Nitrate leaching from grazed grassland lysimeters: effects of fertilizer input, field drainage, age of sward and patterns of weather

Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long-term experimental site in south-west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha^-1 per annum to the existing permanent sward, or at 400 kg N ha^-1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V-notch weirs and sampled daily for the analysis of nitrate-N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha^-1 from the old sward that received 200 and 400 kg N ha^-1, and from the reseed that received 400 kg N ha^-1 fertilizer, respectively. Ploughing and reseeding resulted in a two-fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm^-3 for the drained old sward that received 400 kg N ha^-1 fertilizer, to 12 mg dm^-3 for the undrained sward at 200 kg N ha^-1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm^-3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.     

Denitrification, N2O and CO2 fluxes in rice-wheat cropping system as affected by crop residues, fertilizer N and legume green manure

Use of renewable N and C sources such as green manure (GM) and crop residues in rice-wheat cropping systems of South Asia may lead to higher crop productivity and C sequestration. However, information on measurements of gaseous N losses (N₂O+N₂) via denitrification and environmental problems such as N₂O and CO₂ production in rice-wheat cropping systems is not available. An acetylene inhibition-intact soil core technique was employed for direct measurement of denitrification losses, N₂O and CO₂ production, in an irrigated field planted to rice (Oryza sativa L.) and wheat (Triticum aestivum L.) in an annual rotation. The soil was a coarse-textured Tolewal sandy loam soil (Typic Ustochrept) and the site a semi-arid subtropical Punjab region of India. Wheat residue (WR, C:N=94) was incorporated at 6 t ha^-1 and sesbania (Sesbania aculeata L.) was grown as GM crop for 60 days during the pre-rice fallow period. Fresh biomass of GM (C:N.=18) at 20 or 40 t ha^-1 was incorporated into the soil 2 days before transplanting rice. Results of this study reveal that (1) denitrification is a significant N loss process under wetland rice amounting to 33% of the prescribed dose of 120 kg N ha^-1 applied as fertilizer urea-N (FN); (2) integrated management of 6 t WR ha^-1 and 20 t GM ha^-1 supplying 88 kg N ha^-1 and 32 kg FN ha^-1 significantly reduced cumulative gaseous N losses to 51.6 kg N ha^-1 as compared with 58.2 kg N ha^-1 for 120 kg FN ha^-1 alone; (3) application of excessive N and C through applying 40 t GM ha^-1 (176 kg N ha^-1) resulted in the highest gaseous losses of 70 kg N ha^-1; (4) the gaseous N losses under wheat were 0.6% to 2% of the applied 120 kg FN ha^-1 and were eight- to tenfold lower (5-8 kg N ha^-1) than those preceding rice; (5) an interplay between the availability of NO₃^- and organic C largely controlled denitrification and N₂O flux during summer-grown flooded rice whereas temperature and soil aeration status were the primary regulators of the nitrification-denitrification processes and gaseous N losses during winter-grown upland wheat; (6) the irrigated rice-wheat system is a significant source of N₂O as it emits around 15 kg N₂O-N ha^-1 year^-1; (7) incorporation of WR in rice and rice residue (C:N=63) in wheat increased soil respiration, and increased CO₂ production in WR- and GM-amended soils under anaerobic wetland rice coincided with enhanced rates of denitrification; and (8) with adequate soil moisture, most of the decomposable C fraction of added residues was mineralized within one crop-growing season and application of FN and GM further accelerated this process.     

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.     

