Water drainage and nitrate leaching under traditional and improved management of vegetable‐cropping systems in the North China Plain

Traditional irrigation and nitrogen (N) fertilization in North China may elevate water drainage and nitrate concentrations in soil and groundwater. A field experiment was conducted in an intensively irrigated vegetable (cauliflower, amaranth, and spinach) field for three consecutive years (1999–2002). The main objective was to test to what extent an improved water and fertilizer management, based on the maintenance of field capacity a defined range of the water content in the 0–50 cm soil layer and an N expert system, could reduce drainage and nitrate leaching without impairing vegetable yield. Rates of water drainage and related nitrate leaching were calculated based on measurements of soil water potential and soil‐water nitrate concentrations. Soil water potential was monitored with tensiometers at depths of 75 cm and 105 cm. Nitrate concentrations were analyzed in soil leachates collected at 90 cm soil depth using ceramic suction cups. The results revealed that the average annual drainage related to the cultivation season for cauliflower, amaranth, and spinach was reduced from 275 mm in the traditional system to 29 mm with improved management practice. The average annual cumulative nitrate leaching during the vegetable‐growing period amounted to 301 kg ha^–1 and 13 kg ha^–1 in the traditional and improved management practices, respectively. Vegetable yields were not significantly different under the traditional and improved management practices.     

Developments in the use of porous ceramic cups for measuring nitrate leaching

Porous ceramic cups are widely used for measuring nitrate leaching from agricultural land, but it is not fully clear what procedures give the most reliable results, or what factors could limit the validity of their use. This paper reports improvements in methodology made during tests of the technique when it was first used on a large scale, on light soils. Porous cup assemblies must be installed carefully to avoid preferential flow through the disturbed soil around them, and to maximize contact between cup and soil. Newly-installed and well-established porous cups could give differing results. Sampling must start as soon after return to field capacity as possible, when concentrations are often highest. The estimate of nitrate loss can be greatly affected by the calculated date of start of drainage, and some independent check on this date is advisable. Sampling frequency must be sufficient to define the shape of the curve of concentration against drainage, but this curve is normally fairly smooth. Methods of calculating nitrate loss are discussed. The spatial variability between cups in arable soils is typically 30–60% of the mean, less than between individual soil samples. Because porous cups can be left in situ, changes over time are not confounded with changes due to sampling from differing locations, as they are with successive soil samples.     

Understanding the soil nitrogen cycle

Abstract. A quantitative knowledge of nitrogen cycle processes is required to design strategies for decreasing leakage of N from agriculture to the wider environment. However, it is remarkably difficult to make reliable measurements of many of the key processes under realistic field conditions. In impermeable soils hydrologically separated plots provide an invaluable method of measuring leaching and runoff. Estimates of nitrate leaching using porous ceramic cups agree well with lysimeter measurements on sandy soil but are suspect on more structured soils. Estimates of N₂O flux from soil are subject to great spatial heterogeneity; developing long path-length measuring techniques may overcome this problem.
¹⁵N labelling is valuable for assessing fertilizer N loss, forms of N left in soil and the fate of N from crop residues. The combination of experimental and modelling approaches can provide insights that are otherwise unattainable, including a basis for more precise advice on N fertilization.
Mineralization of soil organic matter and crop or animal residues provides much of the nitrate leached during winter under the climatic conditions of north-west Europe, because mineralization is poorly synchronized with crop N uptake. Maintenance of crop cover during winter can greatly decrease leaching but the long-term effects on the N cycle of winter cover crops or incorporating cereal straw are not yet clear.     

