Polymer-coated Urea Research Articles

Can split or delayed application of N fertiliser to grain sorghum reduce soil N2O emissions from sub-tropical Vertosols and maintain grain yields?

Most soil nitrous oxide (N2O) emissions from rain-fed grain sorghum grown on sub-tropical Vertosols in north-west New South Wales, Australia, occur between fertiliser nitrogen (N) application at sowing and booting growth stage. At three experiments, we investigated the potential for deferring some (split-N) or all (delayed) fertiliser N until booting to mitigate N2O produced without compromising optimum crop yields. N products included urea, 3,4-dimethyl pyrazole phosphate (DMPP)-urea, polymer-coated urea (PCU) and N-(n-butyl)thiophosphoric triamide (NBPT)-urea. For a fourth experiment, the N fertiliser rate was varied according to pre-sowing soil mineral N stocks left by different previous crops. All experiments incorporated 15N mini-plots to determine whether delayed or split-N affected crop N uptake or residual soil N. Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%. Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions. Much of the unused N remained in the soil at harvest. Split-N (33% sowing:67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein. Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%. Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass. Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity. Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions. An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions. Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.

Urea-induced nitrous oxide emissions under sub-tropical rain-fed sorghum and sunflower were nullified by DMPP, partially mitigated by polymer-coated urea, or enhanced by a blend of urea and polymer-coated urea

Delaying the accumulation of soil nitrate from urea applied at sowing should mitigate nitrous oxide (N2O) emissions without compromising optimum crop production. This delay may be achieved chemically using a nitrification inhibitor such as 3,4 dimethylpyrazole phosphate (DMPP), or physically by coating urea with a degradable polymer (PCU). In five field experiments across three summers, the impact of DMPP-coated urea applied at sowing on soil mineral nitrogen (N), N2O emissions and yields of grain sorghum or sunflower grown on sub-tropical Vertosols was assessed. At two experiments, DMPP effects on plant N uptake, soil N movement and total N loss were determined with 15N. One experiment included PCU and several blends: urea+DMPP-urea; urea+PCU; urea+DMPP-urea+PCU. Averaged across all experiments, DMPP reduced cumulative N2O emitted by 92% (range: 65–123%) and N2O emission factor (EF: percent of applied N emitted) by 88%. There was no statistical difference in N2O emitted between the 0N control and DMPP-urea. PCU reduced N2O emitted by 27% and EF by 34%. The urea+DMPP-urea blend also nullified urea-induced N2O, but urea+PCU increased N2O emissions and decreased grain yield due to a mismatch between soil N availability and plant N demand. DMPP arrested 15N movement in soil and reduced total 15N loss from 35% to 15% at one of the two 15N experiments. Applying DMPP-urea at sowing is an effective N strategy that nullifies urea-induced N2O emissions, maintains crop yield, and retains N in the soil–plant system. Negative impacts of the PCU+urea blend highlight the influence of growing season conditions on fertiliser N release.

Controlled-release fertilizer enhances rice grain yield and N recovery efficiency in continuous non-flooding plastic film mulching cultivation system

Non-flooding plastic film mulching (PM) cultivation is a promising water-saving technology for rice cultivation. However, because the N fertilizer can only be applied before transplanting due to technical difficulties with later applications, it results in excessive vegetative growth and potential N shortages during the reproductive stages, which may limit grain yield potential. The use of polymer-coated urea (PCU), a slow release N fertilizer, has become one of the best management practices for increasing crop yield and improving N recovery efficiency in traditional flooded rice cultivation (TF), but has not been tested in PM cultivation. The objective of the eight-year (2008–2015) field experiment in the present study was to compare the effects of PCU with a conventional prilled urea fertilizer (PU) and a control (no N fertilizer applied; CK) on grain yield, N recovery efficiency, yield components, and soil nutrients under PM and TF cultivation systems. Within fertilizer treatment, plant N uptake and N recovery efficiency were almost always significantly higher in the PM than the TF cultivation treatments. PCU application significantly increased these parameters in both cultivation systems, but usually by significantly more with PM cultivation. Compared to the PU treatment, PCU significantly increased rice grain yield in both cultivation systems every year (by means of 11% and 15% in the TF and PM, respectively), except for TF in the first year. Within fertilizer treatment, yields of PM and TF were similar. In comparison with PU, the use of PCU had no effect on soil organic matter or alkali-hydrolyzable N. However, PM cultivation decreased these parameters. In conclusion, PCU application increased the N recovery efficiency and N availability in both cultivation systems during the reproductive stages of rice, and thus improved rice grain yield. We demonstrated that the application of PCU is a practical N fertilizer management technique that improves rice grain yield and N recovery efficiency, and is an effective solution to fertilization challenges in PM rice cultivation systems.

