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.     

An enhanced software tool to support better use of manure nutrients: MANNER‐NPK

MANNER‐NPK (MANure Nutrient Evaluation Routine) is a decision support tool for quantifying manure (and other organic material) crop available nutrient supply. The user‐friendly design of an earlier version of MANNER was retained, but in response to user and stakeholder feedback, additional functionality was included to underpin new and revised nitrogen (N) transformation/loss modules (covering ammonia volatilization, nitrate leaching and nitrous oxide/di‐nitrogen emissions, and organic N mineralization) and also to estimate manure phosphorus (as P₂O₅), potassium (as K₂O), sulphur (as SO₃) and magnesium (as MgO) supply. Notably, MANNER‐NPK provides N availability estimates for following crops through the mineralization of organic N. Validation of the crop available N supply estimates was undertaken by comparing predicted values with data from more than 200 field experimental measurements. For cattle, pig and poultry manures, there was good agreement (P < 0.001) between predicted and measured fertilizer N replacement values, indicating that MANNER‐NPK provides robust estimates of manure crop available N supply and N losses to the wider environment.     

Mineralization of Three Organic Manures Used as Nitrogen Source in a Soil Incubated under Laboratory Conditions

Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg^?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH₄ ⁺–N+NO₃ ^?–N)], NH₄ ⁺–N, and accumulation of NO₃ ^?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg^?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg^?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg^?1 soil day^?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO₃ ^?–N was 13.2, 10.6, and 14.6 mg kg^?1 soil relative to 7.4 mg NO₃ ^?–N kg^?1 in the control soil, indicating that manures accumulated NO₃ ^?–N almost double than the control. The proportion of total mineral N to NO₃ ^?–N revealed that a total of 44–61% of mineral N is converted into NO₃ ^?–N, indicating that nitrifiers were unable to completely oxidize the available NH₄ ⁺. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.     

The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract. In grazed dairy pasture systems, a major source of NO₃^– leached and N₂O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃^– leaching and N₂O emissions from urine patches in a grazed dairy pasture under irrigation. 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 use of DCD decreased NO₃^–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO₃^–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha^–1 yr^–1. The NO₃^–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L^–1, with the latter being below the drinking water guideline of 11.3 mg N L^–1. Total N₂O emissions following two urine applications were reduced from 46 kg N₂O‐N ha^–1 without DCD to 8.5 kg N₂O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha^–1 yr^–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO₃^– leaching and N₂O emissions.     

N-Source Effects on Temporal Distribution of NO3-N Leaching Losses to Subsurface Drainage Water

Understanding the temporal distribution of NO₃-N leaching losses from subsurface drained ‘tile’ fields as a function of climate and management practices can help develop strategies for its mitigation. A field study was conducted from 1999 through 2003 to investigate effects of the most vulnerable application of pig manure (fall application and chisel plow), safe application of pig manure (spring application and no-tillage) and common application of artificial nitrogen (UAN spring application and chisel plow) on NO₃-N leaching losses to subsurface drainage water beneath corn (Zea mays L.)–soybean (Glycine max L.) rotation systems as a randomized complete block design. The N application rates averaged over five years ranged from 166 kg-N ha^?1 for spring applied manure to 170 kg-N ha^?1 for UAN and 172 kg-N ha^?1 for fall applied manure. Tillage and nitrogen source effects on tile flow and NO₃-N leaching losses were not significant (P?<?0.05). Fall applied manure with CP resulted in significantly greater corn grain yield (10.8 vs 10.4 Mg ha^?1) compared with the spring manure-NT system. Corn plots with the spring applied manure-NT system gave relatively lower flow weighted NO₃-N concentration of 13.2 mg l^?1 in comparison to corn plots with fall manure-CP (21.6 mg l^?1) and UAN-CP systems (15.9 mg l^?1). Averaged across five years, about 60% of tile flow and NO₃-N leaching losses exited the fields during March through May. Growing season precipitation and cycles of wet and dry years primarily controlled NO₃-N leaching losses from tile drained fields. These results suggest that spring applied manure has potential to reduce NO₃-N concentrations in subsurface drainage water and also strategies need to be developed to reduce early spring NO₃-N leaching losses.     

