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1.
A deep understanding of crop-water eco-physiological relations is the basis for quantifying plant physiological responses to soil water stress. Pot experiments were conducted to investigate the winter wheat crop-water relations under both drought and waterlogging conditions in two sequential growing seasons from 2000 to 2002, and then the data were used to develop and validate models simulating the responses of winter wheat growth to drought and waterlogging stress. Thee xperiment consisted of four treatments, waterlogging (keep 1 to 2 cm water layer depth above soil surface), control (70%-80% field capacity), light drought (40%-50% field capacity) and severe drought (30%-40% field capacity) with six replicates at five stages in the 2000-2001 growth season. Three soil water content treatments (waterlogging, control and drought) with two replicates were designed in the 2001-2002 growth season. Waterlogging and control treatments are the same as in the 2000-2001 growth season. For the drought treatment, no water was supplied and the soil moisture decreased from field capacity to wilting point. Leaf net photosynthetic rate, transpiration rate, predawn leaf water potential, soil water potential, soil water content and dry matter weight of individual organs were measured. Based on crop-water eco-physiological relations, drought and waterlogging stress factors for winter wheat growth simulation model were put forward. Drought stress factors integrated soil water availability, the sensitivity of different development stages and the difference between physiological processes (such as photosynthesis, transpiration and partitioning). The quantification of waterlogging stress factor considered different crop species, soil water status, waterlogging days and sensitivity at different growth stages. Data sets from the pot experiments revealed favorable performance reliability for the simulation sub-models with the drought and waterlogging stress factors.  相似文献   

2.
A. M. MAHDY 《土壤圈》2011,21(6):773-781
A greenhouse experiment was conducted to test and compare the suitability of saline compost and saline irrigation water for nutrient status amendment of a slightly productive sandy clay loam soil,to study the macronutrient utilization and dry matter production of wheat(Triticum aestivum c.v.Gemmiza 7) grown in a modified soil environment and to determine the effects of compost and saline irrigation water on soil productivity.The sandy clay loam soil was treated with compost of five rates(0,24,36,48,and 60 m 3 ha-1,equivalent to 0,3,4.5,and 6 g kg-1 soil,respectively) and irrigation water of four salinity levels(0.50(tap water),4.9,6.3,and 8.7 dS m-1).The results indicated that at harvest,the electrical conductivity(EC) of the soil was significantly(P < 0.05) changed by the compost application as compared to the control.In general,the soil salinity significantly increased with increasing application rates of compost.Soluble salts,K,Cl,HCO 3,Na,Ca,and Mg,were significantly increased by the compost treatment.Soil sodium adsorption ratio(SAR) was significantly affected by the salinity levels of the irrigation water,and showed a slight response to the compost application.The soil organic carbon content was also significantly(P < 0.05) affected by application of compost,with a maximum value of 31.03 g kg-1 recorded at the compost rate of 60 m 3 ha-1 and the irrigation water salinity level of 8.7 dS m-1 and a minimum value of 12.05 g kg 1 observed in the control.The compost application produced remarkable increases in wheat shoot dry matter production.The maximum dry matter production(75.11 g pot-1) occurred with 60 m 3 ha-1 compost and normal irrigation water,with a minimum of 19.83 g pot-1 with no addition of compost and irrigation water at a salinity level of 8.70 dS m-1.Significant increases in wheat shoot contents of K,N,P,Na,and Cl were observed with addition of compost.The relatively high shoot N values may be attributed to increases in N availability in the tested soil caused by the compost application.Similarly,significant increases in the shoot contents of Na and Cl may be ascribed to the increase in soil soluble K and Cl.The increases in shoot P,N,and K contributed to the growth stimulation since P supplied by the compost was probably responsible in saline and alkaline soils where P solubility was very low.  相似文献   

