Increasing Nitrogen Application Rates Research Articles

Nitrogen Split Application Can Improve the Stalk Lodging Resistance of Maize Planted at High Density

The decrease of maize stalk quality is an important reason for stalk lodging during the grain filling stage. In the present study, a maize cultivar was planted at densities of 7.5, 9.0, 10.5, 12.0, and 13.5 × 104 plants ha−1 and subjected to nitrogen application rates of 0, 270, 360, and 450 kg ha−1 (denoted as N0, N270, N360, and N450). The stalk breaking force, mechanical strength, carbohydrate content, and nitrogen content of basal internodes were determined to study the effects of nitrogen application rate on the stalk lodging resistance of maize under different planting densities with integrated watering and fertilization using drip irrigation. At densities of 7.5 to 10.5 × 104 plants ha−1, the stalk breaking force, rind penetration strength (RPS), and crushing strength (CS) of the basal internode decreased first and then increased with increasing nitrogen application rate, with the lowest values obtained for the N270 treatment. Meanwhile, at planting densities of 12.0 × 104 plants ha−1 and above, the stalk breaking force, RPS, and CS increased with increasing nitrogen application rate. The basal internode dry weight per unit length (DWUL) and total N content increased with increasing nitrogen application rate. The breaking force was significantly positively correlated with the DWUL and mechanical strength of the basal internode. The RPS showed a positive linear correlation with the contents of cellulose, lignin, and total N of the third internode. Under the split application of water and fertilizer, the maize stalk total dry matter and contents of cellulose, lignin, and total nitrogen increased with increasing nitrogen fertilization rate during the grain filling stage at high planting density, so the stalk lodging resistance improved.

Yield and nutritive value of grazed complex legume–grass mixtures under increasing nitrogen application rates

Complex pasture mixtures are advantageous, but little information exists on the best forage species and nitrogen (N) management in eastern Canada. We compared under mob stocking four complex mixtures of one of two legume species [alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.)] plus one of two grass mixes [No. 1 — timothy (Phleum pratense L.), meadow fescue (Schedonorus pratensis (Huds.) P. Beauv.), reed canarygrass (Phalaris arundinacea L.), and Kentucky bluegrass (Poa pratensis L.); No. 2 — tall fescue (Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.), meadow bromegrass (Bromus biebersteinii Roem. and Schult.), reed canarygrass, and Kentucky bluegrass] under three N application rates at three sites over the first three post-seeding years. Legume species had little effect on most forage attributes mainly because of their low contribution to forage dry matter (DM) yield (<30%) in second and third years. The grass mix with tall fescue and meadow bromegrass (No. 2) yielded similar or slightly better than the one with timothy and meadow fescue (No. 1) but tended to have a greater neutral detergent fibre concentration, and lower N and total digestible nutrient concentrations. Nitrogen fertilization increased forage DM yield only in second and third years when the legume contribution to forage DM yield was <30%, and it increased N concentration and decreased nonstructural carbohydrate concentration. These results highlight the challenge of maintaining legume species in rotationally grazed pastures of eastern Canada and confirm recommendations of applying no or little N fertilizer on grazed legume–grass mixtures when the legume contribution to forage DM yield is >30%.

Comparison of Agronomic Performance between Japonica/Indica Hybrid and Japonica Cultivars of Rice Based on Different Nitrogen Rates

Previous studies have revealed that the japonica/indica hybrid rice has a higher yield potential, biomass production, and nitrogen (N) accumulation than japonica rice in China, however, at a single N application rate. It remains unclear whether it also occurs at a higher or lower N application rate under the same field condition. To investigate the effects of nitrogen application rates on grain yield, N uptake, dry matter accumulation, and agronomic N use efficiency, field experiments were conducted in Jinhua City, Zhejiang Province during three consecutive growth seasons in 2016, 2017, and 2018. Two japonica/indica hybrid varieties (Yongyou 12 and Yongyou 538) and two japonica varieties (Xiushui 134 and Jia 58) were exposed to five N application rates (0, 150, 225, 300, and 375 kg ha−1). The results showed that grain yields of all the varieties increased with increasing nitrogen application rates, except for Jia 58 whose optimum nitrogen level was 225 kg ha−1, because no significant difference was observed between N225 and N300. Across the four rice varieties, N uptake increased significantly with increased N-fertilizer rates at all the growth stages (p < 0.05). Across the three planting years, the average grain yield of japonica/indica hybrid rice was higher than that of japonica rice by 75.6% at N0, 57.2% at N150, 41.1% at N225, 38.3% at N300, and 45.8% at N375. We also found that as compared with japonica rice, the japonica/indica hybrid rice had more grain yield, higher dry matter, and higher N uptake at all growth stages, regardless of the N application rate.

