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Research Of Long Term Fertilization On Soil Acidification

Posted on:2013-06-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y C ZhangFull Text:PDF
GTID:1223330398491486Subject:Plant Nutrition
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Soil acidification is a naturally occurring phenomenon and is usually caused by long-term addition of protons to the upper layers of soil and subsequent leaching of exchangeable bases. In recent decades, due to the rapid development of chemical and petroleum industries and frequent agricultural practices including fertilization and crop rotation, soil acidification became more accelerated, which is one of the important soil degradation. In this paper, incubation experiments as well as long-term field experiments in typical paddy soil and alluvial soil in Jiangsu Province were carried out to study acid deposition and nitrogen application on soil acidification rates, the key factors of soil acidification, the characteristics of various factors and their contributions to soil acidification.Analysis on the198soil samples among6categories of paddy soil in Tai Lake region in2004, showed that the organic matter content, total N, available P and K concentration were significantly improved while pH and CEC were reduced by1.1unit and8.3cmol·kg-1, respectively, compared to the results obtained from the Second National Soil Survey. The pH index of fertility, decreased from2.69-2.91in1982to1.73-2.41in2004, becoming the lowest single soil fertility index. Soil limiting factor of low contents of available nutrients in the Second National Soil Survey is now replaced by those of shallow cultivated horizon, increased soil density and reduced soil pH in North Huai in Jiangsu Province.Over26years of different fertilization, the acidification rate of the paddy soil in Tai Lake region was0.50-1.74kmol H+hm-2a-1, and lowest and highest soil acidification rates appeared in the control treatment (no fertilizer) and the treatment of urea plus pig manure and rice straw application, respectively. The required amounts of CaCO3were24.7-87.1kg-hm-2·a-1among all treatments. The pH of major plot of chemical fertilizer (6.10) was0.33higher than the main plot of organic fertilizer addition. Na+, K+, Ca2+and Mg2+concentrations in chemical fertilizer plots were5.24,2.05,39.87and9.04mmol·kg-1, which were2.7%,54.1%,3.1%and13.4%higher than the corresponding organic fertilizer addition plots, irrespectively. Significant differences were found in K+and Ca2+concentration between the two major plots. The soil pH was highest in P and K fertilizer application treatment (pH6.42), followed by the control treatment (pH6.38), the treatment of N plus organic fertilizer and rice straw addition was the lowest (pH5.41), and the main plot with pig manure additional got a low concentration of cation, indicating that the lower pH in the major plot of organic fertilizer amendment might be due to transfer of base cations from soil to plant. The exhaustion of base cations occurred when the yield increased. The buffer capacity of soil amended by organic fertilizers (2.18cmol kg-1) was slightly higher than the chemical fertilzer treatment (2.14cmol-kg-1). Soil buffer capacity was positively correlated to soil organic matter content, and soil pH value decline was due to the cation depeletion.Soil pH, CaCO3and active CaCO3contents, soil buffer capacity significantly changed over continuous30-year fertilization on Alluvial soil in Xuzhou City. The topsoil pH was decreased by0.41-0.70. The soil buffer capacity, ranging from15.82to21.96cmol·kg-1, was lowest in sole N treatment and highest in the treatment of manure plus NPK. The soil buffer capacity of chemical fertilizer treatments (except NP) was lower than the control, while the manure treatments had higher soil buffer capacity than the control. The soil buffer capacities of the treatments of MN, MNP and MNPK were3.23,1.56and4.33cmol·kg-1higher than those of N, NP and NPK, irrespectively. The soil buffer capacity was significantly positively correlated to soil CaCO3content, but had no significant correlation with organic matter content and CEC, indicating that Alluvial soil was still in the CaCO3mediated buffer system, in which organic matter had a small role over long term fertilization. Different long term fertilizations altered CaCO3and active CaCO3contents notably in the0-40cm soil layer, and the contents of active CaCO3which was very significantly positively correlated to soil buffer capacity, showed a greater variation along soil profile than that of CaCO3, suggesting that soil active CaCO3could more sensitively reflect variation of soil physical and chemical properties than CaCO3, and the CaCO3mediated buffer system could be subdivided into the active CaCO3mediated buffer system.A3-year field experiment was carried out to study the effects of different ratios of chicken manure to urea under the same N input on rice grow and soil acidification. The mean rice yields of the treatments of chicken manure/urea ratio of75%,50%and25%were increased by4%than the chemical fertilizer treatment and0.4%-45.3%higher than that