3.
The patterns of soil nitrogen(N) isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N,and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were:i) to investigate the patterns of soil N content and natural abundance of 15N(δ15N) values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii) to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil δ15N values; and iii) to test the relationship between soil δ15N values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest,meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and δ15N values. Our results indicated that soil N and δ15N values(0–40 cm) in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem,while variations of soil δ15N values along soil profiles were not statistically significant among most ecosystems but for mountain meadow,lowland meadow,and temperate steppe where soil δ15N values tended to increase with soil depth. The parabolic relationship between soil δ15N values and mean annual precipitation indicated that soil δ15N values increased with increasing precipitation in desert steppe up to 500 mm,and then decreased with increasing precipitation across all other ecosystems. Moreover,the parabolic relationship between δ15N values and mean annual temperature existed in all individual ecosystem types. Soil N and δ15N values(0–40 cm) increased with an increase in soil silt and clay contents. Furthermore,a threshold of C/N ratio of about 11 divided the parabolic relationship between soil δ15N values and soil C/N ratios into positive(C/N 11) and negative(C/N 11) parts,which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil δ15N values suggested that C and N concentrations,being strongly controlled by precipitation and temperature,were the primary factors determining patterns of soil δ15N on the Qinghai-Tibetan Plateau.  相似文献   

4.
大豆生长期间的土壤呼吸   总被引：5，自引：0，他引：5  
Soil respiration induced by soybean cultivation over its entire growing season and the factors influencing soil respiration were investigated to examine the seasonal pattern of soil respiration induced by soybean cultivation, explore soybean growth and photosynthesis on soil respiration, and determine the temperature dependence on soil respiration. Soil respiration in a pot experiment with and without soybean plants was sampled using the static chamber method and measured using gas chromatograph. Air temperature was a dominant factor controlling soil respiration rate in unplanted soil. Additionally, rhizosphere respiration comprised 62% to 98% of the soil respiration rate in the soybean-planted soil varying with the soybean growth stages. Harvesting aerial parts of soybean plant caused an immediate drop in the soil respiration rate at that stage. After harvesting the aerial parts of the soybean plant, a highly significant correlation between soil respiration rate and air temperature was found at the flowering stage （P 〈 0.01）, the pod stage （P 〈 0.01）, and the seed-filling stage （P 〈 0.05）. Thus, rhizosphere respiration during the soybean-growing period not only made a great contribution to soil respiration, but also determined the seasonal variation pattern of the soll respiration rate.  相似文献   

5.
长期施用堆肥对小麦根际及非根际土壤化学性质的影响   总被引：2，自引：0，他引：2  
Compost of different rates was applied to artificial field plots of a low humic andosol at National Agriculture Research Center (NARC)of Japan for 15 or 28 years,and their effects on the chemical properties of wheat rhizosphere soil and nonrhizosphere soil were measured.Contiuous application of compost for 28 years resulted in raise of soil C,N,P,pH and exchangeable based.The building up of compost for 28 years resulted in raise of soil C,N,P,pH and exchangeale bases,The building up of organic matter in the soil occureed slowly.A residual effect of the compost on soil chemical properties was still present after 13 years of no application,but this effect was weaker in comparison with that of the continuous application treatments.In the rhizosphere soil,NaHCO3-extracted P and exchangeable Ca were higher than those in the bulk soil.The removal of free organic acid slightly affected the soil pH,especially,the rhizosphere soil pH.The raise of soil pH may result from the increase of exchangeable base by the application of compost.  相似文献   

6.
黑土区大豆基因型的根际细菌群落结构时空动态变化   总被引：1，自引：0，他引：1  
The dynamics of rhizosphere microbial communities is important for plant health and productivity, and can be influenced by soil type, plant species or genotype, and plant growth stage. A pot experiment was carried out to examine the dynamics of microbial communities in the rhizosphere of two soybean genotypes grown in a black soil in Northeast China with a long history of soybean cultivation. The two soybean genotypes, Beifeng 11 and Hai 9731, differing in productivity were grown in a mixture of black soil and siliceous sand. The bacterial communities were compared at three zone locations including rhizoplane, rhizosphere, and bulk soil at the third node (V3), early flowering (R1), and early pod (R3) stages using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA. The results of principal component analyses (PCA) showed that the bacterial community structure changed with growth stage. Spatially, the bacterial communities in the rhizoplane and rhizosphere were significantly different from those in the bulk soil. Nevertheless, the bacterial communities in the rhizoplane were distinct from those in the rhizosphere at the V3 stage, while no obvious differences were found at the R1 and R3 stages. For the two genotypes, the bacterial community structure was similar at the V3 stage, but differed at the R1 and R3 stages. In other words, some bacterial populations became dominant and some others recessive at the two later stages, which contributed to the variation of the bacterial community between the two genotypes. These results suggest that soybean plants can modify the rhizosphere bacterial communities in the black soil, and there existed genotype-specific bacterial populations in the rhizosphere, which may be related to soybean productivity.  相似文献   

