Soil bacterial communities are vital for ecosystem functioning in the humid tropics, yet their response to land-use change remains poorly understood. This knowledge gap is exacerbated by the lack of long-term studies. We employed a space-for-time substitution approach to assess the effects of land-use intensification on soil bacterial communities across a gradient of anthropogenic disturbance in Trinidad. Three sub-watersheds (Arouca = pristine, Maracas = intermediate, Tacarigua = intensive) were selected, each containing adjacent forest, grassland, and agricultural land uses. We combined geophysical soil apparent electrical conductivity (ECa-directed) sampling with 16S rDNA gene amplicon sequencing to characterize bacterial communities and their relationships with soil and landscape properties. Soil properties were the primary determinant of bacterial community structure, explaining 56% of the variation (p < 0.001), with pH, clay content, hygroscopic water, and nutrient availability as key drivers. Bacterial α-diversity differed significantly among sub-watersheds (p < 0.01), with Tacarigua exhibiting lower richness and diversity compared to Arouca and Maracas, but not across land uses. While a core microbiome of ten bacterial families was ubiquitous across land uses, indicating a stable foundational community, land-use intensification significantly altered β-diversity (p < 0.01 among sub-watersheds). Agricultural soils showed the greatest divergence from forest soils (p < 0.05), with a marked decline in key Proteobacterial families (e.g., Xanthomonadaceae, Pseudomonadaceae) involved in nutrient cycling and plant growth promotion. Although inherent soil properties shape the core microbiome, land-use intensification acts as a strong secondary filter, shifting soil bacterial communities toward more stress-resistant Firmicutes with potentially less diverse functions. Our findings demonstrate the utility of integrating space-for-time substitution with molecular profiling to predict long-term microbial responses to environmental change in vulnerable tropical ecosystems.

The factors influencing the spatial distribution of fungal communities are commonly examined over large spatial scales but not at smaller scales. Given this, the extent to which soil properties and topographic features contribute to the diversity and distribution of fungal communities in an agricultural field needs to be further explored. We investigated the spatial distribution of soil fungal community composition from an similar to 1100 m long transect with 83 sampling points in a commercial potato field with a rolling landform. The relative abundance of Ascomycota, Basidiomycota, and Mortierellomycota showed medium to strong spatial dependence with an autocorrelation range varying from similar to 43 to 92 m, similar to the autocorrelation range of soil properties and topographic features. Most of the variability in fungal and saprotrophic community composition was explained by soil properties (15% and 11%, respectively) and spatial distance (16% and 15%, respectively) while topographic features contributed 8% and 5% of variability to total fungi and saprotrophic community composition, respectively. The fungal and saprotrophic community compositions were correlated with soil organic carbon, pH, and slope curvature, however, richness and Pielou's evenness of the fungal communities and fungal biomass were not correlated with soil properties or topographic features. The results suggest that the spatial variation in fungal and saprotrophic community composition in response to soil properties and topographic features in this agricultural landscape was due to differences in assemblages of fungal amplicon sequence variants (ASVs) but not in differences in the number of fungal ASVs or fungal biomass measured using phospholipids fatty acids.

Climate change-related warming and increased precipitation may alter winter snow cover and thawing events, and therefore, may carry significant consequences for nitrous oxide (N2O) production pathways such as denitrification, and the abundance and expression of denitrifying microorganisms. We used a soil microcosm study to investigate the combined effect of soil thaw temperature, initial water filled pore space (WFPS) prior to soil freezing, and snowmelt infiltration simulated by the addition of water on N2O emission and denitrification rates, soil respiration rate, and the abundance and transcription of denitrifying (nirK, nirS, and nosZ) bacteria during a single freeze-thaw event. Soil respiration rate was primarily controlled by an increase in soil thaw temperature, whereas soil N2O emission and denitrification rates were generally greater in soils with a higher initial WFPS and soil thaw temperature. In contrast, snowmelt infiltration generally had a negligible effect on these rates, which may be related to pre-existing soil conditions that were already conducive to denitrification. Unexpectedly, the nosZ transcript/nosZ gene abundance ratio was lower in soils thawed at 8.0 °C compared to 1.5 °C; however, this may have resulted in a lower N2O reduction, thus explaining the greater levels of N2O emitted from soils thawed at 8.0 °C. Overall, this study demonstrated that increased N2O production during a single freeze-thaw event was primarily linked to antecedent conditions of high initial WFPS, soil thaw temperature, and a synergistic interplay between these two environmental parameters, and provides evidence that an increase in annual temperature and precipitation, along with the timing of precipitation, may further stimulate N2O production pathways.

