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1.
Abstract. 15N labelled NH4NO3 (fertilizer N) was applied at a rate of 50 kg N ha–1 to an Ando-Humic Nitisol and two maize crops grown on it. About 20 months later, soil cores were taken to a depth of 2.5 m. Leached fertilizer N was found between 1.4 m and 1.8 m deep and was delayed relative to net drainage by between 4.2 and 4.9 pore volumes. Anion exchange capacity (AEC) increased ten-fold down the profile, up to 2.9 cmolckg–1. The delay to fertilizer N leaching was predicted to be between 4.1 and 5.3 pore volumes when calculated from the AEC and from an equation relating delay due to AEC in laboratory columns of repacked soil obtained by Wong et al. (1990b). It was concluded that the nitrate leaching delay equation was also valid in undisturbed field profiles. Two concentration maxima for mineral N were found, which did not usually coincide with the fertilizer N and were thought to result from mineralization of soil organic matter and plant residues at the end of each season. The delay equation overestimated their leaching delay but the results were considered close enough to support the hypothesis for their formation.  相似文献   

2.
Labelled urea was applied to monolith lysimeters in the 1st year of a 2-year experiment at Onne in south-east Nigeria. On eight lysimeters maize and rice were grown in each of the 2 years. Four lysimeters were similarly cropped in the 2nd year after being uncropped in the 1st year. Measurements were made over the 2-year period of labelled and unlabelled mineral nitrogen in the drainage water, and labelled and unlabelled nitrogen in the crops. At the end of the experiment, weeds and the soil were also analysed for labelled and unlabelled nitrogen.
The total recovery of 15N in crop, soil and leachate varied between 70 and 93%. It was lowest when applied to the second season rice crop, which recovered only 15%, and highest when it was leached in the 1st year or was taken up by the maize crop. The highest crop uptake was 31%. The results indicate that, depending on the treatment, between 10 and 30% of the 15N was immobilized in the soil, lysimeters cropped in the 1st year lost between 22 and 29% of the 15N in drainage water, and between 7 and 30% was lost by denitrification. The accuracy of these figures is discussed.  相似文献   

3.
Abstract. Leaching of calcium (Ca), potassium (K) and magnesium (Mg) from urine patches in grazed grassland represents a significant loss of valuable nutrients. We studied the effect on cation loss of treating the soil with a nitrification inhibitor, dicyandiamide (DCD), which was used to reduce nitrate loss by leaching. The soil was a free-draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ). The treatment of the soil with DCD reduced Ca2+ leaching by the equivalent of 50%, from 213 to 107 kg Ca ha−1 yr−1 on a field scale. Potassium leaching was reduced by 65%, from 48 to 17 kg K ha−1 yr−1. Magnesium leaching was reduced by 52%, from 17 to 8 kg Mg ha−1 yr−1. We postulate that the reduced leaching loss of these cations was due to the decreased leaching loss of nitrate under the urine patches, and follows from their reduced requirement as counter ions in the drainage water. The treatment of grazed grassland with DCD thus not only decreases nitrate leaching and nitrous oxide emissions as reported previously, but also decreases the leaching loss of cation nutrients such as Ca2+, K+ and Mg2+.  相似文献   

4.
Abstract. The nitrogen (N) conserving effects of Italian ryegrass ( Lolium multiflorum L.) undersown as a nitrate catch crop in spring barley ( Hordeum vulgare L.) were evaluated over a ten-year period in outdoor lysimeters (1.5 m deep, diam. 1 m) with sandy loam soil. Spring barley grown every year received 11.0 or 16.5 g N m−2 before planting or was kept unfertilized. The N was given either as calcium ammonium nitrate or as ammoniacal N in pig slurry. From 1985 to 1989, ryegrass was undersown in the barley in half of the lysimeters while barley was grown alone in the remaining lysimeters. The grass sward was left uncut after barley harvest and incorporated in late winter/early spring. From 1990 to 1994 all lysimeters were in barley only.
Barley dry matter yields and crop N offtakes were not affected by the presence of undersown ryegrass, although grain yields appeared to be slightly reduced. After termination of ryegrass growing, N offtake in barley (grain+straw) was higher in lysimeters in which catch crops had been grown previously.
The loss of nitrate by leaching increased with N addition rate. Regardless of N dressing, ryegrass catch crops halved the total nitrate loss during 1985–1989, corresponding to a mean annual reduction in nitrate leaching of 2.0–3.5 g N m−2. From 1990 to 1994, lysimeters previously undersown with ryegrass lost more nitrate than lysimeters with no history of ryegrass. The extra loss of nitrate accounted for 30% of the N retained by ryegrass catch crops during 1985–1989.
It is concluded that a substantial proportion of the N saved from leaching by ryegrass catch crops is readily mineralized and available for crop offtake as well as leaching as nitrate. To maximize benefits from ryegrass catch crops, the cropping system must be adjusted to exploit the extra N mineralization derived from the turnover of N incorporated in ryegrass biomass.  相似文献   

