Urea Ammonium Nitrate Application Research Articles

Efficacy of fertilizer nitrogen source, stabilizer, and application timing for corn nitrogen nutrition

AbstractEnhancing fertilizer nitrogen use efficiency (NUE) in corn (Zea mays L.) production is critical for closing yield gaps, increasing producer profitability, and promoting environmental stewardship. In 2014 and 2015, a field experiment was conducted to determine the potential for fertilizer N stabilizer products to improve NUE of granular urea and urea ammonium nitrate (UAN) solution applied to strip‐till corn. A urease inhibitor (UI) or nitrification inhibitor (NI) or both were added at labeled rates to urea or UAN solution for a target rate of 180 kg N ha−1. At V3, a single application of broadcast granular urea and subsurface banded UAN solution with and without fertilizer N stabilizers was made. A split application (50% at V3; 50% at V6) of subsurface banded UAN solution served as a control representing a standard grower practice. Fertilizer N stabilizers improved components of NUE, such as grain N recovery efficiency (GNRE) and partial factor productivity (PFP). A single full rate UAN application did not differ in terms of grain yield each year but did result in less PFP and GNRE in 2015 as compared to the grower standard practice. A timely one‐time full season N rate subsurface banded application of UAN treated with UI and NI to improve NUE could be a viable substitute for the practice of multiple fertilizations. Untreated broadcast urea was inferior to UAN as a N source for corn, but when treated with both a UI and NI, NUE was improved.

Transforming waste to wealth: Impact of food waste‐derived soil amendments and synthetic nitrogen fertilizer on soil dynamics

AbstractApproximately one‐third of all food produced globally goes to waste, highlighting the need for sustainable waste management technologies like composting and anaerobic digestion. These technologies convert food waste into soil amendment products such as compost, liquid digestate (LD) and solid digestate (SD). However, these food waste‐derived soil amendments have relatively low nutrient contents compared with synthetic nitrogen (N) fertilizers such as urea, making their agricultural use challenging. Despite this, food waste‐derived soil amendments can enhance the physical and biological properties of soil, potentially creating synergistic effects when combined with synthetic N fertilizers. This study aimed to investigate effects of food waste‐derived amendments in soil applied at 50 kg ha−1 total N (compost, LD or SD) and synthetic N fertilizer [urea ammonium nitrate (UAN)] at 50 and 100 kg ha−1 total N. Over 56 days of soil incubation, greenhouse gases (CO2, N2O), soil chemistry (–N, –N, pH) and microbial biomass C (MBC) were measured. Results showed that LD + UAN 50 reduced cumulative N2O emissions by 23% compared with UAN 100, despite having the same total N and similar available N rate applied to soil. Replacing UAN with LD in farming practices can supply equivalent available N while lowering N2O emissions, offering a sustainable nutrient strategy. Moreover, applying food waste‐derived soil amendments can enhance N retention in soils, reducing the need for increased applications of synthetic N fertilizers to compensate for N deficits in farming. Food waste‐derived soil amendments can also act as a slower N release compared with UAN, reducing nitrogen run‐off. SD had the highest CO2 emissions, followed by LD and compost. SD + UAN 50 increased MBC levels because of higher carbon content and labile carbon, and available N because of the application of UAN. The major drawback of using SD compared with LD is that the process of evaporating LD to form SD causes high ammonia volatilization (ammonium in solution into ammonia gas) rates, reducing the available N in SD. Therefore, future studies should explore strategies to reduce ammonia volatilization of LD.

Optimising the root traits of summer maize to improve nutrient uptake and utilisation through rational application of urea ammonium nitrate solution

The production of summer maize is greatly affected by nitrogen (N) sources through regulating root growth and distribution. Four N treatments in the field experiment were designed as UAN (urea ammonium nitrate solution was applied under traditional side-dressing method), urea (urea was applied under traditional side-dressing method), UWFI (UAN was applied underwater and fertiliser integration technology) and CK (no N applied). The results showed that the root length density, surface area density and volume of DH605 (mid-late hybrid) and DH518 (mid-early hybrid) under UWFI were higher than other treatments, especially in shallow layers. The root absorption area of each soil layer under N application treatments varied with the growth stage. The grain yield and the accumulations of N, P and K in the shoots showed the trend of UWFI > UAN > urea > CK. Compared with UAN and urea, the nitrogen agronomic efficiency of UWFI treatment increased by 40.5~78.6%, and the nitrogen partial factor productivity increased by 4.75~7.61%. Consequently, rational application of UAN would improve root traits, nutrient uptake and utilisation, and yield of summer maize.

