Significance of timing and method of N fertilizer application for the N-use efficiency in flooded tropical rice

N-use efficiency in flooded tropical rice is usually low. Fertilizer N losses result mainly from losses of volatile NH₃ after broadcast application of urea into floodwater between transplanting and early tillering which is a common practice of farmers. Losses appear predominantly during the first week after urea application. With broadcast and incorporation of N into soil at transplanting losses may be reduced but are still substantial. Deep placement of urea supergranules (USG) has not been adopted by farmers because it is very laborious. A new application technique, namely injection of dissolved urea into the upper soil layer, was developed by which fertilizer N losses were effectively minimized while at the same time allowing flexible timing of application independent of crop stage and water management. It provides N-use efficiency equal to that achieved by USG point placement but is less labor-intensive.     

Effect of level,timing and method of nitrogen application on spring-planted sugarcane

A field experiment conducted at the Indian Agricultural Research Institute, New Delhi during the years 1976–79 involving two planted cane crops and two ratoons showed that nitrogen application to planted cane increased the millable cane and sugar yields of the planted cane and had a significant residual effect on the ratoon. Taking together the yields of planted cane and ratoon, an application of 150 kg N ha^–1 increased the yield of millable cane by 33.3t ha^–1 and that of sugar by 3.9t ha^–1. The results suggested that with 75 kg N ha^–1 three-quarters should be applied at planting, while with 150 kg N ha^–1 only half should be applied at planting. The remaining dose of nitrogen should be applied at earthing up. Foliar application of part of the nitrogen indicated some advantage in the case of millable canes in the planted cane, but this did not show up in the sugar yield.     

高效液相色谱法测定肥料中硝态氮含量

介绍一种简便、准确、快速测定肥料中硝态氮的高效液相色谱法。使用C18柱和紫外检测器,以0.04mol/L磷酸二氢钾水溶液为流动相,在230nm波长下测定硝态氮含量,其RSD值为1.02%,回收率在96.9%～100.6%,线性相关系数为0.9997,最低检测浓度为1×106mg/mL。     

Use and efficiency of a liquid nitrogen fertilizer on grassland

Liquid nitrogen fertilizers are, per unit of N, generally cheaper than granulated ammonium nitrate because of lower production costs. Although very corrosive, the storage and handling of liquid nitrogen fertilizers does not usually present any problems. The applicability and efficiency of a commercial liquid nitrogen fertilizer (containing 39% N, half urea and half ammonium nitrate) on grassland was investigated in comparison with granulated ammonium nitrate (27% N). The liquid nitrogen fertilizer was applied on continuously grazed paddocks without any repercussions for animal health. No scorching was observed provided that certain measures were adopted while spraying the fertilizer: i.e. little dilution with water, use of low pressure and large droplets and application on dry grass in cloudy whether. In comparison with the granulated ammonium nitrate, the liquid nitrogen fertilizer was less efficient; dry matter yield and N-uptake of the grass treated with the liquid nitrogen fertilizer were 76% and 73% respectively of the dry matter yield and N-uptake of the grass treated with the granulated ammonium nitrate fertilizer.Fertilization, especially with nitrogen, represents the biggest single cost in grass production. Because liquid nitrogen fertilizers can be produced less expensively then granulated ones, their price per unit of N, delivered to the farmer, is also lower.Another advantage is that liquid fertilizers are easy to handle (despite being corrosive) and can be distributed uniformly over the field. The greatest advantage can be expected on the large grass areas of continuous grazing systems. Because of these benefits, an investigation was carried out to assess the potential use and efficiency of liquid nitrogen fetilizer in comparison with granulated ammonium nitrate nitrogen, from 1983 up to 1987. In 1983 and 1984, the grass quality, especially NH₃ and NO₃ concentration directly after spraying, and animal behaviour were assessed. From 1985 to 1987, the grass yield and nitrogen uptake were measured under mowing conditions.     