5.
Abstract. Nitrate nitrogen (NO3-N) leaching from animal production systems in the northeast USA is a major non-point source of pollution in the Chesapeake Bay. We conducted a study to measure NO3-N leaching from dairy slurry applied to orchardgrass ( Dactylis glomerata L., cv. Pennlate) using large drainage lysimeters to measure the direct impact of four rates of slurry (urine and faeces) N application (0, 168, 336, 672 kg N ha−1 yr−1) on NO3-N leaching on three soil types. We then used experimentally-based relationships developed earlier between stocking density and NO3-N leaching loss and leachate NO3-N concentration to estimate the added impact of animal grazing. Nitrate N leaching losses from only dairy slurry applied at the 0, 158, 336, and 672 kg N ha−1 yr−1 rates were 5.85, 8.26, 8.83, and 12.1 kg N ha−1 yr−1, respectively with corresponding NO3-N concentrations of 1.60, 2.30, 2.46, and 3.48 mg l−1. These NO3-N concentrations met the 10 mg l−1 US EPA drinking water standard. However, when a scenario was constructed to include the effect of NO3-N leaching caused by animal grazing, the NO3-N drinking water standard was calculated to be exceeded.  相似文献   

6.
Abstract. Nitrate leaching under newly planted Miscanthus grass was measured for three years. The crop received either no fertilizer-N or an annual spring application of 60 kg or 120 kg N ha-1. During three winters soil water was collected from porous cup probes installed 90 cm deep. Nitrate leaching was calculated from the mean drain flow recorded in two drain gauges multiplied by the mean nitrate-N concentration in the soil water solutions collected. In the first year soil water nitrate concentrations were high on all treatments and N losses were 154, 187 and 228 kg ha-1 respectively on the unfertilized treatment and those that received 60 or 120 kg N ha-1. Leaching losses in the second and third years were, in turn, 8, 24 and 87 kg ha-1 and 3, 11 and 30 kg ha-1 for the unfertilized treatment and for the 60 and 120 kg N ha-1 treatments respectively. Leaching losses were closer to those recorded under extensively managed grassland than arable land. The large losses in the first year were probably due to the previous agricultural management at the site and excessive inputs of N on the fertilized plots. In the second and third year, lower drainage volumes may also have influenced losses. The results show that Miscanthus , once established, can lead to low levels of nitrate leaching and improved groundwater quality compared with growing arable crops.  相似文献   

7.
Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.
Cover crop N uptake was variable between years, averaging 25 kg ha−1, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l−1. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c . 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha−1, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.
After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.  相似文献   

8.
15N-labelled ammonium nitrate solution was applied in late April to circular, enclosed micro-plots prepared by pressing open-ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of 15N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of 15N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of 15N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of15N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above-ground components of the sward. By the end of the growing season, half the 15N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following spring.  相似文献   

9.
Abstract. Less Intensive Farming and Environment (LIFE) management is a form of integrated farming which aims to meet farming's economic and environmental requirements. We used a farm-scale LIFE demonstration to measure nitrogen (N) leaching losses over a 6 year period (1995–2001) using ceramic suction cups and a meteorological model to give estimates of drainage volumes. Losses from the system averaged 49 kg N ha−1, with an average drainage nitrate concentration of 15.5 mg N L−1. Rainfall and its distribution strongly influenced the loss, and drainage N concentration only fell below the nominal target of 11.3 mg N L−1 (the EU limit for potable water) in the two wettest seasons. Crop type did not have a significant effect on either postharvest mineral N (PHMN) in soil or the leaching loss in the subsequent winter. However PHMN and overwinter N leaching declined with increasing crop yield. Overwinter crop N uptake increased with early sowing: leaching loss was only 5 kg N ha−1 under grass sown in early September. Measurements of PHMN, crop sowing date and drainage data were used to construct simple equations to predict average drainage N concentration under various scenarios. The large N loss from our site is partially attributable to soil type (shallow over limestone), indeed on similar soil the loss from a conventional farm nearby was greater. The LIFE practices of postharvest harrowing and late cereal sowing will minimize the need for agrochemical use but they stimulate mineralization and reduce plant N uptake in autumn, leaving more N at risk to leaching. Some assessment of all environmental impacts is needed if the benefits of integrated practices such as those used in LIFE are to be quantified.  相似文献   