7.
The fate of urea-and ammonium bicarbonate(ABC)-nitrogen (N) applied by prevailing traditional techniques to winter wheat (Triticum aestivum L.)or maize (Zea mays L.)grown in the fields of Fluvo-aquic soil was investigated using ^15N tracer-micro-plot technique.Results show that:(1) at maturity of wheat,N recovery in plants and N losses of urea and ABC applied at seeding in autumn were 31-39%,and 34-46%,respextively,while the corresponding figures for side-banding at 10 cm depth in early spring were 51-57%,and 5-12%;surface-broadcast of urea followed by irrigation at early spring was as efficient as the side-banding in improving N recovery in plants and reducing N loss,however,such techuique was found less satisfactory with ABC.(2)At the maturity of maize,N recovery in the plants and N loss of urea and ABC sidebanded at seedling stage or prior to tasseling ranged from 23% to 57%,and 9% to 26%,respectively.(3) Either in Wheat or in maize experiment,the majority of residual fertilizer N in soil profile (0-60cm) was in the form of biologically immobilized organic N,however,the contribution of ammonium fixation by clay minerals increased markedly nwith depth in soil profile.(4) Though the proportion of residual fertilizer N was generally highest in the top 20 cm soil layer,considerable reaidual N (nostly 6-11% of the N applied)was found in 60-100 cm soil layers.  相似文献   

8.
影响土壤浸提液电导率的化学因素及其强度研究   总被引：8，自引：1，他引：8  
Time series bioaccumulation of rare earth elements （REEs） in field-grown wheat with and without a dressing of extraneous REE fertilizer at different growth stages and fractionation of REEs during their transport in a soil-wheat system were determined. Time-dependent accumulation of extraneous REEs was found in different parts of wheat. An upward transport of extraneous REEs from roots to shoots under a soil dressing and a downward transport from leaves to roots with a foliar dressing were also observed. Moreover, fractionation of REEs occurred in the soil-wheat system. Compared to the host soil a positive Eu anomaly in the stems and grains as well as heavy REE enrichment in the grains were found. The ability of the different wheat organs to fractionate Eu from the REE series was ranked in the order of sterns 〉 grains 〉 leaves 〉 roots.  相似文献   

9.
氮及相关的酶活性对小麦根际施肥的反应   总被引：1，自引：0，他引：1  
In the present experiment,wheat seedlings(Trticucum aestivum L.)were grown on a purple soil with various fertilizer treatments in order to investigate the responses of nitrogen and related enzyme activities in the rhizosphere,The results revealed the increments of both organic matter and total N in the soil with the proximity to the growing roots,especially in treatment of supplying pig manure in combination with chemical fertilizer,suggesting that they could ome from root and microorganism exudation which could be intensified by inorganic-organic fertiliztion,being of benefit to improving the physical and bilogical envi-ronment in the rhizosphere of wheat.Much more inorganic N was observed in the fertilized soils surrounding wheat roots than in the CK treatment ,indicating ,the improvement of crop N supply in the rhizosphere of wheat by fertilization. The activities of invertase,urease and protease in the root zone were greatly enhanced as compared to those in the other parts of soil except that the urease activities were similar in the rhizospher and nonrhi-zosphere of the CK and pig manure treatments,indicating that invertase and protese could be produced by growing roots and rhizosphere microorganisms,in contrast to urease which could be stimulated by urea,Also,significant increment of chemical fertilizer combined with pig manure,suggested that fertilization not only accelerated the renewal of organic matter bu also enhanced bioavailability of organic N in that soil zone .This could be the reason why the total amount of inorganic N available for plants was increased more obviously in the rhizosphere of wheat of the fertilizaton treatments than in taht of the CK treatment.  相似文献   

