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Residual soil NO3-N (RSN) is susceptible to loss during the non-growing season. This 5 yr study investigated the effects of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] applied at four rates (60, 120, 200, and 280 kg N ha−1) plus an unfertilized control on RSN following potato production and on overwinter NO3-N changes in an irrigated sandy soil in Quebec, Canada. Composite soil samples were collected at the 0–15, 15–30, 30–60, and 60–90 cm depths immediately after potato harvest in fall and again in the following spring from 2008 to 2012. Residual soil NO3-N content within the 0–30 cm depth (RSN0–30) was highly correlated with the RSN content in the 0–90 cm depth (RSN0–90), indicating that RSN0–30 can be used as an indicator of soil profile NO3-N accumulation. Overall, RSN0–90 increased with fertilizer N application rate, particularly for above the minimum fertilizer N rate required to maximize yield (Nmax), and was generally higher for years with greater pre-plant soil NO3-N. The split application of AN and AS resulted in lower RSN0–90 than the single application of PCU at above Nmax. Overwinter losses of soil NO3-N were generally increased with increasing RSN0–90 in fall. The results suggest that reducing the fertilizer N rate is more important than the choice of N source in managing RSN.

A practical means to quantify the response of the rates of net N mineralization and denitrification over a wide range of soil water contents is generally lacking. This study examined the potential to use a nitrification inhibitor (NI) assay system to simultaneously estimate the rates of net N mineralization and denitrification, and applied the NI assay to assess the effect of water content on net N mineralization and denitrification rates in two soils with contrasting soil texture. The compound 3,5-dimethylpyrazole (DMP) applied at a rate of 200 mg kg−1 was found to provide essentially complete inhibition of nitrification over the duration of the soil incubation for two soils with contrasting soil texture (clay loam vs. sandy loam) and over a range of soil water contents (35%, 55%, and 85% water-filled pore space). This allowed net N mineralization to be estimated as the accumulation of soil ammonium ([Formula: see text]) and of denitrification as the disappearance of added nitrate ([Formula: see text]). Addition of DMP resulted in a small increase in soil respiration rate but did not appear to influence the rate of net soil N mineralization. The NI assay provides a practical means to quantify the rates of net N mineralization and denitrification simultaneously over a wide range of soil water contents. The assay can be readily scaled up to routinely test multiple soils in an efficient manner, has limited material costs, and is also relatively simple to perform.

In cool temperate regions, large emissions of nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, have been observed during freeze–thaw (FT) cycles. However, it is unclear how freezing and thawing rates, freezing intensity, and freezing duration influence N2O emissions. We used a laboratory incubation to measure N2O emissions from two soils (sandy loam, silty clay) undergoing a single FT cycle of various freezing and thawing rates [rapid (0.5 °C h−1) vs. slow (0.017 °C h−1)], freezing intensity (−1 vs. −3 °C), and freezing duration (24 vs. 48 freezing degree-days). In general, soil carbon dioxide fluxes during freezing were highest when soils were frozen slowly at −1 °C, whereas fluxes after thawing were highest from the soils frozen and thawed rapidly at −3 °C. Soil N2O emissions during both the freezing and thawing periods were greatest in the soils exposed to rapid freezing to −3 °C, intermediate under rapid freezing to −1 °C and slow freezing to −3 °C, and smallest under slow freezing to −1 °C and the control treatment (constant +1 °C). The similar N2O emissions between the unfrozen control and the slowly frozen −1 °C treatment was unexpected as previous field studies with similar freezing rates and temperatures still experienced high N2O emissions during thaw. This suggests that the physical disruptions caused by freezing and thawing of the surface soil are not the primary driver of FT-induced N2O emissions under field conditions.

Large inputs of nitrogen (N) are required to optimize yield and quality of potato (Solanum tuberosum L.), and it may result in a high potential for N losses including denitrification. This 5 yr study compared the effect of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] at 200 kg N ha−1 (N200) and an unfertilized control (N0) on denitrification rate (DR) from irrigated potato production on a coarse-textured soil in eastern Canada. Fertilizer was banded all at-planting (PCU) or split 40% at-planting and 60% at-hilling (AN and AS). The DR was measured biweekly from planting to harvest at two locations (ridge and furrow) using the acetylene blockage technique. The mean annual DR, averaged across N treatments, ranged from 0.8 to 8.0 μg N2O-N kg dry soil−1 d−1, and it was most closely related to the water inputs in the 72 h before DR measurements. Mean DR averaged across year was greater for N200 than for N0 (4.2 vs. 3.4 μg N2O-N kg dry soil−1 d−1) but did not differ among N sources. Our results suggest that choice of N fertilizer source in sandy soils is more important in controlling losses of N by leaching than by denitrification.

Compost application to agricultural fields can increase soil organic matter content and soil productivity. This study compared diverse compost products with a non-amended control in small plot and on-farm trials for effects on tuber yield and plant nutrient availability under rain-fed potato production in New Brunswick, Canada. In the small plot trial, mature compost products resulted in a small increase in plant N availability, whereas immature products resulted in net N immobilization. Composts high in K increased plant K availability. However, these effects on nutrient availability did not result in a significant effect on tuber yield. In on-farm trials, compost did not significantly increase yield averaged across 19 site-years of trials. This suggests that any short-term nutrient benefit from application of these wood waste and manure based composts is unlikely to influence crop yield, although there may be the potential to reduce nutrient application rates, particularly for K.

Nitrous oxide (N2O) emissions from frozen soils have been observed during winter. Concomitantly, nitrite (NO2−) accumulations were reported in frozen soils and may have contributed to elevated N2O emissions. The objectives of this study were to determine the processes leading to NO2− accumulation and its contribution to N2O emissions in frozen soils. Soil microcosms were incubated for 21 days under frozen (−2 °C) or unfrozen (+0.5 °C) conditions. Soils were amended with either 15N-NH4+ or 15N-NO3 to quantify the contribution of nitrification and denitrification processes to NO2− accumulation, respectively. Production of 15N-N2O was measured to determine the contribution of NO2− accumulation to N2O emissions. Nitrite progressively accumulated over 21 days in soils incubated at −2 °C to concentrations up to 8.87 μg N g−1 dry soil. However, in soils incubated at +0.5 °C, NO2− concentration increased from day 0 to day 7 (up to 3.61 μg N g−1 dry soil) and declined thereafter. At both temperatures, NO2− accumulation was associated with a progressive decrease in NO3− concentration while NH4+ concentration remained relatively stable over time. Greater N2O emissions were observed at +0.5 °C (average of 0.0135 μg N g−1 dry soil h−1) compared with −2 °C (average of 0.0045 μg N g−1 dry soil h−1) from day 2 to day 14. However, N2O emissions were 3.5 fold greater at −2 °C compared with +0.5 °C on day 21. In soils at −2 °C, 97.40–99.75% of the NO2− and over 99.56% of N2O were derived from NO3−. In soils incubated at +0.5 °C, the proportions of NO2− and N2O derived from NO3− slightly decreased while the proportions of NO2− and N2O derived from NH4+ increased up to 4.3% and 4.7%, respectively, from day 2 to day 21. At both temperatures, 15N enrichments of N2O and NO2− were similar. The results indicated that (i) denitrification was the major process leading to soil NO2− accumulation and concomitant production of N2O under both temperatures; and that (ii) N2O emissions were more sustained in frozen soils where NO2− concentrations were greater compared to unfrozen soils.

