Long-Term Effects Of Application Of Organic Manure On Soil Fertility And Corn Yield Of Saline-Sodic Soil In Western Songnen Plain

The saline-sodic soil in the Songnen Plain are poorly structured,high salt content,strong alkalinity and low nutrient effectiveness,resulting in low crop yields.The application of organic manure has been an important tool for improving saline-sodic soil,which is valued and promoted both at home and abroad.Long-term application of organic manure improved soil fertility and increased crop yield.In this study,we conducted a long-term localization experiment by applying organic manure to improve saline-sodic soil,and five treatments were investigated according to the years of application of organic manure:annual manure application since 1995（M1995）,organic manure since 2000（M2000）,organic manure since 2003（M2003）,organic manure since 2006（M2006）and without manure application as a control（CK）.Soil samples were taken after autumn harvest in 2019 and 2020,respectively,to study the effects of long-term organic manure application on soil saline alkaline properties,soil nutrients,physical properties and enzyme activities,with the aim of investigating the fertility status of saline-sodic soil under long-term organic manure application measures and the mechanisms that promote corn yield improvement.The main findings were as follows:（1）Long-term application of organic manure in saline-sodic soil significantly reduced soil salinity barriers.In two consecutive years of sample analysis,the soil pH value and soil electrical conductivity（EC）were significantly decreased in the treatments with different years of manure application compared to the control,and the soil exchangeable sodium percentage（ESP）and sodium adsorption ratio(SAR_1:5)were also significantly decreased.In two consecutive years of sample analysis,at the 0-20 cm soil depth,the soil pH value decreased to 7.97 and 8.25,EC decreased to 0.14 d S·m^-1 and 0.1 d S·m^-1;soil ESP decreased to 2.52%and 0.74%,and soil SAR_1:5decreased to 0.91 mmol·L^-1 and at the 20-40 cm soil depth,the soil pH value decreased to 7.97 and8.53,EC decreased to 0.14 d S·m^-1 and 0.1 d S·m^-1,respectively;soil ESP decreased to 2.52%and1.66%,respectively,and soil SAR_1:5 decreased to 0.91 mmol·L^-1 and 0.75 mmol·L^-1.（2）Long-term application of organic manure significantly affected soil nutrients and enzyme activities in saline-sodic soil.The treatment with organic manure significantly increased the content of soil nutrients compared to the control,and the 0-20 cm soil depth was higher than the20-40 cm soil depth.In two consecutive years of sampling,at the 0-20 cm soil depth,the soil organic matter was significantly increased to 39.31 g·kg^-1 and 38.85 g·kg^-1,respectively,compared to the control.The soil organic matter in the 20-40 cm soil depth was increased to 36.24 g·kg^-1and29.61 g·kg^-1,respectively,compared to the control.The total N,P and available N,P and K in all soil depths were also significantly higher compared with the control.The application of organic manure increased the soil enzyme activities,and the soil urease,invertase,catalase and phosphatase activities were higher after manure application than in the control.（3）The application of organic manure improved the soil physical properties.At the 0-20 and20-40 cm soil depths the soil bulk density after manure application decreased compared with the treatment without organic manure,and the soil density also decreased significantly,the soil field capacity and porosity after fertilization increased significantly compared with the treatment without organic manure.At the 0-20 cm soil depth,the soil bulk density for treatment M1995 is improved well,1.08 g·cm^-3 and 1.36 g·cm^-3,respectively.Soil field capacity and porosity were the highest,with 42.35%and 37.51%for treatment M1995 and 54.90%and 49.84%for treatment M1995,respectively.At 20-40 cm soil depth,it showed improved soil moisture status and aeration and permeability after long-term manure application.The soil bulk density after manure application was significantly decreased compared to the control,at 1.38 g·cm^-3and 1.43 g·cm^-3,respectively.The field capacity reached 42.35%and 30.51%for the treatments with organic manure compared to the control.Soil porosity was also significantly improved.The lowest soil density was reached in treatment M1995 with 2.39 g·cm^-3and 2.27 g·cm^-3,respectively.（4）Corn yield increased significantly after long-term application of organic manure.In both2019 and 2020,treatment M1995 had the highest corn yield of 13,780 kg·hm^-2 and 14,690 kg·hm^-2,respectively,and corn yield was significantly higher in the treatments after organic manure application than in the control,increasing by 34.64%,39.82%,43.73%and 58.57%in 2019,respectively,compared to the control CK.43.11%,48.06%,53.36%and 69.04%respectively in2020.significant differences among all treatments（P<0.05）.Corn yield increased significantly with increasing years of organic manure application.The soil organic matter increased and bulk density decreased after long-term application of organic manure increased field capacity,improved the soil physical properties,effected soil ESP and pH,increased soil nutrients and enzyme activity,and achieved corn yield increase.In summary,long-term application of organic manure significantly decreased soil bulk density increased porosity,increased the soil field capacity.The improvement of soil physical properties promoted salt leaching,saline-alkaline properties were significantly improved,and soil fertility was enhanced.With the increase of organic manure application years,corn yield was significantly improved.Among them,the bulk density plays a major role in improving saline-sodic soil and has an important impact on the improvement and stability of corn yield.