Polymer-coated Urea Treatments Research Articles

Polymer-coated urea applied at one-time mechanical topdressing increases nitrogen use efficiency and rice yield in the cold area

Context The application of slow and controlled release fertilisers can reduce nitrogen loss, but the research is still scarce in the cold rice region of China. Aims The study was conducted to screen slow-release or controlled-release fertilisers which can meet the nitrogen demand of rice and reduce NH3 volatilisation in different pH soils. Methods This experiment includes four fertilisation treatments: no fertiliser (control), urea, urea with N-(n-butyl) thiophosphorictriamide (NBPT), and polymer-coated urea (PCU). The amounts of urea-N, pH, ammonium-N (NH4+-N) in the surface water, and NH3 volatilisation were determined. Thereafter, to evaluate the effects of one-time mechanical topdressing of PCU mixed with compound fertilisers along with farmers’ fertilisation practice (FFP), field experiments carried out in wide soil pH differences were conducted. Key results Cumulative NH3 volatilisation was reduced in the NBPT treatment compared with the urea treatment. There was no significant difference between urea-N, NH4+-N, and pH in the surface water under PCU and control. NH3 volatilisation of PCU is negligible and significantly prolongs the soil nitrogen storage time. In the subsequent experiment, PCU blend increased yield, dry matter, nitrogen uptake, and the partial factor productivity of applied nitrogen (PFPN) compared to FFP. Conclusions PCU treatment slows down urea release and reduces ammonia volatilisation from paddy fields. In turn, it reduces ammonia-nitrogen levels and pH in surface water and further slows down the rate of ammonia volatilisation. Implications Application of PCU as a one-time mechanical topdressing fertiliser in rice fields in cold regions saves nitrogen fertiliser, increases crop yields, and reduces labour.

Polymer-coated urea application can increase both grain yield and nitrogen use efficiency injaponica-indicahybrid rice

AbstractWe investigated whether the one-time application of polymer-coated urea (PCU) before transplanting could simultaneously improve the grain yield and nitrogen use efficiency (NUE) ofjaponica-indicahybrid rice (JIHR) through a field experiment. The local high-yield JIHR cultivar Chunyou-927 was field grown during the rice-growing seasons in 2019 and 2020. The experiment consisted of three treatments: no nitrogen application (0N), application of conventional urea (CU), and the one-time application of PCU. Grain yield was 1.0–1.3 t/ha higher, and agronomic NUE (kg grain yield increase per kg N applied) was 5.2–5.9 kg/kg higher, respectively, under the PCU treatment compared with the CU treatment across the two study years. When compared with the CU treatment, the PCU treatment could (1) improve root morphological trait, (2) reduce redundant vegetative growth during the early growth period, (3) increase matter production during the mid and late growth period, and (4) increase plant activity during the grain-filling period. Overall, our findings indicate that one-time PCU application before transplanting of the JIHR cultivar holds great promise for increasing grain yield and NUE.

Effect of controlled-release fertilizers on leaf characteristics, grain yield, and nitrogen use efficiency of machine-transplanted rice in southwest China

ABSTRACT Controlled-release fertilizers (CRFs) are known to improve grain yield and N-use efficiency (NUE) without intensive labor input in crop production. Here, we report field experiments conducted to investigate the effects of different CRFs [polymer coated complex fertilizer (PCCF), polymer-coated urea (PCU), and sulfur-coated urea (SCU)] on leaf characteristics, biomass, N uptake, grain yield, and NUE of machine-transplanted rice in Sichuan, China, from 2016 to 2017. Grain yield, N recovery efficiency (NRE), N agronomic efficiency (NAE), and N partial factor productivity (PFP) were positively correlated with improved leaf characteristics, dry matter accumulation, and N uptake. Total leaf area, leaf area, chlorophyll content, and net photosynthetic rate of the top three leaves, maximum accumulation rate of dry matter, and N accumulation, as well as panicles per m2 and spikelets per panicle were increased by CRFs, thereby increasing both grain yield and NUE. Furthermore, compared to PCCF and SCU, PCU promoted relatively higher leaf photosynthetic potential of the top three leaves, which is closely related to increased biomass and N uptake. These effects ultimately improved grain yield, NRE, NAE, and PFP under the PCU treatment. Thus, PCU is effective in enhancing grain yield and NUE in machine-transplanted rice.