Effects of nitrogen fertilization on soil nitrogen pools and microbial properties in a hoop pine (Araucaria cunninghamii) plantation in southeast Queensland, Australia

A field study was conducted to investigate the effects of N fertilization on soil N pools and associated microbial properties in a 13-year-old hoop pine (Araucaria cunninghamii) plantation of southeast Queensland, Australia. The treatments included: (1) control (without N application); (2) 300 kg N ha^-1 applied as NH₄NO₃; and (3) 600 kg N ha^-1 as NH₄NO₃. The experiment employed a randomized complete block design with four replicates. Soil samples were taken approximately 5 years after the N application. The results showed that application of 600 kg N ha^-1 significantly increased concentrations of NH₄⁺-N in 0-10 cm soil compared with the control and application of 300 kg N ha^-1. Concentrations of NO₃^--N in soil (both 0-10 cm and 10-20 cm) with an application rate of 600 kg N ha^-1 were significantly higher compared with the control. Application of 600 kg N ha^-1 significantly increased gross N mineralization and immobilization rates (0-10 cm soil) determined by ¹⁵N isotope dilution techniques under anaerobic incubation, compared with the control. However, N application did not significantly affect the concentrations of soil total C and total N. N application appeared to decrease microbial biomass C and N and respiration, and to increase the metabolic quotient (qCO₂) in 0-10 cm soil, but these effects were not statistically significant. The lack of statistical significance in these microbial properties between the treatments might have been associated with large spatial variability between the replicate plots at this experimental site. Spatial variability in soil microbial biomass C and N was found to relate to soil moisture, total C and total N.     

Nitrous oxide and nitric oxide emissions from maize field plots as affected by N fertilizer type and application method

N₂O and NO emissions from an Andisol maize field were studied. The experimental treatments were incorporation of urea into the plough layer at 250 kg N ha^-1 by two applications (UI250), band application of urea at a depth of 8 cm at 75 kg N ha^-1 plus incorporation of urea into the plough layer at 75 kg N ha^-1 (UB150), band application of polyolefin-coated urea at a depth of 5 cm at 150 kg N ha^-1 (CB150), and a control (without N application). N₂O fluxes from UI250 and UB150 peaked following the incorporation of supplementary fertilizer, and declined to the background level after that, while the N₂O flux from CB150 was relatively low but remained at a constant level until shortly after harvest. Accordingly, the total N₂O emissions during the whole cultivation period from the three treatments were not significantly different. The fertilizer-derived N₂O-N losses from UI250, UB150 and CB150 were 0.15%, 0.27% and 0.28% of the applied N, respectively. However, it was suggested that, due to the low plant N recovery, UI250 had a significantly larger potential for indirect N₂O emission than the other treatments. On the other hand, NO emissions from UI250 and UB150 were 12 times higher than that from CB150, and the fertilizer-derived NO-N losses from the three treatments were 0.16%, 0.27% and 0.026% of the applied N, respectively. Significant NO fluxes were detected only when urea-N fertilizer was surface-applied and incorporated into plough-layer soil.     

Evaluation of a new approach to the nitrogen-15 isotope dilution technique, to estimate crop N uptake from organic residues in the field

Field experiments were conducted to test a new approach for estimating crop N uptake from organic inputs. Soils were pre-labelled by applying ¹⁵N fertiliser to soybean [Glycine max (L.) Merr] and common bean [Phaseolus vulgaris L.] crops. Additional ¹⁴N plots which received unlabelled fertiliser were also established in the same way. The above-ground biomass from all four plots was harvested, stored and the plots left to over-winter. In the following summer ¹⁵N-labelled residues were added to the unlabelled soils and unlabelled residues were added to the ¹⁵N-labelled soils at a rate of 150 kg N ha^-1. All plots were cultivated and sown with maize (Zea mays L.). Control plots that did not receive residue application or any additional fertiliser N were also set up. The plots were harvested in late autumn. Maize derived 37 kg N ha^-1 and 31 kg N ha^-1 from the added soybean residues, estimated using the direct and indirect approach, respectively, in plots previously sown to soybean. N derived from the added common bean residues was estimated as 26 kg N ha^-1 and 24 kg N ha^-1 from the direct and indirect methods, respectively. In the plots previously sown to common bean, N derived from added soybean residue was 32 kg N ha^-1 using the direct method and 33 kg N ha^-1 using the indirect method. N derived from common bean residues was 22 kg N ha^-1 and 21 kg N ha^-1 estimated using the direct and indirect approaches, respectively. It was concluded that the modified indirect technique allows a reasonable estimate of N derived from residues and that this will enable further experiments to be conducted in which N derived from more complex matrices, such as manure or sewage sludge, can be determined.     