The Root Zone Water Quality Model (RZWQM) is a one-dimensional process-based model used for simulating major physical, chemical, and biological processes in agricultural systems. To date, the model has not been applied to potato production systems for simulating nitrate leaching. In this study, 35 datasets collected between 2009 and 2016 at a field under a three-year potato (potato–barley–red clover) rotation in Prince Edward Island (PEI), Canada, have been employed for calibrating and validating the water, nitrogen (N) cycling, and plant growth routines of RZWQM and for subsequently estimating nitrate leaching. The model fitness, evaluated using univariate and bivariate indicators, was rated as high for most of the parameters tested. As a result of the combined influence of higher infiltration and reduced plant uptake, the model showed that the highest leaching at the rotation level occurred between September and December. A secondary leaching period occurred in spring, when residual soil nitrate was mobilized by increased percolation due to snowmelt. Most of the nitrate leaching occurred during the potato year (89.9 kg NO3–N ha−1 y−1), while leaching for barley and red clover years had comparable values (28.6 and 29.7 kg NO3–N ha−1 y−1, respectively). The low N use efficiency of the entire rotation (i.e., 30.2%), combined with the high NO3–N concentration in leachate (i.e., 34.9 mg NO3–N L−1 for potato and 16.3 mg NO3–N L−1 for the complete rotation), suggest that significant efforts are required for adapting management practices to ensure sustainability of potato production systems.

A survey of New Brunswick (NB) and Prince Edward Island (PEI) potato fields in crop rotation phase prior to potato production was conducted in fall (October and November) between 2017 and 2021. A total of 113 and 126 fields for NB and PEI, respectively, were surveyed with 20 to 35 fields each year tested in each province. Root lesion nematodes (RLN, Pratylenchus spp.) were detected in 99 and 98% of the fields for NB and PEI, respectively, and two root lesion nematode species, P. crenatus and P. penetrans, were identified in both provinces from 2017 to 2021. Based on 2019 and 2020 results, all surveyed fields in NB and PEI were detected with P. crenatus, while only 29 and 43% of the fields in NB and PEI were detected with P. penetrans, respectively. P. crenatus accounted for 96 and 89% of the populations for NB and PEI, respectively, while P. penetrans accounted for 4 and 11% in commercial fields, respectively. In a single in-depth sampled experimental field with a history of severe potato early dying complex in 2018 in NB, P. crenatus accounted for 88% and P. penetrans was 12%. Verticillium dahliae was detected in 94 and 92% of potato fields in NB and PEI, respectively. All isolates obtained from potato cv. "Russet Burbank" in a baiting trial were V. dahliae, belonging to two lineages. V. albo-atrum was detected in a few fields at very low level, except two fields in NB where V. albo-atrum was predominating over V. dahliae. Rotation crops did not affect V. dahliae population densities for NB and PEI, and did not affect RLN population in NB, but significantly affected RLN in PEI. Fall green cover crop did not affect the populations of RLN and V. dahliae in PEI. The present study revealed that the potato pathogenic root lesion nematode P. penetrans was present in less than 50% of surveyed fields and accounted for around 10% of root lesion nematode population in NB and PEI, and V. dahliae was the dominant species and was present in greater than 90% of surveyed fields in both provinces.

Chemical fumigation is used to reduce soil-borne diseases in agricultural production systems; however, non -targeted soil microorganisms may also be affected. This study investigated the effects of chemical fumigation and substrate carbon (C) availability on the soil bacterial and fungal community diversity under controlled conditions over 128 days. This study consisted of a 3 x 3 factorial arrangement of three fumigant treatments (fumigation with chloropicrin [CP], metam sodium [MS], or no fumigation) and three soil amendment treat-ments (amendment with young barley, mature barley, or no amendment). MS fumigation transiently decreased bacterial species evenness when combined with young barley residues; however, it did not affect fungal diversity indices. CP fumigation, regardless of soil amendment or substrate C availability, decreased bacterial species evenness and richness that did not recover over time. However, CP fumigation only decreased fungal species evenness and richness when combined with young or mature barley residues. Although all treatments resulted in a bacterial and fungal community that was significantly dissimilar to the non-fumigated unamended soil, CP fumigated soils had the most dissimilar bacterial and fungal 0-diversity after 128 days. This study demonstrated that the addition of young or mature barley residues to chemically fumigated soil did not recover microbial diversity. Instead, the addition of plant residues to chemically fumigated soil had a greater impact on microbial diversity and community composition compared to chemical fumigation used alone, subsequently promoting a less diverse and selective community for both fumigation and organic C additions.