10.
Four kinds of plant materials(astragalus,azolla,rice straw and water hyacinth) were allowed to decom-pose for 10 years in two soils with different mineralogical characteristics in fields under upland and submerged conditions.Greater amounts of C and N from azolla were retained in soils throughout the 10-year experi-mental period compared to those from the other plant materials.The residual C of all the plant materials in the two soils under upland conditions mineralized at rates corresponding to half-lives between 4.4-6.6 years,while the corresponding figures for those under submerge conditions were between 6.5-13.1 years,Minera-liztion of residual organic N followed the same pattern as residual C.Compared to residual C,however,the mineralization rates of residual organic N in most cases were significantly lower and the percentages of added N retained in soils were higher.More N from plant materials was retained in the yellow-brown soil than in the red soil,but no consistent differences in the amounts of C from plant materials and in the mineraliztion rates of both residual C and residual organic N between the wto soils could be folund.  相似文献   

11.
Natural 15N abundances (δ15N) in plant and soil can be used as a powerful marker to reveal the history of N fertilization. To investigate whether N fertilizer source and timing of fertilization leave specific δ15N signals in plant tissue and soil inorganic N, Chinese cabbage (Brassica campestris L. cv. Maeryok), one of the most popular vegetables in Asia, was grown in pots for 60 days with a single or split N applications of organic (composted manure; δ15N=+16.4‰) or inorganic N (urea; δ15N=−0.7‰). Seven N treatments were studied: (1) a single basal fertilization with compost or (2) urea; (3) a basal urea application followed by an additional (at 40 days after transplant, same below) compost or (4) urea application; (5) a basal compost application followed by an additional compost or (6) urea application; and (7) no N fertilization. Regardless of the time of N application, δ15N of cabbage treated with compost was higher (>+9.0‰) than that (< +1.0‰) treated with urea, reflecting the effect of isotopically different N sources. In split N fertilization, only the addition of isotopically different N sources in the middle of the growth period significantly affected the δ15N of the whole plant. Specific δ15N signals of basal N inputs were detected in outer cabbage parts formed in the early growth stage, while those of additional N inputs were detected in inner cabbage parts formed in the latter growth stage. We conclude that measurements of temporal variations in δ15N of plant parts formed in different growth stages could reveal the history of N fertilization.  相似文献   

12.
Azolla microphylla Kaulf. (Azolla) biomass was composted to create a high nitrogen (N) organic matter amendment (Azolla compost). We examined the effect of this Azolla compost on carbon (C) and N mineralization and the production of biogenic gases, nitrous oxide (N2O) and carbon dioxide (CO2), in a soil incubation experiment. A pot experiment with upland kangkong (Ipomoea aquatica Forsk.) examined plant growth in silt loam soil treated with three levels of Azolla compost. The results showed that N2O production from soil increased with urea amendment, but not with Azolla compost treatments. The Azolla-amended soil showed enhanced CO2 production throughout the 4-week incubation. The Azolla-treated soils showed a 98% lower global warming potential compared to urea treatment over the 4-week incubation. However, Azolla-amended soil had higher nitrate (NO3–) levels compared to urea-fertilized soil at 1 week of incubation, and these were maintained until the fourth week. Soils amended with Azolla compost showed lower ammonium nitrogen (NH4-N) levels than those in the urea-fertilized soils. The height and dry weight of upland kangkong fertilized with Azolla compost were similar to plants receiving urea fertilization. Therefore, the use of Azolla compost as a substitute for urea fertilizer would be beneficial for reducing the production of N2O while maintaining plant growth.  相似文献   

