Fate and efficiency of nitrogen fertilizers applied to wetland rice. II. Punjab,India

Two modified urea products (urea supergranules [USG] and sulfur-coated urea [SCU]) were compared with conventional urea and ammonium sulfate as sources of nitrogen (N), applied at 58 kg N ha^–1 and 116 kg N ha^–1, for lowland rice grown in an alkaline soil of low organic matter and light texture (Typic Ustipsamment) having a water percolation rate of 109 mm day^–1. The SCU and USG were applied at transplanting, and the whole dose of nitrogen was¹⁵N-labeled; the SCU was prepared in the laboratory and was not completely representative of commercial SCU. The SCU was broadcast and incorporated, whereas the USG was point-placed at a depth of 7–8 cm. The urea and ammonium sulfate applications were split: two-thirds was broadcast and incorporated at transplanting, and one-third was broadcast at panicle initiation. All fertilizers except the last one-third of the urea and ammonium sulfate were labeled with¹⁵N so that a fertilizer-N balance at flowering and maturity stages of the crop could be constructed and the magnitude of N loss assessed.At all harvests and N rates, rice recovered more¹⁵N from SCU than from the other sources. At maturity, the crop recovered 38 to 42% of the¹⁵N from SCU and only 23 to 31% of the¹⁵N from the conventional fertilizers, urea and ammonium sulfate, whose recovery rates were not significantly different. In contrast, less than 9% of the USG-N was utilized. Fertilizer nitrogen uptake was directly related to the yield response from the different sources. Most of the fertilizer N was taken up by the time the plants were flowering although recovery did increase up to maturity in some treatments.Analysis of the soil plus roots revealed that less than 1% of the added¹⁵N was in the mineral form. Between 20 and 30% of the¹⁵N applied as urea, SCU, and ammonium sulfate was recovered in the soil plus roots, mainly in the 0–15 cm soil layer. Only 16% of the¹⁵N applied as USG was recovered in the soil, and this¹⁵N was distributed throughout the soil profile to a depth of 70 cm, which was the lowest depth of sampling.Calculations of the¹⁵N balance showed that 46 to 50% of the urea and ammonium sulfate was unaccounted for and considered lost from the system. Only 27 to 38% of the¹⁵N applied as SCU was not recovered at maturity, but 78% of the USG application was unaccounted for. The extensive losses and poor plant recovery of USG at this site are discussed in relation to the high percolation rate, which is atypical of many ricegrowing areas.     

Fate of nitrogen fertilizer applied to lowland rice on a Sulfic Tropaquept

A field experiment was conducted on an acid sulfate soil in Thailand to determine the effect of N fertilization practices on the fate of fertilizer-N and yield of lowland rice (Oryza sativa L.). A delayed broadcast application of ammonium phosphate sulfate (16-20-0) or urea was compared with basal incorporation of urea, deep placement of urea as urea supergranules (USG), and amendment of urea with a urease inhibitor. Deep placement of urea as USG significantly reduced floodwater urea- and ammoniacal-N concentrations following N application but did not reduce N loss, as determined from an¹⁵N balance, in this experiment where runoff loss was prevented. The urease inhibitor, phenyl phosphorodiamidate (PPD), had little effect on floodwater urea- and ammoniacal-N, and it did not reduce N loss. The floodwater pH never exceeded 4.5 in the 7 days following the first N applications, and application of 16-20-0 reduced floodwater pH by 0.1 to 0.3 units below the no-N control. The low floodwater pH indicated that ammonia volatilization was unimportant for all the N fertilization practices. Floodwater ammoniacal-N concentrations following application of urea or 16-20-0 were greater on this Sulfic Tropaquept than on an Andaqueptic Haplaquoll with near neutral pH and alkaline floodwater. The prolonged, high floodwater N concentrations on this Sulfic Tropaquept suggested that runoff loss of applied N might be a potentially serious problem when heavy rainfall or poor water control follow N fertilization. The unaccounted-for¹⁵N in the¹⁵N balances, which presumably represented gaseous N losses, ranged from 20 to 26% of the applied N and was unaffected by urea fertilization practice. Grain yield and N uptake were significantly increased with applied N, but grain yield was not significantly affected by urea fertilization practice. Yield was significantly lower (P = 0.05) for 16-20-0 than for urea; however, this difference in yield might be due to later application of P and hence delayed availability of P in the 16-20-0 treatment.     

