Nitrate leaching in an organic dairy/crop rotationas affected by organic manure type, livestock densityand crop

Abstract. In dairy farming systems the risk of nitrate leaching is increased by mixed rotations (pasture/arable) and the use of organic manure. We investigated the effect of four organic farming systems with different livestock densities and different types of organic manure on crop yields, nitrate leaching and N balance in an organic dairy/crop rotation (barley–grass-clover–grass-clover–barley/pea–winter wheat–fodder beet) from 1994 to 1998. Nitrate concentrations in soil water extracted by ceramic suction cups ranged from below 1 mg NO₃-N l^?1 in 1^st year grass-clover to 20–50 mg NO₃-N l^?1 in the winter following barley/pea and winter wheat. Peaks of high nitrate concentrations were observed in 2^nd year grass-clover, probably due to urination by grazing cattle. Nitrate leaching was affected by climatic conditions (drainage volume), livestock density and time since ploughing in of grass-clover. No difference in nitrate leaching was observed between the use of slurry alone and farmyard manure from deep litter housing in combination with slurry. Increasing the total-N input to the rotation by 40 kg N ha^?1 year^?1 (from 0.9 to 1.4 livestock units ha^?1) only increased leaching by 6 kg NO₃-N ha^?1. Nitrate leaching was highest in the second winter (after winter wheat) following ploughing in of the grass-clover (61 kg NO₃-N ha^?1). Leaching losses were lowest in 1^st year grass-clover (20 kg NO₃-N ha^?1). Averaged over the four years, nitrate concentration in drainage water was 57 mg l^?1. Minimizing leaching losses requires improved utilization of organic N accumulated in grazed grass-clover pastures. The N balance for the crop rotation as a whole indicated that accumulation of N in soil organic matter in the fields of these systems was small.     

Nitrate leaching and residual soil nitrogen supply following outdoor pig farming

Abstract. Large nitrogen (N) inputs to outdoor pig farms in the UK can lead to high nitrate leaching losses and accumulation of surplus N in soil. We investigated the residual effects of three contrasting outdoor pig systems as compared to an arable control on nitrate leaching and soil N supply for subsequent spring cereal crops grown on a sandy loam soil during 1997/98 and 1998/99 harvest seasons. Previously, the pig systems had been stocked for 2 years from October 1995 and were designated current commercial practice (CCP, 25 sows ha^?1 on stubble), improved management practice (IMP, 18 sows ha^?1 on undersown stubble) and best management practice (BMP, 12 sows ha^?1 on established grass). Estimated soil N surpluses by the end of stocking in September 1997 were 576, 398, 265 and 27 kg ha^?1 N for the CCP, IMP, BMP and continuous arable control, respectively. Nitrate leaching losses in the first winter were 235, 198, 137 and 38 kg ha^?1 N from the former CCP, IMP and BMP systems and the arable control, respectively. These losses from the former pig systems were equivalent to 41–52% of the estimated soil N surpluses. Leaching losses were much smaller in the second winter at 21, 14, 23 and 19 kg ha^?1 N, respectively. Cultivation timing had no effect (P>0.05) on leaching losses in year 1, but cultivation in October compared with December increased nitrate leaching by a mean of 14 kg ha^?1 N across all treatments in year 2. Leaching losses over the two winters were correlated (P<0.001) with autumn soil mineral N (SMN) contents. In both seasons, spring SMN, grain yields and N offtakes at harvest were similar (P>0.05) for the three previous pig systems and the arable control, and cultivation timing had no effect (P>0.05) on grain yields and crop N offtake. This systems study has shown that nitrate leaching losses during the first winter after outdoor pig farming can be large, with no residual available N benefits to following cereal crops unless that first winter is much drier than average.     

