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Composts can be efficient organic amendments in potato culture as they can supply carbon and nutrients to the soil. However, more information is required on the effects of composts on denitrification and nitrous oxide emissions (N2O) and emission-producing denitrifying communities. The effects of three compost amendments (municipal source separated organic waste compost (SSOC), forestry waste mixed with poultry manure compost (FPMC), and forestry residues compost (FRC)) on fungal and bacterial denitrifying communities and activity was examined in an agricultural field cropped to potatoes during the fall, spring, and summer seasons. The denitrification enzyme activity (DEA), N2O emissions, and respiration were measured in parallel. N2O emission rates were greater in FRC-amended soils in the fall and summer, whereas soil respiration was highest in the SSOC-amended soil in the fall. A large number of nirK denitrifying fungal transcripts were detected in the fall, coinciding with compost application, while the greatest nirK bacterial transcripts were measured in the summer when plants were actively growing. Denitrifying community and transcript levels were poor predictors of DEA, N2O emissions, or respiration rates in compost-amended soil. Overall, the sampling date was driving the population and activity levels of the three denitrifying communities under study.

Stagnating potato tuber yields in Prince Edward Island (PEI) are a major economic concern. Identification of factors influencing within-field yield variation may provide insight into strategies for overcoming yield limitations. A survey approach was used where soil samples were collected from 49 commercial fields from 2014 to 2017 from a total of 289 sampling points, with points identified as having either “high” or “low” yield, determined by yield monitor as being 5.6–11.2 t ha−1 above or below average field yield, respectively. A suite of 33 measures of soil physical and chemical properties and soil pathogens were measured. Principal component analysis identified three principal components (PCs) which accounted for 85.6% of the total variation. The PC1 (reflecting 42.3% of the total variance) was associated primarily with soil texture (i.e., sand, clay) and parameters which were highly correlated with soil texture. Under the rainfed potato production on sandy-loam soils in PEI, finer soil texture is likely related to increased yield through its effect on improved soil water holding capacity. The PC2 (reflecting 29.0% of the total variance) was primarily associated with soil fertility and the PC3 (reflecting 14.4% of the total variance) was associated primarily with soil organic matter quality and soil structure. Although soil pathogens were measured at levels high enough to impact yield, they did not differ significantly between high and low yield locations. The findings of this study highlight the value in using multivariate approaches to overcome the challenges in identifying factors which control within-field yield variability.

In humid climates, the risk of nitrate leaching and topsoil loss due to erosion is high on bare soil in the fall after potato (Solanum tuberosum L.) harvest and in the spring with snowmelt. This 2-...

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.

Intensive potato production is an important contributor to groundwater and surface water nitrate contamination in the province of Prince Edward Island (PEI), Canada. In PEI, the presence of a permeability contrast between soil and the underlying compact basal till at approximately 1 m depth is known to cause temporary perched water table conditions, but the implications for agricultural nitrate transport are not well understood. This study is the first detailed field investigation to examine the impact of the soil – compact basal till interface on vertical and lateral subsurface flow of water and solutes on a moderate hillslope in PEI. A surface-applied tracer test was conducted and a shallow drain-tile pipe system, with a tipping bucket gauge, was installed down-gradient of the tracer application to monitor lateral subsurface flow. In addition, three-dimensional electrical resistivity imaging (ERI) was employed to monitor the evolution of the applied tracer plume over a period of 1 year. A small scale, transient flow and transport model was used to simulate the tracer test and to investigate the sensitivity of tracer transport to selected parameters (primarily, the hydraulic conductivities of the soils and underlying compact basal till). Monitoring, conducted from October 2013 to June 2015, and numerical modeling showed a strong tendency for vertical flow of water and tracer through the soil – compact basal till interface as opposed to lateral down-slope subsurface flow. Water balance calculations estimated a total vertical flow of 94.5% of the infiltration for the October 2014 to January 2015 period. The preference for vertical over lateral flow and transport was consistent with electrical resistivity images for the same time period. These findings indicate that the fate of infiltrating water and dissolved nitrate is the deeper bedrock aquifer water table, and that intermittent perched water table conditions do not result in significant lateral flow toward nearby surface waters.

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.