Growing season nitrate leaching as affected by nitrogen management in irrigated potato production

AbstractNitrate leaching from potato (Solanum tuberosum L.) production is of great concern because of its potential effects on water resources. Suction lysimeters were used in combination with a one‐dimensional flow model to quantify NO3–N leaching under irrigated potato produced on sandy soils near Québec City, QC, Canada. The 3‐yr (2010−2012) study compared a single application of polymer‐coated urea (PCU) and split‐applied soluble N fertilizers (ammonium nitrate, AN; ammonium sulfate, AS) at three N rates (120, 200, and 280 kg N ha−1) in addition to an unfertilized control. Fertilizer N application increased total seasonal NO3–N leaching. A single application of PCU increased total seasonal NO3–N leaching in 2011 compared with AN and AS, which was attributed to a greater soil NO3–N concentration under the PCU treatment in combination with increased rainfall during the tuber bulking phase (60−90 d after planting). Total seasonal NO3–N leaching in 2012 was reduced with PCU and AS compared with AN, which was attributed to reduced soil NO3–N concentrations between planting and hilling when rainfall was high. Regardless of the fertilizer N source, NO3–N leaching was primarily driven by precipitation, as leaching occurred when elevated soil NO3–N concentrations coincided with excess water in the soil. The results suggest that a single application of PCU is an effective strategy for reducing NO3–N leaching in years when there is significant rainfall during the period between planting and hilling.

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.

Irrigated Corn Productivity as Influenced by Nitrogen Source, Rate, and Climatic Conditions

Core Ideas Polymer coated N fertilizer was effective in improving crop yields. Chemical inhibitors used in the study was not effective in reducing environmental N losses. Varieties of available different chemical inhibitors may act differently and need to be compared and contrasted. Nitrogen fertilizer modifications such as coating or chemical additives are designed to either slow or inhibit N transformation, thereby to improve grain yield (GY) and reduce N losses. Effectiveness of these specialized products depend on various factors including climate. This field trial compared effects of various fertilizer modifications in irrigated corn (Zea mays L.) in loamy sand in Nebraska. Urea–ammonia–nitrate (UAN), UAN with 30% methylene–urea (UAN–MU), split‐applied UAN‐MU (UAN–MU–SP) and polymer‐coated urea (PCU) were evaluated in 2009. In 2010 and 2011, UAN with nitrapyrin (UAN–IN) and nutrisphere (UAN‐NS) and PCU were evaluated. The PCU treatment consistently improved GY compared to other N treatments in all 3 yr irrespective of inter‐annual climatic variations. In 2009, a dry year, UAN–MU and UAN were not different but UAN–MU–SP increased GY, grain and total N uptake (GNU, TNU) compared to UAN and UAN–MU. In dry (2009) and wet (2011) years, residual N did not differ by N rate while it was the greatest in the highest N rate in 2010, a normal year. The UAN–IN and UAN–NS improved GY, GNU, and TNU compared to UAN in 2010. These treatments performed as well or better than UAN, even when the UAN rate was higher. In 2011 that had high potential for N leaching, UAN–IN and UAN–NS did not increase GY compared to UAN. In extreme weather conditions, chemical additives failed to improve performance of UAN, when N was all applied after corn emergence.

