Nitrogen recovery and nitrate leaching of controlled release nitrogen fertilizer in irrigated paddy soil

Ordinary high nitrogen fertilizer often results in nitrate (NO3--N) leaching and low recovery. Microplot and field plot experiments were conducted to determine the effect of controlled release nitrogen fertilizer (CRNF) on reco very and nitrate leaching on paddy soils. During two early rice cropping seasons (2002 and 2003), a single basal application of CRNF at 90 kg N ha-1 increased grain yields by 7.7%to 11.6%compared with two applications of urea. Estimated by the difference method fertilizer N recovery of CRNF (mean 76.3%) was 38.9 pe rcentage point higher than that of urea (mean 37.4%); estimated by 15N isotope method (mean 49.6%) CRNF (mean 67.1%) was 35.9 percentage point higher than ur ea (mean 31.2%). NO3--N leaching losses were 9.19 and 6.70 kg ha-1 for urea and CRNF, respectively. NO3--N leaching during the early rice cropping season was 27.1 %lower from CRNF than from two applications of urea. These losses repr esent 10.2%and 7.4%of applied urea-N and CRNF-N. Results from this study ind icate that CRNF improves N recovery and reduces NO3--N leaching and increases rice yield.

Recovery of Nitrogen and Phosphorous as Struvite From Swine Waste Biogas Digester Effluent

Objective To investigate the feasibility of nitrogen and phosphorus recovery from swine waste biogas digester effluent and the effects of pH and NH4^＋： Mg2^＋： PO4^3- molar ratio on its precipitation. Methods Precipitation experiments with swine waste biogas digester effluent were conducted at pH 7.5, 8.0, 8.5, and 9.0 together with NH4^＋： Mg^2＋： PO4^3- molar ratios 1： 0.2： 0.08, 1： 1： 1, and 1： 1.5： 1.5. Chemical and X-ray diffraction （XRD） analysis were done to determine the composition of the precipitate. Results The highest removal and recovery of NH4^＋ and PO4^3- were achieved at pH 9.0 in each experiment. The elevation of pH to 9.0 alone could decrease the initial PO4^3- concentration from 42 mg L^-1 to 4.7 mg L-1 and 89.2% PO4^3- recovery was achieved. The pH-molar ratio combination 9.0-1： 1.5： 1.5 effected 76.5% NH4^＋ and 68.5% PO4^3- recovery. The molar ratio of 1： 1： 1 together with pH elevation to 9.0 was determined to be the optimum combination for both NH4＋ and PO4^3- removal as it recovered over 70% and 97% of the initial NH4^＋ and PO4^3-, respectively. Conclusions Nitrogen and phosphorus can be recovered from biogas digester effluent as struvite.

Relay-intercropping soybean with maize maintains soil fertility and increases nitrogen recovery efficiency by reducing nitrogen input

Optimized nitrogen(N)management can increase N-use efficiency in intercropping systems.Legume-nonlegume intercropping systems can reduce N input by exploiting biological N fixation by legumes.Measurement of N utilization can help in dissecting the mechanisms underlying N uptake and utilization in legume-nonlegume intercropping systems.An experiment was performed with three planting patterns:monoculture maize(MM),monoculture soybean(SS),and maize-soybean relay intercropping(IMS),and three N application levels:zero N(NN),reduced N(RN),and conventional N(CN)to investigate crop N uptake and utilization characteristics.N recovery efficiency and 15N recovery rate of crops were higher under RN than under CN,and those under RN were higher under intercropping than under the corresponding monocultures.Compared with MM,IMS showed a lower soil N-dependent rate(SNDR)in 2012.However,the SNDR of MM rapidly declined from 86.8%in 2012 to 49.4%in 2014,whereas that of IMS declined slowly from 75.4%in 2012 to 69.4%in 2014.The interspecific N competition rate(NCRms)was higher under RN than under CN,and increased yearly.Soybean nodule dry weight and nitrogenase activities were respectively 34.2%and 12.5%higher under intercropping than in monoculture at the beginning seed stage.The amount(Ndfa)and ratio(%Ndfa)of soybean N2 fixation were significantly greater under IS than under SS.In conclusion,N fertilizer was more efficiently used under RN than under CN;in particular,the relay intercropping system promoted N fertilizer utilization in comparison with the corresponding monocultures.An intercropping system helps to maintain soil fertility because interspecific N competition promotes biological N fixation by soybean by reducing N input.Thus,a maize-soybean relay intercropping system with reduced N application is sustainable and environmentally friendly.

