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1.
A field experiment primarily designed for simulating the indirect effects of air pollutants for a 25-year-old Norway spruce stand in SW Sweden is presented (The Skogaby project). Treatment include irrigation; artificial drought; ammonium sulphate addition; nitrogen-free-fertilization and irrigation with liquid fertilizers including a complete set of nutrients. The experiment has a randomized block design with four replicates per treatment. Growth response on an areal basis of basal area, height and dry mass of stems, branches and needles after up to four years of treatment are presented. Dry mass is estimated using allometric equations based on destructive samplings of trees.The stand suffered from temporary water stress during all four years investigated despite 970– 1160 mm of annual precipitation. Irrigation resulted in improved above-ground dry mass production (stem, bark, branches, needles, litter fall) by 20% during the first 3 years of treatment, whereas 2 years of drought treatment followed by 1 year of recovery led to 10% reduced dry mass growth. During year 2 of recovery, however, basal area growth was only about half of that of the control.Nitrogen, markedly, was a growth limiting nutrient, although the stand got approx. 20 kg N ha-1 y-1 from deposition. Ammonium sulphate addition (100 kg N ha-1 y-1) resulted in 31% improved dry mass production whereas irrigation with liquid fertilization (100 kg N ha-1 y-1) including all important nutrient elements led to 57% increased dry mass growth after 3 years of treatment. Basal area growth of the latter treatment gradually increased and during year 4 of treatment was 123% larger than the control. Nitrogen-free-fertilization resulted in a small improvement of dry mass production (+10%).After 3 years of treatment, the amount of needles had increased markedly for both treatments including irrigation, whereas drought treated trees instead had decreased their needle amount vs control. The increase in needle amount occurred as a result of both larger formation of needles and higher preservence of old needles, the opposite relations being found for the drought treated trees. At the same point larger needle formation in combination with a higher shedding of older needles was found for trees treated with ammonium sulphate and nitrogen-free-fertilizer.It is concluded that there is no stage of N saturation in the Skogaby site as there is no leaching of N from the control plots and N fertilization results in both increased tree growth and N uptake. 相似文献
2.
The effects on growth, quality and N uptake by turfgrass (Cynodon dactylon L.) during sod production of four fertiliser types applied at three application rates (100, 200 or 300 kg N ha−1 per ‘crop’) under two irrigation treatments (70% and 140% daily replacement of pan evaporation) were investigated. The fertiliser
types were: water-soluble (predominately NH4NO3), control-release, pelletised poultry manure, and pelletised biosolids; and the experiment was conducted on a sandy soil
in a Mediterranean-type climate. Plots were established from rhizomes, with the turfgrass harvested as sod every 16–28 weeks
depending upon the time of the year. Four crops were produced during the study. Applying water-soluble and control-release
fertilisers doubled shoot growth and improved turfgrass greenness by up to 10% in comparison with plots receiving pelletised
poultry manure and pelletised biosolids. Nitrogen uptake into the shoots after four crops (averaged across irrigation treatments
and N rates) was 497 kg N ha−1 for the water-soluble fertiliser, 402 kg N ha−1 for the control-release, 188 kg N ha−1 for the pelletised poultry manure and 237 kg N ha−1 for the pelletised biosolids. Consequently, the agronomic nitrogen-use efficiency (NAE, kg DM kg−1 N applied) of the inorganic fertilisers was approximately twice that of the organic fertilisers. Increasing irrigation from
70% to 140% replacement of pan evaporation was detrimental to turfgrass growth and N uptake for the first crop when supplied
with the water-soluble fertiliser. Under the low irrigation treatment, inorganic N fertilisers applied at 200–300 kg N ha−1 were adequate for production of turfgrass sod.
Section Editor: P. J. Randall 相似文献
3.
Differences in Englemann Spruce Forest Biogeochemistry East and West of the Continental Divide in Colorado, USA 总被引:3,自引:2,他引:3
We compared Englemann spruce biogeochemical processes in forest stands east and west of the Continental Divide in the Colorado
Front Range. The divide forms a natural barrier for air pollutants such that nitrogen (N) emissions from the agricultural
and urban areas of the South Platte River Basin are transported via upslope winds to high elevations on the east side but
rarely cross over to the west side. Because there are far fewer emissions sources to the west, atmospheric N deposition is
1–2 kg N ha−1 y−1 on the west side, as compared with 3–5 kg N ha−1 y−1 on the east side. Species composition, elevation, aspect, parent material, site history, and climate were matched as closely
as possible across six east and six west side old-growth forest stands. Higher N deposition sites had significantly lower
organic horizon C:N and lignin:N ratios, lower foliar C:N ratios, as well as greater %N, higher N:Ca, N:Mg, and N:P ratios,
and higher potential net mineralization rates. When C:N ratios dropped below 29, as they did in east-side organic horizon
soils, mineralization rates increased linearly. Our results are comparable to those from studies of the northeastern United
States and Europe that have found changes in forest biogeochemistry in response to N deposition inputs between 3 and 60 kg
ha−1 y−1. Though they are low by comparison with more densely populated and agricultural regions, current levels of N deposition,
have caused measurable changes in Englemann spruce forest biogeochemistry east of the Continental Divide in Colorado.