To balance economic potato production with environmental risks, it is crucial to understand the effects of forage crops preceding potatoes on soil nitrate (NO3-) leaching potential, soil quality and potato yield. This study compared a legume forage (red clover, RC), a grass forage (timothy, T), and a red clover-timothy mixture (M) over two cycles of a 3-yr rotation (barley underseeded with forage-forage-potato) from 2013 to 2018. The forage crops were grown under low input maintenance system receiving only starter N fertilizer during the establishment year. Legume-based forages (i.e., RC and M) had greater dry matter accumulation and lower C:N ratio, and therefore added a greater quantity and quality of organic matter inputs to the soil compared with the grass-based forage (T). This resulted in increased soil N supply to the subsequent potato crop, and improved soil quality as indicated by increased aggregate stability, permanganate oxidizable carbon (POX-C), autoclaved citrate extractable soil protein (ACE), and flush of CO2 upon rewetting a dried soil for legume- than grass-based forages. Under N limited conditions (i.e., no N fertilizer applied) forage legumes were associated with higher potato yield than forage grass. However, tuber yield was not increased when N fertilizer was applied, a finding attributed to a better synchrony between potato N uptake and soil N supply in the presence of N fertilizer with the forage grass treatment. The legume-based forages improved soil quality, increased soil N supply as well as NO3- leaching losses. Results of this study suggest that there may be a trade-off between selecting forage crops to reduce NO3- leaching and to enhance soil quality.

An improved understanding of the contribution of a preceding forage crop to a subsequent potato crop can improve nitrogen (N) utilization in potato production. This study used two rotation experiments to estimate the N contribution from labelled shoot and root of red clover (RC, Trifolium pratense ), timothy (T, Phleum pratense ) and a red clover/timothy mixture (M) to a subsequent potato crop using microplots in the field. Forage crops were grown with 14 NH 4 14 NO 3 and 15 NH 4 15 NO 3 (98 atom %). The residue exchange technique was used to compare residue treatments of (i) whole plant labelled; (ii) labelled shoot only; and (iii) labelled root only in Experiment 1, and residue treatments of (i) whole plant labelled; (ii) labelled shoot/unlabelled root; and (iii) labelled root/unlabelled shoot in Experiment 2. Averaged across forage treatments, recoverable root biomass represented 64 and 37% of total forage biomass, and the total 15 N recovery from labelled roots was 52 and 62% of the total 15 N recovery from shoots, in Experiments 1 and 2, respectively. Therefore, forage roots represented a substantial source of N for the subsequent crop. However, less than 5% of the 15 N from crop residues was recovered in the potato vines plus tubers, and most of the 15 N was recovered in the soil, regardless of the forage or residue treatments. Potato tuber and vine dry matter was greater for the RC than the T treatment for all residue treatments, a finding attributed to greater potato N accumulation for the RC treatment. It is therefore important to consider the contribution of forage roots when studying N cycling in potato systems. Potato N requirements were satisfied more by soil-derived N rather than from fall incorporated forage residues.

As the climate changes, water scarcity is becoming a major global concern. The accurate prediction of soil depth is critical for hydrological modeling under different climate change scenarios for the effective management of humid tropical watersheds. This study determined the best-fit assumption-based (i.e., ordinary least square (OLS)) and assumption-relaxed (partial least squared, quantile, and elastic net) regression models, and compared them with geospatial models (ordinary kriging, universal kriging, regression kriging, and cokriging), for pre-dicting soil depth in a 50 x 150 m humid tropical watershed. Soil depth, apparent electrical soil conductivity (ECa) at two depths of exploration (ECas, 0-0.5 m, and ECad, 0-1.6 m using a DUALEM-1S EC meter), slope gradient, and soil physical and chemical properties measured in-field or using soil samples (0-0.2 m), were determined at each sampling location. Multivariate regression models explained 86-89% of the variability in soil depth and had a comparative root mean square error (RMSE), Lin's concordance correlation coefficient (LCCC), ratio of performance to deviation (RPD), and prediction error rate (PER) to corresponding ECad univariate models. ECad was a significant predictor in all models except the elastic net regression model. The cokriging model was superior to all regression and geospatial models with the lowest RMSE (0.04) and PER (10 %), and highest LCCC (0.99) and RPD (6.71), and can be used to accurately predict soil depth across the watershed, thereby improving hydrological models for watershed management in this and similar vulnerable humid tropical watersheds. Most interestingly, our results suggest that OLS models are in some cases robust enough to handle violations of their assumptions, implying that data transformation may not always be required for OLS regres-sion. Therefore, it is recommended that the traditional workflow for OLS regression include a validation check using an assumption-relaxed model, the outcome of which would determine the necessity of data transformation.