13.
采用15N示踪技术,选用水稻土和灰潮土在宜兴进行小麦盆栽试验,研究了稻草、猪粪及其堆肥与化肥配施对作物生长及氮素吸收的影响。结果表明,在水稻土和灰潮土上,不同有机物及其堆肥与化肥配施分别比单施化肥增产4.46%～24.82%和1.01%～20.53%,稻草堆肥和猪粪堆肥配施化肥处理籽粒产量分别高于稻草和猪粪直接与化肥配施处理。稻草和猪粪堆肥后更利于作物吸收氮素,增加植物体内15N累积。两种土壤上15N回收率表现为相同配比的堆肥处理未堆肥处理单施化肥处理。随着小麦生育期的推进,土壤微生物量氮和矿质态氮含量均呈下降趋势,稻草和猪粪处理的微生量氮含量始终高于稻草堆肥和猪粪堆肥处理。有机无机肥配施处理土壤矿质态氮在小麦生育前期低于单施化肥,成熟期则高于单施化肥。整个生育期中,稻草堆肥和猪粪堆肥处理土壤矿质态氮含量分别高于稻草和猪粪处理。因此,有机物堆肥后与化肥配施更有利于提高产量,促进作物对氮素的吸收利用。  相似文献   

14.
Nmim content in the soil, N-fertilization and N uptake of winter wheat in the international organic nitrogen long-term fertilization experiment (IOSDV) Berlin-Dahlem During the 9th and 10th year of the long-term IOSDV field experiment micro plots were put in three treatments. Labelled15 N (160 resp. 110 kg/ha N as ammonium sulfate) was fertilized to winter wheat subdivided into three portions. Nmin in soil was determined five times during the season, plant biomass was harvested at different growth stages and N uptake was calculated. Using the15 N-technique permitted a discrimination between fertilizer-N and soil-N. Preferential uptake of fertilizer-N by the wheat crop but also immobilisation in soil were observed until June. Subsequently the immobilized N was remineralized and assimilated by wheat. But the native Nmin of soil was minimaly utilized during the initial growth of wheat. Therefore the absolute amount of soluble N temporarily increased caused by a mineralisation of the organic matter.  相似文献   

15.
Two field experiments were conducted on Andisols in Japan to evaluate the changes in the natural 15N and 13C abundance in the soil profile and to determine whether the values of δ15N could be used as an indicator of fertilizer sources or fertilizer fate. The 6-year experiment conducted at the National Agricultural Research Center (NARC) consisted of the following treatments: application of swine compost (COMPOST), slow-release nitrogen fertilizer (SRNF), readily available nitrogen fertilizer (RANF), and absence of fertilization (CONTROL). Experimental plots located at the Nippon Agricultural Research Institute (NARI) received cattle compost at different rates for 12 years; a forest soil at this site was sampled for comparison. Swine compost application led to a considerable change in the δ15N distribution pattern in the soil profile, with the highest δ15N values recorded in the top 20 cm layers of the COMPOST plot, decreasing in the sequence of CONTROL >- RANF > SRNF, mainly due to the relatively high δ15N value of swine compost and its subsequent decomposition. In contrast, SRNF application resulted in the lowest δ15N values in soil, indicating the presence of negligible nitrogen losses relative to input and low nitrogen cycling rates. Values of δ15N increased with compost application rates at NARI. In the leachate collected at 1-m depth, the δ15N values decreased in the sequence of COMPOST > RANF ≥ CONTROL > SRNF. The δ13C values in soil peaked in the 40–60 cm layers for all the fertilizers. The δ13C value was lowest in forest soil due to the presence of plant residues in soil organic matter. These results indicated that the δ15N values in the upper soil layers or leachate may enable to detect pollution sources of organic or inorganic nitrogen qualitatively in Andisols.  相似文献   

