Variation Of Soil Humus Under Long-term Fertilization And Its Relation To Soil Acidity

Soil acidification is a naturally occurring phenomenon and is usually caused by long-term addition of exchangeable bases. In protons to the upper layers of soil and subsequent leaching of recent decades, due to the rapid development of chemical and petroleum industries and frequent agricultural practices including fertilization and crop rotation, soil degradation, acidification became more accelerated, which is one of the important soil degradation. The northeast black earth area is Chinese important grain production base, having appeared in the acidification trend in recent years. There is a serious threat to our country food security.Studies have shown that soil organic matter has restricted the soil pH value. Soil organic matter has a good buffer for acid-base ion in the soil. The buffering capacity of humus soil can improve soil acidification. It is not clear between the change of soil acidity and composition as well as quantity of soil humus. The mechanism of soil organic matter on soil ph buffer action remains to be revealed.This study is based on the meadow black soil of Jilin test soil, the composition of black soil humus, different types of humic acid and its relationship with soil acidity under long-term fertilization were analyzed. Extract soil humus was accorded to Kumada Method. After adding acid to precipitate, the humic acid(HA) and fulvic acid(FA)were isolated. The HA was diluted with diluent alkali to determine the extinction coefficient(K400 and K600) at the wavelength of 400 and 600 nm. Then HA and FA were quantified according to the potassium permanganate oxidation titration method. The results showed that:(1) different fertilization treatments, chemical fertilizer so that the content of free humus decline. After the addition of organic materials, free humus content increases, and with the increase of the added amount of organic materials is raised. The combined humus content in C, CM1, CM2 three groups tested soil decreased compared with CK.(2) the same fertilization treatments, long-term Organic Materials bound and free form soil humic acid, fulvic acid content increased, and with the increase in the total amount of organic materials in soil humus increases.(3) long-term application of chemical fertilizer to make free form of humic acid type to P-type transformed from Rp type, increasing humification degree of humus degradation; humus component Organic Materials after the free form has changed, humic free state acid type to Rp-through by the P-type, indicating that after the organic materials free state to reduce soil humification degree of humic acid, humus quality.(4) bound soil pH and humic acid content was significantly positively correlated with increased binding form humic acid content increases. Soil exchangeable H+, exchangeable acid and humic acid bound content was significantly negatively correlated with the decrease bound humic acid content increased. Changes of soil-bound humic acid content of soil exchangeable H+, exchangeable acid content, thereby affecting soil pH changes, bound to humic acid soil acidity has a certain buffer.Given all this, Long-term single application of chemical fertilizer made the content of humus decrease and the type of free humic acid transformed into higher type. Meanwhile, the degree of humification was improved and the quality of humus declined. After adding organic material, the content of humus increased and the type of free humic acid transformed into lower type. Meanwhile, the degree of humification was declined and the quality of humus was improved. The change of content of combined humic acid affected the content of humus, and relieved the soil pH value changes that caused by the chemical fertilizer. It showed that combined humic acid could alleviate soil acidity.