Coated and modified urea materials for increasing nitrogen use efficiency of lowland rice in heavy clay soils

Conventional as well as modified nitrogen sources and application methods were evaluated under rainfed lowland conditions in heavy clay soils of Bihar, India for 4 years. Modified nitrogen sources, viz. sulfur-coated urea (SCU) and urea super-granules (USG) were tested against prilled urea (PU) under four levels of N (0, 29, 58 and 87 kg N/ha) in the wet season. A high yielding nonphotoperiod sensitive, long duration variety Pankaj was grown in all the four years.Point placement of USG and basal incorporation of SCU resulted in significantly higher panicle numbers per square meter, 100 grain weight and grain yield at all the levels of N tested. The unfilled grain percentage was lower in USG and SCU treatments.Regression analysis using a multifertilizer response model (MRM) showed that rice responded significantly to PU in three years out of four years, to SCU in four years and USG in three years.Economic analysis viz. input and output analysis based on the price of fertilizer (1 kg N as PU at $0.5; USG and SCU costing 10% more than PU), rough rice (ranging from 18.0 to 20.0 $ per ton) and labour wages at 1.0 $ per man day unit, also showed that USG and SCU are more input efficient than PU.     

Effect of green manuring with Sesbania aculeata and nitrogen fertilization on the performance of direct-seeded flood-prone lowland rice

Green manuring of rice with dhaincha (Sesbania aculeata) is widely practised under irrigated puddle-transplanted conditions. In flood-prone lowlands, the rice is established through direct seeding early in the season and flooding occurs after 1–2 months of crop growth following regular rains. The low yields are due to poor crop stands and difficulty in nitrogen management under higher depths of water. The effect of green manuring with dhaincha intercropped with direct-seeded rice vis-à-vis the conventional practice of incorporating pure dhaincha before transplanting was investigated under flood-prone lowland conditions (up to 50–80 cm water depth) at Cuttack, India. Treatment variables studied in different years (1992, 1994 and 1995) were: rice varieties of different plant heights, crop establishment through direct seeding and transplanting, varying length of periods before dhaincha incorporation, and urea N fertilizer levels. Dhaincha accumulated 80–86 kg N ha^-1 in pure stand and 58–79 kg N ha^-1 when intercropped with direct-seeded rice in alternate rows at 50 days of growth. The growth of rice improved after dhaincha was uprooted manually and buried in situ between the rice rows when water depth was 10–20 cm in the field. The panicle number was lower but the panicle weight was higher with dhaincha green manuring than with recommended level of 40 kg N ha^-1 applied as urea. The grain yield was significantly higher with direct seeding than with transplanting due to high water levels (>60 cm) immediately after transplanting. Dhaincha manuring was at par with 40 kg N ha^-1 as urea in increasing the yield of direct-seeded and transplanted crops. The highest yield of direct-seeded crop was obtained when 20 kg N ha^-1 was applied at sowing and dhaincha was incorporated at 50 days of growth. The results indicate that green manuring of direct-seeded rice with intercropped dhaincha is beneficial for substituting urea fertilizer up to 40 kg N ha^-1 and augmenting crop productivity under flood-prone lowland conditions.     

硫酸脲复合肥对玉米生长指标及产量的影响

通过田间试验方式研究硫酸脲复合肥、普通缓释肥、硫基肥、BB肥对玉米生长和产量的影响。结果表明,4种肥料处理均能促进玉米植株茎粗、穗粗和穗行数的增加,特别是硫酸脲复合肥处理,较CK分别增加了3.8%、3.6%和18.2%;而且4种肥料处理对玉米也有不同程度的增产效应,其中硫酸脲复合肥处理增产率最高,为21.09%。     

Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil

Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH₃) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH₃ could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha^–1 in dry season and 3.0–4.1 Mg ha^–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The¹⁵N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH₃ volatilization was probably responsible for the poor efficiency of broadcast urea in this study.     