Effects of nitrogen application rate on grain filling characteristics and nutritional quality of summer maize.

Suitable nitrogen application rate can significantly increase grain filling rate and yield and improve nutritional quality. Denghai 518 (DH518) and Zhengdan 958 (ZD958) were used as experimental materials in this study. A field experiment with four treatments, no nitrogen treatment (N0), decrement nitrogen application rate (N1, 129 kg N·hm-2), suitable nitrogen rate (N2, 184.5 kg N·hm-2) and excessive nitrogen rate (N3, 300 kg N·hm-2), was conducted to explore the effects of nitrogen fertilization on grain filling parameters and nutritional qualities of summer maize. Results showed that grain filling characteristics, grain dry weight, and yield in N0 treatment was decreased. With increasing nitrogen application rate in the suitable range, average filling rate, grain dry weight, and yield increased. Grain yield of two hybrids in N1 and N2 treatments was higher than that of N0 by 16.4%-57.2% and 35.8%-65.1%, respectively. Grain protein, soluble sugar, starch contents and the ratio of amylopectin and amylase contents were lower and crude fat content was higher in N0 treatment. Grain protein content, soluble sugar content and starch content in N2 of DH518 were higher than that of N0 and N1 by 32.5% and 6.5%, 19.9% and 9.5%, 8.9% and 5.2%, and the ratio of amylopectin and amylose contents was increased. Grain protein, soluble sugar and starch contents in N2 of ZD958 were higher than that of N0 and N1 by 16.9% and 7.8%, 30.5% and 14.8%, 11.5% and 5.7%, and the ratio of amylopectin and amylase contents was increased. Crude fat content in N2 of both hybrids decreased significantly by 4.8%-12.3% than that of N0 and N1. However, yield and nutritional quality was increased in N3 treatment than that of N2. Our results suggested that suitable nitrogen rate could enhance grain filling, grain weight, and grain nutritional quality.

Nitrate subsurface transport and losses in response to its initial distributions in sloped soils: An experimental and modelling study

AbstractTransport and losses of nitrate from sloped soils are closely linked to nitrogen fertilizer management. Previous studies have always focused on different types of fertilizer applications and rarely analysed various initial nitrate distributions as a result of nitrogen fertilizer applications. Under certain conditions, both subsurface lateral saturated flow and vertical leaching dominate nitrate losses. Soil tank experiments and HYDRUS‐2D modelling were used to better understand the subsurface nitrate transport and losses through lateral saturated flow and vertical leaching under various initial nitrate distributions. Low (L: 180 mg L−1), normal (N: 350 mg L−1), and high (H: 500 mg L−1) nitrate concentrations were used in five different distributions (NNNN, NLLN, LHHL, LNLN, and HNHN) along the slope of the tank. The first two treatments (NNNN and NLLN) were analysed both experimentally and numerically. Experiments were conducted under 12 rainfall events at intervals of 3 days. The HYDRUS‐2D model was calibrated and validated against the experimental data and demonstrated good model performance. The other three treatments (LHHL, LNLN, and HNHN) were investigated using the calibrated model. Nitrate concentrations in purple sloped soils declined exponentially with time under intermittent rainfalls, predominantly in the upper soil layers. Non‐uniform initial nitrate distributions contributed to larger differences between four locations along the slope in deeper soil layers. The non‐uniform nitrate distribution either enhanced or reduced decreases in nitrate concentrations in areas with higher or lower initial nitrate concentrations, respectively. Higher nitrate concentrations at the slope foot and along the slope were reduced mainly by lateral flow and vertical leaching, respectively. Increasing nitrogen application rates increased subsurface nitrate losses. Mean subsurface lateral nitrate fluxes were twice as large as mean vertical leaching nitrate fluxes. However, due to longer leaching durations, total nitrate losses due to vertical leaching were comparable with those due to lateral flow, which indicated comparable environmental risks to surface waters and groundwater.

Fusarium Crown Rot Whitehead Symptom as Influenced by Wheat Crop Management and Sampling Date.

