Ambient nitrous oxide emissions from different landform complexes as affected by simulated rain‐fall

Abstract

The Tesponse of ambient nitrous oxide (N₂O) emissions to four levels of simulated rainfall (5, 10, 20, and 40 mm) was assessed using large‐diameter cores of undisturbed soil in a greenhouse. The soil cores were taken from the two dominant soil‐landform groups present in the study area: Mollic Albaqualfs in footslope complexes and Typic Haploborolls in shoulder complexes. The footslope complexes had higher ambient N₂O emission than the shoulder complexes at all rainfall levels which was attributed to the differences in inherent characteristics of the soils occurring at these landscape positions. This demonstrates the importance of a spatially‐based investigative approach to account for landscape‐scale differences in soil characteristics when investigating N₂O emission at a large scale. Rainfall level strongly influenced the aeration status of the soil which, in turn, affected N₂O emission. Rainfall showed to be a potential suitable parameter in a predictive model for N₂O emissions (R² = 0.73** and 0.57** on the footslope and shoulder complexes, respectively). Nitrous oxide emissions also occurred in bursts following high rainfall levels; major increases were observed following 20 and 40 mm rainfall. At these rainfall levels, the N₂O fluxes from the footslope and shoulder complexes returned to the background level after 48 h and 24 h, respectively. In addition to an appropriate spatial sampling scheme, this study also illustrates the importance of rainfall in deriving a reliable temporal sampling scheme that would include rainfall‐induced episodic emissions to obtain meaningful N₂O flux estimates. The potential of using rainfall data for predicting N₂O emission activity warrants further investigation under actual field condition.     

Annual emissions of nitrous oxide and nitric oxide from a wheat–maize cropping system on a silt loam calcareous soil in the North China Plain

Nitrogen amendment followed by flooding irrigation is a general management practice for a wheat–maize rotation in the North China Plain, which may favor nitrification and denitrification. Consequently, high emissions of nitrous oxide (N₂O) and nitric oxide (NO) are hypothesized to occur. To test this hypothesis, we performed year-round field measurements of N₂O and NO fluxes from irrigated wheat–maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system. To interpret the field data, laboratory experiments using intact soil cores with added carbon (glucose) and nitrogen (nitrate, ammonium) substrates were performed. Our field measurements showed that pulse emissions after fertilization and irrigation/rainfall contributed to 73% and 88% of the annual N₂O and NO emissions, respectively. Soil moisture and mineral nitrogen contents significantly affected the emissions of both gases. Annual emissions from fields fertilized at the conventional rate (600 kg N ha⁻¹ yr⁻¹) totaled 4.0 ± 0.2 and 3.0 ± 0.2 kg N ha⁻¹ yr⁻¹ for N₂O and NO, respectively, while those from unfertilized fields were much lower (0.5 ± 0.02 kg N ha⁻¹ yr⁻¹ and 0.4 ± 0.05 kg N ha⁻¹ yr⁻¹, respectively). Direct emission factors (EF_ds) of N₂O and NO for the fertilizer nitrogen were estimated to be 0.59 ± 0.04% and 0.44 ± 0.04%, respectively. By summarizing the results of our study and others, we recommended specific EF_ds (N₂O: 0.54 ± 0.09%; NO: 0.45 ± 0.04%) for estimating emissions from irrigated croplands on calcareous soils with organic carbon ranging from 5 to 16 g kg⁻¹. Nitrification dominated the processes driving the emissions of both gases following fertilization. It was evident that insufficient available carbon limited microbial denitrification and thus N₂O emission. This implicates that efforts to enhance carbon sink in calcareous soils likely increase their N₂O emissions.     

Short-term changes in chemical and microbial characteristics of paddy soil in response to consecutive addition of organic ameliorants in a rice–rice–vegetable rotation system