Biochemical effects of banding limit the benefits of nitrification inhibition and controlled-release technology in the fertosphere of high N-input systems

Enhanced efficiency fertilisers (EEFs) may have an important role in improving nitrogen (N) use efficiency in agricultural systems. The performance of EEFs when applied by broadcasting and incorporation is well documented; however, little information is available for sub-surface banded N-fertiliser. This study aimed to determine the effectiveness of EEFs within the fertosphere in several soils. This was determined by: (i) establishing the key chemical effects and N-transformation activity within a urea band, and (ii) contrasting these findings with nitrification inhibitor (NI)-coated urea and a controlled-release polymer-coated urea (PCU). A 112-day incubation experiment was conducted with the EEFs band-applied in three contrasting soils with a history of sugarcane production. In standard urea and NI-urea treated soils, the pH within the fertosphere significantly increased to a maximum of ~pH 9.2–9.3. Alkaline conditions and high ammonium concentrations promoted elevated aqueous ammonia concentrations, resulting in complete nitrification inhibition. The PCU granules released ~40% of total urea content within 14 days, followed by subsequent release at significantly lower rates. The initial rapid urea release was attributed to damaged polymer coats, while close proximity of neighbouring granules within the band may have contributed to the subsequent slower release phase through reduced concentration gradients and restricted diffusion from granules. Variation between soils suggests that soil properties such as clay content and pH buffer capacity may influence urea hydrolysis, but not nitrification. These results suggest that both NI and controlled-release technology may not have the expected impacts on N transformations and availability when applied in a concentrated band.

Producing more grain yield of rice with less ammonia volatilization and greenhouse gases emission using slow/controlled-release urea.

Ammonia (NH3) volatilization and greenhouse gas (GHG) emission from rice (Oryza sativa L.) fields contaminate the atmospheric environment and lead to global warming. Field trials (2013-2015) were conducted to estimate the influences of different types of fertilization practices on grain yield, NH3 volatilization, and methane (CH4) and nitrous oxide (N2O) emissions in a double rice cropping system in Central China. Results showed that grain yields of rice were improved significantly by using slow/controlled-release urea (S/C-RU). Compared with farmers' fertilizer practice (FFP) treatment, average annual grain yield with application of polymer-coated urea (CRU), nitrapyrin-treated urea (CP), and urea with effective microorganism (EM) treatments was increased by 18.0%, 16.2%, and 15.4%, respectively. However, the effects on NH3 volatilization and CH4 and N2O emissions differed in diverse S/C-RU. Compared with that of the FFP treatment, the annual NH3 volatilization, CH4 emission, and N2O emissions of the CRU treatment were decreased by 64.8%, 19.7%, and 35.2%, respectively; the annual CH4 and N2O emissions of the CP treatment were reduced by 33.7% and 40.3%, respectively, while the NH3 volatilization was increased by 18.5%; the annual NH3 and N2O emissions of the EM treatment were reduced by 6.3% and 28.7%, while the CH4 emission was improved by 4.3%. Overall, CP showed the best emission reduction with a decrement of 34.3% in global warming potential (GWP) and 44.4% in the greenhouse gas intensity (GHGI), followed by CRU treatment with a decrement of 21.1% in GWP and 31.7% in GHGI, compared with that of the FFP treatment. Hence, it is suggested that polymer-coated urea can be a feasible way of mitigating NH3 volatilization and CH4 and N2O emission from rice fields while maintaining or increasing the grain yield in Chinese, the double rice cropping system.