Symptoms of Fusarium crown rot of wheat include premature death of inflorescens (whiteheads), lesions on subcrown internodes, and rotting of crown tissue and lower stem internodes. Each symptom type is influenced by a different set of environmental conditions. Whiteheads are the easiest symptom to quantify and are frequently reported in the Pacific Northwest U.S.A. The objective of this research was to examine factors associated with whitehead expression and relationships with wheat yield and test weight. Incidence of whiteheads differed for inoculations with different isolates of F. pseudograminearum and F. culmorum, and over years due to weather factors. Whiteheads became less as planting dates for winter wheat were delayed until after September, and incidence was increased with increasing nitrogen application rate. Dates of initial and greatest expression of whiteheads differed among cultivars, which was associated in part with the cultivar heading date. Whiteheads were not correlated with subcrown internode lesions or browning of crown tissue. Whiteheads were also not correlated with grain test weight. Whiteheads were sometimes negatively associated with grain yield, but that relationship was variable and could not be considered a reliable, recurrent, or accurate measure of crown rot severity. These results indicate the need for caution in reporting whiteheads as a sole indicator of cultivar susceptibility to Fusarium crown rot.

The consequences of change in management practices on maize yield under climate warming in Iran

The potential impacts of climate warming on grain yield, water, and nitrogen consumptions of maize have been repeatedly assessed across different regions of the world. However, to date, there is no comprehensive, large-scale evaluation on the effects of climate warming on the cropping systems of Iran. The objective of the current study was to quantify the effects of climate warming on the length of the growing period and grain yield of maize. We also tested the potential of changes in irrigation, nitrogen application rate, and using late maturity cultivars of maize to offset the negative impact of climate warming in order to maintain the current levels of grain yield (4 to 10 t ha−1 depending upon the province) in Iran. The crop modeling framework SIMPLACE was used to evaluate the effects of the warming temperatures, nitrogen application rate, and changes in thermal requirements of the cultivar scenario combinations on grain yield of maize in Iran. The climate, soil, and management inputs of the crop model were obtained from global datasets as grid cells at 0.5° × 0.5° resolution, and the outputs of the crop model were aggregated to the province level. Results of the grain yield projections showed a decline (− 0.1 to − 22%) in maize, especially in the Southern provinces (Khuzestan, Fars, and Kerman) under different warming scenarios by + 0.5 to + 2 °C, an increase from the baseline. The grain yield decline appeared to be mainly driven by a shortening of the length of the growing season and extreme heat stress during anthesis, the most sensitive period of crop growth. Increasing temperatures during the growing season lead to a marginal increase of absolute irrigation requirements over the maize growing areas. For all provinces, application of 10–25% more nitrogen than the current rate (170 kg N/ha-1) was able to offset the negative effects of higher temperatures (+ 0.5 and + 1.0 °C) during the growing season. However, the increased nitrogen application rates were not able to maintain the baseline level of grain yield under the + 1.5 and + 2.0 °C warming scenarios. Introducing late maturity cultivars, which required 20% more temperature sum than current cultivars to reach maturity, improved the grain yield in the cooler provinces by up to 10%. In conclusion, the grain yield baseline level may not be maintained under the highest magnitude of warming by increasing nitrogen application rates or using late maturity cultivars. Furthermore, more water is needed to produce a unit of grain under a warming climate. This study also suggests that combined adaptation strategies should be considered by policymakers in order to mitigate the negative impact of climate warming on the cropping systems of Iran.

Safflower (Carthamus tinctorius L.) yield as affected by nitrogen fertilization and different water regimes

En función de su origen y rusticidad, el cártamo se produce generalmente en tierras secas, de baja fertilidad, con pocos insumos y sin riego. En Brasil, poco se sabe de la respuesta de este cultivo a la aplicación de nitrógeno (N) y al riego. Este estudio fue realizado próximo a Ingeniero Coelho, SP, Brasil, en la campaña agrícola de 2014,para determinar el efecto de dosis crescientes de nitrógeno (0; 50; 100; 150; 200; 250; 300; 350: 400; 450; 500; 550 e 600 kg.ha−1) en el cultivo de cártamo en secano e irrigado. La aplicación de riego en periodos secos, posibilitó reducir el estrés y así, aumentar de forma significativa los componentes de producción y el rendimiento de granos. La producción de cártamo es influenciada por la interacción entre el régimen hídrico y la dosis de nitrógeno. El rendimiento del grano puede variar dependiendo de varios factores, sin embargo, el rendimiento máximo se logró con tasas de 208 y 214 kg.N ha-1 en condiciones de riego y de secano, respectivamente. Para el rendimiento de aceite, 200 kg N. ha-1 fueron suficientes, independientemente del régimen hídrico.