Nitrogen losses following application of pig slurry to arable land

Abstract. Emissions of ammonia (NH₃) and nitrous oxide (N₂O), and nitrate (NO^-₃) leaching were measured in two field experiments following application of pig slurry at rates corresponding to 83–96 kg NH₄-N ha^-1 before sowing. In spring and in autumn 1994, slurry was applied by four methods: trenching (T), shallow injection (S), band spreading immediately followed by harrowing (B/H) and band spreading (B). NH₃ emission measurements were made during the first week after application in both experiments. In the spring experiment N₂O emissions and NO^-₃ leaching were measured during 6 and 52 weeks after spreading respectively, and during 11 and 33 weeks after spreading in the autumn experiment. In spring, the increased N₂O emissions (i.e. control subtracted) ranged from 0.27% (T) to 0.45% (B/H), and in the autumn study from 0.92% (T) to 1.14% (B/H), of applied NH₄-N, although showing no statistically significant differences. In order to validate the chamber measurements, a ‘megachamber’(21 m²) was used together with an infrared spectrometer. The emissions agreed well for (B/H), while (B) resulted in lower emissions compared with the smaller chambers. Emissions of NH₃ were about one order of magnitude higher. In spring, (B) gave the highest emission, reaching 19.5% of applied NH₄-N, whereas (S), and (B/H) gave the lowest emissions, reaching 1.2 and 3.5% of applied NH₄-N, respectively. NH₃ emissions in autumn were 15–20% lower compared with spring. In spring the increased nitrate leaching ranged from 10.1 (T) to 24.9 kg ha^-1 (B/H) and from 29.5 (B) to 37.8 kg ha^-1 (T) in the autumn experiment, showing no statistically significant differences. Estimations of indirect N₂O emissions due to ammonia deposition and nitrate leaching, suggested that the N₂O contribution from NH₃ deposition was relatively small, while the indirect N₂O emissions from NO^-₃ leaching were of the same order of magnitude or higher than the direct N₂O emissions.     

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.     

Mitigating methane emissions from irrigated paddy fields by application of aerobically composted livestock manures in eastern China

Livestock manure heaps and wetland rice fields are major sources of CH₄ emissions. A field experiment with an associated composting study were undertaken to investigate CH₄ emissions during manure composting and subsequent land application on paddy. Over a 24‐day period in the composting experiment, CH₄ emissions from stored manure was 17 times higher than that from composting manure, indicating that composting as an aerobic process was effective in mitigating CH₄ emissions compared with manure storage, which is normally under an anaerobic environment. Stored and composted manures were subsequently applied as organic fertilizers in the field experiment. Compared with the non‐fertilized control treatment, stored and composted manures increased grain yields by 30% and 21%, respectively. During the full rice‐growing season, the cumulative CH₄ emission was 15.8 g CH₄/m² with the application of composted manure, only one‐third of that from stored manure. CH₄ emission per unit of grain yield was significantly decreased by composted manure, with a reduction of 56% from the control and 73% from stored manure. The results indicate that composted livestock manure in rice cultivation is a triple‐win option through sustaining rice yield, mitigating CH₄ emissions and re‐utilizing livestock waste.     

