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Potato (Solanum tuberosum L.) production on sandy soils requires added N. Only 40–60% of the applied N is acquired by the crop. Increased N use efficiency (NUE) and its components, N utilization efficiency (NUtE) and N uptake efficiency (NUpE), could reduce fertilizer rates and environmental losses. We compared N efficiency in fresh‐market red potato varieties, in terms of yield and quality traits, and examined potential mechanisms for that efficiency including uptake, utilization, and increased root growth. We grew selections from a red potato breeding population and commercial varieties under two N rates: 101 and 202 kg N ha−1. We compared NUE, NUpE, and NUtE in low and high N. We compared root phenotypes at tuber initiation and yield and skin quality metrics at harvest. Values for NUtE correlated with NUE and yield in low N and NUpE correlated with NUE and yield in high N. Low‐N conditions produced smaller tubers, while high N resulted primarily in medium tubers. Nitrogen did not affect skinning and redness but low N did result in slightly lighter skin color. Total root mass 45 d after planting (DAP) correlated with final yield and NUE but did not correlate with measures of N uptake across treatments. Larger roots correlated with NUpE only in the high‐N treatment. Selection under low N may reveal NUE and expose more stable representations of the genetic components of skin quality phenotypes. While skinning and skin color were more variable among varieties in low N, within variety they exhibited year‐to‐year consistency. [ABSTRACT FROM AUTHOR]

• The nitrification inhibitors DCD and DMPP were effective in mitigating N 2 O emissions from urea applied to potato cultivated on sandy soil. • The biostimulant containing N-fixing microorganisms increased nitrate leaching one growing season and N 2 O emissions over both seasons. • Nitrification inhibitors and biostimulants had modest agronomic benefits due to adequate available N for potato production. • Further studies should assess biostimulants performance and investigate their effects on biological processes in other agro-ecosystems. Urea is the dominant form of nitrogen (N) fertilizer used globally. Various additives have been designed for co-application with urea to improve performance of N-intensive crops including potato (Solanum tuberosum L.). Few if any studies have compared 'inhibitor' additives with 'biostimulants' designed to enhance plant growth or microbial activity. Over two potato growing seasons (2015–2016) in an irrigated loamy sand in Minnesota, we quantified agronomic performance and N losses as both nitrate (NO 3 −) and nitrous oxide (N 2 O) in treatments receiving urea, with and without additives including: nitrification inhibitors dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP), alone or combined with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), or a biostimulant containing N-fixing microbes (NFM) by itself or combined with an amino acid blend (AAB). The biostimulants produced modest (˜10%) improvements in tuber yield, under limited conditions, compared to urea alone. However, NFM increased N 2 O emissions by 32–56%, in contrast to the inhibitors, which decreased N 2 O emissions by 42–75%. Compared to urea alone, the inhibitors tended to increase soil ammonium and decrease soil NO 3 − concentrations; however, no differences in soil inorganic N in the upper 0.3 m of the profile were observed with the biostimulants. During the growing season with greater rates of soil water flux (2015), none of the inhibitors decreased NO 3 − leaching, while NFM increased NO 3 − leaching by 23%. When AAB was combined with NFM, reactive N losses did not differ from the urea-only treatment. Biostimulants can have unintended impacts on reactive N losses and should be used with caution pending additional study to better understand their effects on biological processes, and to quantify their performance in other agro-ecosystems. [ABSTRACT FROM AUTHOR]

Availability of soil moisture and N are primary limiting factors for potato growth on sandy soils in humid climates. This study was conducted to determine whether tuber yield or net economic return were affected by variable rate (VR) N or reduced irrigation management, and to evaluate methods to detect crop N status including remote sensing, chlorophyll meter, and petiole sampling. The effects of six N rate, source, and timing treatments and two irrigation rate treatments on tuber yield, quality, and net profitability for potato [Solanum tuberosum (L.) 'Russet Burbank'] were investigated in 2016 and 2017 at Becker, MN, on a Hubbard loamy sand. A VR N treatment based on the N sufficiency index (NSI) approach using remote sensing was also tested. Irrigation treatments included a conventional rate (100%) and a reduced rate (85%). The VR treatment reduced N applied relative to the recommended rate by 22 and 44 kg N ha-1 in 2016 and 2017, respectively. Irrigation rate was reduced by 29 and 33 mm in 2016 and 2017, respectively. Neither VR N nor reduced irrigation produced significant differences in tuber yield or net return compared to full rate treatments. Using NSI, remote sensing was able to predict crop N status with comparable accuracy to petiole sampling while chlorophyll meter measurements were less sensitive to detecting crop N stress. Managing N using remote sensing and reducing irrigation rate are strategies that could be used on sandy soils in humid climates without having agronomic or economic impacts on potato production. [ABSTRACT FROM AUTHOR]

