Nitrate leaching from cut grassland as affected by the substitution of slurry with nitrogen mineral fertilizer on two soil types

A field experiment was conducted to find out whether there is any difference in risk of N leaching to groundwater when cattle slurry and/or mineral fertilizer-N was applied to cut grassland. The experiment was carried out over two consecutive years on two sites (one with a relatively wet sandy soil and one with a relatively dry sandy soil). Treatments were mineral fertilizer-N at annual rates of 0–510 kg N ha⁻¹ year⁻¹ and combinations of sod-injected cattle slurry (85, 170, 250 and 335 kg N ha⁻¹ year⁻¹) and mineral fertilizer-N (289, 238, 190 and 139 kg N ha⁻¹ year⁻¹). Yield responses indicated that in the short run, 0·44–0·88 (average 0·60) of the slurry-N was as available as mineral fertilizer-N. The total N input from mineral fertilizer and slurry was a worse predictor of nitrate leaching (     0·11) than the N surplus (i.e. the difference between total N input and harvested N) (     0·60). The effective N surplus, based on the difference between the summed inputs of the plant-available N and harvested N, proved to be the best indicator of leaching (     0·86). Annual N application rates of up to 340 kg plant-available N ha⁻¹ complied with the target nitrate concentration in groundwater of 11·3 mg N L⁻¹ set by the European Union in both years on the wet sandy soil, whereas on the dry sandy soil none of the treatments did.     

Nutritional quality of greenhouse lettuce at harvest and after storage in relation to N application and cultivation season

The effect of five levels of nitrogen fertilization on the growth and nutritional quality of Cos lettuce (Lactuca sativa L. cv. Parris Island) at harvest and after storage was studied during autumn and winter in South-West Greece. Plants were cultivated hydroponically in a greenhouse and the nitrate, chlorophyll and ascorbic acid (vitamin C) concentrations within the plant tissues were measured at harvest and following storage at 5 or 10 °C for 10 days. Nitrate accumulated in the leaves with increasing amounts of N within the nutrient solution and was higher in the winter than in the autumn. At the lowest N level (20 mg L⁻¹), the inner leaves accumulated more nitrate than the outer leaves, whereas at higher N levels (140, 200 or 260 mg L⁻¹) nitrate accumulation was higher in the outer leaves. Overall, the highest nitrate concentrations were detected in the petiole and the proximal end of the leaf, but at the lowest N application rate (20 mg L⁻¹) nitrate accumulated in the distal region of the leaf too. Although the nitrate concentrations within the leaves did not change significantly during 10 days storage at 5 or 10 °C, the chlorophyll and vitamin C concentrations decreased. Chlorophyll loss was higher in lettuce that was grown under low N levels and was higher at 10 °C than at 5 °C, but was reduced by enclosure of the lettuce in polyethylene film. It is concluded that the optimum N application rate for Cos lettuce grown hydroponically under cover during autumn and winter in South-West Greece, and in other areas with a similar climate, is 200 mg N L⁻¹ because at this N rate yield is satisfactory and leaf nitrate concentrations are below the maximum acceptable level for human consumption. Nutritional value (vitamin C concentration) and market quality (chlorophyll content) are highest at harvest and decrease during storage, but quality in terms of nitrate concentration does not change.     

Nitrate leaching and pasture yields following the application of dairy shed effluent or ammonium fertilizer under spray or flood irrigation: results of a lysimeter study

Abstract. Nitrate leaching and pasture ( Lolium perenne / Trifolium repens ) yields were measured on monolith lysimeters (80 cm diam. × 120 cm depth) of a Templeton sandy loam soil (Udic Ustochrept), following repeated applications of dairy shed effluent (DSE) or ammonium fertilizer (NH₄Cl), under spray (50 mm/month) or flood (100 mm/month) irrigation. Applications of DSE at 400 kg N/ha per annum resulted in significantly less nitrate leaching (8–25 kg N/ha per yr) compared with NH₄Cl (28–48kg N/ha per yr) ( P < 0.01). Over the two year period, the total mineral N (predominantly nitrate) leached was equivalent to 2.5–3.7% of the total N applied in the DSE and 8.7–9.8% of the N applied in the NH₄Cl. There was a trend of slightly less nitrate leaching under the flood irrigation than under the spray irrigation, probably because of the greater potential for denitrification under the wetter conditions. Average nitrate concentrations in the leachate were generally below the drinking water standard except in the NH₄Cl treatment under spray irrigation where it averaged 10 mg NO₃-N/l over the two year period. DSE was equally as effective as NH₄Cl in stimulating pasture dry matter production. Annual nitrogen uptakes were similar for the DSE (343 kg N/ha) and NH₄Cl (332–344kg N/ha) treatments in the first year but were higher in the DSE (361–412 kg N/ha) than in the NH₄Cl (324–340 kg N/ha) treatments in the second year. Pasture uptakes of phosphorus and sulphur were also higher in the DSE than in the NH₄Cl treatments in the second year. The results emphasize the need to set different regulatory limits for land application of organic wastes of various types and for N fertilizers.     

