Crop response to sulfur-coated urea (SCU) and other N-carriers in sandy soils of Saudi Arabia

Nitrogen losses due to leaching, volatilization and denitrification result in low fertilizer efficiency. Slow-release N fertilizers are proposed to minimize these losses, and sulfur-coated urea (SCU) has been examined. A greenhouse study was conducted using two coarse textured: loamy sand and sandy loam soils from Al-Kharj, Saudi Arabia to compare sulfur-coated urea (SCU) with urea, ammonium nitrate (AN) and ammonium sulfate (AS) and to determine the effectiveness of single appliction of SCU over split application of soluble N sources. Tomato (Lycopersicon esculentum L.) and sorghum (Sorghum bicolor L.) were grown as indicator crops. Dry matter yields showed a significant increase with SCU fertilizers over other sources applied single or split, particularly in loamy sand soil. SCU-22 resulted in a consistent increase of dry matter yield and N-uptake compared to SCU-30 and SCU-40. The potential benefit of using SCU in coarse textured soils appers to be promising for increasing N fertilizer efficiency. Producing these slow release N fertilizers seems feasible if a coating step is added to the manufacturing process of urea produced from some fertilizer plants in Saudi Arabia.Contribution from the Regional Agriculture and Water Research Center (RAWRC), Ministry of Agriculture and Water, Riyadh, Saudi Arabia. Presented in Div. S-8, Am. Soc. Agron. Meeting, Atlanta, GA, November 1981.     

Methylene urea as a slow-release nitrogen source for processing tomatoes

The potential for improved fertilizer N use efficiency was tested using a slow release N fertilizer, methylene urea (MU), on processing tomato (Lycopersicon esculentum Mill.) in a 2-year field study in the Sacramento Valley, California. Fertilizer N use efficiency of urea and a (50:50, w:w) mixture of urea and MU (uMU) was determined in direct-seeded and transplanted tomato plots with winter cover crop (CC) or winter fallow (F) using ¹⁵N labeled fertilizers. Residual MU-N was estimated from tomato N uptake in the ¹⁵N microplots, and from residual ¹⁵N uptake of wheat grown after two tomato crops. No significant differences were found in the quantity and quality of tomato yields among fertilizer and management treatments during the first year. Total yields in transplanted FuMU plots were significantly lower in the second test year, suggesting slow mineralization of MU-N in the F treatment. On average, about 40% of added fertilizer N was taken up in both fertilizer treatments, and the recovery of ¹⁵N in plant biomass and soil was 75–96 and 50–74% in seeded and transplanted blocks, respectively. In the laboratory, mineralization of MU started faster in soils with past MU use, but the enhanced mineralization did not affect the plant N uptake in the field. MU is potentially an environmentally attractive fertilizer, but without an immediate increase in yield and N use efficiency compared to conventional fertilizers, its use on row crops may not be economically feasible unless the positive environmental factors like decreased leaching of N are considered.     

松香包膜尿素的释放特性研究

以松香为成膜物质,制备了一系列的包膜尿素,利用扫描电子显微镜研究了包膜尿素的表面形貌,用浸泡溶解法表征了所得包膜尿素的释放特性,讨论了包覆量与操作条件对包膜尿素释放特性的影响。结果表明,松香是一种优良的尿素包膜材料,包覆量在5%以上时,松香包膜尿素具有显著缓释性能,包覆量越大,缓释效果越好。     

Effectiveness of applying urea solution by furrow irrigation to wheat grown on raised beds of an impervious red-brown earth

The distribution and recovery of urea N (25 kg ha^–1) applied in solution by low-flow furrow irrigation to wheat, direct-drilled in rows in 1.5m wide permanent beds of a red-brown earth, was determined using¹⁵N labelled fertilizer. This method of fertilizer application resulted in an uneven distribution of applied N across the soil bed. Fertilizer N was recovered mainly in the upper 0.15m horizon of the soil. Forty seven percent of the applied N was recovered in the soil and plants within 0.20m of the point of application. Recovery rapidly decreased with increasing distance from the furrow and less than 4% of the urea N was recovered by the plants in the fourth row, 0.67m from the middle of the furrow. The recovery of fertilizer N in the crop was 23, 28, 47 and 40% at 13, 32, 59 and 86 days, respectively; the corresponding total recovery in the crop plus soil was 77, 91, 87 and 75%; the mean being 83 ± 8%.The results suggest that with this method of fertilizer application and these soil properties the furrows should be less than 0.75m apart in order to get uniform distribution of the fertilizer.     

