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1.
Accumulation of biomass and nutrients (N, P, K, Ca, Mg and Mn) was measured during the first 3-year rotation of three Eucalyptus short rotation forest species (E. botryoides, E. globulus and E. ovata) irrigated with meatworks effluent compared with no irrigation. E. globulus had the highest biomass and nutrient accumulation either irrigated with effluent or without irrigation. After 3-year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn, but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca and Mg. 相似文献
2.
Effect of organic and mineral fertilizers on N-use by wheat under different irrigation frequencies 总被引:1,自引:0,他引:1
A field trial was established in Errachidia, southern Morocco, to investigate the interaction between wheat residue management and mineral 15N-labelled ammonium sulphate, under different irrigation treatments, applied to wheat (Triticum durum var. Karim). In treatments I1, I2, I3 and I4, plots were irrigated every 10, 15, 21 and 30 days. Each plot contained three sub-plots that received three fertilization treatments: T1 received 42 kg N ha-1 of ammonium sulphate before seedling, 42 kg N ha-1 of ammonium sulphate labelled with 9.764 at % 15N excess at tillering and 84 N kg ha-1 of ammonium sulphate at flowering; T2 received 42 kg N ha-1 of ammonium sulphate labelled with 9.764 at % 15N excess at seedling, 42 kg N ha-1 at tillering and 42 kg N ha-1 at flowering; T3 received 4800 kg ha-1 of wheat residue labelled with 1.504 at % 15N excess and 42 kg N ha-1 of ammonium sulphate before seedling and 42 kg N ha-1 of ammonium sulphate at flowering. Nitrogen fertilization with 168 kg N ha-1 did no significantly increase grain and straw yields in comparison to the 126 kg N ha-1 application. The combination of the organic input and supplementary application of mineral fertilizer N has been found as a more attractive management option. For all irrigation treatments, the % recovery of N in the whole plant was higher in plants that received 15N at tillering (63%, 49% respectively for irrigation intervals between 10 and 30 d) than in plants that received 15N just after seeding (28% for irrigation each 10- and 30-d intervals). For the irrigation treatment each 10 and 15 days, the 15N was mainly recovered by the grain for all fertilization treatments, whereas for irrigation treatment each 30 days, the grain and straw recovered nearly equal amounts of fertilizer. For grain and straw of wheat, nitrogen in the plant derived from the fertilizer was low, while most of the N was derived from the soil for all irrigation and fertilization treatments. The % nitrogen in the plant derived from the fertilizer values showed no significant difference between the different plant parts. The results suggested a dominant influence of moisture availability on the fertilizer N uptake by wheat. Under dry conditions the losses of N can be allotted to denitrification and volatilisation. 相似文献
3.
Summary Field experiments were conducted during 1979 and 1980 summer seasons on sandy loam soils of low moisture retentive capacity
to study the effect of high frequency irrigation at different levels of N on groundnut yield and nutrient uptake (NPK).
Four irrigation frequencies (irrigation at 2, 4, 6 and 8 cm cumulative can evaporation, corresponding to irrigation once in
3, 5, 7 and 10 days respectively) and four levels of nitrogen (0, 20, 40 and 60 kg N/ha) were tested in a factorial randomized
block design with three replications.
Pod yield of groundnut was maximum (3,293 kg/ha) when irrigations were scheduled at 4 cm cumulative can evaporation (once
in 5 days). Addition of N did not increase the pod yield. N and P uptake by the crop was maximum (180 kg N and 18 kg P/ha)
with high frequency irrigation of scheduling irrigation at 4 cm cumulative can evaporation. Highest uptake of N (183 kg/ha)
and P (19 kg/ha) was with a combination of 20 kg N/ha and high frequency irrigation (4 cm CCE). K uptake was low with low
irrigation frequency, while it was highest (67 kg K/ha) at 20 kg N/ha. 相似文献
4.
