基施磷肥对石灰性土壤上番茄产量的影响

A lysimeter experiment with undisturbed soil profiles was carried out to study nitrogen cycling and losses in a paddy soll with applications of coated urea and urea under a rice-wheat rotation system in the Taihu Lake region from 2001 to 2003. Treatments for rice and wheat included urea at conventional, 300 （rice） and 250 （wheat） kg N ha^-1, and reduced levels, 150 （rice） and 125 （wheat） kg N ha^-1, coated urea at two levels, 100 （rice） and 75 （wheat） kg N ha^-1, and 150 （rice） and 125 （wheat） kg N ha^-1, and a control with no nitrogen arranged in a completely randomized design. The results under two rice-wheat rotations showed that N losses through both NH3 volatilization and runoff in the coated urea treatments were much lower than those in the urea treatments. In the urea treatments N runoff losses were significantly （P 〈 0.001） positively correlated （r = 0.851） with applied N. N concentration in surface water increased rapidly to maximum two days after urea application and then decreased quickly. However, if there was no heavy rain within five days of fertilizer application, the likelihood of N loss by runoff was not high. As the treatments showed little difference in N loss via percolation, nitrate N in the groundwater of the paddy fields was not directly related to N leaching. The total yield of the two rice-wheat rotations in the treatment of coated urea at 50% conventional level was higher than that in the treatment of urea at the conventional level. Thus, coated urea was more favorable to rice production and environmental protection than urea.     

施用控释肥提高直播水稻氮的利用率

Field trials on a silt-loamy paddy soil derived from shallow-sea deposit in direct seeding rice fields were conducted in Zhejing ,China,in 1996 to compare N efficiency of controlled release fertilizers (LP fertilizers) with the conventional urea.Six treatments including CK (no N fertilizer),conventional urea and different types of LP fertilizers at different rates were designed for two succeeding crops of early and late rice.A blend of different types of LP fertilizers as a single preplant “co-situs“ application released n in a rate and amount synchronizing with uptake pattern of direct seeding rice.A single preplant application of the LP fertilizers could meet the N requirement of rice for the whole growth period without need of topdressing,Using LP fertilizer blends ,equivalent grain yields could be maintained even if the N fertilization rates were reduced by 25%-50% compared with the conventional urea .Agronomi efficiency of the LP fertilizers was 13.6%-86.4% higher than that of the conventional urea in early rice and 100%-164.1% in late rice,depending on the amounts of the LP fertilizers applied.N fertilizer recovery rate incereased from 27.4% for the conventional application of urea to 41.7%-54.1%,for the single preplant “co-situs“ application of the LP fertilizers,Use of the LP fertilizers was promising if the increse in production costs due to the hihg LP fertilizer prices could be compensated by increase in yield and N efficiency,reduction in labor costs and improvement in environment.     

海河流域合理生态用水比例的确定

Winter wheat-maize rotations are dominant cropping systems on the North China Plain, where recently the use of organic manure with grain crops has almost disappeared. This could reduce soil fertility and crop productivity in the long run. A 20-year field experiment was conducted to 1） assess the effect of inorganic and organic nutrient sources on yield and yield trends of both winter wheat and maize, 2） monitor the changes in soil organic matter content under continuous wheat-maize cropping with different soil fertility management schemes, and 3） identify reasons for yield trends observed in Xuzhou City, Jiangsu Province, over a 20-year period. There were eight treatments applied to both wheat and maize seasons： a control treatment （C）; three inorganic fertilizers, that is, nitrogen （N）, nitrogen and phosphorus （NP）, and nitrogen, phosphorus and potassium （NPK）; and addition of farmyard manure （FYM） to these four treatments, that is, M, MN, MNP, and MNPK. At the end of the experiment the MN, MNP, and MNPK treatments had the highest yields, about 7 t wheat ha^-1 and 7.5 t maize ha^-1, with each about 1 t ha^-1 more than the NPK treatments. Over 20 years with FYM soil organic matter increased by 80% compared to only 10% with NPK, which explained yield increases. However, from an environmental and agronomic perspective, manure application was not a superior strategy to NPK fertilizers. If manure was to be applied, though, it would be best applied to the wheat crop, which showed a better response than maize.     

