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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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Nitrogen (N) loss from cropping systems has important environmental implications, including contamination of drinking water with nitrate. A 2-yr study evaluated the effects of six N rate, source, and timing treatments, including a variable rate (VR) N treatment based on the N sufficiency index approach using remote sensing, and two irrigation rate treatments, including conventional and reduced rate, on nitrate leaching, residual soil nitrate, and plant N uptake for potato (Solanum tuberosum L. cv. Russet Burbank) production in 2016 and 2017 on a Hubbard loamy sand. Nitrate leaching losses measured with suction-cup lysimeters varied between 2016 and 2017 with flow-weighted mean nitrate N concentrations of 5.6 and 12.8 mg N L -1 , respectively, and increased from 7.1 to 10.4 mg N L -1 as N rate increased from 45 to 270 kg N ha -1 . Despite reductions in N rate of 22 and 44 kg N ha -1 in 2016 and 2017, respectively, for the VR N treatment, there was no significant difference in nitrate leaching compared with the existing N best management practices (BMPs). Reducing irrigation rate by 15% decreased nitrate leaching load by 17% through a reduction in percolation. Residual soil nitrate N in the top 60 cm across all treatments (7.9 mg N kg -1 ) suggests a risk for nitrate leaching during the nongrowing season, and plant N uptake did not explain yearly variation in nitrate leaching and residual soil nitrate. Although existing N BMPs are effective at controlling N losses, development of alternative practices is needed to further reduce the risk of groundwater contamination., (© 2020 The Authors. Journal of Environmental Quality © 2020 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Potato ( L.) is a N-intensive crop, with high potential for nitrate (NO) leaching, which can contribute to both water contamination and indirect nitrous oxide (NO) emissions. Two approaches that have been considered for reducing N losses include conventional split application (CSA) of soluble fertilizers and single application of polymer-coated urea (PCU). The objectives of this study were to: (i) compare NO leaching using CSA and two PCUs (PCU-1 and PCU-2), which differed in their polymer formulations, and (ii) use measured NO leaching rates and published emissions factors to estimate indirect NO emissions. Averaged over three growing seasons (2007-2009), NO leaching rates were not significantly different among the three fertilizer treatments. Using previously reported direct NO emissions data from the same experiment, total direct plus indirect growing season NO emissions with PCU-1 were estimated to be 30 to 40% less than with CSA. However, PCU-1 also resulted in greater residual soil N after harvest in 2007 and greater soil-water NO in the spring following the 2008 growing season. These results provide evidence that single PCU applications for irrigated potato production do not increase growing season NO leaching compared with multiple split applications of soluble fertilizers, but have the potential to increase N losses after the growing season and into the following year. Estimates of indirect NO emissions ranged from 0.8 to 64% of direct emissions, depending on what value was assumed for the emission factor describing off-site conversion of NO to NO. Thus, our results also demonstrate how more robust models are needed to account for off-site conversion of NO to NO, since current emission factor models have an enormous degree of uncertainty., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Increasing groundwater nitrate concentrations in potato (Solanum tuberosum L.) production regions have prompted the need to identify alternative nitrogen management practices. A new type of polymer-coated urea (PCU) called Environmentally Smart Nitrogen (Agrium, Inc., Calgary, AB) is significantly lower in cost than comparable PCUs, but its potential to reduce nitrate leaching and improve fertilizer recovery has not been extensively studied in potato. In 2006 and 2007, four rates of PCU applied at emergence were compared with equivalent rates of soluble N split-applied at emergence and post-hilling. Additional treatments included a 0 N control, two PCU timing treatments (applied at preplant or planting), and a soluble N fertigation simulation. Nitrate leaching, fertilizer N recovery, N use efficiency (NUE), and residual soil inorganic N were measured. Both 2006 and 2007 were low leaching years. Nitrate leaching with PCU (21.3 kg NO(3)-N ha(-1) averaged over N rates) was significantly lower than with split-applied soluble N (26.9 kg NO(3)-N ha(-1)). The soluble N fertigation treatment resulted in similar leaching as PCU at equivalent N rates. Apparent fertilizer N recovery with PCU (65% averaged over four rates) tended to be higher than split-applied soluble N (55%) at equivalent rates (p = 0.059). Residual soil N and NUE were not significantly affected by N source. Under the conditions of this study, PCU significantly reduced leaching and tended to improved N recovery over soluble N applied in two applications and resulted in similar N recovery and nitrate leaching as soluble N applied in six applications.

Land application of wastewater presents potential for ground water pollution if not properly managed. In situ breakthrough tests were conducted using potato (Solanum tuberosum L.)-processing wastewater and a Br tracer to characterize P leaching in seasonally frozen sandy outwash soils. In the first test, P and Br breakthrough were measured in a 7-m deep well following wastewater [2.94 mg L(-1) total P (TP); 280 mg L(-1) Br] application at the site that had 13.1 mg water-extractable P (WEP) kg(-1)and 94.4 mg Bray-1 P kg(-1). Bromide was detected in the well after approximately 0.4 pore volumes, but there was no P break-through after 7 pore volumes. In the second breakthrough test, wastewater containing 3.6 mg L(-1) TP and 259 mg L(-1) Br was applied on 1.5-m deep lysimeters at low (0.8 mg WEP kg(-1); 12.1 mg Bray-1 P kg(-1)) and high soil test P sites (104 mg WEP kg(-1); 585 mg Bray-1 P kg(-1)). Leachate TP concentration during the test remained constant (0.04 mg L(-1)) at the low P sites but increased from approximately 3.5 to 5.6 mg L(-1) at the high P sites. These 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. We conclude that P concentration in land-applied wastewater should be regulated based on soil test-P level plus wastewater P loading.

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]

• 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]