Effects of slow or controlled release fertilizer types and fertilization modes on yield and quality of rice

There is limited information about the influence of slow or controlled release fertilizer (S/CRF) on rice yield and quality. In this study, japonica rice cultivar Nanjing 9108 was used to study the effects of three different S/CRFs (polymer-coated urea (PCU), sulfur-coated urea (SCU), and urea formaldehyde (UF)) and two fertilization modes (both S/CRF and common urea (CU) as basal fertilizer, S/CRF as basal and CU as tillering fertilizer) on rice yield and quality. CU only was applied separately as control (CK). Results showed that, rice grain yield, chalky kernel rate, chalky area, overall chalkiness, and the content of gliadin, glutenin, and protein, all showed the trends of UF>PCU>SCU within the same fertilization mode, and showed the trends of S/CRF as basal and CU as tillering fertilizer>both S/CRF and CU as basal fertilizer within the same type of S/CRF. In contrast, the contents of amylose, amylopectin, and starch, as well as taste value, and peak and hot viscosity showed trends of SCU>PCU>UF, and the trends of both S/CRF and CU as basal fertilizer>S/CRF as basal and CU as tillering fertilizer. Among S/CRF treatments and fertilization modes, taste values of cooked rice were positively correlated with amylose, amylopectin, and starch contents, as well as gel consistency, peak viscosity, hot viscosity, and cool viscosity, while negatively correlated with globulin, gliadin, glutenin, and protein contents. The types of S/CRF and fertilization modes are important for improving rice yield and quality. Compared to CK, higher yield and similar quality of rice was achieved with UF as basal and CU as tillering fertilizer, and similar yield with improved appearance and eating and cooking quality of rice was achieved with either both UF and CU as basal fertilizer, or PCU as basal and CU as tillering fertilizer.

Effects of the reduction of controlled-release urea application on nitrogen leaching in double cropping paddy field.

Nitrogen (N) leaching is a major pathway of N losses in paddy fields. Here, an experiment was conducted to assess the effects of the reduction of controlled-release urea application on grain yield and N leaching in a double-cropping paddy field. Fertilization treatments included zero-N (CK, control, 0 kg N·hm-2), conventional urea (CU, 180 kg N·hm-2), and four polymer-coated urea fertilization levels, i.e., 1.0CRU, 0.9CRU, 0.8CRU, 0.7CRU, which represented 0, 10%, 20% and 30% reduction of fertilizer inputs relative to CU, respectively. Leachate was collected at the soil depth of 60 cm using field leakage pool method. Nitrogen leaching peaked shortly after fertilization, implying that measures should be taken to prevent N leaching in the early period. Nitrogen losses from leaching were 42.3 kg N·hm-2 for 0.8CRU, and by 37.7 kg N·hm-2 for 0.7CRU, significantly lower than the leaching in CU (53.9 kg N·hm-2). Nitrogen leaching in 0.7CRU was significantly lower than that in 1.0CRU (51.3 kg N·hm-2). 11.9%-13.5% of the fertilizer N was lost via leaching across the six treatments with comparable N loss rates. Rice yields, N utilization efficiency and N harvest index were significantly higher in 0.8CRU and 0.7CRU relative to CU. Our findings suggested that the use of CRU would permit a reduction in N application by 20%-30%, which could maintain the rice yield and obtain a reduction in N leaching.

Assessing atmospheric nitrogen losses with photoacoustic infrared spectroscopy: Polymer coated urea.

Although N is beneficial and essential for life, it is also a common atmospheric pollutant as nitrous oxide (N2O) and ammonia (NH3)—contributed largely from N fertilization. Polymer-coated urea (PCU) fertilizer is a promising controlled release fertilizer that provides improved N-release timing. Glasshouse studies were conducted to compare N2O and NH3 emissions from PCU and uncoated urea to an untreated control utilizing a non-static, non-flow-through chamber in conjunction with photoacoustic infrared spectroscopy (PAIRS) for gas collection and analysis. Three short-term 20-Day Studies with sand, sandy loam, and loam soils and a full-term 45-Day Study with loam soil were completed. Volatilization of NH3 was reduced by 72% and 22% in the sandy loam and loam soils, respectively, in two of the short-term studies and by 14% in the loam in the full-term study. Evolution of N2O was reduced by 42% and 63% in the sandy loam and loam soils of the short-term studies and by 99% in the loam soil of the full-term study. No differences were observed in the sand soil. Overall, PCU decreased gaseous losses of N following fertilization while providing a steady supply of N to the plant. Higher temporal resolution was observed with the PAIRS instrumentation as compared to what is typically reported and, as such, we recommend PAIRS analysis as a viable method for studying N gas emissions.