Response of rainfed bread and durum wheat to source,level and timing of nitrogen fertilizer on two Ethiopian Vertisols: II. N uptake,recovery and efficiency

In trials conducted at 2 highland Vertisol sites in Ethiopia in 1990 and 1991, 2 locally popular wheat cultivars, 1 spring bread wheat (Triticum aestivum L.) and 1 durum wheat (T. durum Desf.), were supplied with nitrogen (N) fertilizer at 0, 60 and 120 kg N ha^–1 in the form of large granular urea (LGU), standard urea prills or ammonium sulfate. N was applied all at sowing, all at mid-tillering or split-applied between these two stages (1/3:2/3). While durum wheat exhibited the highest N concentration in grain and straw, bread wheat, because of its higher productivity, resulted in a greater grain and total N uptake. In general, split application of N and use of LGU as N source enhanced grain and total N uptake, apparent N recovery and agronomic efficiency of N, particularly under severe water-logging stress. Where significant, the interactions among the experimental factors substantiated the superior responsiveness of the bread wheat cultivar to fertilizer N, and the beneficial effects of split N application and LGU as an N source. Split application of N tended to nullify the positive effects of LGU, presumably by approximating the delayed release of N achieved with LGU. Considering the potential benefits to Ethiopian peasant farmers and consumers, split application of N should be advocated, particularly on water-logged Vertisols; LGU could be an advantageous N source assuming a cost comparable to the conventional N source urea.     

Effect of the timing and rate of nitrogen fertilization on the growth and recovery of fertilizer nitrogen within the potato (Solanum tuberosum L.) crop

The effect of the timing of N fertilizer application on the uptake and partitioning of N within the crop and the yield of tubers has been studied in two experiments. In 1985 either none, 8 or 12 g N m^–2 was applied and in 1986 none, 12 or 18 g N m^–2. Fertilizer N was applied either at planting, around the time of tuber initiation or half at planting and the remainder in four foliar sprays of urea during tuber bulking.¹⁵N-labelled fertilizer was applied to measure the recovery of fertilizer N in the crops.There was an apparent pre-emergence loss of nitrate from the soil when N was applied at planting in 1986, thereby reducing the efficiency of fertilizer use. Applying the N at tuber initiation delayed and reduced the accumulation of N in the canopy compared with crops receiving all their fertilizer at planting. Foliar sprays of urea slightly increased both tuber yields and tuber N contents when compared to a single application at planting. The proportion of the fertilizer N recovered in the crop was little affected by the rate of N application, but a greater proportion of foliar-applied N was recovered than N broadcast at planting, due partly to pre-emergence losses of nitrate in 1986. It is suggested that late applications of N was foliar sprays can be of benefit to crops with a long growing season and reduce environmental losses of N.     

作物对氮素的吸收特性和对包膜控释肥的释放性能要求

施用包膜控释肥能够改善作物对养分的吸收,提高化肥利用率,而控释肥释放性能需要依据作物对养分的需求特性来设计。本文综述了主要作物全生命周期对氮素的累积吸收规律,通过分析不同生育时期作物对氮素养分吸收的累积量,将作物吸收养分分为苗期—营养期—生殖期3个阶段,累积吸收曲线呈"S"型。而包膜控释肥理想的累积释放曲线也为"S"型,对应滞后期—快速期—衰退期,要从根本上提高养分利用率,控释肥养分释放特性必须与作物吸收特性相匹配。初步分析显示,理想的控释肥释放特性为,对于越冬生长的长生育期作物,应控制滞后期(120～150天)释放20%,快速期(约60天)释放55%,衰退期(约30天)释放25%;对于中生育期(90～130天)作物,控制滞后期(20～30天)氮素释放5%,快速期(30～60天)释放80%,衰退期(约30天)释放15%;对于在营养期采收的蔬菜,控制滞后期(约20天)释放5%,快速期(约40天)释放95%。     