Residual effect and nitrate leaching in grass‐arable rotations: effect of grassland proportion,sward type and fertilizer history

A key point in designing grass‐arable rotations is to find the right balance between the number of cultivations and the length of the grass phase. In a field experiment, we investigated the effect of cropping history (grazed unfertilized grass–clover and fertilized [300 kg N per hectare] ryegrass, proportion of grassland and previous fertilizer use) on crop growth and nitrate leaching for 2 years following grassland cultivation. In the final year, the effect of perennial ryegrass as a catch crop was investigated. The nitrogen fertilizer replacement value (NFRV) of grassland cultivation was higher at 132 kg N per hectare in the rotation with 75% grassland compared with on average 111 kg N per hectare in rotations with 25 and 38% grassland and the NFRV of ryegrass in the rotation was higher than that of grass–clover. Nitrate leaching following cultivation was not affected by the proportion of grassland in the crop rotation or sward type. However, there was a considerable effect of having a ryegrass catch crop following the final barley crop as nitrate leaching was reduced from 60 to 9 kg N per hectare. When summarizing results from the crop rotations over a longer period (1997–2005), management strategy adopted in both the grassland and arable phases appeared to be the primary instrument in avoiding nutrient losses from mixed crop rotations, irrespective of grass proportion. In the arable phase, the huge potential of catch crops has been demonstrated, but it is also important to realize that all parts of the grass‐arable crop rotations must be considered potentially leaky.     

Nitrate leaching from the Broadbalk Wheat Experiment, Rothamsted, UK, as influenced by fertilizer and manure inputs and the weather

Abstract. Nitrate leaching was measured over the eight drainage seasons spanning the nine years from 1990–1998 on the 157‐year old Broadbalk Experiment at Rothamsted, UK. The weather pattern of two dry, three wet and three dry years was the dominant factor controlling nitrogen (N) loss. Both the concentration of nitrate in the drainage waters and the amount of N leached increased with the amount of N applied, mostly because of long‐term, differential increases in soil organic matter and mineralization. On average, losses of N by leaching were 30 kg ha^?1yr^?1 when no more than the optimum N application was applied and were typical of amounts leached from arable land in the UK. Losses increased significantly in both amounts and as the percentage of N applied for supra‐optimal applications of N and from autumn‐applied farmyard manure (FYM). Extra spring‐applied fertilizer was very effective at increasing yields on plots given FYM in the autumn but at the expense of leaching losses three times those from optimum fertilizer N applications. Losses increased after potatoes because they left significant amounts of mineral N in the soil, and decreased after forage maize because it used applied N more effectively. Losses measured 120 years ago from identical treatments were 74% greater than current losses because of today's larger yields and more efficient varieties and management practices. Average concentrations of nitrate in drainage waters did not exceed the EU limit of 11.3 mg NO₃‐N l^?1 until supra‐optimal amounts of N fertilizer (>150–200 kg ha^?1yr^?1) were applied in spring or FYM was applied in autumn. However some drainage waters from all plots, even those that have not received fertilizer for >150 years, exceeded the limit when rain followed a dry summer and autumn. Nitrate leaching into waters will remain a problem for profitable arable farming in the drier parts of Eastern England and Europe despite increased N use efficiency.     

Seasonal pattern of nitrate losses from cultivated soil with subsurface drainage

Subsurface drainage systems have been installed in about 10000 ha of agricultural land in the flat part of the Emilia-Romagna Region in northern Italy. Nitrate loss in drainage water from a representative farm in this area was measured for three consecutive years (1986, 1987, 1988). During this period a total of 369 water samples were collected, filtered at 0.45 µm and analyzed. The nitrate concentration exceeded the limits for surface water set by Italian law regarding water pollution (90 mg NO₃ ^?L^?1 = 20 mg N L^?1) in 84% of the samples. The greatest nitrate loss was recorded during the winter and early spring when drainage was high. After this period loss of nitrate, via drainage water, progressively decreased. This was attributed to a decrease in the amount of drainage water and increase in crop uptake of N. The average annual nitrate loss via drainage water was around 200 kg of NO _inf3 ^sup? ha^?1. Annual nitrate losses of this order of magnitude (? 50 kg N ha^?1) indicate an urgent need for implementation of management practices directed towards achieving considerable reductions in these losses.     

