Banded Urea Research Articles

Placement and nitrogen source effects on N2O emissions for canola production in Manitoba

AbstractThis study examined fertilizer nitrous oxide (N2O) emissions and canola (Brassica napus L.) grain yield for two granular urea sources (conventional and a dual urease and nitrification inhibitor [SuperU]) and three at‐planting placement methods (broadcast‐incorporated, shallow banded, and deep banded) on commercial fields in Manitoba. Nitrogen (N) rates were 100% and 70% of what was recommended based on soil test and target yield, with the 100% treatments having N2O emissions monitored. SuperU fertilizer consistently reduced N2O emissions (area‐, N‐applied‐, and yield‐based) compared to urea. Significant reductions in N2O emissions with SuperU occurred in four of six site‐years and coincided with delayed nitrification. Compared to broadcast‐incorporated, subsurface banding of conventional urea reduced N2O emissions in drier site‐years but increased emissions when rainfall was higher (especially in shallow banded urea). Across all six site‐years, shallow banding of urea resulted in significantly higher emission intensities than all other treatments. Nitrogen placement did not affect the emission reduction benefit of SuperU. N source or placement did not greatly affect canola yield within either 100% or 70% N rates. Fertilizer N recovery efficiency was also not greatly impacted by either N source or placement. The results demonstrate that dual inhibited granular urea fairly consistently reduces N2O emissions in canola production in southern Manitoba, whereas nitrogen placement had variable effects depending on growing season rainfall. However, with little agronomic benefit, the added cost of enhanced efficiency fertilizers must be overcome for widespread adoption and to achieve greenhouse gas reduction targets for the Canadian agriculture sector.

Availability of Nitrogen in Soil for Irrigated Cotton Following Application of Urea and 3,4-Dimethylpyrazole Phosphate-Coated Urea in Concentrated Bands.

Low nitrogen (N) fertilizer use efficiency for irrigated cotton has been attributed to the limited ability of tap roots to access N from concentrated subsurface bands, or the preferential root uptake of microbially-mineralized dissolved organic N. This work investigated how applying high-rate banded urea affects the availability of N in soil and the capacity of cotton roots to take up N. Soil was analyzed for water-extractable total dissolved N and inorganic N species after urea or urea coated with 3,4-dimethylpyrazole phosphate (DMPP) was applied at concentrations of 261, 455, 461, and 597 mg N kg-1 of (air-dry) soil (mean bulk density: 1.01 g cm-3). A mass balance was used to compare N applied as fertilizer and in unfertilized soil (supplied N) with the N recovered from soil within the cylinders (recovered N) at five plant growth phases. Root uptake was estimated by comparing ammonium-N (NH4-N) and nitrate-N (NO3-N) in soil sampled from within cylinders with soil sampled from immediately outside. Recovered N was up to 100% above supplied N within 30 days of applying urea above 261 mg N kg-1 of soil. Significantly lower NO3-N in soil sampled from immediately outside the cylinders suggests urea application stimulates cotton root uptake. The use of DMPP-coated urea prolonged high NH4-N in soil and inhibited the mineralization of released organic N. These results imply the release of previously sequestered soil organic N within 30 days of applying concentrated urea enhances the availability of NO3-N in the rhizosphere, reducing N fertilizer use efficiency.

Seasonal rainfall distribution drives nitrogen use efficiency and losses in dryland summer sorghum

Nitrogen (N) fertiliser inputs represent one of the largest variable costs in dryland cropping systems, and a key determinant of water-limited yield. Despite extensive research into microbial N losses via intermediate denitrification products such as N2O, limited research exists on total N losses, and the effect of increasing soil N surplus has on fertiliser use-efficiency is not clear. In this study, the fate of banded urea fertiliser N across crop uptake, soil residual N and N losses was determined using the 15N recovery technique over nine trials with four N rates (0, plus low, medium and high industry rates) across N responsive and non-N responsive sites over 3 years in dryland sorghum (Sorghum bicolor). On average, crop uptake efficiency ranged from 50% at the low and medium N rate (80 kg N ha−1) to < 38% at the highest N rate, and was as low as 5%. Nitrogen losses averaged 26.5% across all rates and trials. At the medium N rate, losses exceeded 18% in all trials, despite relatively dry seasons, and in some trials exceeded 34%. Losses of N were driven by large cumulative rain events and high early-season rainfall. In dryland systems, the inability of crops to acquire banded N fertiliser can potentially leave fertiliser stranded in the topsoil, leaving it vulnerable to losses.Download : Download high-res image (141KB)Download : Download full-size image