10.
Abstract. Regression equations successfully allowed the calculation of water retained at—0.3 × 105 Pa and–15 × 105 Pa matric potentials from single soil characteristics, such as bulk volume or clay content, in clayey horizons derived in similar ways from a single parent material. It is possible to use these regression equations on other soils with similar clay fabrics. The fabric is expressed numerically using the pore volume associated with clay particles.  相似文献   

11.
Abstract. Nitrate leaching from crop rotations supporting organic grain production was investigated from 1997 to 2000 in a field experiment at three locations in Denmark on different soil types. Three experimental factors were included in the experiment in a factorial design: (1) proportion of N2-fixing crops in the rotation (crop rotation), (2) catch crop (with and without), and (3) manure (with and without). Three, four-course rotations were compared, two at each location. The nitrate leaching was measured using ceramic suction cells. Leaching losses from the crop rotation with grass–clover green manure and without catch crops were 104, 54 and 35 kg N ha−1 yr−1 on the coarse sand, the loamy sand, and the sandy loam, respectively. There was no effect of manure application or time of ploughing-in the grass–clover green manure crop on the accumulated nitrate leaching from the entire rotation. Catch crops reduced nitrate leaching significantly, by 30–38%, on the sandy soils. At all locations catch crops reduced the annual averaged nitrate concentration to meet drinking water quality standards in the crop rotation with green manure. On the coarse sand there was a time lag between the onset of drainage and the start of N-uptake by the catch crop.  相似文献   

12.
Gaseous N loss, through denitrification and NH3−volatilization, was monitored throughout the growing season after spring application of 15N labelled urea fertilizer to peaty gley soils supporting N-deficient Sitka spruce. From the 15N data, it was calculated that only about 0.28% of applied N was lost through NH3-volatilization, almost all within the first few days after fertilizer application. Approximately 0.05% of applied N was calculated to be lost through denitrification. Denitrification decreased slowly over a 4-month period after fertilizer application. Rates of NH3-volatilization correlated with available NH4+ in the litter layer, while for the early part of the study when N-losses were highest, denitrification rates correlated with available NO3− in the litter layer. Observations of gaseous N-loss are also discussed in relation to data from lysimetry, changes in soil pH, and the soil moisture regime.  相似文献   

13.
Abstract. The saline–sodic soils of the dryland Songnen Plain in northeast China are only slowly permeable to fresh water because of their large content of montmorillinite clay and sodium bicarbonate. Use of slightly saline groundwater containing adequate dissolved calcium and magnesium for leaching and reclamation can potentially prevent dispersion of the clay soil particles during treatment. Amelioration was evaluated using shallow, mildly saline groundwater to irrigate sorghum–corn rotations in a two-year field experiment. After two growing seasons during which a total of 400 mm of leaching water was applied, in addition to some supplemental irrigation water, the average electrical conductivity (ECe) of the top 1.2 m of the soil profile decreased from 14.5±3.5 to 2.7±0.2 dS m−1, and the sodium absorption ratio (SARe) decreased from 35.3±4.1 to 10.1±2.5 (meq L−1)0.5. The soil physical properties were improved: infiltration rate with mildly saline groundwater increased from 12.1 to 42 mm h−1. Salinity changes in the top 1.2 m of soil layers after 700 mm of leaching produced no further improvement. Crop yields produced on plots undergoing amelioration increased by 64–562% compared with the rainfed control. The improved soil conditions after leaching resulted in 59–548% greater crop yields.  相似文献   