With regard of the problems of soil acidification and soil degradation caused by high intensive planting in south China, a 2-year pot experiment consisting of six harvests under a rice–rice–vegetable rotation cropping system was conducted to assess the effects of NPK+ rice straw (RS) and combined application of RS with peanut bran, biochar, and organic fertilizer on soil chemical and microbial characteristics in paddy soil. The control treatment received chemical fertilizer alone. Results showed that RS and the combination of RS with organic ameliorants, especially NPK+ rice straw + biochar (RSBC) treatment led to the greatest improvement of soil pH, soil organic carbon, microbial biomass carbon, and total nitrogen (TN) content, and urease (UE), acid phosphatase (ACP) and catalase (CAT) activities concurrently without yield sacrificing, which inferred that RSBC treatment could be an effective measure to alleviate soil acidification, boost carbon sequestration and nutrients content as well as soil enzyme activities in rice-rice-vegetable rotation system. Besides, Pearson’s correlation analysis showed that soil mineral nitrogen (N_min) content was negatively related to pH, and the available potassium (AK) content was positively related to UE and CAT activity but negatively related to ACP activity. Canonical correspondence analysis demonstrated the N_min and AK explained 27.2% and 13.7% of the variation in microbial species, respectively. Therefore, it is believed that soil N_min and AK content could be the primary factors of soil microbial properties under the rice-rice-vegetable rotation system.     

Desorption and transformation of zinc in a mollisol and its uptake by plants in a rice–wheat rotation fertilized with either zinc-enriched biosludge from molasses or with inorganic zinc

Laboratory and greenhouse investigations were carried out with ⁶⁵Zn-labeled sources to study the kinetics of desorption, transformation, and availability of Zn applied to soil as zinc-enriched biosludge from distillery molasses (ZEMB) or as zinc sulfate heptahydrate (ZSH). Desorption (0.5 to 72 h) of added Zn by the column method followed a biphasic kinetics with an initial (up to 12 h) faster phase followed by a slower desorption phase. The desorption rate coefficient (K) of the latter phase and the amount of Zn desorbed during 12 to 72 h were significantly higher with ZEMB than with ZSH. Sequential extraction of Zn added as ZEMB and ZSH showed that Zn added as ZEMB was present in higher proportion as water soluble + exchangeable, carbonate bound, organically bound, and reducible fractions than Zn applied as ZSH, which showed a higher proportion of residual fraction. Under greenhouse conditions, dry matter yield (35 days) and total Zn uptake by rice fertilized with ZSH applied at 5 kg Zn ha⁻¹ were statistically similar to those of rice treated with 2.5 kg Zn ha⁻¹ supplied as ZEMB. The highest Zn uptake (167.08 μg pot⁻¹) by rice was recorded in the treatment with 5 kg Zn ha⁻¹ as ZEMB. For wheat plants grown after the harvest of rice, significantly higher dry matter yield over control was recorded in the treatment with ZEMB applied at 5 kg Zn ha⁻¹ to rice. Total Zn uptake by wheat was statistically similar for both ZEMB and ZSH treatments at 5 kg Zn ha⁻¹ dose. Both zinc derived from fertilizer and the percent utilization of fertilizer Zn by rice and by the subsequent wheat crop were significantly higher with ZEMB than with ZSH. Patent filed No. 757/MUM/2007 dated 19.04.2007     

Soil organic carbon as affected by direct drilling and mulching in sugar beet – wheat rotations

The effect of conventional ploughing, mulching, and direct drilling on the soil organic C (soil C_org) contents through the soil profile and on total soil C_org stocks (0–45 cm) was investigated at five different German sites. All sites showed similar results: after 10–13 years, soil C_org contents in the surface soil (0–10 cm) were 15–71% and 33–42% higher under direct drilling and mulching, respectively, than under ploughing (8–18 g kg^?1). Under ploughing, the soil C_org contents were distributed homogenously through the soil profile. Either mulching or direct drilling resulted in 3–28% higher soil C_org stocks than ploughing (49–116 t ha^?1). However, the tillage management was no significant factor since the sites showed the effects to different extents but were the mathematical replications. Five to six years later, trends and values were similar. We concluded that the main effect of mulching or direct drilling was the stratification with higher soil C_org contents in the surface soil. Since this is a positive means for soil protection, we suggested that the use of mulching or direct drilling can contribute to a sustainable soil management in crop rotations with sugar beet which are characterized by a strong physical impact on the soil during harvest.     

Application rate and composting method affect the immediate and residual manure fertilizer value in a maize–rice–rice–maize cropping sequence on a degraded soil in northern Vietnam

