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1.
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2.
A useful method to evaluate the effectiveness of soil‐erosion models is to compare the models' soil‐loss and runoff calculations with measured data from experimental plots subjected to artificial rainfall. This study was conducted to develop a set of statistics to compare the performance of the soil‐erosion models EUROSEM, WEPP, and MEDRUSH. Rainfall (six rainfall intensities, two replicates), runoff, and soil‐loss data from artificial plots at two locations in Hungary were used to assess the accuracy of the different models. The soil types within the plots represented a wide range of soil properties and are soil types that are commonly used for agriculture. The results showed that the three soil‐erosion models performed with varying effectiveness dependent on basic soil properties. However, statistical analysis showed the EUROSEM model to be the best for estimating soil loss in Hungary.  相似文献   

3.
The production and composition of leaf litter, soil acidity, exchangeable nutrients, and the amount and distribution of soil organic matter were analyzed in a broad‐leaved mixed forest on loess over limestone in Central Germany. The study aimed at determining the current variability of surface‐soil acidification and nutrient status, and at identifying and evaluating the main factors that contributed to the variability of these soil properties along a gradient of decreasing predominance of European beech (Fagus sylvatica L.) and increasing tree‐species diversity. Analyses were carried out in (1) mature monospecific stands with a predominance of beech (DL 1), (2) mature stands dominated by three deciduous‐tree species (DL 2: beech, ash [Fraxinus excelsior L.], lime [Tilia cordata Mill. and/or T. platyphyllos Scop.]), and (3) mature stands dominated by five deciduous‐tree species (DL 3: beech, ash, lime, hornbeam [Carpinus betulus L.], maple [Acer pseudoplatanus L. and/or A. platanoides L.]). The production of leaf litter was similar in all stands (3.2 to 3.9 Mg dry matter ha–1 y–1) but the total quantity of Ca and Mg deposited on the soil surface by leaf litter increased with increasing tree‐species diversity and decreasing abundance of beech (47 to 88 kg Ca ha–1 y–1; 3.8 to 7.9 kg Mg ha–1 y–1). The soil pH(H2O) and base saturation (BS) measured at three soil depths down to 30 cm (0–10 cm, 10–20 cm, 20–30 cm) were lower in stands dominated by beech (pH = 4.2 to 4.4, BS = 15% to 20%) than in mixed stands (pH = 5.1 to 6.5, BS = 80% to 100%). The quantities of exchangeable Al and Mn increased with decreasing pH and were highest beneath beech. Total stocks of exchangeable Ca (0–30 cm) were 12 to 15 times larger in mixed stands (6660 to 9650 kg ha–1) than in beech stands (620 kg ha–1). Similar results were found for stocks of exchangeable Mg that were 4 to 13 times larger in mixed stands (270 to 864 kg ha–1) than in beech stands (66 kg ha–1). Subsoil clay content and differences in litter composition were identified as important factors that contributed to the observed variability of soil acidification and stocks of exchangeable Ca and Mg. Organic‐C accumulation in the humus layer was highest in beech stands (0.81 kg m–2) and lowest in stands with the highest level of tree‐species diversity and the lowest abundance of beech (0.27 kg m–2). The results suggest that redistribution of nutrients via leaf litter has a high potential to increase BS in these loess‐derived surface soils that are underlain by limestone. Species‐related differences of the intensity of soil–tree cation cycling can thus influence the rate of soil acidification and the stocks and distribution of nutrients.  相似文献   

4.
Abstract

Soil Samples (72) were collected from the Delta, Hill, and Northeast Blackland areas of Mississippi. Chemical analyses for manganese, magnesium, and calcium were made using the Mississippi Soil Test Solution (MSTS) and several other extracting solutions chosen for comparison. For the determination of available soil manganese, the MSTS proved to be as effective as either the Double Acid (0.025 N HCl in 0.05 N H2SO4) or 0.1 N H3PO4. The acid extractants removed more manganese than 1 N NH4OAc (pH 7.0) and therefore included forms that are not exchangeable. The methods studied for magnesium determinations were equilibrium extraction with 1 N NH4OAc, MSTS, Double Acid, 0.25 N CaCl2, and leaching with 1 N NH4OAc. All methods were highly correlated and therefore would be equally effective in determining available soil magnesium. Since MSTS and equilibrium extraction with 1 N NH4OAc removed similar amounts of magnesium from the soil, the same calibration can be used. Calcium determinations were made using equilibrium extraction with 1 N NH4OAc, MSTS, and Double Acid, and by leaching with 1 N NH4OAc. All methods proved effective in measuring available soil calcium on acid soils.  相似文献   