14.
Direct drilling of autumn-sown cereal crops reduced the loss of nitrate in drainage. Losses of nitrate nitrogen in water draining from arable land have been measured for 4 seasons, 1980–1984. The field experiment was on a mole-drained clay soil in southern England. Autumn-sown cereal crops were established by direct drilling or after ploughing and traditional seed-bed preparation. Losses ranged from 3 to 75 kg N ha−1 year−1, with an average of 34 kg N ha−1 year−1. Most of the loss (about 90%) was removed via the mole-drain system. Measured loss of nitrate from the direct-drilled soil was 76% (range 48–89%) of that lost from the ploughed soil. Mole drains apparently increased loss of nitrate directly to the river system. In the absence of mole drains, nitrate loss in surface drainage averaged 6 kg N ha−1, compared with 4 kg N ha−1 in the presence of drains. However, in one year, exceptionally high amounts of nitrate (80 kg N ha−1) were lost from undrained, direct-drilled land because of poor crop establishment; deep leaching of nitrate in the undrained soil was not measured. Approximate calculations show that up to half the autumn-applied fertiliser-N was lost by leaching and up to 15% of spring applications.  相似文献   

15.
Abstract. A long-term lysimeter experiment with undisturbed monoliths studied leaching behaviour and balances of phosphorus (P), potassium (K) and nitrogen (N) during a seven year crop rotation on four types of soil receiving inorganic fertilizers, manure and grass compost respectively. It was shown that application of manure did not lead to any direct change in nutrient leaching, unlike the application of fertilizers to soils of normal fertility. However, soil type considerably affected the nutrient concentrations in the drainage water.
Manure applied in amounts equal to the maximum animal density allowed by Swedish legislation slightly oversupplied P and N (0.5–3.5 and 18–38 kg ha−1 y−1 respectively) compared to the crop requirement and leaching losses for most of the soils. The relationship between lactate-soluble P in the topsoil and the concentrations of dissolved P in the drainage water was very strong. However the strength of this relationship was dependent on just one or two soils. P losses from a fertile sandy soil were large (1–11 kg ha−1 y−1) throughout the crop rotation and average crop removal (13 kg ha−1 y−1) plus the leaching losses were not balanced (average deficit 3–6 kg ha−1 y−1) by the addition of fertilizer, manure or grass compost. No decreasing trend was found in the P losses during seven years. However, the K deficit (average 26 kg ha−1 y−1) led to a significant reduction in the leaching trend from this soil. The other soils that had a smaller K deficit showed no significant reduction in the leaching of K.  相似文献   

16.
Abstract. Nitrate leaching was measured for four years at the Royal Agricultural College 's Coates Farm in the Cotswolds, England. Coates is a typical Cotswold mixed farm with thin, well-drained calcareous soils especially prone to leaching. Over the duration of this study there were dairy, sheep and arable enterprises on the farm. A 'Farm Gate' nitrogen (N) budget was constructed. Small 120 m × 20 m 'farmlets' were sited in ten fields across the farm, covering all parts of the rotation, as the sites for detailed measurements. Each farmlet received the same management as the rest of the field in which they were situated. Using ceramic probes inserted to 60 cm, soil water was sampled every two weeks throughout the winter drainage season. The annual drainage varied from 135 mm under grassland in 1996/7 to 600 mm under cereals in 1998/9. Average N losses by leaching were determined mostly by rainfall and were 65 kg N ha–1 yr–1, accounting for 25% of the N inputs. Especially leaky parts of the rotation were the ploughing out of a lucerne ley and the grazing of stubble turnips with sheep, both typical Cotswold farm practices. The research highlights some of the difficulties in developing practicable, profitable management practices to decrease nitrate losses.  相似文献   

17.
Abstract. Eight lysimeters, each with a surface area of 0.5 m2 and a length of 60 cm, were taken over mole drains from a Denchworth soil and divided into two groups with either a standard agricultural tilth or a finer, deeper topsoil tilth. They were variously instrumented to measure soil moisture content at three depths and losses of nitrate, a bromide tracer and radiolabelled isoproturon, all of which were followed over a year. Leaching of isoproturon was initiated by artificial irrigation either 1 or 39 days after application. The finer tilth seemed to increase the water-holding capacity of the topsoil, and this resulted in slower wetting of the subsoil, decreased flow volumes from the first events of the season and a delay of approximately four weeks in the time to the maximum concentration of the bromide tracer in leachate. The finer topsoil tilth also decreased maximum concentrations of isoproturon from 29 to 15 μg l−1 following irrigation 1 day after treatment and from 43 to 9 μg l−1 following irrigation 39 days after treatment. Total losses of isoproturon were three times larger with the standard agricultural tilth. Differences were attributed to a decrease in bypass flow through the topsoil with the finer tilth, particularly during events early in the season. There was a small decrease in total losses of nitrate in leachate from the finer tilth compared to that from the standard tilth.  相似文献   

