The Effects Of Water Management Patterns And Nitrogen Levels On Nitrogen Nutrient Transformation And Nitrogen Supplying Capacity In Paddy Soil

The synergy effect of the interaction of nutrients and environmental factors is the key to increase the nitrogen nutrient bio-availability,reduce nitrogen losses in a specific Cultivation mode.In this paper,the soil from Yangtze River region was selected as the tested soil.By studying the effects and mechanisms of the different water management patterns and nitrogen levels on soluble nitrogen dynamic transformation characteristics and nitrogen supply capacity in order to assess the paddy soil nitrogen supplying and nitrogen loss risk.The main results of this research were as follows:1.A ventilated incubation experiment was conducted to investigate the dynamic trends of the soil NH₄⁺-N,NO₃^--N and soluble organic nitrogen(SON) contents under different water conditions(CW and FW) and nitrogen levels(NO and N25) in the two paddy soil types i.e.Alluvial soil and Purplish clayey soil.(1) During incubating period,the contents of NH₄⁺-N in the Alluvial soil were not obviously enhanced by water-logged incubation or by nitrogen fertilizer added, except for being distinctly elevated at the 7^th day of water-logged incubation with nitrogen fertilizer added.However,the contents of NH₄⁺-N in the Purplish clayey soil were significantly increased by water-logged incubation or by nitrogen fertilizer added.(2) NO₃^--N/TMN was as high as 80%or more by nitrogen fertilizer added not only under water-controlled but also water-logged condition in the Alluvial soil. However,the percentage was less than 40%at the 21^th day of water-logged incubation with nitrogen fertilizer added,and to 35^th day of incubation reached the highest level.it was less than 15%by water-logged incubation.The aforesaid results indicated that the nitrification activity in the Allvial soil was very strong not only under the water-controlled condition but also under the water-logged condition and it started earlier and lasted longer.It is,therefore,important to pay much more attention to the NO₃^--N leaching losses in the Alluvial soil than in the Purplish clayey soil.(3)The contents of TSN and SON in the two soils reached the highest level during the 14^th day to35^th of incubation,but the contents in the Alluvial soil was significantly higher than Purplish clayey soil.On the peak period,the ratio of SON to TSN can reach 80%in the Alluvial soil under the water-logged condition and 60%in the Purplish clayey soil under the water- controlled condition.Therefore,the risk of soluble organic nitrogen losses in the two paddy soils during its peak period could not be neglected either.2.A soil column experiment and field experiment were conducted to investigate the effects of nitrogen supplying capacity under different water conditions(FW and KW) and nitrogen levels(N0,N1,N2 and N3) with Alluvial soil.Results of the soil column experiment showed that NH₄⁺-N of the three nitrogen treatment(N1,N2,N3) declined from high to low,but increased with the amount of nitrogen notability increasing.NO₃^--N under the two kinds of water conditions had a great deal of difference.RAQN- NO₃^--N has experienced from low to high,then high to low,and increased with the amount of nitrogen increasing under CW.But it was small and even under different nitrogen levels had no significant difference throughout the rice growing period under FW.In a word,from dynamics ratio of the soil exchangeable NH₄⁺-N to NO₃^--N,RAQN-NH₄⁺-N was very low,less 20%.the ratio of RAQN-NO₃^--N to total exchangeable nitrogen was high.Indicating under the experiment conditions,NO₃^--N is the main active form of nitrogen supply with Alluvial soil.