Spatiotemporal patterns of edaphic properties can be useful in modeling underlying mechanisms and controls of watershed processes, however, few studies have quantified the spatial variability of soils in watersheds in the humid tropics. A multivariate geostatistical approach was used to examine the relationships between soil apparent electrical conductivity (ECa) and measured soil and landform parameters, as well as to assess the temporal and spatial stability of ECa in a 50 x 150 m sub-watershed with three distinct land uses (forest, savannah grassland, and cultivation) in the Northern Range of Trinidad. Soil samples (0-0.2 m), and ECa measured at shallow (0 - 0.5 m; ECas) and deep (0 - 1.6 m; ECad) depths of exploration using a DUALEM-1S EC meter, were taken approximately 4 m apart along a 120 m transect in the toposequence. Although ECa and soil properties (e.g., soil depth and texture) differed among the steeply sloping forest, gently sloping savannah grassland, and flat cultivated area, there was no evidence of an effect of land use on soil properties other than what could be explained by the slope gradient. Sixty-one percent of the variability in ECas was explained by soil depth and water-stable aggregates whereas, 87% of the variation in ECad was explained by soil depth, clay content, and soil pH. Soil depth explained the greatest proportion of the variability in ECa in both models. Additionally, repeated ECa mappings revealed that ECas and ECad were spatiotemporally stable. Thus, ECad which is strongly influenced by the underlying bedrock can be used to model the spatial variability in soil depth, whereas ECas may be better for predicting surface soil properties. Models developed using this approach can predict field-scale variations of soil depth, thereby improving the accuracy of hydro-ecological models.

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.

Biofumigation has been proposed as an alternative to soil fumigation to manage soil-borne diseases including potato early dying disease complex (PED). This study examined the potential of using brown mustard (Mustard juncea) biofumigation to manage PED under rain-fed potato production in New Brunswick, Canada in two trials between 2017 and 2020 in comparison with chloropicrin fumigation and a conventional barley rotation. Biofumigation increased yield in one trial, but not in a second trial where the potato crop experienced severe drought, whereas chloropicrin fumigation increased yield in both trials. Biofumigation was effective in suppressing root-lesion nematode (RLN, Pratylenchus spp.) counts in both trials, but was ineffective in suppressing V. dahliae population density. Chloropicrin fumigation was effective in suppressing RLN counts and V. dahliae population density only in the hill where injected, but the effect was short-lived as the population density of V. dahliae in the hill increased to the level of the control in one potato growing season. Biofumigation may be an alternative to chloropicrin fumigation in managing PED, particularly in fields with high RLN population but relatively low Verticillium population density. However, neither biofumigation nor fumigation used alone may be sustainable in the short-term potato rotations commonly used in New Brunswick, and additional beneficial practices are required to sustain productivity in the long-term.

Reduced within-field potato (Solanum tuberosum L.) yield variation may lead to increased productivity and reduced environmental impact. Using soil samples collected from 88 site-years in commercial fields in New Brunswick, Canada from 2013-2017, this study examined how within-field variation in potato tuber yield was related to soil properties and topographic features. At each of 774 sampling locations, a wide range of soil physical and chemical properties was measured in the lab and topographic features were assessed using a regional digital elevation model. Principal component (PC) analysis identified three PCs, which accounted for 79.1% of the total variation. The PC1 (41.3% of total variance) was dominated by soil texture (i.e., sand, silt) and the quantity and quality of soil organic matter (i.e., soil organic C, particulate organic matter C, and soil C/N ratio). Under rain-fed potato production in New Brunswick, finer soil texture and increased soil organic matter pools are expected to enhance soil water availability and thereby improve yield. The PC2 (22.7% of total variance) was related primarily to parameters associated with soil fertility, and PC3 (15.1% of total variance) was related primarily with concave or convex landforms, which may influence yield through drought or excess water. This study demonstrated the value in using multivariate approaches to identify the factors that control within-field yield variability in the presence of significant regional variation in soil properties and environmental conditions. The findings point to the value of enhancing the quantity and quality of soil organic matter as a key strategy to overcome yield limitations under rain-fed production.

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 FRCtreated 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 beta-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.