We examined soluble organic nitrogen (SON) leached from long-term, sequentially leached, aerobic incubations. Leached SON, present in all depths (0–60 cm), ranged from 35% to 56% of total nitrogen (N). This unaccounted-for SON may have important implications in the estimation of plant available N and the potential for environmental N losses.

Poultry manure is the primary cause of nitrate ( NO 3 - ) exceedances in the transboundary Abbotsford–Sumas aquifer (ASA; Canada–USA) based on synoptic surveys two decades apart, but questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ 15N and δ 18O of nitrate assays, focusing on shallow groundwater (

The quantification of groundwater NO₃ loading associated with a specific field or set of management practices so that groundwater quality improvements can be objectively assessed is a major challenge. The magnitude and timing of NO₃ export from a single agricultural field under raspberry (Rubus idaeus L.) production were investigated by combining high-resolution groundwater NO₃ concentration profiles (sampled using passive diffusion samplers) with Darcy’s flux estimation at the field’s down-gradient edge (based on field-measured hydraulic gradients and laboratory-estimated hydraulic conductivity). Annual recharge estimated using Darcy’s law (1002 mm) was similar to that obtained using two other approaches. The similarity in the rate of Cl applied to the field and the estimated export flux over the 1-yr monitoring period (51 vs. 56 kg Cl ha⁻¹) suggested the mass flux estimation approach was robust. An estimated 80 kg NO₃–N ha⁻¹ was exported from the agricultural field over the 1-yr monitoring period. The greatest monthly groundwater mass flux exported was observed in February and March (∼11 kg NO₃–N ha⁻¹), and was associated with NO₃ leached from the soil zone during the onset of precipitation in the previous autumn. Provided the groundwater recharged from the field of interest can be isolated within a vertical profile, this approach is an effective method for obtaining spatially integrated estimates of the magnitude and timing of NO₃⁻ loading to groundwater.

Chemical fumigation and biofumigation are used to reduce soil-borne diseases in agricultural production systems; however, other essential soil processes such as the soil nitrogen (N) cycle may also be affected. This study compared the effects of chemical fumigation and biofumigation on soil net N mineralization, nitrification, denitrification, and soil nitrifier and denitrifier abundance. Six treatments were compared using soil microcosms over a 160-day incubation period: fumigation with chloropicrin; fumigation with metam sodium used alone (MS) or combined with barley plant residues (MSBR); biofumigation with mustard residues; addition of non-biofumigant barley residues; and an untreated control. Biofumigation did not inhibit soil nitrification, whereas chemical fumigation with MS (with or without barley) and chloropicrin inhibited nitrification for 16 and 64 days, respectively. Biofumigation, barley residues, and MSBR increased soil respiration, N2O emission, and denitrification rates. However, biofumigation had lower denitrification and N2O cumulative emissions and rates compared to barley residues, suggesting that biofumigation may reduce N2O production pathways. All chemical fumigation treatments significantly decreased nitrifier gene abundance compared to biofumigation; however, only chloropicrin decreased the abundance of denitrifying genes. After 160 days, 22% of the added plant residue dry matter remained in the MSBR-treated soil, which was ∼2-fold greater than the barley-treated soil, indicating chemical fumigation may also affect the carbon cycle. Overall, these results suggest that chemical fumigation, especially with chloropicrin, has a greater impact on nitrification and nitrifier and denitrifier gene abundance than biofumigation with mustard residues.

Nitrate leaching is of great environmental concern, particularly with potatoes grown on sandy soils. This 3-year study evaluated the effect of three N rates (100, 150, and 200 kg ha−1) of single applications of polymer-coated urea (PCU) and a 75% PCU + 25% urea mixture, plus a conventional split application of 200 kg N ha−1 of a 50% ammonium sulfate + 50% calcium ammonium nitrate mixture (CONV) on NO3−-N leaching, potato yield, and N uptake under irrigated and non-irrigated conditions on a sandy soil in Quebec (Canada). Fertilizer N application increased growing season NO3−-N leaching only under irrigation. On average, irrigation increased seasonal NO3−-N leaching by 52%. Under irrigated conditions, PCU reduced NO3−-N leaching compared to PCU + urea. However, both PCU and PCU + urea significantly increased NO3−-N leaching compared to the CONV at the equivalent N rate of 200 kg N ha−1. This was attributed to the timing of soil N availability and deep-water percolation. Total (TY) and marketable (MY) yields in the CONV were similar to those in the PCU applied at the equivalent N rate of 200 kg N ha−1. Despite lower plant N uptake, PCU resulted in greater TY and MY compared to PCU + urea. Residual soil inorganic N was greater for PCU and PCU + urea compared to the CONV, providing evidence that PCU products have the potential to increase NO3−-N leaching after the growing season. In this study, PCU was an agronomically and environmentally better choice than PCU + urea. The results also showed that the efficiency of PCU to reduce seasonal NO3−-N leaching may vary according to the timing of precipitation and irrigation.

Increased cultivar tolerance to nitrogen (N) deficiency may increase productivity and reduce environmental impact of potato crops. In this study we screened 20 cultivars for the tolerance to N-deficient (0.05 mM nitrate) in comparison with N-abundant (7.5 mM nitrate) nitrate supply using plantlets grown for 15 days in a recirculating hydroponic system. Nitrogen deficiency increased the root-to-shoot ratio in 18 cultivars. Plant total dry weight (TDW) was reduced by an average of 61% under N-deficient nitrate supply. Tolerance to N deficiency was assessed as the TDW ratio (TDWR), calculated as the ratio of TDW under N-deficient to N-abundant nitrate supply. The cultivars Norland, Raritan, Nipigon and Langlade were significantly more tolerant to nitrogen deficiency (greater TDWR) than Eramosa, Carleton, and Epicure. The results indicate that the hydroponic system has capacity to rapidly screen a large number of cultivars for tolerance to N deficiency.

Source nitrogen (N) identification of leachate or groundwater nitrate is complicated by N source mixing and N and oxygen (O) isotope fractionation caused by microbial N transformations. This experiment examined the δ¹⁵NNO₃ and δ¹⁸ONO₃ values in leachate collected over 1 yr at 55 cm below raspberry (Rubus idaeus L.) plots receiving either synthetic fertilizer (FT) or poultry manure (MT). The large ranges of δ¹⁵NNO₃ (FT: −2.4 to +8.7‰, MT: +1.6 to +9.6‰) and δ¹⁸ONO₃ (FT: −9.9 to −0.3‰, MT: −10.9 to +1.7‰) values in leachate collected under crop rows prohibited the reliable identification of the applied N sources on individual sampling dates. However, the mass-weighted average δ¹⁵NNO₃ (FT: +3.2‰, MT: +7.3‰) values in leachate were significantly different and can be explained by accounting for the estimated contributions of nitrate and δ¹⁵NNO₃ values of the various N sources, including applied fertilizer (−0.7‰) or manure (+7.9‰), nitrate-rich irrigation water (+9.0‰), and nitrate from soil N mineralization and nitrification (FT: +3.7‰, MT: +4.6‰; the seasonal timing of which is unknown). This study illustrates the importance of characterizing all major N sources and considering the seasonal variation of these sources and of N cycling processes, as they contribute to the δ¹⁵NNO₃ values of leachate.

