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 seasonal rainfall,N fertilizer and tillage on N utilization by dryland wheat in a semi-arid environment

Crop yield and N uptake in semi-arid environments are typically limited by available water and/or N. Since remobilization of shoot N is a major source of grain N, an understanding of how it is influenced by soil N and water supply, and tillage, is required. In 2003, 2005 and 2006, we determined the influence of N supply (0 or 60 kg fertilizer N ha⁻¹) and tillage [no tillage (NT) or conventional tillage (CT)] on N translocation and N use efficiency of wheat (Triticum aestivum L.) at Scott, Saskatchewan, Canada. Wheat production and N use, and their response to N fertilizer or tillage, were largely influenced by water availability. Wheat N uptake and remobilization were strongly correlated with normalized rainfall in May and June (r = 0.985 and 0.935, respectively, both significant at the P = 0.01 level). In a moisture-stressed year (2003), grain yield was higher under NT than CT, and fertilizer N was ineffective due to low N demand. Nitrogen application increased shoot dry matter (DM), and N uptake and remobilization only in 2006, a year with near-average precipitation. In a wet and cool year (2005), wheat showed no response to tillage or fertilizer N as available soil N was high. Root DM and N content varied slightly only with year or treatment. When N uptake at heading was substantially greater than 100 kg ha⁻¹, N loss occurred during plant senescence, and it was higher with N fertilization: in 2005 and 2006, N-fertilized wheat lost 33–35 kg N ha⁻¹. Nitrogen use efficiency was: (1) higher under NT than CT, due to higher N utilization efficiency, (2) higher with no added N due to higher uptake and utilization efficiencies, and (3) low when water availability was low or excessive. Tillage system had little effect on the uptake, remobilization or loss of N. Fertilizer N application in a year with average rainfall increased wheat production, N accumulation and remobilization, and N loss during senescence.     

Yield response and nitrogen uptake of pearl millet (Pennisetum americanum (L.) Leeke) cultivars to nitrogen application in the savanna region of Nigeria

Field experiments were carried out during the wet seasons (May to September) of 1980 and 1981 in order to determine the response of five pearl millet cultivars to nitrogen fertilization in savanna region of Nigeria. There were varietal differences in yield and nitrogen uptake in response to nitrogen rates. Most cultivars responded significantly up to 75 kg N ha^–1. Hybrid outyielded other cultivars at both locations each year. Nitrogen use efficiency was highest with the Hybrid, compared to other cultivars.     

Nitrogen uptake efficiency in maize production using irrigation water high in nitrate

In order to achieve efficient use of nitrogen (N) and minimize pollution potentials, producers of irrigated maize (Zea mays L.) must make the best use of N from all sources. This study was conducted to evaluate crop utilization of nitrate in irrigation water and the effect N fertilizer has on N use efficiencies of this nitrate under irrigated maize production. The study site is representative of a large portion of the Central Platte Valley of Nebraska where ground water nitrate-N (NO₃-N) concentrations over 10 mg L^–1 are common. Microplots were established to accommodate four fertilizer N rates (0, 50, 100, and 150 kg ha^–1) receiving irrigation water containing three levels of NO₃-N (0, 10, 20 mg L^–1). Stable isotope¹⁵N was applied as a tracer in the irrigation water for treatments containing 10 and 20 mg L^–1 NO₃-N. Plots that did not receive nitrate in the irrigation water where tagged with¹⁵N fertilizer as a sidedress treatment. Sidedressed N fertilizer significantly reduced irrigation-N uptake efficiencies. When residual N uptake is added to first year plant usage, total irrigation NO₃-N uptake efficiencies are similar to total sidedress N fertilizer uptake efficiencies for our cropping system over the two year period. Efficiency of irrigation-N use depends on crop needs and availability of N from other sources during the irrigation season.     

