Control of nitrification of fertilizer nitrogen: Effect of inhibitors,banding and nesting

Laboratory incubation and field experiments were conducted to evaluate thiourea, ATC (4-amino-1, 2, 4 triazole hydrochloride) and N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) as inhibitors of nitrification of fertilizer N. In the incubation experiment, most of the added aqueous NH₃ or urea was nitrified at 14 days on both soils, but addition of the inhibitors to fertilizer N decreased the conversion of NH₄−N to NO₃−N markedly. There was less nitrification for ATC and thiourea but not for N-Serve 24 E when the fertilizers and the inhibitors were placed at a point as opposed to when mixed into soil. After 28 days, ATC and N-Serve 24 E were more effective in inhibiting nitrification than thiourea. ATC and N-Serve 24 E also inhibited release of mineral N (NH₄−N+NO₃−N) from native soil N. In the uncropped field experiment, which received N fertilizers in the fall, nitrification of fall-applied N placed in the 15-cm bands was almost complete by early May in the Malmo soil, but not in the Breton soil. When ATC or thiourea had been applied with urea, nitrification of fall-applied N was depressed by May and the recovery of applied N as NH₄−N was greater with increasing band spacing to 60 cm or placing N fertilizer in nests (a method of application where urea prills were placed at a point in the soil in the center of 60×60 cm area). In late June, the percentage recovery of fall-applied N in soil as NH₄−N or mineral N increased with wide band spacing, or nest placement, or by adding ATC to fertilizer N on both soils. These results indicate that placing ammonium-based N fertilizers in widely-spaced bands or in nests with low rates of inhibitors slows nitrification enough to prevent much of the losses from fall-applied N. Scientific Paper No. 552, Lacombe Research Station, Research Branch, Agric, Can.     

An evaluation of carbon disulphide as a sulphur fertilizer and as a nitrification inhibitor

There was little release of extractable SO₄-S during four weeks from CS₂ applied by injecting into two S-deficient soils. In this incubation experiment, the rate of CS₂ was 30 μg S g⁻, placement was injection at 9 cm depth, soil temperature was 20°C, and soil moisture tension was 33 kPa. The yield of barley forage after seven weeks in the greenhouse showed only small increases from 10 or 30 μg S g⁻¹ of CS₂ as compared to Na₂SO₄, on the two soils. While CS₂ supplied little plant available S in the short term, it was an effective inhibitor of nitrification. In the laboratory, or in the field, the injection of CS₂ (with N fertilizers) at a point 9 cm into the soils either stopped or reduced nitrification. In one laboratory experiment, 35 μg of CS₂ g⁻¹ of soil with urea reduced nitrification for at least four weeks; and in another experiment 20 μg of CS₂ g⁻¹ of soil with aqua NH₃ nearly or completely inhibited nitrification at 20 days. In two field experiments, 3 and 12 μg of CS₂ g⁻¹ of soil (or 6 and 24 kg ha⁻¹) with aqua NH₃ inhibited nitrification from October to the subsequent May. In addition, CS₂ reduced the amount of ammonium produced from the soil N, both in these two field experiments and in the laboratory experiments. That is to say, CS₂ injected at a point, inhibited both nitrification and ammonification. In other field experiments, CS₂ at a rate of 10 kg ha⁻¹ was injected in bands 9 cm deep with urea in October, and by May there was still reduced nitrification. Less than half of the fall-applied urea alone was recovered as mineral N, but with the application of CS₂ the recovery was increased to three-quarters. The yield and N uptake of barley grain was increased where fall-applied banded urea or aqua NH₃ received banded CS₂, (NH₄)₂CS₃, or K₂CS₃. The average increase in yield from fall-applied fertilizer, from inhibitor with fall-applied fertilizer, and from spring-applied fertilizer was 800, 1370, and 1900 kg ha⁻¹, respectively. In the same order, the apparent % recovery of fertilizer N in grain was 24, 42, and 60.     