High NO3 concentrations in the Abbotsford‐Sumas aquifer are linked to raspberry (Rubus idaeus L.) production. Passive capillary wick samplers were used to quantify the impacts of N, irrigation, and alley managements on drainage and NO3 leaching from raspberry rows and alleys over 4 yr. Conventional management (100 kg N ha−1 surface broadcast on the row as a split application, clean cultivation of alleys, and fixed‐duration drip irrigation) was compared with different mineral fertilizer N rates, N applied as manure, alleys seeded to a perennial forage grass or an autumn‐seeded spring barley (Hordeum vulgare L.) crop, or evapotranspiration (ET)‐scheduled irrigation. The temporal pattern of drainage and NO3 leaching was driven by seasonal precipitation and growing season irrigation. Growing season drainage and NO3 leaching were much lower under ET‐scheduled irrigation compared with fixed irrigation. Nitrate leaching was high (up to 90 kg N ha−1), even with no managed N inputs due to high inherent soil fertility and large quantities of N applied in irrigation water. Nitrate leaching was insensitive to N fertilizer rate. Application of N as poultry manure more than doubled NO3 leaching compared with fertilizer, emphasizing the need to use organic N inputs judiciously. The perennial grass alley cover crop resulted in the greatest overall reduction in NO3 leaching. Our data indicate that no single management strategy is sufficient to protect groundwater quality. Rather, an integrated package of improved practices (i.e., application of a reduced rate of mineral N through fertigation, combined with ET‐scheduled irrigation and perennial alley crop) is necessary to protect groundwater quality.

The soil application of plant residues characterized by different carbon to nitrogen (C:N) ratios may lead to conditions more suitable to denitrifying and nitrite ammonifying bacteria. While the former microbial group fosters the loss of nitrogen (N) through the production of N 2 and nitrous oxide (N 2 O), the latter may retain N into the agroecosystems. At present time there is no evidence on the effect of plant residues application on ammonifying bacterial populations over the winter. Dynamics of denitrifiers and nitrite ammonifiers abundance, composition and gaseous emissions (i.e. N 2 O and CO 2 ) in soils following fall plough-down of barley (BRL) or red clover (RC) were evaluated at different time points for two consecutive winters in a humid temperate environment. Abundance of denitrifiers ( nirK and nirS ) and nitrite ammonifiers ( nrfA ) was greater in BRL-treated plots compared with RC, despite the higher C:N ratio of BRL. The present (DNA) and active (RNA) community structure of both denitrifiers and ammonifiers was different between BRL- and RC-treated plots and changed continuously during the two winters. The results suggested that both cold-induced edaphic conditions and crop residue application influenced and shaped the targeted functional communities. N 2 O and CO 2 emission rates did not respond to crop residue source, however the emissions were 5–8-times greater in coldest months (i.e. January/February) compared to other dates during both winters. Our findings showed that cold-adapted denitrifying and nitrite ammonifying bacteria had a very similar response to the crop residues in abundance and diversity, suggesting that the application of contrasting C:N ratio crop residues did not create different niches for the nitrite ammonifiers and denitrifiers during the winter.

In agricultural fields at high and mid latitudes, a large percentage of the annual emissions of the greenhouse gas nitrous oxide (N2O) can occur during freeze-thaw (FT) cycles. The objective of the study was to determine the effects of FT cycles of different amplitudes on N2O emissions, denitrifier transcriptional activity, and the abundance and composition of present and active denitrifier communities. Soil microcosms amended with NO3 − (N) and/or NO3 − plus organic C, i.e., red clover residues (N + RC), were subjected to freezing at −5 °C followed by thawing at either +4 or +15 °C. Peaks of N2O emission rates following FT were ∼2-fold greater in N + RC than in N amended soils. In N + RC amended soils, the maximum rates following FT were similar at +4 and +15 °C. However, thawing at +4 °C resulted in a delay in the peak of emissions, suggesting that denitrification enzymatic activity was reduced at colder temperatures. In general, the abundance and the number of transcripts of nirS and nirK were similar over time and among treatments with a few exceptions, including, for example, fewer nirS transcripts under the cooler thawing temperature. Temperature regimes had a significant effect on the compositions of the present and active nirS and present nirK denitrifier communities during FT. Changes in these community compositions were correlated with changes in temperature and N2O emissions, and these variables explained 3.7 to 4.9 % of the changes in community composition. Results indicated that addition of electron donor, i.e., organic C, increased N2O emissions. Furthermore, the composition of active nirS community changed during the peak of N2O emissions following FT events but not the active nirK community. This finding indicated that active nirS community better adapted to the changes in conditions has established suggesting a greater role of this group in N2O production.

Particulate organic matter (POM) is a labile fraction of soil organic matter (SOM) that can contribute to nitrogen (N) mineralization. We added native and non-native POM to soils with contrasting properties and assessed net N mineralization during a 28 days incubation study. Soils (0–15 cm depth) for this study were a clay soil with a 3-year history of corn ( Zea mays L.), a loam soil with a 2-year history of alfalfa ( Medicago sativa L.) and sandy–loam and silty–clay–loam soils that were cropped in the previous 5 years with a corn-soybean ( Glycine max L.) — corn–forage–forage [45% alfalfa + 55% timothy ( Phleum pratense L.)] and corn–soybean–forage–forage–forage rotation, respectively. The POM was separated by size fractionation (> 53 μm) from coarsely sieved (> 6 mm) soil. The N concentration in POM followed the order loam > silty–clay–loam > clay > sandy–loam, whereas the acid unhydrolyzable fraction, a proxy for the lignin concentration, was the reverse. Compared to soil only, addition of N-rich POM from the loam soil increased net N mineralization in the clay soil and gave similar net N mineralization in the other soils, while addition of N-poor POM from the sandy–loam soil resulted in lower net N mineralization in the loam and silty–clay–loam soils. Multiple stepwise regression analysis showed that net N mineralized due to POM addition was related to the N concentration in the POM (partial R 2 = 0.54) and the initial soil mineral N concentration (partial R 2 = 0.33), suggesting that N mineralized from POM was related more to POM chemical composition than soil properties. We propose that information on POM chemistry in conjunction with soil mineral N concentration and texture could be useful for constructing N mineralization prediction models to improve N fertilizer management in agricultural soils.

Soil test indicators are needed to predict the contribution of soil organic N to crop N requirements. Labile organic matter (OM) fractions containing C and N are readily metabolized by soil microorganisms, which leads to N mineralization and contributes to the soil N supply to crops. The objective of this study was to identify labile OM fractions that could be indicators of the soil N supply by evaluating the relationship between the soil N supply, the C and N concentrations, and C/N ratios of water extractable OM, hot-water extractable OM, particulate OM, microbial biomass, and salt extractable OM. Labile OM fractions were measured before planting spring wheat (Triticum aestivum L.) in fertilized soils and the soil N supply was determined from the wheat N uptake and soil mineral N concentration after 6 weeks. Prior to the study, fertilized sandy loam and silty clay soils received three annual applications of 90 kg available N (ha · y)−1 from mineral fertilizer, liquid dairy cattle manure, liquid swine manure or solid poultry litter, and there was a zero-N control. Water extractable organic N was the only labile OM fraction to be affected by fertilization in both soil types (P < 0.01). Across both test soils, the soil N supply was significantly correlated with the particulate OM N (r = 0.87, P < 0.001), the particulate OM C (r = 0.83, P < 0.001), and hot-water extractable organic N (r = 0.81, P < 0.001). We conclude that pre-planting concentrations of particulate OM and hot-water extractable organic N could be early season indicators of the soil N supply in fertilized soils of the Saint Lawrence River Lowlands in Quebec, Canada. The suitability of these pre-planting indicators to predict the soil N supply under field conditions and in fertilized soils from other regions remains to be determined.