Rice responses to single application of coated urea on yield, dry matter accumulation, and nitrogen uptake in Southern China

ABSTRACTNitrogen is the most important element for rice (Oryza sativa L.) growth. However, excessive use of conventional urea leads to serious environmental problems in China. The objective of this study was to evaluate the release patterns of coated urea and response of rice to coated urea on dry matter accumulation, nitrogen uptake, and nitrogen use efficiencies on a clay soil. A two single-year experiment was carried out in southern China to evaluate two coated urea, polymer-coated urea (PCU) and polymer-sulfur coated urea (PSCU). Nitrogen (N) release patterns of PCU and PSCU were determined in the laboratory and in the field. The release rate of PSCU in the field was much higher than that in the laboratory. And PCU had a similar release pattern both in the field and laboratory. Compared with urea, rice fertilized with PCU and PSCU had similar dry matter accumulation, but higher grain yield and N use efficiencies. Recovery efficiency of PCU treatment reached 50% in 2012 and 60% in 2013, around 40% for PSCU, which was only 16% for single application of urea.

Effects of two slow-release nitrogen fertilizers and irrigation on yield, quality, and water-fertilizer productivity of greenhouse tomato

Technical research on efficient water and nitrogen use is crucial for sustainable agricultural development. A field experiment was conducted to investigate the combined effects of two slow-release nitrogen fertilizers (polymer-coated urea (PU) and carbon-based urea (CU)) and two different irrigation water levels (conventional irrigation, CI; 90% of conventional irrigation, RI) on tomato yield, quality, and water-fertilizer productivity. Tomato yield and irrigation water productivity improved when nitrogen fertilizer was applied. Compared with U application, CU application increased tomato fruit diameter, volume, single-fruit weight, yield, and water-fertilizer productivity, therefore increasing yield by 4600kgha−1 and net income from tomato cultivation by 6313yuanha−1. Treatment with the two slow-release nitrogen fertilizers increased soluble sugar and lycopene contents and reduced nitrate content in fruits. Compared with U treatment, PU and CU treatments decreased total nitrate nitrogen residue in the 0–100cm soil layer. Compared with CI, RI significantly reduced tomato yield and net incomes under PU treatment, whereas RI did not significantly reduce tomato yield and net income under CU treatment. RI increased fruit Vc (vitamin C) and lycopene contents. Results of the study indicated that polymer-coated slow-release fertilizers may have great potential for widespread use because they improved tomato fruit quality while reducing the environmental risks caused by soil nitrogen. In addition, carbon-based, slow-release nitrogen fertilizers promise to improve fruit quality, yield, water-fertilizer productivity, and benefits associated with tomato cultivation. These fertilizers also reduce environmental risks caused by soil nitrogen and help reduce irrigation water consumption while sustaining normal tomato growth and fruit yield, making their promotion extremely beneficial.

Enhanced Efficiency Nitrogen Products Influence Ammonia Volatilization and Nitrous Oxide Emission from Two Contrasting Soils

Core IdeasAmmonia volatilization and N2O emissions from N‐sources were assessed in two soils.The N‐(n‐butyl) thiophosphoric triamide reduced NH3volatilization losses from both sandy loam and silty clay soils.Nitrapyrin and SuperU reduced N2O emissions from sandy loam soil only.Polymer coated urea was effective in reducing both NH3and N2O emissions from sandy loam soil.Right N‐source could mitigate gaseous N losses from agroecosystems.Potentials of enhanced efficiency nitrogen (EEN) products to control N losses can vary with soil pH, cation exchange capacity, organic matter, water, temperature, and management. A laboratory experiment was conducted to quantify and compare ammonia (NH3) volatilization and nitrous oxide (N2O) losses with (i) control, (ii) urea, urea treated with (iii) urease inhibitor, NBPT [N‐(n‐butyl) thiophosphoric triamide], (iv) nitrification inhibitor, nitrapyrin (NP) [2‐chloro‐6‐trichloro methyl pyridine], (v) urea stabilized with NBPT and nitrification inhibitor dicyandiamide (SuperU), and (vi) slow release N fertilizer polymer coated urea (PCU) amendments from Ulen sandy loam and Fargo silty clay soils. Across N amendments, cumulative NH3–N losses from sandy loam soil ranged from 0.7 to 4.3% of applied N, and were higher than those from silty clay soil (0.1–0.4% of applied N). In sandy loam, compared to urea, NBPT and PCU reduced NH3–N volatilization by 32.3 and 84.2%, respectively, whereas NP and SuperU increased NH3–N losses by 98.7 and 20.3%, respectively. However, in silty clay soil, only NBPT exhibited significant reduction in NH3–N losses of 71.4%, relative to urea. Cumulative N2O emissions did not differ between soil textures and ranged from 3.7 to 7.4% of applied N across N sources. However, soil N2O emissions differed among N sources in sandy loam soil. In sandy loam soil, NP, SuperU, and PCU treatments significantly reduced N2O‐N emissions by 23.5, 43.8, and 51.1%, respectively, compared to urea. Applicability of using EEN products to mitigate NH3and N2O emission losses varies with soil texture.