Denitrification and total N losses were quantified from an irrigated field cropped to maize and wheat, each receiving urea at 100 kg N ha-1. During the maize growing season (60 days), the denitrification loss measured directly by acetylene inhibition-soil cover method amounted 2.72 kg N ha-1 whereas total N loss measured by 15N balance was 39 kg ha-1. Most (87%) of the denitrification loss under maize occurred during the first two irrigation cycles. During the wheat growing season (150 days), the denitrification loss directly measured by acetylene inhibition-soil cover and acetylene inhibition-soil core methods was 1.14 and 3.39 kg N ha-1, respectively in contrast to 33 kg N ha-1 loss measured by 15N balance. Most (70-88%) of the denitrification loss under wheat occurred during the first three irrigation cycles. Soil moisture and NO
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-N were the major factors limiting denitrification under both crops. Higher N losses measured by 15N balance than C2H2 inhibition method were perhaps due to underestimation of denitrification by C2H2 inhibition method and losses other than denitrification, most probably NH3 volatilization. 相似文献
5.
The Nanjing Declaration on Nitrogen Management, signed in Nanjing in October 2004, calls for national governments to optimize
N management by several strategies including assessment of N cycles. Here we develop a first N budget for New Zealand (267,000 km2), at both national and regional scales. The national inputs are estimated to be 36.5 kg/ha, mainly from biological N fixation,
but also increasingly from fertilizer application and atmospheric deposition. The outputs are estimated at 40.5 kg/ha. Biological
N fixation from legumes in pasture was the most important input in most regions. Exceptions were Auckland, with a large urban
population, and the West Coast of the South Island, with large tracts of rain forest. Outputs were distributed in the order
leaching > ammonia volatilisation > erosion = produce = denitrification. These outputs are very different from global averages
because of the large numbers of grazing animals on pasture. A large loss occurs between the subsoil and the oceans, and further
research is needed to identify these pathways. Riverine export of N was generally well correlated with inputs. 相似文献
6.
Summary A field experiment was conducted on soybean (Glycine max (L.) Merrill) with a view to find out the effect of seed inoculation and scheduling of irrigation on nodulation, accumulation and re-distribution of nitrogen in plant tops and soil. The eight treatment combinations consists of two seed inoculations,viz. uninoculated and inoculated with rhizobium culture, and four irrigation schedules,viz. irrigation water to the cumulative pan evaporation (IW/CPE) ratio of 0.5, 0.7, 0.9 and a control (rainfed). Seed inoculation by, rhizobium culture increased the number, dry-weight and N content of nodules per plant. Inoculation of seeds also increased the N accumulation rate in plant top and it was 2.48 kg/ha/day during the flower-initiation to the pod-initiation stage (30–60 days interval). At harvest, 32.2, 47.8 and 26.2 kg N/ha was re-distributed from the stems, leaves and pods-wall of inoculated plants to the grains, respectively. A total of 186.5 kg N/ha was harvested and 64.7 kg N/ha, was accumulated in soil under the inoculated condition.Scheduling of irrigation at 0.7 IW/CPE proved better, than other irrigation schedules and helped in increasing the nodulation, nitrogen accumulation and grain yield. As compared to control, 8.4, 17.8 and 18.4 kg more of N/ha was redistributed from the stems, leaves and pods-wall respectively when the irrigations were scheduled at 0.7 IW/CPE ratio. Under this irrigation schedule the total N harvest was 200.1 kg/ha while the total N increased by 55.9 kg over that present in soil at the time of sowing. 相似文献
7.
Given the societal concern about groundwater pollution from agricultural sources, public programs have been proposed or implemented to change farmer behavior with respect to nutrient use and management. However, few of these programs designed to change farmer behavior have been evaluated due to the lack of detailed data over an appropriate time frame. The Central Platte Natural Resources District (CPNRD) in Nebraska has identified an intensively cultivated, irrigated area with average groundwater nitrate-nitrogen (N) levels about double the EPA"s safe drinking water standard. The CPNRD implemented a joint education and regulatory N management program in the mid-1980s to reduce groundwater N. This analysis reports N use and management, yield, and groundwater nitrate trends in the CPNRD for nearly 3000 continuous-corn fields from 1989 to 1998, where producers faced limits on the timing of N fertilizer application but no limits on amounts. Groundwater nitrate levels showed modest improvement over the 10 years of this analysis, falling from the 1989-1993 average of 18.9 to 18.1 mg/l during 1994-1998. The availability of N in excess of crop needs was clearly documented by the CPNRD data and was related to optimistic yield goals, irrigation water use above expected levels, and lack of adherence to commercial fertilizer application guidelines. Over the 10-year period of this analysis, producers reported harvesting an annual average of 9729 kg/ha, 1569 kg/ha (14%) below the average yield goal. During 1989-1998, producers reported annually applying an average of 162.5 kg/ha of commercial N fertilizer, 15.7 kg/ha (10%) above the guideline level. Including the N contribution from irrigation water, the potential N contribution to the environment (total N available less estimated crop use) was estimated at 71.7 kg/ha. This is an estimate of the nitrates available for denitrification, volatilization, runoff, future soil N, and leaching to groundwater. On average, between 1989-1993 and 1994-1998, producers more closely followed CPNRD N fertilizer recommendations and increased their use of postemerge N applications--an indication of improved synchrony between N availability and crop uptake. 相似文献
8.