包裹型缓／控释肥对冬小麦产量、土壤无机氮和氮肥利用效率的影响

采用超大区田间试验,以不施氮、传统氯素管理方式和优化氮素管理方式为对照,研究冬小麦施用包裹型缓／控释肥（包裹肥料）对产量、土壤无机氮和氮肥利用效率的影响,并对冬小麦施用包裹型缓／控释肥效果进行评价,结果表明：与传统氮素管理方式相比,优化氮素管理方式和包裹肥料处理在分别节省了78％和67％的氮肥的条件下,获得了和传统氮素管理方式相似的冬小麦子粒产量;采用氮素优化管理模式和施用包裹肥料显著降低了土壤无机氮残留和氮素表观损失,从而显著提高了氮肥利用率;与优化氮素管理方式相比,施用包裹肥料可一次性基施,省时省力,提高了经济效益。     

控释掺混肥对小麦产量、氮素利用率及土壤氮平衡的影响

利用不同类型和不同氮素水平的控释掺混肥与普通复合肥进行对比试验,研究了不同施氮水平对大田小麦产量、氮素利用率和土壤氮平衡的影响。结果表明,控释掺混肥既能够显著提高小麦产量和氮素利用率,又明显减少了氮素损失量,以比常规施氮量减少20%、控氮比75%的控释掺混肥(CRF4)效果最显著,产量增加10.08%,氮素利用率提高15.23百分点,氮素损失量减少75.26 kg/hm2。     

钙镁磷肥复式包膜尿素对冬小麦产量和氮肥效率的影响

通过连续 3年 ( 1999～ 2 0 0 0年 )大田试验 ,研究了钙镁磷肥复式包膜尿素对冬小麦产量、氮效率〔包括 :氮素效率比 ( NER) ,氮吸收效率 ( NUp E) ,氮素使用效率 ( NUE)和氮肥利用效率 ( Nf UE)〕的影响。结果表明 ,钙镁磷肥复式包膜尿素与普通尿素的生物量、籽粒和秸秆量均显著大于对照处理 ;氮素使用效率 ( NUE)和氮肥利用率均显著高于对照。包膜尿素处理的产量和氮效率最高 ,其籽粒、秸秆、生物量平均值比普通尿素处理分别高 9.0 9%～15 .0 6 %、13.11%～ 14 .96 %、11.73%～ 14 .99% ,氮肥利用率高 15～ 16个百分点。在本试验条件下 ,相对于通常氮肥施用量 ( 15 0 kg N/hm2 ) ,少量增加氮肥施用量 (氮肥用量增加 8% )对产量和氮效率 ( NE)没有显著影响 ;而大量增加氮肥施用量 (增加 2 0 % ) ,能明显增加小麦产量、吸氮量和氮肥利用率     

Genotypic variation for potassium uptake and utilization efficiency in wheat

Pot and field experiments were carried out in order to study the genotypic variation in potassium uptake and utilization by winter wheat (T. aestivum L). Fifty-eight genotypes showed variation in K concentration, accumulation and potassium efficiency ratio (KER) in a field experiment. KER had significant positive correlation with grain weight per spike and harvest index (HI), and significantly negative correlation with stem K concentration at maturity. In a subsequent field experiment, three out of four genotypes, Yunmei 5, 94-18 and 94-6 differed in their KER, and had significantly higher grain yield with K application (K1) than without K application (K0). The 4th genotype Zhemei 1 showed no response to K. The yield increase due to K application was mainly due to the improvement in spike development from tillers. K concentration and accumulation in the plant varied between genotypes, K levels and plant parts. Among various plant parts, stem contained the highest K concentration and had the highest K accumulation at maturity, and changed considerably with the K level, while other plant parts remained relatively unchanged. All four genotypes had smaller KER in K1, as compared to K0, but there existed some difference in KER reduction among genotypes.     