16.
不同氮肥处理对土壤和番茄中稳定性氮同位素丰度的影响   总被引：2，自引：0，他引：2  
采用盆栽番茄的方式,根据氮肥类型和施用量,设置8种肥料处理（以纯氮计）：C1（有机肥,9.5g）、CU1（有机肥、化肥均为4.75g）、U1（化肥,9.5g）、C2（有机肥,19g）、CU2（有机肥、化肥均为9.5g）、U2（化肥,19g）、C3（有机肥,29g）、CK（不施肥料）,分析各处理的土壤、番茄叶片和果实δ15N的变化,比较不同部位δ15N的差异.结果表明,（1）施用有机肥能显著提高土壤、叶片和果实的δ15N（P ＜0.05）,而施用化肥则显著降低其δ15N（P＜0.05）.纯有机肥（C1、C2、C3）处理番茄叶片和果实δ15N分别为6.02‰ ～ 12.75‰和4.69‰～8.24‰,纯化肥（U1、U2）处理为2.83‰～5.53‰和2.66‰ ～4.50‰,纯有机肥处理δ15N显著高于纯化肥处理.（2）番茄植株不同部位δ15N的比较结果为老叶＞新叶＞新茎＞果实＞老茎＞侧根＞主根,表明氮素由根部吸收经过茎的运输到达叶片和果实的过程中,15N逐步富集.（3）建议将利用氮稳定同位素技术鉴别番茄果实纯有机肥和纯化肥处理的δ15N的阈值设定为5‰,有机种植检测可以借鉴此法设定相应的临界值,以鉴别有机种植和非有机种植.研究结果表明通过氮稳定同位素技术可以区分植物中氮素的来源,从而得知作物生长过程中的施肥情况,为有机食品检测提供有效方法.  相似文献   

17.
This study investigated the long-term effects of different composts (urban organic waste compost (OWC), green waste compost (GWC), cattle manure compost (MC) and sewage sludge compost (SSC)) compared to mineral fertilisation on a loamy silt Cambisol, after a 7-year start-up period. The compost application rate was 175 kg N ha?1, with 80 kg mineral N ha?1 and without. Soil characteristics (soil organic carbon (SOC), carbon-to-nitrogen (C/N) ratio and soil pH), nutrients (nitrogen (N), phosphorous (P) and potassium (K)) and crop yields were investigated between 1998 and 2012. SOC concentrations were increased by compost applications, being highest in the SSC treatments, as for soil pH. N contents were significantly higher with compost amendments compared to mineral fertilisation. The highest calcium-acetate-lactate (CAL)-extractable P concentrations were measured in the SSC treatments, and the highest CAL-extractable K concentrations in the MC treatments. Yields after compost amendment for winter barley and spring wheat were similar to 40 kg mineral N ha?1 alone, whereas maize had comparable yields to 80 kg mineral N ha?1 alone. We conclude that compost amendment improves soil quality, but that the overall carbon (C) and N cycling merits more detailed investigation.  相似文献   

18.
Grassland ecosystems in south-eastern Australia are important for dairy and livestock farming. Their productivity relies heavily on water availability, as well as the ecosystem services provided by soil microbial communities including carbon and nutrient cycling. Management practices such as compost application are being encouraged as a means to improve both soil water holding capacity and fertility, thereby buffering against the impacts of increasing climate variability. Such buffering consists of two complementary processes: resistance, which measures the ability of an ecosystem to maintain community structure and function during a period of stress (such as drying); and resilience, which measures the ability of an ecosystem to recover community structure and function post-stress. We investigated the effects of compost on the resistance and resilience of the grassland soil ecosystem under drying and drying with rewetting events, in a terrestrial model ecosystem. Overall, compost addition led to an increase in soil moisture, greater plant available P and higher plant δ15N. Soil C:nutrient ratios, mineral N content (NH4+ and NO3−) and soil microbial PLFA composition were similar between amended and unamended soils. Rainfall treatment led to differences in soil moisture, plant above-ground and below-ground biomass, plant δ15N, soil mineral N content (NH4+ and NO3−) and microbial biomass C, N and P composition but had no effects on soil C:nutrient ratios, plant available P and soil microbial PLFA composition. There was little interaction between rainfall and compost. Generally, the soil microbial community was resistant and resilient to fluctuations in rainfall regardless of compost amendment. However, these properties of the soil microbial community were translated to resilience and not resistance in soil functions. Overall, the results below-ground showed much greater response to rainfall than compost amendment. Water was the key factor shaping the soil microbial community, and nutrients were not strong co-limiting factors. Future projections of increasing rainfall variability will have important below-ground functional consequences in the grassland, including altered nutrient cycling.  相似文献   