Total denitrification and the ratio between N2O and N2 during the growth of spring barley 总被引:1,自引:0,他引:1
Finn P. Vinther 《Plant and Soil》1984,76(1-3):227-232
Summary Total denitrification (N2O+N2) and nitrous oxide emission were measured on intact soil cores using the acetylene inhibition technique.Total denitrification from the depth 0–8 cm during the growth period from April to August was 7 kg N/ha from plots supplied with 30 kg N/ha and 19 kg N/ha from plots supplied with 120 kg N/ha. The amounts of precipitation, plant growth, and N application were found to affect the denitrification rate. These factors also affected the ratio (N2O+N2)/N2O, which varied from 1.0 to 7.2. Plant growth and precipitation increased the proportion of N2 produced, whereas a high nitrate content increased the proportion of N2O. 相似文献
9.
Summary Most studies of N relationships in grassland have used cut swards. These have shown that for annual inputs of 200 to 400 kg N/ha from fertilizer or fixation, 55 to 80% of the N is recovered in harvested herbage. Generally, no more than 5 to 15% is lost through leaching and denitrification with most of the remaining N incorporated into soil organic matter. The relatively high efficiency of N use by cut swards reflects rapid uptake of N and the removal of a large part of the input in herbage. Inclusion of the grazing ruminant alters the efficiency of N use; only 5–20% of the input is recovered in meat or milk, and 75 to 90% of the N ingested is excreted, mainly as urea in urine. Application of N in urine ranges from 30–100 g/m2. Too much N is voided for effective recovery by the sward whilst soils usually contain insufficient C to allow appreciable immobilization. The surfeit is lost. Hydrolysis of urea is usually complete within 24 h of urine deposition. For urine-treated pasture in New Zealand (NZ) losses by NH3 volatilization of up to 66% of applied N are found during warm dry weather, with an average of 28% for a range of seasonal conditions. In the UK, the average rate of NH3 loss from an intensively grazed ryegrass sward was 0.75 kg N/ha/day during a 6-month season. NH
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remaining in the soil may be nitrified, nitrification being complete within 3 to 6 weeks. Although some NO
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is recovered by plants, a substantial portion is leached and/or denitrified. On average such losses were 42%, with only 30% of the added N recovered by plants in urine-treated pasture in NZ. In the UK annual leaching of 150 to 190 kg N/ha has been observed for grazed swards receiving 420 kg N/ha/yr. Low retention of N by grazing ruminants results in a breakdown of N relationships in intensively managed grasslands. The substantial losses through NH3 volatilization, leaching and denitrification have serious agronomic, economic and environmental implications. 相似文献
10.