Three-dimensional dynamics of nitrogen from banded enhanced efficiency fertilizers

A range of enhanced efficiency fertilizers (EEFs) have been developed in response to widespread recognition of poor nitrogen (N) use efficiency (NUE) in agriculture; however, their effective utilization is not properly understood when applied in sub-surface bands. This study quantified soil chemical changes and the distribution of N species that arose from sub-surface banding of urea, a controlled release polymer-coated urea (PCU) and urea coated with either nitrification inhibitors (NIs) or a urease inhibitor (UI), over 71 days in a field trial. Banding NIs extended the duration of nitrification inhibition for up to 50 days longer than banded urea, although the duration of NI-conferred inhibition was dependant on the rate of NI-urea application. The UI preserved urea-N at a concentration which was 16-fold higher cf. standard urea over 7 days, but no urea-N was detected after 21 days. This suggests that the NUE benefits of UIs are transient when applied in sub-surface bands. Slow release of urea-N from banded PCU resulted in lower concentrations of N in the soil solution. This reduced N dispersal by ca. 50 mm cf. urea, resulting in a N-enriched zone which was considerably smaller. Relatively benign chemical conditions around PCU bands enabled rates of nitrification (NH4–N:NO3–N ratio of 46%) which were similar to urea. Collectively, these results demonstrate the relative efficacy and risks of the different EEF technologies, when applied in fertilizer bands. This knowledge supports the effective utilization of band-applied EEFs for improved NUE in agricultural systems.

Assessing Effects of Agronomic Nitrogen Management on Crop Nitrogen Use and Nitrogen Losses in the Western Canadian Prairies

Effective agronomic nitrogen management strategies ensure optimum productivity, reduce nitrogen losses, and enhance economic profitability and environmental quality. Farmers in western Canada make key decisions on formulation, rate, timing and placement of fertilizer nitrogen that are suitable for soils, weather, and farming operations within which they operate. Suitability of agronomic nitrogen management options are assessed by estimates from linear interpolations and extrapolations of temporally and spatially discrete field-plot measurements of nitrogen responses. Such estimates do not account for non-linear and offsetting biogeochemical feedbacks of nitrogen cycles and cannot provide comprehensive nitrogen budgets for alternative nitrogen management options. These limitations can be overcome by using process-based agro-ecosystem models that adequately simulate basic processes of nitrogen biogeochemical cycles and are rigorously tested against site observations. Ecosys is a process-based ecosystem model, which successfully simulated the biogeochemical feedbacks among nitrogen, carbon, and phosphorus cycles across different agro-ecosystems. This study deployed ecosys to generate spatially and temporally continuous estimates to assess crop nitrogen use and agronomic nitrogen losses from the crop fields across Alberta for alternative nitrogen fertilizer management scenarios. The study simulated effects of four nitrogen management scenarios: fall banded urea, fall banded ESN (Environmentally Smart Nitrogen), spring banded urea, and spring banded ESN on nitrogen recovery and losses from barley fields on mid-slope landforms. These simulations were done at township grids of ~10km x 10km over 2011-2015 utilizing provincial soil and climate datasets. Modelled annual N2O, N2 and NH3 emissions, and nitrogen losses in surface runoff and sub-surface discharge were lower by about 25%, 30%, 70%, and 40% respectively with spring banding than in fall banding across Alberta. Modelled barley yields and grain nitrogen uptake were similar in spring and fall banding indicating agro-economic and environmental sustainability advantage of spring banding in Alberta. These modelled estimates were consistent with estimates based on plot and laboratory research for Alberta and similar prairie conditions. This study pioneered a methodology of process-based agroecosystem modelling, which is replicable and scalable to assess cumulative impacts of alternative agronomic nitrogen management options on crop production and the environment on provincial, regional, federal, continental and global scales.