Received 22 January 2001; accepted 11 June 2001. 相似文献
4.
Sources of Nitrogen to the Riparian Zone of a Desert Stream: Implications for Riparian Vegetation and Nitrogen Retention 总被引:5,自引:1,他引:4
John D. Schade Eugenia Marti Jill R. Welter Stuart G. Fisher Nancy B. Grimm 《Ecosystems》2002,5(1):68-79
Riparian zones effectively remove nitrogen (N) from water flowing through riparian soils, particularly in agricultural watersheds.
The mechanism of N removal is still unclear, especially the role of vegetation. Uptake and denitrification are the two most
commonly studied mechanisms. Retention of groundwater N by plant uptake is often inferred from measurements of N in net incremental
biomass. However, this assumes other sources of N are not contributing to the N demand of plants. The purpose of this work
was to investigate the relative importance of three sources of available N to riparian trees in a desert stream—input in stream
water during floods, input during baseflow, and mineralization of N from soil organic matter. Two approaches were used; a
mass balance approach in which the mass of available N from each source was estimated, and a correlational approach in which
indexes of each source were compared to leaf N for individual willow trees. Total N from all sources was 396 kg ha−1 y−1, with 172 kg ha−1 y−1 from mineralization, 214 kg ha−1 y−1 from the stream during baseflow, and 9.6 kg ha−1 y−1 from floods. Leaf N was significantly related to N mineralization rates and flood inputs; it was not related to baseflow
inputs. We conclude that mineralization is a major source of available N for willow trees, subsidized by input of N from floods.
Baseflow inputs are most likely removed by rapid denitrification at the stream–riparian edge, while higher rates of flood
supply exceed the capacity of this “filter.”
Received 18 January 2001; accepted 15 June 2001. 相似文献
5.
Improving Sugarcane Growth and Nutrient Uptake by Inoculating Gluconacetobacter diazotrophicus 总被引:5,自引:1,他引:4
Seven Gluconacetobacter diazotrophicus strains from sugarcane roots were screened for their efficiency to promote growth and nutrient uptake in sugarcane at three
levels of urea N (0, 75, and 150 kg N ha−1). Inoculation by these strains improved germination, tiller number and plant height. N-uptake and apparent N-recovery increased
due to inoculation and the effect was more at N75 level. Gluconacetobacter diazotrophicus isolate IS100 was found to be the most efficient in promoting plant growth and nutrient uptake in sugarcane. 相似文献
6.
Nitrogen uptake in relation to water availability in wheat 总被引:2,自引:0,他引:2
Nitrogen uptake and distribution in wheat (Triticum aestivum L.) are dependent on environmental conditions and in particular on the water regime. Under Mediterranean conditions, where high water stress at the end of the crop cycle is frequent, nitrogen uptake can be reduced, affecting yield and quality of the grain. To disclose these relations a field experiment was carried out in Central Portugal. Wheat was grown on a clay soil (Vertisol) at three water treatments: rainfed (WO), with 80 mm of irrigation (W1) and with 50 mm and 70 mm irrigations (W2). All treatments received 50 kg ha–1 of N prior to sowing and were top-dressed with 140 kg ha–1 of N, splitted in two applications, Kjeldahl N was determined in green leaves (GL), yellow leaves (YL), stems (ST), chaff (CH) and grain (GR). N uptake after anthesis was 40% of the total in W2, but was not noticeable in the other two treatments. N concentrations in the total above-ground plant dry matter, and in both YL and ST were not very different according to treatment, but water availability increased grain-N concentration. It seems, therefore, that grain protein concentration and N uptake can be substantially increased by late irrigations. 相似文献
7.