Nitrous oxide emissions, cereal growth, N recovery and soil nitrogen status after ploughing organically managed grass/clover swards

The period after ploughing of grass–clover leys within a ley‐arable rotation is when nitrogen accumulated during the ley phase is most vulnerable to loss. We investigated how ploughing date and timing of cessation of grazing before ploughing affected nitrous oxide (N₂O) losses of the first cereal crop. Ploughing dates were July and October for a winter wheat pilot study and January and March for spring barley in the main experiment. Timings of cessation of grazing (main experiment only) were October, January and March. Spring barley yield, nitrogen uptake and soil mineral nitrogen were also assessed. A separate large‐scale laboratory incubation was made to assess the effect of temperature and rainfall on nitrous oxide emissions and nitrate leaching under controlled conditions. Nitrous oxide emissions in the 1‐ to 2‐month period after autumn or spring ploughing, or sowing were typically between 20 and 150 g N ha^?1 day^?1 and increased with temperature and rainfall. Tillage for crop establishment stimulated N₂O emissions with up to 2.1 kg N ha^?1 released in the month after spring tillage. Cumulative nitrous oxide emissions were greatest (～8 kg ha^?1 over 17 months) after cessation of grazing in March before March ploughing, and lowest (～5.5 kg ha^?1) after cessation of grazing in January before January ploughing. These losses were 1.2–3.9% of the N inputs. In the laboratory study, winter ploughing stimulated nitrate leaching more than nitrous oxide emissions. The optimum time of ploughing appears to be early spring when the cold restricts nitrogen mineralization initially, but sufficient nitrogen becomes available for early crop growth and satisfactory N offtake as temperature increases. Early cessation of grazing is advantageous in leaving an adequate supply of residues of good quality (narrow C:N ratio) for ploughing‐in. Restricting tillage operations to cool, dry conditions, being aware of possible compaction and increasing the use of undersown grass–clover should improve the sustainability of organic farming.     

Nitrogen losses from outdoor pig farming systems

Abstract. Nitrogen losses via nitrate leaching, ammonia volatilization and nitrous oxide emissions were measured from contrasting outdoor pig farming systems in a two year field study. Four 1‐ha paddocks representing three outdoor pig management systems and an arable control were established on a sandy loam soil in Berkshire, UK. The pig management systems represented: (i) current commercial practice (CCP) ‐ 25 dry sows ha^?1 on arable stubble; (ii) ‘improved’ management practice (IMP) ‐ 18 dry sows ha^?1 on stubble undersown with grass, and (iii) ‘best’ management practice (BMP) 12 dry sows ha^?1 on established grass. Nitrogen (N) inputs in the feed were measured and N offtakes in the pig meat estimated to calculate a nitrogen balance for each system. In the first winter, mean nitrate‐N concentrations in drainage water from the CCP, IMP, BMP and arable paddocks were 28, 25, 8 and 10 mg NO₃ l^?1, respectively. On the BMP system, leaching losses were limited by the grass cover, but this was destroyed by the pigs before the start of the second drainage season. In the second winter, mean concentrations increased to 111, 106 and 105 mg NO₃‐N l^?1 from the CCP, IMP and BMP systems, respectively, compared to only 32 mg NO₃‐N l^?1 on the arable paddock. Ammonia (NH₃) volatilization measurements indicated that losses from outdoor dry sows were in the region of 11 g NH₃‐N sow^?1 day^?1. Urine patches were identified as the major source of nitrous oxide (N₂O) emissions, with N₂O‐N losses estimated at less than 1% of the total N excreted. The nitrogen balance calculations indicated that N inputs to all the outdoor pig systems greatly exceeded N offtakes plus N losses, with estimated N surpluses on the CCP, IMP and BMP systems after 2 years of stocking at 576, 398 and 264 kg N ha^?1, respectively, compared with 27 kg N ha^?1 on the arable control. These large N surpluses are likely to exacerbate nitrate leaching losses in following seasons and make a contribution to the N requirement of future crops.     