Topography drives spatial variation of soil edaphic factors at the landscape scale however, it is unclear how it influences the spatial distribution of bacterial communities in distances relevant to agro-ecosystem management. This study examined the influence of soil physico-chemical properties and topographic features on bacterial communities and diversity in a commercial potato field with a rolling landform. Eighty-three soil samples were systematically collected across a transect 1100 m long. A significant negative correlation (r = −0.73) between soil pH (range 4.3–7.0) and slope gradient (range 1.8–11.9%) was observed. Regressions and/or a canonical correspondence analysis showed that pH, slope gradient and organic carbon were the major factors influencing bacterial α-diversity based on 16S rRNA gene sequences. Semivariogram analyses revealed that the bacterial α-diversity, the relative abundance of most phyla, pH and slope gradient showed strong to medium spatial autocorrelations with a range between 20.8 and 217.8 m. These results evidenced that soil pH and slope gradient were the major factors explaining variation in the spatial structure of the bacterial community. Our results showed that the soil bacterial communities varied in a systematic and predictable pattern in an agricultural field in response to variation in soil physico-chemical properties and topographic features.

Stagnating potato (Solanum tuberosum L.) yields in eastern Canada have resulted in loss of competitive advantage in global potato markets. Therefore, there is a need to investigate the potential to increase yield by adopting precision agriculture technology. This study evaluated the efficiency of an apparent soil electrical conductivity (ECa) sensor to delineate management zones (MZs) in two commercial potato fields in New Brunswick, Canada, using an unsupervised fuzzy k-means clustering algorithm. Georeferenced soil samples from 0 to 15 cm depth were analyzed for physicochemical properties. Tuber yields were recorded using a yield monitor. The two MZs delineated using soil ECa differed significantly in soil physicochemical properties for both fields; however, tuber yield differed significantly between MZs only in Field 1. The yield difference (7.1 Mg ha−1) in Field 1 was attributed to a difference in soil moisture (23.5% vs 28.5%) resulting from a difference in clay content (141 vs 189 g kg−1). The lack of a yield difference between MZs in Field 2 may reflect relatively low within-field spatial variability. The soil ECa sensor showed promise for use in commercial potato production in New Brunswick, especially in fields with high spatial variability.

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 (

Soil quality has declined with intensive potato production practices in New Brunswick, Canada. Compost application may rapidly increase soil organic matter (SOM) and reverse declining productivity. This study assessed five diverse compost products for their short-term effects on soil quality, and in particular SOM. Selected compost products derived from a range of forestry, marine, and municipal waste materials were compared with a non-amended control. Treatments were applied to field plots at 45 Mg ha–¹ dry weight in October of 2014 and 2015. Biological, chemical and physical soil properties under potato production in 2015 and 2016 (after one and after two consecutive applications) were used to evaluate soil quality. Compost application increased soil pH and concentrations of Mehlich-3 extractable nutrients (K, Ca, Mg, and S). Compost reduced bulk density in the potato hill by 8% in both years. Particulate organic matter (POM) was the most sensitive indicator to compost-application with twofold increases in POM-C. Compost application increased soil organic carbon by 24% in 2016 and also increased permanganate oxidizable carbon, and soil respiration. Several soil properties were strongly correlated with compost composition, with better quality composts (i.e., more mature; greater in C, N, and other plant-available nutrient concentrations) producing the greatest soil quality response. Overall, mature composts with greater C concentrations (i.e., low ash) and greater dry matter were most suitable for enhancing soil quality in New Brunswick potato production systems.

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.

Climate change-related increases in winter temperatures and precipitation, as predicted for eastern Canada, may alter snow cover, with consequences for soil temperature and moisture, nitrogen cycling, and greenhouse gas fluxes. To assess the effects of snow depth in a humid temperate agricultural ecosystem, we conducted a two-year field study with (1) snow removal, (2) passive snow accumulation (via snow fence), and (3) ambient snow treatments. We measured in situ N2O and CO2 fluxes and belowground soil gas concentration, and conducted denitrification and potential nitrification laboratory assays, from November through May. Snow manipulation significantly affected winter N2O dynamics. In the first winter, spring thaw N2O fluxes in snow removal plots were 31 and 48 times greater than from ambient snow and snow accumulation plots respectively. Mid-winter soil N2O concentration was also highest in snow removal plots. These effects may have been due to increased substrate availability due to greater soil frost, along with moderate gas diffusivities facilitating N2O production, in snow removal plots. In the second winter, spring thaw N2O fluxes and soil N2O concentration were greatest for ambient snow plots. Peak fluxes in ambient snow plots were 19 and 24 times greater than in snow accumulation and snow removal plots, respectively. Greater soil moisture in ambient snow plots overwinter could have facilitated denitrification both through decreased O2 availability and increased disruption of soil aggregates during freeze-thaw cycles. Overall, results suggest that effects of changing snow cover on N cycling and N2O fluxes were not solely a direct effect of snow depth; rather, effects were mediated by both soil water content and temperature. Furthermore, the fact that treatments with greatest mid-winter belowground N2O accumulation also had greatest spring thaw N2O fluxes in both years suggests the hypothesis that high spring thaw fluxes were due not only to spring soil conditions, but also to an effect of soil conditions in frozen soils that had facilitated N2O production throughout winter.