Nutrient and carbon balances in organic vegetable production on an irrigated,sandy soil in northern Oman

Our understanding of nutrient and carbon (C) fluxes in irrigated organic cropping systems of subtropical regions is limited. Therefore, leaching of mineral nitrogen (N) and phosphorus (P), gaseous emissions of NH₃, N₂O, CO₂, and CH₄, and total matter balances were measured over 24 months comprising a total cropping period of 260 d in an organic‐cropping‐systems experiment near Sohar (Oman). The experiment on an irrigated sandy soil with four replications comprised two manure types (ORG1 and ORG2) characterized by respective C : N ratios of 19 and 25 and neutral detergent fiber (NDF)‐to‐soluble carbohydrates (SC) ratios of 17 and 108. A mineral‐fertilizer (MIN) treatment with equivalent levels of mineral N, P, and potassium (K) served as a control. The three treatments were factorially combined with a cropping sequence comprising radish (Raphanus sativus L.) followed by cauliflower (Brassica oleracea L. var. botrytis) or carrot (Daucus carota subsp. sativus). Over the 24‐months experimental period gaseous N emissions averaged 45 kg ha^–1 (59% NH₃‐N, 41%N₂O‐N) for MIN, 55 kg N ha^–1 (69% NH₃‐N, 31%N₂O‐N) for ORG1, and 49 kg N ha^–1 (59% NH₃‐N, 41% N₂O‐N) for ORG2. Carbon losses were 6.2 t ha^–1 (98% CO₂‐C, 2% CH₄‐C) for MIN, 9.7 t C ha^–1 (99% CO₂‐C, 1% CH₄‐C) for ORG1, and 10.6 t ha^–1 (98% CO₂‐C, 2% CH₄‐C) for ORG2. Exchange resin–based cumulative leaching of mineral N amounted to 30 kg ha^–1 for MIN, 10 kg ha^–1 for ORG1, and 56 kg ha^–1 for ORG2. Apparent surpluses of 361 kg N ha^–1 and 196 kg P ha^–1 for radish‐carrot and 299 kg N ha^–1 and 184 kg P ha^–1 for radish‐cauliflower were accompanied by K deficits of –59 kg ha^–1 and –73 kg ha^–1, respectively, for both cropping systems. Net C balances for MIN, ORG1, and ORG2 plots were –7.3, –3.1, and 1.5 t C ha^–1 for radish‐carrot and –5.0, 1.3, and 4.6 t C ha^–1 for radish‐cauliflower. The results underline the difficulty to maintain soil C levels in intensively cultivated, irrigated subtropical soils.     

Ammonia volatilization from poultry manure-amended soil

Summary Poultry manure (PM) is commonly applied to cropland as a fertilizer, usually at rates determined by the nitrogen content of the manure. Limited information is available, however, on the volatilization of ammonia from poultry manure-amended soils, despite the effect these losses may have on the fertilizer value of the manure. This study was initiated to determine the influence of incorporation and residue cover on NH₃ losses from PM-amended soils. In the first experiment, a dynamic flow technique was used to measure NH₃ losses from 18 manures applied to a bare soil surface at a rate of 12 Mg ha^-1. In the second experiment, 3 of the 18 manures were incorporated either immediately, 24 h or 72 h after application. The third experiment compared the same three manures applied to a bare soil surface or to corn or soybean residues. Surface application of the manures resulted in the loss of from 4 to 31% of the total N applied in the manures. Incorporation of the PM with soil significantly reduced NH₃ loss with the greatest decrease following immediate incorporation. Crop residues either had no effect or slightly reduced NH₃ volatilization losses relative to PM application to a bare soil surface. Ammonia volatilization was not well correlated with individual manure properties, but a multiple regression approach using manure pH and total N content offered some promise as a means to segregate manures of the basis of volatilization potential.     

Gaseous emissions of nitrogen and carbon from urban vegetable gardens in Bobo‐Dioulasso,Burkina Faso