A field experiment was carried out in northern Vietnam to investigate the effects of adding different additives [rice (Oriza sativa L.) straw only, or rice straw with added lime, superphosphate (SSP), urea or a mixture of selected microorganism species] on nitrogen (N) losses and nutrient concentrations in manure composts. The composts and fresh manure were applied to a three-crop per year sequence (maize–rice–rice) on a degraded soil (Plinthic Acrisol/Plinthaquult) to investigate the effects of manure type on crop yield, N uptake and fertilizer value. Total N losses during composting with SSP were 20% of initial total N, while with other additives they were 30–35%. With SSP as a compost additive, 65–85% of the initial ammonium-N (NH₄-N) in the manure remained in the compost compared with 25% for microorganisms and 30% for lime. Nitrogen uptake efficiency (NUE) of fresh manure was lower than that of composted manure when applied to maize (Zea mays L.), but higher when applied to rice (Oriza sativa L.). The NUE of compost with SSP was generally higher than that of compost with straw only and lime. The mineral fertilizer equivalent (MFE) of manure types for maize decreased in the order: manure composted with SSP?>?manure composted with straw only and fresh manure?>?manure composted with lime. For rice, the corresponding order was: fresh manure?>?manure composted with SSP/microorganisms/urea?>?manure composted with lime/with straw alone. The MFE was higher when 5 tons manure ha^?1 were applied than when 10 tons manure ha^?1 were applied throughout the crop sequence. The residual effect of composted manures (determined in a fourth crop, with no manure applied) was generally 50% higher than that of fresh manure after one year of manure and compost application. Thus, addition of SSP during composting improved the field fertilizer value of composted pig manure the most.     

Long-term manuring and fertilization influence soil inorganic phosphorus transformation vis-a-vis rice yield in a rice–wheat cropping system

A study on the rice–wheat cropping system was conducted at Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India, to assess the effects of long-term manuring and fertilization on transformation of the inorganic phosphorus (P) fraction in soil after 22 years of the crop cycle. Soil samples were collected after Kharif from seven treated plots having different types of organic amendments like farm yard manure, paddy straw and green manuring with 50% substitution of nitrogen levels in rice crop only. The result showed that the yield trend of rice was maintained due to the buildup of P from various organic inputs. Although cultivation for 22 years without adding any fertilizer caused a significant decrease in almost all the forms of P viz. avail-P, saloid P, iron phosphorus fraction (Fe–P), aluminum phosphorus fraction (Al–P), calcium phosphorus fraction (Ca–P) and total P in control. Partial substitution of inorganic fertilizer N (50%) with organics, however, caused a significant increase in almost all the P fractions in soil over the control. The relative abundance of all the fractions of inorganic P irrespective of treatments was as follows: Fe–P > reductant soluble P fraction > occluded P > Al–P > Ca–P > saloid P. Saloid and Fe–P were the dominating fractions responsible for 92% variation of available P and total P levels, respectively.     

Long-term effect of manure and mineral fertilizer application on the distribution of organic nitrogen fractions in soil under a rice–wheat cropping system

A long-term experiment was used to evaluate the effect of integrated nutrient management on the distribution of soil organic N fractions and their contribution to N nutrition of a rice–wheat system. Continuous application of mineral fertilizers, alone or in combination with organic manures for 7 years, led to a marked increase in total N, hydrolysable N (amino acid-N, amino sugar-N, ammonia-N, hydrolysable unknown-N) and non-hydrolysable N compared with their original status in soil. However, continuous rice–wheat cropping without any fertilization resulted in depletion of total N, hydrolysable N and non-hydrolysable N by 21.3, 23.5 and 15.1% over their initial status in surface soil. The effect of press mud (PM) treatment was more pronounced in increasing total and hydrolysable N compared with farmyard manure (FYM) or green manure (GM) treatment. Incorporation of PM, FYM and GM along with mineral fertilizers increased the total N content by 32.8, 18.3 and 5.1% and that of hydrolysable N by 25.7, 19.6 and 9.5%, respectively, over mineral fertilizer treatment. Among the most important fractions, amino sugar-N, amino acid-N and ammonia-N were found to be most the important fractions contributing to grain yield and nitrogen uptake of rice and wheat crops.     

How does the application of different nitrification inhibitors affect nitrous oxide emissions and nitrate leaching from cow urine in grazed pastures?