Fate of nitrogen applied in different fertilizers to the surface of a calcareous soil in Syria

¹⁵N-labelled ammonium sulphate or¹⁵N-labelled urea were each applied in solutionat a rate of 30 kg N ha^-1 to the surface of 20soil cores (52 mm internal diameter × 100 mm deep)located on a field experiment at the ICARDA station,Tel Hadya, Syria. Recovery of ¹⁵N-label in theammonium, nitrate, organic and/or urea-N pools in thesoil was measured on days 0, 1, 2, 5 and 13 afterapplication. Total recovery of ¹⁵N was initially100%, but by day 13 after application it had declinedto 51% with urea and 73% with ammonium sulphate.Ammonium nitrate labelled either as ammonium or asnitrate was also applied to the soil surface of 8other cores at the same time. ¹⁵N recovery in thefour soil N pools was measured only on day 12 afterapplication. Total recovery of ¹⁵N-label was 75%with labelled ammonium and 57% with labelled nitrate.Volatilization of ammonia from this calcareous soil(pH 8.1) is one probable mechanism of N loss fromammonium and urea fertilizers: with nitrate bothleaching beyond the base of the core (i.e. 100 mm) and denitrification were responsible for Nlosses. These large losses of N immediately afterapplication have implications for fertilizermanagement practices.     

Nitrogen behavior in tropical wetland rice soils. 2. The efficiency of fertilizer nitrogen,priming effect and A-values

Results of tracer pot experiments show that in tropical wetland rice soils, rice plants recovered 50–69% of applied fertilizer N in the first cropping, 7–12% in the second cropping and 1–4% in the third cropping. Recovery of fertilizer N in the presence of incorporated rice straw was decreased to 45–53% (first cropping), 9–12% (second cropping), and 3–5% (third cropping), respectively. Application of fertilizer N resulted in the increase in plant uptake of native soil nitrogen due to priming effect which valued 3–29% of total N uptake by the rice plants. A-values calculated show overestimated amounts of available soil N in relation to plant uptake of native soil N. Perhaps their use in assessing fertilizer requirement in tropical wetland rice soils would be of limited meaning.     

8. New developments in nitrogen fertilizers for rice

The efficiency of nitrogen (N) fertilizer products and practices currently used on rice is low, and improving this efficiency would be very beneficial to rice-growing countries. The development of new N fertilizers is best achieved by following a logical sequence of testing and evaluation procedures in a variety of settings from the laboratory to the farmer's field. Novel N fertilizers currently at various stages of testing include urea supergranules for deep placement, urea coated with various materials to control the N release rate, mixtures of a urease inhibitor with urea to reduce losses, and organic N sources other than urea.     

Processes of nitrogen loss from fertilizers applied to flooded rice fields on a calcareous soil in north-central China

Losses of nitrogen were investigated after applications of ammonium bicarbonate and urea to flooded rice at transplanting. Ammonia (NH₃) volatilization was determined by direct micrometeorological methods, and total loss of fertilizer nitrogen (N) was measured by¹⁵N balance. All the loss appeared to be in gaseous forms, since there was no evidence of leaching and runoff was prevented. The difference between N loss and NH₃ loss was thus assumed to be denitrification loss.Both NH₃ volatilization and denitrification losses were large, being 39% and 33%, respectively, of the ammonium bicarbonate N, and 30% and 33%, respectively, of the urea N applied by farmers' methods.Ammonia fluxes from the field fertilized with ammonium bicarbonate were very high for two days, and then declined rapidly as the NH₃ source in the floodwater diminished. Moderate fluxes from the field fertilized with urea continued over 6 days, but calculations showed that NH₃ transfer from floodwater to atmosphere was retarded during the middle period of the experiment, particularly on day 2 when a thick algal scum appeared on the water surface. The results indicate that this algal mass obstructed the transport of NH₃ across the water-air interface until the scum was dispersed by wind action. Nevertheless, the prolonged NH₃ losses on the urea treatment were due primarily to high floodwater pH values promoted by the strong algal growth during the daylight hours.Nitrogen-15 balance studies showed that incorporation of fertilizer into drained soil substantially increased recoveries of fertilizer N in rice plants and soil compared with incorporation of fertilizer in the presence of standing floodwater. Ammonia loss measurements on these treatments when urea was applied suggested that the improvement in fertilizer N efficiency was due mainly to reductions in NH₃ loss.     