Urban and peri‐urban agriculture (UPA) is an important livelihood strategy for the urban poor in sub‐Saharan Africa and contributes to meeting increasing food demands in the rapidly growing cities. Although in recent years many research activities have been geared towards enhancing the productivity of this land‐use system, little is known about turnover processes and nutrient efficiency of UPA. The aim of our study therefore was to determine horizontal fluxes of N, P, K, and C as well as gaseous N and C emissions in urban vegetable gardens of Bobo‐Dioulasso, Burkina Faso. Two gardens referred to as “Kodéni” and “Kuinima” were selected as representative for urban and peri‐urban systems classified as: (1) “commercial gardening + field crops and livestock system” and (2) “commercial gardening and semicommercial field crop system”, respectively. A nutrient‐balance approach was used to monitor matter fluxes from March 2008 to March 2009 in both gardens. Ammonia (NH₃), nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from the respective soils were measured during the coolest and the hottest period of the day using a closed‐chamber system. Annual partial balances amounted to 2056 kg N ha^–1, 615 kg P ha^–1, 1864 kg K ha^–1, and 33 893 kg C ha^–1 at Kodéni and to 1752 kg N ha^–1, 446 kg P ha^–1, 1643 kg K ha^–1, and 21 021 kg C ha^–1 at Kuinima. Emission rates were highest during the hot midday hours with peaks after fertilizer applications when fluxes of up to 1140 g NH₃‐N ha^–1 h^–1, 154 g N₂O‐N ha^–1 h^–1, 12 993 g CO₂‐C ha^–1 h^–1 were recorded for Kodéni and Kuinima. Estimated annual gaseous N (NH₃‐N + N₂O‐N) and C (CO₂‐C + CH₄‐C) losses reached 419 kg N ha^–1 and 35 862 kg C ha^–1 at Kodéni and 347 kg N ha^–1 and 22 364 kg C ha^–1 at Kuinima. For both gardens, this represented 20% and 106% of the N and C surpluses, respectively. Emissions of NH₃, largely emitted after surface application of manure and mineral fertilizers, accounted for 73% and 77% of total estimated N losses for Kodéni and Kuinima. To mitigate N losses nutrient‐management practices in UPA vegetable production of Bobo‐Dioulasso would greatly benefit from better synchronizing nutrient‐input rates with crop demands.     

Effects of activated charcoal and tannin added to compost and to soil on carbon dioxide,nitrous oxide and ammonia volatilization

Given high mineralization rates of soil organic matter addition of organic fertilizers such as compost and manure is a particularly important component of soil fertility management under irrigated subtropical conditions as in Oman. However, such applications are often accompanied by high leaching and volatilization losses of N. Two experiments were therefore conducted to quantify the effects of additions of activated charcoal and tannin either to compost in the field or directly to the soil. In the compost experiment, activated charcoal and tannins were added to compost made from goat manure and plant material at a rate of either 0.5 t activated charcoal ha^?1, 0.8 t tannin extract ha^?1, or 0.6 t activated charcoal and tannin ha^?1 in a mixed application. Subsequently, emissions of CO₂, N₂O, and NH₃ volatilization were determined for 69 d of composting. The results were verified in a 20‐d soil incubation experiment in which C and N emissions from a soil amended with goat manure (equivalent to 135 kg N ha^?1) and additional amendments of either 3 t activated charcoal ha^?1, or 2 t tannin extract ha^?1, or the sum of both additives were determined. While activated charcoal failed to affect the measured parameters, both experiments showed that peaks of gaseous CO₂ and N emission were reduced and/or occurred at different times when tannin was applied to compost and soil. Application of tannins to compost reduced cumulative gaseous C emissions by 40% and of N by 36% compared with the non‐amended compost. Tannins applied directly to the soil reduced emission of N₂O by 17% and volatilization of NH₃ by 51% compared to the control. However, emissions of all gases increased in compost amended with activated charcoal, and the organic C concentration of the activated charcoal amended soil increased significantly compared to the control. Based on these results, tannins appear to be a promising amendment to reduce gaseous emissions from composts, particularly under subtropical conditions.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung I Einfluss der Beweidungsintensität