Urea Fertilizer Placement Impacts on Corn Growth and Nitrogen Utilization in a Poorly-Drained Claypan Soil

&lt;p&gt;Practices to increase nitrogen (N) use efficiency (NUE) include selecting appropriate N fertilizer sources and application methods, but minimal research has focused on these practices in poorly-drained claypan soils which are prone to N loss. This research assessed the impact of different urea fertilizer placement practices on corn (&lt;em&gt;Zea mays&lt;/em&gt; L.) production and N utilization in a poorly-drained claypan soil. Field trials were conducted in 2014 and 2015 in Missouri. Treatments consisted of pre-plant deep banding (20 cm) urea at 202 kg N ha&lt;sup&gt;-1&lt;/sup&gt; or urea plus a nitrification inhibitor (NI) (nitrapyrin) compared to pre-plant urea broadcast surface-applied or incorporated to a depth of 8 cm. In 2014, incorporating urea, deep banding urea, and deep banding urea plus NI had higher yields (&amp;gt; 10%) of corn compared to the control with grain yields ranging from 13.73 to 14.05 Mg ha&lt;sup&gt;-1&lt;/sup&gt;. In 2015, grain yields were lower than in 2014, ranging from 4.1 to 7.9 Mg ha&lt;sup&gt;-1&lt;/sup&gt;. Deep placing banded urea with a NI yielded an increase in grain yield up to 48% compared to the other treatments. Rainfall amounts were higher in 2015, which could have resulted in poorer root growth and greater N loss in deep banded treatments. In 2014, deep banding urea with a NI produced the highest NUE. Similar to NUE, silage tissue N concentrations in 2014 were greater with deep banded urea plus NI, while in 2015 silage tissue N concentrations were higher with surface applied urea. The results suggest that urea fertilizer incorporation including deep banding may improve corn grain production, N uptake, and NUE, but response was affected by climatic conditions. The addition of an NI may be an important safeguard when deep banding urea in years with excessive precipitation.&lt;/p&gt;

Use of NBPT and ammonium thiosulphate as urease inhibitors with varying surface placement of urea and urea ammonium nitrate in production of hard red spring wheat under reduced tillage management

Grant, C. A. 2014. Use of NBPT and ammonium thiosulphate as urease inhibitors with varying surface placement of urea and urea ammonium nitrate in production of hard red spring wheat under reduced tillage management. Can. J. Plant Sci. 94: 329–335. Field studies were conducted at two locations over 3 yr to evaluate the effect of surface placement of urea ammonium nitrate (UAN) and urea fertilizers, with and without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on straw and grain yield of hard red spring wheat (Triticum aestivum L.) grown under reduced tillage management. Ammonium thiosulphate (ATS) was also evaluated as a urease inhibitor with UAN. Surface sprayed applications of UAN were frequently less effective than dribble-banded UAN applications or broadcast or dribble-banded urea in increasing grain or straw yield of hard red spring wheat. Use of NBPT with the sprayed UAN increased its effectiveness, so that grain and straw yields were similar to those with urea or with surface dribble-banded UAN. Addition of NBPT to broadcast or banded urea did not increase straw or grain yield under the conditions of this study. While there was some indication that use of ATS with UAN may have had a limited effect on fertilizer efficiency, it did not increase final grain yield as compared with dribble-banded or spray UAN applied alone or with NBPT. If surface nitrogen (N) applications are used in reduced tillage systems, spray applications of UAN should be avoided in favour of dribble-band applications, or the use of urea. Alternately, NBPT may be effective in improving the efficacy of spray UAN.

