Effect of granule size and the placement geometry on the efficiency of urea supergranules for wetland rice grown on a permeable soil

In a laboratory experiment 5 cm depth of water was allowed to percolate daily down through a 15 cm thick soil (Typic Ustipsamment) layer. It was observed that leaching losses of urea supergranules (USG)-N could be decreased by about 20% by the placement of four 0.25 g granules at four points instead of one 1 g granule at one point. In field microplots, the placement of approximately 30 granules of 0.30 g size instead of 9 granules of 1.00 g size resulted in reduced leaching of USG-N and, in turn, increased rice yield. In a follow-up field study, the advantage of more frequently placed USG was confirmed. As compared with 1 g USG placed in the usual manner in the center of four rice hills, increasing the density of placement in soil produced 15% more rice grain. Further increase in rice yield could be obtained by increasing the number of USG placed in the soil and decreasing the size of the granule from 1.00 g to 0.70 or 0.35 g. With USG of 0.35 and 0.70 g yields were equal or sometimes even slightly higher than with split application of prilled urea on a heavily percolating, low-CEC, light-textured soil.     

Nitrogen movement and uptake by rice fertilized with urea supergranules in two contrasting Mollisols

In a glasshouse experiment, the periodic movement, loss and uptake of N by lowland rice fertilized with point-placed urea supergranule (USG) was studied in two soils differing in texture. Movement of urea-N, NH ₄ ⁺ -N and NO ₃ ^- -N was significantly faster in Patharchatta sandy loam (Typic Hapludoll) than in Beni silty clay loam (Aquic Hapludoll) and was mostly downward with peak concentration near the placement site.Nitrogen in leachate was higher in Patharchatta sandy loam than in Beni silty clay loam. About 60–70% of leaching of urea-N took place within 2 days of USG placement. The leaching of NH ₄ ⁺ -N and NO ₃ ^- -N increased till 14 and 21 days of USG placement in Patharchatta sandy loam and Beni silty clay loam, respectively. Nitrogen leached through urea, NH ₄ ⁺ and NO ₃ ^- forms was, respectively, 64, 25 and 25% higher from sandy loam. During 49 days, 49 and 32% of the applied N was recovered by rice plants from silty clay loam and sandy loam, respectively.     

Agronomic performance of urea briquette applicator in transplanted rice

Field trials were conducted in the Philippines and India during 1989 and 1990 seasons to study comparative yield responses of transplanted rice (Oryza sativa L.) to pillow-shaped urea briquettes (UB) deep placed by an applicator (prototype developed by IFDC) and by hand immediately after transplanting. The applicator-placed UB consistently increased grain yields over the split-applied prilled urea, and the additional yields ranged from 0.23 to 1.48t ha^–1 (5 to 83%) for 25 to 63 kg N ha^–1. Agronomic responses of transplanted rice to the UB placed by the applicator and by hand were statistically equal. Modified rice hill spacing may be considered as a requirement for efficient use of the applicator. The results demonstrate that with the UB applicator it is possible to deep place UB mechanically and achieve the agronomic efficiency that is achieved by hand deep placement of the UB.     

Effect of algicides on urea fertilizer efficiency in transplanted rice

The effects of the algicides terbutryn and copper sulfate on the potential for reducing the gaseous loss of NH₃ from urea applied to rice were examined in experiments with 2 methods of N fertilizer management, 2 or 3 N rates, and 3 algicide treatments. The experiments were conducted during the 1986 dry and wet seasons in an experimental field at Pila, Laguna, Philippines.Copper sulfate had little effect as an algicide at the rate used, but terbutryn immediately reduced algal growth. The populations of species resistant to terbutryn probably increased, but terbutryn had no long-term effect on the total number of colony-forming units of algae. There was some evidence that terbutryn reduced photodependent N₂ fixation as estimated by acetylene reduction assay.Terbutryn, when applied with urea 10 days after transplanting, reduced the maximum floodwater pH by 0.9 units or more for 7 d in the DS and by about 0.5 units for 8 d in the WS. Terbutryn increased the ammoniacal-N (AN) concentration in the floodwater 100% or more in the DS and 60% in the WS. The combined effect of terbutryn on the floodwater pH and AN concentration was reduced photodependent NH₃ partial pressure (NH₃), about 25% in the DS and 38% in the WS. deceased     

Characteristics of the fate and efficiency of nitrogen in supergranules of urea

Using¹⁵ N tracer technique, the fate and efficiency of nitrogen in supergranules of urea as compared with that in powdered urea were studied in rice fields. The results obtained show that supergranules of urea were characterized by the slight N loss and high N recovery as well as by delayed but long lasting fertilization effects. It follows that the supergranules should be applied earlier and at a lower rate as compared with powdered urea.     