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N I Influence of pasture management Leaching of nitrate (NO₃^—) from two differently managed cattle pastures was determined over four winters between 1993 and 1997 using ceramic suction cup samplers (with min. 34 cups ha^—1); additionally, vertical soil mineral‐N content in 0—0.9 m (N_min) was measured at the beginning and end of two winters (with min. 70 different sample cores ha^—1). The experimental site in the highlands north‐east of Cologne, Germany, is characterized by high annual precipitation (av. 1,362 mm between 1993 and 1996). An intensive continuous grazing management (1.3 ha, fertilized with 250 kg N ha^—1 yr^—1, average stocking density 4.9 LU ha^—1, = [I]) was tested against an extensive continuous grazing system (2.2 ha, av. 2.9 LU ha^—1; no N‐fertilizer but an estimated proportion of Trifolium repens up to 15 % of total dry matter in the final year, = [E]). The results can be summarized as follows: (1) Mean leaching losses of NO₃‐N, estimated from suction cup sampling and balance of drainage volume, were 85 kg NO₃‐N ha^—1 [I] and 15 kg NO₃‐N ha^—1 [E] during three wet winters with drainage volumes between 399 and 890 mm; in a dry winter with 105 mm calculated percolation, nitrate leaching decreased by a factor of 5 for both grazing treatments. (2) Although the amount of mineral N in soil (N_min) sampled in late autumn showed differences between intensive and extensive grazing, the N_min method permits no certain indication of the risk of NO₃ leaching. For example, during the winter period 1994/95 a reduction of mineral N in the soil (0—0.9 m) in both grazing treatments was found (—33 [I] / —8 [E] kg NO₃‐N ha^—1 and —26 [I] / —21 [E] kg NH₄‐N ha^—1) whereas during the winter 1996/97 an increase in almost all mean mineral N values occurred (+10 [I] / +2 [E] kg NO₃‐N ha^—1 and +10 [I] / —10 [E] kg NH₄‐N ha^—1). (3) In spite of the differences between both methods, the experiment shows that NO₃‐N leaching under extensive grazing could be reduced almost to levels close to those under mown grassland.     

Nitrogen leaching from grassland ecosystems managed with organic fertilizers at different stocking rates

This study shows the effect of organic fertilizers at different stocking rates, on nitrogen (N) leaching, measured using zero-tension lysimeters under undisturbed grassland soil. The experiment included two organic fertilizer types – cow dung with dung water (D) and slurry (S), both at a range of stocking rates: 0.9 LU (livestock unit) ha^?1, 1.4 LU ha^?1, 2.0 LU ha^?1 (corresponding to 54, 84 and 120 kg N ha^?1, respectively) and a control (C) treatment. In percolated water, the contents of ammonia nitrogen (NH₄⁺–N) and nitrate nitrogen (NO₃^?–N) were studied. The average concentration of NH₄⁺–N ranged from 0.91 to 1.44 mg l^?1 on fertilized plots compared to 0.55 mg l^?1 on the control plot. The average concentration of NO₃^?–N ranged from 5.2 to 9.5 mg l^?1 on fertilized plots compared to 3.2 mg l^?1 on the control plot. The results of this study showed that the use of organic fertilizers at chosen stocking rates influenced N leaching, but the concentration of N did not exceed the limits for drinking water permitted by Czech legislation. Stocking rates at 2.0 LU ha^?1 and below do not result in elevated N concentrations in percolated water that pose environmental threat.     

Nitrate leaching in forest soils: an analysis of long‐term monitoring sites in Germany