Compost application may be an effective means to rapidly increase soil organic matter, soil quality, and soil microbial community diversity in intensive potato crop production systems. This study compared three contrasting compost products with a no compost control on soil chemical properties and soil bacterial and fungal community composition and diversity. The three composts consisted of municipal source separate waste compost (SSOC), forestry and poultry manure compost (FPMC), and forestry residues waste compost (FRC) with low, medium and high forestry waste percentages in their feedstock, respectively. Soil samples were collected on four dates over 11 months after compost application in October 2014. Soil pH, dissolved organic carbon and readily mineralizable C (respiration) were significantly greater in FPMC- and SSOC-treated soils compared to FRC-treated and control soils. Compost application influenced the relative abundances of several bacterial phyla in soils compared to control soils but not the relative abundances of fungal phyla. Several compost-borne bacterial (average of 383 operational taxonomic units (OTUs)) and fungal (average of 66 OTUs) species could be detected in soil throughout the following growing season after compost product application suggesting that these species succeeded in establishing in soils. The β-diversity of bacterial and fungal communities in soils differed significantly among treatments and sampling dates, indicating that the applied composts resulted in a change in the bacterial and fungal community diversity. Convergence of bacterial community diversity was observed among treatments over time but not for fungal community. The application of diverse compost products clearly changed the soil chemical properties which in turn influenced the bacterial and fungal communities. The effects of compost application on microbial communities were persistent, and could still be observed nearly a year after compost was applied.

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.

Past agronomic practices, particularly cropping sequence and the balance between N applications and crop N removal, will influence soil N supply and crop yield potential. Nitrogen (N) fertilizer applications required to optimize crop yield and quality will be a function of the difference between crop N demand and the amount of N supplied by the soil. Therefore, assessment of the effect of past management practices on crop yield potential and soil N dynamics is important to accurately predict crop fertilizer N requirements. Field studies were conducted at seven locations representative of the varying soil types and ecozones across the Canadian prairies to determine the persistence of the effects of legume and non-legume crops and repeated N fertilizer applications on soil N supply and on the yield and N uptake of spring wheat ( Triticum aestivum L.) and canola ( Brassica napus L.) for two seasons after fertilization had ceased, corresponding to the fourth and fifth season after legume crop production. Field pea ( Pisum sativum L.), lentil ( Lens culinaris Medik.), faba bean ( Vicia faba L.), canola and wheat harvested for grain, and faba bean grown as a green manure were direct-seeded in 2009. Canola was seeded in 2010, barley ( Hordeum vulgare L.) in 2011, and canola again in 2012 with fertilizer N applied at 0, 30, 60, 90 and 120 kg ha −1 in each crop. Fertilizer N applications were then halted and spring wheat was grown in 2013 and canola in 2014, without fertilizer N applications. Very few effects of crops grown in 2009 were apparent on soil NO 3 -N supply, crop yield or crop N accumulation by 2013, which was the fourth year after crop growth, and no effects were observed in 2014. In contrast, fertilizer N applied from 2010 to 2012 had persistent effects, increasing soil NO 3 -N concentration, crop yield and crop N accumulation for two growing seasons after fertilization had ceased, although the magnitude of response varied considerably with location. By fall of 2014, effects of preceding fertilizer applications on soil NO 3 -N were no longer significant. Accumulation of N in wheat grain and straw was closely related (R 2 = 0.86) to soil NO 3 -N across locations while the relationship between soil NO 3 -N and N accumulation in canola seed was not as strong (R 2 = 0.60). Therefore, measurement of soil nitrate is a valuable tool for producers in this region to use when selecting fertilizer N application rates, but mineralization of N over the growing season will also contribute to crop N uptake. Residual effects of N fertilization can be substantial under prairie conditions, increasing N supply to crops for up to two years after the final application, and should be taken into account when assessing fertilizer use efficiency and N requirements for crop production.