Establishment of Critical Sap and Soil Nitrate Concentrations using a Cardy Nitrate Meter for Two Carrot Cultivars Grown on Organic and Mineral Soil

Abstract

Nitrate (NO₃ ^?) meters have been used effectively for crop nitrogen (N) management in many crops, including corn and cabbage. The use of a Cardy NO₃ ^? meter to assess the N status of the carrot crop could improve the utilization of applied N, but critical NO₃‐N concentrations are required. Two carrot cultivars were grown on mineral and organic soils over 3 years at five N application rates to establish critical sap and soil NO₃‐N concentrations and to identify the effects of soil type and cultivar. Although a yield response to N application occurred on mineral soil in 2 of 3 years, consistent critical sap NO₃‐N concentrations could not be established because of variability among years, cultivars, and soil types. Critical soil nitrate concentrations were highly variable, but values of 31 to 36 mg · L^?1 NO₃‐N could be established for the early sampling date to 30 cm deep. Sap NO₃‐N concentrations cannot be used alone for N analysis of carrots, but early‐season soil NO₃‐N assessment could be useful in adjusting N‐fertilization practices.     

Supplements of Nickel Affect Yield,Quality, and Nitrogen Metabolism When Urea or Nitrate is the Sole Nitrogen Source for Cucumber

ABSTRACT

Influences of nickel (Ni) concentrations in the nutrient solution on yield, quality, and nitrogen (N) metabolism of cucumber plants (Cucumis sativus cv ‘RS189’ and ‘Vikima’) were evaluated when plants were grown either with urea or nitrate as the sole N source. The cucumber plants were treated with two N sources, urea and nitrate as sodium nitrate (NaNO₃) at 200 mg L^?1, and three concentrations of Ni as nickel sulfate (NiSO₄·6H₂O; 0, 0.5, and 1 mg L^?1). Treatments were arranged in a randomized block design with six replicates. The highest concentration of Ni in the leaves (1.2 mg kg^?1 Dwt) was observed in the urea-fed plants at 1 mg L^?1 Ni concentration. Additions of Ni up to 0.5 mg L^?1 had no effect on the fruit Ni concentration in the both urea and nitrate-fed plants. Yield significantly (p < 0.05) increased with the Ni supplements from 0 to 0.5 mg L^?1 (10 and 15% in ‘RS189’ and ‘Vikima’, respectively), but decreased when 1 mg L^?1 Ni applied to the solutions in urea-fed plants. Nitrate-fed plants had a higher percentage of total soluble solids compare to those urea-fed plants. Nitrate concentrations of the fruits in urea-fed plants in both cultivars were reduced by approximately 50% compared to those nitrate-fed plants. The reduction of nitrate concentration in the fruits became more pronounced as the Ni concentration increased in the solution. The rate of photosynthesis (Pn) increased with the increase of the Ni concentration in the solution with urea-fed plants. Both N concentration and nitrate reductase (NR) activity of young leaves were higher in urea-fed plants at 0.5 mg l^?1 Ni concentration. Ni supplements enhanced the growth and yield of urea-fed plants by increasing Pn, N concentration and NR activity. It can be concluded that Ni supplements (0.5 mg l^?1) improve yield, quality, and NR activity in urea-fed cucumber plants.     

Potential nitrogen and phosphorus leaching from soils fertilized with meat and bone meal

Abstract

The nitrogen and phosphorus contents of meat and bone meal (MBM) make it a potentially valuable nutrient source in agriculture. Its narrow N:P ratio, however, makes it a potential environmental risk if it is not utilized with caution. A column-leaching experiment was conducted to assess potential nitrogen and phosphorus leaching from bare soils fertilized with MBM. This should give an idea of the efficacy of autumn or early spring MBM application on land devoid of vegetation cover. Earlier greenhouse and field experiments have indicated that nitrogen mineralization after MBM application takes place relatively rapidly. The column experiment conducted here has indicated that spring application of MBM prior to planting can result in the loss of mineral nitrogen, reducing the total amount of N available to the crop. A higher initial loss (up to 47 mg l^?1) of ammonium was found for the MBM treated soils, but this declined to less than 0.1 mg l^?1 by the end of the experiment, 11 weeks later. Nitrate loss was highest at the onset of the experiment for the soils that received mineral N fertilizer. With time, however, the largest nitrate losses were associated with the MBM-treated soils. Nitrate leaching continued to well beyond the end of the experiment. The effect will most certainly be exacerbated when the crop N (rather than crop P) requirement forms the basis for MBM application. The amount of P leached as ortho-P is probably small but may also represent an environmental risk if N remains to be the basis of MBM application. Based on the results presented here and considering the dangers of elevated nutrient losses, autumn and early spring MBM application may not be recommended.     