Effects of N fertilizer application timing on common bean production

There is usually a positive yield response when N is applied to common bean plants grown on N-poor soils. Recommendations include application of some or all of the N at planting, but growth and yield responses to later applications are not well documented. From 50 to 60kg N ha^–1 was applied at different growth stages to three bean lines during three years. All N treatments increased yield compared to the unfertilized control. Nitrogen applied during the vegetative stage produced higher seed yields than N applied at planting, flowering, during podfill or a split application. N applied at planting or during vegetative growth increased pod-set, while application at the vegetative and reproductive stages increased seed weight. Even though N application during the vegetative stage showed a negative effect on nodulation, there was a large shoot growth response. The lower yield from N applied at planting may have been caused by less shoot growth response as well as inhibited nodulation. Based on these results the best management system using N fertilizer was an application during vegetative growth. Further studies are needed to identify bean lines capable of high N₂ fixation in the presence of N and to determine optimum amounts and timing of N application to maximize biological and economic yields.     

Yield response and nitrogen utilization efficiency by drip-irrigated potato

Two field experiments were conducted in the Jordan Valley to evaluate potato response to N fertigation. Nitrogen as ammonium sulphate was supplied through irrigation water (fertigation) at rates of 0, 35, 70 and 105 mg N l^-1. Soil N application treatment equivalent to the fertigation treatment of 70 mg N l^-1 was included. ¹⁵N labelled ammonium sulphate was used to evaluate the N recovery and utilization efficiency. Yield increased by the N rate. The soil N application gave higher yield than the zero N and lower than the fertigated treatments. The increase in yield was due to the increase in the size of the tubers. The specific gravity was the highest with the zero N. The index ratios of potato tubers were similar with all treatments. The N derived from fertilizers by both tubers and shoots, increased with the N rate regardless of the method of application. The soil application treatments had fertilizer utilization as high as the fertigation treatments and produced total tuber yield not significantly different from that obtained by the fertigation treatment with similar rate. This might be attributed to the poor fertilizer distribution in the root zone in the fine textured soil. The low value of the fertilizer utilization of the plant receiving the ¹⁵N in the preceding season suggested possibilities of rapid transformation and immobilization by the soil microorganisms.     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.     

适用于不同作物的凹凸棒复合肥氮元素缓释效果的研究

为开发环境友好、成本低廉、适用于不同作物的面源污染控制型矿物缓释肥,制备以凹凸棒石粉为肥料缓释载体,尿素、磷酸二铵和硝酸钾为肥料原料的面源污染控制型玉米、小麦、水稻、马铃薯、棉花、大豆、油菜、苹果8种凹凸棒复合肥,通过测定已制备的8种凹凸棒复合肥中氮元素初期养分释放率、28 d累积养分释放率、养分释放期的累积养分释放率,对其差异性进行显著性分析和比较分析。结果表明,8种作物专用的凹凸棒复合肥之间氮元素初期养分释放率、28 d累积养分释放率、养分释放期的累积养分释放率存在极显著差异。     

Nitrogen-15 balances and nitrogen fertilizer use efficiency in upland rice

Field experiments were conducted in the 1984 and 1985 wet seasons to determine the effect of N fertilizer application method on¹⁵N balances and yield for upland rice (Oryza sativa L.) on an Udic Arguistoll in the Philippines. The test cultivars were IR43 and UPLRi-5 in 1984 and IR43 in 1985. Unrecovered¹⁵N in¹⁵N balances for 70 kg applied urea-N ha^–1, which represented N fertilizer losses as gases and movement below 0.5 m soil depth, ranged from 11–58% of the applied N. It was lowest (11–13%) for urea split applied at 30 days after seeding (DS) and at panicle initiation (PI), and highest (27–58%) for treatments receiving basal urea in the seed furrows. In all treatments with basal-applied urea, most N losses occurred before 50 DS.Heavy rainfall in 1985 before rice emergence resulted in large losses of native soil N and fertilizer N by leaching and possibly by denitrification. During the week of seeding, when rainfall was 492 mm, 91 kg nitrate-N ha^–1 disappeared from the 0.3-m soil layer in unfertilized plots. Although rainfall following the basal N application was less in 1984 than in 1985, the losses from basal applied urea-N were comparable in the two years. Daily rainfall of 20–25 mm on 3 of the 6 days following basal N application in 1984 may have created a moist soil environment favorable for ammonia volatilization.In both years, highest grain yield was obtained for urea split-applied at 30 DS and at PI. Delayed rather than basal application of N reduced losses of fertilizer N and minimized uptake of fertilizer N by weeds.     