Using Waste Sulfur from Biogas Production in Combination with Nitrogen Fertilization of Maize (Zea mays L.) by Foliar Application.

In Europe, mainly due to industrial desulfurization, the supply of soil sulfur (S), an essential nutrient for crops, has been declining. One of the currently promoted sources of renewable energy is biogas production, which produces S as a waste product. In order to confirm the effect of the foliar application of waste elemental S in combination with liquid urea ammonium nitrate (UAN) fertilizer, a vegetation experiment was conducted with maize as the main crop grown for biogas production. The following treatments were included in the experiment: 1. Control (no fertilization), 2. UAN, 3. UANS1 (N:S ratio, 2:1), 4. UANS2 (1:1), 5. UANS3 (1:2). The application of UAN increased the N content in the plant and significantly affected the chlorophyll content (N-tester value). Despite the lower increase in nitrogen (N) content and uptake by the plant due to the application of UANS, these combinations had a significant effect on the quantum yield of PSII. The application of UANS significantly increased the S content of the plant. The increase in the weight of plants found on the treatment fertilized with UANS can be explained by the synergistic relationship between N and S, which contributed to the increase in crop nitrogen use efficiency. This study suggests that the foliar application of waste elemental S in combination with UAN at a 1:1 ratio could be an effective way to optimize the nutritional status of maize while reducing mineral fertilizer consumption.

The effectiveness of nitrogen fertilizers and nutrition systems for the winter wheat cultivation using no-till technology in the Stavropol Territory arid zone

The article presents materials on the effectiveness of nitrogen fertilizers in the nutrition system for the winter wheat cultivation using no-till technology in the Stavropol Territory arid zone for 2017-2019. As a result of the studies, it was found that all the studied doses of mineral fertilizers relative to the control option (without fertilizers) on average increased the content of nitrate (by 0.9-10.4 mg / kg) and ammonia nitrogen in the soil (by 0, 2-6.7 mg / kg) during the vegetation phases. The urea ammonium nitrate (UAN) application using Duport liquilazer contributed to an increase in the nitrate and ammonium nitrogen content in the soil layer of 0-20 cm in all phases of the winter wheat development in comparison with similar experimental options in which nitrogen fertilizers were applied using a sprayer. According to the two years research results, a steady advantage of the intra-soil application of UAN using Duport liquilazer was noticed and the difference in yield, depending on the variant, was 0.15-0.25 t / ha. However, the more effective option was the introduction of UAN N20 autumn + UAN N87 spring + water-soluble organic substance 20:20:20 (2kg / ha) + water-soluble organic substance 20:20:20 (2kg / ha) Duport liquilazer, which allowed to obtain a yield of 4.66 tons / ha.

Long-term diverse rotation alters nitrogen cycling bacterial groups and nitrous oxide emissions after nitrogen fertilization

Agriculture accounts for a majority of global soil nitrous oxide (N2O) emissions. Increased crop diversity can change soil nitrogen (N), physicochemical properties and alter belowground microbial communities, leading to changes in potential N2O emissions when inorganic N fertilizer is applied. Nitrification and denitrification are two main N cycling pathways under investigation due to their contribution to soil N cycling and production of N2O. The goal of this study was to understand the impacts of 35 years of crop diversification in shaping diversity and the community size and activity of nitrifier and denitrifier bacteria and N2O emissions after N fertilization in corn. In 2017, after fertilizer addition, N2O emissions were continuously measured using automatic chambers from a long-term experiment of simple (corn-corn-soybean-soybean) and diverse (corn-corn-soybean-wheat underseeded with red clover cover crop) four year rotations under second year corn. Soil was collected during peak N2O emissions using high frequency temporal sampling to capture shifts in 16S rRNA, amoA, nirS, nirK, nosZ1 and nosZ2 genes and gene transcripts in soil where urea-ammonium-nitrate (UAN) was applied. An N2O emission event occurred in both rotations following UAN application but was higher in the diverse rotation, which also had persistent higher total and denitrifying (nirK and nosZ2) bacterial abundance. Bacterial amoA significantly increased in both rotations shortly after UAN addition, but gene detection decreased significantly in the simple rotation and remained elevated in the diverse. Transcripts for atypical nosZ2 were consistently detected but higher after UAN addition. Total bacterial diversity did not differ between simple and diverse rotations, however, abundance of microbial pathways leading to soil N2O emissions, ammonia oxidizers and denitrifiers, were elevated in soil with a more diverse cropping history. Best management practices (BMPs) that include crop diversification need to consider microbial communities and greenhouse gas (GHG) production, in order to fully quantify the soil ecosystem services.

