| Weibei region in Shaanxi province has been identified as one of two apple's eugenicsdue to its unique climate and natural ecological conditions. Since the adjustment ofagricultural structure adjustment, fruit production has been started to large scale developmentin great area, which greatly promote the improvement of local ecological landscape andrapidly the development of economy. With the increase of planting age, a series of changes ofsoil quality have taken place in orchards. Deficiency diseases of apple tree increase day byday and become more and more serious. The apple trees appear weakness and even death.Fruit yield is unstable, fruit quality is lower, fruit type is bad, and storage property isdecreased. In orchards, the disease and insect pests occur frequently, and the used amount ofpesticide increase, the used amount of organic fertilizer is less and less, even not application,the application amount of chemical fertilizer is significantly increased, these lead to thedecrease of soil physical, chemical and biological character and soil resistance. The changingof orchard soil quality has seriously impact on the quality and yield of fruit, also impact onthe income and productive enthusiasm of fruit grower. Research on the orchard soil qualityevolution is the urgent needs to explore the sustainable development of orchard industry.There are rich achievements in the orchard soil physical quality and nutrient condition, but thestudies of soil organic carbon are only confined to the surface, so there are still lack of theresearch on the content and composition of soil organic matter (SOM) and the variationcharacteristics of soil enzyme activity in soil profile under long-term planting fruit conditions.Orchards in Weibei arid area are succession of farmlands. Vegetation succession has brought aseries of changes to soil tillage management. There are seldom reports about evolution of soilbiological quality with indexes of organic matter and enzyme activity in those progresses.Analysis on the time and space evolution law of orchard soil organic carbon (SOC) andenzyme activity are of extremely significant scientific implication to comprehensiveevaluation of orchard soil quality and further reveal the ecological succession law.This thesis is selected different ages of apple orchards in Heritage Site Park as theresearch object, the natural conditions, planting scale and history of these orchards canrepresent the characteristics of Weibei. SOC content, labile organic carbon (LOC) content,SOC density, carbon pool management index (CPMI) and enzyme activity in different ages of orchards are measured by using "space replacing time" method. And their relationships wereanalysis on to explore the correlation between the orchard soil quality evolution and appletrees senescence, and to provide theoretical basis of orchard soil management model. Themain results are as follows:1. The average content of SOM in Weibei orchards was10.12~16.57g/kg. It belongedto medium and low level according to the grading standards of SOC content of apple orchardsin Shandong Province and soil fertility for green food producing area. Analysis on the averagecontent of SOC in time scale, the highest SOC content was>15a orchards, the second was10~15a orchards, the lowest was <10a orchards. The SOC content increased with orchard ageincreased, it increased at a significant level only the planting age was above15years. TheSOC content decreased with soil depth increased, and it significantly increased with orchardage increased in0-10cm and20-40cm layers. So the SOC showed a space effect in orchards.The variation range of SOC density was0.95~1.92kg/m~2in0-100cm layers. The significantdifferences of SOC density was also appeared at large time scale. The SOC density of surface0-20cm layer occupied the absolute share of whole SOC density of0-100cm layers. TheSOC density in profiles developed towards evenness with the orchards age increased.2. The SOC composition was changed by vegetation succession process in Weibei aridarea. In0-40cm layers, LOC content of orchard soil was higher than farmland, and was lowerthan farmland in40-100cm layers. It was the same to the evolution of LOC accounting fortotal organic carbon (TOC) ratio. The content of LOC and TOC in orchards both decreasedwith soil depth increased. The SOC composition changed significantly in10-20cm layer, andthe evolution of LOC accounting for TOC was (10~15a orchard)>(>15a orchard)>(<10aorchard). It was different to the evolution of LOC content and TOC content. In10-20cm layerof10~15a orchard, the ratio of soil non-labile organic carbon (NLOC) was lower than in otherlayers, so the quality of SOC in this layer was higher. In0-40cm layer, the activity of carbonpool (A) and activity index (AI) in orchard soil were both higher than farmland, it proved thechanging of SOC composition in orchard. The A and AI in orchard soil both were lower thanfarmland in40-100cm layer. The CPMI increased with orchard age increased in0-40cmlayers, and was higher than farmland in surface0-20cm layer, so the soil in this layerdeveloped toward a positive direction during the period of planting fruit. The CPMI decreasedwith orchard age increase in40-60cm layer, it also increased firstly and then decreased withorchard age increased in60-100cm layers. CPMI in40-100cm layers were all lower thanfarmland, this showed that orchard soil quality was declined in deep layers. All the analysisshowed that LOC in orchards increased in0-40cm layers, and significantly decreased below40cm layers. The evolution of SOC composition in profiles showed that the orchard soil quality was reduced.3. There were obvious differences among soil enzymes activity in orchards. Orchardsoil urease activity and alkaline phosphatase activity both deceased with soil depth increased,the evolution of catalase activity was not obvious. Soil urease activity in0-20cm layer wassignificantly higher than this in20-100cm layers, and in20-100cm layers the changing rangeof urease activity was finite. The orchard soil urease activity was higher than farmland in0-20cm layer, and was slightly lower than farmland below20cm layers. Soil alkalinephosphatase activity was showed a relatively higher trend in0-40cm layer, and was lowerthan farmland. The maximum value of catalase activity was in40-60cm layer, catalaseactivity was higher than farmland. Urease activity and alkaline phosphatase activity deceasedgradually with orchard age increased in0-20cm layer, and the changing of their activitieswere not obvious below20cm layers. Three soil enzymes activities in surface decreased withthe planting age increased, this proved that soil biological quality had a degradation trend.The catalase activity decreased and the capacity of soil detoxification diminished, these wouldlead to toxins accumulation in orchard soil, and threaten to the growth of apple tree roots.4. The correlation study of orchard SOC and enzymes activities showed that the SOC,LOC and CPMI have a significant(P<0.05)or highly significant(P<0.01) correlation to soilurease, catalase and alkaline phosphatase activities. Soil enzymes can promote the conversionof SOC, and improving orchard soil fertility can significantly increase soil enzyme activity.Soil enzyme activity can objectively reflect the changes of soil fertility status causing byenvironmental or management factors. There was a highly significant correlation among TOC,LOC, NLOC and CPMI. There also was a highly significant correlation among soil urease,catalase and alkaline phosphatase activities... |
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