Effect of Increased Nitrogen Application Rates and Environment on Protein, Oil, Fatty Acids, and Minerals in Sesame (<i>Sesamum indicum</i>) Seed Grown under Mississippi Delta Conditions

Information on the effect of nitrogen fertilizer rates and environment on sesame seed composition and nutrition is scarce. The objective of this research was to investigate the effects of nitrogen fertilizer application rates on sesame seed yield, protein, oil, fatty acids, and mineral nutrition. A two-year (2014, 2015) field experiment was conducted. Nitrogen fertilizer (urea ammonium nitrate) solution (UAN, 32% N) was applied by side dressing to four sesame varieties (S-34, S-35, S-38, S-39) at rates of 44.7, 67.2, 89.6 and 112.0 kg·ha-1. Rate of 44.7 kg·ha-1 was used as control since this rate is traditionally recommended in the region. Increasing nitrogen application rates resulted in higher protein and oleic acid contents in two varieties in 2014, and in all varieties in 2015. Increased protein and oleic acid were accompanied by lower total oil and linoleic acid. Increased nitrogen application also resulted in higher seed N, S, B, Cu, Fe, and Zn in 2014 in S-34 and S-35, but either a decline or no clear change was observed in seed levels of these nutrients in S-38 and S-39. In 2015, increased nitrogen application resulted in significantly higher seed N in all varieties, and higher S, B, Cu, Fe, and Zn in some varieties. A significant positive correlation was observed between nitrogen application rate and yield, and with seed levels of protein, oleic, acid, N, B, Cu, Fe, and Zn. A significant negative correlation was observed between nitrogen application rate and seed oil and linoleic acid. Thus, increased nitrogen fertilizer application resulted in higher seed protein, oleic acid, and some mineral nutrients, but lower oil and linoleic acid. However, this effect depended on variety and environmental conditions. Because higher protein and oleic acid are desirable traits for sesame seed nutritional value and oil stability, regional breeders should select sesame varieties for efficient fertilizer response.

The adaptive capacity of maize-based conservation agriculture systems to climate stress in tropical and subtropical environments: A meta-regression of yields

Conservation agriculture is widely promoted across sub-Saharan Africa as a sustainable farming practice that enhances adaptive capacity to climate change. The interactions between climate stress, management, and soil are critical to understanding the adaptive capacity of conservation agriculture. Yet conservation agriculture syntheses to date have largely neglected climate, especially the effects of extreme heat.For the sub-tropics and tropics, we use meta-regression, in combination with global soil and climate datasets, to test four hypotheses: (1) that relative yield performance of conservation agriculture improves with increasing drought and temperature stress; (2) that the effects of moisture and temperature stress exposure interact; (3) that the effects of moisture and temperature stress are modified by soil texture; and (4) that crop diversification, fertilizer application rate, or the time since no-till implementation will enhance conservation agriculture performance under climate stress.Our results support the hypothesis that the relative maize yield performance of conservation agriculture improves with increasing drought severity or exposure to high temperatures. Further, there is an interaction of moisture and heat stress on conservation agriculture performance and their combined effect is both non-additive and modified by soil clay content, supporting our second and third hypotheses. Finally, we found only limited support for our fourth hypothesis as (1) increasing nitrogen application rates did not improve the relative performance of conservation agriculture under high heat stress; (2) crop diversification did not notably improve conservation agriculture performance, but did increase its stability with heat stress; and (3) a statistically robust effect of the time since no-till implementation was not evident.Our meta-regression supports the narrative that conservation agriculture enhances the adaptive capacity of maize production in sub-Saharan Africa under drought and/or heat stress. However, in very wet seasons and on clay-rich soils, conservation agriculture yields less compared to conventional practices.

Effect of water-nitrogen coupling on photosynthesis and ultrastructure of cucumber leaves under CO2 enrichment

