Three Dimensional Fluorescence Characteristics of Soluble Organic Matter From Different Straw Decomposition Products Treated With Calcium Containing Additives

Straw is a high-quality organic resource. Clarifying the differences in the composition and properties of dissolved organic matter (DOM) of different straw decomposition products treated by calcium-containing additives can provide a theoretical basis and technical reference for the efficient utilization of organic materials. Straw decomposition experiments were carried out using peanut straw and rice straw as test materials by adding different calcium additives (CaC2O4 Ca(OH)(2)) with different amounts (4%, 8%). The nutrient contents of decomposition products were determined. At the same time, changes in the DOM chemical composition in straw decomposition products were analyzed using three-dimensional fluorescence spectroscopy (3DEEM) and the parallel factor method (PARAFAC). The results showed that; (1) The total carbon content of straw decomposition products was significantly greater in the calcium oxalate treatment than in the calcium hydroxide treatment. The total carbon content of straw decomposition products was less in the high-amount additive treatment than in the low-amount treatment. The total nitrogen, phosphorus and potassium levels of peanut straw decomposition products were higher than those of rice straw decomposition products. (2) The DOM composition of decomposing products was analyzed by the 3DEEM-PARAFAC method. Three fluorescent components, such as humic acid (C1) humic acid (C2), and tryptophan (C3), were identified. The effect of different additive types, addition amounts, and straw types on fluorescence fractions was complex and had no clear pattern. In general, the proportion of C1 and C2 fractions in DOM from the calcium hydroxide treatment was greater than those from the calcium oxalate treatment, while the proportion of C3 fractions in DOM from the calcium oxalate treatment was significantly higher than that from the calcium hydroxide treatment. Fractions C1 and C2 were significantly negatively correlated with fractions C3. The C2 content of DOM was significantly negatively correlated with total carbon content. (3) The HIX value of the DOM in straw decomposition products treated with calcium hydroxide was significantly higher than that treated with calcium oxalate. The BIX value of DOM treated with calcium oxalate was significantly higher than that treated with calcium hydroxide. DOM of straw decomposition products treated with high amounts of calcium hydroxide was mainly from the transformation of microorganisms, while DOM ofother treatments came from the transformation of microorganisms and terrestrial plants. The fluorescence index of straw decomposition products did not change significantly under different addition treatments. HIX, BIX, and McKnight's index of DOMin peanut straw decomposition products were higher than in rice straw. There was a significant negative correlation between McKnight and HIX and an extremely significant positive correlation with BIX. Meanwhile, the contents of BIX and TC were significantly positively correlated. The above results showed that calcium hydroxide can promote straw decomposition and humification. A higher amount of calcium hydroxide was more effective in peanut straw decomposition.