Eva Ritter 《Plant and Soil》2007,295(1-2):239-251
Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate
and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted
on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth)
and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for
centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species
was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios
significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil
nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands
older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed
to a slow accumulation of organic matter. Soil N concentrations and soil Ptot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material
(400 Mg soil ha−1 in 0–10 cm depth and 600 Mg soil ha−1 in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average
23.6 Mg ha−1 in the upper soil layer and 16.9 Mg ha−1 in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha−1 year−1 in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha−1 in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass
of the growing trees. Soil Ptot pools were in average 220 and 320 kg P ha−1 in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence
on the availability of N and P to the trees.
Responsible Editor: Hans Lambers. 相似文献
8.
Richard D. Bowden Mark S. Castro Jerry M. Melillo Paul A. Steudler John D. Aber 《Biogeochemistry》1993,21(2):61-71
Fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) between soils and the atmosphere were measured monthly for one year in a 77-year-old temperate hardwood forest following
a simulated hurricane blowdown. Emissions of CO2 and uptake of CH4 for the control plot were 4.92 MT C ha−1 y−1 and 3.87 kg C ha−1 y−1, respectively, and were not significantly different from the blowdown plot. Annual N2O emissions in the control plot (0.23 kg N ha−1 y−1) were low and were reduced 78% by the blowdown. Net N mineralization was not affected by the blowdown. Net nitrification
was greater in the blowdown than in the control, however, the absolute rate of net nitrification, as well as the proportion
of mineralized N that was nitrified, remained low. Fluxes of CO2 and CH4 were correlated positively to soil temperature, and CH, uptake showed a negative relationship to soil moisture. Substantial
resprouting and leafing out of downed or damaged trees, and increased growth of understory vegetation following the blowdown,
were probably responsible for the relatively small differences in soil temperature, moisture, N availability, and net N mineralization
and net nitrification between the control and blowdown plots, thus resulting in no change in CO2 or CH4 fluxes, and no increase in N2O emissions. 相似文献
9.
Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature).
In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which
N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We
compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH4
+ or NO3
−. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake
rates varied between 0.5 nmol g−1 root DM s−1 on glycine at 15 °C and 7.5 nmol g−1 root DM s−1 on NH4
+ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate
at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase
their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude
that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake
integrated over a three-week period is severely reduced at 6 °C.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
A field study was carried out near Zürich (Switzerland) to determine the yield of symbiotically fixed nitrogen (15N dilution) from white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L) and from red clover (Trifolium pratense L.) grown with Italian ryegrass (Lolium multiflorum Lam.). A zero N fertilizer treatment was compared to a 30 kg N/ha per cut regime (90 to 150 kg ha−1 annually).
The annual yield of clover N derived from symbiosis averaged 131 kg ha−1 (49 to 227 kg) without N fertilization and 83 kg ha−1 (21 to 173 kg) with 30 kg of fertilizer N ha−1 per cut in the seeding year. Values for the first production year were 308 kg ha−1 (268 to 373 kg) without N fertilization and 232 kg ha−1 (165 to 305 kg) with 30 kg fertilizer N ha−1 per cut. The variation between years was associated mainly with the proportion of clover in the mixtures. Apparent clover-to-grass
transfer of fixed N contributed up to 52 kg N ha−1 per year (17 kg N ha−1 on average) to the N yield of the mixtures.
Percentage N derived from symbiosis averaged 75% for white and 86% for red clover. These percentages were affected only slightly
by supplemental nitrogen, but declined markedly during late summer for white clover. It is concluded that the annual yield
of symbiotically fixed N from clover/grass mixtures can be very high, provided that the proportion of clover in the mixtures
exceeds 50% of total dry mass yield. 相似文献
11.
Archna Suman A. K. Shrivastava Asha Gaur Pushpa Singh J. Singh R. L. Yadav 《Plant Growth Regulation》2008,54(1):1-11
The nitrogen fixing bacterial endophytes Gluconacetobacter diazotrophicus and Herbaspirillum spp. have been proposed to benefit sugarcane (Saccaharum spp. hybrids) growth. Variable populations of these endophytes exist depending upon ontogenic and climatic variations as
well. This study investigates the effect of variable chemical nitrogen application in soil on the population of endophytic
diazotrophs, acetylene reduction ability of excised roots, plant N-nutrient use efficiency and probable interactions among
different parameters in eight commercial sugarcane varieties of subtropical India. Recovery efficiency (RE), agronomic efficiency
(AE), partial factor productivity (PFP) and physiologic efficiency (PE) indicators were used for accounting N-nutrient use
efficiency. The population of G. diazotrophicus was more at N75 compared to N0 and N150, whereas Herbaspirillum population increased from N0 to N150. ARA was positively correlated with Gluconacetobacter population in rhizosphere and root, whereas it had poor correlation with Herbaspirillum population. Positive correlation of RE and AE with ARA of roots, Gluconacetobacter and Herbaspirillum populations in roots and stems indicate their positive contribution in total nitrogen uptake by the plant per kg of N applied.