Effects of nitrogen fertilizer application methods on growth and acetylene reduction activity ofAzolla pinnata and yield of rice

The influence of different methods of N fertilizer application-sub-surface placement (SS) and broadcast application (BC) as a single basal dose of 40 kg N ha^–1 of urea (U) and ammonium sulphate (AS)-on fresh weight (FW) and acetylene reduction activity (ARA) ofAzolla pinnata (Bangkok) and yield of rice was studied for consecutive three seasons. The FW, ARA and N yield ofAzolla were significantly superior with SS placement than with BC application. Of the two N sources, AS was superior to U in recording higher FW, ARA and N yield of Azolla irrespective of methods of N application. Crop yield and crop N uptake were higher with SS application alone and in combination with Azolla as compared to that of surface application of N fertilizers. The combined use of AS and Azolla recorded significantly higher crop yield and crop N uptake than that of U combined with Azolla, irrespective of methods of application.     

Effect of method of N-application and modified urea on N-15 recovery by rice

Rice is a very responsive crop to nitrogen, but the efficiency of the N-fertilizer is low. Greenhouse experiment has been conducted to evaluate several methods to improve fertilizer efficiency and reduce N-losses in rice fields. N-15 labelled urea was applied to 10 kg soils in pots, urea was applied alone, addition of two urease inhibitors N-(n-butyle) thiosphosphoric triamide (NBPT) and hydroquinone (HQ), with addition of nitrification inhibitor Dicyandimide (DCD), or with the combination of both inhibitors. The fertilizer was applied either broadcast on soil surface or at depth of 8 cm below the surface. At maturity, plants were separated into grain and straw, dried and weighted. Soil and plant samples were analyzed for total N and N-15 excess. Both fertilizer placement and inhibitor application significantly increased straw and grain yield, as well as N- uptake. Nitrogen derived from fertilizer (% Ndff) was more than doubled, when urea was applied deep and in combination with inhibitors. Total plant recovery of N-15 labelled urea ranged from 17% to 75% according to treatment. Regardless of inhibitors application, plant recovery was increased from 39% to 65% when urea was applied at depth of 8 cm. Approximately, 2/3 of the applied urea (64%) was lost, when urea was applied alone. Those losses were reduced down to 12% with deep placement and inhibitor application. The two management practices show significant effect on minimizing N-losses and increasing plant recovery.     

Comparative studies on the usefulness of ammonium sulphate and urea as fertilizers for lowland rice

In a pot experiment it was established that NH₄ volatilization losses were larger with urea than with ammonium sulphate used as a basal fertilizer for lowland rice. The difference arose from the pH-increasing effect of urea in the floodwater. This rise in pH promoted the growth of algae which in turn were responsible for large diurnal fluctuations in the pH of the floodwater thus enhancing the loss of NH₃ during daytime. Ammonium sulphate lowered the pH of the water which suppressed the growth of algae.Once the rice canopy had closed, the algal population declined and the diurnal pH fluctuations largely disappeared. Urea as a topdressing was found to be less liable to give rise to NH₃ volatilization than when added as basal dressing. The highest N recovery was obtained with ammonium sulphate used as basal dressing and urea as topdressing. Working a basal dressing into the soil improves the fertilizer-N recovery of urea-N, but not of ammonium sulphate-N, the latter being already high without soil incorporation.     

砂姜黑土区控释尿素与普通尿素掺混对小麦-玉米轮作定位产量及氮肥利用率的影响

在驻马店新坡村进行了小麦-玉米轮作制下的控释尿素与普通尿素掺混比例定位试验研究。结果表明:控释尿素与普通尿素掺混处理的小麦、玉米产量均以70%控释尿素+30%普通尿素处理最好,第1年和第2年的小麦产量分别比100%普通尿素处理增产17.0%和21.1%,玉米产量分别比普通尿素处理增产16.2%和16.2%;氮肥利用率与产量结果一致,均以70%控释尿素+30%普通尿素处理最高,分别为53.9%和54.5%。     

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.     