Nitrogen use efficiency,floodwater properties,and nitrogen-15 balance in transplanted lowland rice as affected by liquid urea band placement

Alternative N fertilizer management practices are needed to increase productivity and N use efficiency in lowland rice (Oryza sativa L.). In 1986 dry season, a field study using¹⁵N-labeled urea evaluated the effect of time and method of fertilizer N application on grain yield and N use efficiency. Conventional fertilizer application was compared with band placement of liquid urea and point placement of urea supergranules (USG). Grain yields were significantly higher with either band or point placement than with broadcast and incorporation or surface application. Partial pressure of NH₃ (NH₃) was significantly reduced when N was deep-placed.¹⁵N balance data show that fertilizer N applied basally and incorporated gave a total¹⁵N recovery of 52% and crop (grain + straw) recovery of 30%. Band placement of liquid urea N resulted in 82–90% total and 57–65% crop¹⁵N recovery. USG point placement gave 94% total and 70% crop¹⁵N recovery. Deep placement of second N application gave only slightly higher (98%)¹⁵N recovery compared with broadcast application (89%).     

Incorporation of urea for transplanted rice as affected by floodwater and growing season

Incorporation of urea into puddled rice soils is known to reduce ammoniacal-N buildup in floodwater and the subsequent loss of N as ammonia. Little is known, however, about seasonal and temperature effects on the effectiveness of basal urea incorporation in puddled soils. A field experiment was conducted in northern Vietnam on an Aquic Ustifluvent in the spring season (February to June) and summer season (July to November) to determine the effect of the presence of floodwater and method of fertilizer incorporation on floodwater ammoniacal-N, floodwater urea-N, andpNH₃ following urea application. During the 4 d following basal urea application, floodwater temperature at 1400 h was 7 to 15°C higher in summer (July) than that in spring (February), and floodwater pH at 1400 h was 0.5 to 1.0 higher in summer than that in spring. ThepNH₃ was much higher in summer than that in spring, suggesting a high potential for ammonia volatilization in summer. The movement of transplanters through the field did not reducepNH₃, irrespective of floodwater depth (0 or 5 cm) and season. Harrowing and subsequent transplanter movement partially reducedpNH₃ in the summer;pNH₃ reduction, however, was greater when floodwater depth was 0 rather than 5 cm during harrowing and transplanting. This partial reduction ofpNH₃ in summer did not result in a corresponding increase in rice yield, presumably because N losses were only slightly reduced and because yield was constrained by additional factors, such as the adverse climate. In spring, the removal of floodwater before urea application and incorporation increased grain yield by 0.2 Mg ha^–1, even thoughpNH₃ was consistently low and was not reduced by urea incorporation. This result suggests that water management and tillage during basal urea application may influence rice growth and yield in ways other than reduced N loss.     

Yield response of wetland rice to band placement of urea solution in various soils in the tropics

Alternative N-fertilizer management practices are needed to increase productivity and the N-use efficiency of flooded rice (Oryza sativa L.). Seven field experiments were conducted at various sites in Bangladesh and Indonesia to evaluate the effect of time and method of fertilizer-N application on grain yield in transplanted rice. Conventional fertilizer application was compared with band placement of liquid urea using a mechanical push-type injector and point placement of urea supergranules. With band placement, grain yields were up to 38 and 55% higher than with researchers' and farmers' practices, respectively, and similar to those with point placement of urea supergranules.     

Growth and yield of rice as affected by spacing,time and depth of placement of urea briquettes

A field study was conducted on a sandy clay soil (Entisol) in India to examine urea briquettes (UB) for lowland rice during 1986 and 1987. Grain yield was significantly greater for UB than a split application of prilled urea. At equal rates of N application, a spacing of 30 cm between two UBs was significantly better than 60 to 90 cm spacing. Two applications (10 DAT and at panicle initiation) of UB was no better than a single application (10 DAT). Placement of UB at 3–4 cm depth was significantly better than its surface application or placement at 0–1 cm depth.     