Average PFP was 808.9 at N75 compared to 408.7 at N150 indicating that N was utilized efficiently at low N input status in sugarcane. Strong positive correlations of AE75 (agronomic efficiency from 75 kg N ha−1 to 150 kg N ha−1) with N-uptake (r
2 = 0.615), cane yield (r
2 = 0.758) and PFP (r
2 = 0.758) and other parameters compared to AE (agronomic efficiency from 0 kg N ha−1 to 75 kg N ha−1 or 150 kg N ha−1) correlations with N-uptake (r
2 = 0.111), cane yield (r
2 = 0.368) and PFP (r
2 = 0.190) indicated that the AE of sugarcane was strongly directed towards producing more cane yield per unit of N fertilizer
once the sugarcane plant has established using initial dose of nitrogen and thus AE75 seems to be a more appropriate indicator for accounting N-nutrient use efficiency in sugarcane. 相似文献
12.
Akinori Yamada Tetsushi Inoue Decha Wiwatwitaya Moriya Ohkuma Toshiaki Kudo Atsuko Sugimoto 《Ecosystems》2006,9(1):75-83
Nitrogen (N) fixed by termites was evaluated as a N input to decomposition processes in two tropical forests, a dry deciduous
forest (DDF) and the neighboring dry evergreen forest (DEF), Thailand. A diverse group of termite species were assayed by
acetylene reduction method and only the wood/litter-feeding termites were found to fix N. More intensive samplings of two
abundant species, Microcerotermes crassus and Globitermes sulphureus, were done across several seasons, suggesting N fixation rates of 0.21 and 0.28 kg ha−1 y−1 by termites in the DDF and DEF, respectively. Also, estimates of asymbiotic N fixation rates were 0.75 and 3.95 kg ha−1 y−1. N fixed by termites and by asymbiotic fixers is directly supplied to decomposers breaking down dead plant material and could
be a major source of their N. N fixed by termites was 7–22% of that fixed by termites and asymbiotic fixers. Although N fixed
by termites is a small input compared to other inputs, this N is likely important for decomposition processes. 相似文献
13.
Changes in the Above- and Below-ground Biomass and Nutrient Pools of Ground Vegetation After Clear-cutting of a Mixed Boreal Forest 总被引:3,自引:0,他引:3
Marjo Palviainen Leena Finér Hannu Mannerkoski Sirpa Piirainen Michael Starr 《Plant and Soil》2005,275(1-2):157-167
Ground vegetation may act as a sink for nutrients after clear-cutting and thus decrease leaching losses. Biomass and nutrient
(N, P, K, Ca) pools of ground vegetation (mosses, roots and above-ground parts of field layer) were determined one year before
and five years after clear-cutting of a Norway spruce (Picea abies (L.) H. Karst.) dominated boreal mixed forest stand in
eastern Finland (63°51′ N, 28°58′ E). Before clear-cutting the average biomass of ground vegetation was 5307 kg ha−1, with nutrient contents of 46.9 kg N ha−11, 4.1 kg P ha−11, 16.2 kg K ha−11 and 13.9 kg Ca ha−11. The biomass and nutrient pools decreased after clear-cutting being lowest in the second year, the biomass decreasing by
46–65% in the cut plots. The nutrient pools decreased as follows: N 54–72%, P 36–68%, K 51–71% and Ca 57–74%. The decrease
in ground vegetation nutrient uptake, and the observed reduced depth of rooting may decrease nutrient retention after clear-cutting
and decomposing dead ground vegetation is a potential source of leached nutrients. These negative effects of clear-cutting
on the nutrient binding capacity of ground vegetation was short-lived since the total biomass and nutrient pools returned
to pre-cutting levels or were even greater by the end of the 5-year study period. 相似文献
14.
The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire 总被引:22,自引:8,他引:14
Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream
N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories
ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic
N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US,
a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate
export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional
status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns
of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in
DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained
at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological
removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate
may occur much sooner.
Received 27 April 1999; accepted 30 May 2000. 相似文献
15.