Nitrogen source and rate effects on grain and potential biodiesel production of camelina in the semiarid environment of northern Nevada

AbstractThe objective of this two‐year study (2016–2017 spring) carried out at the University of Nevada, Reno Main Station Field Laboratory, Reno, NV, was to evaluate the effects of nitrogen source, rate, and camelina cultivar on grain yield and potential biodiesel production irrigated with reclaimed water. Treatments were two sources of urea fertilizer [conventional urea (CU) and polymer‐coated urea (PCU)], four N rates (0, 40, 80, and 120 kg N ha–1), and two cultivars of camelina (“Blaine Creek” and “Pronghorn”) arranged in a 4 × 2 × 2 factorial combinations with four replications each in a RCBD experiment. Plot size was 7.6 m long × 1.8 m wide, and camelina was seeded at a rate of 5 kg PLS seed ha‐1. The quantity of light intercepted increased linearly from 44.9% to 65.9% as N application rate increased from 0 to 120 kg N ha–1, and it was greater for CU (59.6%) compared to PCU (54.0%) fertilized plots. There was a linear increased in grain yield ranging from 534 to 1,010 kg/ha as N application rate increased from 0 to 120 kg N ha‐1. In Year 2, grain yield of Blaine Creek (898 kg/ha) was greater than that of Pronghorn (464 kg/ha). Also, there was a linear increase in estimated biodiesel from 51.2 to 94.2 L/ha as N application rate increased. For both grain and biodiesel production, there was no advantage of using controlled‐release PCU fertilizer and 80 to 120 kg N ha–1 is sufficient for the cultivation of camelina in this environment. Based on the range of grain yield obtained in this study, camelina can be a potential alternative crop to integrate into the annual crop production cycle in water‐limited environments like Nevada.

Combined controlled-released nitrogen fertilizers and deep placement effects of N leaching, rice yield and N recovery in machine-transplanted rice

In the Taihu region of China, overuse of chemical nitrogen (N) fertilizer is often associated with low nitrogen recovery (NRE) and leads to serious groundwater pollution caused by N leaching losses. Controlled-released nitrogen fertilizers (CRNFs) and mechanized deep placement are promising alternatives to broadcasting urea to increase crop yield and NRE in machine-transplanted rice production. However, their interactions with regard to soil N status, N leaching and crop performance are unclear. A two-year (2015 and 2016) field experiment was conducted in a randomized complete block using two fertilization techniques (broadcast and deep placement by mechanical side-dressing fertilization) and three CRNFs (sulphur-coated urea (SCU), polymer-coated urea (PCU) and a bulk blended mixture (BBF)). Conventional high-yield fertilization (four split applications of urea at 216 kg N ha−1 (CK)) and 0–N treatments were established as controls. The results showed that the variation in NH4+-N concentration in the percolation and surface water varied across the different CRNFs, irrespective of the techniques used. NO3− -N concentration in the percolation water varied with water conditions in the field. Deep placement with CRNF correspondingly increased mineral N concentration in percolation at depths of 20 and 60 cm but reduced it in the surface water compared to that of the broadcast, although the benefits varied depending on the CRNF type and growth stage. Deep placement of SCU and PCU significantly increased N leaching and the mineral N in the 40–60 cm soil layer compared to that of the broadcast, due to the intensive N release during tillering and ineffective stage when the rice plant had a weak N uptake capability. Deep placement of SCU had the highest N leaching of 6.65 and 5.34 kg N ha−1 during 2015 and 2016. In contrast, BBF exhibited the lowest N leaching, regardless of fertilization placement, which apparently synchronized N release rates with rice N uptake patterns. In the present study, BBF obtained higher rice yields and N recoveries, without significantly enhancing mineral N leaching losses, when compared to CK. Our results suggest that the use of BBF is a promising alternative to a conventional high-yield fertilization practice, especially if combined with deep placement.