Urea Ammonium Nitrate Solution Treated with Inhibitor Technology: Effects on Ammonia Emission Reduction, Wheat Yield, and Inorganic N in Soil

Urea is the most used fertilizer nitrogen (N), and is often applied as urea ammonium nitrate (UAN), which may be an ammonia (NH3) emission source after application. This study examined whether the addition of urease inhibitors reduced NH3 emission, and, in combination with nitrification inhibitors, enhanced fertilizer N crop uptake. In three experiments, NH3 emission was measured from plots (100 m2) to which UAN was added with and without inhibitors. In March and May, the plots were covered with Triticum aestivum L., Sheriff (var), and in July, the soil was bare. The inhibitor mixed with urea was N-(n-butyl) thiophosphoric triamide (NBPT) and a mixture of NBPT and the new nitrification inhibitor DMPSA (3,4-Dimethylpyrazole succinic acid). Ammonia emissions were negligible from all plots after the first application of UAN due to the wet and cold weather while an average of 7% of applied UAN was emitted after application of UAN in April, where no significant effect of additives was observed. The harvest yield was low due to drought from May till August. Yield was highest when UAN was mixed with NBPT and lowest for untreated UAN. The highest emission from the bare plots was obtained from untreated UAN (17% of N), in contrast to 11% of N from the plots with added UAN + NBPT (not significant) and 7% from the plots with added UAN + NBPT + DMPSA (significantly different). Under the conditions of the current study, urease inhibitors reduce NH3 emissions in periods where the risk of emission is high, and the combination of urease and nitrification inhibitors increased yields.

Management of Nitrapyrin and Pronitridine Nitrification Inhibitors with Urea Ammonium Nitrate for Winter Wheat Production

Synchrony between soil mineral nitrogen (N) supply and crop N demand is important for optimal plant growth. Excessively wet conditions expose poorly drained soils to an increased potential of N loss and reduced N use efficiency. A two-year experiment with wheat (Triticum aestivum L.) was initiated in 2014 and concluded in 2016 in northeastern Missouri in the United States (USA). The objective of this experiment was to evaluate the effects of nitrapyrin and pronitridine nitrification inhibitors (NI) applied as an early or late-split application timing (40:60%) of 79 kg N ha−1 or 112 kg N ha−1 on winter wheat soil and plant N status, as well as grain yield. Both NIs had no effect (p = 0.3917) on yield, while there was an interaction between year and the urea ammonium nitrate (UAN) rate on grain yield. Yields were similar (3550 kg ha−1 to 3686 kg ha−1) in 2015 between UAN application rates. UAN at 112 kg N ha−1 resulted in a 551 kg ha−1 greater yield than UAN at 79 kg N ha−1 in 2016. Nitrapyrin and pronitridine did not significantly affect soil ammonium or nitrate–N concentrations at depths of 0–15 cm and 16–30 cm compared to the absence of NI over the period of three months after application. Nitrapyrin with UAN at 112 kg N ha−1 had the highest grain test weight. Further testing of these NIs in combination with UAN for winter wheat production is needed under different climatic and environmental conditions to develop comprehensive management recommendations.

Pronitridine Nitrification Inhibitor With Urea Ammonium Nitrate for Corn

Nitrification inhibitors have been used to enhance the efficiency of nitrogen fertilizers. This research evaluated the effectiveness of nontreated urea ammonium nitrate (UAN) at 0, 67, 135, 202, and 270 kg N ha-1 as well as UAN treated with nitrification inhibitors (pronitridine at 9.4 and 18.8 L ha-1 or nitrapyrin at 0.5 kg a.i. ha-1) to enhance N uptake and increase yield of corn (Zea mays L.). The study took place from 2012-2014 in upstate Missouri on a claypan soil. During the experiments, environmental conditions (high, medium, and low yielding years) affected corn response to pronitridine and nitrapyrin. In general, UAN plus pronitridine at 9.4 L ha-1 had similar effects on corn compared pronitridine at a higher (18.7 L ha-1) rate. During a high-yielding year (2014), in order to produce yields equivalent to 67 kg N ha-1 plus pronitridine at 9.4 L ha-1 or nitrapyrin, UAN needed to be increased 14 to 19%. Similarly, the amount of nontreated UAN needed to be increased 8 to 11% for yields to be equivalent to UAN at 135 kg N ha-1 plus pronitridine at 9.4 L ha-1 or nitrapyrin. Grain N removal and agronomic efficiency was highest with pronitridine at 9.4 L ha-1 and nitrapyrin combined with 67 and 135 kg N ha-1, respectively. This research indicates that pronitridine was as effective as nitrapyrin when added to a pre-emergence application of UAN placed between the rows in a dribble band.

