Effects Of Reclamation Methods On The Quality Of Cultivated Land In Black Soil Farmland

The black soil area of Northeast China is the largest food production base in China.It has only one hundred years of history of reclamation.Normally,the stability of organic matter is in a period of rapid change in the first 10 years of reclamation.In order to find out the root cause of the decline in the quality of black soil farmland,this research relies on The long-term positioning test platform of the Hailun Ecological Experiment Station of the Chinese Academy of Sciences.From October 2011 to October 2019,1 control grassland and 3reclaimed corn fields were set up,namely natural grassland(ZR),horizontal sowing reclamation(PB),and ridge reclamation(NS),horizontal ridge reclamation(WE),the field size is 3m×4m,each treatment is repeated 3 times,arranged randomly,and the planting and farming methods are the same as the local traditional farming methods.The soil samples were collected from the corn harvest season in October each year,using the "S" 5-point sampling method,using 1 kg of 0-20 cm plow layer soil,dried indoors,and removing debris for use.Indoor agglomerates are sieved with a wet sieve,ultrasonic disperser is used for density grouping,Fourier infrared spectrometer is used to measure the infrared spectrum of organic matter,and organic matter,exchangeable sodium,potassium,cation exchange capacity,and ammonium nitrogen are measured in the laboratory.The main results are as follows:(1)Reclamation makes the soil large aggregates(>2mm)broken,sticky and powder particles(<0.053mm)agglomerate,and the stability of the aggregates is enhancedBefore reclamation,grassland aggregates were mainly concentrated in the two dominant particle sizes of 0.5?1mm and <0.053 mm.After reclamation,the soil aggregates gradually took 0.5?1mm and 0.25?0.5mm as the dominant particle size,with a viscosity of <0.053 mm.The proportion of powder particles is decreasing year by year,while the proportion of four particle size aggregates> 0.25 mm is increasing year by year.By 2019,the three reclamation processes have increased the number of four-size agglomerates> 0.25 mm to varying degrees.Among them,the 0.25?0.5mm agglomerates of flat sowing reclamation have increased the most.At the same time,after reclamation,the number of powder and clay particles of<0.053 mm has been increased.The content decreases year by year compared with before reclamation.The decline in flat sowing reclamation is the largest,and the decline in ridge reclamation is the smallest.The change trend of the number of 0.053?0.25 mm aggregates varies with different reclamation methods,and the proportion of aggregates of this size during the flat sowing reclamation process Decrease,while the proportion of the size aggregates increased under the reclamation along the ridge and the reclamation across the ridge.Correlation analysis shows that the changes in the proportions of the three size aggregates of1?2mm,0.25?0.5mm and <0.053 mm are the most important factors affecting soil water stability.In terms of soil stability,both horizontal sowing and horizontal ridge reclamation are higher than those along ridge reclamation.(2)Reclamation significantly reduces soil organic matter content and organic matter reservesCompared with flat sowing and ridge reclamation,horizontal ridge reclamation has the best protection for soil organic matter loss,and ridge reclamation accelerates the loss of soil organic matter.The organic matter of various soil aggregates in different reclamation processes continues to decrease with the advancement of the reclamation period,and the decline is different.Among them,the organic matter of >2mm,1?2mm aggregates decreases by more than 20%,and the organic matter of 0.053?0.25 mm,<0.053 mm aggregates Organic matter decreased within 10%.Except for powders and clay particles of <0.053 mm,the decline of organic matter in the remaining aggregates is lower than that of non-ridged reclamation.In ridged reclamation,the decline rate of straight ridge reclamation is higher than that of horizontal ridge.On the whole,the reduction of organic matter by reclamation along ridges is the least,and its protection of organic matter is mainly reflected in aggregates >0.5mm.(3)Reclamation simplifies the structure of organic matter and reduces stabilityAfter the grassland was reclaimed into farmland,the content of polysaccharide C-O in the whole soil increased,the content of aromatic C=C decreased,and the stability of organic matter decreased.>0.25 mm agglomerates have the most obvious changes in the structure of organic matter.Among them,the content of alcohol-phenol-OH and aliphatic-CH increases,the content of carbonyl C=O and aromatic C=C decreases,the CO content of polysaccharides slightly decreases,and the change range is not obvious.The stability is significantly reduced.The content of alcohol-phenol-OH and aromatic C=C of LF and OF in each density component decreased,while the trend of polysaccharide CO was opposite.After reclamation,the organic matter structure stability of MF was in a stable state,while the organic matter stability of LF and OF components reduce.Principal component analysis showed that the main effects of reclamation were>0.053 mm agglomerates,LF and OF organic matter structure,and the greatest impact on aromatic C=C and polysaccharide C-O.In general,after reclamation,the stable aromatic substances in the organic matter of the farmland soil decrease,the active polysaccharides increase,and the structure tends to be simplified,resulting in a decrease in the stability of the chemical structure of the black soil organic matter.(4)Reclamation reduces the level of farmland fertility,The horizontal ridge has the highest land reclamation capacityCompared with the natural control,the reclamation significantly reduced the soil exchangeable sodium,potassium,cation exchange capacity and ammonium nitrogen content.The cation exchange capacity of the soil was the lowest among the three reclamation processes,and the soil cation exchange was the highest in the horizontal ridge reclamation process.And the content of ammonium nitrogen in the soil is equivalent to that of flat sowing,which is significantly higher than that of reclamation along ridges,indicating that reclamation along ridges has the greatest damage to the soil fertility level.Using multiple linear regression and membership function model to calculate the minimum data set soil tillage index,to evaluate the soil quality,it is found that,compared with the local natural grassland,the average minimum data set tillage index of farmland is 0.270 after 9 years of reclamation,which belongs to the category of low-yield fields.Among them,the horizontal ridge reclaimed land has the highest level of fertility,and the smallest data set tillage index is 0.347,reaching the level of middle-yield fields.The correlation analysis between the minimum data set tillage index and the aggregate structure stability index and the full data set tillage index found that the smallest data set tillage index can be used to evaluate the level of cultivated farmland fertility.In summary,reclamation reduces the soil micro-aggregates,increases the overall stability of the soil,and increases the polysaccharides in the organic matter structure,resulting in a decrease in structural stability and a decrease in organic matter content.In farmland reclamation,horizontal ridge reclamation has high soil stability,better protection of organic matter,and the highest soil fertility,which is suitable for reclamation of sloping land in the black soil area of Northeast China.