Nitrogen Oxide Fluxes and Nitrogen Cycling during Postagricultural Succession and Forest Fertilization in the Humid Tropics 总被引:2,自引:0,他引:2
The effects of changes in tropical land use on soil emissions of nitrous oxide (N2O) and nitric oxide (NO) are not well understood. We examined emissions of N2O and NO and their relationships to land use and forest composition, litterfall, soil nitrogen (N) pools and turnover, soil
moisture, and patterns of carbon (C) cycling in a lower montane, subtropical wet region of Puerto Rico. Fluxes of N2O and NO were measured monthly for over 1 year in old (more than 60 years old) pastures, early- and mid-successional forests
previously in pasture, and late-successional forests not known to have been in pasture within the tabonuco (Dacryodes excelsa) forest zone. Additional, though less frequent, measures were also made in an experimentally fertilized tabonuco forest.
N2O fluxes exceeded NO fluxes at all sites, reflecting the consistently wet environment. The fertilized forest had the highest
N oxide emissions (22.0 kg N · ha−1· y−1). Among the unfertilized sites, the expected pattern of increasing emissions with stand age did not occur in all cases. The
mid-successional forest most dominated by leguminous trees had the highest emissions (9.0 kg N · ha−1· y−1), whereas the mid-successional forest lacking legumes had the lowest emissions (0.09 kg N · ha−1· y−1). N oxide fluxes from late-successional forests were higher than fluxes from pastures. Annual N oxide fluxes correlated positively
to leaf litter N, net nitrification, potential nitrification, soil nitrate, and net N mineralization and negatively to leaf
litter C:N ratio. Soil ammonium was not related to N oxide emissions. Forests with lower fluxes of N oxides had higher rates
of C mineralization than sites with higher N oxide emissions. We conclude that (a) N oxide fluxes were substantial where the
availability of inorganic N exceeded the requirements of competing biota; (b) species composition resulting from historical
land use or varying successional dynamics played an important role in determining N availability; and (c) the established
ecosystem models that predict N oxide loss from positive relationships with soil ammonium may need to be modified.
Received 22 February 2000; accepted 6 September 2000. 相似文献
16.
Summary Inoculation of water fernAzolla pinnata R. Brown (Bangkok isolate) at the rate of 500kg fresh weight ha−1 in rice fields at weekly intervals after planting in addition to 30 kg N ha−1 as urea showed a decrease in its growth and N2-fixation with delay in application. Use of Azolla up to 3 weeks after planting (WAP) during wet and 4 WAP during dry season
produced significantly more grain yield than 30 kg N ha−1, whereas its application upto one WAP produced more grain yield than 60 kg N ha−1. Grain yield with Azolla applied at the time of planting was similar to that of 60 kg N treatment during the wet season.
Higher grain yields in zero and one WAP Azolla treatments resulted due to increase in both number of panicles m−2 and number of grains/panicle while the subsequent Azolla inoculations increased grain yield mainly by producing more number
of grains/panicle.
Dry matter and total N yields at maturity of rice crop were more with Azolla application upto 3 WAP during wet and 2 WAP during
dry season while the reduction in sterility (%) was observed upto one WAP over 30 kg N ha−1 during both seasons. Number of tillers m−2 and dry matter production at maximum tillering and flowering were more than 30 kg N ha−1 with the use of Azolla upto one WAP. Increased grain N yield was observed with the use of Azolla upto 4 WAP during two seasons
whereas straw N yield increased upto one WAP during wet and 2 WAP during dry season. 相似文献
17.
Relay intercropping of wheat and cotton is practiced on a large scale in China. Winter wheat is thereby grown as a food crop
from November to June and cotton as a cash crop from April to October. The crops overlap in time, growing as an intercrop,
from April till June. High levels of nitrogen are applied. In this study, we analyzed the N-economy of the monocultures of
cotton and wheat, and of four relay intercropping systems, differing in number of rows per strip of cotton or wheat. Field
experiments were carried out from 2001/02 to 2003/04 in the Yellow River region in China. We quantified the nitrogen uptake
and nitrogen use efficiency of wheat and cotton in relay intercropping systems to test if intercrops are more resource use
efficient in comparison to monocrops. Nitrogen (N) yields of wheat per unit area in the four intercropping systems were lower
than in the monocrop, which ranged from 203 to 288 kg ha−1. The total N-uptake per unit biomass was similar between wheat in mono- and intercrops. On average, the N-yield of cotton
per unit area was lower in intercrops than in monocrops, which ranged from 110 to 127 kg ha−1, but the total N-uptake per unit biomass was higher in intercropped cotton, as dry matter production was reduced to a greater
extent by intercropping than N-uptake. The N-uptake of cotton was diminished during the intercropping phase, but recovered
partially during later growth stages. The physiological nitrogen use efficiency (IE) of wheat was not much affected by intercropping,
but it was reduced in cotton, due to delayed flowering and less reproductive growth. Total N-efficiency of the system was
assessed by comparing the relative nitrogen yield total (RNT), i.e. the sum of the ratio’s of total N-uptake by a component
crop in the intercrop relative to the N-uptake in the monocrop, to the relative yield total. RNT ranged from 1.4 to 1.7, while
the relative yield total (RYT) ranged from 1.3 to 1.4, indicating that intercrops used more nitrogen per unit production than
monocrops. An analysis of the crop nitrogen balance showed that the nitrogen surplus of sole crops amounted to 220 kg ha−1 for wheat and 140 kg ha−1 for cotton, while in the intercropping systems, the annual N surplus exceeded 400 kg ha−1. Conventional N-management in intercrops thus results in high N-surpluses that pose an environmental risk. The N management
could be improved by means of a demand-based rate and timing of N applications. 相似文献
18.