Impact of grazed grassland management on total N accumulation in soil receiving different levels of N inputs

Nitrogen balances and total N and C accumulation in soil were studied in reseeded grazed grassland swards receiving different fertilizer N inputs (100–500 kg N ha^?1 year^?1) from March 1989 to February 1999, at an experimental site in Northern Ireland. Soil N and C accumulated linearly at rates of 102–152 kg N ha^?1 year^?1 and 1125–1454 kg C ha^?1 year^?1, respectively, in the top 15 cm soil during the 10 year period. Fertilizer N had a highly significant effect on the rate of N and C accumulation. In the sward receiving 500 kg fertilizer N ha^?1 year^?1 the input (wet deposition + fertilizer N applied) minus output (drainflow + animal product) averaged 417 kg N ha^?1 year^?1. Total N accumulation in the top 15 cm of soil was 152 kg N ha^?1 year^?1. The predicted range in NH₃ emission from this sward was 36–95 kg N ha^?1 year^?1. Evidence suggested that the remaining large imbalance was either caused by denitrification and/or other unknown loss processes. In the sward receiving 100 kg fertilizer N ha^?1 year^?1, it was apparent that N accumulation in the top 15 cm soil was greater than the input minus output balance, even before allowing for gaseous emissions. This suggested that there was an additional input source, possibly resulting from a redistribution of N from lower down the soil profile. This is an important factor to take into account in constructing N balances, as not all the N accumulating in the top 15 cm soil may be directly caused by N input. N redistribution within the soil profile would exacerbate the N deficit in budget studies.     

Effects of dicyandiamide, farmyard manure and irrigation on crop yields and ammonia volatilization from an alluvial soil under a rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system

Volatilization of NH₃ from soil is a major N-loss mechanism that reduces the efficiency of applied N fertilizers, and causes environmental pollution. Strategies are needed to reduce the loss. The influences of dicyandiamide (DCD), farmyard manure (FYM) and irrigation on NH₃ volatilization from an alluvial soil in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system was studied using the acid trap method. The loss of NH₃ in the rice-wheat system ranged from 38.6 kg N ha^-1 from the unfertilized soil to 69.0 kg N ha^-1 in the treatment with urea+DCD. Substitution of 50% N provided through urea by FYM reduced NH₃-N volatilization by 10% in rice and wheat as compared to the urea treatment. Application of DCD increased NH₃ volatilization in wheat by 7% but in rice it had no effect. The irrigation level had no effect on NH₃ volatilization in rice but fewer irrigations with fewer splits of N in wheat resulted in higher NH₃ volatilization. Application of DCD and FYM with urea had similar effects on grain yield and N uptake by rice and wheat as that of the urea treatment. The study showed that integrated use of organic manure and chemical fertilizer has the potential to reduce the loss of N due to volatilization and thereby minimize environmental pollution. Nitrification inhibitors, which are reported to be useful in increasing the N-use efficiency by reducing the leaching and denitrification losses of N, however, may increase N loss due to volatilization.     

Biomass production of Lolio‐Cynosuretum grassland is not increased by plant‐species richness