Leaching of dissolved organic carbon and nitrogen under cotton farming systems in a Vertisol

Leaching with deep drainage is one of the loss pathways of carbon (C) and nitrogen (N) in cropping fields. However, field studies in irrigated row cropping systems are sparse. A 3‐year investigation on C and N leaching associated with deep drainage was overlaid on a long‐term experiment on tillage practices and crop rotations in Australia. The treatments included cotton (Gossypium hirsutum L.) monoculture and cotton–wheat (Triticum aestivum L.) or maize (Zea maize L.) rotations with maximum or minimum tillage. The deep drainage C and N concentrations at 0.6 and 1.2 m depth were measured after furrow irrigation with ceramic cup samplers during the 2014–15, 2015–16 and 2016–17 cotton seasons. Pre‐planting dissolved organic carbon (DOC) concentration in soil at 0.6–1.2 m depth during 2016–17 was 64 mg kg^?1 for maximum tilled cotton monoculture, 36 mg kg^?1 for minimum tilled cotton monoculture and 39 mg kg^?1 for cotton–wheat, and in maize and cotton subplots 51 and 41 mg kg^?1, respectively. Post‐harvest DOC values in soil were similar in all treatments (average of 32 mg DOC kg^?1). Total organic carbon (TOC) losses in deep drainage were equal to 2%–30% of TOC gained in irrigation water. Oxidized N losses in deep drainage ranged from 0.7% to 12% of applied N (260 kg ha^?1). NOx‐N concentrations in leachate under maize systems (20 mg L^?1) were up to 73% lower than those in cotton systems (75 mg L^?1). Maize sown in rotation with cotton can improve cotton yield, reduce N leaching and improve N use efficiency of subsequent cotton.     

Ideal transition pattern of nitrate concentration for improving quality of spinach Spinacea oleracea L. and effect of drip fertigation on the sugar and oxalate concentration

(pp. 25–32)

The effectiveness of drip fertigation, which is known to control fertilizer application, for reducing nitrate in spinach and for improving the other qualities of spinach was investigated. Fertilizer application can be controlled effectively by drip fertigation. In 2002 and 2003, two spinach cultivars were grown in a plastic greenhouse with 4, 8 or 12 g N m^?2 of fertilizer application by drip fertigation, and with 8, 12 or 16 g N m^?2 of fertilizer application as a basal application. Nitrate concentration of petiole sap extracted by a garlic squeezer was significantly correlated with the water-extractable nitrate concentration. Nitrate concentrations of petiole sap extracted from plants treated with 12, 8 and 4 g N m^?2 of fertilizer by drip fertigation were constant, gradually decreased and significantly decreased, respectively, during the last 2 weeks. When nitrate concentration decreased during the last week, nitrate concentration in spinach at harvest was less than 3,000 mg kg^?1 FW. Thus it was thought that the pattern of the time course of nitrate in petiole xylem sap is a good indicator for getting spinach with low nitrate. The sugar concentration was negatively correlated with applied nitrogen quantity and the nitrate concentration. The total oxalic acid concentration in spinach treated by drip fertigation was significantly lower than that in spinach treated by basal application, independent of the amount of applied nitrogen. Thus drip fertigation is advantageous for improving crop quality.     