提高硫基复合肥生产中氮的利用率

结合生产实践,从工艺操作条件(中和度、干燥温度、混酸密度、返料倍数)、产品氮含量、控制法、原料配方(硫酸、磷酸用量,氨与尿素用量比例)、磷酸杂质、产品水分控制法、装置稳定运行等方面分析其对高浓度硫基复合肥氮利用率的影响,提出提高氮利用率的一些做法和控制要求。     

Fate of fertiliser N applied to winter wheat growing on a Vertisol in a Mediterranean environment

A field study using 15N was conducted on a Vertisol in semi-arid Morocco to assess the fate and efficiency of fertiliser N split applied to winter wheat (Triticum aestivum L.). Splitting of fertiliser N is highly crucial in semi-arid regions, considering the increased moisture stress towards the end of the growing season. A N fertilisation rate of 100 kg N ha-1 was split according to two schemes: i) 25% at planting, 50% at tillering and 25% at stem elongation; or ii) 50% at tillering and 50% at stem elongation. The application of 100 kg N ha-1increased the vegetative dry matter production with more than 2000 kg dry matter ha-1 in comparison with the control treatment. Nitrogen fertilisation had no significant effect on the grain yield production. Moreover, the 1000 grain weight decreased from 32 to 26 g due to N fertilisation. Total N uptake was about 50 kg N ha-1 higher for the fertilised plants in comparison with the unfertilised plants, but it was not affected by the splitting pattern of the fertiliser N. Recoveries of 15N-labelled fertiliser by the plant (above-ground plant parts plus roots from the upper 20 cm layer) were low (31% and 24% for the 3-split and 2-split application, respectively). More N in the plant was derived from fertiliser when applied early in the growing season than when applied late in the season. About 13% of the N in the plants was derived from the 50 kg N ha-1 at tillering, while only 5% was derived from the N application (50 kg N ha-1) at stem elongation. At harvest, a high residual of fertiliser-derived N was found in the 0–90 cm profile (62% and 72%, for the 3-split and 2-split application, respectively). Less than 10% of the applied N could not be accounted for, the amount being highest for the application at tillering. This N not accounted for was mainly ascribed to denitrification after an important rainfall event. The application of fertiliser N led to an increase of about 20 kg N ha-1 in soil N uptake by the crop (positive ANI). The results suggested a dominant influence of moisture availability on the fertiliser N uptake by wheat.     

Yield,water use and nitrogen uptake for different water and N levels in winter wheat

In an effort to establish an optimum combination of water and nitrogen for winter wheat a field investigation was carried out on a coarse loamy sand soil during 1984–85 and 1985–86 to assess effects of irrigation regime (IR) and N application on yield, water use and N uptake. The treatments compromised all combinations of three irrigation regimes (IR) based on ratios of irrigation water to cumulative pan evaporation viz.1.2 (I-1), 0.9 (I-2) and 0.6 (I-3) and four rates of N, viz. 0, 60, 120 and 180 kg ha^–1. Grain yield increased with increase in frequency of irrigation. In spite of wide differences in weather during the two years, scheduling of irrigation at IW/CPE = 1.2 gave the highest wheat yield on the coarse-textured soil. During 1984–85, the rainless year, grain yield under I-1 was 20 and 32 per cent higher than I-2 and I-3, respectively. With increasing N rate the yield and water use efficiency increased progressively upto 180 kg N under I-1 and upto 120 kg N ha^–1 under I-2 and I-3 regimes. During 1985–86, the wet year, grain yield response to IR was relatively low. Irrespective of IR, yield increased progressively upto 180 kg N ha^–1 during the wet year. Irrigation water regimes and N application also influenced leaf area index and root growth of wheat. The yield of unfertilized wheat was relatively less affected by seasonal rainfall and IR.Both N uptake and grain yield of wheat were found to increase linearly with increase in water use. Water use efficiency was highest under I-1 regime at all levels of N in the dry season of 1984–85 and under I-3 regime in the wet season of 1985–86. Increase in N uptake with increasing N rates was significantly higher under I-1 than I-2 and I-3 regimes. The N use efficiency being maximum at 60 kg N ha^–1, decreased at higher N levels irrespective of IR.     

