Effects Of Long-Term Fertilization On The Forms And Distribution Of Organic Nitrogen And Phosphorus In Several Typical Soils In China

As the macronutrients for plants, Nitrogen and phosphorus are the main yield limiting factors in agriculture. Although scientists have gone deep into inorganic nitrogen and phosphorus, our knowledge on the forms and distribution of organic nitrogen and phosphorus on different fertilization conditions is very few. In this research, the methods proposed by Bremner(1965) and Bowman-Cole(1978) were adopted to study systematically the Black soil, Aquic cinnamon soil, Purple soil and Red soil, which are four typical soils of the National Monitoring Base of Soil Fertility and Fertilizer Efficiency. The main results are as follows:1. In Black soil, Aquic cinnamon soil, Purple soil and Red soil, about 45.54%~-88.68% of the soil nitrogen can be hydrolyzed by 6 mol/L HC1 at all the soil layers after 10 years of plantation. Nonhydrolysable N of soil nitrogen is changeable at the range between 11.32% and 54.46%. The content sequence of forms of organic N is Nonhydrolysable N> Amino acid N> Ammonium N> Hydrolysable unidentified N> Amino sugar N as a general rule. The content of Amino acid N decreased faster than the other forms with the increasing depth of soil. The effect of fertilization on content and distribution of forms of organic N is significant, and its influencing depth reach 80cm. In the tilth layers, the average content of the total N in the four types of soil applied organic-chemical fertilizers is greater than that applied only chemical fertilizers, and at the soil layers under tilth layer their contents are not greater. It demonstrated that the former fertilization had greater ability in holding nutrients. In addition, the contents of the total N in the tilth layers of the four soils are all low at the treatment of NPK+S(stalk ). In Black soil, Aquic cinnamon soil and Purple soil, the content sequence of forms of soil organic phosphorus in each soil layer of all the three soils is Moderately labile organic phosphorus(MLOP) > Moderately resistant organic phosphorus(MROP)> Highly resistant organic phosphorus(HROP) > Labile organic phosphorus(LOP). The contents of organic phosphorus and the ratio of organic phosphorus to the total phosphorus decrease with the increase of the depth of the soilprofiles.2 In the Black soil , the contents of forms of organic N decrease with the increase of the depth of soil profiles, the ratio of Ammonium N to the total organic N increases, the ratio of Amino acid N to the total organic N decreases, the ratio of others have no obvious tendency. A majority of soil phosphorus is organic phosphorus at the soil layers of 0~40cm in Black soil, but the inorganic phosphorus is the majority at 40 ~ 60cm soil layers. The influencing depth of fertilization on the contents and distribution of organic nitrogen reaches 60cm. The ratio of MLOP to TOP increases smoothly with the depth of soil profiles, but the ratio of MROP to TOP drops gradually, the ratio of HROP is not obvious.3 In the Aquic cinnamon soil, the contents of Nonhydrolysable N, Amino acid N and Ammonium N drops smoothly with the depth of soil profiles, and enrichs at the soil layers of 60~80cm. The ratios of forms of organic nitrogen to TOP had no obvious distribution rule. A major portion of soil phosphorus is inorganic phosphorus, and the content and distribution of organic phosphorus decrease with the depth of soil profiles. The influencing depth of fertilization on the contents and distribution of organic nitrogen reaches 60cm. The ratio of MLOP to TOP decrease smoothly with the depth of soil profiles, but the ratio of MROP and HROP have the trend of increasing with the depth of soil profiles.4 In the Purple soil, the contents of forms of organic nitrogen remain constant in the soil profiles, but the contents of Amino acid N and Nonhydrolysable N drops firstly and then increases gradually with the depth of soil profiles. The ratios of each forms of organic N to the total organic N were not changeable greatly. A major portion of soil phosphorus is inorganic phosphorus, and the content and distribution of organic...