Effect of ATC,N-Serve 24 E and thiourea nitrification inhibitors on yield and N uptake of barley fertilized with fall-applied N1

Solution urea and aqua NH₃ were injected in bands 9 cm deep and spaced 45 cm apart with and without nitrification inhibitors during October in 10 field experiments in north-central Alberta. ATC (4-amino-1,2,4-triazole hydrochloride), N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) and thiourea were used in two experiments, ATC only in another six experiments, and N-Serve 24 E only in another two experiments. Yield and apparent recovery of applied N in barley grain were determined. In the two experiments where fall treated plots were soil sampled in the following spring, 44% of the fall-applied N was recovered in the soil when inhibitors were not used. But where the inhibitors were added to the fall-applied N as NH₄−N in May was 4% and 31% without and with addition of inhibitors, respectively. Likewise, in experiments where three inhibitors were used, the treatments with inhibitors increased the yield and N recovery in grain by more than 50% compared to fall application without inhibitors. In the other experiments, fall-applied ATC or N-Serve 24 E did not always increase yield or N recovery in grain. Considering all experiments with ATC, the average recovery of applied N in barley grain was 28, 40 and 57% for fall banding, fall banding with ATC and spring application, respectively. In view of this and previous work in north-central Alberta, inhibitors injected in bands in the fall slowed nitrification and improved yield, but nests or large granules of urea were more effective. Scientific paper No 553, Lacomba Research Station, Research Branch, Agriculture Canada.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Rate of hydrolysis of urea as influenced by thiourea and pellet size

Summary Two incubation experiments and a number of field experiments were conducted to determine the effect of soil moisture tension, pellet size and addition of thiourea to urea on the rate of urea hydrolysis. In the incubation experiments at 20°C, the rate of hydrolysis of urea increased from 15 bar to 1/3 bar soil moisture tension, with the largest change (doubling) occurring from 15 bar to 7 bar moisture tension. Increasing pellet size reduced the rate of urea hydrolysis by about 12% with urea pellets weighing 0.21 g as compared to 0.01 g urea pellets after 114h. When thiourea (a metabolic inhibitor) was pelleted with urea in a ratio of two parts urea and one part thiourea, the rate of hydrolysis was halved.In a field experiment, the addition of thiourea to urea and increasing pellet size suppressed the rate of urea hydrolysis considerably for 8 days. The amount of urea hydrolyzed with urea+thiourea (21) pellets weighing 2.51 g was one-fourth of the amount of urea hydrolyzed with 0.01 g pellets of urea alone. In the other six field experiments which were set out in October, only 22% to 39% of urea +thiourea (21) was hydrolyzed at two weeks after application, while almost all of the urea was hydrolyzed when it was mixed into the soil without an inhibitor.Unter our field conditions, we would estimate that the hydrolysis of urea can be inhibited for at least one week. The inhibition of urea hydrolysis appears to be great enough that the problems encountered from the rapid hydrolysis of urea, wherever these occur, may be reduced by combined use of thiourea and either increased pellet size or band placement.     

The fate of labelled15N urea and ammonium nitrate applied to a winter wheat crop

Labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France. Two applications of fertilizer were given: 50 kg N ha^–1 at tillering (early March) and 110 kg N ha^–1 at the beginning of stem elongation (mid-April). The kinetics of urea hydrolysis, nitrification of ammonium and the disappearance of inorganic nitrogen were followed at frequent intervals. Inorganic nitrogen soon disappeared, mainly immobilized by soil microflora and absorbed by the crop. Net immobilization of fertilizer N occured at a very similar rate for urea and ammonium nitrate. Maximum immobilization (16 kg N ha¹) was found at harvest for the first dressing and at anthesis for the second dressing (23 kg N ha¹). During the nitrification period, the labelled ammonium pool was immobilized two to three times faster than the labelled nitrate pool. No significant net¹⁵N remineralization was found during the growth cycle.The actual denitrification and volatilization losses were probably more important than indicated from calculations made by extrapolation of fluxes measured over short intervals. However microbial immobilization was the most important of the processes which compete with plant uptake for nitrogen.     