Profitability of Enhanced Efficiency Urea Fertilizers in No‐Tillage Corn Production

Core Ideas Urea + NBPT and PCU provided significantly higher mean yields and net returns than conventional urea. Urea + NBPT and PCU provided significantly lower yields and net returns than ammonium nitrate. Urea + NBPT and PCU offer greater potential to improve net returns than urea + MICP. This study determined the effects of enhanced efficiency (EE) urea fertilizers relative to ammonium nitrate (AN) on no‐tillage (NT) corn (Zea mays L.) yields and net returns (NRs) in Tennessee. Corn yields were from experiments conducted at two N fertilization rates of 123 and 168 kg ha−1 with four replications in a split‐plot design from 2013 through 2015 at three locations in middle (Springfield) and west Tennessee (Milan and Jackson). ANOVA analyses were used to identify differences in EE urea treatment yields and NRs. Breakeven and sensitivity analysis was used to compare yield and identify the threshold of positive NR of EE urea fertilizers relative to AN for a given premium price over conventional urea. Results indicated that urea + 20% or 26.7% N‐(n‐butyl)‐thiophosphoric triamide (NBPT) and polymer‐coated urea (PCU) provided significantly higher mean yields (2.0 Mg ha−1 more on average) and NRs ($283 ha−1 more) than conventional urea. Notwithstanding, these EE urea fertilizers had lower yields and produced lower benefits than AN in the course of this study. On the other hand, mean yield (8.7 Mg ha−1) and NR ($1012 ha−1) for urea + maleic–itaconic acid copolymer (MICP) were not significantly different from conventional urea (8.3 Mg ha−1 and $959 ha−1). In general, N fertilizer sources behaved similarly among N rates and locations. Given the growing reliance on urea fertilizer in NT corn production in Tennessee, urea + NBPT and PCU offer the greatest potential to improve expected NRs relative to conventional urea.

Early-Season Soil Waterlogging and N Fertilizer Sources Impacts on Corn N Uptake and Apparent N Recovery Efficiency

Soil waterlogging resulting from extreme precipitation events creates anaerobic conditions that may inhibit plant growth and increase N losses. A three-year (2013–2015) field experiment was conducted in poorly-drained claypan soils to assess the effects of waterlogging [0 or 7-days waterlogging at V3 growth stage of corn (Zea mays L.)] and pre-plant application of different N fertilizer sources and post-waterlogging rescue N application (0 or 84 kg N ha−1 of urea plus urease inhibitor (NCU + UI) at V7) on chlorophyll SPAD meter (CM) readings, stomatal conductance, ear leaf and silage N concentrations, N uptake and apparent N recovery efficiency (ARE) of two corn hybrids with varying amounts of flood tolerance. Pre-plant N fertilizer sources included a non-treated control (CO), urea (NCU), urea plus nitrification inhibitor (NCU + NI) and polymer coated urea (PCU) applied at 168 kg N ha−1. In 7-days waterlogged plots, rescue N applications increased N uptake in PCU treatments 33% and 40% in 2013 and 2014, respectively, as well as in NCU by 48% in 2013. In 7-days waterlogged plots which received rescue N applications, NCU and PCU in 2013 resulted in higher N uptake than CO and NCU + NI by 47 to 77 kg ha−1. PCU had higher N uptake than NCU and NCU + NI by 78 and 72 kg ha−1 in 7-days waterlogged plots that received rescue N applications in 2014. Corn hybrid showed no differences in N uptake and ARE in our study. Our results indicate combining pre-plant N fertilizer source selection and rescue N applications may be a strategy to reduce possible decreases in corn N uptake caused by early season soil waterlogging in average rainfall years.

No evidence for higher agronomic N use efficiency or lower nitrous oxide emissions from enhanced efficiency fertilisers in aerobic subtropical rice