中国西北旱地小麦和玉米提高产量与水分利用率的氮肥管理效果

A field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to 2002. The local cropping sequence of wheat, wheat-beans, maize, and wheat over the 4-year period was adopted. A micro-plot study using ^15N-lahelled fertilizer was carried out to determine the fate of applied N fertilizer in the first year. When N fertilizer was applied wheat （years 1, 2 and 4） and maize （year 3） grain yield increased significantly （P 〈 0.05） （〉 30%）, with no significant yield differences in normal rainfall years （Years 1, 2 and 3） for N application at the commonly application rate and at 2/3 of this rate. Grain yield of wheat varied greatly between years, mainly due to variation in annual rainfall. Results of ^15N studies on wheat showed that plants recovered 36.6%-38.4% of the N applied, the N remained in soll （0-40 cm） ranged from 29.2% to 33.6%, and unaccounted-for N was 29.5%-34.2%. The following crop （wheat） recovered 2.1%- 2.8% of the residual N from N applied to the previous wheat crop with recovery generally decreasing in the subsequent three crops （beans, maize and wheat）.     

中国洞庭湖区稻田土壤氮素淋溶损失的系统研究

A two-year lysimeter study was conducted to study the effects of different fertilizers and soils on nitrogen leaching loss in a double rice cropping system by considering three major types of paddy soils from the Dongting Lake area. The results showed that N concentration in the leachate did not differ significantly among the treatments of urea, controlled release N fertilizer and pig manure and that all these fertilizers produced higher total nitrogen (TN) concentrations in the leachate compared to the case where no fertilizer was applied. The TN leaching loss following urea treatment accounted for 2.28%, 0.66%, and 1.50% of the amount of N applied in the alluvial sandy loamy paddy soil (ASL), purple calcareous clayey paddy soil (PCC), and reddish-yellow loamy paddy soil (RYL), respectively. Higher TN loss was found to be correlated with the increased leachate volume in ASL compared with RYL, and the lowest TN loss was observed in the PCC, in which the lowest leachate volume and TN concentration were observed. Organic N and NH4+ -N were the major forms of N depleted through leachate, accounting for 56.8% and 39.7% of TN losses, respectively. Accordingly, soil-specific fertilization regimens are recommended; in particular, the maximum amount of fertilizer should be optimized for sandy soils with a high infiltration rate. To avoid a high N leaching loss from rice fields, organic N fertilizers such as urea or coated urea should primarily be used for surface topdressing or shallow-layer application and not for deep-layer application.     

长期施肥对华北平原土壤生产力的影响

Soil productivity is the ability of a soil, in its normal environment, to support plant growth and can be evaluated with respect to crop production in unfertilized soil within the agricultural ecosystem. Both soil productivity and fertilizer applications affect crop yields. A long-term experiment with a winter wheat-summer maize rotation was established in 1989 in a field of the Fengqiu State Key Agro-Ecological Experimental Station, a region typical of the North China Plain, including seven treatments: 1) a balanced application of NPK chemical fertilizers(NPK); 2) application of organic fertilizer(OM); 3) application of 50% organic fertilizer and50% NPK chemical fertilizers(1/2OMN); 4) application of NP chemical fertilizers(NP); 5) application of PK chemical fertilizer(PK);6) application of NK chemical fertilizers(NK); and 7) unfertilized control(CK). To investigate the effects of fertilization practices on soil productivity, further pot tests were conducted in 2007–2008 using soil samples from the different fertilization treatments of the long-term field experiment. The soil sample of each treatment of the long-term experiment was divided into three pots to grow wheat: with no fertilization(Potunf), with balanced NPK fertilization(PotNPK), and with the same fertilizer(s) of the long-term field experiment(Potori). The fertilized soils of the field experiment used in all the pot tests showed a higher wheat grain yield and higher nutrient uptake levels than the unfertilized soil. Soil productivity of the treatments of the field experiment after 18 years of continuous fertilizer applications were ranked in the order of OM 1/2OMN NPK NP PK NK CK. The contribution of soil productivity of the different treatments of the field experiment to the wheat grain yield of Potoriwas 36.0%–76.7%, with the PK and NK treatments being higher than the OM, 1/2OMN, NPK, and NP treatments since the soil in this area was deficient in N and P and rich in K. Wheat grain yields of PotNPKwere higher than those of Potoriand Potunf. The N, P, and K use efficiencies were higher in PotNPKthan Potoriand significantly positively correlated with wheat grain yield. Soil organic matter could be a better predictor of soil productivity because it correlated more strongly than other nutrients with the wheat grain yield of Potunf. Wheat yields of PotNPKshowed a similar trend to those of Potunf, indicating that soil productivity improvement was essential for a further increase in crop yield. The long-term applications of both organic and chemical fertilizers were capable of increasing soil productivity on the North China Plain, but the former was more effective than the latter. The balanced application of NPK chemical fertilizers not only increased soil productivity, but also largely increased crop yields, especially in soils with lower productivity. Thus, such an approach should be a feasible practice for the sustainable use of agricultural soils on the North China Plain, particularly when taking into account crop yields, labor costs, and the limited availability of organic fertilizers.     