Cumulative release characteristics of controlled-release nitrogen and potassium fertilizers and their effects on soil fertility, and cotton growth.

To investigate the interacting effects of polymer coated urea (PCU) and polymer coated potassium chloride (PCPC) on cotton growth, an experiment was conducted with containerized plants in 2014 and 2015. There were two kinds of nitrogen fertilizer, PCU and urea, which were combined with PCPC at three application rates (40, 80 and 120 kg ha−1). The kinds of nitrogen fertilizer formed the main plot, while individual rates of PCPC were the subplots. The results suggested N and K release patterns for PCU and PCPC in the soil were closely matched to the N and K requirements by cotton. Soil inorganic nitrogen contents significantly increased by using PCU instead of urea, and the same trend was observed with soil available potassium contents, which also had increased rates. Meanwhile, the number of bolls and lint yields of cotton in the PCU treatments were 4.9–35.3% and 2.9–40.7% higher than from urea treatments. Lint yields also increased by 9.1–12.7% with PCPC80 and PCPC120 treatments compared with PCPC40 treatment at the same nitrogen type. Hence, application of PCU combined with 80 kg ha−1 of PCPC fertilizer on cotton increased the yields and fertilizer use efficiencies in addition to improving fiber quality and delaying leaf senescence.

Combined application of polymer coated potassium chloride and urea improved fertilizer use efficiencies, yield and leaf photosynthesis of cotton on saline soil

Conventional potassium fertilizers had been used widely, but few studies paid attention to controlled-release potassium fertilizer. The objective of this study was to explore the effects of polymer coated potassium chloride (PCPC) -an innovation product, especially the interaction application of PCPC and polymer coated urea (PCU) on cotton yield, fiber quality, leaf photosynthesis and fertilizer use efficiencies under salinity stressed conditions. A two-year experiment was conducted in two nearby fields with the similar fertility but varying salinity, using a split-plot design in the Yellow River Delta area of China. The main plots were assigned to the types of K fertilizers (K1-180kgha-1K from potassium sulfate, K2-90kgha-1K from potassium sulfate+90kgha-1K from PCPC, K3-54kgha-1K from potassium sulfate+126kgha-1K from PCPC, hereafter referred to as 0, 50% and 70% PCPC), while the types of N fertilizers (N1-220kgha-1N from urea, N2-110kgha-1N from urea+110kgha-1N from PCU, N3-66kgha−1N from urea+154kgha-1N from PCU, hereafter referred to as 0, 50% and 70% PCU) were assigned to the subplots. The results indicated that the lint yield, number of bolls, boll weight, lint percentage, fiber qualities, leaf photosynthesis and fertilizer use efficiencies were significantly affected by the types of K, N fertilizers and their interaction. The K and N release characteristics of PCPC and PCU under field condition were closely matched to the nutrients requirements of cotton growth. The contents of soil available K and inorganic N were significantly augmented from the first bloom stage to the initial boll-opening stage by using PCPC and PCU compared to potassium sulfate and urea treatments. Meanwhile, PCPC and PCU interaction increased lint yields by 11.16–26.44% and 14.17–32.11% in comparison with potassium sulfate and urea in 2014 and 2015, respectively, and the maximum lint yield was achieved by the combination of 70% PCPC and 50% PCU. Besides, the boll number and boll weight were improved 5.2–18.2% and 4.75–10.29% by the PCPC and PCU treatments compared to both potassium sulfate and urea treatments, respectively. The potassium recovery efficiency (KRE) and nitrogen recovery efficiency (NRE) of PCPC and PCU treatments were significantly raised by 24.34–33.77% and 19.68–36.25%, respectively, compared with potassium sulfate and urea treatments in 2014 and 2015. PCPC owned the great potential to alter the current application of potassium fertilizer due to its ubiquitous traits. The interaction of PCPC and PCU at optimal dose was significant on cotton growth in saline soil. Consequently, the application of 70% PCPC in combination with 50% PCU is recommended to increase cotton yield and fertilizer use efficiency, and to improve the fiber quality and leaf photosynthesis properties in the Yellow River Delta area of China.