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.     

Time and mode of nitrogen fertilizer application to tropical wetland rice

In experiments with transplanted rice (Oryza sativa L.) at the International Rice Research Institute, Philippines, two methods of split application of urea and ammonium sulfate were compared with deep, point placement (10 cm) of urea supergranules and broadcast application of a slow-release fertilizer sulfur-coated urea (SCU). Comparisons were made in the wet and dry seasons and were based on rice yield and N uptake. Urea- and ammonium-N concentrations and pH of the floodwater were measured to aid interpretation of the results.Split applications of urea were generally less efficient than ammonium sulfate. The split in which the initial fertilizer dose was broadcast and incorporated into the soil before transplanting was more effective than the split in which the fertilizer was broadcast directly into the floodwater 21 days after transplanting. Both split applications were inferior to the urea supergranules and SCU, in terms of both yield and N uptake efficiency; average apparent N recoveries ranged from 30% for the delayed split urea to 80% for the urea supergranule.Broadcast applications of urea and ammonium sulfate produced high floodwater concentrations of urea- and ammonium-N, which fell to zero within 4–5 days. Floodwater pH was as high as 9.3 and fluctuated diurnally due to heavy algal growth. Ammonia volatilization and algal immobilization of N in the floodwater were probably responsible for the poor efficiency of the split applications; the supergranules and SCU on the other hand produced low floodwater N concentrations and were efficiently used by the rice crop.     

Fate and efficiency of sulfur fertilizer applied to food crops in West Africa

Increased food production in West Africa must be linked to increased fertilizer use. However, the increased use of the high analysis sulfur-free materials currently available in the region will lead to increased incidence of sulfur (S) deficiency. In order to determine the S fertilizer requirements of major cereal crops, and compare the fate and efficiency of alternative S sources, experiments were conducted at six sites in semiarid and subhumid West Africa from 1985–1988. Sulfur fertilizers increased grain yields from 10% to 65% (200 to 2000 kg/ha) in 14 out of 20 site-years (at 5 out of 6 sites). Maximum response was generally obtained with only 5–10 kg S/ha. Both powdered (–60 mesh S⁰) and granular (S⁰-fortified TSP) elemental S sources were usually as effective as sulfate sources (gypsum or SSP). The residual effectiveness of S⁰, however, was superior to that of sulfate at most sites. Sulfur-35 balances demonstrated substantial leaching and low crop recovery (5%–10% of S applied) of fertilizer S. Up to 50% of the applied S was lost from sulfate sources, whereas <20% was lost from S⁰ sources. Although S⁰ sources were at least as effective as sulfate sources, the low S rates required suggest that S deficiencies in the region can be corrected at relatively low cost with sulfate-containing fertilizers, provided they can be supplied at more appropriate nutrient ratios.     

