Mechanism Of Soil N Supply In Paddy Soil And Reaching Optimal N Application For Rice

In this dissertation, we studied the mechanisms of nitrogen transformation and nitrogen supply to rice in paddy soils through incubation experiments, and field experiments. A long-term fertilization experiment was conducted with researching optimal nitrogen application for rice in Jinhua, Zhejiang Province of China. Information provided in this work may contribute to a better understanding of soil nitrogen supply capacity in paddy soil environment, which will be useful reference for reasonable fertilizer application. Main original conclusions are shown as follows.(1) Dynamics of grain yields and nutrient uptake of rice, and the ecological characteristics of microorganism of the paddy soil were investigated in a long-term split-block experiment with different fertilization treatment, including control (CK), PK, NK, NP, NPK fertilization, in the main block, and conventional rice and hybrid rice comparison, in the sub block. The results showed that grain yield of rice was positively correlated with N uptake, P uptake and K uptake(r=0.7353**, 0.5461**and 0.5599**, respectively), and soil available nutrient pool depletion might occur very fast under consecutive crops grown without fertilizer application. The results also showed that microbial biomass N varied from 33.78⁷0.44 mg kg^-1, about 2.04 percent of total soil nitrogen. The soil microbial biomass N showed a marked increase in the NPK treatment as compared to values in the unbalanced nutrient treatments (NP, PK and NK). CK treatment could also support a higher level of soil microbial biomass N. The results of BIOLOG showed that in the first 32h of incubation, AWCD changed very little but afterwards AWCD increased continuously. At the same time, AWCD of NPK treatment was the highest in all treatments. AWCD of CK treatment increased gradually and were higher than that of NP, PK and NK treatments at the late stage of incubation. It was showed here that soil nutrient deficiency andunbalanced fertilization to rice crop had a negative effect on the diversity of the microbial community and total microbial biomass in the soil. We concluded that balanced application of N, P and K increased microbial community and total microbial biomass of the soil. Unbalanced fertilization reduced microbial N and increased C/N ratio of the microbial biomass.(2) Changes of soil organic nitrogen forms and soil nitrogen supply under continuous rice cropping were investigated through the long-term NPK experiment. It was found that after 6 years of continuous double-rice cropping, the soil total N and hydrolysable N contents were maintained in the N-supply plots, while the hydrolysable N contents were substantially reduced in the N omission plots. Balanced application of N, P and K promoted the percentages of hydrolysable ammonium N in the total N compared to the unbalanced fertilization treatments, also maintained higher rice grain yield and nitrogen uptake. It was found that grain yield was positively correlated with total N uptake, hydrolysable N, hydrolysable ammonium N and HUN fraction N (r = 0.875 , 0.608 , 0.560 , and 0.417**, respectively); total N uptake was positively correlated with hydrolysable N, hydrolysable ammonium N and HUN fraction N (r = 0.608* , 0.440 , and 0.431 , respectively). The hydrolysable N had contribution to rice grain yield and N uptake.(3) In this paper, the chemical group components in soil humic acids(HA) and fulvic soids(FA) isolated from soil of different fertilization treatments were studied by using infrared spectrum(IR) and *H nuclear resonance spectroscopy(NMR), and it was also researched the effect of different fertilization treatments on chemical groups structure of humic substance. The IR analysis of HA indicated that polycondensation and conjugation of the unstaturated structure and the content of aromatic compounds in HA isolated from the long term no fertilization soil increased, while aromatization degree and simple organic molecular fraction in HA isolated from fertilization soil increased, and effect was NPK> PK. It was found that there were more aliphatic groups and less sugar components in HA extracted using O.lmol/L Na4P2O7 and O.lmol/L NaOH compared with HA extracted only using O.lmol/L NaOH. The 'H NMR results showed that the positions of the major spectral bands of these NMR spectra were similar to each other, and it was found the effect of different fertilization treatment on carbon-H and aliphatic-H were NPK>CK>PK and PK>CK>NPK.(4) Direct-seeding for early rice as a laborsaving technique has been spreading rapidly in the past several years in Zhejiang Province. The agronomic performance of a newly developed site-specific nutrient management (SSNM) technique was tested against the farmer's fertilizer practice (FFP) in...