NH3 volatilization, soil concentration and soil pH following subsurface banding of urea at increasing rates

Rochette, P., Angers, D. A., Chantigny, M. H., Gasser, M.-O., MacDonald, J. D., Pelster, D. E. and Bertrand, N. 2013. NH 3 volatilization, soil [Formula: see text] concentration and soil pH following subsurface banding of urea at increasing rates. Can. J. Soil Sci. 93: 261–268. Subsurface banding of urea can result in large ammonia (NH3) emissions following a local increase in soil ammonium ([Formula: see text]) concentration and pH. We conducted a field experiment to determine how application rates of subsurface banded urea impact NH3 volatilization. Urea was banded at a 5 cm depth to a silty loam soil (pH=5.5) at rates of 0, 6.1, 9.2, 13.3 and 15.3 g N m−1. Ammonia volatilization (wind tunnels), and soil [Formula: see text] concentration and pH (0–10 cm) were monitored for 25 d following urea application. Volatilization losses increased exponentially with urea application rate to 11.6% of applied N for the highest urea rate, indicating that as more urea N was added to the soil a larger fraction was lost as NH3. Cumulative NH3-N emissions were closely related (R 2≥0.85) to maximum increases in soil [Formula: see text] concentration and pH, and their combined influence likely contributed to the nonlinearity of the volatilization response to urea application rate. However, the rapid increase in NH3 losses when soil pH rose above 7 suggests that soil pH was the main factor explaining the nonlinear response of NH3 volatilization. When compared with previous studies, our results suggest that the response of NH3 volatilization losses to urea application rate in acidic soils are controlled by similar factors whether urea is broadcasted at the soil surface or subsurface banded.

Evaluation of Polymer‐Coated Urea and Urease Inhibitor for Winter Wheat in Southern Alberta

Nitrogen fertilization of winter wheat (Triticum aestivum L.) in the drier regions of the Canadian prairies is currently accomplished by banding urea or anhydrous ammonia at seeding or broadcasting urea in early spring. This study was conducted to determine if the efficacy of urea could be improved by using polymer‐coated urea (PCU) or treatment with urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT). Two field experiments were conducted for 3 yr on wheat stubble and on fallow at Bow Island and at Lethbridge. Grain yield and protein concentration response of winter wheat was determined for noncoated urea (NCU) and PCU banded in the soil at seeding at seven rates from 30 to 210 kg N ha−1 (Exp. 1) and for four N fertilizer types broadcast on the soil surface in early spring at rates of 30, 60, and 90 kg N ha−1 (Exp. 2): NCU, ammonium nitrate (AN), NBPT‐treated urea (NTU), and PCU. When N fertilizer was banded at seeding, grain yield was higher for PCU than NCU, but differences were small (&lt;100 kg ha−1, &lt;5%) and likely not due to reduced N losses. Grain protein concentration was unaffected by fertilizer type. When N fertilizer was broadcast on the soil surface in the spring, grain yield and protein concentration were similar for NCU, AN, and NTU, but reduced for PCU due to excessive delay in N release. The negligible impact of polymer coating or treatment with NBPT on urea efficacy reflects the low risk of urea N loss in this region.

Reducing ammonia volatilization in a no-till soil by incorporating urea and pig slurry in shallow bands

Incorporation of broadcast pig slurry and urea into soil is incompatible with no-till production systems and alternative application methods that reduce NH3-N loss are required. The objective of this study was to assess the impact of incorporating urea and pig slurry in shallow furrows (banding) on NH3 volatilization. A field study was conducted on a silty loam soil that had been under no-till for 2 years. Ammonia volatilization was measured for 29 days after urea and pig slurry (140 kg N ha−1) were broadcast or incorporated (5 cm) in bands. High urease activity and soil temperatures as well as an absence of rainfall combined to result in large losses of NH3-N from all treatments. Broadcast urea lost the greatest proportion of applied N (64%) followed by banded urea (31%), broadcast pig slurry (29%) and banded pig slurry (16%). High emissions from broadcast urea were consistent with previous reports of large volatilization losses on no-till soils. Presence of crop residues and associated high urease activity (288 μg NH4-N g−1 h−1) at the surface of no-till soils were likely important factors contributing to these high emissions. Incorporation of slurry and urea in bands was not as efficient in reducing volatilization as expected but not for the same reason. Relatively high emissions from banded slurry were the result of an incomplete incorporation of slurry in the shallow bands and indicate that the benefit of this practice is limited at high slurry application rates. In banded urea plots, hydrolysis of concentrated urea likely resulted in high localized NH4+ concentrations and pH, which increased NH3 source strength and emissions. Our results therefore suggest that incorporating urea in bands may not be as efficient for reducing NH3 emissions as incorporation of broadcasted urea which results in lower soil urea concentrations.