In experimental grasslands, a positive relationship between biomass production and plant diversity has often been found. Here, we compared a moderately species‐rich old sward with its grass‐dominated counterpart (12 vs. 8 species per 2.5 m², or 8.3 vs. 0.7% yield proportion of dicots at the start of the experiment) established by herbicide application. We hypothesized an increased N, P and K uptake in the diverse sward related to a higher colonization rate with arbuscular mycorrhizal fungi (AMF), the presence of legumes, and complementary nutrient use of plant species. Phosphorus or N fertilizer application (according to contributions of AMF or legumes) were expected to balance the assumed smaller biomass production of the grass compared to the diverse sward. In two experimental years, N, P and K uptake, biomass production, N₂ fixation, and intra‐ and extraradical AMF colonization were investigated in an untreated control and plots that were fertilized with P and N in a low (P1: 20 kg P ha^?1; N1: 50 kg N ha^?1) or a high dose (P2: 100 kg P ha^?1; N2: 500 kg N ha^?1) in both swards. Biomass production was larger in the grass compared to the diverse sward. The N, P and K uptake, accumulated over three harvests (or 1.5 years), was also larger in the grass sward. The biomass production ranged from 5.3 to 10.0 t ha^?1 and accumulated nutrient uptake from 82 to191 kg N ha^?1, 19 to 31 kg P ha^?1 and 112 to 221 kg K ha^?1. Small legume proportions resulted in an accumulated N₂ fixation between 0 and 3 kg ha^?1. In the second year, the root length colonized with AMF structures was larger in the diverse compared to the grass sward, and the root length colonized with arbuscules and coils was larger in the N2 treatment compared to the control in the diverse sward. There were hints to higher AMF abundance under conditions of limited P availability (low soil P content, high N:P ratio in plant biomass). We conclude that in semi‐natural grassland of moderate species richness several factors may affect the relationship between plant diversity and productivity, i.e., management, plant species identity, and the number of the plant species of the low‐diversity level.     

Nitrogen cycling in organic farming systems with rotational grass–clover and arable crops

Organic farming is considered an effective means of reducing nitrogen losses compared with more intensive conventional farming systems. However, under certain conditions, organic farming may also be susceptible to large nitrogen (N) losses. This is especially the case for organic dairy farms on sandy soils that use grazed grass–clover in rotation with cereals. A study was conducted on two commercial organic farms on sand and loamy sand soils in Denmark. On each farm, a 3‐year‐old grass–clover field was selected. Half of the field was ploughed the first year and the other half was ploughed the following year. Spring barley (Hordeum vulgare L.) was sown after ploughing in spring. Measurements showed moderate N leaching during the pasture period (9–64 kg N ha^?1 year^?1) but large amounts of leaching in the first (63–216 kg N ha^?1) and second (61–235 kg N ha^?1) year after ploughing. There was a small yield response to manure application on the sandy soil in both the first and second year after ploughing. To investigate the underlying processes affecting the residual effects of pasture and N leaching, the dynamic whole farm model farm assessment tool (FASSET) was used to simulate the treatments on both farms. The simulations agreed with the observed barley N‐uptake. However, for the sandy soil, the simulation of nitrate leaching and mineral nitrogen in the soil deviated considerably from the measurements. Three scenarios with changes in model parameters were constructed to investigate this discrepancy. These scenarios suggested that the organic matter turnover model should include an intermediate pool with a half‐life of about 2–3 years. There might also be a need to include effects of soil disturbance (tillage) on the soil organic matter turnover.     

Comparison of the decomposition and N and P mineralization of canola, pea and wheat residues

Insight into nutrient cycling is gained by understanding the dynamics and quantifying nutrient mineralization from decomposing crop residues. Since wheat (Triticum aestivum L.), canola (Brassica napus L.) and pulse crops such as pea (Pisum sativum L.) are commonly grown in rotation, our objectives were to: (1) compare, using the mesh bag technique, the dry matter (DM) loss and release of N and P of straw and root residues of those crops in the 10-11 months following harvest, and (2) determine the influence of N fertilizer on residue decomposition and nutrient release. The no-tillage study started in autumn 1997 when straw residues were placed on the soil surface and root residues were buried in the soil, and sampled periodically through the 1998 growing season. Wheat was grown in 1998 and received 0 or 60 kg N ha^-1. The study was repeated in 1998/1999. Wheat straw decomposed more slowly than canola or pea straw (losing an average of 12%, 24% and 25%, respectively, of initial DM in 10-11 months), however, the converse was noted for root residues (42%, 26% and 19% of initial DM). Average net N mineralization from wheat, canola and pea straw was essentially 0, 0.7 and 5.6 kg N ha^-1, respectively. Phosphorus released from straw ranged from 0.5 kg ha^-1 for pea to 0.75 kg ha^-1 for canola. Net N and P mineralization from root varied little between crop species: 0.9-1.6 kg N ha^-1 and 0.1-0.3 kg P ha^-1. Nitrogen fertilization increased DM loss, and N and P release from straw residues.     