New cultivars 'Alpine Russet', 'Dakota Trailblazer' and 'Ivory Crisp' have lower tuber reducing sugars and acrylamide-forming potential. Adoption of new cultivars by growers requires information about their responses to agronomic factors such as nitrogen (N) fertilizer. The objective of this study was to determine the effect of N rate on yield and quality of new cultivars relative to conventional cultivars 'Russet Burbank' and 'Snowden'. The experiment was conducted over two years as a randomized complete block design replicated four times with five N rates and five cultivars. The new cultivars had comparable or higher marketable yields, and a higher percentage of large tubers (greater than170 g) than the standard cultivars. Total and marketable yields responded quadratically to N and optimized at 231 kg ha in 2011 and 319 kg ha in 2012 for all cultivars. 'Dakota Trailblazer' had high hollow heart incidence (greater than 10% at N rates above 125 kg ha), and excessively high specific gravity, making it undesirable for processing but with potential to be a parent in a breeding program. 'Alpine Russet' and 'Ivory Crisp' had specific gravity suitable for commercial processing, and low hollow heart incidence at all N rates. Critical petiole nitrate-N concentrations 50 and 70 days after planting for all cultivars were greater in 2012 than in 2011, suggesting that interpretation of critical values can be affected by growing conditions. [ABSTRACT FROM AUTHOR]

Management of fertilizer phosphorus (P) is a critical component of potato production systems as potato has a relatively high P requirement and inefficiently uses soil P. Phosphorus promotes rapid canopy development, root cell division, tuber set, and starch synthesis. Adequate P is essential for optimizing tuber yield, solids content, nutritional quality, and resistance to some diseases. Although soil test P is the primary tool for assessing P fertilizer needs, in some areas petiole P analysis has been successfully utilized to guide in-season P applications. Potato has been shown in some studies to respond to fertilizer P at soil test levels considered very high for most other crops (100+ mg kg Bray P or Mehlich I or III and 20+ mg kg sodium bicarbonate) especially on medium- to finer-textured soils. Even on high-testing soils, fertilizer P rates for top yields sometimes exceed 150 kg PO ha. In addition, many states/provinces continue to recommend half or more of the amount of P in the harvested portion of the crop irrespective of soil test P level. In most situations, few differences are expected among fertilizer P sources; however, high rates of diammonium phosphate (DAP) or urea-phosphate (UAP) should not be band-applied in contact or near the seed piece. Most research determined that fertilizer P was most efficiently used when band-applied at planting (e.g., 5 cm to each side of the seed piece); however, some western USA work on high-pH soils showed increased yields and petiole P levels with preplant broadcast applications. In-season applications with the irrigation water can be successful when the potato roots are sufficiently close to the soil surface; however, most research indicates that P applications are more effective when applied at planting or early in the season. Potato fertilizer phosphorus best management practices include: (1) apply the fertilizer P rate calibrated for local soils; (2) band-apply fertilizer P at least 5 cm from the seed piece, especially on very sandy soils or where DAP or UAP are used; (3) use petiole P tests to determine the need for in-season applications; (4) account for all P sources applied, including animal manures; and (5) utilize the best soil conservation practices to reduce P losses to surface waters. [ABSTRACT FROM AUTHOR]