The effect of plant residues on plant uptake and leaching of soil and fertilizer nitrogen in a tropical red earth soil

Two field experiments, in which differing amounts and types of plant residues were incorporated into a red earth soil, were conducted at Katherine, N.T., Australia. The aim of the work was to evaluate the effect of the residues on uptake of soil and fertilizer N by a subsequent sorghum crop, on the accumulation and leaching of nitrate, and on losses of N.Stubble of grain sorghum applied at an exceptionally high rate (~ 18 000 kg ha^–1) reduced uptake of N by sorghum by 13% and depressed the accumulation of nitrate under a crop and particularly under a fallow.Loss of fertilizer N, movement of nitrate down the profile, and uptake by the crop was studied in another experiment after application of N as¹⁵NH₄ ¹⁵NO₃ to field microplots. By four weeks after fertilizer application 14% had been lost from the soil-plant system and by crop maturity 36 per cent had been lost. The pattern of¹⁵N distribution in the profile suggested that losses below 150 cm had occurred during crop growth. The recovery of¹⁵N by the crop alone ranged from 16 to 32 per cent. There was an apparent loss of N from the crop between anthesis and maturity. Residue levels common to sorghum crops in the region (~ 2000 kg ha^–1) did not significantly affect uptake by a subsequent sorghum crop, N losses, or distribution of nitrate in the profile.     

Effects of varying nitrogen supply at different growth stages on nitrogen uptake and nitrogen partitioning efficiency in two wheat cultivars

The objective of this work was to determine the effect of N availability upon N uptake and nitrogen partitioning efficiency and its relationship with %N in the grain in two wheat cultivars, differing in their grain protein content.Plants were grown in a nutrient solution with 2 nitrogen levels, 200 ppm (H) and 40 ppm (L). Four treatments were imposed: HH, HL, LH and LL. Nutrient solution exchange was done at maximum floret number. Plants were harvested at terminal spikelet stage, maximum floret number, 10 days after anthesis and maturity.Nitrogen content, N uptake and N distribution at maturity were significantly affected by N supply. Nitrogen content in the grain was similar in both cultivars, but varied significantly between treatments and decreased as follows: LH; HH; LL and HL. In both cultivars a low leaf %N was observed in HL 10 days after anthesis, which suggest early N utilization and its premature depletion, resulting in a low %N in the grain. Total %N in the plant, for both cultivars was higher in HH and LH than other treatments. When N availability was high during the whole crop cycle (HH), N distribution to the ear was improved.It is concluded that late N availability is necessary to achieve high %N in the grain. On the other hand if high and initial N availability is not maintained, %N in the grain decreased in a significant way.     

Residual fertilizer nitrogen as influenced by timing and nitrogen forms in a silty clay soil under sugarcane in Mauritius

A field study was initiated to investigate the influence of application time on the disposition of 100 kg N ha^–1 applied as¹⁵N-labelled NaNO₃ and (NH₄)₂SO₄ to a silty clay soil (a ustic eutropept) under sugarcane (Saccharum hybrid sp.) in Mauritius. The results showed that the vertical and lateral distribution of residual fertilizer N remaining in the soil 2 years after fertilization was not influenced by the chemical nature of N used nor by the time of application. On account of rapid biological immobilization more than 50% of the residual N in the soil remained in the surface 15-cm layer and less than 30% of fertilizer N had moved laterally more than 30 cm away from the zone of fertilization. There was however more residual fertilizer N in the soil when the N was applied in September (23 kg N ha^–1) than in December (16 kg N ha^–1) because fertilizer N applied during the active sugarcane growth in December was used more efficiently than similar applications in September when growth was slow. The present study provides further evidence to substantiate that N leaching is not of significant concern in soils located in a tropical environment similar to that of Mauritius.     