Nitrous oxide (N₂O) is a potent greenhouse gas, and nitrate () is a water contaminant. In grazed grassland, the major source of both leaching and N₂O emissions is nitrogen (N) deposited in animal excreta, particularly in the urine. The objective of this study was to determine the effectiveness of two nitrification inhibitors: (i) a solution of dicyandiamide (DCD) and (ii) a liquid formulation of 3,4‐dimethylpyrazole phosphate (DMPP) for reducing N₂O emissions and leaching from urine patch areas in two grazed pasture soils under different environmental conditions. In the Canterbury Templeton soil, the nitrification rate of ammonium from the animal urine applied at 1000 kg N/ha was significantly decreased by the application of DCD (10 kg/ha) and DMPP (5 kg/ha). N₂O emissions, measured over a 3‐month period, from dairy cow urine applied to the Canterbury Templeton soil were 1.14 kg N₂O‐N/ha, and this was reduced to 0.43 and 0.39 kg N₂O‐N/ha by DCD and the liquid DMPP, respectively. These are equivalent to 62–66% reductions in the total N₂O emissions. Nitrate leaching losses from dairy cow urine applied to the Waikato Horotiu soil lysimeters were reduced from 628.6 kg ‐N/ha to 400.6 and 451.5 kg ‐N/ha by the application of DCD (10 kg/ha) or DMPP (1 kg/ha), respectively. There was no significant difference between the DCD solution and the liquid DMPP in terms of their effectiveness in reducing N₂O emissions or leaching under the experimental conditions of this study. These results suggest that both the liquid formulations of DCD and DMPP have the potential to be used as nitrification inhibitors to reduce N₂O emissions and leaching in grazed pasture soils.     

Biochar and organic fertilizer changed the ammonia-oxidizing bacteria and archaea community structure of saline–alkali soil in the North China Plain

Journal of Soils and Sediments - The application of a large amount of inorganic nitrogen (N) fertilizer resulted in an increasing N loss. It is an effective practice that biochar and organic...     

Effect of long-term balanced and imbalanced inorganic fertilizer and FYM application on chemical fraction of DTPA-extractable micronutrients and yields under rice–wheat cropping system in mollisols

The imbalanced use of chemical fertilizers under intensive cultivation practices over a period of years leads to various soil-associated problems particularly nutrient availability. Thus, to examine the effect of long-term application of balanced and imbalanced inorganic fertilizer and farm yard manure (FYM) application on the chemical fraction of DTPA-extractable micronutrients under rice–wheat cropping system after 29 years, the observations were recorded from the ongoing field experiment at Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, India. An application of balanced inorganic fertilizer with FYM in rice, while without FYM in wheat significantly improved the DTPA-extractable Zn, Fe, Mn and Cu after rice and wheat crops in both the surface and sub-surface soil layers. Lowest DTPA-extractable Zn, Fe, Mn and Cu were recorded, in surface and sub-surface soil under rice and wheat crops in control. The highest DTPA-extractable Zn, in both surface and sub-surface layers of rice (3.31, 1.62 mg kg⁻¹, respectively) and wheat (2.96, 0.99 mg kg⁻¹, respectively) was recorded because of application of N₁₈₀+P₈₀+K₄₀+Zn(F) + FYM in rice and N₁₈₀+P₈₀+K₄₀+Zn(F) in wheat. However, the DTPA-extractable Fe, Mn and Cu were highest in rice and wheat because of N₁₂₀+P₄₀+K₄₀+FYM and N₁₂₀+P₄₀+K₄₀ application, respectively. The balanced use of inorganic fertilizer with FYM (N₁₈₀+P₈₀+K₄₀+Zn(F) + FYM) in rice and without FYM [N₁₈₀+P₈₀+K₄₀+Zn(F)] in wheat supported the highest rice (6.74 t ha⁻¹) and wheat (3.50 t ha⁻¹) grain yields, while lowest in control. Based on the study results, long-term application of FYM at 5 tonnes ha⁻¹ in rice crop sustained the availability of DTPA-extractable cationic micronutrients to rice and wheat in Mollisols.     

Soil organic carbon pools and productivity in relation to nutrient management in a 20-year-old rice–berseem agroecosystem

Labile fractions of soil organic C (SOC) can respond rapidly to changes in C supply and are considered to be important indicators of soil quality. An attempt is made in this paper to investigate into the dynamics of total organic C (C _tot), oxidisable organic C (C _oc), very labile C (C _{frac 1}), labile C (C _{frac 2}), less labile C (C _{frac 3}), non-labile C (C _{frac 4}), microbial biomass C (C _mic), mineralizable C (C _min) and particulate organic C (C _p) in relation to the system productivity of a 20-year-old rice (Oryza sativa L)–berseem (Trifolium alexandrium L) cropping system with different management strategies [no fertilization, only NPK and NPK + FYM (farmyard manure) applied in different seasons] in the hot humid, subtropics of India. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC. About 62% of the C applied as FYM was stabilized into SOC. The passive pool (C _{frac 3} + C _{frac 4}) constituted about 55% of the C _tot. A larger proportion (63%) of applied C was stabilized in the passive pool of SOC. Of the analysed pools, C _{frac 1}, C _mic, C _p and C _min were influenced most by the treatments imposed and explained higher per cent variability in the yield of the crops.     