The nitrogen sufficiency index (NSI) can be used for in-season variable rate management of nitrogen (N) fertilizer to maintain productivity of potato ( Solanum tuberosum, L.) while reducing leaching losses. The objective of this study was to evaluate the implications of using high spatial resolution broad-band imagery for determining N prescriptions at different growth stages. Aerial images were obtained for research plots, as well as for a commercial potato field (59 ha) near Becker, Minnesota on 30, 56 and 79 days after emergence (DAE) with a Redlake MS4100 multispectral camera. In research plots, experimental treatments included five N treatments with varying rates and timing of N fertilizer, and two potato varieties, Russet Burbank and Alpine Russet. Spectral indices investigated in this study adequately predicted N stress based on leaf N concentration ( r values within dates ranged from 0.49 to 0.82). On 56 and 79 DAE, the Green Ratio Vegetation Index (GRVI) normalized by an NSI that used the recommended rate and timing from the research plots as a reference showed that most areas of the commercial field did not require supplemental N fertilizer (using an NSI over-sufficiency threshold of 120 %). Based on regional guidelines, N was over-applied to the commercial field, but in situations where N is applied more sparingly, a GRVI NSI threshold of 80 % should be used to identify areas that are most suitable for supplemental N fertilizer. A practical approach and the implications associated with using spectral data for in-season N management are proposed. [ABSTRACT FROM AUTHOR]

The article presents a study on the effects of nitrate leaching and indirect nitrous oxide emissions in irrigated potato production on fertilizer management. Potato is a nitrogen (N)-intensive crop with high potential for nitrate leaching contributing to water contamination and indirect nitrous oxide emissions. Approaches considered for the reduction of N losses include conventional split application (CSA) of soluble fertilizers and polymer-coated urea (PCU). The study compares leaching using CSA and two PCUs to demonstrate how more robust models are needed in accounting off-site conversion of nitrous oxide because emission factor models have higher degree of uncertainty.

Potato (Solanum tuberosum L.) is the fourth most important food crop in the world after corn, wheat, and rice. It is adapted to a wide range of growing conditions, producing high yields with a near-optimum balance of nutrients for human consumption. China is the world's largest potato producer and continues to account for a large part of the global increase in potato production. Although the potato can be highly productive, it has a relatively shallow root system and often requires significant nutrient inputs to maintain tuber productivity and quality. Each metric ton of tubers removes approximately 3.8 kg nitrogen (N), 0.6 kg phosphorus (P), and 4.4 kg potassium (K). Proper nutrient management, therefore, is extremely important for sustaining high tuber yield and quality. Lack of adequate balanced fertilization in China is reportedly a yield-limiting factor in some areas. For example, potassium (K) is very important for producing a potato crop with high tuber yield and quality. Limited K resources in China and continued cropping have resulted in below-adequate levels of soil K in many regions of the country, which will impact potato production. On the other hand, based on U.S. experience, the high nutrient demand by potato, application of high rates of fertilizer, and production on coarser textured soils can result in nutrient losses. Nutrient best-management practices are developed with the objective of optimizing production, net returns, and minimizing environmental degradation. In general, optimal N management has had the most important impact on tuber yield and quality compared with the other essential elements. Best management practices for N fertilization include appropriate selection of rate, source, timing, and method of application. Optimal management of irrigation is also important to improve N-uptake efficiency and minimize N losses while maintaining high yields and quality. Phosphorus is another key nutrient important from both production and environmental standpoints. Adequate P is required for optimum tuber-set, while excessive rates may result in soil-P buildup and potential runoff problems. This review will focus on various management techniques to maximize nutrient-uptake efficiency by potatoes. [ABSTRACT FROM AUTHOR]

Irrigated potato (Solanum tuberosum L.) production requires large inputs of N, and therefore has high potential for N loss including emissions of N2O. Two strategies for reducing N loss include split applications of conventional fertilizers, and single applications of polymer-coated urea (PCU), both of which aim to better match the timing of N availability with plant demand. The objective of this 3-yr study was to compare N2O emissions and potato yields following a conventional split application (CSA) using multiple additions of soluble fertilizers with single preplant applications of two different PCUs (PCU-1 and PCU-2) in a loamy sand in Minnesota. Each treatment received 270 kg of fertilizer N ha-1 per season. An unfertilized control treatment was included in 2 of 3 yr. Tuber yields did not vary among fertilizer treatments, but N2O emissions were significantly higher with CSA than PCU-1. During 3 consecutive yr, mean growing season emissions were 1.36, 0.83, and 1.13 kg N2O-N ha-1 with CSA, PCU-1, and PCU-2, respectively, compared with emissions of 0.79 and 0.42 kg N2O-N ha-1 in the control. The PCU-1 released N more slowly during in situ incubation than PCU-2, although differences in N2O emitted by the two PCUs were not generally significant. Fertilizer-induced emissions were relatively low, ranging from 0.10 to 0.15% of applied N with PCU-1 up to 0.25 to 0.49% with CSA. These results show that N application strategies utilizing PCUs can maintain yields, reduce costs associated with split applications, and also reduce N2O emissions. [ABSTRACT FROM AUTHOR]