菜地土壤中氮肥的反硝化损失和N2O排放

A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.     

红壤地油菜上施用的尿素态氮的去向及尿素在提高油菜产量中的效率

Fate of urea nitrogen(N) applied to rape grown on a red soil was investigated by the 15N mass balance technique.and efficiency of urea and effect of nutrients balance in raising rape yield were investigated in a field plot experiment.One hundred and thirty -eight kg N/ha,86kg N/ha as basal dressing and 52 kg N/ha as top dressing,was applied with band application technique.The experiment was conducted in the southeast of china ,near Yingtan City,Jianxi Province.Results from 15N mass balance study showed that when urea urea was applied as basal dressing the plant recovery was 44.0% of the applied N for Treatment T (with application of N,P,K,B and lime),Plant recoveries were 38.0%-40.5% for Treatments-K,-B-lime and RS(without application of K,B or lime as well as with additional rice straw compared with Teatment T),which were not significantly different from Treatment T.In contrast ,plant recovery was only 5.1% for Treatment-P(without application of P), indicating that P was the factor limiting N uptake by rape.However,N remaining in 0-0.30 m soil was high up to 71.6% for Treatment-P,while the corresponding data were 33.0%-42.6% for the other treatments.The total recovery of applied N(including plant recovery and N remaining in 0-0.60 m soil) was 91.5% for Treatment T when urea was applied as basal dressing,while almost all the applied N was recovered when ureawas applied as top drssing,It was suggested that N loss was greatly controlled by using band application method in this experiment.Results from the field plot experiment field plot experiment showed that N supply capacity of this red soil was very low,and the efficiency of the applied N was quite high,7.1kg rape seed was increased by application of one kg N for Treatment T.Nitrogen and phosphorus were the key factors limiting rape yield,and the yield was very low when neither of them was applied.The yield in Treatment-K was significantly lower than that in Treatment T,With the former accounting for 77% of the later.     

表施尿素的冬小麦土壤氨挥发损失

Ammonia volatilization was measured with a continuous air flow enclosure method from a winter wheat field in the Experimental Farm of Jurong Agricultural School to investigate its main influencing factors. The experiment with five treatments in triplicate, no N (control), 100, 200 and 300 kg N ha^-1 with rice straw cover at a rate of 1 500 kg ha^-1 and 200 kg N ha^-1 without rice straw, started when the winter wheat was sown in 1994. Sixty percent of the total amount of N applied was basal and 40% was top-dressed. The measurement of ammonia volatilization was immediately conducted after urea was top-dressed on soil surface at wheat elongation stage in spring of 1996 and 1997. The results showed that there was a diurnal variation of ammonia volatilization rate from the winter wheat field, which synchronized with air temperature. N losses through ammonia volatilization increased with increasing N application rate, but the ratio of N lost through ammonia volatilization to applied N was not significantly affected by N application rate. The coverage of rice straw had no significant effect on ammonia volatilization. Soil moisture and rain events after urea was top-dressed affected ammonia volatilization significantly.     