Zebarth, B. J., Forge, T. A., Goyer, C. and Brin, L. D. 2015. Effect of soil acidification on nitrification in soil. Can. J. Soil Sci. 95: 359–363. This laboratory experiment examined the effect of elemental S-induced variation in soil pH (3.97–5.29) on nitrification enzyme activity and conversion of [Formula: see text] to [Formula: see text]. Nitrification rate generally decreased with decreasing soil pH, but still proceeded rapidly within the pH range (4.5 to 5.2) recommended for blueberry production, contrary to what is generally assumed.

Poultry manure is the primary source of nitrate (NO 3 − ) exceedances in the transboundary Abbotsford-Sumas aquifer (Canada-USA) based on synoptic surveys two decades apart, but serious questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ 15 N and δ 18 O of nitrate assays, focusing on newly recharged groundwater ( 5 yr.-old) over a five-year period to gain new insight on spatiotemporal sources and controls of groundwater nitrate contamination. NO 3 − concentrations in recharge ranged from 1.3 to 99 mg N L −1 ( n = 1041) with a mean of 16.2 ± 0.4 mg N L −1 . These high-frequency isotope data allowed us to identify 3 distinctive nitrate flux patterns, i) nitrate in recharge influenced by synthetic fertilizer inputs ii) nitrate in recharge impacted by short-term climatic and local agricultural crop rotations and iii) long-term widespread manure and synthetic fertilizer inputs. A key finding was that the source(s) of nitrate in recharge could be quickly influenced by short-term near-field management practices and stochastic climatic factors, which linger and ultimately impact long-term nitrate contamination trends. Overall, the isotope data affirmed a subtle decadal-scale shift in agricultural practices from manure towards fertilizer nitrate sources, nevertheless poultry-derived N remains a predominant source of nitrate contamination. Because the aquifer does not support denitrification, remediation of the Abbotsford-Sumas aquifer is possible only if agricultural N sources are seriously curtailed, a difficult proposition due to longstanding high-value intensive poultry and berry operations over the aquifer.

The potential to use gene expression as an indicator of plant N status has been identified, however how such expression indicators may vary with time of day (TOD) has not been examined. This study quantified variation in gene expression at four times during the day (8:00, 11:00, 14:00 and 17:00) on potato plots receiving 0 or 180 kg N ha−1. Expression of 24 experimental genes was quantified by nCounter and normalized by reference genes. Expression of all but one of the experimental genes varied significantly with time of day. Most (15) genes, across a range of gene function categories, had greater expression at 8:00 and 17:00 than during midday, and 10 of these genes had least expression at 14:00, the sampling time with greatest solar radiation. For 7 genes, expression was greater during midday, and for carbohydrate metabolism or chlorophyll-related genes maximum expression occurred at 14:00. Expression of ammonium transporter AT1, previously identified as a good predictor of potato N status, varied strongly with TOD and became insensitive to potato N status during midday. TOD effects on both experimental and reference genes must be considered in developing gene expression based diagnostic tests of crop N status, and ideally, genes which are sensitive to crop N status, but insensitive to TOD, can be identified for such diagnostic purposes.

Potato production is critical to economy of Prince Edward Island (PEI), but has been linked to increasing groundwater nitrate contamination and anoxic events in estuaries. Given that PEI is entirely groundwater-dependent for potable water, this has resulted in considerable pressure to find solutions to protect water quality. However, our understanding of the controls on nitrate loading to groundwater, and the consequent potential to mitigate nitrate loading through beneficial management practices (BMPs), is limited. In PEI, flow and nitrate transport in the vadose zone are controlled by the matrix porosity of the till and sandstone, while flow and transport in the saturated zone are controlled by a conductive fracture network with limited storage capacity. Diffusion of nitrate stored in the matrix may introduce a significant time lag between reduced nitrate loading from implementation of BMPs and measureable improvement in groundwater quality. BMPs with potential to mitigate nitrate loading to groundwater through improved nitrogen fertilizer practices in producing potato crops have been identified, but implementation of these practices alone is not sufficient to control nitrate loading due to the economic context of potato production. Additional BMPs for improved potato cropping systems have also been identified; however, reducing the intensity of agricultural production, including the proportion of land in potato production, at the watershed level may be required to meet the drinking water guideline for nitrate in PEI. Given the important role of market forces in determining profitability of crop production, it becomes challenging to modify crop production practices to meet an environmental goal without some additional external incentive or public pressure.

Assessment and monitoring of soil organic matter (SOM) quality are important for determining and developing management practices that will enhance and maintain the productivity of agricultural soils. This requires routine analysis of multiple soil parameters, which can be time-consuming and expensive. Research has suggested that visible near infrared reflectance spectroscopy (VNIRS) may be used as a rapid and cost-efficient tool for SOM quality assessment. In this study, VNIRS (400–2498 nm) was used for the first time to simultaneously predict microbial biomass nitrogen (MBN), water-extractable organic N (WEON), light fraction organic matter N (LFOMN), particulate organic matter N (POMN), soil total N (TN), soil organic carbon (SOC) and soil C/N ratio as soil SOM quality indicators in Chernozemic soils of western Canada. The soil samples (n = 200) were collected at the 0–15 cm depth from a crop rotation experiment conducted at 6 sites in 2010 and 2011. After removal of outliers (five samples) identified by principal components analysis (PCA), 75% of the sample set was randomly selected for calibration (n = 146) and the remainder used for validation (n = 49). Modified partial least squares regression with cross-validation was used to develop prediction models. The reliability of the models was assessed using the coefficient of determination in validation (R2V) and the ratio of standard deviation of the reference data in the validation set to the standard error of prediction (RPDV). The VNIRS predictions were considered reliable for LFOMN, POMN, TN, and SOC (R2V > 0.80, RPDV > 2.4), as well as for MBN (R2V = 0.74, RPDV = 1.93), but less reliable for WEON (R2V = 0.67, RPDV = 1.70) and soil C/N ratio (R2V = 0.54, RPDV = 1.45). This study showed that VNIRS has the potential as a non-destructive and cost-efficient tool for rapid determination of SOM quality indicators.

Polymer-coated urea (PCU) is used in potato (Solanum tuberosum L.) production to maintain or improve tuber yield while minimizing N losses, but the mode of N release is different from conventional soluble N sources. Hence, it is not known how soil- and plant-based indices of N availability would perform in response to PCU application. A 3-yr study was conducted on a sandy-loam soil in Quebec, Canada, to examine the effect of PCU application rate (0, 60, 120, 200, and 280 kg N ha –1 ) on petiole NO 3 –N concentrations, chlorophyll meter readings (SPAD readings), soil mineral N content, and total tuber yield. Nitrate availability throughout the growing season was monitored by measuring NO 3 adsorbed by anion exchange membranes (NO 3AEM ). The NO 3AEM values, petiole NO 3 –N concentrations, SPAD readings, soil mineral N content, and total tuber yield increased with PCU application rate. The NO 3AEM values fluctuated during the growing season due to plant N uptake and variations in soil moisture content. Using all the PCU rates across years, we found that relative yield was better related to petiole NO 3 –N concentrations measured at 45 to 50 d after planting (DAP) ( R 2 = 0.95) and to cumulative NO 3AEM values measured up to 49 DAP (R 2 = 0.91) than soil mineral N (R 2 = 0.67), soil NO 3 –N (R 2 = 0.65), and SPAD readings (R 2 = 0.53) measured at 45 to 50 DAP, respectively. This study showed that soil- and plant-based indices of N availability can be used as early indicators of yield response in potato fertilized with PCU.