Potassium leaching from cut grassland and from urine patches

In grassland farming, especially on coarse‐textured soils, K can be a critical element. On these soils, the actual K management as well as fertilizer history to a large extent determine the leaching of K. The effects of four fertilizer regimes on the nutrient balances and leaching of K from grassland grown on a sandy soil were investigated. The swards differed in the source and level of N input and K fertilizer: no fertilizer N + 166 kg K ha^?1 year^?1 (Control), 320 kg inorganic N ha^?1 + 300 kg K ha^?1 year^?1 (MIN 320), 320 kg N + 425 kg K ha^?1 year^?1 in form of cattle slurry (SLR 320) and a grass–clover sward + 166 kg K ha^?1 year^?1 (WCL 0) without any inorganic N input. In a second experimental phase, cores from these swards were used in a mini‐lysimeter study on the fate of K from urine patches. On cut grassland after 6 years K input minus removal in herbage resulted in average K surpluses per year of 47, 39, 56 and 159 kg K ha^?1 for the Control, MIN 320, WCL 0 and SLR 320, respectively. Related leaching losses per year averaged 7.5, 5, 15 and 25 kg K ha^?1. Losses of urinary‐K through leaching were 2.2–4.5 and 5.7–8.4% of the K supplied in summer and autumn applications, respectively. Plant and soil were the major sinks for K from fertilizer or urine. High levels of exchangeable K in the soil and/or large and late fertilizer or urine applications stimulated leaching of K.     

A 10‐year study of phosphorus balances and the impact of grazed grassland on total P redistribution within the soil profile

Phosphorus (P) inputs (wet deposition and fertilizer P) and outputs (animal product and drainflow) were studied on reseeded grazed grassland swards receiving different nitrogen (N) inputs (100–500 kg N ha^?1 year^?1) for 10 years (March 1989–February 1999), at an experimental site in Northern Ireland. All plots received the same maintenance application of P fertilizer (8.5 kg P ha^?1 year^?1) to meet grass requirements, to minimize the P surplus and to quantify the impact on P losses to land drainage water. The annual flow weighted mean total P concentrations in drainflow ranged from 187 to 273 μg P litre^?1 and were well above the concentrations believed to trigger eutrophication. Annual total P lost to drainage water ranged from 0.28 to 1.73 kg P ha^?1, but was unaffected by N input. As the average annual P balance was zero, there was no significant change in total P in the top 15 cm of soil. However, there was a highly significant redistribution of P to the soil surface from the 10–15 cm depth, possibly as a result of root acquisition and earthworm activity. Total P in the top 5 cm of soil increased from 0.85 g kg^?1 to 1.04 g kg^?1, over the 10 years of the study, despite there being no net P input. This P accumulation in the top few cm of soil is likely to exacerbate P losses in overland flow and make improvements in water quality difficult to achieve.     