The use of porous ceramic cup water samplers to measure solute leaching on chalk soils

Abstract. This paper reports results from a four year study to investigate the suitability of porous ceramic cups to measure solute leaching on shallow chalk soils. Measurements were carried out in one field following surface applications of nitrate and bromide tracers and in two fields after only bromide was applied. Soil water samples were collected from porous cups at 30,60 and 90cm depth after every 25 mm of drainage, and soil samples from 0–30, 30–60 and 60–90 cm were collected monthly eachwinter. Soil matric suctions andvolumetric moisture content were measured in one winter. Leaching losses, measured with ceramic cups were compared with those measured by soil analysis. Porous cups installed in chalk at 60 and 90 cm depth were only able to collect samples regularly when soil matric suctions were less than 15 kPa. Water held at such low suctions is likely to move quickly through relatively large fissures in the chalk. The slow rate of equilibration between solute concentrations in water moving in macrofissures and those in water moving through micropores of the chalk matrix, means that porous cups may not provide good estimates of leaching losses if they are installed in chalk rock.     

Calculation of nitrogen mineralization and leaching in fallow soil using a simple dynamic model

Simple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1-day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing-cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers. The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a ¹⁵N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha^?1. In the treatments without crop residues, the mineralization rate followed first-order kinetics (against normalized time) in the loamy soil, and zero-order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time.     

Effects of grazing strategy on limiting nitrate leaching in grazed grass‐clover pastures on coarse sandy soil

Urinations of ruminants on grazed pastures increase the risk of nitrate leaching. The study investigated the effect of reducing the length of the grazing season on nitrate leaching from a coarse sandy, irrigated soil during 2006–2007 and 2007–2008. In both years, precipitation was above the long‐term mean. The experiment was initiated in a 4‐yr‐old grass‐clover sward in south Denmark. Three treatments were as follows grazing only (G), spring cut followed by grazing (CG) and both spring and autumn cuts with summer grazing (CGC). Nitrate leaching was calculated by extracting water isolates from 80 cm depth using ceramic suction cups. Because of considerable variation in measured nitrate concentrations, the 32 installed suction cups per treatment were insufficient to reveal differences between treatments. However, weighted nitrate leaching estimations for G, CG and CGC showed estimated mean nitrate N concentrations of 23, 19 and 13 mg/L for an estimated proportion area occupied by urine patches of 0.33, 0.26 and 0.16, respectively. Thus, N concentrations in G and CG exceeded the EU limit of 11.3 mg N/L. Under the prevailing conditions, the time of urination did not appear important. The estimated background leaching calculated from suction cups presumably not situated under urine patches resulted in mean nitrate N concentrations of 2.6 mg/L.     

Nitrogen leaching losses under a less intensive farming and environment (LIFE) integrated system

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.     

可变电荷与恒电荷稻田土壤硝态氮和铵态氮淋失规律

A variable-charge (VC) and a permanent-charge paddy soil (PC) were selected to study nitrate (NO3--N) and ammonium (NH4+-N) leaching with N isotopes for one consecutive year. An irrigation and intermittent drainage pattern was adopted to mimic natural occurrence of rainfall during the upland crop season and drainage management during the flooded rice season. Treatments to each soil type were no-N controls (CK), 15N-labeled (NH4)2SO4 (NS) and milk vetch (NV) applied at a rate equivalent to 238 kg N ha–1 to unplanted lysimeters, totaling six treatments replicated in triplicates. Results indicated that the soil type dominated N leaching characteristics. In the case of PC, NO3--N accounted for 78% of the total leached inorganic N; NS was prone to leach three times more than the NV, being 8.2% and 2.4% of added 15N respectively; and > 85% of leached NO3--N came from native N in the soil. In the case of VC, NH4+-N made up to 92% of the total inorganic N in leachate. Moreover, NH4+-N leaching was detected throughout the whole incubation, and was particularly high during the flooded season. NO3--N leaching in VC occurred later at a lower rate compared to that in PC. The findings of this study indicate that NO3--N leaching during the drained season in permanent-charge paddy soils and NH4+-N leaching in variable-charge soils deserve more attention for regional environmental control.     