Long-term effects of fresh (FM) versus composted (CM) beef manure application to barley (Hordeum vulgare L.) on potentially mineralizable nitrogen (N 0 ), and mineralizable nitrogen (N) pools, were evaluated in a clay loam soil in southern Alberta, Canada. A suite of laboratory-based indices were evaluated for prediction of soil N supply. The treatments were three rates (13, 39, 77 Mg ha−1 dry wt.) of FM or CM containing either straw or wood-chip bedding, 100 kg N ha−1 as inorganic fertilizer, and an unfertilized control. Treatments were fall-applied annually for 8 years (1998–2005). Soil samples (top 15 cm) were collected in spring 2006. The medium and high rates of organic amendment resulted in increases in N 0 , and readily (Pool I) and intermediate (Pool II) mineralizable N pools in ranges of 140–355 % compared with the average of the fertilizer and control treatments. Fertilizer application had no significant effect on mineralizable N pools, but increased the mineralization rate constant (k) compared with the control. Application of FM and use of straw bedding resulted in a greater quantity of readily available and intermediate mineralizable N, and also increased the rate of N turn-over as indicated by greater values of k, compared with CM and wood-chip bedding. Among laboratory-based measures of soil N supply, CaCl2–NO3 (r2 = 0.84) and NaHCO3-205 (r 2 = 0.79) were strong predictors of plant N uptake (PNU). Increased soil mineralizable N did not translate into greater barley dry-matter yield or PNU. Composted beef manure and use of wood-chip bedding can be recommended as alternatives to FM and use of straw bedding for barley production is Southern Alberta.

Labile organic nitrogen (N) fractions are actively involved in short-term N mineralization, but the extent to which each fraction contributes to N mineralization is not fully understood. The objective of this study was to examine the flow of 15N-labelled faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) residues through the soil microbial biomass N (MBN), water-extractable organic N (WEON), light fraction organic matter N (LFOMN), particulate organic matter N (POMN) and mineral N pools in sandy-loam and clay soils under controlled conditions. After 3 d, 17–30% of the residue 15N was recovered in the POMN fraction, with a greater proportion of the wheat than faba bean residue recovered as POM15N. This POM15N probably included undecomposed residues and LFOM15N. Net N mineralization was greater in faba bean- than wheat-amended soils and greater in the sandy-loam than the clay soil. The LFOM15N concentrations decreased throughout the study, while POM15N concentrations increased or remained constant for 28 d in the sandy-loam and until 56 d in the clay soil. This suggests possible encrustation of LFOMN with soil mineral particles causing increased densification and recovery in the POMN fraction. The subsequent decrease in POM15N concentrations corresponded with mineral 15N accumulation in the soils. Mineral 15N concentration after 112 d was positively related to the initial POM15N concentration (r = 0.78, P 0.05). The WEON and MBN appeared as transient, intermediary pools. The results of this study suggest that mineralization of POMN is a major pathway through which mineral N is supplied in agricultural soils, with C/N ratio of crop residues and to a lesser extent soil properties, influencing the mineralization rate.

Changes in nitrifier and denitrifier abundance, composition and nitrous oxide (N2O) emissions during the winter period in soils with spring application of nitrogen (N) as mineral fertilizer, cattle manure or poultry manure were evaluated. Soil samples were collected from an agricultural field in Eastern Canada during winters of 2009–2010 and 2010–2011. Surprisingly, N2O emission rates were up to 150 fold greater in the coldest dates compared to other dates for the two winters, however rates were similar among N sources. Abundance of nitrifiers (Nitrobacter-like nxrA, archaeal amoA) and denitrifiers (nirK, nirS) increased in March and April compared with other sampling dates. Nitrifier abundance (nxrA) was the greatest in soils amended with cattle manure, while denitrifiers (nirK, nirS) were more abundant in soils amended with poultry manure. Nitrifiers and denitrifiers showed different composition depending on sampling date and N sources in the two winters, suggesting that changes in environmental conditions and N sources both influenced these communities. Our findings demonstrate that N2O emissions occur at significant rates in snow covered agricultural soils. Moreover, the abundance and diversity of denitrifier and nitrifier communities evolved throughout winter and appeared to be influenced by soil conditions and N sources applied in the previous spring.

Nitrate loading from an intensively managed commercial red raspberry field to groundwater in the Abbotsford-Sumas Aquifer, British Columbia was estimated over a 1 yr period and compared with the nitrogen surplus calculated using a simple nitrogen budget. Nitrate loading was estimated as the product of recharge (estimated from climate data as total precipitation minus potential evapotranspiration (PET)) and monthly nitrate concentration measured at the water table. Most nitrate loading occurred when nitrate, accumulated in the root zone over the growing season, was leached following heavy autumn rainfall events. Elevated groundwater nitrate concentrations at the water table during the growing season when recharge was assumed to be negligible suggested that the nitrate loading was underestimated. The estimate of annual nitrate loading to the water table was high (174 kg N ha−1) suggesting that the tools currently available to growers to manage N in raspberry production are not adequate to protect groundwater quality. The calculated nitrogen surplus from the nitrogen budget (180 kg N ha−1) was similar to the measured nitrate loading suggesting that simple nitrogen budgets may be relatively effective indices of the risk of nitrate loading to groundwater.

Georgallas, A., Dessureault-Rompre, J., Zebarth, B. J., Burton, D. L., Drury, C. F. and Grant, C. A. 2012. Modification of the biophysical water function to predict the change in soil mineral nitrogen concentration resulting from concurrent mineralization and denitrification. Can. J. Soil Sci. 92: 695–710. Uncertainty in soil N supply is an important limitation in making crop fertilizer N recommendations. This study modified a biophysical water function developed to predict net soil N mineralization, making it possible to consider how both N mineralization and denitrification processes affect the rate of soil mineral N accumulation. Data were from a published experiment measuring changes in soil mineral N concentration in five soils of varying texture (loamy sand to clay loam) incubated for 3 mo with or without addition of red clover residue and at two levels of compaction. The biophysical water function was effective in fitting the relationship between scaled change in the rate of soil mineral N accumula...

This study examined the expression of genes in leaf tissue of greenhouse-grown potatoes to the form of N supplied in the context of development of a diagnostic tool for detection of N status. Potato cultivar ‘Shepody’ was grown over a two-week period at three stages of growth (tuber initiation, flowering and early tuber bulking) with three forms of N (NO3− only, NH4+ only, or 1:1 NO3−:NH4+) at two levels of N supply (0.75 or 7.5 mM). Leaf disks were collected and extracted for RNA, and 28 genes examined for expression using nCounter. Expression of ammonium transporter AT1 was increased when the N supply was reduced, regardless of N form, and was generally independent of growth stage. Expression of AT1 was less influenced by N form than currently used chemical or optical measures of plant N status. Expression of AT1 can be used as a quantitative indicator for plant N status of potato regardless of nitrogen form and crop growth stage.

