Fate of Fertilizer Nitrogen in the Rice Root Zone 1
Fate of Fertilizer Nitrogen in the Rice Root Zone 1
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DOI：
10.2136/sssaj1986.03615995005000030021x
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发表时间：
1986
影响因子：
2.9
通讯作者：
K. R. Reddy;W. H. Patrick
中科院分区：
文献类型：
--
作者：
K. R. Reddy;W. H. Patrick
水稻氮素利用效率低在世界许多地区，这是由于系统中损失机制的强度。在适宜水稻根区硝化和反硝化的Crowley（Typic Albaqualfs）粉质壤土上进行了肥料氮最大潜在损失的研究。在根际（有水稻植株的土芯）和非根际（无水稻植株的土芯）土壤系统中测定了氮素损失。在有植物的系统中，潜在的N损失被发现是193 mg N m d '，而由于根际效应单独的N损失是143 mg N m 2 d '（18%的施用N）。约5%的应用N被认为是由于向上移动的NH 4到上覆洪水损失。附加索引词：硝化作用，氮素损失，根际，稻田，淹水土壤。Reddy，K.R.，和W. H.小帕特里克1986.肥料氮在水稻根区的去向。土壤科学美国社会J. 50：649-651.水稻氮素的盈亏植物-土壤系统是利用各种途径的许多过程的结果（Reddy和帕特里克，1984）。在这些途径中，对氮的转化了解较少的是发生在低地水稻和其他水生植物的根区（Savant和DeDatta，1982; Reddy和帕特里克，1984）。由于淹水土壤的厌氧性质，这些植物通过从大气中通过叶和茎扩散到根部来获得根部呼吸所需的大部分O2（Armstrong，1964）。如果O2通过通气组织扩散到根部超过植物呼吸需求，则O2将从根部扩散到周围的根区（Barber等人，1962; Mitsui and Tensho，1952）。这一过程导致了被无氧厌氧土壤区包围的充氧根际（Aimi，1960; Armstrong，1964; 1967）。一个广泛的总面积的好氧-厌氧界面存在，因为大的总根表面积涉及。Armstrong（1964）测定了水稻根系以12 g × 10-cm-1根表面积/min的速率扩散的O2。Rodriguez-Kabana等（1965）在一项盆栽研究中，在无氧条件下生长的水稻根部附近的土壤水中测得约4 mg L~（-1）O ~ 2。佛罗里达大学和路易斯安那州立大学佛罗里达农业实验站期刊系列第6498号的联合贡献。1985年10月10日。2教授，佛罗里达大学，食品与农业科学研究所，中佛罗里达研究和教育中心，桑福德，佛罗里达州32771，和博伊德教授，路易斯安那州立大学湿地资源中心，巴吞鲁日，洛杉矶70803。根区可以潜在地影响N转换。与氧化根际相邻的厌氧土壤中的铵态氮可以扩散到根际，在那里它被氧化成NO_3。由于其流动性，在此过程中形成的Np^-离子可以扩散回厌氧区，在那里发生反硝化。近年来，有几项研究试图评估水稻对淹水土壤氮素损失的影响（Broadbent和Tusneem，1971年; Reddy和帕特里克，Jr.，1980; Fillery和Vlek，1982; Smith和Delaune，1984）。这些研究中的结果并没有得出任何关于水稻植株对氮素损失的影响的明确结论。本研究的目的是确定肥料氮在水稻根区和周围厌氧土壤区的去向。研究的目的不是评估该过程的实际意义，而是确定在实验条件有利于根区硝化和反硝化的系统中的最大潜在损失。材料和方法使用的土壤是从Rice Exp. Stn.，克劳利，洛杉矶。它含有0.8 g总N kg-1、7.0 g总C kg-1、9.4 cmol（+）kg-1土壤的阳离子交换容量（CEC）和5.8的pH（1：1土壤/水比）。土壤中有10.8%的粘土，70.7%的淤泥和9.5%的沙子。将研磨通过0.84-mm网筛的风干土壤置于聚氯乙烯（PVC）管（20-cm长和10-cm i.d.）并在底部用PVC盖密封（图1）。在PVC管的底部安装六个橡胶隔片（每侧三个，间隔2 cm）。在加入土壤之前，向管中加入足够的含有N、P和K的去离子水，以获得饱和土壤条件和最终浓度为50 mg N kg-1、25 mg P kg-1和50 mg K kg-1的土壤。将所有土芯置于温室中。在一组核心中，两个健康的20 d龄水稻幼苗（变种。“Labonett”）进行移植，而第二组芯保持没有植物。在植物生长20天后，将另外500 g含有1%稻草的土壤添加到核心中。添加额外的水以保持饱和的土壤条件。将另外200 g含有2%稻草的土壤添加到核心中作为缓冲区。在土壤中添加稻草的主要目的是减少由于向上扩散的N从底部的核心覆盖洪水的N损失。初步试验结果表明，如果我们要区分水稻根系对氮素损失的影响，与土壤-水界面发生的硝化-反硝化反应造成的氮素损失相比，防止NH +4向上扩散是很重要的。由于稻草的高C/N比（90：1），任何扩散的N将容易被固定。标记
Poor N use efficiency by rice (Oryza sativa L.) in many regions of the world is due to the intensity of loss mechanisms functioning in the system. A study was conducted to determine the maximum potential loss of fertilizer "N in a Crowley (Typic Albaqualfs) silt loam soil where conditions are favorable for both nitrification and denitrification in the root zone of rice. Nitrogen losses were measured in the rhizosphere (soil core with rice plants) and nonrhizosphere (soil core without rice plants) soil systems. The potential N loss in the system with plants was found to be 193 mg N m d ', while N loss due to the rhizosphere effect alone was 143 mg N m 2 d ' (18% of the applied N). About 5% of the applied N was found to be lost due to upward movement of NH4 into overlying floodwater. Additional Index Words: nitrification, nitrogen loss, rhizosphere, paddy field, flooded soil. Reddy, K.R., and W.H. Patrick, Jr. 1986. Fate of fertilizer nitrogen in the rice root zone. Soil Sci. Soc. Am. J. 50:649-651. N GAINS AND LOSSES in a rice (Oryza sativa L.) plant-soil system occur as a result of a number of processes utilizing various pathways (Reddy and Patrick, 1984). Among the more poorly understood of these pathways are the transformations of N that take place in the root zone (Savant and DeDatta, 1982; Reddy and Patrick, 1984) of lowland rice and other aquatic plants. Because of the anaerobic nature of the flooded soil these plants obtain most of the O2 required for root respiration by diffusion from the atmosphere through the leaves and stems to the roots (Armstrong, 1964). If O2 diffusion through the aerenchyma tissue to the roots exceeds the plant respiratory requirement, O2 will diffuse from the root into the surrounding root zone (Barber et al., 1962; Mitsui and