Nitrogen Dynamics and Losses in Direct‐Drilled Maize Systems

Abstract

The knowledge of nitrogen (N) losses in direct‐drilling agrosystems is essential to develop strategies to increase fertilizer efficiency and to minimize environmental damage. The objectives were i) to quantify the magnitude of N volatilization and leaching simultaneously as affected by different urea fertilization rates and ii) to evaluate the capacity of these specific plant–soil systems to act as a buffer to prevent nitrate leaching. Two experiments were conducted during 2001/02 and 2002/03 growing seasons in Alberti, Argentina. The crop was direct‐drilled maize and the soil a Typic Argiudoll. Ammonia losses, N uptake by crop at flowering and harvest, grain yield, N in previous crop residues, and soil nitrate content up to 2‐m depths were determined. Nitrogen availability, soil nitrate (NO₃)‐N up to 1 m plus fertilizer N, was linearly and highly associated with crop N uptake at flowering (R²=0.93, P<0.01) and at harvest (R²=0.852, P<0.01). Around 17.5% of fertilizer N was lost by volatilization in 10 days. The obtained values of residual nitrate N up to the 150‐cm depth were associated (R²=0.960, P<0.001) with those predicted by the nitrate leaching and economic analysis package (NLEAP) model. Maize in the direct‐drilling system was able to cycle N from the previous crop residues, N from soil organic matter, and N from fertilizers with few losses.     

Nutrient leaching losses from a sandy soil in lysimeters

Abstract

Two lysimeter experiments were conducted on annual leaching losses of calcium (Ca), potassium (K), sodium (Na), chloride (Cl), sulphate‐sulphur (SO₄‐S), and magnesium (Mg) (one experiment only) from a sandy soil in central England during 1988–1995 to provide information on typical nutrient losses under arable agriculture below 1.2 m (Experiment 1) or 1.5 m (Experiment 2). Total annual losses, in the absence of manure additions, were highly dependent on the amount of drainage; flow‐weighted average concentrations were similar between years within experiments. Concentrations, averaged over the duration of the experiments were 74 and 78 mg L^‐1 Ca, 17 and 27 mg L^‐1 Na, 11 and 8 mg L^‐1 K, 74 and 77 mg L^‐1 Cl, and 57 and 38 mg L^‐1 SO₄‐S for the two experiments respectively; Mg concentration was 17 mg L^‐1. Applications of chicken litter were made to some of the lysimeters in the last three years, and all nutrients showed increased leaching as a result. Application rates akin to disposal (rather than for crop fertilization) produced the largest losses. Following a total application of 125 t ha^‐1 over three years, average concentrations in water draining below 1.5 m in the final year were 57 and 277 mg L^‐1 Ca, 22 and 75 mg L^‐1 Cl, 7 and 14 mg L^‐1 K, 22 and 57 mg L^‐1 Na, 27, and 125 mg L^‐1 SO₄‐S for the untreated and manured soils, respectively.     

Effect of nitrate leaching in oxisol columns on 15N abundance and nitrate breakthrough curves

Abstract

Nitrate (20 mg N0₃‐ N l^?1) was leached through 180 cm columns of oxisol subsoil until the leachate attained the initial nitrate concentration. Leaching was continued with water until no nitrate was detectable in the leachate.

The Δ¹⁵N for the first aliquot of leachate containing nitrate was 2.2 units lower than that of the added solution indicating that ¹⁵Nwas preferentially adsorbed to ¹⁴N. The breakthrough curve for nitrate indicated that nitrate adsorption decreased after six pore volumes. The implications for modelling nitrate leaching are discussed.     