Raspberry fields in the Pacific Northwest, USA and British Columbia, Canada are often prepared for replanting by fumigating with broad-spectrum biocides to control root-lesion nematodes, Pratylenchus penetrans . Nematode-suppressive organic amendments have been advocated as reduced risk alternatives to fumigation but may pose other risks to the environment. This study compared alternative pre-plant soil management practices with respect to their effects on plant-parasitic nematode populations, soil quality parameters and risk of nitrate leaching. In fall of 2009 and 2010, a mature raspberry field was mowed down and plowed, and replicate plots were randomly allocated to each of six treatments: (1) a non-amended control, (2) fumigation with Basamid ® , (3) fall seeded barley cover crop, (4) recommended rate (20 m 3 ha −1 ) and (5) historical “biofumigant” high rate (250 m 3 ha −1 ) of spring incorporated poultry manure, and (6) spring incorporated compost (250 m 3 ha −1 ). Raspberry cv Saanich was planted approximately one month after incorporation of amendments. Composite soil samples were taken from each plot at multiple times during two subsequent growing seasons and analyzed for nematode populations and soil chemical and physical properties. Primocane biomass was assessed at the end of each of the first two growing seasons as an index of crop vigor. The high poultry manure and compost treatments suppressed root-lesion nematode populations nearly as well as fumigation over two growing seasons. These treatments also improved soil bulk densities and aggregation relative to control, cover crop and fumigation treatments, while compost addition beneficially increased soil pH, CEC and Ca concentrations more than manure. Primocane production in the manure and compost treatments was greater than in the control and cover crop treatments, but less than in the fumigated treatment. Substantial nitrate accumulation in soil amended with the high rate of manure indicated that application of sufficient manure to suppress parasitic nematodes would pose a significant risk of nitrate leaching. In contrast, soil nitrate accumulation was not significantly increased in the compost amended plots. Overall, compost application reduced nematode populations, improved crop growth and did not increase the risk of nitrate leaching in the short term and may be a viable alternative to fumigation.

Denitrification losses from agricultural land have been identified as a significant nitrogen (N) loss pathway that contributes to poor utilization of applied N. Higher losses have been reported when inorganic fertilizer N is substituted with an organic N source such as livestock manure. This research examines the relationships between denitrification rates, land management practices and soil processes when using spring applied liquid dairy manure (LDM) as principal N source. Mean daily denitrification rates (DDRs) in a perennial hayfield (PH) rotation and a corn–soybean–wheat (CSW) rotation with or without tillage (T and NT respectively) ranged between 0.9 and 27.0 g N ha−1 day−1. Mean, seasonal DDRs in the PH rotation were significantly lower in three out of six seasons when compared with the CSW-T and (or) CSW-NT rotation. When averaged across the six season study period, the mean DDR in PH of 4.4 g N ha−1 day−1was also significantly lower than CSW-T and NT (7.6 and 8.1 g N ha−1 day−1, respectively). There were no significant effects of tillage in the CSW rotations in any of the six growing seasons. When treatment and growing season data were combined, a positive relationship between water-filled pore space (WFPS) and DDR indicated a threshold of approximately 40% WFPS for onset of significant denitrification. Similarly, the relationship between soil nitrate levels and denitrification rates in the population data set demonstrated that NO3−began to limit DDR below 2–5 mg N kg−1. This 6-year study of denitrification losses suggests a primary effect of WFPS, a secondary effect of O2consumption as reflected by soil respiration, and nitrate limiting only at relatively low concentrations. Environmental variables were more consistent drivers of denitrification in three manure-fed crop rotations typical of Atlantic Canada dairy operations than were land management decisions and practices.