Comparison of soil solution chemistry assessment using zero-tension lysimeters or centrifugation

The composition of soil solutions obtained from the field varies with the method of extraction. Variations in sampling methods and the difficulties in extracting representative samples from soils in space and time, can explain divergent results. In this study we compared soil solutions from a forest soil in northern Sweden obtained by a centrifuge drainage technique and by zero-tension monolith lysimeters. Zero-tension lysimeters were destructively sampled, and centrifuge solutions from this soil were compared with that from soil outside. In our study we found three major differences in the solute composition between the centrifugate and the lysimeter leachate: (i) larger concentrations of most solutes in the mor layer centrifugate than in the mor layer leachate, (ii) accumulation of nitrate in the lysimeters, and (iii) larger concentrations of base cations in the zero-tension lysimeters below 0.3 m depth. Water contents within the lysimeters were up to 3.5 times greater than under natural conditions and the water yields from the lysimeters indicate that water residence time ranged from < 1 to >5 years. This study shows that differences in results from the two methods are due to inherent differences in the methods themselves and not just to the collection of different soil waters. The hydrological anomaly and disturbance induced by the zero-tension lysimeters affects the solute chemistry and thus the applicability of the results to field conditions.     

How important is plant litter to the regulation of mineral‐N leaching to streams in winter? An observations‐led experimental approach

Ammonium‐N concentrations were frequently observed to exceed nitrate‐N concentrations in an intermittently flowing stream draining acid grassland in North Yorkshire. This prompted the design of a soil microcosm experiment to investigate the role of litter in the leaching of ammonium and nitrate from soil profiles during winter. Drainage water was analysed weekly for N species, pH, mineral acid anions and dissolved organic carbon (DOC) for a period of 11 weeks, while extractable mineral‐N was determined after 5 and 11 weeks. The results demonstrate that litter plays an important role in reducing mineral‐N leaching in winter months. They also suggest that DOC from the litter participates in mineral‐N retention in the soil profiles in winter. Ammonium‐N and nitrate‐N concentrations measured in the microcosm drainage water are similar to those of the stream.     

Retarded leaching of nitrate measured in monolith lysimeters in south-east Nigeria

At Onne in South-east Nigeria, drainage water was collected from four monolith lysimeters and analysed for nitrate. The lysimeters contained an acid sandy loam. At the start of the first rainy season two lysimeters received urea labelled with ¹⁵NO₃^– and two received no nitrogen fertilizer; all four were uncropped in the first year.
The peak concentrations of ¹⁵NO₃^– and of unlabelled (soil) NO₃^– were found after 2.5 pore volumes of water had passed through the lysimeters. Using the same soil in the laboratory after fine sieving, the peak concentration of tritiated water was found at 1 pore volume whereas nitrate leaching was retarded. The pattern of nitrate leaching was well described by miscible and immiscible models which included an adsorption coefficient for nitrate. Over the 2 years 81.4% of the ¹⁵N added at the start of the first rainy season was recovered in the drainage water.     

Use of long-term monitoring data to derive a relationship between nitrogen surplus and nitrate leaching for grassland and arable land on well-drained sandy soils in the Netherlands

The decrease in nitrogen (N) use in agriculture led to improvement of upper groundwater quality in the Sand region of the Netherlands in the 1991–2009 period. However, still half of the farms exceeded the European nitrate standard for groundwater of 50 mg/l in the 2008–2011 period. To assure that farms will comply with the quality standard, an empirical model is used to derive environmentally sound N use standards for sandy soils for different crops and soil drainage conditions. Key parameters in this model are the nitrate-N leaching fractions (NLFs) for arable land and grassland on deep, well-drained sandy soils. NLFs quantify the fraction of the N surplus on the soil balance that leaches from the root zone to groundwater and this fraction represents N available for leaching and denitrification. The aim of this study was to develop a method for calculating these NLFs by using data from a random sample of commercial arable farms and dairy farms that were monitored in the 1991–2009 period. Only mean data per farm were available, which blocked a direct derivation of NLFs for unique combinations of crop type, soil type and natural soil drainage conditions. Results showed that N surplus leached almost completely from the root zone of arable land on the most vulnerable soils, that is, deep, well-drained sandy soils (95% confidence interval of NLF 0.80–0.99), while for grassland only half of the N surplus leached from the root zone of grassland (0.39–0.49). The NLF for grassland decreased with 0.015 units/year, which is postulated to be due to a decreased grazing and increased year-round housing of dairy cows. NLFs are positively correlated with precipitation surplus (0.05 units/100 mm for dairy farms and 0.10 units/100 mm for arable farms). Therefore, an increase in precipitation due to climate change may lead to an increase in leaching of nitrate.     