Nitrogen loss and rice profits with matrix-based slow-release urea

Paddy fields account for a large proportion of cultivated land, with huge N consumption each year. Reducing N loss via application of low-cost slow-release fertilizers is beneficial for eco-friendly rice production. The current study aimed to investigate the effects of matrix-based urea on soil N availability, rice yield, agronomical efficiency (AE), and rice profits. A 2-year field experiment was conducted during 2015 and 2016 following a randomized block design. It included three treatments, i.e., control test (CK, without urea application), common urea (CU, 150 kg N ha^?1), and matrix-based urea (MU, 150 kg N ha^?1). Besides, three laboratory experiments were conducted to investigate the N leaching, ammonia volatilization, and slow-release mechanism. Results showed that application of MU increased rice yields by > 10%, biomass by > 6%, and AE by > 30% in both seasons. Greater yield, biomass, and AE in MU were largely attributed to higher soil available N, resulted from lower risk of N leaching and ammonia volatilization. Aggregate structure was partly responsible for lower N loss in MU. Greater soil available N in MU increased rice height, leaf area, root area, leaf total chlorophyll, and activity of nitrate reductase and glutamine synthetase in flag leaves, and thus favored rice growth. Compared with CU, MU increased fertilizer cost by about 23 USD ha^?1, but increased rice profits by > 230 USD ha^?1 due to greater yield. Overall, matrix-based urea is suitable for application in field rice production, due to its low risk of N loss and acceptable profitability.     

Efficiency of modified urea fertilizers for tropical irrigated rice

An objective of the International Network on Soil Fertility and Fertilizer Evaluation for Rice (INSFFER) network is to field evaluate deep-point placement (urea supergranules) and slow-release (sulfur coated urea) N fertilizers in irrigated rice. These N sources were compared for performance with split application of prilled urea at 19 sites in Asia in wet season 1981.SCU or USG differed significantly in response curves from prilled urea at 12 of the 17 sites where N response was observed. Over these 17 sites, 22–25% less N as SCU or 29–31% less N as USG provided the same yield increment as the comparatively higher level of N as prilled urea.High profit N rates were derived for 5 sites. The optimal N levels for SCU or USG were less than for prilled urea. However, in one case for both test materials prilled urea was more profitable than SCU or USG. The marginal rates of return of using SCU or USG as opposed to OPU were calculated for the 11 sites where the response functions of the test materials differed significantly from prilled urea. In other than 2 sites for SCU the MRR exceeded 2.0 for 29 and 58 kg N ha^–1, indicating the general profitability of these materials when compared to prilled urea.     

Agronomic effectiveness of urea deep placement technology for upland maize production

Nutrient Cycling in Agroecosystems - Effective fertilizer management is critical for sustainable maize production. Field trials were conducted in six locations in northern Ghana during the 2016 and...     

Penetration depth of broadcast urea granules in puddled wetland rice soils

The efficiency of urea in wetland rice cultivation is known to be increased by placement below the soil surface. The penetration of broadcast urea into puddled soil might be a way to achieve placement of urea in soil. This paper combines an analysis of the free fall of urea granules in the atmosphere and a layer of water on the soil surface with measurements of granule penetration into puddled soils. The process of free fall can be described in terms of the height of fall in air, the depth of the water layer, and the terminal velocities and characteristic distances for free fall in air and water. The penetration depth of a particular granule with a particular velocity at the water/soil interface depends on the type of soil and its physical condition. Granule mass ranged from 0.1 to 0.5 g, granule velocity from 1 to 10 m s^–1, depth of the water layer from 0 to 30 mm and penetration depth from 0 to 35 mm. There is some indication that the penetration depth is proportional to the square root of the kinetic energy at the water/soil interface.     