Enhanced efficiency nitrogen (N) fertilisers (EENFs) contain chemical urease or nitrification inhibitors, or physical barriers (e.g. polymer coating) to minimise the rapid build-up of nitrate (NO3−) in soils. They have the potential to improve N use efficiency and lower N2O emissions from soils. However, evidence of the efficacy of EENFs in warm, wet subtropical conditions is lacking. We therefore developed N response curves (0, 30, 60, 90, 120 and 150 kg N ha-1) for urea, polymer coated urea (PCU), 3,4-dimethylpyrazole phosphate (DMPP)-urea (Entec®), N-(n-butyl) thiophosphoric triamide (NBPT)-urea (Green urea®) and a carbon-coated urea (Black urea®) in subtropical, aerobic rice (Oryza sativa L) crops in two fields with contrasting soils (Gleysol and Histosol), and quantified N2O emissions from nil-N and 90 kg N ha-1 treatments for all EENFs and urea. In the Gleysol, cumulative in-crop N2O emissions were relatively high (approximately 2 kg N2O-N ha-1 season-1 with 90 kg N ha-1 applied) with no significant mitigation from any EENFs compared to urea. Grain yield data fitted with an exponential model indicated that 95% of the estimated maximum grain yield (6.8 t ha-1 at 14% moisture) was achieved with 81 kg N ha-1 for the urea treatment. The yield response curves for all tested EENF products did not differ significantly from the urea-N yield response curve. In the Histosol, cumulative in-crop N2O emissions were negligible (around 0.05 kg N2O-N ha-1 season-1), with no significant difference (p < 0.05) between N fertiliser or nil-N treatments, and 95% of the estimated maximum grain yield (5.63 t ha-1 at 14% moisture) was achieved with only 11 kg N ha-1 for urea. There was no evidence that EENFs could achieve the maximum yield at a lower applied N rate. We hypothesised that the low soil pH of 4.9 (1:5 CaCl2 extract) may have inhibited nitrification in the Histosol, leading to low N2O emissions and a limited response to N fertiliser. Ultimately, the results of this study found no evidence that EENF products could improve agronomic N use efficiency or lower N2O emissions in the two aerobic rice crops studied.

Urea fertigation sources affect nitrous oxide emission from a drip-fertigated cotton field in northwestern China

Drip-fertigated systems are widely used for crop production in arid regions to improve water and nutrient use efficiency. However, the effect of fertilizer nitrogen (N) sources on nitrous oxide (N2O) emissions from such systems is not well understood. A field experiment was conducted in 2015 and 2016 on a sandy loam soil in Xinjiang, China with plastic-mulch, drip-fertigated cotton (Gossypium hirsutum L.) to determine N2O emissions from different fertilizer N sources. Treatments were established in a factorial design consisting of a 0 N control and three treatments receiving 240 kg N ha−1 as (1) polymer-coated urea (ESN), (2) urea alone, or (3) urea with both urease (NBPT) and nitrification (DCD) inhibitors. ESN was banded in the row at planting, whereas the two urea treatments were applied through banding and fertigation. In these treatments, 20% of the urea was banded in the row at planting and the remaining 80% was applied with six fertigation events over the growing season. Seasonal cumulative N2O emissions (ƩN2O) for urea alone were 330 g N ha−1 and were 27% greater than the control. Compared to urea alone, the ESN treatment increased ƩN2O by 43% due to the one-time application at planting that resulted in high soil N availability and high N2O emissions shortly after planting. Compared to urea alone, urea plus the two inhibitors decreased ƩN2O by 21%. Cotton seed yield and total N uptake was not affected by N sources, while ESN had significantly higher yield-based emission intensity compared to the other N treatments. In general, the seasonal N2O emissions and N-applied emission factors under the drip-fertigated system were lower than those reported for other agricultural systems. This was likely because of low soil moisture preventing appreciable N2O emissions. These results demonstrated that addition of urease and nitrification inhibitors could further reduce already low N2O emissions with soluble urea with drip-fertigation and under plastic mulch condition.

Enhanced nitrogen management strategies for winter wheat production in the Canadian prairies

To address knowledge gaps around enhanced efficiency urea fertilizer efficacy for nitrogen (N) management, a study was designed to improve integrated nutrient management systems for western Canadian winter wheat producers. Three factors were included in Experiment 1: (i) urea type [urea, urea + urease inhibitor—Agrotain®; urea + urease and nitrification inhibitor—SuperU®, polymer-coated urea—Environmentally Smart Nitrogen®(ESN®), and urea ammonium nitrate (UAN)], (ii) application method (side-band vs. spring-broadcast vs. 50% side-band: 50% spring-broadcast), and (iii) cultivar (AC Radiant hard red winter wheat vs. CDC Ptarmigan soft white winter wheat). The Agrotain®and CDC Ptarmigan treatments were removed in Experiment 2 to allow for additional application methods: (i) fall side-band, (ii) 50% side-band — 50% late fall broadcast, (iii) 50% side-band — 50% early spring broadcast, (iv) 50% side-band — 50% mid-spring broadcast, and (v) 50% side-band — 50% late spring broadcast. CDC Ptarmigan produced superior grain yield and N utilization over AC Radiant. Grain yield and protein content were influenced by N form and application method. Split applications of N usually provided the maximum yield and protein, particularly with Agrotain®or SuperU®. An exception to the poor fall-application results was the SuperU®treatments, which produced similar yield to the highest-yielding treatments. The results suggest that split applications of N might be most efficient for yield and protein optimization when combined with an enhanced efficiency urea product, particularly with urease or urease + nitrification inhibitors, and if the majority of N is applied in spring.