In-soil banded versus post-seeding liquid nitrogen applications in no-till spring wheat and canola

Delaying nitrogen (N) applications into the growing season as a risk management tool is a concept that has received considerable attention in recent years. A 3-yr field study with spring wheat (Triticum aestivum L.) and canola (Brassica napus L.) was conducted at two Saskatchewan locations, Indian Head and Scott. The effects of postponing N applications for up to 30 d after seeding and several application methods were evaluated against mid-row banded urea at seeding. Liquid urea ammonium-nitrate (UAN) was applied at four separate times relative to seeding, either as an in-soil coulter band or a surface band. The surface band applications were applied either with or without the addition of 5% ammonium thiosulphate (ATS), a potential urease inhibitor. The dependent variables considered included plant density and grain yield for both crops, and grain protein in wheat. The only effect on plant density occurred in canola, where the post-seeding coulter applications slightly reduced stands compared with the other treatments. Postponing N fertilization for up to 30 d after seeding compared with N fertilization at seeding did not affect the yield of canola or protein in spring wheat, but reduced the yield of spring wheat at Indian Head in 2003, which was a very dry growing season. The coulter applications only showed a slight advantage over the surface band applications. For the surface band applications, the addition of 5% ATS did not provide a noticeable advantage over UAN alone. Canola appeared to be less sensitive to post-seeding applications than spring wheat. Deferring the entire amount of fertilizer N into the growing season appears to be a viable option but it is not without risk, especially when dry conditions are encountered. Key words: Triticum aestivum L., Brassica napus L., nitrogen management, no-till, surface dribble, urea-ammonium nitrate

Transformation of Fall‐Banded Urea: Application Date, Landscape Position, and Fertilizer Additive Effects

A 2‐yr study was initiated in the fall of 2000 to generate fundamental information on the effects of application date, landscape position, and a combined urease and nitrification inhibitor (NBPT [N‐(n‐butyl) thiophosphoric triamide] and DCD [dicyandiamide], respectively) on the rate of transformation of fall‐banded urea fertilizer into NH4+ and eventually NO3− under conditions typical for Manitoba, Canada. Landscape position did not have a large effect on the conversion of banded urea to NO3− under the moisture conditions present during the autumn period at the sites. Delaying application of fall‐banded urea fertilizer into the late fall and the presence of NBPT and DCD slowed nitrification and increased the recovery of fertilizer N as NH4+ (%RFN as NH4+) in the soil before it froze. Date of application, the soil temperature on the date of application, and the accumulation of SHU (soil heat units) and NHU (nitrification heat units) were all linearly related to the %RFN as NH4+ Accumulated SHU and NHU were most strongly correlated with the %RFN as NH4+ at the end of the fall, with and without inhibitors. The interactions between time, temperature, and nitrification demonstrate that producers in the Northern Great Plains region must consider the overall length of time that fall‐applied N fertilizer will be exposed to the soil before the soil freezes, even after the soil temperature has reached a given level and even if the fertilizer is banded.

Feasibility of applying all nitrogen and phosphorus requirements at planting of no-till winter wheat