Elevated atmospheric inputs of NH₄⁺ and NO₃^– have caused N saturation of many forest ecosystems in Central Europe, but the fate of deposited N that is not bounded by trees remains largely unknown. It is expected that an increase of NO₃^– leaching from forest soils may harm the quality of groundwater in many regions. The objective of this study was to analyze the input and output of NH₄⁺ and NO₃^– at 57 sites with mature forest stands in Germany. These long‐term study sites are part of the European Level II program and comprise 17 beech, 14 spruce, 17 pine, and 9 oak stands. The chloride balance method was used to calculate seepage fluxes and inorganic N leaching below the rooting zone for the period from 1996 to 2001. Nitrogen input by throughfall was significantly different among most forest types, and was in the order: spruce > beech/oak > pine. These differences can be largely explained by the amount of precipitation and, thus, it mirrors the regional and climatic distribution of these forest types in Germany. Mean long‐term N output with seepage was log‐normal distributed, and ranged between 0 and 26.5 kg N ha^–1 yr^–1, whereby 29 % of the sites released more than 5 kg N ha^–1 yr ^–1. Leaching of inorganic N was only significantly lower in the pine stands (P < 0.05) compared with leaching rates of the spruce stands. Median N output : input ratio ranged between 0.04 and 0.11 for the beech, oak, and pine stands, while the input : output ratio of the spruce stands was 0.24, suggesting a higher risk of NO₃^– leaching in spruce forests. Following log‐transformation of the data, N input explained 38 % of the variance in N output. The stratification of the data by the C : N ratio of the O horizon or the top mineral soil revealed that forests soils with a C : N ratio < 25 released significantly more NO₃^– (median of 4.6 kg N ha^–1 yr^–1) than forests with a C : N ratio > 25 (median of 0.8 kg N ha^–1 yr^–1). The stratification improved the correlation between N input and N output for sites with C : N ratios < 25 (r² = 0.47) while the correlation for sites with C : N ratios > 25 was weaker (r = 0.21) compared with the complete data set. Our results suggest that NO₃^– leaching may increase in soils with wide C : N ratios when N deposition remains on a high level and that the potential to store inorganic N decreases with C : N ratios in the O horizons becoming more narrow.     

High N fertilizer application to irrigated wheat in Northern Mexico for conventionally tilled and permanent raised beds: Effects on N balance and short term N dynamics

Nitrogen (N) surpluses from fertilizer application can cause major environmental harm including pollution of surface water, groundwater, and air. To assess such negative externalities, N balances are a complex but useful tool to predict surpluses and to measure effects of nutrient optimization strategies in agriculture. The Yaqui Valley in north‐western Mexico is representative for thousands of square kilometres of intensive, irrigated wheat production under arid conditions worldwide and has been targeted for conservation agriculture in recent years. For these cropping systems, detailed N balances are scarce and often incomplete. To help fill this knowledge gap, data from a long‐term experiment were collected in 2013/14 on a Vertisol to examine the impact of three tillage‐straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning) on N dynamics. Tillage had significant effects on soil NO₃‐N, NH₄‐N, and total N contents across the cropping period. Soil total N content was at all sampling depths lowest in CTB. Soil NO₃‐N in the 0–90 cm profile was highest in PB‐burn over the cropping period and ranged from 77 kg ha^?1 in the bed before pre‐planting fertilizer application up to 269 kg ha^?1 in the furrow after the second fertilizer application. Annual simple N balances were +59 kg N ha^?1 in CTB, +39 kg N ha^–1 in PB‐straw, and +46 kg N ha^?1 in PB‐burn. Residual mineral soil N was significantly affected by tillage‐straw management and lowest for PB‐straw (+205 kg N ha^?1) and highest for CTB, and for PB‐burn (+283 kg N ha^?1 each) in the 0–90 cm soil profile. Soil NO₃‐N moved out of the effective wheat root zone, as indicated by the high residual NO₃‐N content at 30–90 cm depth, which is an important pathway of N leaching. Quantifiable N losses through leaching and volatilization averaged 100 kg N ha^?1. Our findings suggest that there is potential for substantial reductions in N inputs in all tillage‐straw systems to decrease N losses and to reduce mineral residual soil N, but care should be taken to avoid reducing grain protein content, which in PB straw was already below the quality standard. A knowledge transfer of the European “N_min” concept is advisable in this region to regulate N fertilizer over‐application.     

Dicyandiamide effects on nitrification and total inorganic soil nitrogen in sandy soils

Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO₃‐N) to ammonium‐nitrogen (NH₄‐N). If the conditions for NO₃‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH₄‐N + NO₃‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH₄NO₃) at 67, 134, and 202 kg N ha^‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha^‐1. Soil NH₄‐N, NO₃‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO₃‐N/(NH₄‐N + NO₃‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH₄‐N.     