Assessing Management of Nitrapyrin with Urea Ammonium Nitrate Fertilizer on Corn Yield and Soil Nitrogen in a Poorly-Drained Claypan Soil

Use of nitrification inhibitors (NI) in agricultural production systems is considered a risk management strategy for both agricultural and environmental considerations. It can be utilized when risk of reduced nitrogen (N) fertilizer use efficiency or yield, and risk of pollution from mineral N is high which can occur in poorly-drained soils that are vulnerable to waterlogging and runoff. Field research was conducted on corn (Zea mays L.) from 2012 to 2015 in Missouri, USA on a poorly-drained claypan soil. Treatments consisted of two application timings of urea ammonium nitrate (UAN) fertilizer solution [pre-emergence (PRE) and V3 growth stage], two application rates (143 and 168 kg N ha-1) in the presence or absence of nitrapyrin, and a non-treated control. UAN at 143 kg ha-1 with nitrapyrin at the V3 growth stage resulted in the highest yield (8.6 Mg ha-1). Similarly, pre-emergence application of UAN 168 kg ha-1 with nitrapyrin resulted in greater yields (7.7 Mg ha-1). UAN application rates and timings affected soil NO3-N and NH4-N concentrations more than the presence or absence of nitrapyrin during the growing season. A side-dress application of a lower rate of UAN with nitrapyrin at V3 was effective in poorly-drained soils when risk of N losses during the growing season due to unfavorable precipitation events and other environmental variables was high. A pre-emergence application of UAN with nitrapyrin was also effective and it may eliminate the need for split-application of N fertilizer later in the season thereby reducing the workload on growers during the growing season.

Nitrogen Fertilizer Management Practices to Reduce N2O Emissions from Irrigated Processing Potato in Manitoba

Nitrogen fertilizer practices affect nitrous oxide (N2O) emissions from agricultural soils. The “4R” nutrient stewardship framework of using N fertilizer at the right rate, right source, right placement and right time can reduce N2O emissions while maintaining or improving yield of field crops, but understanding of how the various factors affect N2O emissions from irrigated processing potato is lacking. We examined the effects of selected 4R practices on emissions, using results from two irrigated processing potato studies each conducted in 2011 and 2012 in Manitoba, Canada. Experiment 1 examined combinations of source (urea, ESN), placement (pre-plant incorporation [PPI], banding), and rate (100 and 200 kg N ha-1) on a clay loam soil. Experiment 2 examined timing and source treatment combinations (urea PPI, ESN PPI, urea split, urea split/fertigation) on a loamy fine sandy soil. For Experiment 1, use of ESN at 200 kg ha-1 did not reduce area-, yield- and applied fertilizer N- based N2O emissions compared to urea at 200 kg ha-1, irrespective of placement. Emissions from pre-plant banding ESN at 200 kg ha−1, however, were 32% lower than from PPI ESN. For Experiment 2, compared to single pre-plant urea application, fertigation simulated by in-season application of urea ammonium nitrate (UAN) gave lower area-, yield- and applied fertilizer N- based emissions. Split urea ( \( \raisebox{1ex}{$2$}\!\left/ \!\raisebox{-1ex}{$3$}\right. \) pre-plant, \( \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right. \) hilling) also reduced area- and yield- based N2O emissions compared to single pre-plant urea application. Emissions were generally lower at the site with loamy fine sandy soil than the site with clay loam soil. These results demonstrate that combinations of “4R” practices rather than source alone are best to achieve reductions in N2O emissions from irrigated potato production.