Use of data from long-term fertilizer experiments to model plant nitrogen uptake

Correct values for plant N-uptake are particularly important when correctly modelling the dynamics of nitrate leaching from agricultural soils. The general abundance of grain yield statistics represent a potential source of information for modelling plant N-uptake, provided that grain yield dry weight can be used to predict the total plant N-uptake (Vold & Søreng, 1997). In this paper, a nonlinear relationship for plant N-content as a function of grain yield dry weight and fertilizer N-level is derived. Data from long-term field experiments of grain dry weight (g N m^-2) and N-content in grains plus straw (g N m^-2) at harvest was used with nonlinear regression to estimate the parameters of the function. The parameters of a linear function were estimated similarly. Both models obtained could equally well describe the harvested N as a function of fertilizer N-level and grain dry weight, but the year-to-year variation of each fertilizer level was best described by the nonlinear model. An independent dataset, consisting of series of dry weight and N-content of grain yield from farm level experiments conducted in the same region (southeast Norway), was used to validate the nonlinear model.     

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.     

Comparative response of bread and durum wheat cultivars to nitrogen fertilizer in a rainfed Mediterranean environment: soil nitrate and N uptake and efficiency

A 3-year multi-site study was carried out on rainfed Vertisols under Mediterranean conditions in southern Europe to determine the influence of the N fertilizer rate on soil nitrates, N uptake and N use efficiency in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. Durum Desf.) in rotation with sunflower (Heliathus annuus L.). Nitrogen fertilizer rates were 0, 100, 150 and 200 kg N ha⁻¹ applied in equal proportions at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with a split plot arrangement and four replications. Nitrogen harvest index (NHI), N uptake/grain yield (NUp/GY), N use efficiency (NUE), N utilization efficiency (NUtE), N uptake efficiency (NUpE) and N apparent recovery fraction (NRF) were calculated. Differences were observed in N use efficiency between the two modern bread wheat and durum wheat cultivars studied. In comparison to durum, bread wheat displayed greater N accumulation capacity and a more efficient use of N for grain production. While under N-limiting conditions, the behavior was similar for both wheat types. No difference was noted between wheat types with regard to changes in soil residual levels over the study period at the various sites. The 100-kg ha⁻¹ N fertilizer rate kept soil nitrates stable at a moderate level in plots where both wheat types were sown.     

10. Improving nitrogen fertilizer efficiency in lowland rice in tropical Asia

Rice production in Asia must increase 2.2–2.8% annually to keep abreast of increasing population. Greater fertilizer use and crop intensification together with varietal improvement and investment in irrigation will all contribute to increased rice supply. Because fertilizer and input prices have risen faster than the price of rice, increasing fertilizer N efficiency will be a major challenge for rice researchers and farmers. Greater fertilizer N efficiency may be achieved through improved timing and application methods, and particularly through better incorporation of basal fertilizer N without standing water. Other promising alternative practices are use of N-efficient rice varieties, hand or machine deep placement of urea supergranules, and use of slow release N fertilizers. Research challenges include development of placement machines for prilled urea and identification of cost-efficient nitrification and urease inhibitors. Under the present resource-scarce situation in many tropical Asian countries, several complementary practices must be followed to supplement inorganic N sources. Fertilizer supplies and proper price support should be maintained and wherever possible increased, and appropriate fertilizer materials and application methods must be devised to increase N use efficiency in lowland rice, so that increasing rice requirements are fulfilled.