Assessment of the soil N supply capacity is essential to optimize N fertilizer use. The soil N supply capacity of 102 soil samples (0–15 cm) from 25 sites collected from 2004 to 2007 across four Canadian provinces was evaluated by comparing a group of chemical N availability indices with soil mineralizable N pools and a field-based measure of soil N supply. Soil N supply was estimated by corn (Zea mays L) N uptake corrected for starter fertilizer N. Two subgroups were created based on the soil texture and were compared to the whole data set. Grouping soils provided limited benefits in predicting soil potentially mineralizable nitrogen (N₀), but improved the prediction of soil N supply. The N₀ was weakly related to soil N supply for the whole data set (r = 0.09) and in fine-textured soils (r = 0.37) but the relationship was improved (r = 0.68) in medium- to coarse-textured soils. The N₀ was not necessarily a good predictor of soil N supply under field conditions which emphasizes the need to also consider environmental conditions. The UV absorbance of a 0.01 M NaHCO₃ extract at 205 nm (NaHCO₃–205), the hot KCl extractable NH₄–N (HotKCl–N) and Pool I (a labile mineralizable N pool) plus NO₃–N were the most promising N availability indices because they are easy to perform and they were positively and significantly related to soil N supply in the whole data set as well as the soil texture subgroups (0.28 ≤ r ≤ 0.62). This study demonstrated that grouping soils based on texture can increase the proportion of variation in soil N supply explained by N availability indices when data from contrasting environmental conditions, soil types, and years are used.

Controlled release urea (CRU) has been shown to improve nitrogen fertilizer use efficiency in a number of production systems. However, the effectiveness of CRU will be strongly affected by the environmental conditions of the region. Research trials were conducted at five locations across four major ecoregions spanning 1600 km across the Northern Great Plains and Pacific Maritimes of North America from 2004 to 2006 to evaluate the effects of a single application of polymer-coated urea (CRU) or split applications of urea fertilizer as compared with non-coated urea for their effects on crop growth, crop N concentration, and crop N accumulation of wheat (Triticum aestivum L.), barley (Hordeum vulagre L.) canola (Brassica napus L.) and corn (Zea mays L.) across a wide range of environmental conditions. Urea applied as an in-soil band at the time of seeding was generally as or more effective than similarly placed CRU, split application of urea or blended urea and CRU in the semi-arid Mixed Grassland, moist Aspen Parkland or wet Boreal Transition ecoregions in increasing early season dry matter yield and seed or grain yield of canola, wheat or barley. Similarly, broadcast urea was as or more effective than broadcast CRU, split applications or blended applications in increasing corn dry matter yield under the wet conditions in the Lower Mainland ecoregion. There were some situations where use of split applications or use of the CRU in a blend with the non-coated urea resulted in increases in grain yield as compared to the non-coated urea, primarily under moist conditions in the Boreal Transition or Aspen Parkland ecoregions. Some yield losses occurred from use of the CRU as compared with the non-coated urea and were attributed to delays in release of N from the granule that limited early season N availability and crop growth, especially in corn with a high N demand. Effects on grain N concentration and accumulation of N in the crop at harvest were mixed, with the CRU, blended applications of CRU and urea or split applications occasionally producing higher grain N concentration and N accumulation in the crop than the non-coated urea. Benefits of CRU on grain N concentration were more frequent than benefits on grain yield, but were not large or consistent. Response of crop growth and N uptake to N management was generally similar under CT and RT, with occasional differences occurring due to changes in yield potential or N deficit associated with the differences in tillage management. Therefore, under growing conditions across a wide range of ecoregions in the Northern Great Plains and the Pacific Maritimes, the use of CRU or split applications do not appear to provide a consistent improvement in crop yield, N concentration in the grain, total N accumulation at harvest, or nitrogen use efficiency as compared to standard regional timing and placement of non-coated urea.

The ability of the soil to supply some of the crop nitrogen (N) requirements via the mineralization of organic matter is of economic and environmental importance to producers and society. Water, or its absence, controls microbial activity in soil and thus rates of net N mineralization. Development of a general relationship between soil water content and net N mineralization rate can therefore improve prediction of soil N mineralization and hence soil N supply. The objectives of this study were to use previously published data sets to: 1) evaluate a new biophysical water function to predict the effect of soil water content on net soil N mineralization rate and 2) examine the effect of the origin of the soil and soil properties on the response of soil N mineralization to water content. A biophysical water function was developed which included the contribution of two physical processes: the wetting of surfaces presented by soil particulate matter (i.e. clays, organic matter), and the filling of free volume between the particles (i.e. pores). Scaled water-filled pore space (WFPS) between a minimal and optimal value for mineralization was used as the unit for water content. Four different water functions were compared in this study (biophysical, sigmoidal, logistic and Gaussian) and although they explained a similar percentage of the variability in scaled mineralization rate, the functions had distinctly different shapes. The biophysical water function was found to be valid across a range of soil properties and origins. The biophysical water function includes a surface activity parameter (λ) which was found to be consistently about 0.80, indicating that 80% of the mineralization reaction takes place at a surface. The shape of the biophysical water function was found to be controlled to a large extent by parameter b which reflects the increase in net N mineralization rate associated with surface wetting. Parameter b was found to vary with climatic zone of soil origin and soil properties. The b parameter was higher for soils from warmer (≥ 6 °C) than colder ( −1 ) content. The biophysical function presented in this study was found to show a behavior representative of the underlying biological processes and has the advantages that the three fitted parameters all have a biophysical interpretation that allows new and original biological interpretations based on the fitted parameters related to surface and pore domains.

This study was conducted to investigate the effects of incubation temperature on mineralization of native pools of C from a soil with a history of manure application, compared to a non-manured soil. Net C mineralization, microbial community structure, biomass size, and metabolic quotient (qCO2) were measured. Mineralization at cooler temperatures followed zero-order kinetics, indicating a non-limiting supply of substrate. First-order kinetics dominated at warmer temperatures as substrate supply increasingly limited microbial respiration. The soil with a history of manure application had a larger microbial biomass than the non-manured soil, and higher rates of C mineralization. There was a trend toward decreased biomass sizes with increasing incubation temperature. Bacterial DNA T-RFLP profiles were affected by incubation temperature and time with a significant difference in community structure detected after soils had been incubated for 120 days, as well as after incubation at 35 °C. Fungal DNA T-RFLP profiles indicated a distinct community in soils incubated at 35 °C, regardless of the length of the incubation. The key findings from the study were that C mineralization from native pools of organic matter does not follow Arrhenius kinetics at high temperatures, and that incubation of soils outside of their normal temperature range can alter soil biological characteristics which may impact estimates of mineralization parameters.

