The Character Of Fertilization On Phosphorus Transformation And Movement In Fertilizer Microsites

A nutrient concentration gradient was formed in fertilizer microsites around fertilizer particles by adding phosphorus into soil. The fertilizer nutrient moved into soil in the effect of soil solution and transformed to different formations. High concentration of phosphate in fertilizer microsites strongly destroyed the soil minerals which played a main role in phosphorus availablility. In this thesis, effects of four fertilization on phosphorus transformation and movement in fertilizer microsites in soils under three temperatures were studied by an incubation experiment using soil column. The main conclusions were as follows.In a short period after adding phosphorus into soil, phosphorus mainly existed as W-P and Ca2-P while some of the others transformed into Ca8-P, Fe-P an Al-P. Less of them transformed into O-P and Ca10-P. However, the percentage of transformation differed in soils. In paddy soil, phosphorus mainly existed as Ca2-P and Cag-P while Fe-P and Al-P made secondary contribution. In calcareous soil, Ca2-P and Ca8-P were the main formations. Temperature also effected the transformation even in one soil. By increasing the soil temperature from 5 degree centigrade to 20 degree centigrade, percentages of W-P and Ca2-P decreased while Ca8-P, Fe-P and Al-P had positive increasement. By adding organic acid and manure into soil, percentages of W-P and Ca2-P increased which indicated higher phosphorus availablility. This changing energy depended on the additives. They had a decreasement which followed as manure>oxalic acid>citric acid.The movement of phosphorus also differed in soils.In this paper, phosphorus migrated to 57.5 mm in paddy soil while the distance was 42.5 mm in calcareous soil. Concentration of water-extractable phosphorus, available phosphorus and acid-extractable phosphorus quickly decreased with the distance to fertilization site increased. Most phosphorus were quickly fixed in these two soils and the fixation was more efficient in paddy soil which indicated lower availablility. By adding oxalic acid into the fertilizer, fixation of soil was decreased and the amount of phosphorus that was migrated increased. However the additive didn't effect the movement distance. Coated fertilizer that was studied in this paper had extremly low release rate in soil that only about 20% nutrient was released in 120 days which caused a short movement distance. Furthermore, the slow releasement of phosphorus would strengthen the fixation by soil.The transformation and movement were effected by the temperature. In this paper, three temperatures were studied. The nutrient moved to about 57.5 mm under 5 degree centigrade,57.5 mm under 20 degree centigrade and 42.5 mm under 35 degree centigrade. Adding oxalic acid obviously didn't change the movement distance under these three temperatures. With the increase of temperature, concentration of water-extractable phosphorus and available phosphorus in soil decreased. Adding oxalic acid in all temperature treatments weakened the fixation by soil and increased the migrate amount especially in low temperature. Coated fertilizer released faster in high temperature but did not release more even after 120 days. Under 35 degree centigrade, the coated fertilizer treatment had high percent of water-extractable phosphorus and available phosphorus and had low fixation by soil.Submerging the soil obviously effected the transformation and movement of phosphorus in soil. In this study, comparing two water contant situation(60% soil water contant and fully submerge), the movement distance had obvious difference which was 57.5 mm in 60% soil water contant and was 65 mm in fully submerge situation. When soil was fully submerged in water, phosphorus moved further than in 60% soil water contant situation while the soil available phosphorus and water-extractable phosphorus were lower than in 60% soil water contant situation which indicated decreasing bioavailablility of soil phosphorus. Adding oxalic acid into the two experiments did not obvious increase the movement distance but increased the phosphorus availablility in 60% soil water contant situation while the negative result was observed in fully submerged situation. In these two experiments, coated fertilizer also released only about 20% after 120 days and had the same movement distance.