Using side-dressing technique to reduce nitrogen leaching and improve nitrogen recovery efficiency under an irrigated rice system in the upper reaches of Yellow River Basin, Northwest China

The excessive nitrogen （N） fertilizer input coupled with flood irrigation might result in higher N leaching and lower nitrogen recovery efficiency （NRE）. Under an intensive rice system in the Ningxia irrigation region, China, environmental friendly N management practices are hreavily needed to balance the amount of N input for optimum crop production while minimize the nitrogen loss. The objective of this study was to determine the influences of side-dressing （SD） technique in mechanical transplanting systems on the NRE, N leaching losses and rice yield in anthropogenic-alluvial soil during two rice growing seasons （2010-2011）. Four fertilizer N treatments were established, including conventional urea rate （CU, 300 kg ha-1 yr-1）; higher SD of controlled-release N fertilizer rate （SD1,176 kg ha-1 yr-1）; lower SD of controlled-release N fertilizer rate （SD2, 125 kg ha-1 yr-1）; and control （CK, no N fertilizer）. Field lysimeters were used to quantify drainage from undisturbed soil during six rice growing stages. Meanwhile, the temporal variations of total nitrigen （TN）, NO3--N, and NH4＋-N concentrations in percolation water were examined. The results showed that SD1 substantially improved NRE and reduced N leaching losses while maintaining rice yields. Across two years, the averaged NRE under SD1 treatment increased by 25.5% as relative to CU, but yet the rice yield was similar between two treatments. On average, the nitrogen loss defined as TN, NH4＋-N, and NO3--N under the SD1 treatment reduced by 27.4, 37.2 and 24.1%, respectively, when compared with CU during the study periods. Although the SD2 treatment could further reduce N leaching loss to some extent, this technique would sharply decline rice yield, with the magnitude of as high as 21.0% relative to CU treatment. Additionally, the average NRE under SD2 was 11.2% lower than that under SD1 treatment. Overall, the present study concluded that the SO technique is an effective strategy to reduce N leaching and increase NRE, thus potentially mitigate local environmental threat. We propose SD1 as a novel alternative fertilizer technique under an irrigated rice-based system in Ningxia irrigation region when higher yields are under consideration.

Effects of Combined Application of Inorganic Fertilizer and Organic Manures on Nitrogen Use and Recovery Efficiencies of Hybrid Rice (Palethwe-1)

We conducted two field experiments to investigate combined effects of organic and inorganic fertilizers on nitrogen use and recovery efficiencies of hybrid rice (Palethwe-1) during dry and wet seasons, 2015. Four levels of inorganic fertilizer (0%, 50%, 75%, and 100% NPK), based on recommended rates of 150 kg N ha-1, 70 kg P2O5 ha-1, and 120 kg K2O ha-1, were used with cow manure, poultry manure, and vermicompost (5 t·ha-1each) in a split-plot design with three replicates. In both seasons, with 50% NPK, the N uptake level achieved with poultry manure was similar to that obtained with 75% and 100% NPK. The greatest N use, internal, agronomic N use, and recovery efficiencies were obtained with 50% NPK + poultry manure, but were similar to those obtained from cow manure and vermicompost subplots. As the amount of applied N from organic and inorganic fertilizer increased, the N use efficiency and related parameters decreased, due to similar yields among plots with different NPK application levels. Poultry manure resulted in the highest significant correlations between applied N and N accumulation, followed by cow manure and vermicompost, in both seasons. Neither chemical fertilizer nor organic manure alone led to optimum N use and N recovery efficiencies. The combination of 50% inorganic fertilizer (75 kg N ha-1) and poultry manure (5 t·ha-1) enhanced the N uptake, the N use and recovery efficiencies of hybrid rice. Cow manure (5 t·ha-1) in combination with 75% inorganic fertilizer (112.5 kg N ha-1) was an adequate substitute for reduced chemical fertilizer usage. Therefore, this study highlighted combined application of inorganic fertilizers and organic manures had the benefits not only in reducing the need for chemical fertilizers but also in improving N uptake by hybrid rice (Palethwe-1) leading to the better environment.