长期定位试验尿素和堆肥处理下冬小麦自然同位素15N研究

We investigated 15N abundance （δ15N） of winter wheat （Triticum aestivum cv. Jinmai 1） plants and soil at different growth stages in a field with a 13-year fertilization history of urea and compost, to determine whether or not the δ15N of plant parts can be used as an indicator of organic amendment with compost. Plant parts （roots, leaves, stems and grains） and soil were sampled at re-greening, jointing, grain filling and mature growth stages of winter wheat. There were significant differences between the urea and compost treatments in 815N of whole plants, plant parts and soil over the whole growing season. Determination of the δ15N of plant parts was more convenient than that of whole plant to distinguish between the application of organic amendment and synthetic N fertilizer.     

长效尿素的供氮过程及其在稻—麦轮作下的生物学效应

采用磷酸盐包膜工艺制成长效尿素PCU,含N 33.8%,全磷(P)5.15%,有效磷(P)4.10%。同日本产品SCU和IBDU进行了盆栽和田间小区及微区试验,发现:(1)PCU作基肥穴施其供氮强度和供氮容量均高于SCU和IBDU;(2)PCU在红壤上对中稻的产量效应显著高于普通尿素分次施。但在黄泥土和白土上对单晚的肥效不及普通尿素分次施;(3)PCU作基肥穴施在中稻上其氮素利用率最高,达到79%,而SCU和IBDU作基肥混施以及普通尿素分次施的氮素利用率分别为60%,42%和34%;(4)长效肥的后效与释放率呈反相关的趋势,即释放率越低,后效越长,如释放率最低的IBDU的后效比SCU和PCU分别高89%和47%。     

Labile soil organic carbon,soil fertility,and crop productivity as influenced by manure and mineral fertilizers in the tropics

In recent years, organic agriculture has been receiving greater attention because of the various problems like deterioration in soil health and environmental quality under conventional chemical‐intensive agriculture. However, little information is available on the comparative study related to the impact of use of mineral fertilizers and organic manures on the soil quality and productivity. A long‐term field experiment was initiated in 2001 to monitor some of the important soil‐quality parameters and productivity under soybean–wheat crop rotation. The treatments consisted of 0, 30, and 45 kg N ha^–1 for soybean and of 0, 120, and 180 kg N ha^–1 for wheat. The entire amount of N was supplied to both the crops through urea and farmyard manure (FYM) alone or in combination at 1:1 ratio. Results indicated that Walkley‐and‐Black C (WBC; chromic acid–oxidizable) exhibited a marginal increase under only organic treatments as compared to control treatment (without fertilizers and manure) after completion of five cropping cycles. In case of labile‐C (KMnO₄‐oxidizable) content in soil, relatively larger positive changes were recorded under organic, mixed inputs (integrated) and mineral fertilizers as compared to WBC. Maximum improvement in the values of C‐management index (CMI), a measure of soil quality was recorded under organic (348–362), followed by mixed inputs (268–322) and mineral fertilizers (198–199) as compared to the control treatment after completion of five cropping cycles. Similarly there was a substantial increase in KCl‐extractable N; in Olsen‐P; as well as in DTPA‐extractable Zn, Fe, and Mn under organic treatments. Although labile soil C positively contributed to the available N, P, K, Zn, Fe, and Mn contents in soil, it did not show any relationship with the grain yield of wheat. After completion of the sixth cropping cycle, organic treatments produced 23% and 39% lower grain yield of wheat as compared to that under urea‐treated plots. Relatively higher amount of mineral N in soil at critical growth stages and elevated N content in plant under mineral‐fertilizer treatments compared to FYM treatments were responsible for higher yield of wheat under mineral fertilizers.     

太湖地区稻麦轮作条件下施用包膜尿素的氮素循环和损失

A field experiment was conducted to investigate the fate of ^15N-labeled urea and its residual effect under the winter wheat （Triticum aestivum L.） and summer maize （Zea mays L.） rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha^-1 （N360）, a reduced rate of 120 kg N ha^-1 （N120） led to a significant increase （P 〈 0.05） in wheat yield and no significant differences were found for maize. However, in the 0-100 cm soil profile at harvest, compared with N360, N120 led to significant decreases （P 〈 0.05） of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile, 25.6%-44.7% and 20.7%-38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%-3.0% and 11.2%-24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N （NH4^＋-N and NO3^--N） in the soil profile after harvest. Therefore, N120 could be considered ngronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.     

几种聚氨酯包膜尿素的氮素释放特征研究

以聚氨酯为主要包膜材料,以石蜡、改性高岭土和双氰胺(氧化钙)为组合材料,采用滚转包衣法制备了3种聚氨酯包膜尿素。通过静水浸泡和盆栽试验,探讨了3种自研制聚氨酯包膜尿素的氮素释放特性,在氮磷钾等养分供应下研究了6个施肥处理对春玉米生长发育和氮素吸收利用的影响。结果表明,3种自研制聚氨酯包膜尿素在静水(25℃)中氮素累积释放比例的变化趋势基本一致,其24 h 初期释放率为2.04％~3.64％(≤15％),28 d累积释放率为29.88％~34.80％(≤80％),符合缓释肥料的国家标准要求。相对于NPK处理,自研制聚氨酯包膜尿素能明显促进春玉米对氮素吸收利用,其氮肥利用率达32.5％~40.0％,但其与商品包膜尿素(19.5％)之间无显著差异。自研制聚氨酯包膜尿素和商品包膜尿素处理下土壤无机氮素含量峰值分别出现在28和15 d前后,其在土壤中氮素释放时间分别达70和60 d以上。春玉米全生育期内(91 d),自研制聚氨酯包膜尿素处理下土壤无机氮含量都高于商品包膜尿素和NPK处理。因此,与商品包膜尿素和NPK处理相比,自研制聚氨酯包膜尿素的氮素释放时间长且氮素供应充足。     

缓释氮肥运筹对稻麦轮作周年作物产量和氮肥利用率的影响

【目的】稻麦轮作是我国一种重要的农业种植模式。缓/控释肥作为高效兼环境友好的肥料类型,在多种作物单季种植上具有增产和提高肥效的作用,但是缓释肥在周年轮作体系中的肥效研究鲜有报道。因此研究稻麦轮作体系中的肥料施用模式,有助于提高稻麦产量,降低化肥用量,提高化肥利用率。【方法】本文通过稻麦轮作两周年四季作物的田间小区试验,以不施氮和习惯施氮为对照,研究了4种不同缓释肥减氮处理[进口树脂包膜尿素减氮24.3%、 国产硫包衣尿素减氮24.3%、 国产尿素加NAM(长效氮肥添加剂)减氮24.3%和国产尿素加NAM减氮10.8%]对水稻和小麦产量、 氮肥利用率、 第二周年稻麦收获后土壤养分含量和两周年土壤氮养分表观平衡的影响。【结果】与不施氮对照相比,所有施氮处理均提高了两周年稻麦4季作物产量,习惯施氮增产幅度最高,小麦的氮肥增产效果总体高于水稻,第二周年高于第一周年; 与当地习惯施氮量相比,所有的缓释氮肥减氮24.3%或10.8%处理均无显著降低两季小麦产量,进口树脂包膜尿素减氮24.3%处理和国产尿素加NAM减氮10.8%处理也无显著降低两季水稻产量,但是国产尿素加NAM减氮24.3%处理显著降低了第二季水稻产量,国产硫包衣尿素减氮24.3%显著降低了两季水稻产量; 与当地习惯施氮量相比,4个缓释氮肥减氮处理均提高了第一和第二周年氮肥利用率,显著降低了两周年稻田土壤养分氮盈余量,其中国产尿素加NAM减氮24.3%处理氮肥利用率较高,同时土壤氮盈余量较少,说明缓释氮肥减量在提高肥料利用率和降低氮的环境效应上具有一致的优势; 不同缓释氮肥对土壤养分含量的影响无明显规律性。【结论】在目前稻麦轮作体系中,缓释氮肥减施对小麦产量具有较好的稳定效果,但是个别缓释氮肥减施对水稻有减产风险,有必要依据稻田土壤氮素转化特点,研制水稻专用缓释氮肥,适当降低水稻季缓释氮肥的施用量。     

Fate of 15N after combined application of rabbit manure and inorganic N fertilizers in a rice–wheat rotation system

The present study was carried out on pot experiments with rice (Oryza sativa L. cv. Wuyujing 7) and winter wheat (Triticum aestivum L. cv. Yangmai 6) rotation in a sandy and a clayey soil fertilized with ¹⁵N-labeled ammonium sulfate (AS) and ¹⁵N-labeled rabbit feces so as to study the mechanisms of reduction of fertilizer N loss by organic fertilizers. The treatments included: (1) control without any N fertilizer application; (2) fertilization with ¹⁵N-labeled AS (IF); (3) fertilization with labeled rabbit feces (OF); (4) fertilization with either 40% ¹⁵N-labeled rabbit feces and 60% unlabeled AS (IOF1) or (5) 40% unlabeled rabbit feces and 60% ¹⁵N-labeled AS (IOF2). In the rice season, the IOF treatments compared to the IF treatment decreased the percentage of lost fertilizer N from the sandy and clayey soils, whereas it increased the percentage of fertilizer N, present as mineral N and microbial biomass N (MBN). During the second season, when soils were cropped to winter wheat, the IOF treatments in comparison with the IF or OF treatment increased mineral N and MBN contents of soils sampled at tillering, jointing, and heading stages, and such increases were derived from the organic N fertilizer in the sandy soil and from the inorganic N fertilizer in the clayey soil. The increased MBN in the IOF treatments was derived from inorganic fertilizers applied both soils. Therefore, in the IOF treatment, during the rice season, the organic N increased the immobilization of inorganic N in MBN, while the inorganic N fertilizer applied to both soils stimulated the uptake of organic N and the organic N fertilizer increased the uptake of inorganic N by winter wheat; the inorganic N increased the recovery of organic N in the plant-soil system after harvesting the winter wheat.     

Effect of mineral nitrogen fertilizer forms on N2O emissions from arable soils in winter wheat production

Nitrogen fertilizers are supposed to be a major source of nitrous oxide (N₂O) emissions from arable soils. The objective of this study was to compare the effect of N forms on N₂O emissions from arable fields cropped with winter wheat (Triticum aestivum L.). In three field trials in North‐West Germany (two trials in 2011/2012, one trial in 2012/2013), direct N₂O emissions during a one‐year measurement period, starting after application of either urea, ammonium sulfate (AS) or calcium ammonium nitrate (CAN), were compared at an application rate of 220 kg N ha^?1. During the growth season (March to August) of winter wheat, N₂O emission rates were significantly higher in all three field experiments and in all treatments receiving N fertilizer than from the non‐fertilized treatments (control). At two of the three sites, cumulative N₂O emissions from N fertilizer decreased in the order of urea > AS > CAN, with emissions ranging from 522–617 g N ha^?1 (0.24–0.28% of applied fertilizer) for urea, 368–554 g N ha^?1 (0.17–0.25%) for AS, and 242–264 g N ha^?1 (0.11–0.12%) for CAN during March to August. These results suggest that mineral nitrogen forms can differ in N₂O emissions during the growth period of winter wheat. Strong variations in the seasonal dynamics of N₂O emissions between sites were observed which could partly be related to weather events (e.g., precipitation). Between harvest and the following spring (post‐harvest period) no significant differences in N₂O emissions between fertilized and non‐fertilized treatments were detected on two of three fields. Only on one site post‐harvest emissions from the AS treatment were significantly higher than all other fertilizer forms as well as compared to the control treatment. The cumulative one‐year emissions varied depending on fertilizer form across the three field sites from 0.05% to 0.51% with one exception at one field site (AS: 0.94%). The calculated overall fertilizer induced emission averaged for the three fields was 0.38% which was only about 1/3 of the IPCC default value of 1.0%.     

Yield and protein content of barley as affected by release rate of coated urea and rate of nitrogen application

Coated urea consists of a urea core and a polymer coating. It meters out urea over a period of time. In the market place, price is favorable for high protein content feed barley. The objectives of this study were to determine release rate of urea from coated urea products and relative effectiveness of urea, coated urea or a mixture of coated urea products with different release rates in increasing yield and protein content of barley. Release rate of coated urea Mini I (quick release) and Mini II (slow release) in water was determined at 23°C by recovering ten pre‐weighed granules from 500 mL water at 6 h, 2, 4, 6, 8, 10, and 12 days. The recovered granules were dried and then weighed. Barley (Hordium vulgare L. cv. Duke) was grown in potted soil (2 L) at 15°C for 90 days in a growth chamber with treatments of Nil, non‐coated urea, Mini I, Mini II, Mixture I (1/3 urea+1/3 Mini I+1/3 Mini II) and Mixture II (1/5 urea+2/ 5 Mini I+2/5 Mini II). The nitrogen (N) application rates were 100, 200 and 300 kg N ha^‐1. Above‐ground plant samples were taken at 22, 44, 66, and 90 (maturity) days after seeding, and dry matter mass per pot and N content of the plant samples were determined. The release of urea from Mini I and Mini II followed a lognomial pattern. Increasing N application rate increased dry matter yield of barley. Dry matter yield from urea tended to be higher than other treatments at each rate of N application, but that did not couple with high grain protein content. At 100 kg N ha^‐1, there was no post anthesis N assimilation (PANA) for urea and Mini I, but there were 4, 14, and 13% PANA for Mini II, Mixture I, and Mixture II, respectively. However, when N application rate was increased to 200 and 300 kg N ha^‐1, there was PANA even for urea treatment. Protein content of barley grain was higher with coated urea or mixture treatments than with urea at each rate of N application. The potential N loss (i.e., difference between percentN released from fertilizers and percent fertilizer N recovered by barley) was Mini II<Mini I<Mixture II<Mixture I for the same N application rate, and was 100<200<300 kg N ha^‐1 for the same fertilizer treatment. In conclusion, at a limited N application rate, coated urea with a slow release rate or a combination of two coated urea products (quick and slow release) with urea increased grain protein content of barley. The potential N loss was less with coated urea applied alone than with a mixture of coated urea and urea.     

Effects of 15N-labelled ammonium nitrate and urea on soil nitrogen during growth of wheat (Triticum aestivum L.) under field conditions

We studied the effects of ¹⁵N-labelled ammonium nitrate and urea on the yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L., cv. Mexi-Pak-65) in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 33.6–51.5 and 30.5–40.9% of the N from ammonium nitrate and urea, respectively. Splitting the fertilizer N application had a significant effect on the uptake of fertilizer N by the wheat. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the two N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied according to the fertilizer N split; six split applications gave the highest added N interaction compared to a single application or two split applications for both fertilizers. Ammonium nitrate gave 90.5, 33.5, and 48.5% more added N interaction than urea with one, two, and six split N applications. A values were not significantly correlated with the added N interaction (r=0.557). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N replaced unlabelled soil N.     

Assessment of urea coated with pomegranate fruit powder as N slow-release fertilizer in maize

It has been hypothesized that plant polyphenol plus lignin, cellulose, and hemicelluloses can immobilize/remineralize inorganic fertilizers, such as urea, better than polyphenol alone. To test this hypothesis, urea was coated with pomegranate (Punica granatum L.) fruit powder (containing polyphenol+lignin+cellulose) at rates of 0%, 30%, 70%, and 100% (w/w) of fertilizer urea. Fertilizer nitrogen was applied at 100 and 200 mg kg^?1 soil in a clay loam soil. This natural coating material, particularly at the rate of 100% (w/w), improved the distribution of mineral nitrogen (N) and available phosphorus (P) in soil during both early and advanced growth stages of maize and significantly increased total crop N and P uptake at both rates of fertilizer nitrogen compared to urea alone. The results suggest that urea coated with the powder of pomegranate fruit could potentially be an N slow-release fertilizer for use in better synchronizing crop N demand with soil N supply.