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.     

Yield and uptake response of lettuce to cadmium as influenced by nitrogen application

A screen house experiment was conducted to determine the effect of N (0, 50, 100 and 150 mg N kg^–1) and Cd (0, 5, 10, 25 and 50 mg Cd kg^–1) on growth and concentration and uptake of N and Cd in lettuce grown for 70 days. Nitrogen application increased significantly fresh yield, dry matter yield, N concentration and uptake, whereas these parameters were significantly decreased by Cd application at all levels of N. The concentration and uptake of Cd were significantly increased by Cd application at all levels of N. This increased Cd uptake was related to increased availability of Cd in soil. Application of N upto 100 mg N kg^–1 increased Cd uptake, whereas there was sharp reduction in Cd uptake at 150 mg N kg^–1 treatment at all levels of Cd. The plant dilution effects and reduced translocation of Cd from roots to tops or the competition at the root absorption sites at highest level of N seem to be the mechanisms responsible for N suppressed Cd uptake in this study.     

Growth rate,yield and nitrogen uptake response of grain sorghum (Sorghum bicolor (L) Moench) to nitrogen rates in humid subtropics

Field experiments were conducted during wet seasons (June to October) of 1974, 1976 and 1977 to determine the response of newly developed hybrids and varieties of grain sorghum to N fertilization under humid subtropical conditions of Pantnagar in India. In addition to the enhancement in flowering and maturity stages brought about by N application, it also resulted in increased plant dry weight, translocation coefficients, grain yield plant^–1 and grain yield ha^–1. Varietal differences existed with respect to their responses for yield and N uptake to N rates. Most of the entries responded up to 120 kg N ha^–1. Hybrid CSH 5 utilized applied N more efficiently than other varieties.Publication No 1612 of GBPUA and T, Experiment Station, Pantnagar.     

Dryland wheat yields in relation to soil organic carbon, applied nitrogen, stored water and rainfall distribution

Correlations of long-term yields with soil, climatic and management variables would increase our understanding about their contribution to yield and help balance them for optimising the same. Therefore, grain yields of dryland wheat which received variable N ranging from 0–100 kg ha^–1 collected over 13 years, were analysed statistically. Wheat responded significantly to applied N in all but two years when the yields were the lowest. Grain yields across years did not relate with applied N alone (r ² = 0.00), but inclusion of seasonal water supply and organic carbon content of soil (OC) in the regression accounted for 64 per cent variation in yield. When water supply was split into stored water and growing season rain the relationship improved further (R ⁴ = 0.68) and the regression exhibited a significant interaction between seasonal rain and applied N.Three splits of seasonal water supply,viz. rain during 45 days after sowing (DAS) plus available water storage at seeding, rain during 46-120 DAS and rain during 121 DAS till a week before physiological maturity; soil OC and applied N explained 80 per cent variation in grain yield. Response to increase in post seeding water supplies was larger than that to the preseeding storage. Validation of the best regression against independent published data gave excellent agreement.     

Recovery of 15N labeled wheat residue and residual effects of N fertilization in a wheat–wheat cropping system under Mediterranean conditions

A field study was conducted in arid-Saharan Morocco to assess the fate of fertilizer N in a wheat (Triticum durum var. Karim)–wheat cropping sequence. Therefore, 85 kg N ha^–1 labeled with 9.764 atom % excess ¹⁵N was applied in a three-split application. The fertilizer N recovery by the wheat in the first year was 33.1%. At harvest, 64.8% of fertilizer N was found in the 0–80 cm profile as residual fertilizer-derived N. 2.1% of the applied N could not be accounted for in the season 1996/1997. The recovery of the residual labeled fertilizer N by the subsequent wheat crop was 6.4% for the treatment without residue incorporation and 7.4% for the treatment with residue incorporation. The possible reason for this low plant recovery was immobilization of the fertilizer N. The total recovery of fertilizer N over the two growing seasons was 82.3% and 86.1% for the treatment without and with residue incorporation, respectively. The not recovered N after the second cropping season was 15.6% and 11.8% for the treatment without and with residue incorporation, respectively. The loss of labeled N by the soil–plant system was not due to leaching but to denitrification and volatilization. In the treatment (N+*R) with labeled residue incorporation, the percentage of N recovery by plant was 16.2, indicating the mineralisation of the residue applied.     