Using split plot and then-split plot design, effects of water-nitrogen coupling on photosynthesis and ultrastructure of cucumber (Cucumis sativus) (Jinyou No.35) under CO2 enrichment were investigated. The main plot had two CO2 concentrations: ambient CO2 concentration (400 μmol·mol-1, A) and doubled CO2 concentration (800±20 μmol·mol-1, E). The split plot had two treatments: no drought stress (95% of field capacity, W) and drought stress (75% of field capacity, D). The then-split plot contained low nitrogen treatment (450 kg·hm-2, N1) and high nitrogen treatment (900 kg·hm-2, N2). The results showed that under the condition of drought and high nitrogen, increasing CO2 enhanced the cucumber plant height, and no matter what kinds of water treatment, CO2 enrichment increased the leaf area significantly under high nitrogen. Under the condition of normal irrigation, the photosynthetic rate, stomatal conductance and transpiration rate of high nitrogen treatment were higher than low nitrogen treatment, while it was under the drought condition. Elevated CO2 enhanced the water use efficiency of cucumber leaf which increased with increasing nitrogen application rate. Under drought stress, cucumber adaxial surface porosity density was increased, and the CO2 enrichment and high nitrogen significantly reduced the stomatal density. Increasing nitrogen application improved the number of chloroplast, and reduced that of starch grains. Drought stress decreased the number of chloroplast, but tended to promote the number of starch grains. Drought stress increased the chloroplast length and width, and the size of the starch grains, while high nitrogen reduced the length and width of the chloroplast and starch grains. CO2 enrichment and high nitrogen increased grana thickness and layers (except ADN2), and the slice layer of EDN2 was significantly higher than that of ADN2. In conclusion, CO2 enrichment and suitable water and nitrogen could promote the development of chloroplast thylakoid membrane system, significantly increase the thickness of grana and the number of grana lamella, and effectively improve the chloroplast structure of cucumber, which would benefit the photosynthesis of cucumber plants and ability to utilize CO2 and water and nitrogen.

Integrated fertilization systems effects on yield, nodulation state and fatty acids composition of soybean (Glycine max)

Combined application of organic and inorganic fertilizers can play an important role for increasing yield and quality of soybean (Glycine max L.). In order to study of effects of biofertilizers and nitrogen rates on yield, nodulation state and fatty acids composition of soybean, a factorial experiment was conducted based on randomized complete block design with three replications in 2012 and 2013. Factors were different rates of nitrogen fertilizer in four levels (without nitrogen and application 25, 50 and 75 kg urea/ ha) and seed inoculation with as biofertilizers in five levels (without inoculation, seed inoculation with Pseudomonas putida strain 41, P. putida strain 186, Azotobacter chroococcum strain 5 and Bradyrhizobium japonicum). The results showed that maximum of grain yield, plant height, number of filled pods and number of grains per plant were obtained from the highest level of nitrogen fertilizer (75 kg urea/ha) and Rh. inoculation. Furthermore, the highest rate of nitrogen usage (75 kg urea/ha) adversely inhibited nodulation of soybean. Number and dry weight of nodules/plant increased significantly with increasing nitrogen application rates up to 50 kg urea/ha. Seed inoculation with biofertilizers increased oil and protein contents. The maximum oil content was obtained by applying 50 kg urea/ha and seed inoculation with Bradyrhizobium. The saturated fatty acids (palmitic and stearic acids) declined in seed inoculation with Bradyrhizobium than the control, while it was vice versa in unsaturated fatty acids (linoleic, linoneic and oleic acids). Based on the results, it was concluded that application of suitable amounts of nitrogen fertilizer (i.e. between 50 and 75 kg urea/ha) as starter in seed inoculation with Bradyrhizobium japonicum can be recommended for profitable soybean production in the study area.

Changes of Grain Yield and Nitrogen Use Efficiency of Maize Hybrids Released in Different Eras in Shaanxi Province

Identifying the changes of grain yield and nitrogen use traits will facilitate the development of new maize hybrids with high yield and nitrogen use efficiency. In this study, 12 typical maize hybrids released from 1981 to 2010 in Shaanxi Province were grown in the field under three N rates(0, 120, and 240 kg ha–1) from 2011 to 2012 in Shaanxi, Northwest China. Nitrogen use efficiency and agronomic traits of maize were investigated. The result indicates that grain yield of maize hybrids increased with the increase of nitrogen rates, and the modern maize hybrids(2000s) showed better grain yield than the old ones(1980s) at three nitrogen levels. The yield genetic gains were 46, 65, and 83 kg ha–1 per year at N0, N120, and N240 levels repeat. The modern hybrids showed better biomass and grain yield than the old ones, but there was no clear changing trend in stover yield between hybrids of different ears. Increments of grain yield were achieved mainly through increasing the kernel number per ear, 1000-kernel weight and biomass, and the coefficient of light extinction decreased with the time process of cultivar development from 1981 to 2010. Changes of plant structure would allow the modern maize hybrids to improve light capture resulting in better grain yield than those of the old ones. For nitrogen use point of view, irrespective of nitrogen treatments, nitrogen use efficiency(NUE) of hybrids released increased in responses of time. But nitrogen use efficiency decreased with increasing nitrogen application rates, and nitrogen use efficiency(NUE) was highly correlated with N uptake efficiency(NUpE, r = 0.75), and not with N physiological efficiency(NUtE, r = 0.42). Increased NUE positively correlated with improved N uptake efficiency(NUpE), due to the greater post-anthesis N accumulation. The results indicated that improvements of 1000-kernel weight, kernel number per ear and nitrogen uptake efficiency(NUpE) should be considered during breeding for high yield and high nitrogen use efficiency of maize under low nitrogen and water limited conditions.