Management zones (MZs) are delineated areas within an agricultural field with relatively homogenous soil properties, and therefore similar crop fertility requirements. Consequently, such MZs can often be used for site-specific management of crop production inputs. This study evaluated the effectiveness of four classification methods for delineating MZs in an 8-ha commercial potato field located in Prince Edward Island, Canada. The apparent electrical conductivity (ECa) at two depths from a commercial Veris sensor were used to delineate MZs using three classification methods without spatial constraints (i.e., fuzzy k-means, ISODATA and hierarchical) and one with spatial constraints (i.e., spatial segmentation method). Soil samples (0.0–0.15 m depth) from 104 sampling points was used to measure soil physical and chemical properties and their spatial variation in the field were used as reference data to evaluate four delineation methods. Significant Pearson correlations between ECa and soil properties were obtained (0.22 &lt, r &lt, 0.85). The variance reduction indicated that two to three MZs were optimal for representing the field’s spatial variability of soil properties. For two MZs, most soil physical and chemical properties differed significantly between MZs for all four delineation methods. For three MZs, there was greater discrimination among MZs for several soil properties for the spatial segmentation-based method compared with other delineation methods. Moreover, consideration of the spatial coordinates of the data improved the delineation of MZs and thereby increased the number of significant differences among MZs for individual soil properties. Therefore, the spatial segmentation method had the greatest efficiency in delineation of MZs from statistical and agronomic perspectives.

Groundwater NO–N contamination in the Abbotsford-Sumas Aquifer in British Columbia, Canada, has been attributed primarily to NO–N leaching from red raspberry ( L.); however, direct estimates of NO–N leaching are lacking. This study quantified the magnitude and timing of NO–N leaching under a commercial red raspberry field over 30 mo (October 2010–March 2013) using passive capillary wick samplers installed below the root zone at three row locations (irrigated row, nonirrigated row, and alley) after the critical period of field renovation and replanting. Substantial NO–N leaching (240 kg N ha) during the first year of monitoring was attributed to the effects of field renovation (including autumn chopping and incorporation of raspberry canes and soil fumigation and spring poultry broiler manure application) in the year prior to the initiation of monitoring. Lower NO–N leaching (80 kg N ha) occurred in the second year of monitoring under typical mineral fertilizer management practices. Strong seasonality of NO–N leaching was observed in both years, with ∼48% in autumn, 34% in spring and summer, and 17% in winter. Approximately 60% of the NO–N leaching was attributed to the alleys between raspberry rows, which did not receive mineral fertilizer or irrigation. The high proportion of leaching during spring and summer and from the alleys suggests that growing-season irrigation practices and alley vegetation management, respectively, would be good targets for the development of improved practices. The samplers were effective in quantifying the magnitude and timing of NO–N leaching from a commercial agricultural field and informing the development of improved practices.

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 Abbotsford-Sumas Aquifer is arguably the most studied case in Canada of groundwater nitrate contamination associated with agricultural production. Underlying some of the most productive agricultural land in Canada, this highly vulnerable trans-boundary aquifer provides a unique case study on the opportunities and challenges of addressing water quality issues. A groundwater monitoring program initiated in the early 1990s has been important in tracking spatial and temporal variation in groundwater nitrate concentration. However, small land parcels with spatially and temporally variable land use and management practices and sub-horizontal flow in this highly permeable sand and gravel aquifer make it difficult to relate groundwater monitoring results to specific agricultural practices. Other approaches pointed to the historical over-application of N relative to crop requirement (primarily as manure used to increase soil organic matter during replanting but also as a nutrient source during production). Despite changes in agricultural practices, and programs aimed at raising grower awareness, no appreciable change in average groundwater nitrate concentration has occurred over the monitoring period. On individual land parcels, nitrate contamination may be reduced through development and adoption of an integrated suite of beneficial management practices (BMPs) to improve N fertilization, irrigation and alley vegetation management, and in particular to eliminate application of any organic soil amendment such as untreated manure in which the N has not been stabilized (e.g., by composting). However, the substantial N imbalance on a regional scale, and the lack of an effective on-going consultative process among stakeholders, remain major barriers to the development, demonstration and adoption of BMPs.

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.

Precision agriculture (PA) involves more precise seeding, fertilizer application, irrigation, and pesticide use in order to optimize crop production for the purpose of increasing grower revenue and protecting the environment. High-value crops, like potato (Solanum tuberosum L.), are recognized as good candidates for the adoption of PA because of the high cost of inputs. In addition, the sensitivity of potato yield and quality to crop management and environmental conditions makes precision management economically important. The spatial and temporal variability of soil conditions and crop growth are well documented. The PA uses geospatial information and technologies to manage this variability more precisely. Intensive soil sampling techniques, yield monitors, and soil and plant sensors can be used to identify where, when, and how much variability is present in a field. The agronomist’s role is to analyze the within-field variability in order to determine how best to manage it. Two main approaches are available for addressing crop and soil variability: (1) variable rate applications (VRA) and (2) management zones (MZ). Research spanning 15 years has shown that the MZ approach based on a detailed soil survey map (e.g., scale ≤1:10,000), soil property data, or ideally, apparent soil electrical conductivity, was more effective than VRA at managing variability and enhancing potato productivity and profitability while reducing the environmental impacts of agricultural practices.