5.
Recent studies indicate that soil soluble organic nitrogen (SON) plays an important regulatory role in the soil–plant N cycle. The aims of this study were to identify the vertical distribution of SON and its correlation with N mineralization, nitrification, and amidohydrolase activities, in a soil repeatedly amended with cow manure or chemical fertilizer. For this purpose, soil samples were collected from 0–20, 20–40, 40–60, 60–80, and 80–100 cm depths of a calcareous soil, which has been annually amended for 5 y with cow manure (CM) at two rates of 50 (CM50) and 100 (CM100) Mg CM ha–1 y–1. Treatments with chemical fertilizer (CF) and a control (CT) were also included. Soluble organic N, N mineralization, nitrification rates, as well as L‐glutaminase and L‐asparaginase activities were determined. Both CM50 and CM100 enhanced SON content throughout the soil profile. Nitrogen‐mineralization rate (Nm) was increased at the 0–20 cm depth of the CM100 treatment and remained unaffected at the deeper depths. Nitrification rate (Nn) was significantly higher at the 0–60 cm depth of CM100 compared to CF and CT. L‐glutaminase and L‐asparaginase activities were significantly increased at the 0–40 cm depth in both CM50 and CM100 compared to CF and CT. The amidohydrolase activities could not be detected below 40 cm, regardless of the fertilizer treatments. Our results suggest that SON makes a minor contribution to N mineralization in deep soil layers. It was also concluded that changes in the SON throughout the soil profile were not associated with changes in the N‐transformation rates (Nm and Nn) and amidohydrolase activities. While we conclude that SON is a major N pool in the whole profile of the manure applied soil further investigation is required to characterize SON and to investigate the bioavailability of SON for microbial activity in different soil depths.  相似文献   

6.
Industrial activities can contribute to the accumulation of heavy metals in soils, which could potentially threaten public health and the environment. This research was conducted to investigate the relationships between pH and total organic carbon (TOC) with soil chemical parameters, including exchangeable and total Cu, Zn, Cd, Pb, K, and Mg concentrations in soils near Panevėžys and Kaunas, Lithuania. Principal component regression (PCR) and non‐linear regression were used to find statistical relationships between pH, TOC, and the other soil properties studied. The results of correlation tests indicated that pH and TOC had strong relationships with most of the soil properties. The results of PCR [R 2 = 0·87, RMSE = 0·046] and non‐linear regression [R 2 = 0·91, RMSE = 0·041] (pH and the entire parameters), PCR [R 2 = 0·777, RMSE = 0·058] and non‐linear regression [R 2 = 0·871, RMSE = 0·046] (pH and the exchangeable parameters) to model the relationships between pH and soil chemical properties were promising and significant. Exchangeable heavy metal concentrations increased for pH > 5. Even though the relationships between TOC and heavy metals were significant, they were not as powerful as the relationships between pH and these metals. It was concluded that total metal concentrations in the study soils can be predicted by either pH or TOC. Metal mobility could most likely be controlled at the study site by manipulating soil pH and/or TOC. Finally, it is suggested that when there are financial and time limitations, assessment of total exchangeable metal concentrations using soil pH and/or TOC could be productive. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