Effect of rice straw management on nitrogen balance and residual effect of urea-N in an annual lowland rice cropping sequence

Two field experiments were conducted in 1999 (wet season) and 2000 (dry season) on a Ustic Endoaquerts in central Thailand to examine the impact of rice straw management practices on rice yield, N uptake and fertilizer-N use efficiency. Treatments included a combination of urea broadcast at a rate of 70 kg N ha^у with either straw or compost which were incorporated at a rate of 5 Mg ha^у. At maturity of the wet season rice, ¹⁵N recovery by the grain was low (11-14%) as well as straw-N derived from labeled N (5-7%). After harvest, 25-29% of applied N still remained in the soil, mainly in the 0 to 5-cm layer. Large amounts of fertilizer-N (53-55%) were lost (unaccounted for) from the soil/plant system during the first crop. Residual fertilizer-N recovery in the second rice crop was less than 3% from the original application. During both fallow seasons NO₃^m-N remained the dominant form of mineral N (NO₃^m + NH₄⁺) in the soil but its concentration was low. In the wet season grain yield response to N application was significant (P =0.05). Organic material sources did not significantly change grain yield and N accumulation in rice. In terms of grain yield and N uptake at maturity, there was no significant residual effect of fertilizer-N on the subsequent rice crop. These results indicated that the combined use of organic residues with urea did not decrease total N losses or increase crop yield or uptake of N compared to urea alone.     

Nitrous oxide concentrations in an Andisol profile and emissions to the atmosphere as influenced by the application of nitrogen fertilizers and manure

A field experiment was conducted to determine N₂O concentrations in the soil profile and emissions as influenced by the application of N fertilizers and manure in a typical Japanese Andisol, which had been under a rotation of oat and carrot for the previous 3 years. The treatments include ammonium sulphate (AS), controlled-release fertilizer (CRF) and cattle manure (CM) in addition to a control; all the fertilizers were applied either at 150 kg N ha^-1 or 300 kg N ha^-1 at the time of sowing carrot. N₂O emissions from the soil surface were measured with closed-chamber techniques, while N₂O concentrations in the soil profile were measured using stainless steel sampling probes inserted into the soil at depths of 10, 20, 40, 60, 80 and 100 cm. Moreover, soil water potential, soil temperature and rainfall data were also recorded. The results indicated that N₂O concentrations in the soil profile were always greater than in the atmosphere, ranging from 0.36 µl N₂O-N l^-1 to 5.3 µl N₂O-N l^-1. The relatively large accumulation of N₂O in the lower profiles may be a significant source for N₂O flux. Taking the changes of soil mineral N into consideration, most emissions of N₂O were probably produced from nitrification. The accumulation of N₂O in the soil profile and emissions to the atmosphere were differently influenced by the amendments of N fertilizers and manure, being consistently higher in CRF than in CM and AS treatments at the corresponding application rates, but no significant difference existed with respect to the various N sources.     

半干旱区施氮和灌溉条件下覆膜对春玉米产量及氮素平衡的影响

以典型半干旱区干湿砂质新成土（Ust-Sandic Entisols）为供试土壤进行田间试验,研究地膜覆盖、施氮及补充灌水量对春玉米（Zea mays L.）产量、土壤矿质氮（NO3--N和NH4+-N）及氮素平衡的影响。结果表明,0—100 cm土体范围内,随着土层加深,播前和收获后土壤NO3--N含量呈降低趋势,NH4+-N有所增加,但变幅不大;总矿质氮量（NO3--N和NH4+-N）表现为下降。说明地膜覆盖和施氮并没有使NO3--N深层累积量增加,这可能与土壤本身供氮能力严重不足有关。与不施氮相比,施氮各处理氮肥表观损失量增加;与不覆膜相比,作物氮素累积量比不覆膜显著增加（P0.05）。在低灌（80 mm）覆膜和高灌（160 mm）覆膜条件下,玉米的氮肥利用率均比不覆膜均提高了18.8%,说明覆膜低灌在相同施氮条件下,可节约80 mm灌水。但低灌（80 mm）与高灌（160 mm）不覆膜间氮肥利用率差异不显著,表明在相同施氮条件下,覆膜可有效提高氮肥利用率,减少氮素损失。综合考虑籽粒产量和氮肥利用率,“覆膜+补灌80 mm+施氮90 kg/hm2”可能为本试验条件下较优的栽培模式。     

A closed ammonia cycle within a plant canopy

Ammonia losses to the atmosphere from a grass-clover pasture were measured by a combined chemical-micrometeorological technique. Losses from the pasture when grazed were quite considerable (~13g N ha^?1 h^?1) but when ungrazed they were comparatively small (2 g N ha^?1 h^?1).Measurements within the canopy of the ungrazed pasture at maturity indicated a large production of NH₃ near the ground surface and almost complete absorption of it by the plant cover. The amounts of NH₃ absorbed appeared to be too large for stomatal uptake alone.This closed NH₃ cycle has important consequences for the field assessment of N₂ fixation and gaseous N losses.     