of the control. Chicken manure/urea ratio of50%(7978.5kg-hm"2) had the highest rice yield, followed by the ratio of25%(929.0kg·hm-2). No significant difference in rice yields was found between the chicken manure/urea ratios of75%,50%and25%. Soil CEC increased with the increasing of the proportion of chicken manure, the ratios of75%and100%had significantly higher CEC than other treatments, while only urea treated soil had the lowest CEC. With the increasing of chemical fertilizer, soil pH showed a significant declining tendency. The decline of soil pH was significantly and linearly related to increasing of the proportion of urea (R2=0.998**). Soil buffer capacity ranged from2.07-2.36cmol-kg"1and was increased with the increasing of the proportion of chicken manure. Soil buffer capacity showed a similar trends to soil organic matter contents and CEC, with the correlation co-efficiency of0.903**and0.859*. The above results indicated that under the same N input, soil base cation accumulation and improved organic matter contents caused by the elevated proportion of chicken manure should be an important reason for enhancing soil buffer capacity.Application of rice straw with different N concentrations led to a0.01-0.99reduction in pH of0-40cm soil layer. The total amounts of induced acid ranged from56.77to136.18mmol, which was increased with the increasing of rice straw input under the same N contents. However, little difference existed between treatments of the same rice straw amounts under different N contents. The total amounts of induced acid were increased with the increasing of exogenous N input. The proportion of HCO3induced acid amount accounted for82.01%-92.97%, and N leaching took up6.92-13.04%. The amount of acid induced by N leaching increased with the increasing of straw and N input. Little difference was found in HCO3induced acid amount, while there was great difference in N leaching induced acid between treatments. The proportion of organic anion cycling induced acid took up0.11-9.98%, and showed a similar trend to N leaching. The proportion of exogenous H+induced acid was little, only0.001-0.005%.Results from the indoor experiment on different application rates of pig manure showed that soil organic matter content was significantly correlated to soil buffer capacity and pH, with the correlation co-efficiencies of0.6726and0.5363, respectively. Increased application of pig manure caused increased leaching of Ca2+and Mg2+.Indoor simulation experiment was carried out to compare the effects of3pH values and3nitrogen application rates on soil acidification. Soil acidification accumulation varied from4.73to15.57mmol H+/column, among which the highest and lowest soil acidification accumulation occurred on the treatments of pH6.5depositions without N and pH2.5 depositions with high N input, respectively. Soil acidification accumulation was elevated with the increase of N input under the same pH deposition. Soil acidification accumulation increased with the decrease of pH in zero N application treatment, when the same amounts of N were provided. However, within medium (150mg·kg-1soil) and high (300mg·kg-1soil) N input, soil acidification accumulation was lower in pH4.5deposition than pH6.5deposition. Nitrate-induced soil acidification accumulation was4.32-12.88mmol per column, and ammonia leaching consumed H+by0.01-0.29mmol per column. In case of normal deposition (pH6.5), soil acidification accumulation was greater than other pH deposition treatments under medium and high N inputs. The above results indicated that soil acidification accumulation induced by N input was greater than acid deposition. Nitrate leaching played a leading role in the acceleration of soil acidification.In conclusion, Hapli-Stagnic Anthrosols was silicate and cations buffering system, soil acidification induced either by matter single application of chemical fertilizer, or of chemical fertizer, or by combined appliacation of chemical fertilizer and organic fertilizer, or by mixed application of organic fertilizer, rice straw and chemical fertilizer, was influenced by soil buffering capacity which in turn was affected by soil organic matter content; Accumulation or depletion of base cations was a major factor to the in-consistent acidification trend between different fertilization treatments. The content of calcium carbonate was a key factor affected pHBC for the sandy loam calcareous fluvor-aquic soil, and the active calcium carbonate more sensitively response to different fertilizer treatments, calcium carbonate buffering system can be further broken down into the soil active calcium carbonate buffering system. Compared to different pH rainfall, nitrogen application contributed more to soil acidification and nitrate was the key acidity inducing factor. Rice straw addition induced acidification in neutral soils was mainly affected by bicarbonate ion caused by soil respiration and nitrogen leaching, and bicarbonate ion induced acidity amount was the major factor.
Keywords/Search Tags:Long-term fertilization, soil acidification, soil buffering capacity, Simulated acid deposition
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