Fate of fertilizer nitrogen applied to wheat under simulated mediterranean environmental conditions

Triticum aestivumThe fate of fertilizer nitrogen applied to dryland wheat was studied in the greenhouse under simulated Mediterranian-type climatic conditions. Wheat, L., was grown in 76-cm-deep pots, each containing 50–70 kg of soil, and subjected to different watering regimes. Two calcareous clay soils were used in the experiments, Uvalde clay (Aridic Calciustoll) and Vernon clay (Typic Ustochrept). Fertilizer nitrogen balance studies were conducted using various¹⁵N-labeled nitrogen sources, including ammonium nitrate, urea, and urea amended with urea phosphate, phenyl phosphorodiamidate (a urease inhibitor), and dicyandiamide (a nitrification inhibitor). Wheat yields were most significantly affected by available water. With additional water during the growing period, the recovery of fertilizer nitrogen by wheat increased and the fraction of fertilizer nitrogen remaining in the soil decreased. In the driest regimes, from 40 to 65% of the fertilizer nitrogen remained in the soils. In most experiments the gaseous loss of fertilizer nitrogen, as estimated from unaccounted for¹⁵N, was not significantly affected by water regime. The¹⁵N not accounted for in the plant and the soil at harvest ranged from 12 to 25% for ammonium nitrate and from 12 to 38% for regular urea. Direct measurement of labeled ammonia loss from soil indicated that ammonia volatilization probably was the main N loss mechanism. Low unaccounted-for¹⁵N from nitrate-labeled ammonium nitrate, 4 to 10%, indicated that N losses due to denitrification, gaseous loss from plants, or shedding of anthers and pollen were small or negligible. Amendment of urea with urea phosphate to form a 36% N and 7.3% P product was ineffective in reducing N loss. Dicyandiamide did not reduce N loss from urea presumably because N was not leached from the sealed pots and denitrification was insignificant. Amendment of urea with 2% phenyl phosphorodiamidate reduced N loss significantly. However, band placement of urea at as 2-cm soil depth was more effective in reducing N loss than was amendment of broadcast urea with phenyl phosphorodiamidate.     

Nitrogen-15 and sulfur-35 balances for fertilizers applied to transplanted rainfed lowland rice

A field experiment was conducted on a poorly-drained Aeric Paleaquult in northeastern Thailand to determine the effect of N and S fertilizers on yield of rainfed lowland rice (Oryza sativa L.) and to determine the fate of applied¹⁵N- and³⁵S-labeled fertilizers. Rice yield and N uptake increased with applied N but not with applied S in either sulfate or elemental S (ES) form. Rice yield was statistically greater for deep placement of urea as urea supergranules (USG) than for all other N fertilizer treatments that included prilled urea (PU), urea amended with a urease inhibitor (phenyl phosphorodiamidate), and ammonium phosphate sulfate (16% N, 8.6% P).The applied¹⁵N-labeled urea (37 kg N ha^–1) not recovered in the soil/plant system at crop maturity was 85% for basal incorporation, 53% for broadcast at 12 days after transplanting (DT), 27% for broadcast at 5–7 days before panicle initiation (DBPI), and 49% for broadcast at panicle initiation (PI). The basal incorporated S (30 kg ha^–1) not recovered in the soil/plant system at crop maturity was 37% for sulfate applied as single superphosphate (SSP) and 34% for ES applied as granulated triple superphosphate fortified with S (S/GTSP). Some basal incorporated¹⁵N and³⁵S and some broadcast¹⁵N at PI was lost by runoff. Heavy rainfall at 3–4 days after basal N incorporation and at 1 day after PI resulted in water flow from rice fields at higher elevation and total inundation of the 0.15-m-high¹⁵N and³⁵S microplot borders. Unrecovered¹⁵N was only 14% for 75 kg urea-N ha^–1 deep placed as USG at transplanting. This low N loss from USG indicated that leaching was not a major N loss mechanism and that deep placement was relatively effective in preventing runoff loss.In order to assess the susceptibility of fertilizer-S to runoff loss, a subsequent field experiment was conducted to monitor³⁵S activity in floodwater for 42 days after basal incorporation of SSP and S/GTSP. Maximum³⁵S recoveries in the floodwater were 19% for SSP after 7 days and 7% for S/GTSP after 1 day. Recovery of³⁵S in floodwater after 14 days was 12% for SSP and 3% for S/GTSP.This research suggests that on poorly drained soils with a low sorption capacity, a sizeable fraction of the fertilizer S and N remains in the floodwater following application. Runoff could then be an important mechanism of nutrient loss in areas with high probability for inundation following intense rainfall.     