The article presents a study on the impact of polymer-coated urea (PCU) on the maintenance of groundwater nitrate concentrations in the potato production regions of the U.S. The agricultural products retailer Agrium Inc. had developed a type of PCU called Environmentally Smart Nitrogen, wherein its potential to reduce nitrate leaching has not been scrutinized in a potato. A comparison of four PCUs were studied during the leaching years of 2006 and 2007, and measurements of nitrate leaching, fertilizer nitrogen (N) recovery, N use efficiency (NUE) and residual N soil were determined.

Potato (Solanum tuberosum L.) production in irrigated coarse-textured soils requires intensive nitrogen (N) fertilization which may increase reactive N losses. Biological soil additives including N-fixing microbes (NFM) have been promoted as a means to increase crop N use efficiency, though few field studies have evaluated their effects, and none have examined the combined use of NFM with microbial inhibitors. A 2-year study (2018–19) in an irrigated loamy sand quantified the effects of the urease inhibitor NBPT, the nitrification inhibitor DMPSA, NFM, and the additive combinations DMPSA + NBPT and DMPSA + NFM on potato performance and growing season nitrous oxide (N 2 O) emissions and nitrate (NO 3 −) leaching. All treatments, except a zero-N control, received diammonium phosphate at 45 kg N ha−1 and split applied urea at 280 kg N ha−1. Compared with urea alone, DMPSA + NBPT reduced NO 3 − leaching and N 2 O emissions by 25% and 62%, respectively, and increased crop N uptake by 19% in one year, although none of the additive treatments increased tuber yields. The DMPSA and DMPSA + NBPT treatments had greater soil ammonium concentration, and all DMPSA-containing treatments consistently reduced N 2 O emissions, compared to urea-only. Use of NBPT by itself reduced NO 3 − leaching by 21% across growing seasons and N 2 O emissions by 37% in 2018 relative to urea-only. In contrast to the inhibitors, NFM by itself increased N 2 O by 23% in 2019; however, co-applying DMPSA with NFM reduced N 2 O emissions by ≥ 50% compared to urea alone. These results demonstrate that DMPSA can mitigate N 2 O emissions in potato production systems and that DMPSA + NBPT can reduce both N 2 O and NO 3 − losses and increase the N supply for crop uptake. This is the first study to show that combining a nitrification inhibitor with NFM can result in decreased N 2 O emissions in contrast to unintended increases in N 2 O emissions that can occur when NFM is applied by itself. [Display omitted] • DMPSA + NBPT reduced N 2 O emissions and NO 3 − leaching from urea applied to potato. • Applied as single inhibitors, DMPSA mitigated N 2 O and NBPT reduced NO 3 − leaching. • Double-inhibitors increased potato N-uptake when extreme rainfall events occurred. • Tuber yield was not affected by either inhibitor or by N-fixing microbes. • N-fixing microbes demonstrated a potential to increase N 2 O emissions. DMPSA + NBPT reduced growing season N 2 O emissions and NO 3 − leaching from urea applied to potato cultivated in irrigated coarse-textures soils. [ABSTRACT FROM AUTHOR]

Accurate high-resolution yield maps are essential for identifying spatial yield variability patterns, determining key factors influencing yield variability, and providing site-specific management insights in precision agriculture. Cultivar differences can significantly influence potato (Solanum tuberosum L.) tuber yield prediction using remote sensing technologies. The objective of this study was to improve potato yield prediction using unmanned aerial vehicle (UAV) remote sensing by incorporating cultivar information with machine learning methods. Small plot experiments involving different cultivars and nitrogen (N) rates were conducted in 2018 and 2019. UAV-based multi-spectral images were collected throughout the growing season. Machine learning models, i.e., random forest regression (RFR) and support vector regression (SVR), were used to combine different vegetation indices with cultivar information. It was found that UAV-based spectral data from the early growing season at the tuber initiation stage (late June) were more correlated with potato marketable yield than the spectral data from the later growing season at the tuber maturation stage. However, the best performing vegetation indices and the best timing for potato yield prediction varied with cultivars. The performance of the RFR and SVR models using only remote sensing data was unsatisfactory (R2 = 0.48–0.51 for validation) but was significantly improved when cultivar information was incorporated (R2 = 0.75–0.79 for validation). It is concluded that combining high spatial-resolution UAV images and cultivar information using machine learning algorithms can significantly improve potato yield prediction than methods without using cultivar information. More studies are needed to improve potato yield prediction using more detailed cultivar information, soil and landscape variables, and management information, as well as more advanced machine learning models. [ABSTRACT FROM AUTHOR]