7.
Glomalin‐related soil protein (GRSP) is well‐known for its soil conditioning functions, but compositional traits are rarely considered. Farmland in northeastern China is the most important commercial grain basis, and soil degradation becomes the bottleneck for keeping crop productivity. The objective of this study was to uncover the possible associations between GRSP (amount and composition) and soil properties, and make suggestions for soil improvement from soil glomalin rehabilitation in northeastern China. Here, spatial variation in GRSP amount (Easily‐extractable‐GRSP, EE‐GRSP; Total‐GRSP, T‐GRSP) and its compositional traits from infrared spectroscopy, UV‐absorbance, X‐ray diffraction (XRD) and 3‐D fluorescence spectroscopy were surveyed in 360 soil samples across northeastern China, and their association with 11 soil properties were also analyzed for finding the possible influence of soil properties on GRSP composition in farmland. There about 3‐fold spatial variation in GRSP amount was observed, while functional group variations were ranged from 1.2‐fold (O–H & N–H stretching) to 2.4‐fold (C–O stretching & O–H bending of –COOH) in different locations. The XRD showed that grain size was 113–180Å and crystallinity was 0.71–1.42%, and GRSP contained seven fluorescent compounds of tyrosine‐like, tryptophan‐like, fulvic acid‐like, soluble microbial byproduct, humic acid‐like, nitrobenzoxadidole‐like, and calcofluor white‐like. Both, EE‐GRSP and T‐GRSP positively associated with soil organic carbon (SOC), soil N (SON), soil P (SOP), alkali‐hydrolyzed N (AN), available P (AP), available K (AK), and soil water, while negatively associated with soil pH and soil bulk density. Structural equation model (SEM) analysis indicates that direct effects on GRSP amounts were mainly from soil bulk density (coefficient: –0.27), soil pH (coefficients: –0.51 to –0.57), SOC (coefficients: 0.51 to 0.69) and AP (coefficients: 0.18 to 0.26), while all other soil properties had indirect effects on GRSP amounts via their close associations with these four parameters. Compared with the GRSP amounts, soil properties laid fewer effects on GRSP compositional traits. Of 16 compositional traits, five of them showed possible regulations from soil properties, which were three infrared functional groups (IR‐II: aliphatic C–H stretching; IR‐V: C–O stretching & O–H bending of –COOH; IR‐VII: O–H binding) and two fluorescent compounds (tyrosine‐like and humic acid‐like). SEM analysis indicates that soil water, pH and EC could directly affect IR‐II, IRV, tyrosine‐like and humic acid‐like, while available nutrients showed more evident influences on infra‐red functional groups than total amounts of N, P and K. Moreover, SOC, as a media of various soil nutrients, gave the strongest influence on GRSP compositional traits. As a supplement to previous studies, we found that GRSP is a mixture of different fluorescent compounds with different functional groups. Our findings highlight that soil properties could strongly change both GRSP accumulation in soil and their compositional traits, and the definition of the most probable soil properties in regulating glomalin amount and composition in this paper could favor good soil management in farmland at northeastern China.  相似文献   

8.
Soil degradation is a mounting problem on many smallholder lands in developing countries. Economic analysis has been an important tool in addressing this problem, beginning with assessments of the financial attractiveness of investing in soil conservation works. Data compiled from 67 studies of the financial attractiveness of conservation technologies suggest that many can provide positive net returns at the farm level (64·2 per cent). While such studies have made a valuable contribution, economists have been exploring additional applications of economics to the problem, such as the development of new perspectives under the guise of ecological economics. As a result, this paper argues it is an opportune time to assess progress in the field of economic analysis of soil degradation and to consider the policy ramifications of this research. Key issues are grouped into farm‐level considerations, national policy linkages and global issues. A number of policy implications emerge. Clearly, devising effective incentives at the farm or community (collective action) level must be a priority. As part of this effort, even more attention should be paid to the influence of macroeconomic and sectoral policies on soil productivity. Since soil degradation is also a problem with global ramifications, there is a clear rationale for intervention at the international level via mechanisms such as international transfers. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

9.
This study investigated the effect of different farming practices over long time periods on the sorption‐desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long‐term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients KF increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO3)2 < animal manure ≤ grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants KF and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water‐soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.  相似文献   