Polymer‐Coated Urea Improved Corn Response Compared to Urea‐Ammonium‐Nitrate When Applied on a Coarse‐Textured Soil

Increasing economic and environmental concerns in corn (Zea mays L.) production have prompted the need for improved N management. In this study, effects of two N sources [urea‐ammonium‐nitrate (UAN) and polymer‐coated urea (PCU)] on corn response were evaluated at different N rates over three site‐years. An additional N treatment of split‐applied UAN (UAN‐SP) based on the University of Nebraska‐Lincoln recommendation algorithm was also included. Leaf chlorophyll was indirectly measured using a chlorophyll meter at different corn growth stages for all N treatments to determine in‐season corn N status. Both PCU and UAN‐SP increased grain yield compared to UAN, even when the UAN rate was higher than that of PCU or UAN‐SP. The PCU treatment applied at 168 kg N ha−1 was as effective as UAN‐SP applied at ∼200 kg N ha−1. At early growth stages, leaf chlorophyll was higher in a dry year than in wet years, when more N loss was likely. At different growth stages taken individually or together, chlorophyll meter readings were significantly correlated to grain yield. Temporal N release from PCU in the conditions of this study was not an issue, as shown by the consistently greater chlorophyll meter readings in PCU treatments than in UAN treatments, regardless of interannual climatic variations. These results indicate that PCU consistently performed better than UAN.

Polymer-Coated Urea Delays Growth and Accumulation of Key Nutrients in Aerobic Rice but Does Not Affect Grain Mineral Concentrations

Enhanced efficiency nitrogen (N) fertilizers (EEFs) may improve crop recovery of fertilizer-N, but there is evidence that some EEFs cause a lag in crop growth compared to growth with standard urea. Biomass and mineral nutrient accumulation was investigated in rice fertilized with urea, urea-3,4-dimethylpyrazole phosphate (DMPP) and polymer-coated urea (PCU) to determine whether any delays in biomass production alter the accumulation patterns, and subsequent grain concentrations, of key mineral nutrients. Plant growth and mineral accumulation and partitioning to grains did not differ significantly between plants fertilized with urea or urea-DMPP. In contrast, biomass accumulation and the accumulation of phosphorus, potassium, calcium, magnesium, copper, zinc and manganese were delayed during the early growth phase of plants fertilized with PCU. However, plants in the PCU treatment ultimately compensated for this by increasing growth and nutrient uptake during the latter vegetative stages so that no differences in biomass or nutrient accumulation generally existed among N fertilizer treatments at anthesis. Delayed biomass accumulation in rice fertilized with PCU does not appear to reduce the total accumulation of mineral nutrients, nor to have any impact on grain mineral nutrition when biomass and grain yields are equal to those of rice grown with urea or urea-DMPP.