18.
Abstract. Slurry from farm animals may contaminate water supplies, rivers and bathing waters with faecal coliforms, such as Escherichia coli . Where animals harbour the O157 strain the hazard to human health is particularly high, but both the hazard level, and the low incidence and sporadic nature of the excretion of E. coli O157 make it difficult to study this strain under field conditions. The survival of total E. coli and of E. coli O157 were compared in the laboratory for two soils under controlled temperature and moisture. E. coli O157 die-off rate was the same as or quicker than for total E. coli . This result meant that field experiments studying the fate of total E. coli should give a satisfactory evaluation of the risk of water contamination by the O157 strain. In four field experiments at three sites, slurry containing total E. coli numbers of 2.2 × 104 to 5.7 × 105 colony forming units per mL (c.f.u. mL–1) was applied to drained field plots. Field die-off was faster than expected from laboratory experiments, especially in one experiment where two weeks dry weather followed application. In all but this experiment, the first drain flow events after slurry application led to very high E. coli concentrations in the drains (103 to 104 c.f.u. mL–1). E. coli O157 was present in the slurry used for two of the experiments (33 c.f.u. per 100 mL in each case). However the proportion of E.coli O157 was very low (about 1 in 105) and it was not detected in the drainage water. After the first week E. coli drainage water numbers decreased rapidly but they were 1–10 c.f.u. mL–1 for much of the sampling period after slurry application (1–3 months).  相似文献   

19.
Comparisons were made between 1988 and 1991 to evaluate three methods of estimating the leaching of mineral nitrogen (N) from unstructured freely draining sandy loam and loamy sand soils. The studies compared the drainage patterns and quantities of N (almost exclusively nitrate) leached from monolith lysimeters with those estimated from ceramic suction cups and soil core extracts. The latter two methods gave direct measurements of the mineral N concentrations in drainage, but required an estimate of the drainage volume calculated from meteorological observations and evapotranspiration equations to give total N leached. A bromide tracer was also used to confirm conclusions from nitrate leaching studies. There was a delay in the onset of drainage from free draining lysimeters because they lack the subsoil matric potential of field soils. However, total annual drainage measured by lysimeters or calculated from meteorological observations was similar, providing that return to field capacity was correctly identified in the field soil. During the first year there were discrepancies between methods which were attributed to soil disturbance during lysimeter and/or ceramic cup installation. In the second and third years of the experiment, estimates of N leaching losses using the lysimeters and ceramic cups were in good agreement. Nitrate concentrations in soil solution at a depth of 130 cm measured from soil core extracts were smaller than found by the other methods during the second year and the peak concentrations were significantly different (P<0.05). However, total overwinter N leached was not significantly different. Thus, while lysimeters and cups can be used to quantify leaching losses on unstructured, free draining soils if used correctly, the use of soil core extracts is questionable.  相似文献   

20.
Abstract. Nitrate leaching measurements in Denmark were analysed to examine the effects of husbandry factors. The data comprised weekly measurements of drainage and nitrate concentration from pipe drains in six fields from 1971 to 1991, and weekly measurements of nitrate concentration in soil water, extracted by suction cups at a depth of 1 m, from 16 fields in 1988 to 1993. The soils varied from coarse sand to sandy clay loam.
The model used for analysing the data was: Y = exp (1.136–0.0628 clay + 0.00565N + crop ) D0.416, with R2= 0.54, where Y is the nitrate leaching (kg N/ha per y), clay is the % clay in 0-25 cm depth (%), N is the average N-application in the rotation (kg/ha/y) and D is drainage (mm/y). The most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17-24 kg/ha/y). Winter cereal following a grass crop, beets, winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36-46 kg/ha/y). High rates of leaching were estimated from winter cereals following rape/peas, bare soil following cereals and from autumn applications of animal manure on bare soil (71-78 kg/ha/y). Estimates of leaching from soil of 5, 12 and 20% clay were 68, 44 and 26 kg/ha/y, respectively. Leaching was estimated to rise significantly with increasing amounts of applied N.
The model is suitable for general calculations of the effects of crop rotation, soil type and N-application on nitrate leaching from sandy soil to sandy clay loarns in a temperate coastal climate.  相似文献   

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