A model to predict changes in soil moisture,NO3-N content and N uptake by wheat

A simulation model to predict fertilizer N behaviour in a soil-plant (wheat) system has been developed and tested. The model predicts components of field water balance (evaporation, transpiration, drainage and run-off) and changes in soil nitrogen amounts due to N transformations (urea hydrolysis, mineralization, nitrification and volatilization), N movement and plant N uptake using information on N transformation coefficients for the soil, atmospheric evaporative demand (E_pan), leaf area development and root growth characteristics of the crop. The model predicts N uptake by wheat through mass flow using a new simplified crop cover function. The coefficients of correlation between the measured and predicted N uptake by wheat grown under three different moisture regimes in the two years (1987–88 and 1988–89) approached unity. The computed amount of residual NO₃-N in the soil profile at wheat harvest matched well with the measured amount with a root mean square error of 13.7 percent. The close matching of the measured and model predicted components of nitrogen and water balances under three widely different set of irrigation treatments suggests of model's capabilities to help in on-farm N management both under irrigated and rainfed conditions.     

Effects of mulch,N fertilizer,and plant density on wheat yield,wheat nitrogen uptake,and residual soil nitrate in a dryland area of China

Understanding mulching influences on nitrogen (N) activities in soil is important for developing N management strategies in dryland. A 3 year field experiment was conducted in the Loess Plateau of China to investigate the effects of mulching, N fertilizer application rate and plant density on winter wheat yield, N uptake by wheat and residual soil nitrate in a winter wheat-fallow system. The split plot design included four mulching methods (CK, no mulch; SM, straw mulch; FM, plastic film mulch; CM, combined mulch with plastic film and straw) as main plot treatments. Three N fertilizer rates (N0, 0 kg N ha⁻¹; N120, 120 kg N ha⁻¹; N240, 240 kg N ha⁻¹) were sub-plot treatments and two wheat sowing densities (LD, low density, seeding rate = 180 kg ha⁻¹; HD, high density, seeding rate = 225 kg ha⁻¹) were sub-subplot treatments. The results showed that wheat yield, N uptake, and N use efficiency (NUE) were higher for FM and CM compared to CK. However, soil nitrate-N contents in the 0–200 cm soil profile were also higher for FM and CM compared to CK after the 3 year experiment. Wheat grain yields were higher for SM compared to CK only when high levels of nitrogen or high planting density were applied. Mulching did not have a significant effect on wheat yield, nitrogen uptake and NUE when soil water content at planting was much high. Wheat yield, N uptake, and residual nitrate in 0–200 cm were significantly higher for N240 compared to N120 and N0. Wheat yield and N uptake were also significantly higher for HD compared to LD. When 0 or 120 kg N ha⁻¹ was applied, HD had more residual nitrate than LD while the reverse was true when 240 kg N ha⁻¹ was applied. After 3 years, residual nitrate-N in 0–200 cm soil averaged 170 kg ha⁻¹, which was equivalent to ~40% of the total N uptake by wheat in the three growing seasons.     

Aboveground nitrogen in relation to estimated total plant uptake in maize and bean

The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments. Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m⁻² 30 day⁻¹) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N that was taken up by the plant daily varied more in maize (about 0.03–0.12 day⁻¹) than in bean (about 0.05–0.08 day⁻¹). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize depending on period within season, whereas for bean it was more constant and smaller (about 40%).     

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.