Nitrous oxide emission and fertiliser nitrogen efficiency in a tropical sugarcane cropping system applied with different formulations of urea

Nitrous oxide (N2O) emissions from sugarcane cropped soils are usually high compared with those from other arable lands. Nitrogen-efficient management strategies are needed to mitigate N2O emissions from sugarcane farming whilst maintaining productivity and profitability. A year-long field experiment was conducted in wet tropical Australia to assess the efficacy of polymer-coated urea (PCU) and nitrification inhibitor (3,4-dimethylpyrazole phosphate)-coated urea (NICU). Emissions of N2O were measured using manual and automatic gas sampling chambers in combination. The nitrogen (N) release from PCU continued for >5–6 months, and lower soil NO3– contents were recorded for≥3 months in the NICU treatments compared with the conventional urea treatments. The annual cumulative N2O emissions were high, amounting to 11.4–18.2kg N2O-Nha–1. In contrast to findings in most other cropping systems, there were no significant differences in annual N2O emissions between treatments with different urea formulations and application rates (0, 100 and 140kgNha–1). Daily variation in N2O emissions at this site was driven predominantly by rainfall. Urea formulations did not significantly affect sugarcane or sugar yield at the same N application rate. Decreasing fertiliser application rate from the recommended 140kgNha–1 to 100kgNha–1 led to a decrease in sugar yield by 1.3tha–1 and 2.2tha–1 for the conventional urea and PCU treatments, respectively, but no yield loss occurred for the NICU treatment. Crop N uptake also declined at the reduced N application rate with conventional urea, but not with the PCU and NICU. These results demonstrated that substituting NICU for conventional urea may substantially decrease fertiliser N application from the normal recommended rates whilst causing no yield loss or N deficiency to the crop. Further studies are required to investigate the optimal integrated fertiliser management strategies for sugarcane production, particularly choice of products and application time and rates, in relation to site and seasonal conditions.

Controlled‐Release Fertilizer Effect on Potato and Groundwater Nitrogen in Sandy Soil

Controlled‐release fertilizer, specifically polymer coated urea (PCU), may reduce nitrate‐nitrogen (NO3–N) leaching to ground water; however, few if any field scale studies have been performed in Wisconsin on sandy soils to validate these assertions. A 2‐yr field experiment was conducted at the Hancock Agricultural Research Station using potato (Solanum tuberosum L.) planted in Plainfield sand. Experimental design was a randomized complete block with three replicates and four N fertilizer treatments: (i) no N, (ii) 224 kg N ha−1 as PCU, (iii) 280 kg N ha−1 as PCU, and (iv) 280 kg N ha−1 split‐applied as ammonium sulfate [(NH4)2SO4] and ammonium nitrate (NH4NO3) fertilizer. Three groundwater monitoring wells were installed in each plot, sampled weekly during the growing season, and analyzed for NO3–N, ammonium (NH4–N), and dissolved organic N. Potato N uptake and yields were similar among conventional fertilizer and the PCU treatments; PCU may only be economically viable when applied at lower than recommended rates. Significant increases in the partial nutrient balance (PNB) were calculated for 224 kg N ha−1 of PCU compared to 280 kg ha−1 of PCU or conventional fertilizer. These large gains in N use efficiency were not reflected in the groundwater quality. The plot‐to‐plot variation in groundwater nitrate concentration was too large to statistically determine differences among fertilizer treatments. Therefore, relying on measurements of N uptake and N use efficiency are the clearest way to assess impacts of N fertilizer on groundwater quality.

Effect of dietary polymer-coated urea and sodium bentonite on digestibility, rumen fermentation, and microbial protein yield in sheep fed high levels of corn stalk