Use of chlorophyll meter for nitrogen management in lowland rice

The chlorophyll meter (SPAD-502) can be used to diagnose the nitrogen (N) status of rice (Oryza sativa L.) to decide for fertilizer-N side-dressing. The objective of this study was to determine the relationships between SPAD meter readings, unadjusted and adjusted for specific leaf weight (SLW) and N on dry weight basis (Ndw), N on leaf area basis (Na) and yield. The correlation coefficients (r) between SPAD and Ndw ranged from 0.82 to 0.90; between SPAD and yield, from 0.75 to 0.90; and between SPAD/SLW and yield from 0.77 to 0.85 on pooling the data experiment-wise. The corresponding r values over all experiments were 0.87, 0.81 and 0.80, respectively. The results of better relationship between SPAD and Ndw; and between SPAD and yield in the late reproductive and early ripening phases allows prediction of plant N status based on direct SPAD meter readings. It is quick, simple and non-destructive unlike N prediction based on Kjeldahl procedure or SPAD/SLW.     

Foliar urea fertilization of cereals: A review

It has been suggested that there are several potential benefits of providing nitrogen to cereals via the foliage as urea solution. These include: reduced nitrogen losses through denitrification and leaching compared with nitrogen fertilizer applications to the soil; the ability to provide nitrogen when root activity is impaired e.g., in saline or dry conditions, and uptake late in the season to increase grain nitrogen concentration. Factors that influence the degree of foliar absorption in field conditions have not, however, been clearly defined and losses to the atmosphere and soil can occur. Foliar urea applications may also hinder crop productivity although the explanations for this vary, and include desiccation of leaf cells, aqueous ammonia and urea toxicity, biuret contamination and the disruption of carbohydrate metabolism. It has not yet been determined which one, or combinations, of these mechanisms are most important in field situations. When damage has not been severe, foliar urea applications have increased grain yield, particularly when applied before flag leaf emergence and when nitrogen availability is limiting. Increases in grain nitrogen content are often larger when applications of nitrogen fertilizers to the soil are reduced, and when the urea solution is sprayed either at anthesis or during the following two weeks. It is during this period that foliar urea sprays can be of greater benefit than soil applications with regard to nitrogen utilization by the crop. Increases in wheat grain nitrogen concentration following urea application can improve breadmaking quality. Responses in loaf quality may, however, be variable particularly when increases in grain nitrogen content have been large, and/or when the nitrogen: sulphur ratio in the grain is increased. These circumstances have lead to alterations in the proportions of the different protein fractions which influence breadmaking potential.To exploit the full potential benefits of foliar urea application to cereals, more needs to be known about the mechanisms, and thus how to prevent losses of nitrogen from the foliage, and to reduce the phytotoxic influences of sprays. More information is also required to exploit the reported effects that urea may have on limiting the development of cereal diseases.     

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.     

Effect of prilled urea and modified urea materials on yield and quality of geranium (Pelargonium graveolens L. Her.)

Two field experiments were conducted to study the effect of prilled urea, neem cake coated urea, dicyandiamide treated urea and urea supergranules applied to a perennial aromatic herb, geranium (Pelargonium graveolens L. Her'.) grown on a sandy loam soil. Application of nitrogen increased the biomass and essential oil yields. Neem cake coated urea significantly increased the yields over prilled urea. There was no residual effect of N levels and N carriers. The concentration and quality of essential oil were not influenced either by levels or carriers of N.     

Effect of foliar sprayings of urea during or after anthesis on dry matter and nitrogen accumulation in the grain of two wheat cultivars ofT. aestivum L.

The objective of this work was to determine the effect of foliar urea spraying during or after anthesis, on dry matter and nitrogen accumulation in the wheat grain of two cultivars, differing in grain protein content. The experiment was carried out in the field, and 20 kg N ha^–1 as urea (46-0-0) was sprayed at anthesis, 7 or 14 days after anthesis. Dry weight, N content and N percentage of the grain were determined at several stages of its development.Neither the rate nor the duration of dry matter accumulation in the grain was significantly modified by N sprayings at anthesis or later and, consequently, not its final weight. Nitrogen sprayings at anthesis or later increased the grain N content and N percentage at ripeness in both cultivars, but to a greater extent in the low grain protein cultivar. Greater N content in the grain was attributed to a rapid uptake of the N applied and not to a longer duration of the period of N accumulation.The different responses of the cultivars to N sprayings can be related to differences in N demand, and is probably associated, also, to a genetic ability to accumulate N in the grain.     