13C isotope discrimination correlates with biological nitrogen fixation in soybean (Glycine max (L.) Merrill)

Ammonium sulphate was applied at the rate of 300 kg N ha^–1 with or without the nitrification inhibitor 1-carbamoyl-3(5)-methylpyrazol (4 kg ha^–1) to plots measuring 1.5 × 1.5 m. The fertilizer and the inhibitor were washed into the top 15-cm layer of the soil, which was highly calcareous (55% CaCO₃), and the plots were kept bare. The process of nitrification was monitored by regular soil sampling. In the absence of the inhibitor, nitrification was completed in three weeks. In the presence of the inhibitor only 10% of applied N was nitrified by the end of the third week and 42% by the end of the eighth week. Average soil temperature at 5–, 10– and 20-cm depth over the first six weeks was 26.0, 24.8 and 24.2°C, respectively.     

Efficiency of soil and fertilizer nitrogen of a sod–potato system in the humid,acid and cool environment

It was hypothesized that soil N variability, and fertilization and cropping management affect potato (Solanum tuberosum L.) growth and fertilizer N efficiency. Following a 20-year sod breakup on a loamy soil in eastern Quebec, Canada (46°37 N, 71°47 W), we conducted a 3-year (1993–1995) study to investigate the effects of soil pool N and fertilizer N management on non-irrigated potato (cv. Superior) tuber yield, fertilizer N recovery (NRE), and residual N distribution in soils under humid, cool and acid pedoclimatic conditions. The fertilizer N treatments consisted of a control, side-dress at rates of 70, 105 and 140 kg ha^–1, and split applications (at seeding and bloom) at rates of 70+70, 105+70 and 140+70 kg ha^–1, respectively. Soil acidity was corrected with limestone following the plow down of the sod. Years of cropping, main effect of N treatment, and year and fertilizer N interaction were significant on total and marketable tuber yields and N uptake, which were significantly related to soil N, and root growth. Apparent NRE ranged between 29 and 70%, depending on years and N rates. Total tuber yield, N uptake, soil N use and NRE were significantly higher in the first (sod–potato) year, but decreased by 41.8, 22.7, 21.4 and 14.7%, respectively, in the third (sod–potato–potato–potato) year. Initial soil N pool was declined by 75% following the 3-year cropping. In 2–3 years, the side-dress N (140 kg ha^–1) increased significantly tuber yields (11.4–19.8%) compared to the split N (70+70 kg ha^–1). Higher split N had no effect on tuber yield and N uptake but increased residual N at harvest. Unused fertilizer N was strongly linked (R ²=0.98) to fertilizer N rates. Time factor and N treatment had significant effects (P<0.0001) on loss of N to below the root zone. Smaller scale rate and timing of split N need to be further determined. Increasing fertilizer N use efficiency could be expected with sod breakup and 75% of regional recommendation rate under humid, cool and acid pedoclimatic conditions.     

A meta‐analysis of fertilizer‐induced soil NO and combined NO+N2O emissions

Soils are among the important sources of atmospheric nitric oxide (NO) and nitrous oxide (N₂O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer‐reviewed publications with 520 field measurements were synthesized using meta‐analysis procedure to examine the N fertilizer‐induced soil NO and the combined NO+N₂O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO‐N fluxes were estimated to be 4.06 kg ha^?1 yr^?1, with the greatest (9.75 kg ha^?1 yr^?1) in vegetable croplands and the lowest (0.11 kg ha^?1 yr^?1) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO (EF_NO) and combined NO+N₂O (EF_c) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71–1.61% and 1.81–3.35%, respectively. Forests had the greatest EF_NO (2.39%). Within the croplands, the EF_NO (1.71%) and EF_c (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EF_NO (2.93%) and EF_c (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands.     

