Effects Of Long-Term Fertilization On Organic Phosphorus And Its Fractions In Aggregates Of Loess Soil

Phosphorus (P) is not only one of the necessary elements for the plant, and is the absolutely necessarity nutritional element of plant in the life cycle, but also has significant effect on keeping high productivity of crop and the good characteristic of crop cultivars. The P of plant requirement is mainly from the soil. As an important component of soil phosphorus pool, soil organic P has important effect on the soil fertility and plant nutrition, thus its role on plant has been paid more and more attention to.Effects of long-term fertilization on organic phosphorus and its fractions in aggregates of Loess Soil is studied in this thesis which is one part of the project from Ministry of Agriculture named"Research on the evolution of soil fertilizer and fertilizer efficiency of Loess soil", based on a long-term field experiment for 16 years. The concrete research contents are as follows: Composition of loess soil aggregates under irrigation and rainfed condition. Effect of long-term fertilizer on available phosphorus (AP), organic phosphorus (OP), labile organic phosphorus (LOP), moderately labile organic phosphorus (MLOP), moderately resistant organic phosphorus (MROP) and highly resistant organic phosphorus (HROP) in loess soil under irrigation and rainfed condition.. Relationships among available phosphorus (AP), total phosphorus (TP), organic matter (OM), organic phosphorus (OP) and its fractions under irrigation and rainfed condition. Effect of long-term fertilizer on available phosphorus (AP), total phosphorus (TP), organic matter (OM), organic phosphorus (OP) and its fractions in Loess soil aggregates under irrigation and rainfed condition. Distribution of total phosphorus (TP), organic matter (OM), organic phosphorus (OP) in Loess soil aggregates under irrigation and rainfed condition.We made the following conclusions:1. Composition of soil aggregates: In soil plough horizon of both irrigation and rainfed field, the aggregates of > 5mm size and > 2mm size are the subjectivity, approximately 91.89%~97.01% of gross weight. The percentage of < 0.25mm size aggregate in rainfed field is over twice that in irrigation field. All these showed that long-term fertilizer and irrigation would increase the content of large size aggregates in loess soil.2. Changes of soil organic phosphorus (OP): In general, the content of organic phosphorus (OP) is various in different soil treatments. It makes up 103.89 mg/kg to 195.50 mg/kg in rainfed field while from 80.71 mg/kg to 526.96 mg/kg in irrigation field. And the content of organic phosphorus (OP) in the former is significantly higher than that in the later collected from CK, NK, Fallow and Set-aside without applied phosphorous fertilizer. However, the difference of organic phosphorus (OP) content among CK, NK, and Fallow is not obvious. Furthermore, Set-aside helped to more conservation and accumulation of organic phosphorus (OP) than Fallow because the organic phosphorus (OP) content in Set-aside is higher than that in Fallow.3. Changes of soil organic phosphorus fractions: Under different fertilizing conditions, the results show that the content and percentage of organic phosphorus fractions in rainfed and irrigation field are different in term of absolute content, and the percentage content of moderately resistant organic phosphorus (MROP) is higher than that of labile organic phosphorus (LOP), and highly resistant organic phosphorus (HROP) in term of ralative content. Moderately labile organic phosphorus (MLOP) is the main of organic phosphorus (OP) in the tested soils.4. Changes of soil available phosphorus (AP): In soil plough horizon of both irrigation and rainfed field, the results show that the content of available phosphorus (AP) in the treatments with applied phosphorous fertilizer is five to ten times that in the treatments without applied phosphorous fertilizer. Evidently, applying phosphorous fertilizer will improve the content of available phosphorus (AP) greatly. The contents of available phosphorus (AP) in Set-aside soil are lower than that in Fallow soil from both rainfed and irragation field.5. Relationships among available phosphorus (AP), total phosphorus (TP), organic matter (OM), organic phosphorus (OP) and its fractions: In soil plough horizon of both irrigation and rainfed field, the results show that there are positive correlations significantly between organic phosphorus (OP) and available phosphorus (AP), total phosphorus (TP), organic matter (OM) respectively, between total phosphorus (TP) and its different fractions ,between available phosphorus (AP), and total phosphorus (TP) , organic phosphorus (OP), labile organic phosphorus (LOP), moderately labile organic phosphorus (MLOP), highly resistant organic phosphorus (HROP), between organic matter (OM) and organic phosphorus (OP), moderately labile organic phosphorus (MLOP), moderately resistant organic phosphorus (MROP), labile organic phosphorus (LOP), in addition, between total phosphorus (TP) and organic phosphorus (OP), labile organic phosphorus (LOP), moderately resistant organic phosphorus (MROP), highly resistant organic phosphorus (HROP), organic matter (OM). There are no correlations between available phosphorus (AP) and highly resistant organic phosphorus (HROP), between highly resistant organic phosphorus (HROP) and organic matter (OM), between labile organic phosphorus (LOP) and total phosphorus (TP) in rainfed field. But then, in irrigation field, they are positive correlations significantly.6. Changes of available phosphorus (AP), total phosphorus (TP), organic matter (OM), organic phosphorus (OP) and its fractions in Loess soil aggregates with different sizes: In soil plough horizon of both irrigation and rainfed field, tests show that macro-aggregates contain less amount of available phosphorus (AP), total phosphorus (TP), organic matter (OM), organic phosphorus (OP) and its fractions than micro- aggregates collected from the same treatment.7. Distribution of total phosphorus (TP), organic matter (OM), organic phosphorus (OP) in different Loess soil aggregates: Altough the contents of total phosphorus (TP), organic matter (OM), organic phosphorus (OP) in aggregates of <0.25 mm size are higher than that of the other sizes, the test indicates that these matters exsit mainly in aggregates of > 0.25mm size while there are few allocations in aggregates of <0.25 mm size owing to their less proportion in soil gross weight. The formation of micro–aggregates by measures of tillage and irrigation will contribute to the conservation of phosphorus in soil.