This article cites a study on phosphorus (P) leaching in sandy outwash soils following potato-processing wastewater application. Land application is commonly used by food processing facilities as a disposal method for the large quantities of wastewater generated during processing of food products. The wastewater typically contains large amounts of nutrients of environmental significance, particularly nitrogen and phosphorus. Irrigation with large volumes of such wastewater presents potential for ground and surface water contamination from P and other pollutants, if not properly managed. If applied in accordance with crop water and P use, land disposal works well during the growing season. Results indicate no P leaching in low P soils, but leaching in high P soils, thus suggesting that most of the P leached at the high P sites was mainly due to desorption and dissolution of weakly adsorbed P from prior P applications. This was consistent with P transport simulations using the convective-dispersive equation. It is concluded that P concentration in land-applied wastewater should be regulated based on soil test-P level plus wastewater P loading.

Potassium (K) is a primary macronutrient for overall plant growth, yield potential, product quality and stress resistance of crops. Potato (Solanum tuberosum L.) crops require a high amount of potassium to achieve the ideal yield and quality. Therefore, the determination of optimum K rate and efficient source for potato is necessary because K affects crop physiological processes, dry matter production, cooking, and processing requirements. Through modeling on the pooled data extracted from 62 studies, the highest tuber yields might be obtained at an exchangeable soil K level of 200 mg kg−1 approximately, dependent on soil pH, texture, and organic matter. Through modeling on the data of 48 studies, it also revealed that application of potassium sulfate (K2SO4) and potassium chloride (KCl) at rates of 200 kg ha−1 and potassium nitrate (KNO3) at a rate of 100 kg ha−1 might achieve the ideal yield, implying the importance of K sources in potato production. However, these values (either soil exchangeable K content, or fertilizer rates) might not be applicable in a specific growing environment for a specific potato variety. It seems that there is no discrimination among split, pre-plant or in-season application of K, although pre-plant fertilization might be a trustworthy strategy for economic tuber yield. Owing to the luxury consumption of K by potato crop, a combination of factors, including soil exchangeable K level, petiole K concentration, crop removal amount, soil conditions, management practices, climatic conditions, and potato variety, should be considered in order to make rational K fertilizer recommendations. [ABSTRACT FROM AUTHOR]

Recently released potato cultivars Dakota Russet and Easton were bred for low reducing sugars, and low acrylamide-forming potential in French fries. The objectives of this study were to determine: (1) the effects of nitrogen rate and storage time on tuber glucose concentrations in different cultivars; (2) the relationships between acrylamide, glucose, and asparagine for the new cultivars and Russet Burbank. The study was conducted at Becker, Minnesota over a period of two years on a loamy sand soil under irrigated conditions. All cultivars were subjected to five N rates from 135 to 404 kg ha−1 in a randomized complete block design. Following harvest, tubers were stored at 7.8 °C and sampled at 0, 16, and 32 weeks. Dakota Russet and Easton had significantly lower concentrations of stem- and bud-end glucose, asparagine, and acrylamide than those of Russet Burbank in both years. The effect of storage time on glucose concentration was significant but differed with cultivar and year. N rate effects on stem- and bud-end glucose concentrations were cultivar and storage time dependent. After 16 weeks of storage, both asparagine and acrylamide concentrations linearly increased with increasing N rate. Glucose concentration was positively correlated with acrylamide concentration (r2 = 0.61). Asparagine concentration was also positively correlated with acrylamide concentration (r2 = 0.45) when the asparagine:glucose ratio was <1.306. The correlation between fry color and stem-end glucose concentration was significant over three cultivars in both years, but stronger in a growing season with minimal environmental stress. Taken together, these results suggest that while acrylamide formation during potato processing is a complex process affected by agronomic practices, environmental conditions during the growing season, and storage conditions, cultivar selection may be the most reliable method to minimize acrylamide in fried products. [ABSTRACT FROM AUTHOR]

