Study On The Effect Of Natural Succession Process On Soil Aggregates And Forage Characteristics In Abandoned Land

To clarify the effects of natural succession on the stability of soil aggregates and nutrient characteristics of degraded meadow soils,a total of five natural succession sites were set up in Zalut Banner,Inner Mongolia from 2017 to 2020,including overgrazing(F),alfalfa fallow land(M),oat fallow land(Y),alfalfa-oat mixed fallow land(H)and sealing(G),to study the stability of soil aggregates,nutrient characteristics and effects on forage The effects of soil aggregation stability,nutrient characteristics and forage diversity and quality were investigated.The soil stability characteristics were investigated by dry sieving and wet sieving,and the forage characteristics in the study area were investigated by the sample method,and the effects of natural succession on the distribution of soil agglomerates of different grain sizes,the stability of agglomerates,the content of different nutrients in each grain size,the importance value,richness,diversity,uniformity,forage nutrients and forage quality were analyzed.The results showed that.(1)Soil agglomerate distribution: natural succession process can significantly enhance the content of large soil agglomerates in the shallow layer.Soil agglomerate content increases with decreasing particle size and then decreases.The content of agglomerates in each particle size in the same site is significantly different,with >0.25 mm agglomerates as the main particle size in the natural succession sample of closed and abandoned land,and <0.053 mm particle size agglomerates are the least than other particle sizes.The soil is disturbed by tillage and other anthropogenic factors,and land use practices influence the predominance of >2 mm and 0.053-0.25 mm size agglomerates.Because the soil is less disturbed by sealing measures,the content of water-stable large agglomerates is the highest in different soil sealing samples,and the content of >2 mm agglomerates decreases significantly with the depth of soil layer.(2)Soil agglomerate stability: with the natural succession process,there is a tendency for the soil small size agglomerates to change to large size agglomerates,among which the soil stability of the sealed sample site is the highest.The mean weight diameter(MWD)and geometric mean diameter(GMD)values of the sealed sample sites were significantly higher than those of the natural succession sample sites and overgrazed sample sites.The natural succession process has a protective effect on the stability of soil aggregates,of which sealing is the best measure.The MWD and GMD of soil agglomerates tend to decrease significantly with the depth of the soil layer,indicating that natural succession acts firstly on the transition from microagglomerates to large agglomerates in the topsoil layer.(3)Nutrient content of soil aggregates: Natural succession has the effect of improving organic carbon and nitrogen in the top soil layer,and the sealing measures have the greatest effect of improving soil organic carbon and nitrogen.There was no significant difference(P > 0.05)in total phosphorus content among the natural succession sites,and the lowest total potassium content was found in each soil layer M site.The natural succession process could increase the effective phosphorus content of the soil.The content of fast-acting potassium tended to decrease significantly with the depth of soil layer,and the highest content of fast-acting potassium was found in the sealed sample site,and the highest content of fast-acting potassium was found in the Y sample site.(4)Forage diversity index: The natural succession process can effectively improve the forage diversity index.The Simpson dominance index of 0.84 and Shannon-Wiener diversity index of 2.03 were significantly greater than those of other natural succession sites(P < 0.05);the species richness index of 1.48 was the highest in the enclosed sites,and was significantly greater than those of natural succession and overgrazed sites(P < 0.05);the community evenness Pielou index of 0.89 was the highest in the enclosed sites.The highest Pielou index was 0.89,and there was no significant difference between the Pielou index of community evenness in the natural succession sample sites(P>0.05).(5)Forage nutrients: natural succession process had an effect on the N,P and K contents of forage.The natural succession process had a significant effect on forage K content(P < 0.05),with the highest K content in sample site H,which was significantly different from other natural succession sample sites in terms of forage K content(P < 0.05),while the natural succession process did not have a significant effect on forage P content(P > 0.05)and the natural succession process did not have a significant effect on forage N content(P > 0.05).(6)Forage quality: The natural succession process can effectively improve the nutritional quality and forage value of forage.There was no significant difference(P>0.05)in crude fat content of forage in each natural succession site,among which the highest crude fat content of forage in site H was 0.99%;the crude protein content of forage was significantly different(P < 0.05),and the highest crude protein content of forage in site M was 12.66%;the neutral detergent fiber content was significantly different(P < 0.05),and the highest neutral detergent fiber content of forage in site Y was 60.06%;the acid detergent fiber content of forage was significantly different(P<0.05).The difference between the effects of different natural succession processes on forage yield was significant(P< 0.05),and the forage yield showed a decreasing trend with the influence of human and animal,among which the forage yield of the closed sample was significantly higher than that of other natural succession samples(P < 0.05).The effect of different natural succession processes on forage ash content was significantly different(P < 0.05),and the highest ash content was found in the sealed sample plots.