The recent advances in no-till seeding technology are providing new N management options for crop production on the prairies. The objectives of this study were to evaluate the potential interaction between P and N fertilizer on winter wheat production in a one-pass seeding and fertilizing system and to determine the feasibility of side-banding all N requirements using urea or anhydrous ammonia at planting as compared with the current practice of broadcasting ammonium nitrate early in the spring. Three forms of N fertilizer (urea, anhydrous ammonia, ammonium nitrate), three rates of N (50, 75 and 100 kg ha–1) and three rates of P (0, 9 and 17 kg P ha–1) were investigated. Urea and anhydrous ammonia were applied during the seeding operation, whereas ammonium nitrate was broadcast the following spring. Applying P fertilizer to the side and below the seed at planting with rates &gt; 9 kg Pha–1 increased grain yield in 3 out of 6 site-years when ammonium nitrate was broadcast early in the spring. The positive yield response to P corresponded to soil test levels of 24 kg P ha–1. With soil test levels greater than 34 kg P ha–1, grain yield response to P fertilizer was not observed. When urea was banded at planting, together with P fertilizer, the yield increases with the increased P rates was shown only in 1 out of 6 site-years. At 5 of th e 6 site-years, grain protein concentration was not affected by P fertilizer; while for 1 site-year, the high rate of P fertilization decreased grain protein concentration. Responses of total grain N and P yields to P fertilization were parallel to the corresponding responses of P fertilization to grain yield, and were rarely associated with N or P concentrations in the grain. Applying N fertilizer at rates of 50 to 100 kg N ha–1 increased winter wheat grain yields by 3 to 8% in 3 out of 6 site-years. The high N rates increased grain protein concentrations in all 6 site-years. Grain protein concentration was 6% greater with N fertilizer applied as ammonium nitrate in early spring than when banding urea or anhydrous ammonia at planting. More consistent improvements in grain yield and grain protein concentration were obtained when the N fertilizer was applied as ammonium nitrate in the spring. Further research is required to determine the benefits of applying some of the crop’s N fertilizer requirements at planting, to reduce the risks of N stresses when the spring application is delayed because of adverse weather or soil conditions. Key words: Ammonium nitrate, anhydrous ammonia, grain yield, nitrogen timing, phosphorus, protein, urea

Management of rhizoctonia bare patch in the South Australian mallee using a modified direct drilling system, deep-banded urea, and sowing time in relation to the break in the season

Tillage experiments in the South Australian mallee, over 8 years (1990–97), have demonstrated that cultivation directly below the seed at sowing controls rhizoctonia bare patch as effectively as 1 or 2 cultivations prior to sowing. When combined with a short chemical fallow and the use of press-wheels, this modified direct drilling technique can yield as well as, or better than, conventional farming systems. The combination of modified direct drilling and deep-banded urea increases the control of the disease in the first 2 weeks after the break in the season. In the first 2 weeks after the break, deep banding urea at sowing is more likely to increase yield, than modified direct drilling with urea broadcast at tillering, when both treatments are compared with standard direct drilling. In a reduced tillage system, a cultivation 6–11 days after the break in the season may be more effective in reducing bare patch than a cultivation at other times after the break.

Urea Placement and Nitrification Inhibitor Effects on Growth and Nitrogen Accumulation by No‐Till Winter Wheat

Reduced forage production, grain yield, and visual N deficiency symptoms in no‐till winter wheat (Triticum aestivum L.) prompted this study. Our objectives were to determine the effect of urea placement and two nitrification inhibitors—nitrapyrin [2‐chloro‐6 (trichloromethyl) pyridine] (NP) and dicyandiamide (DCD)—on aerial dry matter and N accumulation. A 4‐yr field study was conducted on a Renfrow silt loam soil (fine‐silty, mixed, thermic Udertic Paleustoli) silt loam near El Reno, OK. The seven treatments included urea fertilizer (60 kg N ha−1) with and without the two inhibitors, surface broadcast or banded 3 to 4 cm below the seed row, and an unfertilized control. Aerial dry matter accumulation during autumn was higher for banded urea plus DCD (22%) and broadcast urea plus DCD (25%), than for broadcast urea without an inhibitor. Whole plant N content during autumn also was higher for banded urea plus DCD (28%) than for broadcast urea without an inhibitor. Neither inhibitor nor placement affected total dry matter accumulation measured at tillering, but differences were noted at spike emergence, gainful, and final harvest. At spike emergence in 1991, when climatic conditions were favorable for early season wheat growth, N content was greater for broadcast urea plus nitrapyrin than for broadcast urea or banded urea without inhibitor. At final harvest, both DCD treatments exhibited greater N content than all other N treatments. In 1993, when dimatic conditions were favorable for leaching, DCD was effective in slowing nitrification and increasing N uptake, regardless of fertilizer placement. Our results suggest that fall application of DCD with urea can potentially increase autumn forage production and N content, thus prolonging the grazing season or accommodating increased stocking rates.