In an alley cropping system, prunings from the hedgerow legume are expected to supply nitrogen (N) to the associated cereal. However, this may not be sufficient to achieve maximum crop yield. Three field experiments with alley-cropped maize were conducted in a semi-arid environment in northern Australia to determine: (1) the effect of N fertilizer on maize growth in the presence of fresh leucaena prunings; (2) the effect of incorporation of leucaena and maize residues on maize yield and the fate of plant residue15N in the alley cropping system; and (3) the15N recovery by maize from15N-labelled leucaena, maize residues and ammonium sulphate fertilizer.Leucaena residues increased maize crop yield and N uptake although they did not entirely satisfy the N requirement of the alley crop. Additional N fertilizer further increased the maize yield and N uptake in the presence of leucaena residues. Placement of leucaena residues had little effect on the availability of N to maize plants over a 2 month period. The incorporation of leucaena residues in the soil did not increase the recovery of leucaena15N by maize compared with placement of the residues on the soil surface. After 2 months, similar proportions of the residue15N were recovered by maize from mulched leucaena (6.3%), incorporated leucaena (6.1%) and incorporated maize (7.6%). By the end of one cropping season (3 months after application) about 9% of the added15N was taken up by maize from either15N-labelled leucaena as mulch or15N-labelled maize residues applied together with unlabelled fresh leucaena prunings as mulch. The recovery of the added15N was much higher (42.7%) from the15N-labelled ammonium sulphate fertilizer at 40 kg N ha-1 in the presence of unlabelled leucaena prunings. Most of the added15N recovered in the 200 cm soil profile was distributed in the top 25 cm soil with little leached below that. About 27–41% of the leucaena15N was apparently lost, largely through denitrification from the soil and plant system, in one cropping season. This compared with 35% of the fertilizer15N lost when the N fertilizer was applied in the presence of prunings. ei]H Lambers 相似文献
11.
Leaf-litter and changing nutrient levels in a seasonally dry tropical hardwood forest,Belize, C.A. 总被引:3,自引:0,他引:3
Summary Total above ground plant biomass in a 45 year old seasonally dry tropical hardwood forest was estimated to be approximately 56,000 kg/ha oven dry weight. Nutrients immobilized in the standing vegetation were: N, 203 kg/ha; P, 24 kg/ha; K, 234 kg/ha; Ca, 195 kg/ha; Mg, 47 kg/ha; Na, 9 kg/ha; Mn, 1 kg/ha; Cu, 0.5 kg/ha; Zn, 3 kg/ha; Fe, 4 kg/ha. Total nutrients returned each year through the litter were: N, 156 kg/ha; P, 9 kg/ha; K, 59 kg/ha; Ca, 373 kg/ha; Mg, 32 kg/ha; Na, 5 kg/ha; Mn, 1 kg/ha; Al, 21 kg/ha; Zn, 0.3 kg/ha; Fe, 9 kg/ha. Half of the nutrients immobilized in the standing vegetation were found in the leaves and are returned annually to the soil. Although litter fall is interrupted during the year, the mean nutrient content of the litter was high –5.2%.A decomposition rate of 0.48 percent per day was considered high for a seasonally dry tropical hardwood forest. Fluctuations in soil nutrient levels showed a sharp increase at the start of the rainy season. Later during the dry season nutrient levels decreased to concentrations similar to what they were just prior to the rainy season. Soil organic matter levels were very high –20% in the top 12 cm. 相似文献
12.
Controls Over Leaf Litter and Soil Nitrogen Fixation in Two Lowland Tropical Rain Forests 总被引:1,自引:0,他引:1
Global comparisons suggest that rates of N fixation in tropical rain forests may be among the highest on earth. However, data supporting this contention are rare, and the factors that regulate N fixation within the biome remain largely unknown. We conducted a full-factorial (N × P) fertilization experiment in two lowland tropical rain forests in Costa Rica to explore the effects of nutrient availability on rates of free-living N fixation in leaf litter and soil. P fertilization significantly increased N fixation rates in both leaf litter and soil, and the effect was dependent on sampling date. Fertilization with N did not affect rates of N fixation at any time. In addition, variation in N fixation rates measured in unfertilized plots at four sampling time points suggested seasonal variability in N fixation: leaf litter N fixation ranged from 0.36 kg/ha/yr in the dry season to 5.48 kg/ha/yr in the wet season. Soil N fixation showed similar patterns ranging from a dry season low of 0.26 kg/ha/yr to a wet season high of 2.71 kg/ha/yr. While the observed temporal variability suggests potential climatic control over free-living N fixation in these forests, data suggest that neither soil nor leaf litter moisture alone regulate N fixation rates. Instead, we hypothesize that a combination of ample C availability, low leaf litter N:P ratios, and high rainfall coincide during the latter portions of the rainy season and drive the highest free-living N fixation rates of the year. 相似文献
13.