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     

Effect of urea and salt on micelle formation of zwitterionic surfactants

The effect of urea on micelle formation of zwitterionic surfactants was investigated by measuring conductivity, critical micelle concentration (CMC), relative viscosity, and the spectrophotometric shift in wavelength. We examined two zwitterionic surfactants, N,N-dimethyl dodecylamine N-oxide and N,N-dimethyl tetradecylamine N-oxide (DMTAO). The CMC values of the surfactants increased with the addition of urea. Also, the relative viscosity of the surfactant solutions decreased at higher concentrations of urea and increased with increasing KCl concentration. The absorbance maxima of the surfactants decreased with increasing urea concentration.     

Growth and acetylene reduction activity ofAzolla caroliniana Willd. as influenced by split applications of urea fertilizer and their response on rice yield

Experiment with different split applications of 40 kg N ha^–1 of urea (U) at transplanting:30 days after transplanting:40 days before crop maturity with different proportions of 50:25:25, 25:50:25 and 0:50:50 splits, with and without Azolla, carried out for two consecutive seasons, revealed that fresh weight (FW), N₂-fixation measured by acetylene reduction activity (ARA) and N yield of newly introducedAzolla caroliniana were higher with 0:50:50 treatment followed by 25:50:25 and 50:25:25.Azolla was unincorporated and left for self decomposition. The crop yield (grain yield, straw yield) and crop N uptake data indicated that among the no Azolla treatments, the use of 50:25:25 split resulted in highest crop yield and crop N uptake followed by 25:50:25 and 0:50:50 treatments, while these parameters recorded maximum value with 25:50:25 split in combination with Azolla followed by 50:25:25 and 0:50:50 treatments. The use of Azolla increased crop yield and crop N uptake significantly over no Azolla treatments.     

Ammonia volatilization from point-placed urea in upland,sandy soils

The upland fertilization practice in Africa of placing N fertilizer below the soil surface near the plant might be facilitated through use of urea supergranules (USG). Since little is known about N losses from point-placed urea on light-textured African soils, laboratory studies were conducted in a forced-draft system to determine (a) the influence of soil properties on ammonia loss from USG and (b) to compare N loss from USG with that from broadcast N sources. Ammonia loss from 1.1 g USG placed at a 4-cm soil depth ranged from 2.9 to 62% of the added N on six light-textured soils. Ammonia loss was correlated with soil clay content (r = –0.93^**) but not with pH. A more detailed study on a soil from Niger revealed significantly less ammonia loss from either surfaced applied urea (18%) or surface-applied calcium ammonium nitrate (7%) than from USG placed at a 4-cm depth (67%). Amendment of surface-applied urea with 1.7% phenyl phosphorodiamidate (PPD), a urease inhibitor, essentially eliminated ammonia loss (1.9%). An¹⁵N balance confirmed that ammonia volatilization was the major loss mechanism for all N sources. The results suggest that point-placed urea may be prone to ammonia volatilization loss on light-textured African soils moistened by frequent light rainfall. In such cases, broadcast application of urea, CAN, or urea amended with PPD may be less prone to N loss.     

Compound fertilizer placement for potatoes

Sixteen experiments were carried out on maincrop potatoes (Solanum tuberosum) in the main growing areas of the United Kingdom to compare broadcast, sideband placed and split applications of compound fertilizer. In experiments without irrigation, yield increased up to about 1250 kg ha^–1 of compound fertilizer (N:P:K 15:6.6:15.8 or 15:8.3:15.8), while with full irrigation there was a response to at least 1875 kg ha^–1. Placement gave a higher yield than broadcast at 625 kg ha^–1, while at 1250 kg ha^–1 and 1875 kg ha^–1 broadcast, placed and split applications gave similar yields.     

Fate of urea applied to winter spinach in New Zealand

Field trials were conducted during three years (1996–1998) to follow the fate of N fertiliser applied to spinach (Spinacea oleracea L.) grown over winter (May–September) in New Zealand. Urea labeled with ¹⁵N was applied to the spinach at different rates (0, 200 or 400 kg N/ha), times (as two or three split applications) and placement methods (broadcast or banded). The results showed that the typical fertiliser practice of applying 350 kg N/ha near planting time followed by 50 kg N/ha 4 weeks later, resulted in leaching losses of 119–292 kg N/ha depending on the rainfall. Plants recovered only a small proportion of the fertiliser N (3–18% of the ¹⁵N). Better utilization of the fertiliser and lower leaching losses occurred when the fertiliser was applied strategically in split applications with only a small amount (10%) applied near sowing and the majority applied to match crop demand. For example, in 1998 applying 200 kg N/ha (20 kg N/ha initially+100 kg N/ha after 4 weeks and 80 kg N/ha after 8 weeks) resulted in twice the spinach yield (25 t/ha compared with 13 t/ha) and less than half the leaching loss (108 kg N/ha leached compared with 246 kg N/ha) compared with the typical fertiliser practice.     