THE EFFECT OF NITROGEN SOURCES ON YIELD AND QUALITY OF SALAD ROCKET GROWN IN DIFFERENT MONTHS OF THE YEAR

The effects of months of the year and nitrogen (N) sources on salad rocket (Eruca sativa Mill.) yield, quality, and nitrate accumulation was investigated during the years 2002 and 2003. In both years, seeds were sown on the first day of April, May, June, July, August and September. Three different nitrogen sources were used: farmyard (cattle) manure (100 tonnes·ha^?1), calcium nitrate [Ca(NO₃)₂]-15.5% N (150 kg N·ha^?1) and ammonium sulfate [(NH₄)₂SO₄)]-21% N (150 kg N·ha^?1). Yield, leaf color, dry matter, vitamin C and total glucosinolate content and nitrate accumulation was assessed. Growing months affected all the assessed parameters significantly both years, with the exception of hue angle in 2003, whereas nitrogen source only influenced yield and nitrate accumulation in 2003. In both years the highest yield was obtained in April, but vitamin C and total glucosinolate contents were higher during summer months, and leaves were slightly darker colored. Chemical fertilizers increased the yield compared to farmyard manure; however, they also increased nitrate accumulation slightly, without any significant difference between them. Nitrate accumulation never exceeded 300 mg kg^?1 fresh weight (FW), which is well below the acceptable daily intake of 3.7 mg nitrate per kg^?1 bodyweight set by European Commission's Scientific Committee on Food.     

Influence of different agricultural management systems on nitrogen leaching: results of lysimeter studies

The objective was to estimate the potential risk of N leaching into the groundwater under various types of agriculture by using lysimeter experiments on the nitrogen(N)‐cycle of various soil types. Results were obtained with 12 weighable, monolithic lysimeters with a surface area of 1 m², a total depth of 3 m, and free drainage. Mean annual N‐leaching losses of 5 to 44 kg ha^—1 and nitrate concentrations of the seepage water (leachate) between 80 and 200 mg l^—1 were measured during the period of intensive agricultural use. On fallow land with a well‐established grass vegetation, some nitrate was removed by the plants. As a result, the nitrate concentrations in the leachate were reduced significantly. Ecological farming measures generally reduced N leaching losses and kept the N‐concentration in the leachate below the German threshold value for drinking water with 50 mg l^—1 nitrate. However, ploughing in of clover or leguminous vegetation and the application of farmyard manure in autumn caused the nitrate concentration in the leachate to rise significantly above the mentioned threshold value.<?show $6#>     

Nitrate leaching loss under annual and perennial pastures with and without lime on a duplex (texture contrast) soil in humid southeastern Australia

Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl₂) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO₃^– concentrations. The soil contained more mineral N in autumn (64–133 kg N ha^?1 to 120 cm) than in spring (51–96 kg N ha^?1), with NO₃^– comprising 70–77%. No NO₃^– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l^?1 as NO₃^– initially but < 1 mg N l^?1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l^?1 during winter. Losses of NO₃^– were small in surface runoff (0–2 kg N ha^?1 year^?1). In 1995, 9–19 kg N ha^?1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha^?1 in 1995 and 4–10 kg N ha^?1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha^?1 year^?1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha^?1 year^?1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha^?1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.     

Redox condition and nitrate change in a newly flooded rice soil under percolation as influenced by oxidative iron and manganese

Nitrate leaching from intermittently flooded rice fields contributes to nitrate pollution in groundwater. In this study, redox conditions and nitrate change in a newly flooded rice soil under the influence of oxidative iron (Fe) and manganese (Mn) were investigated using flooded soil columns under moderate percolation (4.2?mm?d^?1). The amendments of α-Fe₂O₃ and β-MnO₂ powder (5 and 2.7?mg?g^?1, respectively) delayed the establishment of reducing conditions and lowered the rate of nitrate removal in the soil column, and subsequently increased the percolation of soil indigenous nitrate (8.3?mg nitrogen [N]?kg^?1) from 2.0% to 8.0%, and the percolation of externally amended nitrate (250?mg?N?kg^?1) from 11.0% to 26.0%. The pool of oxidative iron-centered metal oxidants needs to be jointly considered with the availability of organic carbon and hydrological conditions in evaluating redox conditions and nitrate change in intermittently flooded rice soils.     

Nitrogen application rates for greenhouse tomato based on real-time diagnosis of petiole sap: Effects of soil nitrate contents before cultivation

(pp. 825–831)

This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L^?1.

For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg^?1 dry soil or higher in the 0–30 cm layer; 38 kg ha^?1 of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg^?1 dry soil; 75 kg ha^?1 of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg^?1 dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L^?1 from early harvest time to topping time under these conditions.