Assessing Tillage Systems for Reducing Ammonia Volatilization from Spring-Applied Slurry Manure

The effect of tillage management on NH₃-N volatilization and its influence on succeeding corn (Zea mays L.) silage production were studied at the University of Massachusetts Agricultural Experiment Station (South Deerfield, MA) during 2010–2012 growing seasons. Tillage treatments consisted of disking before and after manure application, solid-tine aeration before and after manure application, and no-till management. The greatest NH₃-N loss (61 percent) occurred within the first 8 h after slurry manure application regardless of tillage management. The greatest NH₃-N emission occurred with surface application (no-till), which ranged between 5.2 and 10.3 kg NH₃-N ha^?1 (9–20 percent of NH₃-N applied) over the 3 years of the study. Immediate incorporation of manure into soil through disking reduced NH₃-N loss by 66 to 75 percent. Ammonia loss abatement with aeration before or after manure application ranged from 13 to 41 percent compared with surface manure application. Tillage management did not influence corn silage yield or quality.     

Leachability of Nitrate from Sandy Soil using Waste Amendments

Environmental issues associated with intensive use of nitrogenous fertilizers have generated an interest in alternative management systems. An experiment was conducted to mitigate nitrate leaching from sandy soil using different waste materials such as charcoal, manure, sawdust, wood ash, and control (no amendment). Urea was applied at the rate of 300 kg nitrogen (N) ha^?1. Nitrate was determined during six leaching events. During an incubation experiment, nitrate release was also determined in soil amended with charcoal at the rates of 0, 10, 20, and 40 t ha^?1. Urea was applied at the rates of 0, 100, 200, 400, and 1000 ppm N. Results indicated that urea application increased nitrate (NO₃) concentration in leachate. Soil amendments substantially reduced NO₃ in leachates irrespective of the type of material used. Waste amendments differed for NO₃ leaching as follows: charcoal < wood ash < sawdust < manure. Leaching of NO₃ enhanced up to the fourth leaching event and thereafter reduced significantly. Nitrate retention in soil varied among material in the order of manure > charcoal > wood ash > sawdust. Nitrate accumulation occurred in the lower layer (25–50 cm) of soil column after the leaching process. Application of charcoal retained greater NO₃ level as compared to control soil during an incubation. Enhanced urea applications also enhanced NO₃ release. This experiment suggests that waste material can be viably recycled to mitigate NO₃ concentration in water.     

Verbesserungsvorschlag zur gefahrlosen Beheizung brennbarer Lösungsmittel zur Fettextraktion (Kurzmitteilung)

A crop rotation field study with manure application was established at Tartu in 1985. Biological and chemical properties were evaluated on fine sandy loam Podzoluvisol in May 1989. The treatments included unmanured (N_o and N₈₀) controls, two peat based composts and five manures of different origin. The procedures of the most probable number (MPN) and spread plate counts were used for microbiological investigation, but also enzymatic activities, nitrogen forms, total‐C and pH were simultaneously estimated in plough layer soil. The most variable i.e. the most clearly differentiated physiological groups within manures were cellulolytic and ammonifying bacteria followed by Azotobacter spp. together with actinomycetes. Abundance of aerobic cellulolytic and ammonifying bacteria correlated positively with the number of soil algae and fungi, and negatively with nitrate‐ and nitrite‐reductase. The number of actinomycetes correlated positively with urease and catalase activity. Soil enzymatic activity was mainly modified by nitrite‐reductase. Peat composts had the highest C‐content and highest pH value compared with other soils. Pig slurry and NH₄NO₃ (N80) treatment had the highest level of fixed NH⁺ ₄ ‐ions in soil. Nine months after manure application no differences were found in the unstable NO^– ₃content of soil. Variation in the number of the studied microbial physiological groups between treatments remained insignificant.