| Saline-alkali soil is one of the most important middle and low yield soil types in our country, its productive level and quality status have a very close relationship. Under the background of research about building poplar plantation on severe saline-alkali soil, by using the treatment of "一"-shaped channel (Small hole improvement-Bar foraging ditch-In situ repair), "十 "-shaped channel (Small hole improvement-Cross foraging ditch-In situ repair) and "井"-shaped channel (Small hole improvement-Grid form of foraging ditch-In situ repair), changes in improved soil colloid and particle size, the soil infrared functional groups, soil morphology structure and their influence on poplar growth are studied by using modern instruments and analytical methods, such as laser particle size analyzer, infrared spectrometer, atomic force microscopy and scanning electron microscopy. The research results are as follows:1. Changes of soil colloids and particle size:Saline soil colloids appeared mostly cluster-like aggregates, and after improvement, soil colloidal particles dispersed and reduced significantly. Fine particles and a small amount of spherical aggregates occurred during amelioration, and by comparing the height of the particles, improved soil had significantly smaller colloidal particles than bare saline soil, their shape and size were similar to the situation of agricultural soil. Measured by laser particle size analyzer, soil colloid particle, part of the soil, of before and after improvement could be studied. At the beginning of amelioration (2009), soil colloid particle size changed quite different after "一"-shaped channel, "十’ shaped channel and "井"-shaped channel three harnessing measures of improvement. At the late period of amelioration (2014), in each layer of soil (0 cm,20 cm,40 cm), colloidal particle size was smaller than the bare saline soil colloid (646.5 nm,578.8 nm,665 nm), and close to the average particle diameter (377.5 nm) of normal agricultural soil colloid, especially in the 20 cm of soil depth, soil colloid particle size of three improved measures were 385.1 nm,418.7 nm,477.5 nm, respectively.2. Infrared analysis of soil functional groups:Infrared absorption characteristic of soil and humic acid was similar on the whole, and some of the peaks appeared different absorption. Compared with severe saline-alkali soil, soil carbonate (1442 cm-1) content decreased by improving of three measures, soil organic matter (2926 cm-1) content increased; in the soil humic acid, content of carbohydrates, sugars, inorganic matter (1028 cm-1) and organic compounds (2848 cm-1,2926 cm-1) increased, and the ratio of 2920/1720 increased.3. Scanning electron microscope observation:With compact and dense soil matrix, low porosity, flaky structure, fissures, poor structure, bare saline-alkalized land before improvement contrasted obviously with agricultural cultivated soil. In the improved soil, soil crumb structure increased and loosely formed, soil fragmentation effect was obvious, soil porosity increased, and parts of the plant residues or roots could be observed. Energy dispersive spectrum analysis showed that weight percentage of Na element had a significant reduction in the improved soil, compared with bare saline-alkalized land (2.36%) reduced by an average of 82.4%; at the same time, weight percentage of C element increased by an average of 29.7%; the weight percentage of Fe element in 2014, compared with saline bare land (11.85%) increased by an average of 13.9%.4. Compared with poplars grown in severe saline-alkali land, after amelioration, poplar photosynthetic rate increased about 3.5 times on average, respiration rate increased about 1.3 times, the height increased 23.8%, DBH increased 35.3%, crown diameter increased 73.5%, branch number increased nearly 1.6 times, and branch length increased nearly 1 times, root length increased 2.3 times. By the discussion of improved soil structure change and the reflection of poplar growth, the amelioration of severe saline-alkali soil achieved good effect. |
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