Lodging Resistance of Super-Hybrid Rice Y Liangyou 2 in Two Ecological Regions

Experiments were conducted with super-hybrid rice Y Liangyou 2 at Taoyuan,Yunnan Province and Danyang,Jiangsu Province in 2011 and 2012.The main objective of this study was to reveal the difference of lodging resistance and effects of nitrogen on rice lodging resistance between two ecological regions.Rice lodging indexes were 15% lower at Taoyuan than at Danyang.Bending moment of whole plant was 74.2% at Taoyuan lower than that at Danyang.Bending stress and dry matter weight of leaf sheath at basal stem made up the deficiency in stem diameter and wall thickness.There exited significantly negative correlations between lodging indexes and bending stress,snapping resistance at Taoyuan and Danyang.Plant height,height of ear-neck,height of gravity center increased significantly and bending stress,stem weight per centimeter decreased significantly with increasing nitrogen application rate in special high yield eco-region.For Tai Lake rice region,plant height,dry weight of three leaves from top increased significantly,and snapping resistance decreased significantly with increasing the rate of nitrogen.Thus increasing nitrogen application reduced lodging tolerance.Physical strength of stem decreased significantly with delaying nitrogen application,but it was beneficial to promoting the development of basal stem diameter and wall thickness.

基于上部叶片SPAD值估算小麦氮营养指数

快速、准确的监测诊断小麦氮营养状态对于评价小麦长势、指导氮肥运筹并预测籽粒产量均具有重要的意义。基于2009-2011年的大田试验,系统分析了小麦上部4张单叶不同叶位的SPAD值和归一化SPAD指数(NDSPAD_<em>ij</em>)与氮营养指数的定量关系,通过简单分组线性回归筛选出在不同年际和不同品种间表现稳定的氮营养指数(NNI)定量方程。结果表明,小麦上部不同叶位SPAD值和NNI随施氮量提高而提高,而NDSPAD_<em>ij</em>随施氮量的提高而降低。小麦单叶SPAD值与NNI的关系呈显著正相关,但这种关系在品种或年份之间不稳定,对小麦氮素诊断存在风险;除NDSPAD₁₂外,NDSPAD_<em>ij</em>与NNI之间呈显著负相关,经简单分组线性分析发现NDSPAD₁₄与NNI之间在年份和品种之间表现最稳定,能够较好的定量估算氮营养指数,从而快速诊断小麦氮素是否亏缺。;Rapid, accurate, and dynamic diagnosis of nitrogen nutrition status is essential for evaluating vigor, for predicting production rates, and for agricultural management of cultivated wheat. To determine the critical nitrogen concentration dilution curve for wheat, two field experiments with different levels of N application (0, 75, 150, 225, 300 and 375 kg/hm²) were conducted in Yizheng, China. According to the procedure in Justes's curve, the dry matter and nitrogen concentrations under different nitrogen treatments could be compared by analysis of variance at the 5% probability level. Based on this curve, we developed a nitrogen nutrition index (NNI). In this index, when NNI=1, nitrogen nutrition was considered to be optimum, NNI>1 indicated excess nitrogen, and NNI<1 indicated nitrogen deficiency. We further investigated relationships between NNI and soil and plant analyzer development (SPAD) chlorophyll meter values and normalized differential SPAD_<em>ij</em> (NDSPAD_<em>ij</em>) values obtained at the top four leaf positions in wheat. We conducted a linear parallel curve analysis with grouped data to determine if the linear quantitative equation relating NNI to SPAD value or NDSPAD_ijshowed differences between varieties and/or years. The results showed that the curve had specific biological significance. The relationship between the critical nitrogen concentration and wheat dry matter could be described by the following negative power equations Y16: N_cnc=4.65DM^-0.44 and N13: N_cnc=4.33DM^-0.45. The critical nitrogen curves of the two cultivars of wheat had the same coefficient b but different coefficients a. Y16 had a higher nitrogen accumulation capacity than N13. The NNI values ranged from 0.37 to 1.28, and increased with higher nitrogen application rates under the different nitrogen levels. The optimum nitrogen level was 150 kg/hm² in 2009–2010, but was 225 kg/hm² in 2010-2011. The SPAD values increased with increasing N application rates, and ranged from 34.3 to 52.8. In contrast, the NDSPAD_<em>ij</em> value decreased with increasing nitrogen application rates, which showed that increasing amounts of nitrogen could decrease the differences in SPAD value among the top four single leaves of wheat. The NDSPAD_ijvalues ranged from 0.01 to 0.143. The SPAD value at the top four single leaf positions were significantly positively related to NNI. The correlation coefficients ranged from 0.666 to 0.823. The strongest correlation was between the SPAD value at the top leaf (T1) and NNI, while the weakest correlation was between the SPAD value at the second leaf (T2) and NNI. A linear parallel curve analysis with grouped data approximated the relationship between SPAD and NNI and its differences between varieties and years. This will be useful for diagnoses of wheat nitrogen nutrition. In contrast, NDSPAD_<em>ij</em> was significantly negatively related to NNI, except for NDSPAD₁₂. The correlation coefficients ranged from 0.01 to -0.849. The strongest correlation was between NDSPAD₁₄ and NNI, while the weakest correlation was between NDSPAD₁₂ and NNI. A linear parallel curve analysis with grouped data demonstrated the relationship between NDSPAD₁₄and NNI (NNI=-2.019NDSPAD₁₄+1.18, <em>R</em>=-0.838^{* *}) stably across variety and year differences. This analysis could be used to assess NNI quantitatively and to diagnose wheat nitrogen deficiency quickly.