Tensho, 1952). This process results in an oxygenated rhizosphere surrounded by an O2-free anaerobic soil zone (Aimi, 1960; Armstrong, 1964; 1967). An extensive total area of aerobic-anaerobic interface exists because of the large total root surface involved. Armstrong (1964) measured the O2 diffusing from the roots of the rice plant at a rate of 12 g X 10~ cm~ root surface min~'. In a pot study, Rodriguez-Kabana et al. (1965) measured approximately 4 mg L~' O2 in the soil water adjacent to the roots of rice plants grown under submerged O2-free conditions. The development of two distinct soil layers in the 1 Joint contribution from the Univ. of Florida and Louisiana State Univ. Florida Agricultural Experiment Stations Journal Series no. 6498. Received 10 Mav 1985. 2 Professor, Univ. of Florida, Institute of Food and Agricultural Sciences, Central Florida Research and Education Center, Sanford, FL 32771, and Boyd Professor, Center for Wetland Resources, Louisiana State Univ., Baton Rouge, LA 70803. root zone can potentially influence N transformations. Ammonium N in the anaerobic soil adjacent to the oxidized rhizosphere can diffuse into the rhizosphere where it is oxidized to NOj. Because of its mobility, the Np^~ ion formed by this process can then diffuse back into the anaerobic zone where denitrification takes place. In recent years, several studies have attempted to evaluate the effect of rice plants on N loss from flooded soils (Broadbent and Tusneem, 1971; Reddy and Patrick, Jr., 1980; Fillery and Vlek, 1982; Smith and Delaune, 1984). The results presented in these studies did not arrive at any definitive conclusions on the effects of rice plants on N loss. The objective of this study was to determine the fate of applied fertilizer N in the root zone of rice plants and the surrounding anaerobic soil zone. The purpose of the study was not to assess the practical significance of the process, but to determine maximum potential loss in a system where experimental conditions are favorable for both nitrification and denitrification in the root zone. MATERIALS AND METHODS The soil used was a Crowley silt loam (Typic Albaqualfs) collected from the Rice Exp. Stn., Crowley, LA. It contained 0.8 g total N kg^, 7.0 g total C kg~', a cation exchange capacity (CEC) of 9.4 cmol (+) kg" of soil, and a pH of 5.8 (1:1 soil/water ratio). The soil had 10.8% clay, 70.7% silt, and 9.5% sand. Air-dried soil ground to pass through 0.84-mm mesh sieve was placed in polyvinyl chloride (PVC) tubes (20-cm long and 10-cm i.d.) and sealed at the bottom with a PVC cap (Fig. 1). Six rubber septa (three on each side placed 2 cm apart) had been installed at the bottom portion of the PVC tubes. Prior to the addition of soil, adequate deionized water containing N, P, and K was added to the tube to obtain saturated soil conditions and a final concentration of 50 mg N kg-', 25 mg P kg-', and 50 mg K kg-' of soil. All soil cores were placed in a greenhouse. In one set of cores, two healthy 20-d-old rice seedlings (var. 'Labonett') grown in sand culture were transplanted while the second set of cores was maintained with no plants. After the plants were grown for a period of 20 d, an additional 500 g of soil containing 1% rice straw was added to the core. Additional water was added to maintain saturated soil conditions. An additional 200 g of soil containing 2% rice straw was added to the core as a buffer zone. The main purpose for the addition of rice straw to the soil was to reduce N loss due to upward diffusion of N from the bottom portion of the core to the overlying floodwater. Results obtained in preliminary experiments indicated that it is important to prevent upward diffusion of NH^ if we are to be able to distinguish the effect of rice roots on N loss as compared to N losses due to nitrificationdenitrification reactions taking place at the soil-water interface. Because of the high C/N ratio of the rice straw (90:1), any N diffused will be readily immobilized. Labeled