Labeled nitrogen fertilizer research with urea in the semi-arid tropics

Summary Field studies with bordered microplots were conducted on an Alfisol in the semiarid tropics of India to determine (1) the fate of¹⁵N-labeled urea applied to dryland sorghum in two successive rainy seasons and (2) the effect of method of application on N fertilizer efficiency. Recoveries of¹⁵N-labeled fertilizers by above-ground plant parts ranged from 46.7% to 63.6% in 1981 when the rainfall was above the average and from 54.4% to 66.9% in 1980 when the rainfall was near the average. Small (0.014 g) pellets of urea applied twice as postemergent applications in separate 5 cm deep bands were more effective than single preemergent applications either surface applied or incorporated. Both banding and the split applications contributed to overall fertilizer efficiency. Large (1.0 g) pellets of urea (supergranules) placed at a depth of 5 cm were also superior to the incorporated, small-pellet treatment in 1981. The¹⁵N-balance data for the soil (0–90 cm in depth)-plant system in 1981 showed that the unaccounted-for fertilizer N ranged from 5.1% to 20.6%. An important finding was that high grain yields, in excess of 6,000 kg/ha, with N fertilizer losses of less than 10% could be obtained through fertilizer management during a very wet season. The data from the Alfisol experiments were compared with data from similar Vertisol experiments; N fertilizer losses resulting from incorporated and surface applications were greater for Vertisols than for Alfisols in the wetter year.     

Land-use change effects on soil C and N transformations in soils of high N status: comparisons under indigenous forest, pasture and pine plantation

Globally, land-use change is occurring rapidly, and impacts on biogeochemical cycling may be influenced by previous land uses. We examined differences in soil C and N cycling during long-term laboratory incubations for the following land-use sequence: indigenous forest (soil age = 1800 yr); 70-year-old pasture planted after forest clearance; 22-year-old pine (Pinus radiata) planted into pasture. No N fertilizer had been applied but the pasture contained N-fixing legumes. The sites were adjacent and received 3–6 kg ha^–1 yr^–1volcanic N in rain; NO₃ ^–-N leaching losses to streamwater were 5–21 kg ha^–1 yr^–1, and followed the order forest < pasture = pine. Soil C concentration in 0–10 cm mineral soil followed the order: pasture > pine = forest, and total N: pasture > pine > forest. Nitrogen mineralization followed the order: pasture > pine > forest for mineral soil, and was weakly related to C mineralization. Based on radiocarbon data, the indigenous forest 0–10 cm soil contained more pre-bomb C than the other soils, partly as a result of microbial processing of recent C in the surface litter layer. Heterotrophic activity appeared to be somewhat N limited in the indigenous forest soil, and gross nitrification was delayed. In contrast, the pasture soil was rich in labile N arising from N fixation by clover, and net nitrification occurred readily. Gross N cycling rates in the pine mineral soil (per unit N) were similar to those under pasture, reflecting the legacy of N inputs by the previous pasture. Change in land use from indigenous forest to pasture and pine resulted in increased gross nitrification, net nitrification and thence leaching of NO₃ ^–-N.     

Natural 15N abundances of maize and soil amended with urea and composted pig manure

To investigate the effect of inorganic fertilizer and composted manure amendments on the N isotope composition (delta ¹⁵N) of crop and soil, maize (Zea mays L.) was cultivated under greenhouse conditions for 30, 40, 50, 60, and 70 days. Composted pig manure (delta ¹⁵N= +13.9) and urea (-2.3) were applied at 0 and 0 kg N ha^–1 (C0U0), 0 and 150 kg N ha^–1 (C0U2), 150 and 0 kg N ha^–1 (C2U0), and 75 and 75 kg N ha^–1 (C1U1), respectively. The delta ¹⁵N of total soil-N was not affected by both amendments, but delta ¹⁵N of NH⁺ ₄ and NO^– ₃ provided some information on the N isotope fractionation in soil. During the early growth stage, significant differences (P < 0.05) in delta ¹⁵N among maize subjected to different treatments were observed. After 30 days of growth, the delta ¹⁵N values of maize were +6.6 for C0U0, +1.1 for C0U2, +7.7 for C2U0, and +4.5 for C1U1. However, effects of urea and composted manure application on maize delta ¹⁵N progressively decreased with increasing growth period, probably due to isotope fractionation accompanying N losses and increased uptake of soil-derived N by maize. After 70 days of growth, delta ¹⁵N of leaves and grains of maize amended with composted pig manure were significantly (P < 0.05) higher than those with urea. The temporal variations in delta ¹⁵N of maize amended with urea and composted manure indicate that plant delta ¹⁵N is generally not a good tracer for N sources applied to field. Our data can be used in validation of delta ¹⁵N fractionation models in relation to N source inputs.     