Sustainable management of phosphorus (P) is a critical component of potato production systems because of a comparatively high plant P requirement, soil reactions that create management challenges, and potential environmental degradation from inappropriate P management. Phosphorus affects potato plant growth in many ways including its effects on plant metabolism, cellular structural components, canopy development, tuber set, nutritional quality, and resistance to some diseases. [ABSTRACT FROM AUTHOR]

To use remotely sensed spectral data for determining rates and timing of variable rate nitrogen (N) applications at a commercial scale, the most reliable indicators of crop N status must be determined. This study evaluated the ability of hyperspectral remote sensing to predict N stress in potatoes ( Solanum tuberosum ) during two growing seasons (2010 and 2011). Spectral data were evaluated using ground based measurements of leaf N concentration. Two canopy-scale hyperspectral images were acquired with an AISA-Eagle hyperspectral camera in both years. The experiment included five N treatments with varying rates and timing of N fertilizer and two potato cultivars, Russet Burbank (RB) and Alpine Russet (AR). Partial Least Squares regression (PLS) models resulted in the best prediction of leaf N concentration ( r 2 = 0.79, Root Mean Square Error of Cross Validation (RMSECV) = 14% across dates for RB; r 2 = 0.77, RMSECV = 13% across dates for AR). Applying the Nitrogen Sufficiency Index (NSI) formula to spectral indices/models made them mostly insensitive to the effects of cultivar. The most promising technique for determining N stress in potato based on spectral indices was found to be the MERIS Terrestrial Chlorophyll Index (MTCI) due to a combination of relatively high r 2 values, lower RMSECVs, and high accuracy assessment. Pairwise comparison tests from the means separation showed that spectral indices/models from the imagery resulted in more statistically significant groupings of crop stress levels for the spectra than leaf N concentration because canopy-scale spectral data are affected by both tissue N concentration and biomass. The results of this study suggest that upon proper sensor calibration, canopy-scale spectral data may be the most sensitive tool available to detect N status of a potato crop. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a non-renewable resource that will become an economic limiting factor for food production in the future. Potato (Solanum tuberosum L.) is a relatively shallow rooted crop and often responds positively to P fertilizer even in soils with high soil-test P. Therefore, high-rate P fertilizers are commonly applied to produce high tuber yields in commercial potato fields. The purpose of this study was to evaluate the effects of P rate, cultivar, and soil fumigation on potato yield, quality, P uptake, P use efficiency and economic returns under high soil test P conditions. A field study with a split-plot randomized complete block design was conducted in 2021 and 2022, with fumigation treatments (no fumigant or fall-applied metam sodium) being the main plots and cultivars (Ivory Russet or Russet Burbank) as subplots. Each subplot was further divided into five sub-subplots with different P rates: 0, 37, 73, 147 and 220 kg P ha-1. The results indicated that Russet Burbank produced higher total yield than Ivory Russet. Fumigation significantly increased tuber yield and dry matter percentage. Both cultivars responded to P application and tuber P uptake increased with P rate even under very high soil test P conditions. Both partial factor productivity (PFP) and P recovery efficiency (PRE) were very low and significantly decreased with the P rate. Russet Burbank had higher PFP and PRE than Ivory Russet, and fumigated plots had significantly higher PRE than non-fumigated plots. The tuber yield output and net revenue of Russet Burbank was higher than Ivory Russet, and the highest economic return was obtained in fumigated plots at 147 kg P ha-1. These results suggest that cultivar selection and control of soil-borne diseases should be considered to optimize P input, tuber yield, and to conserve P resources. [Display omitted] • Tuber yield of Russet Burbank was higher than Ivory Russet due to higher tuber set. • Fumigation significantly increased tuber yield and its response to P application. • Potato P use efficiency was very low, especially when high P rates were applied. [ABSTRACT FROM AUTHOR]