Use of Several Plant Materials and Chemicals to inhibit Soil Urease Activity and Increase Nitrogen Recovery Rate of Urea by Plant

Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodoraHook., P_1), robust eucalyptus (E. robusta Smith, P_2), Nepal camphortree (Cinnamomum glanduliferum(Wall.) Nees, P_3), tea (Camellia sinensis (Linn.) O. Ktze. f., P_4), oleander (Nerium indicum Mill,P_5), rape (Brassica campestris L., P_g), Chinese tallow tree (Sapium sebiferum L., P_7), tung(Vernicia fordii (Hemsl.), P_8), and croton (Croton tiglium L., P_9), 7 chemicals, boric acid (C_1),borax (C_2), oxalic acid (C_3), sodium oxalite (C_4), sodium dihydrogen phosphate (C_6), sodiumsilicate (C_7) and sodium citrate (C_8), and a natural organic substance, humic acid (C_5), onurease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied throughincubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. Afterincubation at 37℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity wereselected and then incubated for 14 days at 25℃. Results of the incubation experiments showed thatsoil urease activity was greatly inhibited by them, and the inhibition effect followed an order ofP_2>P_4>C_3>C_2>P_3>C_1>HQ>P_1. The 7 selected materials reduced the accumulative amounts of Nreleased from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively,and postponed the N release peak by 2～4 days in the incubation period of 14 days under constanttemperature, as compared to the control (no inhibitor). In the pot experiment with the 7 materialsat two levels of addition, low (L) and high (H), the C_1 (H), C_3 (H), C_1 (L), P_4 (L) and C_2 (L)treatments could significantly increase the dry weights of the aboveground parts and the totalbiomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% ascompared to the control (no hibitor).

Effects of nitrogen fertilization strategies on nitrogen use efficiency in physiology, recovery, and agronomy and redistribution of dry matter accumulation and nitrogen accumulation in two typical rice cultivars in Zhejiang, China

Field experiments were conducted in farmers’ rice fields in 2001 and 2002 to study the effects of nitrogen (N) man-agement strategies on N use efficiency in recovery (RE), agronomy (AE) and physiology (PE) and redistribution of dry matter accumulation (DMA) and nitrogen accumulation (NA) in two typical rice cultivars in Jinhua, Zhejiang Province. This study aimed mainly at identifying the possible causes of poor fertilizer N use efficiency (NUE) of rice in Zhejiang by comparing farmers’ fertilizer practice (FFP) with advanced site-specific nutrient management (SSNM) and real-time N management (RTNM). The results showed that compared to FFP, SSNM and RTNM reduced DMA and NA before panicle initiation and increased DMA and NA at post-flowering. There is no significant difference between SSNM and FFP in post-flowering dry matter redistribution (post-DMR) and post-flowering nitrogen redistribution (post-NR). These results suggest that high input rate of fertilizer N and improper fertilizer N timing are the main factors causing low NUE of irrigated rice in the farmer’s routine practice of Zhejiang. With SSNM, about 15% of the current total N input in direct-seeding early rice and 45% in single rice could be reduced without yield loss in Zhejiang, China.

Nitrogen recovery and agronomic efficiency of forages with nitrogen fertilization under flooded condition

The cow-calf (Bos taurus) industry in subtropical United States and other parts of the world that depends almost totally on grazed pastures is facing several production constraints like changing climatic conditions and increasing cost of fertilizers, especially nitrogen (N). Particularly little is known about the response of forage species to the combined effect of water-logging and the addition of N. A two-year greenhouse study was conducted in 2008 and 2009 to determine i) the effect of flooding duration on N recovery and agronomic efficiency of bahiagrass (Paspalum notatum Fluegge) compared with two flooding tolerant forages, limpograss (Hemarthria altissima Poir), and maidencane (Panicum hematomon Schult) and ii) if N fertilization could mitigate the negative effect of flooding. Nitrogen recovery and agronomic efficiency varied significantly (P ≤ 0.001) among forage species. Averaged across levels of N, N recovery of bahiagrass and limpograss was reduced by about 41% and 56%, respectively after 84 d of continued flooding while N recovery of maidencane was slightly increase by about 5% between 0 and 84 d of flooding. Agronomic efficiencies of bahiagrass (41% to 26%) and limpograss (44% to 31%) were reduced by flooding while agronomic efficiency of maidencane was increased from 24% (no flooding) to 46% at 84 d of continued flooding. However, N recovery and agronomic efficiency of three forage species was positively affected by N fertilization. The overall N recovery of bahiagrass, limpograss, and maidencane ranged from 44% to 59%. Nitrogen fertilization could improve N recovery and agronomic efficiency of forage species under waterlogged condition.