控释尿素与普通尿素配施比例对玉米产量及效益的影响

为推广缓控释肥在玉米上的应用,进行了控释尿素和普通尿素不同掺混比例的复混肥对玉米肥效的试验。结果表明,玉米施用控释氮比例为40%的控释氮肥时,玉米产量及其构成因素、叶面积、种植效益较高。     

Effects of rate and timing of nitrogen dressings on grain yield formation of winter wheat (T. aestivum L.)

A field experiment with the winter wheat cultivar Donata was carried out on a fine-textured river clay soil in 1978. The rates of nitrogen dressing ranged from 0 to 160 kg N per ha and were split over from one up to three application times: autumn, early spring and late spring.Total above-ground dry matter and grain dry-weight yields ranged from 9.1 to 13.7 tons per ha and from 4.17 to 6.35 tons per ha, respectively. Late top-dressings increased the harvest-index, whereas an autumn dressing had the opposite effect. Number of culms per m², grain weight (mg) and grain number per m² increased from 350 to 430, from 35.5 to 36.8 and from 11 680 to 16 980, respectively, as the nitrogen dosage was raised from 0 to 160 kg N per ha.The linear rate of grain growth ranged from 111 to 172 kg dry matter per ha per day with nitrogen doses from 0 to 160 kg N per ha. Differences in rate of grain growth per unit area were mainly related to number of grains per m². The association between grain number and grain yield was reflected by a correlation coefficient of 0.97 (n = 32). A higher level of nitrogen dressing enhanced the leaf area index and leaf area duration. However, we could not derive an effect of nitrogen on the duration of grain growth.Total nitrogen yield ranged from 71 to 166 kg N per ha and grain nitrogen yield from 54 to 122 kg N per ha with nitrogen dosages of 0 and 160 kg N per ha, respectively. The nitrogen concentration of the grains varied between 1.3 and 2.0 N.An autumn dressing of 40 kg N per ha generally showed only minor effects on yield and yield components. Top dressings during spring resulted in a higher recovery and efficiency of the applied nitrogen. Therefore, it may be concluded from this experiment and literature that on fertile soils an autumn dressing of nitrogen will not be economical, but split-dressings in spring are very beneficial. In particular, a late nitrogen application during the boot stage increased grain number, harvest-index and grain yield as well as protein concentration of the grain.     

Cotton growth and yield as influenced by different timing of late-season foliar nitrogen fertilization

Foliar fertilization to meet the nitrogen (N) requirement of the cotton crop during the latter fruiting stages is a production practice that is not well understood. The objective of this study was to investigate the benefits of late-season foliar-N fertilization on growth and yield of cotton in relation to soil-N level and timing based on weeks after first flower (WAFF) and nodes above white flower (NAWF). A 4-year field study was conducted with four foliar-N treatments consisting of a control with no foliar-N, and one, two, or three foliar-N sprays under different soil-N regimes. In 1990, the foliar-N treatments were based on WAFF sprayed during fifth, sixth and seventh WAFF. Foliar-N significantly increased nodes above white flower (NAWF) over the control with no significant differences among the three foliar-N treatments. A negative relationship (r2=0.98) existed between NAWF and days after planting (DAP). Foliar-N also significantly increased plant height, leaf number, leaf area, leaf dry weight, boll number, boll dry weight and yield. The same foliar-N treatments were applied on low and high soil-N regimes in 1991 and 1992, and in 1993 on four different soil-N regimes, 0, 55, 82, and 110 kg N ha-1 at NAWF = 7, 6 and 5. No significant difference was found in NAWF among the four foliar-N treatments within each soil-N level during 1991. Significant differences between the control and the three foliar-N sprays were found for leaf area, boll number, and boll dry weight. In 1992, the NAWF of control plants showed a similar response to the 1990 control plants. In contrast, the foliar-N sprayed plants extended the highest NAWF for an additional week, after which it steadily declined below 5. Foliar-N significantly increased yield in 1990, yield and yield components in 1991 and 1992, and yield in 1993. Neither WAFF nor NAWF appear to be good indicators for timing late-season foliar-N fertilization. The study clearly demonstrated, however, that late-season foliar-N fertilization is beneficial to cotton plants, although the precise timing of such N application is still unclear.     