Agronomic and Economic Effects of Two Enhanced‐Efficiency Urea Fertilizer Technologies on Southern Great Plains Winter Wheat

Core Ideas Stabilized urea improved wheat grain yield and protein in the Southern Plains.Stabilized urea at a higher rate brought higher net profits than untreated urea at all price points.A safe seed‐placed rate for polymer‐coated urea in regional wheat is lower than 30 kg N ha–1.No benefit was observed in splitting nitrogen application in this study. In no‐till wheat (Triticum aestivum L.) cropping systems of the US Southern Great Plains, urea fertilizer is commonly surface broadcast and producers rely on unpredictable precipitation in dryland conditions for incorporation into the soil. Several enhanced‐efficiency fertilizer technologies are designed to reduce N loss in this scenario, though there are not published reports on evaluations of these in regional wheat systems. Here we report on an evaluation of two enhanced‐efficiency fertilizer technologies, polymer‐coated urea (PCU) and urease/nitrification inhibitor‐stabilized urea (SU), which were compared to untreated urea at different application rates (0, 31.5, and 70 kg N ha−1) and timings (at‐planting and split) in two locations differing in soil type (clay loam and loamy fine sand). The fertilizer was broadcast, except for PCU, which was drilled in‐row. The greatest yield was observed with a high at‐planting rate of SU, where yield was 26% greater than with untreated urea and 34% greater than with no fertilizer. Yield improvement with SU was associated with greater grain N uptake efficiency and protein content. The high SU rate brought higher net profits than untreated urea at all price points analyzed and surpassed the no‐fertilizer control as price increased. As might be expected with seed placement, there was substantial crop damage at the high rate of PCU, but even minor damage at the lower rate. The results suggest that a safe seed‐placed rate for PCU in wheat in this environment is somewhat lower than 30 kg N ha−1. No benefit was observed in splitting the N application.

Yield and Nitrogen Use of Irrigated Processing Potato in Response to Placement, Timing and Source of Nitrogen Fertilizer in Manitoba

Optimizing nitrogen (N) fertilizer management in irrigated potato (Solanum tuberosum L.) on coarse-textured soils is challenging. The “4R” nutrient stewardship framework of using N fertilizer at the right rate, right source, right placement and right time provides approaches to improve fertilizer use efficiency while maintaining or improving yield. This 3-years replicated field plot study evaluated effects from a series of N fertilization strategies including 10 combinations of sources, placement and timing, as well as fertigation, on irrigated processing potato (cv. Russet Burbank) grown for a total of five site-years in the Province of Manitoba, Canada. Treatments were designed to provide early to late availability of N to the potato crop. Nitrogen was applied to 80% of Provincial N recommendation to increase the likelihood of observing improved fertilizer use efficiency and effects of treatments on yields. Measurements were tuber yield, size distribution, specific gravity, hollow-heart rate, fertilizer apparent N recovery (ANR) and agronomic nitrogen use efficiency (NUE). Results showed differences in yield, quality, ANR and NUE between fertilizer treatments were generally very small or absent. Average tuber marketable yields for fertilizer treatments were significantly greater than those for the unfertilized control (P < 0.001). Split application of urea at planting and hilling, and urea at planting with fertigation occasionally increased tuber marketable yields on sites of coarse textured soils (P < 0.05). Use of polymer-coated urea (ESN) or stabilized urea with inhibitors (SuperU) did not affect yield, quality or N use of potato. Site-year difference (P < 0.001) were apparent for all measures highlighting the importance of soil and climatic conditions on agronomic and environmental effects of N management practices. The results indicate current grower practice of split urea application at planting and hilling and urea at planting following by in-season fertigation are sound. Results indicate growers could shift to the more convenient practice of ESN at planting without reducing yields. Absence of treatment effects suggests N was generally not a limiting factor for the current study, indicating that the current recommendation for potato production in Manitoba over-estimate site-specific crop N needs.