Multiple critical N dilution curves [CNDCs] have been previously developed for potato; however, attempts to directly compare differences in CNDCs across genotype [G], environment [E], and management [M] interactions have been confounded by non-uniform statistical methods, biased experimental data, and lack of proper quantification of uncertainty in the critical N concentration [%N c ]. This study implements a partially-pooled Bayesian hierarchical method to develop CNDCs for previously published and newly reported experimental data, systematically evaluates the difference in %N c [∆%N c ] across G × E × M effects, and directly compare CNDCs from the Bayesian framework to CNDCs from conventional statistical methods. The partially-pooled Bayesian hierarchical method implemented in this study has the advantage of being less susceptible to inferential bias at the level of individual G × E × M interactions compared to alternative statistical methods that result from insufficient quantity and quality of experimental datasets (e.g., unbalanced distribution of N limiting and non-N limiting observations). This method also allows for a direct statistical comparison of differences in %N c across levels of the G × E × M interactions. Where found to be significant, ∆%N c was hypothesized to be related to variation in the timing of tuber initiation (e.g., maturity class) and the relative rate of tuber bulking (e.g., planting density) across G x E × M interactions. In addition to using the median value for %N c (i.e., CNDC), the lower and upper boundary values for the credible region (i.e., CNDC lo and CNDC up) derived using the Bayesian framework should be used in calculation of N nutrition index (and other calculations) to account for uncertainty in %N c. Overall, this study provides additional evidence that%N c is dependent upon G × E × M interactions; therefore, evaluation of crop N status or N use efficiency must account for variation in %N c across G × E × M interactions. • Critical N dilution curves [CNDCs] for potato are subject to G x E x M effects. • Bayesian methods can quantify uncertainty in critical N concentration [%N c ]. • Partial pooling Bayesian method enables direct comparison of G x E x M effects. • Variation in %N c for potato due to tuber initiation timing and tuber bulking rate. • N use efficiency and N nutrition index depend on %N c variability and uncertainty. [ABSTRACT FROM AUTHOR]

• A comprehensive assessment of the effectiveness of nitrification inhibitor DMPP under varying N rates and application timings on potato yield and NUE under tropical conditions was performed. • Compared to the conventional practice, split applied ammonium sulfate nitrate with DMPP (ASN + DMPP), at either 75% or 100% of recommended N rate (RNR), reduced N surplus in site-years with greater rainfall events and consistently increased potato tuber yield. • At reduced N rate (75% of RNR), single ASN + DMPP application at planting decreased potato yield, but at 100% of RNR potato production was not different from that receiving conventional N fertilization. • The mutual agronomic, economic, and environmental benefits of split-applied ASN + DMPP at 75% of RNR can contribute to the increased sustainability of tropical potato cropping systems. However, further studies are needed to confirm these benefits in other agro-ecosystems. Urea is the dominant nitrogen (N) fertilizer used for potato (Solanum tuberosum L.) cultivation in most parts of the world. Fertilizers containing a nitrification inhibitor (NI) claim to improve performance of crops including potato. No studies to date have conducted comprehensive assessment of N sources and the effectiveness of NI under varying N rates or application timings to enhance potato yield, tuber quality or N-use efficiency (NUE) in tropical regions. Three field experiments were conducted on irrigated sandy soils in southeastern Brazil to determine whether single or split application of ammonium sulfate nitrate (ASN) with the NI 3,4-dimethylpyrazole phosphate (DMPP) at reduced (75%) or recommended N rates (RNR, 100% = 160 kg ha-1) could improve yield, quality and/or NUE of 'Agata' potato over conventional split-applied urea at 100% of RNR. Compared to the conventional practice, split-applied ASN + DMPP, at either 75% or 100% of RNR, increased fresh tuber yield by an average of 15% across all site-years (SYs) and reduced N surplus in SYs with greater rainfall events suggesting that reactive N losses to the environment were also reduced. With split-applied ASN + DMPP at 75% of RNR, fresh tuber yield per unit of applied N increased by 34% compared to split-applied ASN + DMPP at 100% of RNR, and by 50–75% compared to a single application of ASN + DMPP at planting. These results demonstrate a mutually beneficial opportunity, where the rate of split-applied ASN + DMPP can be reduced by 25% while at the same time increasing yields, thus resulting in agronomic, economic, and environmental benefits due to the decreased potential for off-site reactive N losses. [ABSTRACT FROM AUTHOR]