脲醛缓释肥料在水稻上的应用研究

对脲醛缓释肥料在水稻上的应用进行肥效试验。结果表明:施用脲醛缓释肥料可延长水稻生育期5~7 d;有效提高分蘖苗数、有效穗和株高,增加总粒数和实粒数,降低空秕率,提高千粒质量;增产增收效果明显,增产幅度达4.73%~10.22%,每667 m2增加纯收益21.52~86.62元。     

Effects of fertilizer price on feasibility of efficiency improvement: Case study for an urea injector for lowland rice

Efficiency improving techniques, such as the introduction of a urea injector for lowland rice production, appear to lead to higher yields, lower fertilizer use and less environmental pollution at the same time. If farmers are free to decide on the amount of fertilizer they use, economic rationality leads to a choice between using the improved technique for saving fertilizer while obtaining the same yield, for increasing yield (at the same fertilizer rate) or for a mixed strategy (a slightly higher yield and a different fertilizer rate). The economic optimum fertilizer rate was calculated with a simple yield model for a low and a high fertilizer application efficiency to predict which strategy would be best for the farmer.Calculations for a standard data set for lowland rice show that the greatest benefit from an increase in application efficiency by urea deep placement instead of broadcast application can be expected when a marginal efficiency of about 9 kg rice per kg fertilizer N is used for determining the fertilizer rate. For a marginal efficiency of less than 6, savings on fertilizer are the main benefit of efficiency improvement; for higher marginal efficiencies yield increases become the main component of total benefit; for marginal efficiencies above 9, fertilizer use will increase when a more efficient technique is used, but increased yields compensate for their costs. In the four countries where a manually operated pneumatic urea injector was tested (Togo, Bangladesh, Indonesia and Ivory Coast) the price ratio of rice and fertilizer N ranged from 1.1 to 2.5. Even when a risk-avoidance multiplier of 2 is used, we may conclude that fertilizer prices were too low relative to rice to make optimum use of the existing techniques for efficiency improvement. An equation is derived for estimating the price ratio at which the probability of farmer acceptance of techniques for improving fertilizer use efficiency is highest.     

Improving head rice yield of glutinous rice by novel parboiling process

Most commercial parboiled rice is produced from high-amylose content rice. Glutinous rice, which is lacking in amylose content, is generally consumed in Southeast Asian countries. Rare study of parboiling glutinous rice has been observed. In this study, glutinous rice was improved in head rice yield by a novel parboiling process. Two rough glutinous rice, rice department 6 (RD6) and black glutinous rice (BGR) cultivars, were soaked in hot water at 70?±?5°C for 3?h. The ricer 3moisture content after soaking was 50–52% (d.b.), it was dried with hot air and superheated steam (SHS) at 110, 130, and 150°C in a fluidized bed dryer. The results show that SHS at all drying temperatures can improve the high head rice yield in both parboiled glutinous rice cultivars better than hot air drying. Higher temperature drying caused L* value to decrease but the b* value increases in RD6, whereas in BGR, all color values decreased and ΔE* was increased when the drying temperature increased. Increasing drying temperature presented a softer texture of both glutinous rice cultivars. Upper 130°C, completed gelatinization of both varieties can be obtained and seen by scanning electron microscope and differential scanning calorimeter (DSC). This technique of using high-temperature fluidized bed drying can produce completely parboiled glutinous rice in a single process instead of two conventional processes, steaming and drying, in series.