Summary Results of a two year study on the fate on15N-labelled urea (9.95 atoms percent excess15N) applied @ 180 kg N/ha to flooded rice in monolith lysimeters at the Punjab Agricultural University Farm, Ludhiana are reported. The soil of the experimental field was sandy clay loam in texture (Typic Ustochrept), had pH 7.9, organic carbon 0.36 percent, available N 187 kg/ha and total N 0.08 percent. The results revealed that 18.1 to 53.0 per cent of the fertilizer N was utilized by the rice plant, 25.1 to 41.1 percent was immobilized in the soil and 4.8 to 7.2 percent was lost by denitrification. The losses due to ammonia volatilization and leaching were negligible. The data on vertical distribution of labelled N in the soil profile reflected a higher concentration (38.3 to 39.5 per cent) in the surface (0–30 cm) soil. The content sharply decreased (1.8 to 2.4, percent) in lower soil layers (30–150 cm). A balance sheet of the various pathways of applied N showed that 58.8 to 72.2 and 66.2 to 83.0 percent N was recovered in 1976 and 1977, respectively and 17 to 41.2 per cent of labelled N still remained unaccounted for. Utilization of fertilizer N by rice was increased and losses decreased when N was applied in three equal splits as compared to the single N application at transplanting.Availability of fertilizer N immobilized in the soil was investigated in the succeeding crops of wheat and rice. The results showed that 2.1 tot 3.4 per cent of the N applied to the preceding rice was utilized by the second rice crop grown in succession. This may look small but cannot be neglected on a long term basis. But there is need to initiate long term studies to investigate the, turnover of residual N and to determine the fate of applied N in varying soil and cropping systems by using improved techniques. 相似文献
14.
Studies were carried out to optimize the use of water and nutrients by the crop with three moisture regimes [0.9, 1.2 and 1.5 irrigation water:cumulative pan evaporation (IW:CPE) ratios], two variables of organic mulch (control and sugarcane trash at 7 t/ha) and three levels of nitrogen (0, 100 and 200 kg/ha). Soil moisture regimes maintained at 1.2 IW:CPE ratio significantly increased the crop growth and herb and essential oil yields as compared with that of 0.9 IW:CPE ratio. The increase in herb yield due to 1.5 and 1.2 IW:CPE ratios was recorded to be 28.5% and 19%, respectively, over the irrigation given at 0.9 IW:CPE ratio, with the corresponding increase in essential oil yield to the extent of 23.5% and 15.5%. Interaction effect of moisture regimes and nitrogen rates indicated that increasing levels of irrigation at the highest level of N (200 kg/ha) improved essential oil yield of the crop. Application of N at 200 kg/ha in the mulched plots significantly enhanced the N uptake by the crop and essential oil yield over the control and 100 kg N/ha applied in the mulched/or unmulched plots and 200 kg N/ha applied in the unmulched plots. Application of organic mulch and nitrogen at 200 kg/ha improved the water use efficiency (WUE) in menthol mint crop. Higher moisture regimes maintained up to 1.2 IW:CPE ratio increased the WUE. The quality of essential oil in terms of its major constituent, menthol, improved slightly with 1.2 IW:CPE ratio as compared to 0.9 and 1.5 IW:CPE ratios at first and second harvests of the crop. It is recommended that menthol mint crop could be grown profitably by providing 16 irrigations, that is 80 cm water (based on 1.2 IW:CPE ratio) and nitrogen at 200 kg/ha in the sugarcane trash mulched plots, which could give a highest benefit:cost ratio from menthol mint cropping. 相似文献
15.
用顶盖埋管法(Close-Top Tube Incubations)就西双版纳3种热带森林(热带季节雨林、片断热带雨林、橡胶林)研究了土壤铵态氮(NH4-N)和硝态氮(NO3-N)以及土壤氮素矿化速率的季节动态情况。结果表明:西双版纳3种不同林型土壤NH4-N、NO3-N和氮素矿化速率均具有明显的季节性变化。NH4-N以干热季(4月末)最高(平均为26.92 mg*kg-1)和干季(2月末)最低(平均为12.01 mg*kg-1);NO3-N则以雨季中期(7月中旬)最高(平均为8.9 mg*kg-1)和干季(2月末)最低(平均为4.04 mg*kg-1);矿化速率则以干热季((2月末~4月末)最高(平均为0.496 mg*kg-1*d-1),以雨季(7月中旬~11月初)最低(平均为0.0037 mg*kg-1*d-1)。就不同林型而言,季节雨林年均氮矿化速率(0.319 mg*kg-1*d-1)>片断热带雨林(0.25 mg*kg-1*d-1)>橡胶林(0.074 mg*kg-1*d-1)。 相似文献
16.