The Effect of N Fertilizer Placement on the Fate of Urea-15N and Yield of Winter Wheat in Southeast China

A field micro-plot experiment using nitrogen isotope (¹⁵N) labeling was conducted to determine the effects of placement methods (broadcast and band) and N rates (60, 150 and 240 kg ha^–1) on the fate of urea-¹⁵N in the wheat–soil system in Guangde County of Anhui Province, China. N fertilizer applied in bands increased grain yield by 15% compared with broadcast application. The N fertilizer application rate had a significant effect on grain yield, straw yield and aboveground biomass, as well as on N uptake and N concentration of wheat. The recovery of urea-¹⁵N was a little higher for broadcast (34.0–39.0%) than for band treatment (31.2–38.2%). Most of the soil residual N was retained in the 0–20 cm soil layer. At the N rates of 60 and 240 kg ha^–1, the residual ¹⁵N was higher for band (34.4 and 108.7 kg ha^–1, respectively) than for broadcast application (29.6 and 88.4 kg ha^–1, respectively). Compared with broadcast treatment, banded placement of N fertilizer decreased the N loss in the wheat–soil system. Band application one time is an alternative N management practice for winter wheat in this region.     

Cyanobacterial (unicellular and heterocystous) biofertilization to wetland rice influenced by nitrogenous agrochemical

Comparative growth and N₂-fixation of cyanobacteria, namely Aphanothece sp. (unicellular) and Gloeotrichia sp. (heterocystous, filamentous), were studied after their inoculation to rice crop in the absence and presence of urea nitrogen fertilizer. In the absence of N-fertilizer application (control), inoculation of both cyanobacterial species showed significant increase in growth and acetylene reduction activity (ARA), but gradual reduction in these parameters was observed at 30 and 60 kg N ha^?1 of urea application. In inoculation of Gloeotrichia sp. at control, 30 and 60 kg N ha^?1 increased grain yield significantly over uninoculated control in both wet and dry seasons, but grain yield with Aphanothece sp. inoculation was statistically similar to the control at N levels during both seasons. The inoculation study showed that heterocystous cyanobacteria contributed better than unicellular ones, and application of N-fertilizer adversely affected both growth and N₂-fixation of native as well of inoculated cyanobacteria.     

Mineralization of nitrogen in long-term pasture soils: effects of management

A field incubation technique with acetylene to inhibit nitrification was used to estimate net N mineralization rates in some grassland soils through an annual cycle. Measurements were made on previously long-term grazed pastures on a silty clay loam soil in S.W. England which had background managements of +/– drainage and +/– fertilizer (200 kg N ha^–1 yr^–1). The effect of fertilizer addition on mineralization during the year of measurement was also determined. Small plots with animals excluded, and with herbage clipped and removed were used as treatment areas and measurements were made using an incubation period of 7 days at intervals of 7 or 14 days through the year. Soil temperature, moisture and mineral N contents were also determined. Mineralization rates fluctuated considerably in each treatment. Maximum daily rates ranged from 1.01 to 3.19 kg N ha^–1, and there was substantial net release of N through the winter period (representing, on average, 27% of the annual release). Changes in temperature accounted for 35% of the variability but there was little significant effect of soil moisture. Annual net release of N ranged from 135 kg ha^–1 (undrained soil, no previous or current fertilizer) to 376 (drained soil, +200 kg N ha^–1 yr^–1 previous and current fertilizer addition). Addition of fertilizer N to a previously unfertilized sward significantly increased the net release of N but there was no immediate effect of withholding fertilizer on mineralization during the year in which measurements were made.     