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.

Summary Sensitivity analysis is a useful tool to identify key model parameters as well as to quantify simulation errors resulting from parameter uncertainty. The Root Zone Water Quality Model (RZWQM) has been subjected to various sensitivity analyses; however, in most of these efforts a local sensitivity analysis method was implemented, the nonlinear response was neglected, and the dependency among parameters was not examined. In this study we employed a comprehensive global sensitivity analysis to quantify the contribution of 70 model input parameters (including 35 hydrological parameters and 35 nitrogen cycle parameters) on the uncertainty of key RZWQM outputs relevant to raspberry row crops in Abbotsford, BC, Canada. Specifically, 9 model outputs that capture various vertical-spatial and temporal domains were investigated. A rank transformation method was used to account for the nonlinear behavior of the model. The variance of the model outputs was decomposed into correlated and uncorrelated partial variances to provide insight into parameter dependency and interaction. The results showed that, in general, the field capacity (soil water content at −33 kPa) in upper 30 cm of the soil horizon had the greatest contribution (>30%) to the estimate of the water flux and evapotranspiration uncertainty. The most influential parameters affecting the simulation of soil nitrate content, mineralization, denitrification, nitrate leaching and plant nitrogen uptake were the transient coefficient of fast to intermediate humus pool, the carbon to nitrogen ratio of the fast humus pool, the organic matter decay rate in fast humus pool, and field capacity. The correlated contribution to the model output uncertainty was

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.

Widespread global changes, including rising atmospheric CO2 concentrations, climate warming and loss of biodiversity, are predicted for this century; all of these will affect terrestrial ecosystem processes like plant litter decomposition. Conversely, increased plant litter decomposition can have potential carbon-cycle feedbacks on atmospheric CO2 levels, climate warming and biodiversity. But predicting litter decomposition is difficult because of many interacting factors related to the chemical, physical and biological properties of soil, as well as to climate and agricultural management practices. We applied 13C-labelled plant litter to soil at ten sites spanning a 3500-km transect across the agricultural regions of Canada and measured its decomposition over five years. Despite large differences in soil type and climatic conditions, we found that the kinetics of litter decomposition were similar once the effect of temperature had been removed, indicating no measurable effect of soil properties. A two-pool exponential decay model expressing undecomposed carbon simply as a function of thermal time accurately described kinetics of decomposition. (R2 = 0.94; RMSE = 0.0508). Soil properties such as texture, cation exchange capacity, pH and moisture, although very different among sites, had minimal discernible influence on decomposition kinetics. Using this kinetic model under different climate change scenarios, we projected that the time required to decompose 50% of the litter (i.e. the labile fractions) would be reduced by 1–4 months, whereas time required to decompose 90% of the litter (including recalcitrant fractions) would be reduced by 1 year in cooler sites to as much as 2 years in warmer sites. These findings confirm quantitatively the sensitivity of litter decomposition to temperature increases and demonstrate how climate change may constrain future soil carbon storage, an effect apparently not influenced by soil properties.

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.

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.

This study evaluated different strategies for use of a simple first-order kinetic model (N min = N 0 [1-e ―kt ] where No is potentially mineralizable N and k is the mineralization rate constant) to predict growing season soil N supply (SNS) in potato (Solanum tuberosum L.) fields under cool humid climatic conditions. Direct application of the kinetic model for the 0- to 15-cm depth significantly underestimated a field-based measure of plant available soil N supply (PASNS). Modeling strategies that considered the soil mineral N (SMN) present at the start of the growing season, or included a pool of labile mineralizable N (Pool I) not normally considered in determination of N 0 , performed better, but still underestimated high values of PASNS. Strategies which included a greater soil depth (0-30 cm), or which assumed that the mineralizable N pool was replenished during the growing season, overestimated PASNS. A strategy which used a higher value of k for Pool I gave the most promising results. Results of this study highlight the importance of considering both SMN and labile mineralizable N pools in predicting SNS, and suggest that it is possible to estimate growing season SNS in humid regions using simple kinetic models.

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.

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.