Estuarine eutrophication in the UK: current incidence and future trends

• 1. Increased inputs of nutrients to estuaries can lead to undesirable effects associated with eutrophication, including algal blooms, changes in species composition and bottom anoxia. Several estuaries and coastal areas around the UK have increased nitrogen (N) and phosphorus (P) concentrations, elevated concentrations of chlorophyll a and changes in algal community composition and abundance. This paper reviews the pressures that lead to high nutrient concentrations in estuaries and considers the likely effectiveness of current and proposed regulatory actions.
• 2. The main sources of nutrients to estuaries are river runoff, sewage discharges, atmospheric inputs and possibly submarine groundwater discharges, although little is known about the latter. Significant reductions in N and P inputs have been realized following application of the EU's Urban Waste Water Treatment Directive. Atmospheric NO_x and NH_x emissions have also decreased and are expected to decrease further in the next decade as implementation of existing legislation continues, and new controls are introduced for activities such as shipping.
• 3. Agricultural inputs reach estuaries principally through diffuse sources, either in surface water (and in some areas possibly groundwater) or, for N, via the atmosphere. Over 10 years ago the Nitrates Directive was introduced to tackle the problem of N discharges from agriculture but little change in N loads to estuaries has been recorded.
• 4. To meet the aims of the EU Water Framework Directive, for at least ‘good’ ecological status, more rigorous application and implementation of the Nitrates Directive, together with changes in the Common Agriculture Policy and farming practice are likely to be needed. Even then, the slow response of the natural environment to change and the inherent variability of estuaries means that their responses may not be as predicted. Research is needed into the relationship between policy drivers and environmental responses to ensure actions taken will achieve the planned results.

Copyright © 2008 John Wiley & Sons, Ltd.     

Interpreting pH and nitrate concentration in solutions drained from acid soils. Possible artefacts of lysimeters

Abstract. Solutions collected from lysimeters of acid soils can show pH values close to or even above neutral. Laboratory experiments on an acid soil from Burundi were planned to test if denitrification or CO₂ degassing might explain such a paradox. In the first experiment, soil profiles were reconstituted in columns and leached with 55 μ m Ca(NO₃)₂ solutions at 30 °C and 4 °C. Two drainage regimes were applied: intermittent suction or no suction at the bottom of the columns. In the second experiment, pH values were measured in solutions drained from different horizons at 30 °C, before and after equilibration with ambient air. Sterilized soil was also tested in the same way. Results from experiment 1 showed that despite the accumulation of water in the bottom of soil profiles when no suction was applied, aeration still existed so that reduction reactions, namely denitrification, are not expected to affect greatly the percolate composition. Indeed nitrate concentration was similar in both drainage regimes and was close to the input value. The pH values in percolates were close to 7 at 30 °C and they dropped to about 5.5 when the columns were at 4 °C. In experiment 2, equilibration of percolates with ambient air resulted in pH increase which was greater for the top horizon (C-rich) but negligible when the soil was first sterilized. These convergent results illustrate the very important effect of CO₂ degassing on pH of drained solutions when microbial activity is stimulated at high temperatures, in C-rich soil. This is of prime importance when interpreting results from lysimeter experiments. By chance, this study also showed that large quantities of nitrate can be produced in soil at low temperatures.     

Nitrate leaching from reseeded pasture

Abstract. Nitrate leaching and soil mineral N status under grassland were measured on three contrasting soils, spanning winters 1995/96, 1996/97 and 1997/98, in Western England. The soils investigated were a freely draining silty clay loam (Rosemaund), a well drained loam (IGER 1) and a poorly drained clay loam (IGER 2). The effects of reseeding (ploughing and resowing grass) at IGER 1 and IGER 2 in autumn 1995 or 1996 were compared with undisturbed pasture. Reseeding at Rosemaund, in autumns 1995 or 1996, or spring 1996 was compared with undisturbed pasture of 3 sward ages (2, 5, >50 years).
Nitrate-N leaching losses during the winter immediately following autumn reseeding ranged between 60 and 350 kg N ha^–1 in 1995/96, depending on soil type, sward management history and rainfall. Losses were much less in the following winter when treatments were repeated (10–107 kg N ha^–1).
Reseeding in spring had little effect on soil mineral N content or leaching losses in the following autumn, compared with undisturbed pasture. Similarly, leaching losses from autumn reseeds in the second winter after cultivation were the same as undisturbed pasture (1-19 kg N ha^–1). The effect of ploughing grassland for reseeding was relatively short-term, in contrast to the effect of repeated annual cultivation associated with arable rotations.     

Agreement on New EU Groundwater Directive

Journal of Soils and Sediments -     

Efficacy of a single oral dose of isorsorbide 5-mononitrate in normal dogs and in dogs with congestive heart failure

Isosorbide 5-mononitrate (5-ISMN) was evaluated in normal dogs and dogs with congestive heart failure (CHF) in a randomized, blinded, and placebo-controlled study. Equilibrium blood pool imaging was used to detect changes in regional blood volume distribution. Six normal dogs were administered placebo, 2, 3, and 4 mg/kg 5-ISMN PO on separate days with a 1-week washout period between randomized dosings. Six dogs with CHF were administered placebo or 4 mg/kg 5-ISMN on separate days with a 1-week washout period between randomized dosings. Data were collected at baseline and at 15, 30, 45, 60, 90, 120, 150, 180, 210, and 240 minutes after dosing. Measured variables included indirect arterial blood pressure (BP), heart rate (HR), packed cell volume (PCV), scintigraphic count rates for normal dogs, and scintigraphic count rates for CHF dogs. Blood for plasma 5-ISMN concentration determination was collected at 60 minutes. Scintigraphic counts were corrected for decay and expressed as a percentage of the whole. No differences were detected in BP, HR, PCV, thoracic blood volume percentage (TBVP), or abdominal blood volume percentage (ABVP) between placebo and 5-ISMN in normal dogs at any dose. No differences were detected in TBVP or ABVP between placebo and 5-ISMN in dogs with CHF Plasma 5-ISMN concentration exceeded the minimum therapeutic concentration in all dogs and at all doses 60 minutes after drug administration. Equilibrium blood pool imaging failed to detect a shift in blood volume with oral 5-ISMN administration at any dose tested in normal dogs and dogs with CHF, despite adequate drug absorption. On the basis of the results of this study, 5-ISMN may not be beneficial in the treatment of dogs with CHF.