Use of large granular urea (LGU) to improve efficiency of broadcast urea in wetland rice cultivation

Laboratory and greenhouse experiments were conducted to determine whether the efficiency of broadcast urea in wetland rice cultivation can be improved by using large granules which penetrate the puddled soil. In laboratory experiments the penetration increased with increasing granule size. Penetration was improved by having only a waterfilm on the soil and by the granules entering the soil with speed.In pot experiments with rice, N concentrations in the floodwater were lower with large granular urea (LGU, 6 to 8 mm diameter) dropped from a height of 2 m or shot with force into the puddled soil than with either prilled urea (PU) or LGU placed on top of the soil (+0cm). N concentrations in the floodwater were reduced even further by placement of LGU at 1 and 4 cm depths (–1 and –4cm, respectively). At all rates of N, the N uptake by grain plus straw increased with decreasing N concentrations in the floodwater. The apparent recovery of N in grain plus straw increased in an experiment on sandy soil from 61 to 85% in the order PU +0cm, LGU +0cm, LGU dropped, LGU –1cm, LGU shot and LGU –4cm. In an experiment on clay soil apparent recovery increased from 47 to 90% in the order PU +0cm, LGU +0cm, LGU dropped, LGU –0cm, LGU shot, LGU –1cm and LGU –4cm. LGU placed at –1 and –4cm resulted in significantly greater N uptake by grain plus straw than the other treatments.The experiments showed that the efficiency of broadcast urea is improved by using large urea granules, at least when conditions are favourable for penetration into the puddled soil.     

Incorporation of urea in puddled rice soils as affected by tillage implements

Thorough incorporation of urea into the soil is known to reduce the high N losses associated with the traditional practice of broadcasting urea onto puddled lowland rice fields. Few studies have, however, examined the effectiveness of farm-level implements for incorporating broadcast urea during final land preparation in small rice fields. A field experiment was conducted at two sites in the Philippines to compare the effectiveness of several commonly available and experimental tillage implements for basal incorporation of urea. The relative effectiveness of N incorporation and relative susceptibility of N to ammonia volatilization losses were assessed from floodwater (urea + ammoniacal)-N and partial pressure of ammonia (pNH₃) following urea application to puddled, unplanted soil.Conventional water buffalo- and single axle tractor-drawn comb harrows were equally, but only partially, effective in reducing floodwater (urea + ammoniacal)-N andpNH₃ by 42 to 56% of the values for broadcast prilled urea (PU) without incorporation. Removal of the comb harrow from the single axle tractor did not reduce the effectiveness of PU incorporation, indicating that the cagewheel rather than the comb harrow was largely responsible for fertilizer incorporation. An experimental conical puddler was slightly more effective than the conventional comb harrow. The movement of transplanters through the field did not effectively incorporate PU. A power weeder, frequently used by researchers to incorporate fertilizer in small experimental plots, was less effective than traditional comb harrows, reducing floodwater (urea + ammoniacal)-N by only 35%. No tillage implement for incorporating urea reducedpNH₃ as effectively as did the liquid urea band injector.Results suggest that sizeable losses of fertilizer N still occur following incorporation of PU with tillage implements commonly used by small rice farmers. Considerable scope remains for the improvement of fertilizer incorporation in puddled rice soils.     

Urea briquettes containing diammonium phosphate: a potential new NP fertilizer for transplanted rice

The rapid rise in fertilizer prices over the past 2 years coupled with the notoriously low nutrient recovery of fertilizer by lowland rice as managed by farmers of most developing countries has prompted a re-examination of urea briquette agrotechnology that improves fertilizer use efficiency.Urea briquettes containing diammonium phosphate (UB-DAP) can be cost effectively produced using a portable fertilizer briquetter on a small scale (200 kg^-1 h^-1) at the village level and at a price affordable by small rice farmers. Their improved management consists of hand placement of properly sized (weight) UB-DAP (N:P = 4:1) per briquette for every four rice hills, and at 7–10 cm soil depth, on the day of or the day after transplanting using modified 20 × 20 cm spacing (25 hills m^-2). This management is simple to adopt, saves up to 50% of the labor normally required for its conventional hand placement, and helps to reduce the lag period of spatial nonavailability of DAP-P to the rice plants. Results of several farmer-managed field trials conducted during the 1990–95 wet seasons in India demonstrate that the UB-DAP management makes the fertilizer agronomically more efficient, economically more attractive with less risk, and reduced losses of nutrients as compared with conventional use of prilled urea and single superphosphate. The fertilizer use offers women farmers a unique opportunity to play an important role in increasing rice productivity. The management of UB-DAP can be integrated with plant nutrient recycling and limited Gliricidia green manuring (an agroforestry approach). This integrated use of UB-DAP has the potential to increase rice production of small resource-poor rice farmers with less fertilizer and in sustainable manner in rainfed as well as irrigated transplanted rice ecoregions of developing countries, while protecting the environment. Therefore, the UB-DAP fertilizer can be an important NP source for transplanted rice in the 21^st century.     