Soluble organic nitrogen in agricultural soils

 The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha^–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding. Received: 10 June 1999     

The impact of pasture improvement on the soil solution chemistry of some stagnopodzols in mid-Wales

Abstract. The impact of three methods of pasture improvement on soil water chemistry were studied: ploughing plus 15 t ha^-1 lime c. 40 years ago, 5 t ha^-1 surface spread lime c. 20 years ago and surface cultivation with 7 t ha^-1 lime plus compound fertilizer 10 years ago. Soil solution was sampled using tensionless lysimeters and porous ceramic cups. Concentrations of several solutes were higher in the treated soils than a control, including solutes not added in lime or fertilizers. Calcium, magnesium and bicarbonate concentrations showed the largest increases; these were apparent in all horizons, and all treatments. Bicarbonate had become the dominant anion. Solute concentrations varied between treatments and were related to the amount of an element added rather than time since treatment. Highest mean calcium concentrations, 6.25 mg l^-1 were still low compared with drainage from lowland arable soils but could have a significant impact on the calcium-poor surface waters of the uplands.     

Lysimeter Study on the Effects of Different Rain Qualities on Element Fluxes from Shallow Mountain Soils in Southern Norway

This study focuses on fluxes of elements from, and changes in the soil properties of shallow organic material rich soil as a result of changes in precipitation acidity. Intact soil columns including natural vegetation from two areas (one exposed to acidic precipitation and one unpolluted) were used in a lysimeter experiment. The lysimeters were watered with simulated normal rain (pH 5.3) or simulated acidic rain (pH 4.3) for four years. Sulphuric acid and ammonium nitrate were used to regulate the quality of the simulated rain. Significantly more SO₄ ^2? was leached from lysimeters receiving acid rain. Rain acidity had no significant effect on NO₃ ^? leaching. Significantly more Mg²⁺ was leached from lysimeters receiving acid rain, but this only applied for the soils from the unpolluted area. Four years of treatment did not cause any significant effect on the soil acidity and the amounts of base cations in the soil. The more acidic rain did, however, cause a significant lower cation exchange capacity. For the soils from the polluted area the acid precipitation did cause a lowering of the exchangeable K⁺ in the upper 5 cm of the soil. Different quality of the soil organic material indicated by different vegetation types appeared to cause significant differences in the amount of components leached from the soil, but did not cause any difference in response to the different rain qualities.     

大型蒸渗仪的设计、建造与安装（英）

蒸渗仪是用来研究营养元素在农田中的运移的系统,本文系统描述了一种大型蒸渗仪的设计,建造与安装。试验采用湖北地区典型土壤类型黄棕壤与潮土,在华中农业大学校园内每种土壤安装16个大型蒸渗仪。蒸渗仪采用减少土柱的扰动的方法建造,并填充凡士林减少土壤水分的边缘流动。蒸渗仪采用外径630 mm高700 mm厚10 mm的PVC管作材料。土柱建成后安装在预制PVC底座上,底座中间有一圆孔外接淋失液收集装置。淋失液收集后用来测定淋失液离子含量。试验结果表明,相同土壤土柱之间淋失量差异不显著,没有检测到水分的边缘流动;同时建设效率高,费用低。     

