| Orchard is a special ecological environment with high output, large uptake intensity of soilnutrients and moisture, frequent management activities and large consumption of fertilizers andpesticides. Therefore, orchard soil is characterized by has the highly evolved dynamics andenvironmental conditions. In this study, with the study object of soil in a representativeapple-pear Orchard in Yanbian Area, we explored the influences of profiles, slope positions,cultivation years, planting space utilization ways on soil fertility indicators and humus status andobtained the evolution rule of orchard soil humus and fertility factors. The evolution rules areconcluded as follows:1) Soil fertility evolution rule of the apple-pear orchardApple-pear orchard profile soil conditions is characterized by acidic pH, significant changesin organic matters total nitrogen content, and total phosphorus content in the AB Horizon andhigh levels of nitrogen and rapidly available phosphorus. The density of the AB Horizon is1.35g/cm3at least. The natural moisture content in the AB Horizon is the lowest and field waterholding capacity is high. The microaggregate structure (0.25to0.05mm) is the main soilmicro-structure. The fractal dimension of soil particles is the least in the AB Horizon (2.6136).Soil pH in apple-pear orchard decreased gradually with cultivation years. Soil organic mattercontent declined firstly and then gradually increased with the annual average growth rate of0.43%. Total nitrogen content and total phosphorus content annually increased. The contents ofalkali-hydrolysable nitrogen, rapidly available potassium, and rapidly available phosphorusincreased year by year. The density decreased year by year with an average annual decrease of0.23%, while porosity and pore ratio showed the opposite change trend. Hygroscopic watercontent, heavy clay soil content, and clay particle content gradually decreased. The contents oflarge aggregates (>10mm) and medium aggregates (0.25~10mm) increased year by year.Fractal dimension decreased year by year. MWD and GMD increased gradually with theaverage annual growth rate of0.76%and1.10%, respectively. The content of water-stableaggregates increased year by year and destruction rate and density gradually decreased year byyear. 2) Combined humus distribution features of apple-pear orchard soilIn apple-pear orchard profile soil, the content of loosely combined humus in the ABHorizon decreased significantly. In A1Horizon, surface salt accumulation was fierce. Thecontent of stably combined humus decreased with soil depth and FA content showed the high-low-high trend. HA content decreased with soil depth. The content of tightly combined humusdecreased with soil depth. The content of loosely combined humus in the A1Horizon washigher than that in the AB Horizon; the content of stably combined humus in the A1Horizonwas lower than that in the AB Horizon. The loose/tight ratio in the A1Horizon in orchard soilwas higher than that in the A1Horizon in uncultivated soil; the loose/tight ratio in the ABHorizon in orchard soil was lower than that in the A1Horizon in uncultivated soil. In differentslope positions, the contents of loosely combined humus, stably combined humus, and tightlycombined humus were the highest in the middle slope. The contents of FA and HA as well asH/F ratio in loosely combined humus and stably combined humus showed the same decreasingcontent trend: middle slope, lower slope, and upper slope. Total organic carbon content in soilaggregates and aggregates (>0.25mm) showed the decreasing content trend: middle slope,lower slope, and upper slope; total organic carbon content in aggregates (<0.25mm) showed theincreasing content trend: middle slope, lower slope, and upper slope. The content of total soilhumus as well as the content of loosely combined humus and stably combined humus increasedwith cultivation years, while the content of tightly combined humus decreased with cultivationyears. The average annual growth rates of loosely combined humus and stably combined humuswere respectively1.09%and0.63%. The contents of FA and HA as well as H/F ratio wereincreased year by year. HA content was lower than FA content in loosely combined humus,indicating that FA was the dominant organic acid. HA content was higher than FA content instably combined humus, indicating that HA was the dominant organic acid. The contents ofloosely combined humus and stably combined humus increased year by year and the content oftightly combined humus was decreased year by year. After60years of cultivation, the looselycombined humus and the tightly combined humus were the dominant components in soil humus.3) Elemental composition, structure and functional group characteristics of soil humus inapple-pear orchardIn FA and HA in loosely combined humus, in the contents of N and C content increasedyear by year and the contents of H and O content decreased year by year. In HA in looselycombined humus, the contents of N, C, and H were lower than those in FA. The atomic ratio ofN/C increased year by year and the atomic ratios of H/C and O/C decreased year by year. The content variation trends of N, C, H, and O in stably combined humus were consistent with thosein loosely combined humus. The contents of N, C, and O in stably combined humus were higherthan those in loosely combined humus. The humification degree in stably combined humus washigher