Effect of fertilizers with the new nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on yield and quality of agricultural and horticultural crops

In 1997-1999, 136 field trials were conducted under various soil-climatic conditions in western and southern Europe in order to assess the effects of N fertilizers with the new nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the yield and quality of various agricultural and horticultural crops. Results show that DMPP may increase the mean crop yield (grain yield, winter wheat +0.25 t ha^-1, wetland rice +0.29 t ha^-1, grain maize +0.24 t ha^-1; tuber yield, potatoes +1.9 t ha^-1; corrected sugar yield, sugar beets +0.24 t ha^-1; biomass, carrots +4.9 t ha^-1, lambs' lettuce +1.9 t ha^-1, onions +0.5 t ha^-1, radish +4.6 t ha^-1, lettuce +1.4 t ha^-1, cauliflower +5.2 t ha^-1, leek +1.7 t ha^-1, celeriac +2.2 t ha^-1) and/or improve crop quality (e.g. reduced NO₃^- concentration in leafy vegetables). In some crops, the same yield level as obtained with the control (fertilizer without DMPP) was achieved with one fewer applications of N, or with a reduced N application rate. The positive effect of DMPP on crop yield was especially pronounced at sites with a high precipitation rate or intensive irrigation, and/or light sandy soil. DMPP had a negative effect on the crude protein concentration of winter wheat and on the biomass yield of spring-grown spinach.     

Phosphorus losses in surface run-off from grazed permanent pastures on a volcanic soil from Chile

Reactive (RP) and organic phosphorus (OP) losses from grazed paddocks were determined on a volcanic soil during 2004 and 2005. Paddocks were grazed by Holstein Friesian steers (3.5 steers ha^?1) and received N (67.5 kg ha^?1) and P fertilizer (30 kg P ha^?1). Total losses ranged between 4 and 15 g P ha^?1 year^?1 and were greatly affected by incidental P losses associated with spring P fertilizer application. Reactive P constituted 90% of the total losses on average. Due to the high water infiltration capacity of the soil, run‐off was <1% of total drainage, therefore, phosphorus losses in run‐off were small.     

Effects of temperature, soil water status, and soil type on swine slurry nitrogen transformations

Manure N dynamics are affected by manure characteristics, soil factors, and environmental conditions. An incubation experiment was conducted to assess the relationship of these factors. The effects of temperature (11, 18, and 25°C), soil texture (three soils, silt loam to sandy loam), and soil water status (constant at 60% water filled pore space, WFPS, and fluctuating between 30% and 60% WFPS) on net mineralization and nitrification of swine manure N were assessed. Swine manure was applied at an equivalent rate of 350 kg total N ha^-1 to 250 g air-dry soil in 2-l canning jars. Subsamples were taken from each jar for NO₃^- and NH₄⁺ determination when fluctuating moisture treatment dried to 30% WFPS, with sampling continuing through four wet-dry cycles at each temperature. Manure NH₄⁺ was rapidly nitrified to NO₃^-. The relationship between NO₃^- accumulation and degree days after application (DDAA, 0°C base) could be described across temperatures using a single pool exponential model for each soil. More NO₃^- accumulated in coarser-textured soils (150-200 mg N kg^-1 soil), compared to 130 mg N kg^-1 soil in the silt loam soil. Fluctuating soil water status did not alter estimates of rate and extent of NO₃^- accumulation, but slowed NH₄⁺ disappearance somewhat.