Simulation of nitrogen dynamics in farmland areas of Denmark (1989–1993)

Abstract. Each year since 1986 information has been collected about the farming systems at intersections of a nationwide 7 km square grid in Denmark. These management data and corresponding soil analyses were used in the model DAISY to simulate water and nitrogen dynamics. The model was validated with respect to harvested dry matter yield and nitrogen content in the soil. Simulated nitrate leaching from farmland areas from 1 April 1989 to 31 March 1993 was related to precipitation zones, soil type, fertilizer strategies and cropping systems. The mean simulated nitrate leaching for the whole of Denmark was 74 kg N/ha/yr, with a large yearly variation in the period considered. The simulated nitrate leached from soils with a sandy subsoil corresponded to 51% of the applied fertilizer, twice that leached from soils with a loamy subsoil. The application of pig manure resulted in average leaching losses of 105 kg N/ha/yr. The simulated nitrate leaching losses at sites where only artificial fertilizer was applied were in the following order: cereal with undersown grass < crop followed by winter cereal or winter rape < cereal or rape without a catch crop < root crops without a catch crop. Where only artificial fertilizers were applied, the simulated mean annual leaching was 59 kg N/ha from spring barley and 40 kg N/ha from winter wheat. A map of simulated nitrate leaching in Denmark was produced using a Geographical Information System.     

Nitrate leaching as affected by long-term N fertilization on a coarse sand

Abstract. A field experiment on a coarse sand (1987–92) was conducted with spring barley ( Hordeum vulgare L.), in order to evaluate the effects of increasing N fertilization on nitrate leaching under temperate coastal climate conditions. The N fertilizer levels were 60 and 120 kg N/ha. The experiment was conducted on a 19-year old permanent field trial with continuous spring barley, initiated in 1968, and included treatments with ploughing in autumn or spring, with or without perennial ryegrass ( Lolium perenne L.) as a catch crop undersown in spring. Prior to 1987, the low and high levels of N fertilizer were 70 and 150 kg N/ha, respectively. To calculate nitrate leaching, soil water samples were taken from a depth of 0.8 m using ceramic cups. The average annual nitrate leaching from plots with 60 and 120 kg N/ha was 38 and 52 kg N/ha/y, respectively. The increased leaching associated with increasing fertilizer application was not caused by inorganic N in the soil at harvest, but rather by greater mineralization, mainly in autumn. Growing of a catch crop was relatively more efficient for reducing nitrate leaching than a long-term low fertilizer application. A 50% reduction in N application decreased average yield by 26%, while nitrate leaching decreased by 27%.     

The effect of crop, N-level, soil type and drainage on nitrate leaching from Danish soil

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 ) D^0.416, 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.     

Stickstoffverlagerung unter spätbeweidetem Grünland

Leaching of nitrogen from pastures at the end of the grazing season A trial was carried out to describe nitrogen dynamics under excrement patches. On three grassland sites differing in water capacity, soil water was extracted by porous ceramic cups placed under the patches. Soil water was analyzed for different nitrogen fractions. Infiltration water and the amount of leached nitrogen was calculated by a simulation model. The rapid rise in concentrations under the urine patches to 30–60 mg NH₄?N/I was due to the rapid hydrolysis of urea in spite of low soil temperatures. While the rates of ammonium decreased, the concentration of nitrate increased continuously up to 160 mg NO₃?N/I and did not fall until the beginning of plant growth in early spring. Under the dung patches almost no nitrogen was found. For the urine patches the calculated nitrogen leaching was between 150 and 320 kg/ha, for the dung patches between 3 and 28 kg/ha. From the total of leached nitrogen the nitrate fraction (83%) was the most significant, followed by the organic nitrogen fraction (11%) and ammonium (6%). Taking account of an estimated grazing pressure, the urine-affected soil surface was calculated between 1% and 3