LEACHN was employed to simulate nitrate leaching from a representative potato production system in Prince Edward Island (PEI), Canada and enhance the understanding of impacts of potato (Solanum tuberosum L.) production on groundwater quality. The model’s performance on predicting drainage was examined against water table measurements through coupled LEACHN and MODFLOW modeling. LEACHN was calibrated and verified to data from tile-drain leaching experiments of potato grown in rotation with barley (Hordeum vulgare L.) and red clover (Trifolium pratense L.) during 1999–2008. Long-term simulations using the calibrated model were performed to evaluate the effects of climate and N fertilization for the potato crop on nitrate leaching. The modeling suggests LEACHN can be an effective tool for predicting nitrate leaching from similar cropping systems in PEI. Both measurements and simulations showed nitrate leaching primarily occurred during the non-growing season when crop uptake diminishes, and nitrate from mineralization and residual fertilizer coexists with excessive moisture from rainfall and snowmelt infiltration. Annual average nitrate leaching following potato, barley and red clover phases was predicted to be 81, 54 and 35 kg N ha−1, respectively, and the corresponding leached concentrations were 15.7, 10.1 and 7.3 mg N l−1. Increased N input for potato alone increased nitrate leaching not only during potato phase but also during the rotation crop phases. To reduce the risk of nitrate leaching, practices should be developed to minimize nitrate accumulation in soil both during and outside of the growing season and in both the potato and the rotation crop phases.

Use of an in-season measure of crop N sufficiency to guide fertilizer management is one approach to match the supply of N to the crop N demand. This study examined use of gene expression in leaf tissue of field-grown potatoes for use in assessment of potato N sufficiency. Potato cultivar ‘Shepody’ was grown with six fertilizer N rates (0–250 kg N ha–1). Leaf disks were collected weekly for quantification of the expression of N uptake/transport, N assimilation, and amino acid metabolism genes in leaf tissue by nCounter. Many of the genes evaluated were responsive to crop N supply, but the response varied widely among sampling dates. The exception was an ammonium transporter gene (AT1) which was highly expressed, was relatively consistent across sampling dates, was closely related to root zone soil nitrate concentration across N rates and sampling dates, and was highly negatively correlated with total tuber yield. The level of expression of AT1 in leaf tissue was as good as or better than conventional chemical or optical measures of potato N sufficiency in the current study.

Livestock manure is an important source of N for forage grass production. The long-term effects of semisolid beef manure application to forage grass on potentially mineralizable N (N 0 ), mineralizable N pools, and field estimates of soil N supply were evaluated in dike-land (heavy textured, poorly drained) and upland (medium-textured) soils in Nova Scotia, Canada. Treatments included an unfertilized control, annual spring application of 100 kg N ha ―1 mineral fertilizer or annual applications of 75, 150, or 300 kg total Kjeldhal N ha ―1 as manure (M75, M150, and M300, respectively) from 1995 to 2004. Soil samples collected in fall 2004 were used to estimate N 0 using a 44-wk aerobic incubation at 25°C. The N 0 values were 62 and 49% higher in the M300 treatment (324 and 480 kg N ha ―1 ) than the other manure treatments (199 and 323 kg N ha ―1 ) for the upland and dike-land soils, respectively. The mineralization rate coefficient ranged from 0.045 to 0.082 wk ―1 . Manure application increased the readily mineralizable N pool (Pool I); higher rates of application resulted in higher values in both soils. The intermediate and stable mineralizable N pools were increased only by the M300 treatment in the upland soil but not in the dike-land soil. Long-term manure application of the M300 treatment resulted in high N 0 with no yield benefits, which can increase the risk of N losses to the environment in both soils, whereas Pool I was responsive to all manure application rates.

Accurate prediction of soil nitrogen (N) mineralization in agricultural soils is of major concern because uncertainty in making fertilizer N recommendations can lead to economic losses and environmental pollution. This study examined the suitability of three temperature functions (Q10, Arrhenius, Logistic) as predictors of the temperature dependence of soil N mineralization rate, k, in soil using previously published data sets. Each function fits k/k0, where k0 is the reference mineralization rate, against soil temperature T, where k/k0 = 1 at the reference temperature, T0. No single value of soil temperature was common to all data sets, and consequently a series of values of T0 from 5 °C to 35 °C were tested. The influence of the temperature zone, land use and soil textural class of soils in the data set on the temperature response function was also tested. Despite the different mathematical forms of the functions evaluated, the fitted curves for each function were very similar and choice of temperature response function had a limited effect on prediction of soil N mineralization rate. An additional model, the LogisticFixed M model, is proposed which fits the data sets as well as the previous models, but also takes into account the existence of optimal and maximal temperatures in a reasonable temperature range for biological organisms. In contrast, choice of T0 had a much more pronounced impact on the k/k0 values, and thus on the predicted N mineralization rate, than choice of temperature model. A greater response of N mineralization rate (i.e. k/k0) to changes in temperature was observed in soils originating from colder climatic zones (mean annual temperature 6 °C). There was also a greater temperature response of soil N mineralization rate for agricultural compared with forested soils. Among agricultural soils, sand-loam soils had a greater temperature response compared with clay soils. Overall, selection of temperature response model did not appear to be critical to prediction of soil N mineralization rate, and consequently a form of the model which best represents the biological system is therefore preferable, whereas more attention should be given to the choice of the appropriate T0 for field prediction of N mineralization.

0 ) was estimated by curve fi tting using N mineralized from 2 to 24 wk, and Pool I, a labile mineralizable N pool, was determined as the N mineralized in the fi rst 2-wk period. Soil properties were relatively eff ective predictors of N 0 with soil organic N (SON) and sand explaining 40 and 34% of the variability, respectively. Particulate organic matter N (POM-N) and pH explained 18 and 25%, respectively, of the variability in Pool I. Simple climate normals were generally poor predictors of pool size except for potential evapotranspiration (PET), which predicted 24% of the variability in Pool I. Th e re_clim indices, normally applied to the activity of soil decomposers and applied here for the fi rst time to explain soil mineralizable N pool size variability, performed better than simple climate indices and explained up to 26% of the variation in N 0 . By including soil and climatic parameters in a multiple regression model, it was possible to explain about 63 and 40% of the variability in N 0 and Pool I, respectively, across a wide range of arable soils in Canada.

Limited research exists on the effect of fresh versus composted beef cattle manure containing straw or wood chips on available N and P in the Great Plains region of North America. Barley was grown (1999-2007) on an irrigated clay loam soil in southern Alberta where organic amendments and fertilizer were applied annually for 9 yr from 1998 to 2006. The treatments were three rates (13, 39, 77 Mg dry wt. ha-1) of fresh manure (FM, stockpiled for up to 2 m) or composted manure (CM) containing either straw (ST) or wood chip (WD) bedding, one inorganic (IN) fertilizer treatment, and a unamended control. The soil was sampled in the fall of 1999 to 2002, 2004, 2006, and 2007 and was analyzed for soil inorganic N (SIN), NO3-N, NH4-N, and soil test P (STP). Soil mineralizable N was also determined on surface soil samples collected from 1999, 2002, 2004, and 2007. Manure type had a significant effect on SIN, NO3-N, STP, and soil mineralizable N, but the effects varied with year or bedding and rate (SIN), rate or year (NO3-N), rate and year (soil mineralizable N), or bedding and year (STP). Analysis of covariance for total N or P applied versus SIN or STP after nine applications (2007) indicated greater N release for FM and CM bedded with straw than with wood, whereas P release was similar for FM and CM with straw or wood. Soil NO3-N for the organic amendments exceeded the maximum agronomic limit of 21 mg NO3-N kg-1 for Alberta after 6, 4, and 3 yr of application at the three increasing application rates. The STP for the organic amendments exceeded the maximum agronomic limit of 60 mg kg-1 for Alberta after 4, 2, and 2 yr of application at the three increasing rates. Overall, manure type and bedding material influenced the potential for nutrient losses to the environment through accumulation of soil inorganic N and soil test P; however, their effects on nutrient accumulation varied with year and application rate. Key words: Soil available nitrogen, soil available phosphorus, fresh manure, composted manure, mineralizable N