than that in the stably combined humus. The O content in loosely combined humus washigher than that in stably combined humus. The E4/E6ratio and hue coefficient ΔlgK in HA inthe loosely combined humus and stably combined humus increased year by year, and the E4/E6ratio in the loosely combined humus were higher than those in stably combined humus. Looselycombined humus showed the significant specific HA peaks in UV-Vis spectra. And the specificHA peak density of loosely combined humus and stably combined humus was decreased year byyear. The absorption density of specific HA peaks in IR spectra increased year by year andreached its maximum value after60years of cultivation. The2920/1720ratio of looselycombined humus increased year by year and that in the stably combined humus increased firstlyand then decreased. The extension of aliphatic functional groups in stably combined humus wasweaker than that in loosely combined humus and the quantity of functional groups increasedslightly. The contents of aromatic compounds, amide, and amino acids in stably combinedhumus were higher than those in loosely combined humus and the aromatization degreeincreased year by year. FA absorption intensity increased year by year and reached its maximumvalue after60years. The2920/1720ratio decreased year by year. In differential thermal analysisof HA in loosely combined humus and stably combined humus, peak temperature of lowtemperature, medium temperature and high temperature ranges increased year by year and theratio of high temperature to medium temperature increased year by year. The ratio of hightemperature to medium temperature in stably combined humus was higher than that in looselycombined humus. Total reaction heat of FA in loosely combined humus and stably combinedhumus increased year by year. Total reaction heat of FA in stably combined humus was lowerthan that in loosely combined humus.Solid-state NMR analysis of humus showed that alkyl carbon and alkoxy carboncomponents were the main structure in HA in loosely combined humus, indicating strongaliphatic property, simple structure, and low aromatization degree. The contents of alkyl carbonand alkoxy carbon showed the gradually decreasing trend from the20thyear to the40thyear andthe60thyear, while the contents of aromatic carbon and carboxyl carbon showed the contrarytrend. The relative content of aliphatic carbon declined year by year. The aromatization degree(fa) of HA in loosely and stably combined humus increased year by year with an average annualincrease ratio of0.95%and0.60%, respectively. The alkoxy carbon content in stably combined humus was lower than that in loosely combined humus. The contents of alkyl carbon andaromatic carbon in stably combined humus were higher than those in loosely combined humus.And the sum of the contents of alkyl carbon and aromatic carbon in stably combined humus wasless than those in loosely combined humus and the aromatization degree in in stably combinedhumus was largely highly than those in loosely combined humus. The aliphatic property of HAin loosely combined humus decreased year by year and the aromatization degree increased yearby year. The compound structure in loosely combined humus became complex year by year andthe molecular weight increased year by year. Annual change ratios of various functional groupsand the aromatization degree in loosely combined humus were higher than those in stablycombined humus.In loosely combined humus, the contents of total acid groups, carboxyl group, and phenolichydroxyl group increased year by year and the contents of total hydroxyl group and alcoholichydroxyl group decreased year by year. In stably combined humus, the contents of total acidgroups and carboxyl groups increased year by year and the content of phenolic hydroxyl groupdecreased year by year. In FA in loosely combined humus, the contents of total acid groups,carboxyl group, total hydroxyl group, phenolic hydroxyl group, and alcoholic hydroxyl groupincreased year by year and the ratio of carboxyl group/phenol hydroxyl group decreased year byyear. In FA in stably combined humus, the contents of total acid groups, carboxyl group, andtotal hydroxyl group increased year by year and the content of alcoholic hydroxyl groupdecreased year by year. The total acid groups, carboxyl group, hydroxyl group and total phenolichydroxyl group were the dominant compounds in stably combined humus and alcoholichydroxyl group was the dominant compound in loosely combined humus. The total acid groups,carboxyl group, hydroxyl group, and alcohol hydroxyl group were mainly distributed in fulvicacid and the total hydroxyl group and phenolic hydroxyl group were mainly distributed in humicacid.4) Humus distribution features in soils in the planting spacing with various utilizationwaysIn soils in the planting spacing with various utilization ways, The total amount of humus,loosely combined humus content, and stably combined humus content showed the decreasingtrend in soils in the planting spacing with the following various utilization ways: grass> soiltillage> potato> initial status. For the planting spacing utilization way of grass, relative contentsof loosely combined humus and stably combined humus increased and that of tightly humusdecreased. The loose/tight ratio was the highest for the planting spacing utilization way of grass. |
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