Availability of banded triple superphosphate with urea and phosphorus use efficiency by corn

Phosphorus fixation results in low P use efficiency in acid soils. Increase in soil pH through urea hydrolysis may improve P availability and use efficiency. Growth chamber and field experiments were conducted to evaluate effects of urea on triple superphosphate (TSP) transformation and P use efficiency. A Ste. Rosalie clay (Typic Humaquept), an Ormstown silty clay loam (Typic Humaquept) and a Chicot sandy clay loam (Typic Hapludalf) were used in the growth chamber experiment with three rates of N (0, 200 and 400 mg N kg-1), two N sources, either urea or NH4 NO3, based on 87 mg P kg-1 soil. In the field, three rates of urea (0, 60 and 120 kg N ha-1) and two rates of TSP (26 and 52 kg P ha-1) were compared on a Ste. Rosalie clay and an Ormstown silty clay loam. Compacted or blended mixtures of urea-TSP with different ratios of N:P were used in the field experiment. In the growth chamber experiment, soil pH and dissolved organic carbon (DOC) concentration was increased by added urea, and Mehlich (3) and water extractable P thus increased with increased urea. Soil pH, DOC and available P levels were not significantly affected by added NH4 NO3. Phosphorus uptake increased with added N, either urea or NH4 NO3, but P concentration increased only with addition of urea. In the field, soil Mehlich (3)-P at day 20, P uptake and use efficiency, corn yields increased when urea was applied with TSP. Compacted mixtures of urea-TSP increased P uptake and use efficiency, corn yields in comparison with blended mixtures. The beneficial effects of banded urea with TSP on P availability and P use efficiency were primarily attributed to urea hydrolysis, subsequent pH increase and organic matter dissolution as well as synergistic effect of N and P. These results indicate that compaction of urea plus TSP may offer a significant advantage over blended mixtures.

Phytotoxicity of Banded Urea Amended with Triple Superphosphate and Potassium Chloride

AbstractBanded urea can result in toxicity to corn (Zea mays L.) germination and growth, due to accumulation of NH3 and NO‐2s as a result of urea hydrolysis. Delaying urea hydrolysis through addition of acidic materials may reduce urea toxicity. Laboratory and field experiments were conducted to study phytotoxicity of banded urea amended with triple superphosphate (TSP) or KCI. A Ste. Rosalie clay (fine, mixed, frigid Typic Humaquept), an Ormstown silty clay loam (fine‐silty, mixed, frigid Typic Humaquept), and a Chicot sandy clay loam (fineloamy, mixed, frigid Typic Hapludalf) were used in the laboratory to investigate corn germination and growth across distances of 2.0 and 4.0 cm from the fertilizer band with four rates of TSP (0, 0.11, 0.22, and 0.33 g P kg−1), two rates of KCI (0 and 0.42 g K kg−1), 0.50 g urea‐N kg−1 and an unfertilized control. Field experiments were conducted on a Ste. Rosalie clay and an Ormstown silty clay loam with two rates of urea (60 and 120 kg N ha−1) and three rates of TSP (0, 26, and 52 kg P ha−1), either compacted or blended. In the laboratory experiment, NO‐2‐N, and pH decreased with TSP and KCI, due to delayed urea hydrolysis. Soil electrical conductivity (EC) increased with KCI, but was not affected by TSP. Corn growth decreased with increased soil NH3 concentration and EC. In the field, corn germination decreased with banded urea and increased with banded TSP at Day 10 after planting, but no difference was found at Day 20. Compacted mixtures of urea‐TSP increased corn germination, growth, N uptake, and yield compared with blended mixtures for the same rate of P. Compaction of urea and TSP may provide an effective way to improve efficiency of banded urea for corn production.