Effect of lime nitrogen on the efficiency of urea and other ammonium nitrogen fertilizers

Five pot experiments were conducted with wheat and rice in a net house to study the effect of lime nitrogen (LN, contains about 55% calcium cyanamide) amendment rates on the efficiency of urea, the recovery urea-¹⁵N, the efficiency of the three nitrogen fertilizers(NF), on the efficiency of urea in the three soils, and on NO ₃ ^- -N leaching from a flooded soil. A rate of LN-N of 5–8% of applied fertilizer N increased the recovery of labeled urea-N by 9.42%. The effect of LN on the efficiency of NF was urea > ammonium sulfate > ammonium chloride. Under flooded conditions, LN decreased NO ₃ ^- formation and leaching.Responses of several crops to LN amended fertilizers were also studied in field experiments. At equal NPK applications, the efficiency of basal applications to rice, wheat, corn, potatoes, soybean, peanut, grapes, peaches, melon and watermelon were bette r with LN than without. Efficiency with a basal fertilizer for rice or wheat with LN were the same as with the same fertilizer without LN applied in split applications.     

Relative ammonia loss from urea-based fertilizers applied to rice under different hydrological situations

Relative ammonia volatilization loss from prilled urea, urea supergranule (USG), neem cake-coated urea (NCU), rock phosphate-coated urea (RPCU), gypsum-coated urea (GCU), and prilled urea supplemented with dhaincha (Sesbania aculeata) green manure (Dh + PU) was measured in the fields under different hydrological situations of rice growing. Ammoniacal-N and pH of flood water were less with point placement of USG and Dh + PU treatments than with single basal broadcast applications of urea-based fertilizers. Ammonia collected with an acid trap in an enclosed chamber ranged from 1.47–3.07, 0.24–3.74, 0.80–3.50 and 0.50–1.20% of the applied N in upland, alternate wetting and drying, shallow submergence and intermediate deep water situations, respectively. The collected ammonia was less with point placement of USG at 5 cm depth in all situations and with Dh + PU treatment in shallow submergence than with other sources of N. Single basal broadcast applications of RPCU or NCU resulted in relatively higher loss. The loss from top-dressed urea was less than that from basally applied urea because of larger crop canopy at later stages of crop growth.     

Risk and nitrogen use on rainfed rice: Bicol,Philippines

Year to year variability in nitrogen response is widely believed to be responsible for low levels of fertilizer application by risk averse farmers. Certain authors have claimed that production risk is not responsible for sub-optimal applications of fertilizer. Since these studies estimated fertilizer response in irrigated areas or in simulated rainfed areas in experiment stations they may have underestimated the degree of risk faced by the majority of farmers.This study seeks to address this issue of risk under farmers' conditions by using data from rainfed farmers fields in a risky rice growing area of the Philippines.Long term distributions of factors responsible for temporal variability in N-response, such as moisture stress and typhoons, are derived by using a rainfall simulator and a water balance model. These distributions are combined with a hetereoscedastic nitrogen response function to simulate long term yield distributions at different N-rates. The application of risk averse and risk neutral decision making models shows that risk aversion reduces fertilizer application by only 7–9%. These results occur because as N-rates increase, the benefits from increased average profits outweigh the disadvantages of increased variability in profits. These findings provide additional evidence to support the emerging consensus that the impact of risk aversion on fertilizer use is much smaller than previously believed.     

Maize production and nitrous oxide emissions from enhanced efficiency nitrogen fertilizers

Nutrient Cycling in Agroecosystems - Enhanced efficiency nitrogen fertilisers (EENFs) attempt to improve nitrogen use efficiency (NUE) by synchronizing nitrogen (N) supply with crop demand to...     