10.
Bone char is a potential clean and renewable P fertilizer with Cd‐immobilization capabilities, but the P–Cd interactions in cropping of vegetable, grain, and tuber crops are unknown. In the present pot experiment bone char was evaluated on its effect on the growth and P supply of various crops (lettuce, wheat, potatoes) as well as its capability to reduce the uptake of Cd from a moderately Cd‐contaminated and P‐deficient soil (soil 1) and a highly Cd‐contaminated soil with sufficient P supply (soil 2). When averaging the dry‐matter yield over the treatments for each crop for the P‐sufficient soil 1, the following order was obtained: triple superphosphate (TSP) > diammonium phosphate (DAP) > BC, whereas for the soil 2 with sufficient P supply it was inverted with BC > DAP > TSP. The P‐deficiency resulted in a more pronounced effect of TSP and DAP on the plant growth, whereas P sufficiency in the soil promoted a crop‐quality‐enhancing effect of bone char. The Cd concentration in the consumption‐relevant plant parts was mostly insignificantly affected by treatments; however, the total Cd concentration in the whole plants tended to decrease with fertilizer addition for all crops in soil 1 even at very low bone‐char application levels. Similar results were obtained for soil 2 with an exception for the Cd concentration in potatoes, as the total Cd concentration was significantly increased in the TSP and DAP treatments. This most likely results from the introduction of Cd with TSP and DAP as they contained ≈ 27–28 mg Cd kg–1. Thus, this study demonstrated the potential of bone char as a clean P fertilizer, which can efficiently decrease the Cd contamination of potato on contaminated soils.  相似文献   

11.
土壤培肥过程中氯离子累积与分布规律研究   总被引：3，自引：0，他引：3  
以陕西杨凌杜寨村为中心,沿南、西、北3条辐射线分别采取耕层和剖面土样,探讨土壤中Cl^-的累积与垂直分布情况,揭示受人类生活影响历史较长的杜寨村农田土壤中Cl^-的累积状况与迁移规律。结果表明,在半干旱偏湿润气候地区,由于受自然环境因素和人为因素的强烈影响,Cl^-在村庄附近的土壤耕层呈现出累积趋势,随着离村庄距离的增加而明显减少;土壤剖面上Cl^-的含量随着土壤深度的增加也逐渐减少;Cl^-在土壤耕层虽然表现出一定的累积趋势,但累积量并不高,暂时不会影响作物的产量和品质。  相似文献   

12.
In the Transmexican Volcanic Belt a traditional fallow system is practiced, called “ año y vez ” (AV), which does not benefit soil conservation due to its low level of nutrient recycling and because soil protection is poor during the cultivation year. The objective of the present work was to measure runoff and soil and nutrient losses during three annual cycles (2002–2004) in Central Mexico under AV rotation and two alternative systems: improved traditional (IT) and traditional organic (TO). Soil losses in the three systems were moderate (<1.2 Mg ha−1 y−1) except during 2002, in which significant soil losses were recorded in IT and TO due to the scarcity of plant cover (<20 per cent) that was present throughout the rainy season. During the resting period of the AV system (2003), the annual runoff increased from 19 to about 600 per cent, compared to IT and TO without grazing. The difference in runoff was attributed to an 18 per cent increase in bulk density of soil surface (0–5 cm) caused by cattle trampling while grazing. Nutrient losses in the three treatments were mainly of N, Ca2+, Mg2+, Na+, and K+. These results suggest that AV has a higher topsoil degradation effect during the resting year than during the cultivation period. The study shows that incorporating the maize/beans‐black oat rotation and residue cover causes a low runoff response that is important in reducing soil degradation. A spatial analysis is presented of erosion at watershed level for two soil management systems assessed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
In the present study, we have investigated relationships among several soil parameters (pH, organic matter, total carbonate, macronutrients, electrical conductivity, cation‐exchange capacity) and macronutrient and cardenolide contents in leaves of wild Digitalis obscura plants. Young and mature leaves and soil samples were collected in ten different areas, corresponding to three Mediterranean bioclimatic belts (thermo‐, meso‐, and supramediterranean belts). Soil and leaf macronutrient (N, P, K, Ca, and Mg) contents and leaf cardenolide contents were determined. Bioclimatic conditions influenced the development of D. obscura, biomass being lowest in plant populations of the supramediterranean belt, but they did not exert any relevant effect on the contents of macronutrients in soils and plants. Magnesium (total and EDTA‐extracted) was the only soil macronutrient significantly correlated with its content in the plant. Cardenolide contents were negatively correlated with the N, P, and K contents in young leaves, whereas such correlations were highly significant and positive for Mg.  相似文献   