Uptake and use patterns of nitrogen from urea,oxamide, and isobutylidene diurea by rice plants

Summary Two¹⁵N-labelled slow-release nitrogen (N) sources, oxamide and isobutylidene diurea (IBDU), each at two particle sizes, and¹⁵N-labelled urea were compared at two rates as sources of N for rice (Oryza sativa) under two watering regimes which simulated a transplant (continuous flood, CF) and a direct-seeded (A/F) system of paddy rice culture. Highest grain yields were obtained from −8+10-mesh oxamide particles applied at the rate of 2,000 mg of N/5 kg of soil, CF series; this yield was slightly higher than that obtained from −3+4-mesh oxamide, A/F series. Incubating the N fertilizers in moist (22% water) soil for 21 days immediately before flooding and transplanting rice greatly reduced N supply because of nitrification during the preflood period, followed by denitrification after flooding. This resulted in less plant uptake of N and less grain yield from urea, fine oxamide and IBDU, A/F series. For coarse oxamide, N release during the preflood period resulted in higher N uptake and grain yield in the A/F rather than in the corresponding CF series. The pattern of fertilizer N uptake by rice plants was affected by kind of fertilizer, particle size of oxamide and IBDU, and watering regime. Uptake of fertilizer N generally paralleled uptake of soil N throughout the growth period. Plant tops continued to accumulate some N during the period of grain filling, but much of the N in plant tops was translocated to the grain after heading. There was a large decrease in dry weight, N content, and¹⁵N content of tops after heading. Root weight and N content increased rapidly at first, and then at a diminishing rate until maturity. Unexplained N deficits occurred in the CF series (14–23% of the N applied, depending on N rate and source), and in the A/F series for IBDU (37–43% of the N applied).     

Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain

Aims

A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China.

Methods

Biochar was applied at rates of 0, 20 and 40?t?ha^?1 with or without N fertilization. With N fertilization, urea was applied at 300?kg?N ha^?1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO₂, CH₄ and N₂O were monitored using closed chambers at 7?days intervals throughout the whole maize growing season (WMGS).

Results

Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1, respectively. Total N₂O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1 compared to no biochar amendment with N fertilization. The high rate of biochar (40?t?ha^?1) increased the total CO₂ emission by 12% without N fertilization. Overall, biochar amendments of 20?t?ha^?1 and 40?t?ha^?1 decreased the total global warming potential (GWP) of CH₄ and N₂O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N.

Conclusions

These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.     

五氯酚在稻田中的降解动态及生物有效性

利用江西鹰潭红壤生态实验站的长期施肥定位试验,采用田间微域研究了五氯酚(pentachlorophenol, PCP)在红壤性水稻田生态系统中的降解动态和稻谷的富集特征。四种长期施肥处理包括:未施肥(对照,CK)、施尿素(N)、施有机肥(OM)以及施有机肥+尿素(N+OM)。结果表明,长期施用OM或N+OM能显著增加土壤微生物活性。PCP在土壤-水稻生态系统中的降解遵循一级动力学方程,在CK、N、OM 和 N+OM 4 种处理土壤中降解半衰期分别为 27.7、35.2、24.8、22.4 d。表明长期施用OM或N+OM能加速PCP降解,而长期施用N抑制PCP降解。土壤中PCP(初始浓度85 mg/kg)显著减少水稻茎和稻谷生物量,但是对水稻根生物量并没有显著影响。在4种处理中水稻稻谷中PCP含量并没有显著差异,且稻谷的生物富集系数均小于0.01。PCP虽然在土壤-水稻生态系统中的降解半衰期较短,但是仍可以在水稻稻谷中有一定的生物富集,潜在的食品安全风险依然存在。     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Nonlinear response of N2O flux to incremental fertilizer addition in a continuous maize (Zea mays L.) cropping system

The relationship between nitrous oxide (N₂O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N₂O regardless of input level. We conducted a 3‐year, high‐resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N₂O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0–292 kg N ha^?1) to four replicate plots of continuous maize. We measured N₂O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N₂O fluxes were moderately low (ca. 20 g N₂O‐N ha^?1 day^?1) at levels of N addition to 101 kg N ha^?1, where grain yields were maximized, after which fluxes more than doubled (to >50 g N₂O‐N ha^?1 day^?1). This threshold N₂O response to N fertilization suggests that agricultural N₂O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs.