Synergistic effects of planting density and nitrogen fertilization on chlorophyll degradation and leaf senescence after silking in maize

Regulating planting density and nitrogen(N)fertilization could delay chlorophyll(Chl)degradation and leaf senescence in maize cultivars.This study measured changes in ear leaf green area(GLA_(ear)),Chl content,the activities of Chl a-degrading enzymes after silking,and the post-silking dry matter accumulation and grain yield under multiple planting densities and N fertilization rates.The dynamic change of GLA_(ear)after silking fitted to the logistic model,and the GLA_(ear) duration and the GLAearat 42 d after silking were affected mainly by the duration of the initial senescence period(T_(1))which was a key factor of the leaf senescence.The average chlorophyllase(CLH)activity was 8.3 times higher than pheophytinase activity and contributed most to the Chl content,indicating that CLH is a key enzyme for degrading Chl a in maize.Increasing density increased the CLH activity and decreased the Chl content,T1,GLAear,and GLA_(ear) duration.Under high density,appropriate N application reduced CLH activity,increased Chl content,prolonged T1,alleviated high-density-induced leaf senescence,and increased post-silking dry matter accumulation and grain yield.

Effects of Reduced Nitrogen Fertilization and Biochar Application on CO_2 and N_2O Emissions from a Summer Maize-Winter Wheat Rotation Field in North China

This experiment was conducted in Xinxiang, Henan from June 2013 to June 2014. Total four treatments were designed including farmers ’ common practice （F, 250 kg/hm^2）, 80% F （LF, 200 kg/hm^2）, 80% F＋biochar （LFC） and no fertilizer （CK） to measure the dynamic emissions of CO2 and N2O from a summer maize-winter wheat field by static chamber-gas chromatography method. The results showed that the soil CO2 emission was 21.8-1 022.7 mg/（m^2·h）, and was mainly influenced by soil temperature and moisture content. During the growth of summer maize, the soil CO2 emission was more significantly affected by soil moisture con-tent; and in winter wheat growing season, it was more significantly affected by soil temperature in the top 5 cm. The LF and LFC treatments significantly reduced the soil cumulative CO2 emission, especial y during the growth of winter wheat. Fertiliza-tion and irrigation were the main factors influencing the soil N2O emission. The soil N2O emission during the fertilization period accounted for 73.9%-74.5% and 40.5%-43.6% of the soil cumulative N2O emission during the summer maize-and winter wheat-growing season, respectively. The peak of emission fluxes was determined by fertilization amount, while the occurrence time of emission peak and emission re-duction effect were influenced by irrigation. The LF treatment reduced the soil cu-mulative N2O emission by 15.7%-16.8% and 18.1%-18.5% during the growth period of summer maize and winter wheat, respectively. Reduced nitrogen fertilization is an effective way for reducing N2O emission in intensive high-yielding farmland. Under a suitable nitrogen level （200 kg/hm^2）, the application of biochar showed no significant effect on the soil N2O emission in a short term. The N2O emission factors of the L and LF treatments were 0.60% and 0.56%, respectively. ln the intensive high-yield-ing farmland of North China, reducing the nitrogen application amount is an appro-priate measure to mitigate greenhouse gas emissions without crop yield loss.

Impact of Silicon,Zinc,Boron Combined with Reduced Nitrogen Fertilization on Rice Growth

Under the condition of reduced application of nitrogen fertilizer, the impact of silicor）, zinc and boron on rice growth was investigated by field experiment. The results showed that when the application amount of nitrogen fertilizer was reduced by 20%, the application of silicon, zinc and boron did not reduce the yield of rice, but reduced the incidence of panicle blast in rice and optimized the structure of rice production.

Effects of Panicle Nitrogen Fertilization on Non-Structural Carbohydrate and Grain Filling in Indica Rice

Grain filling, a crucial stage of grain yield formation in rice, is usually affected by the panicle nitrogen （N） fertilization. Field and pot culture experiments were conducted to explore the underlying mechanisms of N effect. Two rice cultivars with high lodging resistance were grown in the field and pot. Four panicle N fertilization treatments were conducted in 2006 and repeated in 2007. The result showed that medium level of panicle N fertilization treatment （NM） enhanced the accumulation and translocation of non-structural carbohydrate （NSC） in the stem and sheath. Compared with non-nitrogen treatment （NO）, NM promoted the translocation of labeled ^13C from stem and sheath to grain. But, low level of panicle N fertilization treatment （NL） and high level of panicle N fertilization treatment （NH） showed the negative effect. The endosperm cell, grain length, and grain width of NM increased more quickly than that of NO from 4 to 10 d after anthesis. During the early period of grain filling, sucrose-phosphate synthase （EC 2.4.1.14, SPS） activity were significantly higher for the NM treatment than those of the NL and NH treatments. Sucrose synthase （EC 2.4.1.13, SuSase） activity in the grains was substantially enhanced by NM, with the duration of higher activity being longer than those of the other treatments. At maturing stage, NM significantly increased the filled grain number, the seed-setting rate, and the grain weight compared with NL and NH. The results suggest that NM have a positive effect on the activities of enzymes of physiological importance, thereby increasing the grain size and promoting grain filling.

Optimization of nitrogen fertilization improves rice quality by affecting the structure and physicochemical properties of starch at high yield levels

A major challenge in modern rice production is to achieve the dual goals of high yield and good quality with low environmental costs.This study was designed to determine whether optimized nitrogen(N)fertilization could fulfill these multiple goals.In two-year experiments,two high yielding‘super’rice cultivars were grown with different N fertilization management regimes,including zero N input,local farmers’practice(LFP)with heavy N inputs,and optimized N fertilization(ONF).In ONF,by reducing N input,increasing planting density,and optimizing the ratio of urea application at different stages,N use efficiency and the physicochemical and textural properties of milled rice were improved at higher yield levels.Compared with LFP,yield and partial factor productivity of applied N(PFP)under ONF were increased(on average)by 1.70 and 13.06%,respectively.ONF increased starch and amylose content,and significantly decreased protein content.The contents of the short chains of A chain(degree of polymerization(DP)6-12)and B1 chain(DP 13-25)of amylopectin were significantly increased under ONF,which resulted in a decrease in the stability of rice starch crystals.ONF increased viscosity values and improved the thermodynamic properties of starch,which resulted in better eating and cooking quality of the rice.Thus,ONF could substantially compensate the negative effects caused by N fertilizer and achieve the multiple goals of higher grain quality and nitrogen use efficiency(NUE)at high yield levels.These results will be useful for applications of high quality rice production at high yield levels.

A Dynamic Knowledge Model for Nitrogen Fertilizationin Wheat Management

By analyzing and extracting the research progress on nitrogen fertilization in wheat, a dynamic knowledge model for management decision-making on total nitrogen rate, ratios of organic to inorganic and of basal to dressing nitrogen under different environments and cultivars in wheat was developed with principle of nutrient balance and by integrating the quantitative effects of grain yield and quality targets, soil characters, variety traits and water management levels. Case studies on the nitrogen fertilization model with the data sets of different eco-sites, cultivars, soil fertility levels, grain yield and quality targets and water management levels indicate a good performance of the model system in decision-making and wide applicability.

Effects of Combined Organic-inorganic Fertilization on Quality and Water Use Efficiency of Spring Maize under Equal Nitrogen Fertilization

The experiment was conducted in the abandoned land of Liangjia Village,Huayin City,Shaanxi Province from April to September 2019.The experimental crop was spring maize.A total of six treatments were set up in a randomized block design.The moisture content of the top 0-60 cm soil was determined regularly,and the yield and quality indices of maize at maturity were checked.The results show that:(i)combined organic-inorganic fertilization increased the yield of spring maize by 3%-8%.(ii)Compared with CK,fertilization treatments significantly improved the water use efficiency of spring maize,with an increase of 59.2%.The average water use efficiency of three combined organic-inorganic fertilization treatments was 27.81 kg/(ha·mm).Compared with CON,combined application of organic and inorganic fertilizers significantly improved the water use efficiency of spring maize,with an increase of 12.5%.(iii)The combined application of organic and inorganic fertilizers increased the moisture,total starch,crude protein and crude fat contents,and reduced crude fiber content of maize kernels.However,with the increase of the proportion of organic fertilizer,the crude protein content of maize kernels decreased.(iv)Yield of spring maize showed a significant parabolic relationship with soil water consumption.In summary,70%inorganic fertilizer+30%organic fertilizer is a scientific and reasonable way of fertilization.

Effects of Nitrogen Fertilization and Genotype on Rice Grain Macronutrients and Micronutrients

High nitrogen （N） input features China＇s intensive rice production system. To elucidate N and genotype effects on accumulation of macronutrients and micronutrients in grains of japonica rice, and to discuss its significance in rice production, a three-year field experiment involving six japonica rice varieties and seven N treatments were performed. Macronutrients （Ca, Mg, K, and Na） and micronutrients （Cu, Fe, Mn, and Zn） concentrations in brown and milled rice were measured using an atomic absorption spectrophotometer. For macronutrients, no consistently significant effect of N was detected in both brown and milled rice. For micronutrients, N showed significant effect, especially in lowering Zn accumulation in brown and milled rice. In addition, N tended to increase Fe concentration in milled rice. Genotype showed larger effect on distribution of minerals in milled rice than N. The high-yielding variety, Wuyunjing 7, accumulated larger proportion of Mg, K, and Zn in the milled rice as compared with the other five varieties and could be of value for rice breeding programs aiming at high nutritional quality. The results demonstrated differences in response to N between macronutrients and micronutrients, and are of significance for coping with ＇hidden hunger＇ both in humans and crops through agronomical practices.

Effects of Nitrogen Fertilization Amount on the Prophase Yield of Phaseolus vulgaris and Available Nitrogen Content of Soil

[Objective] This study aimed to provide certain scientific basis for reasonable application of nitrogen fertilizer in the pollution-free cultivation of Phaseolus vulgaris. [Method] A field experiment was conducted to investigate the effects of different nitrogen fertilization amounts on the prophase yield and economic efficiency of P. vulgaris and available nitrogen content of soil. [Result] With the increased application amount of nitrogen fertilizer, the prophase yield and economic efficiency of P. vulgaris reached the peaks in the Treatment 3 （8 690.48 kg/ hm^2 and 32 222 yuan/hm^2）, and significant differences were found among different treatment groups. With the increased nitrogen fertilization amount, the soil available nitrogen content increased, showing a positive correlation with correlation coefficient of 0.856 5. Excess nitrogen fertilizer reduced the prophase yield and economic efficiency of P. vulgaris. For the open field cultivation of P. vulgaris, the optimum application amount of nitrogen fertilizer was 178 kg/hm^2. [Conclusion] Application of nitrogen fertilizer could effectively increase the soil available nitrogen content.

Proton accumulation accelerated by heavy chemical nitrogen fertilization and its long-term impact on acidifying rate in a typical arable soil in the Huang-Huai-Hai Plain

Cropland productivity has been significantly impacted by soil acidification resulted from nitrogen （N） fertilization, especially as a result of excess ammoniacal N input. With decades＇ intensive agricultural cultivation and heavy chemical N input in the Huang-Huai-Hai Plain, the impact extent of induced proton input on soil pH in the long term was not yet clear. In this study, acidification rates of different soil layers in the soil profile （0-120 cm） were calculated by pH buffer capacity （pHBC） and net input of protons due to chemical N incorporation. Topsoil （0-20 cm） pH changes of a long-term fertilization field （from 1989） were determined to validate the predicted values. The results showed that the acid and alkali buffer capacities varied significantly in the soil profile, averaged 692 and 39.8 mmolc kg-1 pH-1, respectively. A significant （P〈0.05） correlation was found between pHRC and the content of calcium carbonate. Based on the commonly used application rate of urea （500 kg N ha-1 yr-1）, the induced proton input in this region was predicted to be 16.1 kmol ha-1 yr-1, and nitrification and plant uptake of nitrate were the most important mechanisms for proton producing and consuming, respectively. The acidification rate of topsoil （0-20 cm） was estimated to be 0.01 unit pH yr-1 at the assumed N fertilization level. From 1989 to 2009, topsoil pH （0-20 cm） of the long-term fertilization field decreased from 8.65 to 8.50 for the PK （phosphorus, 150 kg P205 ha-1 yr-1; potassium, 300 kg K20 ha-1 yr-1; without N fertilization）, and 8.30 for NPK （nitrogen, 300 kg N ha-1 yr-1; phosphorus, 150 kg P2Os ha-1 yr-1; potassium, 300 kg K20 ha -1 yr-1）, respectively. Therefore, the apparent soil acidification rate induced by N fertilization equaled to 0.01 unit pH yr-1, which can be a reference to the estimated result, considering the effect of atmospheric N deposition, crop biomass, field management and plant uptake of other nutrients and cations. As protons could be consumed by some field practices, such as stubble return and coupled water and nutrient management, soil pH would maintain relatively stable if proper management practices can be adopted in this region.

Effect of Nitrogen Fertilization on Leaf Chlorophyll Fluorescence in Field-Grown Winter Wheat Under Rainfed Conditions

The effect of nitrogen fertilization on leaf chlorophyll fluorescence was studied in field-grown winter wheat during grain filling underrainfed conditions in Loess Plateau. Results showed that the actual photochemical efficiency of PSⅡ reaction center (F PSⅡ)decreased significantly as leaf water stress progressed, however, the F PS was increased by nitrogen fertilization. The F PSⅡ of 0, 90 and180 kg ha-1 nitrogen treatments at noon were 0.197, 0.279 and 0.283, respectively, which decreased by 57.7, 56.4 and 40.2% as comparedto those in the morning. In the afternoon, the F PSⅡ partialy or completely recovered to the levels in the morning. The values of F PS Ⅱin 0 and 90kgha-1 treatments recovered to 87.3 and 81.5% of those in the morning. In 180kgha-1 treatment, the F PSⅡ in the afternoonwas even higher than that in the morning. Application of nitrogen fertilizer significantly increased maximum photochemical efficiency(Fv/Fm), photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (qNP). These results indicated thatapplication of nitrogen fertilizer could increase the light energy conversion efficiency, the potential activity of photosynthetic reactioncenter, and the non-photochemical dissipation of excess light energy, which can prevent leaf photosynthetic apparatus from damage ofenvironmental stress. However, there was no significant difference in the values of F PSⅡbetween 90 and 180kgha-1 nitrogentreatments, indicating that the excess nitrogen was unfavorable to photosynthesis.

Effects of Slow-release Nitrogen Fertilizer on Yield and Nitrogen Accumulation of Summer Maize in Shajiang Black Soil Area

[Objectives] This study was conducted to verify the field application effect of slow-release nitrogen fertilizer on summer maize in Shajiang black soil area by simultaneous sowing and fertilization, and explore the application scope and nitrogen metabolism mechanism, so as to lay a foundation for fertilizer reduction and efficiency improvement. [Methods] With maize variety Beiqing 340 and sulfur-coated urea as experimental materials, five nitrogen application levels were set, namely, control (C0), slow-release nitrogen 70 kg/hm^(2) (C70), slow-release nitrogen 140 kg/hm^(2) (C140), slow-release nitrogen 210 kg/hm^(2) (C210) and slow-release nitrogen 280 kg/hm^(2) (C280). The phosphorus and potassium fertilizers were all in accordance with the unified standard. [Results] With the application rate of slow-release nitrogen increasing, the nitrogen accumulation in organs increased first and then decreased after tasseling stage of maize. In order to reduce the fertilizing amount and increase efficiency, 210 kg/hm^(2) of slow-release nitrogen fertilizer was the best fertilizing amount for summer maize in Shajiang black soil area. [Conclusions] This study provides reference for fertilizer reduction, efficiency improvement and sustainable development of summer maize in Shajiang black soil area.

Effects of Slow-release Nitrogen on Dry Matter Accumulation,Translocation and Yield of Summer Maize

[Objectives]This study was conducted to investigate the effects of slow-release nitrogen fertilizer on dry matter accumulation and translocation of summer maize.[Methods]With Zhoudan 9 as the test variety,six different treatment were set up:blank control(CK1),slow-release urea 75 kg/hm^(2)(C1),slow-release urea 150 kg/hm^(2)(C2),slow-release urea 225 kg/hm^(2)(C3),slow-release urea 300 kg/hm^(2)(C4)and ordinary urea 300 kg/hm^(2)(CK2),to study the change law of dry matter accumulation and translocation in summer maize.[Results]Treatment slow-release urea 225 kg/hm^(2)(C4)showed summer maize yield,dry matter translocation between organs,grain contribution rate and proportion of grain dry matter in the full ripe stage higher than other treatments.Considering the weight loss and cost factors,slow-release urea 225 kg/hm^(2)(C3)could be recommended as the fertilizing amount for summer maize.[Conclusions]This study provides theoretical reference for rational selection of fertilizers for reducing fertilizer application and increasing fertilizer efficiency,and for production of summer maize in Shajiang black soil region.

Improvement of Wolfberry(Lycium barbarum L.)Fruit Yield and Quality and Enhancement of Soil Fertility by Nitrogen Reduction Combined with Organic Fertilizers

Excessive amounts of nitrogen(N)fertilizers are applied during wolfberry production,resulting in some soil problems as well as potential environmental risks in the Qinghai-Tibet Plateau.In this study,organic fertilizers were used to replace part of the N fertilizer in wolfberry fields with different fertility levels.N fertilizer rates had 0,50,100,150,200,and 250 g N/plant.Organic fertilizer rates had 0,2,4,6,8,and 10 kg organic fertilizer/plant.The experimental treatments included 6 combinations of N0M10,N50M8,N100M6,N150M4,N200M2,and control was N250M0.The results showed that in the high-fertility soils,combinations of N150M4,N100M6 and N50M8 treatments were increased in yields,fruit shape index,flavonoid content,total phenol content,mineral nutrient content,and antioxidant activity of wolfberry fruits.Also they were improved in soil fertility and decreased in residual nitrate through the soil depth of 0-300 cm.In the soil with less fertility,fruit yield,amino acid contents,flavonoids,total phenols,mineral nutrients and antioxidant activity of fruits were increased by the N200M2,N150M4 and N100M6 treatments and soil fertility was improved as well.Also more residual nitrate was found in the depth of 0-100 cm of soil with both chemical and organic fertilizer compared with the control.Therefore,in the Qinghai-Tibet Plateau,combining decreased N fertilizer with organic fertilizer rather than chemical fertilizer alone could help farmers achieve satisfactory yields and quality of wolfberry fruits and reduce the risk of nitrate leaching.In conclusion,50-150 g/plant of N fertilizer combined with 4-8 kg/plant of organic fertilizer in high-fertility gardens and 100-200 g/plant of N fertilizer combined with 2-6 kg/plant of organic fertilizer in low-fertility gardens are recommended for wolfberry cultivation.

Species-specific Response of Photosynthesis to Burning and Nitrogen Fertilization

The present study was conducted to examine photosynthetic characteristics of three dominant grass species （Agropyron cristatum, Leymus chinensis, and Cleistogenes squarrosa） and their responses to burning and nitrogen fertilization in a semiarid grassland in northern China. Photosynthetic rate （Pn）, stomatal conductance （gs）, and water use efficiency （WUE） showed strong temporal variability over the growing season. C. squarrosa showed a significantly higher Pn and WUE than A. cristatum and L. chinensis. Burning stimulated Pn of A. cristatum and L. chinensis by 24-59% （P 〈 0.05） in the early growing season, but not during other time periods. Light-saturated photosynthetic rate （Pmax） in A. cristatum and the maximum apparent quantum yield （Фmax） in A. cristatum and L. chinensis were significantly enhanced by burning （16-67%） in both the fertilized and unfertilized plots. The main effect of burning on Pn, Pmax and Фmax was not significant in C. squarrosa. The burning-induced changes in soil moisture could explain 51% （P= 0.01） of the burning-induced changes in Pn of the three species. All three species showed positive responses to N fertilization in terms of Pn, Pmax, and Фmax. The stimulation of Pn under N fertilization was mainly observed in the early growing season when the soil extractable N content was significantly higher in the fertilized plots. The N fertilization-induced changes in soil extractable N content could explain 66% （P = 0.001） of the changes in Pn under N fertilization. The photosynthetic responses of the three species indicate that burning and N fertilization will potentially change the community structure and ecosystem productivity in the semiarid grasslands of northern China.

Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years

Degraded soil aggregation arising from nitrogen(N)fertilization has been reported in many studies;however,the mechanisms have not yet been clarified.Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production.The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents.A 12-year(2008–2019)N fertilization field experiment on a Vertisol was performed,covering a wide range of N application rates(0,360,450,540,630,and 720 kg ha-1 year-1)and including straw management(straw return and straw removal)in a wheat(Triticum aestivum L.)-maize(Zea mays L.)cropping system.Soil samples of 0–20 cm depth were collected from 12 field treatments with 3 replications in 2019.Soil aggregate stability(mean weight diameter(MWD))and contents of soil organic carbon(SOC),glomalin-related soil protein(GRSP),microbial biomass carbon(MBC),and mineral N(NH4+and NO3-)were determined.Long-term N fertilization under straw removal conditions reduced soil MWD by 12%–18%at N rates from 0 to 720 kg ha-1 compared to that under straw return(P<0.05).Soil MWD was positively associated with pH(P<0.05)and MBC(P<0.05),but negatively correlated with NH4+(P<0.05)and NO3-(P<0.05).Compared with the straw removal treatment,the straw incorporation treatment significantly improved the contents of aggregating agents(SOC,GRSP,and MBC)(P<0.001),but did not affect that of the dispersing agent(NH4+)(P>0.05);consequently,it improved soil aggregation.Overall,our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions(H+and NH4+)and the decrease in MBC during soil acidification,especially when the applied N dose exceeded 360 kg ha-1 year-1.Our finding can minimize the negative structural impacts on Vertisol.

Ammonia and greenhouse gas emissions from a subtropical wheat field under different nitrogen fertilization strategies

Minimizing soil ammonia（NH_3） and nitrous oxide（N_2O） emission factors（EFs） has significant implications in regional air quality and greenhouse gas（GHG） emissions besides nitrogen（N） nutrient loss.The aim of this study was to investigate the impacts of different N fertilizer treatments of conventional urea,polymer-coated urea,ammonia sulfate,urease inhibitor（NBPT,N-（n-butyl） thiophosphoric triamide）-treated urea,and nitrification inhibitor（DCD,dicyandiamide）-treated urea on emissions of NH_3 and GHGs from subtropical wheat cultivation.A field study was established in a Cancienne silt loam soil.During growth season,NH_3 emission following N fertilization was characterized using active chamber method whereas GHG emissions of N_2O,carbon dioxide（CO_2）,and methane（CH_4） were by passive chamber method.The results showed that coated urea exhibited the largest reduction（49%） in the EF of NH_3-N followed by NBPT-treated urea（39%） and DCD-treated urea（24%） over conventional urea,whereas DCD-treated urea had the greatest suppression on N_2O-N（87%） followed by coated urea（76%） and NBPT-treated urea（69%）.Split fertilization of ammonium sulfate-urea significantly lowered both NH_3-N and N_2O-N EF values but split urea treatment had no impact over one-time application of urea.Both NBPT and DCD-treated urea treatments lowered CO_2-C flux but had no effect on CH_4-C flux.Overall,application of coated urea or urea with NPBT or DCD could be used as a mitigation strategy for reducing NH_3 and N_2O emissions in subtropical wheat production in Southern USA.

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

The priming effect is well acknowledged in soil systems but the effect of nitrogen(N)fertilization remains elusive.To explore how N modifies the priming effect in soil organic matter(SOM),one in situ experiment with 13C labeled glucose addition(0.4 mg C g^–1 soil,3.4 atom %^13C)was conducted on soil plots fertilized with three gradients of urea(0,4 and 16 g N m^–2 yr^–1).After glucose addition,the soil CO2 concentration and phospholipid fatty acid(PLFA)were measured on day 3,7,21 and 35.The study found that N fertilization decreased soil CO2,PLFA and the fungi to bacteria ratio.Glucose triggered the strongest positive priming in soil at 0 g N m^–2 yr^–2,meanwhile N fertilization decreased SOM-derived CO2.Soil at 4 g N m^–2 yr^–2 released the largest amount of glucose-derived carbon(C),likely due to favorable nutrient stoichiometry between C and N.Stable microbial community biomass and composition during early sampling suggests"apparent priming"in this grassland.This study concludes that N fertilization inhibited soil priming in semi-arid grassland,and shifted microbial utilization of C substrate from SOM to added labile C.Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Optimum nitrogen fertilization of Calophyllum inophyllum seedlings under greenhouse conditions

A greenhouse pot experiment was conducted to study the effects of nitrogen fertilization on Calophyllum inophyllum seedlings grown with 0, 50, 100, 150,200, 300, 400 and 600 mg N per seedling according to exponential functions. Seedling height, root collar diameter, leaf area and total biomass increased with increasing fertilization from 0 to 200 mg N per seedling and decreased with further increase in fertilization from300 to 600 mg N per seedling. The net photosynthetic rate,stomatal conductance, intercellular CO_2 concentration and transpiration rate of C. inophyllum seedlings showed a unimodal parabolic trend, with peak values of7.29 mmol·m^(–2)·s^(–1), 0.071 mol·m^(–2)·s^(–1), 220 mmol·mol^(–1) and 1.34 mmol·m^(–2)·s^(–1), respectively, when the rate of fertilization was 200 mg N per seedling. Photosynthetic gas exchange parameters were significantly different among nitrogen treatments. Based on the critical values of leaf N and P concentration and N/P ratio, the optimum amount of nitrogen of C. inophyllum seedlings was 200–400 mg per seedling for leaf N and P concentration, and100–400 mg per seedling for N/P ratio. It was concluded that 200–400 mg N per seedling was the most suitable nitrogen range for C. inophyllum seedlings.

Response of seed yield and fatty acid compositions for some sunflower genotypes to plant spacing and nitrogen fertilization

A field experiment was conducted at the experiment Farm of Kafr-El-Hamam Research Station,Zagazig,Sharkia Governorate,Agricultural Research Center,Egypt during the two successive summer seasons of 2015 and 2016 to achieve the highest yield and good oil quality of three tested sunflower genotypes.In both seasons,the experiment was conducted using the split split plot design in randomized complete block design with three replicates arrangement keeping plant spaces(15,20 and 25 cm apart between hills)in main plots,nitrogen fertilization levels(15,30 and 45 N fad.^-1)in sub plots and sunflower genotypes(Giza 102,Sakha 53 and promising line of L120)in sub sub plots.Yield and quality traits were significantly influenced by plant spaces,nitrogen fertilization levels and genotypes as well as interactions in both seasons and their combined analysis.The wider plant spacing of 25 cm seems to be a good compromise between the highest seed yield fad.^-1 and good acid composition of oil.Gradually increasing of nitrogen fertilization level had a positive reflected on yield and desirable acid composition of oil.Sakha 53 was ranked in the first order in stem diameter,head diameter,100-seed weight,seed weight plant^-1,flowered late and hence seed yield fad.^-1 as well as seed oil content whereas,Giza 102 characterized with its contained the highest proportion of oleic and linoleic unsaturated fatty acids.The highest values of head diameter,100-seed weight,seed weight plant^-1 and hence seed yield fad.^-1 as well as the highest proportion of oleic and linoleic unsaturated fatty acids composition were obtained by grown sunflower cv.Sakha 53 at wider spacing of 25 cm with application of nitrogen fertilization levels of 45 N fad.^-1.Correlation and path analyses revealed that 100-seed weight and head diameter had the highest direct and indirect influence on seed weight plant
1,at the same time also,oleic acid content and linoleic acid content had the highest direct and indirect effect influence on seed oil content indicating their importance as selection criteria to improve yield and oil quality of sunflower.