Effect of conservation agriculture on soil organic and inorganic carbon sequestration and lability: A study from a rice–wheat cropping system on a calcareous soil of the eastern Indo-Gangetic Plains

Increasing soil carbon (C) in arable soils is an important strategy to achieve sustainable yields and mitigate climate change. We investigated changes in soil organic and inorganic carbon (SOC and SIC) under conservation agriculture (CA) in a calcareous soil of the eastern Indo-Gangetic Plains of India. The treatments were as follows: conventional-till rice and wheat (CT-CT), CT rice and zero-till wheat (CT-ZT), ZT direct seeded rice (DSR) and CT wheat (ZT-CT), ZTDSR and ZT wheat without crop residue retention (ZT-ZT), ZT-ZT with residue (ZT-ZT+R), and DSR and wheat both on permanent beds with residue (PB-PB+R). The ZT-ZT+R had the highest total SOC in both 0–15 and 15–30 cm soil layers (20% and 40% higher (p < .05) than CT-CT, respectively), whereas total SIC decreased by 11% and 15% in the respective layers under ZT-ZT+R compared with CT-CT. Non-labile SOC was the largest pool, followed by very labile, labile and less labile SOC. The benefits of ZT and residue retention were greatest for very labile SOC, which showed a significant (p < .05) increase (~50%) under ZT-ZT+R compared with CT-CT. The ZT-ZT+R sequestered ~2 Mg ha⁻¹ total SOC in the 0–15 cm soil layer in 6 years, where CT registered significant losses. Thus, the adoption of CA should be recommended in calcareous soils, for C sequestration, and also as a reclamation technique.     

Barley yield and weed development as affected by crop sequence and tillage systems in a semi‐arid environment

Abstract

In order to monitor barley and weed development on a loamy sand soil subjected to different agronomic practices, field experiments were conducted for three growing seasons (1992–95) in a semi‐arid agrosystem in central Spain. For eight years, independent plots were managed with three crop sequences: barley (Hordeum vulgare L.)?vetch (Vicia sativa L.); barley? sunflower (Helianthus annuus L.); and a barley monoculture. In all cases, two tillage systems were implemented: no‐tillage and conventional tillage. In the years with standard rainfall (400 mm) an improvement in growth‐related cultivation variables and yield components of barley were observed in plots under barley?vetch rotation and/or conventional tillage. In drier conditions (<350 mm) the growth rate, crop yield and yield components of barley tended to improve under the no‐tillage system. Barley?vetch rotation and/or conventional tillage increased nitrate‐nitrogen (NO₃‐N) content in barley plants. Similar results were found for the concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). In addition, the plots under crop rotation showed a weed biomass with a high concentration of N, K, and Ca in comparison with plots under monoculture. The lack of spring herbicide treatment in the no‐tillage plots led to a 3‐fold increase in weed density compared with the plots under conventional tillage.     

Fate of 15N after combined application of rabbit manure and inorganic N fertilizers in a rice–wheat rotation system

The present study was carried out on pot experiments with rice (Oryza sativa L. cv. Wuyujing 7) and winter wheat (Triticum aestivum L. cv. Yangmai 6) rotation in a sandy and a clayey soil fertilized with ¹⁵N-labeled ammonium sulfate (AS) and ¹⁵N-labeled rabbit feces so as to study the mechanisms of reduction of fertilizer N loss by organic fertilizers. The treatments included: (1) control without any N fertilizer application; (2) fertilization with ¹⁵N-labeled AS (IF); (3) fertilization with labeled rabbit feces (OF); (4) fertilization with either 40% ¹⁵N-labeled rabbit feces and 60% unlabeled AS (IOF1) or (5) 40% unlabeled rabbit feces and 60% ¹⁵N-labeled AS (IOF2). In the rice season, the IOF treatments compared to the IF treatment decreased the percentage of lost fertilizer N from the sandy and clayey soils, whereas it increased the percentage of fertilizer N, present as mineral N and microbial biomass N (MBN). During the second season, when soils were cropped to winter wheat, the IOF treatments in comparison with the IF or OF treatment increased mineral N and MBN contents of soils sampled at tillering, jointing, and heading stages, and such increases were derived from the organic N fertilizer in the sandy soil and from the inorganic N fertilizer in the clayey soil. The increased MBN in the IOF treatments was derived from inorganic fertilizers applied both soils. Therefore, in the IOF treatment, during the rice season, the organic N increased the immobilization of inorganic N in MBN, while the inorganic N fertilizer applied to both soils stimulated the uptake of organic N and the organic N fertilizer increased the uptake of inorganic N by winter wheat; the inorganic N increased the recovery of organic N in the plant-soil system after harvesting the winter wheat.     