Nitrogen loss from ammonium bicarbonate and urea fertilizers applied to flooded rice

Total nitrogen loss and ammonia volatilization from applications of ammonium bicarbonate and urea to flooded rice (Oryza sativa L.) grown on an acidic lacustrine clay in China were measured by¹⁵N balance and micrometeorological methods. Attempts were also made to reduce nitrogen loss by using different methods of applying the fertilizers.Ammonia volatilization from ammonium bicarbonate was greater than that from urea (18.2% and 8.8%, respectively, of the applied N). The total loss of ammonia from urea in this study was less than the losses observed in similar studies elsewhere. This was presumably because of the low incident radiation and low floodwater pHs in this experiment.Denitrification losses, calculated as the difference between total nitrogen loss and ammonia loss, were 42.2% and 39.3%, respectively, for ammonium bicarbonate and urea, and thus were more important than ammonia losses from both types of fertilizer.The different management treatments studied had an appreciable effect on ammonia flux densities but did not reduce the overall loss as measured by¹⁵N-balance.     

Movement and distribution of fertilizer nitrogen as affected by depth of placement in wetland rice

Experiments were conducted to monitor the movement and distribution of ammonium-N after placement of urea and ammonium sulfate supergranules at 5, 7.5, 10, and 15 cm. By varying depths of fertilizer placement, it is possible to determine the appropriate depth for placement machines. There were no significant differences in grain yields with nitrogen placed 5 and 15 cm deep. However, grain yields were significantly higher with deep placement of nitrogen than with split application of the fertilizer. The lower yields with split-applied nitrogen were due to higher nitrogen losses from the floodwater. The floodwater with split application had 78–98µg N ml^–1 and that with deep-placed nitrogen had a negligible nitrogen concentration.Movement of NH ₄ ⁺ -N in the soil was traced for various depths after fertilizer nitrogen application. The general movement after deep-placement of the ammonium sulfate supergranules was downward > lateral > upward from the placement site. Downward movement was prevalent in the dry season: fertilizer placed at 5–7.5 cm produced a peak of NH ₄ ⁺ -N concentration at 8–12 cm soil depth; with placement at 15 cm, the fertilizer moved to 12–20 cm soil depth. Fertilizer placed at 10 cm tended to be stable. In the wet season, deep-placed N fertilizer was fairly stable and downward movement was minimal.A substantially greater percentage of plant N was derived from¹⁵N-depleted fertilizer when deep-placed in the reduced soil layer than that applied in split doses. The percent N recovery with different placement depths, however, did not vary from each other. The results suggest that nitrogen placement at a 5-cm soil depth is adequate for high rice yields in a clayey soil with good water control. In farmers' fields where soil and water conditions are often less than ideal, however, it is desirable to place nitrogen fertilizer at greater depths and minimize NH ₄ ⁺ -N concentration in floodwater.     

The influences of organic residues on utilization of urea N by rice

The organic materials of vetch straw, isotopically labeled with¹⁵N and unlabeled, rice straw and¹⁵N-enriched urea were applied to rice in a greenhouse experiment to evaluate the release of available N during the decomposition of vetch material and its uptake by rice, and to measure the effect of organic materials on the efficiency of urea-N utilization by rice. Measurements were made at three sampling stages during the growth period. As expected, vetch material decomposed readily and furnished a continuous supply of N for the growth of rice, although only 18.1% of vetch-N was utilized by the rice crop. However, this was not sufficient to support the survival of all tillers until harvest. After harvest, 70% of vetch-N still remained in paddy soil. The influence of organic materials on urea-N absorption by rice became apparent at about the stage of panicle initiation. The highest urea-N uptake by rice was 42.2% in vetch straw-mixed soil. Otherwise, rice straw retarded urea-N uptake by rice. Nitrogen distribution data indicated that the vetch material would stimulate urea-N uptake by rice plants.The residual effect of vetch material was evaluated by planting Sudan grass immediately after rice was harvested. Only 4.4% of residual vetch-N was utilized in 20 weeks. This low percentage of N uptake and its low availability ratio demonstrated the poor residual effects of this leguminous material.