Optimizing nitrogen (N) fertilization in crop production by in-season measurements of crop N status may improve fertilizer N use efficiency. Hyperspectral measurements may be used to assess crop N status indirectly by estimating leaf and canopy chlorophyll content. This study evaluated the ability of the PROSAIL canopy-level reflectance model to predict leaf chlorophyll content of spring wheat (Triticum aestivum L.) during the growth stages between pre-tillering (Zadoks Growth Stage (ZGS 15)) to booting (ZGS50). Spring wheat was grown under different N fertility rates (0-200 kg N ha-1) in 2002. Canopy reflectance, leaf chlorophyll content, N content and leaf area index (LAI) values were measured. There was a weakly significant trend for the PROSAIL model to over-estimate LAI and under-estimate leaf chlorophyll content. To compensate for this interdependency by the model, a canopy chlorophyll content parameter (the product of leaf chlorophyll content and LAI) was calculated. The estimation accuracy for canopy chlorophyll content was generally low earlier in the growing season. This failure of the PROSAIL model to estimate leaf and canopy variables could be attributed to model sensitivity to canopy architecture. Earlier in the growing season, full canopy closure was not yet achieved, resulting in a non-homogenous canopy and strong soil background interference. The canopy chlorophyll content parameter was predicted more accurately than leaf chlorophyll content alone at booting (ZGS 45). A strong relationship between canopy chlorophyll content and canopy N content at ZGS 45 indicates that the PROSAIL model may be used as a tool to predict wheat N status from canopy reflectance measurements at booting or later.

A better understanding of the spatial distribution of denitrifiers and their activity may lead to an improved understanding of the denitrification process in soil. This study determined the spatial distribution of the total bacterial community (16S rRNA), components of the denitrifier community (cnorB(p); Pseudomonas mandelii and related species; nosZ), and denitrification activity across a range of soil aggregate size fractions (4-8, 1-2, and 0.25-0.5 mm) under permanent grassland (PG) and arable cropping (AC) systems. Aggregate size fraction had no significant effect oil the abundance of the nosZ or cnorBp gene-bearing bacteria in soil from the AC system. The highest abundance of denitrifier bacteria was measured ill the smallest size fraction in the PG system. Respiration did not differ among aggregate size fractions within the PG system; however, respiration was higher for the PG system than the AC system for all aggregate size fractions. For the AC system, higher respiration was measured in the 0.25- to 0.5-mm aggregate fraction than the 4- to 8-mm aggregate fraction. Denitrifying enzyme activity (DEA) was higher in the largest size fraction of the PG system than the AC system; however, DEA did not differ among aggregate size fractions within each management system. Cumulative denitrification during a 72-h incubation was significantly higher in the largest aggregate size fractions under both management systems. The results indicate that the differences among the aggregate size fractions were small in magnitude and that the spatial location of the denitrification activity and the abundance of the denitrifier bacteria were uncoupled across aggregate size fractions in the contrasting management systems. Refereed/Peer-reviewed

In-season chemical or optical measures of crop N status can be effective tools in optimizing potato fertilizer N management. The feasibility of using a gene expression as an alternative approach for early detection of potato nitrate deficiency was examined using three potato cultivars (Shepody, Russet Norkotah, and Red Pontiac) with abundant (7.5 mM NO3), limited (0.75 mM NO3) or deficient (0 mM NO3) nitrate supply in nutrient culture over a 7 d period. RNA was extracted from the last fully expanded leaf and quantified using realtime RT-qPCR. Reduced nitrate supply had no measurable effect on shoot dry weight or leaf chlorophyll concentration, but decreased petiole nitrate concentration. Under deficit nitrate supply, down-regulation of nitrate reductase and nitrite reductase was measured within 3 days for all cultivars, and down-regulation of asparagine synthetase was measured in two cultivars. Nitrate supply had no effect on expression of ammonium transporter. In this experimental system, plant gene expression markers detected a reduction of nitrate supply prior to measureable reductions in plant growth or in N status measured using common chemical or optical methods.

Limited research exists on the long-term effect of fresh (FM) versus composted manure (CM) from beef cattle on barley (Hordeum vulgare L.) yield and nutrient uptake. Barley was grown (1999-2007) as silage on an irrigated clay loam soil in southern Alberta where organic amendments and fertilizer were annually applied for 9 yr in the fall of 1998 to 2006. The treatments were three rates (13, 39, 77 Mg ha -1 dry wt.) of FM or CM containing either straw or wood-chip bedding, one inorganic fertilizer treatment, and a nonfertilized control. Nine years of annual application ofFM and CM resulted in similar aboveground dry matter yield, and total N and total P uptake compared with inorganic fertilizer. However, apparent nitrogen recovery (ANR) and phosphorus recovery (APR) were significantly lower for FM and CM (5-9%) than inorganic (22-47%). Barley dry matter yield, ANR, and APR were similar for FM and CM. Manure type influenced N and P uptake, but the effects varied with bedding type and year. The N and P uptake were greater for CM with straw than the other three treatments except FM with straw. The DM yield was similar for straw and wood bedding, but ANR was greater for straw (10%) than wood (7%). Bedding influenced N uptake, P uptake, and APR, but the effects varied with manure type, rate, and year. Based on the results of this study, producers converting from FM to CM, or from straw to wood-chip bedding, should suffer no loss in barley silage production.

Soil total nitrogen (N) concentration is commonly measured by Kjeldahl and combustion methods. In this study, a method based on determination of ammonium (NH4)‐N produced by steam distillation of the soil sample with sodium hydroxide solution (NaOH‐DD) is developed and evaluated for estimating soil total N concentration. The method was evaluated using two sample sets: (A) 44 samples collected from contrasting land uses in central Iran and (B) 344 samples collected from contrasting arable soils across Canada and Maine, USA. Based on this experiment, 10‐min distillation of 5.0 g soil with 20 mL 12.5 M NaOH were selected as the optimum conditions. The NH4‐N released by the NaOH‐DD method was highly correlated with total N concentration in the sample sets A and B (r = 0.79 and 0.94, respectively). The NaOH‐DD method provides a simple, rapid means of analysis with reduced measurement cost and better health and safety precautions than the traditional Kjeldahl method. Current address for Mehdi Sharifi: Nova Sc...

Nitrogen (N) supply from organic sources to the potato (Solanum tuberosum L.) crop is difficult to predict and to synchronize with crop demand. In this study, Plant Root Simulator™ (PRS™) probes were evaluated as a tool for prediction of N supply from two rates (300 vs. 600 kg N ha−1) of either a hog manure-sawdust compost (HMC) or a pelletized dehydrated poultry manure (NW) in Atlantic Canada. The cumulative PRS mineral N supply rate (PRS-N) measured for the period of 31 days after planting (DAP), soil mineral N at 10 DAP and soil NO3-N at 31 DAP were closely related to plant N uptake (PNU) (r = 0.77, 0.71 and 0.73, respectively; P < 0.001) and PNU plus soil mineral N to 30 cm depth at tuber harvest (PNU + SMNh) (r = 0.77, 0.81 and 0.74, respectively; P < 0.001). The supply of N from organic sources to a potato crop can be predicted by PRS-N early in the growing season.