Effects of rice cropping intensity on soil nitrogen mineralization rate and potential in buried ancient paddy soils from the Neolithic Age in China’s Yangtze River Delta

Purpose

Rice cropping density, rice cropping duration, and fertilization can affect soil nitrogen (N) supply, but rice cropping intensity (RCI) on soil N fertility is not fully understood, particularly for ancient paddy soils without N fertilization.

Materials and methods

Eight buried ancient paddy soils from the Neolithic Age in China’s Yangtze River Delta, and its parent material, and seven present paddy soils in the same fields were used to investigate the effects of RCI on soil nitrogen mineralization rate and potential. In the present study, concentration of phytolith of rice in soils was used to indicate the RCI.

Results and discussion

Soil N content was obviously greater in the buried Neolithic paddy soils than in the parent material. Total soil N increased with increasing phytolith from 5,200 to 60,000 pellets g^?1, but tended to decrease with increasing phytolith from 60,000 to 105,000 pellets g^?1. A possible reason for RCI-induced increase of soil N was due to biological N₂ fixation in the rice field because there was a significant negative relationship between total N and δ¹⁵N in the buried Neolithic soils. The mineralization rate constant (k) ranged from 0.0126 to 0.0485 d^?1 with an average of 0.0276 d^?1, which was similar to that of the parent material, but lower than those in the present paddy soils. The k value increased with increasing RCI in the Neolithic paddy soils. There was a significant positive relation between RCI and the percentage of cumulative mineralizable N in the 14 d of that within 103 d incubation.

Conclusions

Soil N content tended to increase with the increasing intensity of rice cropping and then decreased under the high intensity of rice cropping; the excessive high intensification of rice cropping could facilitate fast N mineralization (labile N) fraction in the cumulated mineralized N. The unfertilized paddy field could only meet soil N supply under the low intensification of cropping rice in the Neolithic Age. The N fertilization is necessary in order to improve soil fertility for sustaining the present high-yield rice production.     

Use of pyrolysis/GC–MS combined with thermal analysis to monitor C and N changes in soil organic matter from a Mediterranean fire affected forest

In Mediterranean ecosystems, forest fires are a common phenomenon. They involve the transformation of vegetation and litter, leaving charred residues and so influencing the carbon cycle by changing (a) the amounts of soil organic matter and (b) the proportions within it of pools with differing stability. In addition to affecting C cycles, fires also affect the amounts of N within soil organic matter, and its availability.     

Dry matter yield and n recovery from bromegrass in south‐central alberta as affected by time of application of urea and ammonium nitrate

Abstract

Field experiments were conducted for periods of 14 or 15 years at four sites on Thin Black Chernozemic soils in south‐central Alberta to determine the effect of source and time of N application on dry matter yield (DMY), protein yield (PY), protein concentration, N use efficiency and recovery of N applied to bromegrass (Bromus inermis Leyss.) grown for hay. Two sources of N (urea and ammonium nitrate ‐ A.N.) were applied at four times (early fall, late fall, early spring and late spring) at a rate of 112 kg N ha^‐1. Urea was generally less effective in increasing DMY, PY, protein concentration, N use efficiency and % N recovery than A.N. The average, DMY, PY, protein concentration, N use efficiency and % N recovery with A.N. were 4.38 t ha^‐1, 445 kg ha^‐1, 104 g kg^‐1, 21.2 kg DM kg^‐1 N ha^‐1 and 40.2%, respectively. In the same order, the values with urea were 3.90 t ha^‐1, 376 kg ha^‐1, 99 g kg^‐1, 16.9 kg DM kg^‐1 N ha^‐1 and 30.2%, respectively. The DMY was greatest with early spring application for A.N., while the protein concentration, PY and % N recovery were greatest with the late fall application for both urea and A.N. The increase in DMY or recovery of applied N with urea as a percentage of the increase with A.N., was greatest with application in late spring and least with application in early fall. In conclusion, urea was less effective than A.N. as a forage fertilizer and early spring application was most effective for increasing DMY.