The Study On The Effect Of Lowmolecular Weight Acid Activating The Phosphorus Iron And Zinc In Thealkaline Soil

The phosphorus, iron and zinc are essential for the growth of plants and play a importantrole in the biochemical reaction. The Lou soil that is typical calcareous soils is the main soiltype in the Guanzhong Area. It has the characteristic of high pH value and high content ofcalcium carbonate, which result in the low contents of phosphorus, iron and zinc even belowthe critical value and makes the influence on the growth of plants and agricultural production.The low molecular weight organic acids (LMWOAs) are the ubiquitous organic matters in theecological system, which mainly come from organic matter’s degradation, microorganism andplant root system’s secretion and the conversion and decomposition of the organic matter inthe soil. The researches in the recent years showed that the LMWOAs can activate thenutrient elements by the effects of acid soluble, reducing action, on-exchange, complexationand chelation, improving the contents of effective states.In this experiment, the oxalic acid, citric acid and lactic acid were chosen as the reagents.Five concentration treatments of0.5,1,5,10,25mmol L-1were set and the soil sampleswere incubated for48h in the incubator. In the16h,32h, and48h, the samples were takenand the pH value, phosphorus, iron and zinc were measured.By the experiment, several conclusions were concluded. The three kinds of LMWOAsall had the ability in activating the phosphorus of the soil and promoting the release of thephosphorus. The sequence of activating ability was: the oxalic acid> citric acid> lactic acid.To the same soil, the higher the concentration was, the much more amount of the activatingphosphorus it had. Further, the proton played an important role in the activating thephosphorus of soil. There was a highly significant relationship between the concentration ofthe LMWOAs and the content of phosphorus, and it meant the higher the concentration, thehigher concentration of the phosphorus was.There was differences among between the different varieties and different concentrationin the activating the iron and zinc, meanwhile to the same variety acid there was alsodifference. In general, the oxalic acid and citric acid had the larger activating abilitycompared with the lactic acid. The sequences of activating abilities: oxalic acid> citric acid>lactic acid. The different varieties of LMWOAs had different influences on the soil pH value. TheLMWOAs impact on the pH value was also related to its concentration. When theconcentration of the LMWOAs was below5mmol·L-1, the difference among the differentprocesses was not obvious. However when the concentration reached10mmol·L-1, the pHvalue reduced sharply, and the pH value processed by citric acid, oxalic acid and lactic acidrespectively reached7.0,7.4and7.4. The higher the concentration was, the more obviously itshowed. With the incubation time prolonged, the pH value would rose gradually, because itresulted from the buffer action and passivation of the soil.The analysis of correlation showed there was a negative correlation between theconcentrations of the acid and the pH value.Compared with the CK, when the concentration of acids was below1mmol·L-1, with thetime extended, the contents of available phosphorus, iron and zinc did not change obviously.When the concentration was5mmol·L-1, the contents of available phosphorus iron and zincwould rise with the incubation time.