Effects of nitrogen application rate and a nitrification inhibitor dicyandiamide on ammonia oxidizers and N2O emissions in a grazed pasture soil

Ammonia oxidizers, including ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) are important drivers of a key step of the nitrogen cycle — nitrification, which affects the production of the potent greenhouse gas, nitrous oxide (N2O). A field experiment was conducted to determine the effect of nitrogen application rates and the nitrification inhibitor dicyandiamide (DCD) on the abundance of AOB and AOA and on N2O emissions in a grazed pasture soil. Nitrogen (N) was applied at four different rates, with urea applied at 50 and 100kgNha−1 and animal urine at 300 and 600kgNha−1. DCD was applied to some of the N treatments at 10kgha−1. The results showed that the AOB amoA gene copy numbers were greater than those of AOA. The highest ratio of the AOB to AOA amoA gene copy numbers was 106.6 which occurred in the urine-N 600 treatment. The AOB amoA gene copy numbers increased with increasing nitrogen application rates. DCD had a significant impact in reducing the AOB amoA gene copy numbers especially in the high nitrogen application rates. N2O emissions increased with the N application rates. DCD had the most significant effect in reducing the daily and total N2O emissions in the highest nitrogen application rate. The greatest reduction of total N2O emissions by DCD was 69% in the urine-N 600 treatment. The reduction in the N2O emission factor by DCD ranged from 58% to 83%. The N2O flux and NO3−-N concentrations were significantly correlated to the growth of AOB, rather than AOA. This study confirms the importance of AOB in nitrification and the effect of DCD in inhibiting AOB growth and in decreasing N2O emissions in grazed pasture soils under field conditions.

English

In order to determine the effect of water deficit and nitrogen fertilizer application on growth indices, yield and yield component of three soybean (Glycine Max&nbsp;L. Merr) genotypes a split plot factorial experiment based on randomized complete block with three replications was carried out. Soybean genotypes (Williams, K1410 and HS95-4118) were subjected to three irrigation regimes (90, 120 and 150 evaporation from class A lysimeter) and three levels of nitrogen fertilizer (30, 60 and 90 kg N/ha). The results showed that, water deficit significantly decreased 1000 grain weight, yield, total dry mater and harvest index. The highest seed per pod (2.59) and maximum 1000 grain weight were obtained from HS95-4118 from Williams&rsquo;s genotypes, respectively. Although, the HS95-4118 genotype had the highest seed yield (499.89 g/m2). Increasing nitrogen application rates up to 90 kg N /ha increased pod per plant, grain per pod, 1000 grain weight, yield and total dry mater significantly. Maximum harvest index (33.8) obtained from 60 kg N /ha. &nbsp; Key words:&nbsp;&nbsp;Growth indices, nitrogen, soybean, water deficit.