The toxicity of banded urea to corn growth and yield as influenced by triple superphosphate

Banding of urea in corn (Zea mays L.) production is restricted by toxic conditions from urea hydrolysis, but higher urea rates could reduce application cost. A growth chamber experiment and a field experiment were conducted to study toxicity of banded urea when applied with triple super-phosphate (TSP). In the growth chamber experiment, surface samples from a Ste. Rosalie clay (Humic Gleysol), a Chicot sandy clay loam (Grey-brown Podzol), and an Uplands sandy soil (Humo Ferric, Podzol), were used. The field experiment was conducted on a Ste. Rosalie clay, a St. Bernard loam (Eutric Brunisol), and a Chicot sandy clay loam soil. In the growth chamber experiment, banded urea increased soil pH to 7.2–7.5 at a distance of up to 4 cm from the fertilizer band, and NH3 concentrations were as high as 2.1 mM at 2 cm from the fertilizer band after 20 d. The high pH and NH3 concentrations from urea hydrolysis inhibited corn root and seedling growth. Banding TSP with urea reduced soil pH increases from urea hydrolysis and reduced NH3 concentrations. Root weights increased with added TSP in urea bands. In the field experiment, banding urea at &gt; 40 kg N ha−1 reduced plant density and shoot dry weight in early growth stages. Banding TSP with urea increased seedling growth in all soils. Maximum rates of urea compatible with increased corn yield could be increased from 40 to 80 kg ha−1 when banded with TSP. Key words: Urea, nitrogen, ammonia, triple superphosphate, phosphorus, pH, fertilization, corn (Zea mays L.)

Corn Yield and Phosphorous Uptake with Banded Urea and Phosphate Mixtures

AbstractLow fertilizer P use efficiency is a problem in crop production on acid soils, but efficiency can be affected by methods of fertilizer application. A field experiment was conducted on two eastern Canadian soils (fine‐silty to fine, mixed, frigid Typic Humaquepts) with different pH (5.0 and 6.0 initially) to evaluate the effect of banding different rates of urea with acidic P fertilizers on corn (Zea mays L.) yield and fertilizer use efficiency. Three rates of urea (0, 30, and 60 kg N ha−1) banded with two sources of P (triple superphosphate [TSP] and monoammonium phosphate [MAP] at 38.7 kg P ha−1) or alone without P fertilizer, as control, were studied in 1990. In 1991, three rates of TSP (0, 19.4, and 38.7 kg P ha−1) were used in combination with the same three rates of urea to determine the effect of banding ratio of urea‐N/TSP‐P. The residual fertilizer effects of the 1990 treatment were investigated in 1991. Banding urea with TSP or MAP increased soil extractable P (Mehlich III). At the six‐leaf stage, plant P concentrations and dry matter yield increased linearly with both banded N and P in the Ste. Rosalie soil, and quadratically in the Ormstown soil. Total N and P uptake by corn increased in both years by banding urea with TSP or MAP, and fertilizer P use efficiency increased by 40 to 80%. Urea banded with P increased grain yield in both soils. No interactions were found between banded N rates and P sources in 1990, and between banded N rates and P rates in 1991. Greater residual effects of P fertilizer were found on grain yields and P uptake where P was banded with urea compared with no urea.

Effects of rates and placement methods of urea and potassium chloride on soil nitrogen and potassium and corn dry matter yield

Placement and interaction of urea and KCl fertilizers for corn production needs to be evaluated to develop rational fertilizer management programs. A field study, involving three rates of urea and KCl with band and broadcast placements, was conducted with corn on two Quebec soils in 1988 and 1989 to determine nutrient interactions on corn (Zea mays L.) dry matter yields, N and P uptake and on soil N and K. In two sites (Chicot 1988 and Ormstown 1989) with dry surface soils, no rainfall for 5 d and significant rainfall after 5 d, broadcast urea resulted in higher dry matter yields and uptake of N than banded urea. In the Chicot 1989 site where urea application was on moist soil and followed by rainfall insufficient to move broadcast urea into the soil, banded urea was more effective than broadcast urea. Banded urea generally resulted in increased inorganic N and fixed [Formula: see text] in soil sampled from within fertilizer bands but lower levels in soil between bands in comparison with broadcast urea. Banding KCl resulted in increased exchangeable K+ in the band. Compared with exchangeable K+, fixed K+ was less affected by placement methods and rates of added N and K. Interactions between rates and placement methods of N and K on dry matter yield, N and K uptake and soil N and K were few and relatively small. Key words: Fertilizer placement, urea, KCl, Zea mays, grain, corn