Four ruminally cannulated thin-tailed Han×Dorper crossbreed wethers were used in a 4×4 Latin square design experiment to evaluate the effect of polymer-coated urea (PCU) (Optigen II, Alltech Inc., Nicholasville, KY) and sodium bentonite (SB) on intake, nutrient digestibility, nitrogen retention, rumen fermentation and microbial nitrogen in sheep fed high levels of corn stalk. Four isonitrogenous and isocaloric dietary treatments composed of 60% corn stalk and 40% concentrate (DM basis) were offered twice daily in two equal portions at 7:00 and 19:00 h ad libitum to ensure about 5% ort. The treatments were control (CON), PCU (soybean meal replaced by 1.8% Optigen), SB (CON diet with an additional 2% SB), and PCUSB (PCU diet with an additional 2% SB). Sheep on PCU treatment showed a greater OM digestibility (P<0.05), and nitrogen digestibility (P<0.01) compared to other treatments, but digestibility of other nutrients and dry matter intake (DMI) did not change. SB did not alter nutrient digestibility except for nitrogen. Different treatments did not affect nitrogen intake, or its urinary excretion. Nitrogen retention tended to be higher (P=0.09) in sheep fed Optigen. Moreover, purine derivatives (PD) and microbial nitrogen were not influenced by different treatments. The pH and total VFA were also not influenced by the treatments. Propionate proportions increased (P<0.01) in diets that included Optigen, but an addition of SB to Optigen did not alter the ratios. NH3–N levels in PCU continuously increased, with the highest level achieved 3h after feeding, which were sustained for up to 7h. No differences were discerned in ruminal kinetics of corn stalk DM for different treatments. The PCU improved the effective degradability (ED) of corn stalk DM in 0.02 or 0.04 flow rates out of the rumen compared to both CON and PCUSB (P<0.05), but SB improved ED in 0.06 flow rates out of the rumen compared to CON. Thus, using Optigen as a new source of non-protein nitrogen to replace soybean meal in sheep fed high levels of corn stalk improved the digestibility of OM, nitrogen, and ED. Addition of SB to Optigen had no beneficial effects on nutrient digestibility, nitrogen retention, microbial nitrogen, or rumen fermentation and ED.

Effect of polymer-coated urea and tillage on the dynamics of available N and nitrous oxide emission from Gray Luvisols

Two field experiments were conducted to assess the effectiveness of polymer-coated urea (PCU) vs. conventional urea (urea) in minimizing nitrate accumulation in soil and nitrous oxide (N2O) emission while optimizing available N supply. The trials were located on Dark Gray Luvisols (Typic Cryoboralf) near Beaverlodge, Alberta (2004–2007) and Star City, Saskatchewan (2004–2006), in the north western Canadian Prairies. The treatments comprised of combinations of two tillage systems (conventional and no tillage), the two forms of urea (applied at commercial rates, 50–60 kg N ha−1), and time of application (side-banded in spring or fall). Tillage had little effect on the measured soil variables. Available N at the anthesis growth stage was higher with spring- than fall-banded N in three of four site-years, and with PCU than urea in two site-years. At seeding, nitrate in the soil layers to 60-cm depth, especially the top 15 cm, was mostly higher for fall- than spring-banded treatments but differed less between the forms of urea. Fall application, therefore, has greater potential for gaseous N and leaching losses early in the growing season when crops have low N requirements, and hence is not advisable. Nitrous oxide emission from spring to fall was higher with the fertilized treatments in three of five site-years and not different between fertilized and unfertilized treatments in the other site-years. At Beaverlodge, N2O loss was low in 2 years and showed few significant treatment effects. At Star City, N2O loss was 1.5- to 1.7-fold higher from urea than PCU treatments, and up to 1.5-fold lower from spring than fall application. It is concluded that although PCU can increase available N during the growth period and reduce N2O loss in some years compared with urea, the time of N application had a consistently greater effect than the type of urea in enhancing crop N recovery and reducing N loss to the environment.