The comparative effects of ammonium nitrate,urea or a combined ammonium nitrate/urea granular fertilizer on the efficiency of nitrogen recovery by perennial ryegrass

The comparative effects of ammonium nitrate (AN), urea or a combined 1:1 (w/w) AN/urea granular fertilizer with two different fillers (CaCO₃ or silica) were investigated on the efficiency of dry matter production and¹⁵N recovery by perennial ryegrass grown in pots under controlled environmental conditions.There was no significant difference between CaCO₃ and silica as the filler and therefore no indication that the presence of CaCO₃ in the pellet enhanced N loss from urea. Ammonium nitrate was the most efficient N source and urea the least efficient in terms of all the parameters studied. The¹⁵N budget in shoots, roots and soil indicated that only 60% of the nitrogen from urea was recovered at the end of the experiment compared with 95% for AN. However, the % recovery of¹⁵N from urea was increased by 17% in the presence of AN whereas the % recovery of AN was decreased by 19% in the presence of urea. The combined 1:1 (w/w) AN/urea source therefore gave intermediate yields between AN and urea alone. The results indicate that an interaction occurred between AN and urea in the granule.     

Nitrogen utilization by lowland rice as affected by fertilization with urea and green manure

Field studies were conducted during two consecutive wet seasons in flooded rice (Oryza sativa L.) to determine the effect of green manure on urea utilization in a rice-fallow-rice cropping sequence. Replicated plots were fertilized with 60 to 120 kg of urea N ha^–1 in three split applications (50, 25 and 25%) with or without incorporation of dhaincha (Sesbania aculeata L.) (100 kg N ha^–1). During the first crop only 31 to 44% of the urea added was used by the rice. Incorporatingin situ grown dhaincha (GM) into the soil at transplanting had little effect on urea utilization. Forty-four to 54% of the N added was not recovered in the soil, rice crop, or as nitrate leachate during the first cropping season. Incorporation of GM had no effect on fertilizer N recovery. Only about 2% of the urea N added to the first rice crop was taken up by the second rice crop and, as in the first crop, the GM had little effect on residual N, either in amount or utilization.     

以尿素为氮源的高氮复合肥生产技术

笔者根据多年的实践经验 ,阐述以尿素为氮源 ,生产高氮〔w(N)≥ 2 0 %〕复肥的现实意义及生产技术要点 ,具体介绍 2个高氮复肥 (2 30 7)、(2 0 10 15 )的配方实例及操作要点     

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.     

Nitrogen fertilizer in leucaena alley cropping. I. Maize response to nitrogen fertilizer and fate of fertilizer-15N

Field microplot experiments were conducted in the semi-arid tropics of northern Australia to evaluate the response of maize (Zea mays L.) growth to addition of N fertilizer and plant residues and to examine the fate of fertilizer¹⁵N in a leucaena (Leucaena leucocephala) alley cropping system, in which supplemental irrigation was used. Leucaena prunings, maize residues and N fertilizer were applied to alley-cropped maize grown in microplots which were installed in the alleys formed by leucaena hedgerows spaced 4.5 metres apart. The¹⁵N-labelled fertilizer was used to examine the fate of fertilizer N applied in the presence of mulched leucaena prunings and maize residues.Application of leucaena prunings increased maize yield while addition of N fertilizer in the presence of the prunings produced a further increase in maize production. There was a significant positive interaction between N fertilizer and leucaena prunings in increasing maize production. The addition of maize residues in the presence of N fertilizer and leucaena prunings decreased maize yield and N uptake and increased fertilizer¹⁵N loss from 38% to 47%. Maize recovered 24–79% of fertilizer¹⁵N in one cropping season, depending on application rate of N fertilizer and field management of plant residues. About 20–34% of fertilizer¹⁵N remained in the soil. More than 37% of fertilizer¹⁵N was apparently lost from the soil and plant system largely through denitrification when N fertilizer was applied at 40 kg N ha^–1 or more in the presence or absence of plant residues. Application of N fertilizer improved maize yield and increased the contribution of mulched leucaena prunings to crop production in the alley cropping system.     