19.
《Geoderma》2002,105(3-4):223-241
In spite of the known below-ground biomass production of plant roots that concurrently introduce significant amounts of carbon and nitrogen into the soil, the effects of these inputs on N cycling in the soil–plant system are seldom considered. Here, we report on two field experiments carried out between 1995 and 1997 at the FAM Research Station Scheyern: (1) a N-turnover experiment to determine the N fluxes derived from 15N-labeled clover residues incorporated into the plough layer of defined plots, and (2) a root production experiment to assess the above (shoot) and below ground (gross and net root) biomass production of winter wheat in different fields, but nearby the 15N plots. An initial 50% decrease in soil organic 15N at 0–20-cm soil depth was recorded between fall, 1996 (incorporation of clover straw) and spring, 1997 (138 days after incorporation), which was then followed by a period of stability in 15N levels in the soil organic N until the harvest of winter wheat (286 days after incorporation). This stability may be explained in two ways: (a) actual stability of clover-derived 15N remaining in the second phase, e.g., due to recalcitrant compounds or microbial immobilization; or (b) apparent stability, e.g., because the actual mineralization of clover-derived 15N in the soil was compensated by secondary inputs of organic 15N (recycling). Further results showed that the first explanation was unlikely, as (1) between 138 and 286 days after clover incorporation, the mean 15N signature in soil mineral N was 2.1 at.%, indicating a persistent mineralization of clover residues; and (2) a decrease in soil microbial biomass 15N occurred in the second phase, indicating a continued N turnover in the soil. The amount of clover-derived 15N accumulated below the plough layer at 20–110-cm soil depth (11.5%) between early spring and the harvest of wheat also corroborated the return of mineralized 15N into the soil being due to the root N inputs by winter wheat. Based on the depth distribution of winter wheat net root biomass (root production experiment) and on soil organic 15N depth distribution (15N-turnover experiment), the root N input into soil was estimated to be 282 kg ha−1, equivalent to 54% of total net N assimilation of winter wheat. Thus, the results of this study give substantial evidence for a N loop between soil and growing plants, whereby a part of the net mineralized N taken up by plants is continuously returned into the soil by their roots. The implications of this N loop for the interpretation of 15N experiments and for plant nutrition are discussed.  相似文献   

20.
To efficiently use nitrogen (N) while protecting water quality, one must know how a second-year crop, without further N fertilization, responds in years following a manure application. In an Idaho field study of winter wheat (Triticum aestivum L.) following organically fertilized sugarbeet (Beta vulgaris L.), we determined the residual (second-year) effects of fall-applied solid dairy manure, either stockpiled or composted, on wheat yield, biomass N, protein, and grain N removal. Along with a no-N control and urea (202 kg N ha?1), first-year treatments included compost (218 and 435 kg estimated available N ha?1) and manure (140 and 280 kg available N ha?1). All materials were incorporated into a Greenleaf silt loam (Xeric Calciargid) at Parma in fall 2002 and 2003 prior to planting first-year sugarbeet. Second-year wheat grain yield was similar among urea and organic N sources that applied optimal amounts of plant-available N to the preceding year’s sugarbeet, thus revealing no measurable second-year advantage for organic over conventional N sources. Both organic amendments applied at high rates to the preceding year’s sugarbeet produced greater wheat yields (compost in 2004 and manure in 2005) than urea applied at optimal N rates. On average, second-year wheat biomass took up 49% of the inorganic N remaining in organically fertilized soil after sugarbeet harvest. Applying compost or manure at greater than optimum rates for sugarbeet may increase second-year wheat yield but increase N losses as well.

Abbreviations CNS, carbon–nitrogen–sulfur  相似文献   

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