Distribution Characteristics Of Soil Aggregates And Their Associated Carbon,Nitrogen And Phosphorus Under Different Irrigation Modes With Reclaimed Water

Soil aggregates and their carbon,nitrogen,and phosphorus contents are the key factors affecting soil fertility.In order to reveal the effect of reclaimed water irrigation mode on soil aggregates and its distribution of carbon,nitrogen,and phosphorus,An indoor simulation experiment was conducted at the Irrigation and Drainage Laboratory.Four treatments were designed as follows:fresh water irrigation（CK）,reclaimed water irrigation（RW）,alternative irrigation of fresh water and reclaimed water（ARW）,and mixed irrigation of fresh water and reclaimed water（RW-2）.Soil samples were collected from 0–15 cm soil layers in the plots of the four treatments for measure the soil bulk density,total porosity,soil aggregate composition and its stableility,soil carbon,nitrogen,and phosphorus distribution.The main research results are as follows:（1）Repeated irrigation promoted the tidal soil,purple soil and paddy soil bulk density increased significantly.Compared with the initial bulk density（1.20 g/cm³）,the bulk density of each treatment of tidal soil,purple soil and paddy soil increased by7.11%～13.07%,9.23%～14.95%and 0.10%～4.58%.Compared with CK,RW and RW-2 showed a decrease in the bulk density of the three soils.The ARW is the opposite.However,the differences in soil bulk density among the three soil were not significant.The total porosity of the three soils was highest with RW,and the lowest with ARW.Compared with CK,the total porosity of the three soils showed a slight downward trend under ARW treatment,while the soil porosity under RW and RW-2treatments showed a different degree of increase.Compared with CK,except for the significant difference in RW treatment of tidal soil（p<0.05）,there was no significant difference in each treatment of purple soil and paddy soil.（2）Under three irrigation modes of reclaimed water,the content of mechanically stablele macroaggregates in tidal soil,purple soil,and paddy soil all reached more than 89.56%.RW reduces the mechanical stableility of tidal soil and purple soil,while ARW and RW-2 can promote it.RW-2 reduces the mechanical stableility of paddy soil,while RW and ARW is the opposite.The wet sieving significantly reduced the content of macroaggregates in the three soils（p<0.05）.The content of microaggregates increased significantly（p<0.05）.Reclaimed water irrigation reduces the water stableility of tidal soil aggregates and enhances the water stableility of purple soil.RW-2 can enhance the water stableility of paddy soil aggregates.>2 mm particle size aggregates contribute the most to soil structural stableility.The three indicators of R_0.25,GMD and MWD are consistent in the process of characterizing the stableility of soil aggregates.Under dry sieve treatment,the sensitivity of GMD to characterize the stableility of soil aggregates is weak.（3）Repeated irrigation significantly increased the total organic carbon and total nitrogen mass fractions in each treatment of tital soil and purple soil（p<0.05）,but did not change significantly under each treatment of paddy soil.The total phosphorus content of the tital soil and paddy soil treatments showed a downward trend.Except for the RW-2,which increased by 45.83%,the RW and ARW treatments decreased by32.82%and 10.29%.The organic carbon,nitrogen and phosphorus mass fractions of the three soil aggregates were significantly higher than those of the microaggregate organic carbon,nitrogen and phosphorus mass fractions（p<0.01）,and their ratios were between 8.83～29.95,8.07～52.14 and 7.94～56.12.The macroaggregate organic carbon,nitrogen and phosphorus mass fractions contributed 89.42%～97.09%,89.42%～97.09%,and 88.79%～98.27%of the soil organic carbon,nitrogen and phosphorus mass fractions respectively.Microaggregate contribution rate is only2.91%～10.58%,1.73%～11.21%and 1.73%～11.21%,respectively.（4）Correlation analysis showed that both nitrogen and total nitrogen of large aggregates were extremely significantly positively correlated with the mechanical stability and water stability of soil aggregates（p<0.01）;Phosphorus and total phosphorus at each aggregate were significantly（p<0.05）or extremely significantly（p<0.01）positively related to the mechanical and water stability of soil aggregates,Except for 2～5 mm agglomerate carbon,0.25～0.5 mm agglomerate carbon and total organic carbon have a significant positive correlation with the water stability of soil aggregates（p<0.05）,there was no obvious correlation between the carbon of other aggregates and the stability index of aggregates.The comprehensive indexes of soil physical and chemical properties are positively correlated with standardized GMD and MWD indexes.R²is 0.699 and 0.80,respectively.Principal component analysis shows that K⁺,Ca²⁺,and p H may be the main factors affecting the stability of soil aggregates.（5）Consider from improving soil structural properties and carbon,nitrogen,and phosphorus distribution.Reclaimed water irrigation promotes the accumulation of carbon and nitrogen in tital soil,reduces the water stableility of the tital soil aggregates and soil phosphorus content.Reclaimed water irrigation promotes the accumulation of carbon and nitrogen in the purple soil,and enhances the water stableility of the purple soil aggregates.Irrigation water on purple soil is more sui Tablele.RW-2 can be used for irrigating paddy soil with reclaimed water.