Nitrogen source and application method impact on corn yield and nutrient uptake

ABSTRACTFarmers are looking for better management practices to utilize animal manure as an alternative to chemical fertilizers. A 2-year field experiment was conducted to study the effects of nitrogen (N) fertilizer source and application methods to Nicholson silt loam soil in central Kentucky, USA for no-till corn (Zea mays) production. The region has a temperate climate with a mean temperature of 14.5°C and rainfall of 1300 mm year−1. Treatments included a control, 179 kg N ha−1 urea ammonium nitrate (UAN) applied as preplant and sidedress, and swine effluent that was applied by three methods: broadcast, injection, and Aerway. Injection method produced the greatest corn grain yield (11.88 Mg ha−1) and biomass yield (18.9 Mg ha−1) in 2007. Results demonstrated that the effluent application methods and the timing of UAN application may not be agronomically important for corn production in this region. Hence, more studies are needed on different soils in this region.

Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO3-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha−1 and the optimum N rate for corn at one location was 327 kg total sludge N ha−1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha−1, respectively, on a whole-plant basis and 2 and 10 kg N ha−1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha−1). From the 327 kg ha−1 of sludge N applied to corn, 249 kg N ha−1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH3) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO3 from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha−1), downward movement of NO3-N through the soil was similar to that for the 168 kg N ha−1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.

Long-Term Effects of Poultry Manure Application on Nitrate Leaching in Tile Drain Water

A long-term study (1998 to 2009) was initiated on eleven tile-drained field plots, ranging in size from 0.19 to 0.47 ha, to investigate the effects of poultry manure application on subsurface drainage water quality in Iowa under a corn-soybean rotation system. The experimental treatments included poultry manure at rates of 168 kg N ha-1 (PM) and 336 kg N ha-1 (PM2), each with three replications; nitrogen application from chemical fertilizer, urea ammonium nitrate (UAN), at a rate of 168 kg N ha-1 with four replications; and a control treatment that received 0 kg N ha-1. Subsurface drainage (tile) flow volume was monitored, and drainage samples were collected and analyzed for nitrate-nitrogen (NO3-N). The results from this 12-year study show that NO3-N losses with tile drainage were more likely to occur during the early stages of crop production (April to June) and were more related to the monthly distribution of precipitation than the total rainfall amount. The overall results of this study indicate that applying poultry manure at 168 kg N ha-1 resulted in significantly lower flow-weighted nitrate concentrations (PM < UAN < PM2) and the lowest nitrogen losses to subsurface drain water compared to UAN and PM2 application(PM < UAN < PM2), as well as higher crop yields compared to UAN application. Therefore, it can be concluded that poultry manure application at a rate of 168 kg N ha-1 is an environmentally sound N application practice with good yield potential for corn and soybean production systems with poorly drained soils in the upper Midwest. Future work is recommended to identify new practices and technologies to reduce nitrate loss to water systems.

Sequential Applications for Mesosulfuron and Nitrogen Needed in Wheat

Mesosulfuron is often applied to wheat at a time of year when top-dress nitrogen is also applied. Current labeling for mesosulfuron cautions against applying nitrogen within 14 d of herbicide application. Soft red winter wheat response to mesosulfuron and urea ammonium nitrate (UAN) applied sequentially and in mixtures was determined at three locations in North Carolina and Georgia during 2005 and 2006. Mesosulfuron at 0, 15, and 30 g ai/ha was applied in water to wheat at Feekes growth stage (GS) 3 followed by UAN at 280 L/ha 2 h, 7 d, 14 d, and 21 d after mesosulfuron. Mesosulfuron applied in UAN was also evaluated in 2006. Mesosulfuron injured wheat 6 to 9% in 2005 and 12 to 23% in 2006 when UAN was applied 2 h or 7 d after the herbicide. Wheat injury did not exceed 8% when UAN was applied 14 or 21 d after the herbicide. Greatest injury, 35 to 40%, was noted when mesosulfuron and UAN were combined. Wheat yield was unaffected by mesosulfuron or time of UAN application in 2005. In 2006, yield was affected by the timing of UAN application relative to mesosulfuron; wheat yield increased as the interval, in days, between UAN and herbicide applications increased. To avoid crop injury and possible yield reduction, mesosulfuron and UAN applications should be separated by at least 7 to 14 d. These findings are consistent with precautions on the mesosulfuron label.