Comparative Efficiency of Nitrogen Sources for Lowland Rice Production

ABSTRACTRice (Oryza sativa L.) is the staple food for more than 50% world population and nitrogen (N) is one of the most yield-limiting nutrients for rice production worldwide. A greenhouse experiment was conducted to evaluate the efficiency of three N sources for lowland rice production. The N sources used were ammonium sulfate, common urea, and polymer-coated urea. There were three N rates, i.e. 100, 200, and 400 mg N kg−1 applied with three sources plus one control treatment (0 mg N kg−1). Growth, yield, and yield components were significantly increased either in a linear or quadratic fashion with the addition of N fertilizers in the range of 0–400 mg kg−1 soil. Maximum grain yield was obtained with the addition of ammonium sulfate at 100, 200, and 400 mg kg−1 of soil. Common urea and polymer-coated urea were more or less similar in grain production at 100 and 200 mg N kg−1. However, at 400 mg N kg−1 treatments, polymer-coated urea produced the lowest grain yield. Most of the growth and yield components were positively related to grain yield, except spikelet sterility which was negatively related to grain yield. Nitrogen use efficiency decreased with increasing N rate in all the three N sources. Maximum N use efficiency was obtained with the addition of ammonium sulfate at lower as well as at higher N rates compared with other two N sources.

Nitrogen Fertilization of Soybean Affects Root Growth and Nodulation on Two Soil Types in Mississippi

ABSTRACTGreenhouse studies were conducted to evaluate the influence of nitrogen (N) sources [urea + ​N-(n-butyl) thiophosphoric triamide, NBPT (urease inhibitor) and polymer-coated urea (PCU)] and rates on soybean root characteristics, nodule formation, and biomass production on two soil types (silt loam and clay) commonly cropped to soybean in Mississippi. About 15% less belowground biomass was produced in clay soil than in silt loam soil directly corresponding to all other root parameters including root length, root area, root diameter, and nodule number. Pooled across N rates, N additions resulted in 19% and 52% decrease in belowground biomass and number of nodules, respectively, across soils compared to soybean receiving no N. The N rate was the most critical factor as it influenced all root growth parameters. Number of nodules were 24% greater with PCU than urea + NBPT. Nitrogen additions and clay soil negatively impacted soybean root growth, nodulation, and belowground biomass production.Abbreviations: Polymer-coated urea, PCU; N-(n-butyl) thiophosphoric triamide, NBPT

Polymer‐Coated Urea Application Could Produce More Grain Yield in “Super” Rice

Core Ideas Polymer‐coated urea could increase both grain yield and nitrogen use efficiency in rice production, particularly in super rice.Larger sink size, more productive tillers and deeper root distribution are important agronomic performances in super rice.Higher plant activities are important physiological traits in super rice. Extensive economic reforms have resulted in a significant decrease in the involvement of rural labor force in rice (Oryza sativa L.) production in China. One of the most effective ways in minimizing the use of labor in field management while maintaining or even increasing grain yield is by using polymer‐coated urea (PCU) instead of conventional urea (CU). This study investigated whether super rice (SR) cultivars could exhibit better yield performance and nitrogen use efficiency (NUE) under PCU application than non‐super rice (NSR) cultivars. Two representative SR cultivars and two representative NSR cultivars were field grown. Three treatments, no nitrogen application (0N), CU application, and PCU application, were conducted, the application N rate of CU and PCU were both 200 kg N ha−1. Compared to NSR cultivars, SR cultivars had larger sink size, more productive tillers, larger root biomass and deeper root distribution, higher root oxidation activity at mid‐ and late grain‐filling period, greater aboveground biomass production at mid‐ and late growth stages, and greater nonstructural carbohydrate (NSC) accumulation in the stem and more nonstructural carbohydrate per spikelet (NPS) at anthesis under PCU. Polymer‐coated urea increased grain yield and agronomic NUE by 11.6 and 5.5% in SR cultivars and 4.8 and 2.2% in NSR cultivars, respectively. We conclude that using PCU could increase both grain yield and NUE in rice production, especially in SR cultivars. Improved agronomic and physiological performance contributes to an increase in grain yield and NUE in SR cultivars under PCU.