Powdered granite is not an effective fertilizer for clover and wheat in sandy soils from Western Australia

Granite (silicate) rock dust, a by-product of quarry operations, is being advocated and used as a fertilizer in the wheatbelt of south-western Australia (WA). The dust is insoluble and based on its nutrient element content (1.9% K and 0.3%P and negligible N) it is not expected to be a useful fertilizer. Previous laboratory studies and glasshouse experiments in WA suggest the dust is a slow release K fertilizer. This paper extends the previous studies to consider the dust as an NP or K fertilizer in the year of application in a field experiment on a soil deficient in N, P and K. In addition, the effectiveness of the dust as a K fertilizer was compared with the effectiveness of KCl (muriate of potash), the K fertilizer used in WA at present, in glasshouse experiments using K deficient soils. In the field experiment, compared with NP fertilizer or NPK fertilizer (urea, supplying N; superphosphate, providing P, S, Ca, Cu, Zn and Mo; KCl providing K), the dust had no effect on grain yield of wheat (Triticum aestivum); in fact dust applied at 20 t ha^-1, for unknown reasons, reduced yields by about 65% compared to the nil (no fertilizer, no dust) treatment. Relative to the nil treatment, applying NPK fertilizer increased yields about threefold, from 0.54 to 1.79 t ha. The glasshouse experiments showed that, relative to KCl, the dust was from about 0.02 to 14% as effective in K deficient grey sandy soils for producing dried tops of 30-day old wheat plants or 42-day old clover (Trifolium subterraneum) plants. In soils with adequate K (yellow sands, sandy loams or clays, loamy clays, clay loams and clays), neither KCl nor the dust affected yields of 30 to 42-day old wheat or clover plants grown in the glasshouse. In the glasshouse experiments, no yield depressions were measured for the dust applied up to 17 g dust per kg soil (equivalent to 17 t dust ha^-1 mixed into the top 10 cm of soil in the field). It is concluded that the dust has no value as a fertilizer.     

Comparing how Lupinus angustifolius and Lupinus luteus use zinc fertilizer for seed production

Zinc (Zn) deficiency is a common problem on the sandy acidic soils insouth Western Australia (WA) for seed (grain) production of Lupinus angustifolius, and L. luteus. The Zn requirement of L. luteus is not known; while that of L. angustifolius has only been measured in one field experiment in WA. The effectiveness of Zn fertilizer was measured in 1997 for grain production of L. angustifolius cv. Gungurru, and L. luteus cvv. Motiv and Teo, for Zn applied once only to plots not treated with Zn before, either in 1997 (current Zn) or in a previous year (previous Zn, applied in one of the following years: 1983, 1984, 1986, 1990,1992). For each lupin species, the effectiveness of previous Zn decreased relative to the effectiveness of current Zn, the decrease being larger with increasing time since application. Fourteen years after application, the decrease was 96% for L. luteus cv. Teo compared with about 65% for the other two lupins. When no Zn was applied, L. luteus produced larger grain yields than L. angustifolius. For Zn applied in the current year, relative to L. angustifolius cv. Gungurru, L. luteus cv. Motiv used the Zn about 45% less effectively and so required about twice as much Zn to produce the same percentage of the maximum (relative) yield. L. luteus cv. Teo used the Zn about 70% more effectively so only required about two thirds the Zn needed by L. angustifolius to produce the same relative yield. For Zn applied in each of the previous years, and relative to L. angustifolius cv Gungurru in each of those years, L. luteus cv. Motiv used the previously applied Zn from about 3 to 33% more effectively for producing grain, whereas L. luteus cv. Teo used previously applied Zn about 15 to 88% less effectively. Both currently and previously applied Zn fertilizer increases lupin seed yields. The effectiveness of the previously applied Zn fertilizer declines with time since it was originally applied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Response of tomato to nitrogen fertilization and irrigation frequencies in a semi-arid tropical soil

The effect of different irrigation frequencies (5, 7 and 9 days interval) and N rates (0, 50, 100 and 150 kg N ha^–1) on applied N in tomato was studied in a field experiment during 3 growing seasons. The application of 100 kg N ha^–1 with irriga tion scheduled at 7 days interal resulted in significantly higher N uptake and recovery rate than the other combinations of N rate and irrigation frequencies studied.     

Effects of urea fertigation of apple trees on soil pH,exchangeable cations and extractable manganese in a sandy loam soil in New Zealand

Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha^–1 yr^–1 or 0, 16.9, 33.8 g N emitter^–1 yr^–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha^–1 yr^–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg^–1 and 78µg g^–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha^–1 yr^–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth.     

Effects of ultrasound-assisted air-drying on vitamins and carotenoids of cherry tomatoes

This work examined the influence of the ultrasonic-assisted air-drying on the dehydration of cherry tomatoes (Solanum lycopersicum var. cerasiforme) and on the availability of vitamins B, E, and carotenoids in the dried product. This study allowed estimating the effective water diffusivity for the air-drying process and for the air-drying process subjected to ultrasonic waves. The water effective diffusivity increased by 33–89%, depending on the operating conditions, when subjected to ultrasound. The application of ultrasound increased the availability of vitamins B₁, B₂, B₃, B₆, and B₅, releasing the vitamins bounded to membrane, protein, or apoenzyme. The use of ultrasound allowed the retention of carotenoids in the dried product when drying was carried out at a low temperature (45°C) and low air velocities (1 m/s).