14.
Land use choices differentially affect soil physical and biological properties. Tillage choices in particular affect soil erosion, the retention of soil organic matter, and the biological activity that organic matter supports. The present study evaluated the consequences of different cropping and tillage systems (undisturbed forest, coffee plantation, conventional, and no‐tillage row cropping) for soil microbial indicators and sulfur mineralization after 24 years of cropping on an Oxisol (Typic Haplorthox) in an experimental area at Londrina, Brazil. Soil samples were taken at 0–5, 5–10, and 10–20 cm depths and evaluated for microbial biomass P and S, S mineralization, and phosphatase and arylsulfatase activities. Land use affected microbial biomass P and S, and enzyme activity at all depths studied. The cultivated sites had lower values of microbial activity than the undisturbed forested site. Although the coffee site was not tilled and had high organic carbon content, there was low microbial activity, probably due to higher soil acidity and Al content. The estimates of pool stock for microbial P and annual P flux through the soil microbial biomass suggest that these pools are large enough to significantly affect plant nutrient availability. The greater microbial biomass and activity under forested and no‐tillage sites may be attributed, at least partially, to higher organic matter content. The soil microbial variables examined proved to be strong indicators of soil sustainability. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
Although enzyme activities were extensively investigated in soils with reference to abiotic environmental conditions and human impact, their role in litter decomposition is not fully understood. Therefore, decomposition rates and enzyme activities were studied using nylon bags and three litter types buried in silty‐loamy Cambisols and Luvisols in northern, central, and southern Germany under similar averaged temperature and precipitation and a maritime to continental gradient. After 180 d, the ash‐free mass remaining ranged between 15% and 68% for the Triticum, Secale, and Lolium litter. The enzyme activities were mainly controlled by the litter type and the decomposition time and less but significant by site. The highest decomposition rate occurred at the central German site for Lolium litter associated with highest arginine ammonification and urease activity in litter. In contrast, the recalcitrant Secale and Triticum litter were decomposed more rapidly at the northern and southern site where urease, protease, and arginine ammonification was high in the bulk soil. The β‐glucosidase activity was similar in soil and litter at the three locations and was not correlated to the velocity of litter decomposition. Since the abiotic environmental factors at the maritime to continental gradient did not explain the site‐specific velocity of both rapidly decomposing and refractory litter, enzyme activities related to the N cycling like arginine ammonification and urease activity were recognized to velocity of litter decomposition.  相似文献   

16.
Rock fragments (particles > 2 mm) are usually considered chemically inert for plant growth. In this paper, the potential fertility in terms of exchangeable Ca, Mg, and K of rock fragments from sandstone and siltstone derived soils from northern Apennines (Italy) is reported and contrasted with that of the fine earth (particles < 2 mm). The results show that rock fragments are a source of Ca, Mg, and K. When expressed on a volume basis, the abundance of these exchangeable nutrients sometimes may equal or surpass that of the fine earth. The plant uptake of Mg and K has been demonstrated in growth experiments with Agrostis under controlled conditions.  相似文献   

17.
The production of secondary metabolites by plants growing in natural populations is conditioned by environmental factors. In the present study, we have investigated the relationships among soil properties, micronutrients in soils and plants, and cardenolide production from wild Digitalis obscura (Scrophulariaceae) populations. Young and mature leaves and soil samples were collected in ten different populations, corresponding to three Mediterranean bioclimatic belts (Thermo‐, Meso‐, and Supramediterranean belts). Soil (total and EDTA‐extractable) and leaf micronutrients (Fe, Mn, Zn, and Cu), and leaf cardenolide accumulation have been determined. Significant negative correlations were observed between Fe, Mn or Zn concentration in leaves and soil pH, as well as between Fe or Mn in leaves and carbonate content of soils. Only EDTA‐extractable Mn was significantly correlated with Mn content in the plants. With regard to cardenolide content in leaves, this parameter was negatively correlated with Znleaf in young leaves and with Mnleaf in old leaves. Positively correlated, however, were Fe and cardenolide content in young leaves. The influence of environmental conditions and leaf micronutrient contents on cardenolide accumulation is discussed.  相似文献   