The global increase in potato production and yield is expected to lead to increased irrigation needs and this has prompted concerns with respect to the sustainability of irrigation water sources, such as groundwater. The magnitude, and inter- and intra-annual variation, of the crop water requirements and irrigation needs for potato production together with their impact on aquifer storage in a temperate humid region (Prince Edward Island, Canada) were estimated by using long-term (i.e., 2010–2019) daily soil water content (SWC). The amount of supplemental irrigation required for the minimal irrigation scenario (SWC = 70% of field capacity; 0.7 FC) was relatively small (i.e., 17.0 mm); however, this increased significantly, to 85.2 and 189.6 mm, for the moderate (SWC = 0.8 FC) and extensive (SWC = 0.9 FC) irrigation scenarios, respectively. The water supply requirement for the growing season (GS) increased to 154.9 and 344.7 mm for a moderately efficient irrigation system (55% efficiency) for the SWC = 0.8 FC and SWC = 0.9 FC irrigation scenarios, respectively. Depending on the efficiency and the areal extent of the irrigation system, the irrigation water supply requirement can approach or exceed both the GS and annual groundwater recharge. The methodology developed in this research has been translated into a free online tool (SWIB—Soil Water Stress, Irrigation Requirement and Water Balance), which can be applied to other areas or crops where an estimation of soil water deficit and irrigation requirement is sought.

Chemical fumigation and biofumigation are used to reduce soil-borne diseases in agricultural production systems; however, non-targeted soil microorganisms may also be affected. This study compared the effects of chemical fumigation, either used alone or combined with an organic amendment, and biofumigation on soil bacterial community diversity and composition under controlled conditions over 160 days. Treatments included: fumigation with chloropicrin (CP), fumigation with metam sodium used alone (MS) or combined with barley plant residues (MSBR); biofumigation with mustard plant residues; addition of barley plant residues; and untreated control. Biofumigation had a greater impact on bacterial diversity at early time points, transiently decreasing species evenness and yielding the most dissimilar β-diversity after 3 days. MS fumigation did not affect bacterial diversity indices; however, MSBR transiently decreased species evenness after 8 days. CP-treated soil had decreased species evenness that did not recover over time and had the most dissimilar β-diversity at the end of the incubation compared to all other treatments. This study demonstrated that CP fumigation had the greatest and most persistent impact on bacterial diversity, whereas MS fumigation and biofumigation led to transient decreases in bacterial diversity.

Chemical fumigation is used to reduce soil-borne diseases in agricultural production systems; however, soil carbon (C) and nitrogen (N) dynamics may also be affected. This study investigated the effects of chemical fumigation and substrate C availability on soil respiration, soil nitrous oxide (N2O) production, and soil inorganic N concentrations under controlled conditions over 128 days. This study consisted of a 3 x 3 factorial arrangement of three fumigant treatments (fumigation with chloropicrin, metam sodium, or no fumigation) and three soil amendment treatments (amendment with young barley, mature barley, or no amendment). In soils amended with young barley, chemical fumigation delayed the maximum rate of soil respiration and N2O production by five days compared to the amended non-fumigated soil. Additionally, chloropicrin fumigation decreased cumulative soil respiration in amended soils, regardless of substrate C availability, compared to non-fumigated soil. Chemical fumigation used alone or combined with young barley amendments significantly inhibited nitrification compared to non-fumigated soil, whereas amendment with mature barley resulted in N immobilization, regardless of chemical fumigation. This study demonstrated that chemical fumigation significantly affected soil C and N dynamics in soils amended with high and low available C substrates, indicating decreased microbial activity and significant implications for soil function.

There is a need to improve raspberry crop nitrogen (N) management practices, particularly when grown over aquifers vulnerable to nitrate (NO3) leaching. This study quantified the effects of N, irrigation and alley management strategies on berry yield, indices of crop vigor and N status, growing season soil N dynamics, and root-lesion nematode (RLN) population dynamics under red raspberry production in British Columbia, Canada. Conventional management (100 kg N ha(-1) surface broadcast on the row, clean cultivation of alleys, and drip irrigation for a fixed duration regardless of evapotranspiration [ET]) was compared with different mineral fertilizer N rates, application of N as manure, seeding the alley to either a perennial forage grass (perennial ryegrass [Lolium perenne L.] and 'Bridgeport II' chewings fescue [Festuca rubra subsp. commutate]) or an autumn-seeded spring barley crop, or ET-scheduled irrigation. In addition, the combination of ET-scheduled irrigation plus fertigation of a reduced rate of N was compared with conventional practices at a reduced N rate. There was little or no crop response to N source and rate, a finding attributed primarily to high nonmanaged N inputs, and possibly also to RLNs present at population densities (grand mean = 4 per cm(3) soil) expected to suppress raspberry growth. ET-scheduled irrigation reduced water use similar to 50% compared with fixed-duration irrigation without compromising crop performance. The perennial forage grass in the alley reduced soil mineral N but not yield. Taken together, these findings demonstrate that more environmentally sustainable raspberry production can be achieved through integrated management systems even in soils vulnerable to NO3 leaching.

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.

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.