat yield,and nutrients use efficiency.The major results were illustrated as follows:?1?Simulation soil incubation showed that when the application rate of humic acid was more than 1.50 g/kg,soil DOC content was increased significantly by 27.50%⁴6.67%after 80 days of incubation,and soil DON content was increased by 12.94%³8.82%.Meanwhile,soil NO₃^--N and NH₄⁺-N content showed an increasing trend,but the effect on DIC content was not obvious.AHA and MHA achieved similar effects at the same application rate.These results indicated that the application of humic acid could facilitate the soil carbon pools,and increase the supply of carbon and nitrogen nutrients.?2?After three consecutive seasons of humic acid application,the DOC content in the0⁴0 cm soil layer increased by 44.39%to 61.90%compared with the control,and the DOC stability in the 0¹0 cm soil layer was improved.The application of humic acid also resulted in the increase of DON content by 13.30%²1.96%,and it was also beneficial to increase the content of NO₃^--N and NH₄⁺-N.The soil MBC and MBN was increased significantly by 41.26%⁴8.39%and 46.08%⁵2.32%,respectively.It indicated that application of humic acid could improve soil fertility.When DCD was applied alone,soil DOC,MBC and MBN contents were also higher than those in control,but lower than humic acid treatments by 12.57%³2.45%,19.41%³3.97%and 2.38%¹7.79%,respectively.However,the major effects of DCD on soil inorganic nitrogen were the reduction of NO₃^--N content and increase of NH₄⁺-N content,while there was no significant effect on DON content.It showed that the application of DCD had less effect on soil fertility than humic acid.?3?There was no obvious effects on maize yield after applying humic acid and DCD in the first season.However,the second-season wheat yield showed increase trend,and the third-season maize yield was increased by 9.17%¹8.98%significantly.After continuous application of humic acid and DCD for three seasons,the cumulative utilization efficiency of nitrogen,phosphorus,and potassium increased by 22.38%²9.90%,109.42%¹51.17%and 40.60%⁴4.09%,respectively.The agronomic efficiency and partial productivity of N,P,K fertilizer were also significantly increased.?4?The combination of humic acid and DCD was also beneficial to increase soil DOC and DIC content,and improve the stability of DOC.Simultaneously,it increased soil DON,NH₄⁺-N and NO₃^--N contents.Continuous application of humic acid and DCD also stimulated soil microbial activity,increased MBC and MBN significantly after three seasons.Compared with control,combined application of humic acid and DCD after three seasons,maize yield increased significantly by 17.29%¹8.98%.Nitrogen,phosphorus and potassium accumulation in maize was increased by 24.63%²7.43%,63.57%⁶7.05%and9.70%¹3.02%,respectively.The cumulative utilization efficiency of nitrogen,phosphorus and potassium,agronomic efficiency and partial productivity were also increased significantly.In conclusion,taking humic acid or combined it with DCD as soil amendment and nutrient synergist under a relatively higher soil fertility,the effectiveness may not necessarily obvious immediately.But after continuous application,there will be significant impact on the soil carbon and nitrogen storage and transformation,crop yield and nutrient use efficiency.