18.
Abstract

Production of high‐quality sugar beets requires precise nitrogen (N) fertilizer management with N recommendations based on a measurement of residual nitrate‐N to 120 cm (4 ft) soil depth. The objective of this study was to determine the agronomic and economic aspects of using different grid cell sizes for sampling soil nitrate‐N. A 5‐ha field (12.4 acre) was soil sampled for nitrate‐N using 18.3×18.3 m grid cells in 1997 and 1998. Nitrogen application maps for four different grid cell sizes 18.3×18.3 m (60×60 ft), 54.9×54.9 m (180×180 ft), 91.4×91.4 m (300×300 ft), and 128×128 m (420×420 ft) were developed from these soil samples and compared with a conventional average for each field. The five nitrogen fertilizer treatments adjusted for grid cell size were applied with a fertilizer truck equipped with a variable rate applicator in two replicates of 274‐m long strips. Sugar beet quality was determined on root samples taken immediately before root harvest on a 18.3×18.3 grid. Root yield was determined with a conventional harvester equipped with a yield monitor. The nitrogen fertilizer application maps derived from the 54.9×54.9 m, 91.4×91.4 m, and 128×128 m soil sampling grids were similar in 1997. The application map derived from 18.3×18.3 m grid cell size was different from the application maps derived from larger grid cell sizes. Although there were differences in N application maps, there were no differences in root yield, root quality, or recoverable sucrose among grid cell sizes or constant rate applications in either 1997 or 1998.  相似文献   

19.
The Podzol has been elected “Soil of the year 2007” in Germany. This article reviews the present knowledge on the development, functions, and threats of Podzols. The main theories on mobilization and transport of organic matter, Fe, Al, and Si are (1) metal‐organic migration, (2) metal reduction, and (3) inorganic sol migration. Immobilization theories include precipitation or polymerization due to increasing pH/abundance of base cations with depth, mechanical filtering in soil pores, oxidation of metal‐organic complexes, biodegradation of the organic part, decreasing C‐to‐metal ratios during translocation, adsorption to soil particles, and flocculation at the point of zero charge. Podzolization is discussed also on the catena scale, where vertical and lateral translocation processes (across pedon boundaries) need to be considered to understand Podzol patterns in landscapes. Chronosequence studies show that incipient podzolization usually becomes visible between 100 and 500 y and mature Podzols develop in 1,000–6,000 y. The occurrence of Podzols worldwide is concentrated mainly on the boreal zone and mountain regions within the humid temperate zone. Smaller Podzol areas are found in some perhumid tropical and subtropical regions. In Germany, Podzols occur in the Alps, in the glaciofluvial valleys and heathlands of N Germany, and in the mountain ranges. They fulfil several ecological functions, especially for groundwater recharge. Main threats for these mostly sandy soils are wind erosion and surface mining of sand. Two pedons which were chosen to represent the “Soil of the year 2007” are presented. Finally, some conclusions about podzolization processes are drawn, which may explain the diverse observations reported in the literature.  相似文献   

20.
Abstract

Greenhouse and field experiments were conducted to study the effects of water regime on growth of rice. The greenhouse experiment investigated the effects of two water regimes‐continuous flooding and flooding with soil drying between crops for 2 to 3 weeks on the growth of rice during six cropping (for six week each) on seven soils varying widely in total N contents (0.07 to 0.35%). The results averaged for the 7 soils indicated that the drymatter production or N uptake of rice was not affected by the water regimes during the six croppings.

The field experiment conducted during the dry season for two consecutive years (1976 and 1977) on a near neutral clay soil studied the effects of three water regimes (continuous flooding alternate flooding and soil drying every 2 weeks, and continuous flooding with 2 weeks mid season soil drying after 6 weeks of transplanting) and three levels of fertilizer N (0, 100 and 200 kg N/ha as urea) on grain yield and N uptake of rice. The results confirmed the absence of any significant reduction in grain yield or N uptake as a result of any of the soil drying treatments during the growing season on the unfertilized plots carrying a rice crop. On the plots fertilized with 100 or 200 kg N/na, alternate flooding and drying resulted in a significant depression in both grain yield and N uptake. Soil analysis supported heavy losses of N in the fertilized plots that underwent alternate flooding and soil drying apparently by nitrification and denitrification reactions.

The results of this study suggest that alternate flooding and drying of soils in the presence of established rice plants itiay not cause a significant loss of nitrogen in unfertilized plots although in plots fertilized with high rates of N the losses may be large as indicated by the performance of rice crop.  相似文献   

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