Winter Wheat and Maize Response to Urea Ammonium Nitrate and a New Urea Formaldehyde Polymer Fertilizer

Slow release N fertilizers have potential to improve yield and nitrogen use efficiency (NUE) in winter wheat (Triticum aestivum L.) and maize (Zea mays L.). A slow release urea formaldehyde polymer (UFP) was compared with aqueous urea ammonium nitrate (UAN) [(NH2)2CO, NH4NO3] during a 2‐yr field experiment in North Carolina. Crops were grown on Candor (sandy, siliceous, thermic Grossarenic Kandiudults), Portsmouth (fine‐loamy over sandy or sandy‐skeletal, mixed, semiactive, thermic Typic Umbraquults), and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquults) soils. Treatments were N source (UFP and UAN) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha−1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha−1 for maize). Both sources were band applied as a split application for wheat, whereas maize received UFP at planting and split application of UAN, which is the current standard practice. Based on years of research, NC producers' apply less than one‐third of UAN at planting, with the remainder applied before the end of tillering (wheat) or at V4–6 (corn). For both crops and both sites, grain yield and NUE with UAN were statistically similar to or better than UFP. Laboratory incubations suggested UFP release of urea and urea hydrolysis were complete in less than 2 wk. Hence, UFP release was limited to a time scale of days, considered insignificant for summer crop (corn) growth conditions. Since the UFP did not significantly improve yield, UFP may only be economical if priced similar to UAN.

Enhancing No‐Tillage Systems for Corn with Starter Fertilizers, Row Cleaners, and Nitrogen Placement Methods

No‐till production of corn (Zea mays L.) often gives slower early plant growth, lower yields, and reduced profitability in the northern Corn Belt. The objective of this field experiment was to determine if N source/placement method and row cleaner and starter fertilizer use on high‐phosphorus testing soils would enhance no‐till production of continuous corn (CC) and corn after soybean [Glycine max (L.) Merr.] (CSb). Experiments were conducted for each cropping system on a tile‐drained Nicollet–Webster clay loam complex (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll and fine loamy, mixed, superactive, mesic Typic Endoaquoll, respectively) from 1996 to 1998. A 23 factorial design included combinations of with or without row cleaners, 0.0 or 93.5 L ha−1 (0 or 10 gal acre−1) of 10–15–0 starter fertilizer, and N sources anhydrous ammonia (AA) or spoke‐injected urea‐ammonium nitrate (UAN). A preplant broadcast application of UAN plus N‐(n‐butyl)thiophosphoric triamide (NBPT) also was compared with spoke‐injected UAN. Averaged across 3 yr, surface residue coverage during the growing season remained &gt;60% for CC and &gt;40% for CSb for all treatments, but was about 8% lower with knife application of AA compared with spoke‐injecting UAN. Grain yields were not affected by N source. Yield response to starter fertilizer depended on N source and row cleaners. Continuous corn responded to starter fertilizer (0.5 Mg ha−1 or 7 bu acre−1) when AA was used, but not when UAN was used. Yields of CSb were increased 0.5 Mg ha−1 (8 bu acre−1) by starter fertilizer when row cleaners were not used, but by only 0.2 Mg ha−1 (3 bu acre−1) when row cleaners were used. Injecting UAN increased CC and CSb yields 0.7 Mg ha−1 (10 bu acre−1) and 0.4 Mg ha−1 (6 bu acre−1), respectively, compared with preplant broadcasting of UAN plus NBPT. The data suggest that no‐till corn yields on fine‐textured, high P testing soils can be enhanced most consistently by using starter fertilizer and by injecting N below the soil surface.

Effect of nitrogen concentration of urea ammonium nitrate, and application level, on the dry matter and chemical composition ofPennisetum clandestinumandCynodonhybrid dryland pastures

Liaraquid urea ammonium nitrate (UAN) was applied to dryland Pennisetum clandestinum (Kikuyu (Chiov)) and Cynodon hybrid (Coastcross II (L.) (Pers.)) pastures at two levels (207 and 414 kg N/ha/season) and at three concentrations (10,5; 21 and 42% N) of nitrogen. The degree of leaf scorch increased as both the amount of N and the concentration of UAN increased, but persisted in all treatment combinations for between 10 and 14 days only. Scorch did not appear to materially affect yields measured six weeks after UAN application. Significant interactive effects were evident between the quantity of N applied and UAN concentration in estimates of yield and many of the quality factors. In general, however, herbage yield declined with increasing N concentration in the UAN at the low N (207 kg N/ha) level, but was highest at the 21% N concentration when the amount of N applied was twice this level (414 kg N/ha). Herbage N, K, Ca and Mg content generally declined as N concentration in the UAN increased, but P leve...