Quanxiao Fang Qiang Yu Enli Wang Yuhai Chen Guoliang Zhang Jing Wang Longhui Li 《Plant and Soil》2006,284(1-2):335-350
There is a growing concern about excessive nitrogen (N) and water use in agricultural systems in North China due to the reduced
resource use efficiency and increased groundwater pollution. A two-year experiment with two soil moisture by four N treatments
was conducted to investigate the effects of N application rates and soil moisture on soil N dynamics, crop yield, N uptake
and use efficiency in an intensive wheat–maize double cropping system (wheat–maize rotation) in the North China Plain. Under
the experimental conditions, crop yield of both wheat and maize did␣not␣increase significantly at N rates above 200 kg N ha−1. Nitrogen application rates affected little on ammonium-N (NH4-N) content in the 0–100 cm soil profiles. Excess nitrate-N (NO3-N), ranging from 221 kg N ha−1 to 620 kg N ha−1, accumulated in the 0–100 cm soil profile at the end of second rotation in the treatments with N rates of 200 kg N ha−1 and 300 kg N ha−1. In general, maize crop has higher N use efficiency than wheat crop. Higher NO3-N leaching occurred in maize season than in wheat season due to more water leakage caused by the concentrated summer rainfall.
The results of this study indicate that the optimum N rate may be much lower than that used in many areas in the North China
Plain given the high level of N already in the soil, and there is great potential for reducing N inputs to increase N use
efficiency and to mitigate N leaching into the groundwater. Avoiding excess water leakage through controlled irrigation and
matching N application to crop N demand is the key to reduce NO3-N leaching and maintain crop yield. Such management requires knowledge of crop water and N demand and soil N dynamics as
they change with variable climate temporally and spatially. Simulation modeling can capture those interactions and is considered
as a powerful tool to assist in␣the␣future optimization of N and irrigation managements.
Section Editor: L. Wade 相似文献
19.
Mark S. Castro Keith N. Eshleman Louis F. Pitelka Geoff Frech Molly Ramsey William S. Currie Karen Kuers Jeffrey A. Simmons Bob R. Pohlad Carolyn L. Thomas David M. Johnson 《Biogeochemistry》2007,84(3):333-348
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha−1 year−1 and a range of 4.4–18.4 kg N ha−1 year−1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha−1 year−1 and 6.3 kg N ha−1 year−1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha−1 year−1 and 5.3 kg N ha−1 year−1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha−1 year−1 and 18.4 kg N ha−1 year−1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha−1 year−1 in 2003) and three (5.5 kg N ha−1 year−1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l−1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献
20.
S. K. Kavimandan 《Plant and Soil》1986,95(2):297-300
Summary Soil + charcoal (1∶3) carrier based and liquid cultures of Rhizobia were used to inoculate wheat seed cv. HD2329. The plants
received 100 kg N in two equal splits and 60 kg P2O5 and 40 kg K20 ha−1. Inoculation with rhizobia had little effect on grain yield of wheat. Significant increase in straw yield and N-uptake occurred
due to inoculation.
A comparison of results of a similar experiment conducted during 1983–84, showed that inoculation with the same strains of
rhizobia and application 50 kg N ha−1 as basal dressing, was more effective in increasing yield and N-uptake in wheat cv. HD2329. It appears reasonable to assume
occurrence of nitrogen fixation by root nodule bacteria in rhizosphere of wheat. 相似文献