Effect of Seed-Row Placement of Conventional and Polymer-Coated Urea on Winter Wheat Emergence

Polymer-coated urea (PCU) may facilitate nitrogen (N) placement with the seed. Laboratory experiments evaluated the effect of (i) variety and N treatment and (ii) urea contact with the seed on winter wheat (Triticum aestivum L.) emergence. Four varieties were grown in a silt loam soil (–200 kPa Ψm, where Ψm is matric potential) with control (0 kg N ha−1), PCU treatment (44% N) at 56, 112, and 168 kg N ha−1, or urea treatment (56 kg N ha−1) placed with the seed. One variety had less emergence than the control with PCU at N rates ≥112 kg ha−1. Urea delayed and decreased emergence of all varieties. In another experiment, urea (56 kg N ha−1) was placed in contact with or between seeds. The contact treatment exhibited delayed and lower emergence. The no-contact treatment behaved similar to controls. Large amounts of 44% N PCU can be placed with the seed without reducing wheat emergence when soil Ψm is at least –200 kPa.

Performance of polymer-coated urea in transplanted rice: effect of mixing ratio and water input on nitrogen use efficiency

Polymer-coated urea (PCU) is an important alternative to uncoated urea for improving nitrogen (N) use efficiency (NUE). Only a few studies discuss their utility for lowland rice systems. A 2-year field study was conducted to examine if nitrogen loading is reduced in lowland rice ecosystem by using mixture of PCU and uncoated urea without sacrificing yield. Five treatments involving two mixtures of PCU with 50 and 70% coated urea each at 70 and 50% of recommended dose (80 kg N ha−1) and one with uncoated urea at 100% recommended dose were laid out in a completely randomized design. Selected plant growth parameters and plant available N contents (NH4–N plus NO3–N) in soil solution and ponded water were measured over a period of 65 days after transplanting. Results showed no significant difference for vegetative and yield parameters among different treatments suggesting that treatments receiving lower doses of nitrogen exhibited higher NUE. Analysis of partial factor of productivity (PFP) for N suggested that the total N dose may be reduced by 50% using mixtures of coated and uncoated urea. Similarly, statistically similar PFP values for treatments receiving the same amount of total N for both years and for both total N dose suggested that the proportion of coated urea may also be reduced to as low as 50% without sacrificing yield. Correlation analysis on nitrogen contents in ponded water and soil solutions and the analysis of water productivity and PFP showed that soil water regime could also significantly influence the nitrogen status in soil even when PCU are applied. In turn, both the water regime and N contents in soil ultimately influences grain yield. Although the constant release of N from coated fertilizer ensures adequate N supply for plant uptake, it may not completely avoid N deficit condition especially during heavy rainfall. Analysis of the developed production function suggested that 55–65% polymer coating and about 100 cm total water input may be ideal for achieving maximum yield. The production function was developed for PCU treatments using data observed in treatments receiving 70% recommended N dose. The range of water input in these treatments was 86.5–174.0 cm.

Corn Response to Conventional and Slow‐Release Nitrogen Fertilizers across a Claypan Landscape

Improvement of N fertilizer recovery efficiency (NRE) is necessary to reduce excess N entering the environment and to increase economic returns. A 2‐yr field trial was established in 2005 in Northeast Missouri to determine the effects of conventional and slow‐release N fertilizer sources and landscape position (summit, sideslope, and low‐lying) on crop growth and NRE in corn (Zea mays L.) in a claypan soil. Nitrogen fertilizer treatments at 168 kg N ha−1 consisted of pre‐plant applied and incorporated polymer‐coated urea (PCU), urea, 50% PCU/50% urea mix by weight, anhydrous ammonia (AA), and a nontreated control. Gravimetric soil water content data in 2005 and 2006 indicated that the low‐lying position was often wetter than the summit and sideslope positions. Anhydrous ammonia and PCU treatments increased grain yield 1470 to 1810 kg ha−1 over urea in the low‐lying position in 2005 and 2006. Corresponding increases in plant N uptake and NRE were observed in the low‐lying position in 2005 with use of PCU and AA compared to urea, but not in 2006. Based on the grain yield results in this research and different fertilizer cost and crop prices, gross profit differences for use of PCU and preplant‐applied AA compared with urea in the low‐lying position could range from $50 to $642 ha−1. These results demonstrate that targeted use of different N fertilizer sources in claypan landscapes may increase grain yields and profitability.