The fate of15N-ammonium sulphate fertilizer that was applied to four lysimeters in the 1990/91 summer was studied over three consecutive growing seasons during which either maize or wheat was grown. Aboveground portions of15N-labelled maize plants from the first harvest were applied to four other lysimeters at 5 t ha–1. Two lysimeters in each of the sets of four were assigned a low and a high moisture treatment using irrigation. In both moisture treatments, plant recovery of fertilizer-15N in the first season was 27% and a further 2% was recovered by plants during the next two seasons. During the second and third seasons, total recovery of15N by aboveground plant portions from lysimeters that received15N-labelled maize material was equivalent to 2.5% of applied fertilizer-15N. This corresponded to ca. 18% recovery of the15N added in maize material. Leaching of fertilizer-N over the three growing seasons did not exceed 0.3% in total. During the first season, a maximum of 0.25 kg N ha–1, equivalent to 0.25% of the applied fertilizer-N, was leached in the high moisture treatment. This represented 1.8% of the nitrate load in leachates. Less than 0.002% of the applied fertilizer-N was leached in the low moisture treatment during the first season. 相似文献
17.
In a mass balance of 15N-labelled nitrate added to soil grown with pea or barley, denitrification estimates using the acetylene-inhibition technique
were compared with unaccounted for 15N. During the growth season of 1989, which was drier than average, N losses due to denitrification estimated by the acetylene-inhibition
technique were negligible. A substantial amount of fertilizer N was unaccounted for by the 15N mass balance, especially in the pea plots. The loss took place during the period of grain-filling in which no leaching occurred,
and was accompanied by a decrease in 15N content of the plants. Volatilization of ammonia from the aerial parts of the plants is a possible explanation of the observed
loss. An estimation of denitrification relying only on the 15N mass balance would have resulted in an overestimation of denitrification. 相似文献
18.
Peter Sørensen 《Plant and Soil》2004,267(1-2):285-296
About 50–60% of dairy cattle slurry nitrogen is ammonium N. Part of the ammonium N in cattle slurry is immobilised due to
microbial decomposition of organic matter in the slurry after application to soil. The immobilisation and the remineralisation
influence the fertiliser value of slurry N and the amount of organic N that is retained in soil. The immobilisation and the
remineralisation of 15 N-labelled dairy cattle slurry NH4-N were studied through three growing seasons after spring application under temperate conditions. Effects of slurry distribution
(mixing, layer incorporation, injection, surface-banding) and extra litter straw in the slurry on the plant utilisation of
labelled NH4-N from slurry were studied and compared to the utilisation of 15N-labelled mineral fertiliser. The initial immobilisation of slurry N was influenced by the slurry distribution in soil. More
N was immobilised when the slurry was mixed with soil. Surface-banding of slurry resulted in significant volatilisation losses
and less residual 15N in soil. Much more N was immobilised after slurry incorporation than after mineral fertiliser application. After 2.5 years
the recovery of labelled N in soil (0–25 cm) was 46% for slurry mixed with soil, 42% for injected slurry, 22% for surface-banded
slurry and 24% for mineral fertiliser N. The total N uptake in a ryegrass cover crop was 5–10 kg N/ha higher in the autumn
after spring-application of cattle slurry (100–120 kg NH4-N/ha) compared to the mineral fertiliser N reference, but the immobilised slurry N (labelled N) only contributed little to
the extra N uptake in the autumn. Even in the second autumn after slurry application there was an extra N uptake in the cover
crop (0–10 kg N/ha). The residual effect of the cattle slurry on spring barley N uptake was insignificant in the year after
slurry application (equivalent to 3% of total slurry N). Eighteen months after application, 13% of the residual 15N in soil was found in microbial biomass whether it derived from slurry or mineral fertiliser, but the remineralisation rate
(% crop removal of residual 15N) was higher for fertiliser- than for slurry-derived N, except after surface-banding. Extra litter straw in the slurry had
a negligible influence on the residual N effects in the year after application.