Effect of cultivation pattern and nitrogen application rate on soil fertility and nitrate accumulation under maize-wheat rotation system

以在陕西关中土垫旱耕人为土区进行的连续6年定位试验为对象, 研究了长期覆盖栽培及施氮量对玉米-小麦轮作体系下土壤有机质、全氮及土壤剖面硝态氮残留量和分布的影响。结果表明, 不同栽培模式对土壤有机质和全氮含量的影响为覆草>垄沟>常规>节水, 其中覆草模式影响达显著水平。增施氮肥不同程度地提高了土壤有机质和全氮含量。经过12季玉米-小麦的轮作, 不同栽培模式0~200 cm土壤剖面硝态氮残留量为垄沟>节水>覆草>常规, 垄沟和节水栽培模式与常规栽培硝态氮累积量差异达显著水平。随种植年限和施氮量增加, 0~200 cm土壤中硝态氮累积量明显增加, 施240 kg·hm<sup>-2</aup> N (N240)处理 0~200 cm土壤硝态氮累积量显著高于施120 kg·hm<sup>-2</aup> N (N120)处理。不同施氮量下硝态氮在0~200 cm土壤剖面的分布存在差异, 与不施氮(N0)和N120处理相比, N240处理下各栽培模式在120 cm以下的土壤硝态氮含量随深度增加而显著增加。

Effects of Plant Density and Nitrogen Application Rate on Grain Yield and Nitrogen Uptake of Super Hybrid Rice

The nitrogen uptake, yield and its components for two super-high-yielding hybrid rice combinations, Guodao 6 and Eryou 7954 were investigated under different plant densities (15, 18, and 21 plants/m 2) and different nitrogen application rates (120, 150, 180, and 210 kg/hm 2). The experiment was conducted on loam soil during 2004–2006 at the experimental farm of the China National Rice Research Institute in Hangzhou, China. In these years, the two hybrid rice clearly showed higher yield at a plant density of 15 plants/m 2 with a nitrogen application rate of 180 kg/hm 2. Guodao 6 produced an average grain yield of 10 215.6 kg/hm 2 across the three years, while the yield of Eryou 7954 was 9 633.0 kg/hm 2. With fewer plants per unit-area and larger plants in the plots, the two hybrid rice produced more panicles per plant in three years. The highest nitrogen uptake of the two hybrid rice was at a plant density of 15 plants/m 2 with a nitrogen application rate of 180 kg/hm 2. Further increasing nitrogen application rate was not advantageous for nitrogen uptake in super-high-yielding rice under the same plant density.

Optimum Nitrogen Fertilization for Production of Containerized Raphiolepis × delacourii ‘Snow White’

Abstract Rooted stem cuttings of ‘Snow White’ raphiolepis (Raphiolepis × delacourii Andre ‘Snow White’) were grown in 3.8-liter (#1) black plastic containers containing a pine bark:sand (8:1, by vol) substrate. Plants were fertilized at every irrigation, for 17 weeks, with a 4:1:2 nitrogen (N):phosphorus (P):potassium (K) nutrient solution containing N at 20, 60, 100, 140, 180, 220, or 240 mg·L−1 (ppm) supplied as ammonium nitrate (NH4NO3). Maximum top and root dry weights were achieved with N at 145 mg·L−1. Substrate solution electrical conductivity increased linearly with increasing nitrogen application rate (NAR) with maximum growth occurring at 1.28 dS·m−1, whereas substrate solution pH decreased linearly with increasing NAR with a pH of 5.3 at 145 mg·L−1. Increasing the N rate beyond 145 mg·L−1 had minimal effect on top or root dry weight. Leaf area peaked at a NAR of 171 mg·L−1 with a plateau at 524 cm2. Leaf area increased 275% as the NAR increased from 20 to 171 mg·L−1. Specific leaf area increased linearly with increasing NARs. Carbon allocation between tops and roots was unaffected by NARs from 60 to 280 mg·L−1. Root:top ratio decreased 56% between the pooled NARs (60 to 240 mg·L−1) and N at 20 mg·L−1. Leaf area ratio increased linearly with increasing NARs. Foliar mineral nutrient concentrations of N, P, and sulfur increased linearly with increasing NAR, whereas concentrations of K, calcium, magnesium, and copper responded quadratically to increasing NARs. Top growth increased from inadequate at a NAR of 60 mg·L−1 to optimum at 145 mg·L−1, whereas root growth was relatively similar over the same range. At 145 mg·L−1, mineral nutrient concentrations of the top are well within or exceed accepted levels reported, and growers can expect rapid growth of rooted cuttings.