Effect of phenyl phosphorodiamidate on the fate of urea applied to wetland rice fields

The effect of phenyl phosphorodiamidate (PPD) on floodwater properties, N uptake,¹⁵N recovery, and grain yield of wetland rice (Oryza sativa L.) was evaluated in a series of field studies conducted at Muñoz and Los Baños, Philippines. Prilled urea and PPD-amended urea were applied to soil and incorporated immediately prior to transplanting or applied to floodwater after transplanting. Urea was also deep-placed or added in a coated form in two studies.The addition of PPD with urea retarded urea hydrolysis by 1–3 days, depending on the time and method of application. Significant reductions in the concentration of ammoniacal-N in floodwater resulted when PPD-amended urea was applied between 18 and 26 days after transplanting (DT). In contrast, PPD did not appreciably affect the concentration of ammoniacal-N in floodwater when applied with urea either immediately before or after transplanting of the seedlings.Plant N uptake and grain yield were not significantly affected by the addition of PPD with urea in three of the four experiments conducted, even though PPD substantially reduced the concentration of ammoniacal-N in the floodwater in several treatments in these studies. The¹⁵N balance studies conducted at both field locations showed PPD to increase total¹⁵N recovery by between 10% and 14% of the¹⁵N applied, 14 days after the application of urea. No further loss of¹⁵N occurred between the initial sampling (40 DT) and grain harvest at Los Baños. An increase in¹⁵N recovery occurred at grain harvest at Muñoz because¹⁵N-labeled urea was applied at 50 DT in the study. PPD increased the amount of¹⁵N in the plant and nonexchangeable soil N fraction at all harvests at Los Baños. In contrast, at Muñoz, PPD increased the quantity of¹⁵N in the KCL-extractable pool 14 days after urea was applied. Reasons for the discrepancies in results between experiments and the overall failure of PPD to increase grain yield are discussed.     

Ammonia volatilization from nitrogen fertilizers applied to cereals in two cropping areas of southern Australia

As farmers in southern Australia typically apply nitrogen (N) to cereal crops by top-dressing with ammonia (NH₃) based fertilizer in late winter or early spring there is the potential for large losses of NH₃. This paper describes the results of micrometeorological measurements to determine NH₃ loss and emission factors following applications of urea, urea ammonium nitrate (UAN), and ammonium sulfate (AS) at different rates to cereal crops at two locations in southern Australia. The amounts of NH₃ lost are required for farm economics and management, whilst emission factors are needed for inventory purposes. Ammonia loss varied with fertilizer type (urea?>?UAN?>?AS) and location, and ranged from 1.8 to 23?% of N applied. This compares with the emission factor of 10?% of applied N advocated by IPCC ( 2007). The variation with location seemed to be due to a combination of factors including soil texture, soil moisture content when fertilizer was applied and rainfall after fertilizer application. Two experiments at one location, 1?week apart, demonstrated how small, temporal differences in weather conditions and initial soil water content affected the magnitude of NH₃ loss. The results of these experiments underline the difficulties farmers face in timing fertilization as the potential for loss, depending on rainfall, can be large.     

Nitrogen losses from fertilizers applied to maize, wheat and rice in the North China Plain

Ammonia volatilization, denitrification loss and total nitrogen (N) loss (unaccounted-for N) have been investigated from N fertilizer applied to a calcareous sandy loam fluvo-aquic soil at Fengqiu in the North China Plain. Ammonia volatilization was measured by the micrometeorological mass balance method, denitrification by the acetylene inhibition – soil core incubation technique, and total N loss by ¹⁵N-balance technique. Ammonia loss was an important pathway of N loss from N fertilizer applied to rice (30–39% of the applied N) and maize (11–48%), but less so for wheat (1–20%). The amounts of unaccounted-for fertilizer N were in the order of rice > maize > wheat. Deep placement greatly reduced ammonia volatilization and total N loss. Temperature, wind speed, and solar radiation (particular for rice), and source of N fertilizer also affect extent and pattern of ammonia loss. Denitrification (its major gas products are N₂ and N₂O) usually was not a significant pathway of N loss from N fertilizer applied to maize and wheat. The amount of N₂O emission (N₂O is an intermediate product from both nitrification and denitrification) was comparable to denitrification loss for maize and wheat, and it was not significant in the economy of fertilizer N in agronomical terms, but it is of great concern for the environment.