It is concluded that a significant part of the organic N retained in soil after cattle slurry application is derived from
immobilised ammonium N, but already a few months after application immobilised N is stabilised and only slowly released. The
immobilised N has negligible influence on the residual N effect of cattle slurry in the first years after slurry application,
and mainly contributes to the long-term accumulation of organic N in soil together with part of the organic slurry N. Under
humid temperate conditions the residual N effects of the manure can only be optimally utilised when soil is also covered by
plants in the autumn, because a significant part of the residual N is released in the autumn, and there is a higher risk of
N leaching losses on soils that receive cattle slurry regularly compared to soils receiving only mineral N fertilisers. 相似文献
19.
Summary The importance of initial exchangeable soil NH
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in nitrogen nutrition and grain yield of rice was studied in a number of representative lowland rice soils in the Philippines. The initial exchangeable soil NH
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+fertilizer N plotted against nitrogen uptake by the crop resulted in a highly significant linear relationship (R2=0.91), suggesting that the presence of exchangeable NH
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in the soil at transplanting behaved like fertilizer nitrogen. The correlation between N fertilizer rate and N uptake by the rice crop was relatively poor (R2=0.73). On the other hand, relative grain yield was more closely correlated with the initial exchangeable soil NH
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+fertilizer N than with fertilizer nitrogen applied alone. These results indicate that the initial exchangeable NH
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in the soil contributed substantially to the nitrogen uptake of the crop.Critical nitrogen levels in the soil defined as the initial exchangeable soil NH
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+fertilizer N at which the optimum grain yield (95% of the maximum yield) is obtained, varied from 60 to 100 kg N/ha in the wet season and from 100 to 120 kg N/ha in the dry season for the different fertilizer treatments. The results further suggest that the initial exchangeable soil NH
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should serve as a guide in selecting an optimum nitrogen fertilizer rate for high grain yields. 相似文献
20.
Hemmati E Vazan S Oveisi M 《Communications in agricultural and applied biological sciences》2011,76(3):551-554
Pre-planting irrigation and planting patterns are important factors in weed management that effect on seed bank. Additionally, the nitrogen is the most important factor in plant growth that affects weed-crop competition and ultimately, seed rain into the soil. A field experiment was conducted to study the effect of nitrogen application rates, pre-planting irrigation and maize planting patterns on weed seed bank population. Experimental factors were nitrogen rates at 4 levels (200, 300, 400 and 500 kg per hectare) as main plot; and pre-planting irrigation at 2 levels (irrigation before planting plus weeding emerged seedlings and, irrigation after sowing), and maize planting patterns (one-row and two-row planting of maize with same density per square of row length) that were assigned in a factorial arrangement to the sub plots. Soil samples were taken at the beginning of the season (before planting of maize) and at the end of the season (after harvest) at depth of 0-5 cm in the fixed quadrates (60 cm x 60 cm). The weed seeds were extracted from the soil samples and were identified using standard methods. The majority of weed seed bank populations included 6 weed species: Portulaca oleracea, Chenopodium album, Amaranthus retroflexus, Sorghum halepense, Daturea stramonium, Xanthium strumarium. Results showed that population of weed seed bank increased significantly with increasing nitrogen rate. The increasing rate was different between one-row and two-row planting patterns. The parameters indicated that seed bank population was much higher in a one row planting pattern of maize. With two-row planting, seed bank was decreased by 34, 26, 20 and 5% at 200, 300, 400 and 500 kg N/ha, respectively. Pre-planting irrigation was also found an effective implement to reduce the weed seed bank. When pre-planting irrigation was applied, seed bank was decreased by 57, 43, 34 and 9% at 200, 300, 400 and 500 kg N/ha. Increasing nitrogen because of weed's better growth and higher seed production neutralized the decreasing effect of pre-planting irrigation and two-row planting of maize on weed seed bank population. 相似文献