Effects of controlled-release urea application on the growth, yield and nitrogen recovery efficiency of cotton

Field experiments were conducted to study the effects of the controlled release urea (CRU) application on growth yield and nitrogen recovery efficiency of cotton in the main cotton zone of the Yangtze River basin in 2010. Different nitrogen levels were set in order to determine the suitable dosage of CRU on cotton. The special purpose was to provide evidence for the CRU application in cotton fields. The results show that the application of CRU promotes the growth of cotton significantly and enhances the nitrogen supply in the whole period. Compared to the treatment with total N as base fertilizer (UB), the bod, flower, little bolls and total bolls are increased significantly. There are no significant differences in the yield between the CRU treatment and the treatment of controlled release urea and urea combined application (60%CRU + 40%U), but an increase by 12.38%-22.67% compared to the UB treatment, and an increase by 4.49%-7.23% compared to the treatments of total N split application (UD). The nitrogen uptake of CRU treatment was significantly increased by 13.01%-48.32% and 30.27%-13.01% than UB treatment and UD treatment, respectively. The nutrient recovery efficiency of CRU treatment is increased by 16.42-20.59, 5.92-11.29 and 4.22-12.59 percentage points compared to the UB treatment, UD treatment and 60%CRU + 40%U treatment, respectively. In this study, there was a good linearity relationship between the cotton yield and amount of CRU in Wuxue site. The yield of cotton response to amount of CRU could be described by the model of linear plus plateau in Jingzhou site.

NR硫化返原的研究 Ⅰ普通硫黄硫化体系

研究了ＮＲ的返原反应。通过测定硫化曲线、物理性能和溶胀指数考察了常见的几种工业化抗返原剂（ＤＨＴＳ，ＨＶＡ２和Ｓｉ６９）对ＮＲ硫化返原反应的抑制效果。实验结果表明，以ＨＶＡ２的抗返原效果最好，ＤＨＴＳ次之，Ｓｉ６９最差，同时ＨＶＡ２和ＤＨＴＳ还能改善ＮＲ的热氧老化性能。对硫化曲线进行解析发现硫黄硫化反应服从一级反应规律。

不同蛋白质含量小麦品种叶片NRA与氮素积累关系的研究

以鲁麦５号和昌乐５号两种不同蛋白质含量小麦品种为材料，研究了各生育期叶片ＮＲＡ与氮素积累的关系。其结果是，在不同施氮量下，各生育期叶片ＮＲＡ、ＮＯ－３－Ｎ、ＮＨ２－Ｎ、还原Ｎ含量皆随施氮量增加而增加，但生育前期昌乐５号的皆大于鲁麦５号，而生育后期则相反，鲁麦５号的皆大于昌乐５号，籽粒蛋白质含量亦为鲁麦５号高于昌乐５号。

不同生物制剂处理对烤烟打顶后碳氮代谢关键酶活性和Inv/NR比值的影响

采用不同生物制剂处理对打顶后烤烟烟叶中碳氮代谢关键酶硝酸还原酶(Nitrate reductase,NR)、转化酶(invert-ase,Inv)和淀粉酶(amylase,AM)活性变化以及Inv/NR比值进行了研究。结果表明:施加生物制剂在一定程度上提高了叶片中NR、Inv和AM酶活性,增强了叶片的碳氮代谢,刺激上部叶扩展开片,各个处理间碳氮代谢调节效果表现为T1>T2>T3;施加生物制剂10 d后Inv/NR比值开始较CK高,中下部叶T3处理在成熟后期Inv/NR比值过高,对烟叶品质不利,T1和T2处理后氮代谢向碳代谢的转化较CK晚,上部叶碳氮代谢的减弱缓慢,延长了烟叶的成熟时间。综上所述,T1处理对碳氮代谢的调节效果最好,T2其次,T3最差。

CO_2倍增对不同氮水平下小麦幼苗根系及叶片NR活性的影响

以小麦品种‘小偃22’幼苗为材料,采用开顶式气室和水培实验研究了不同供氮水平(2.5、5.0、10.0和15.0 mmol.L-1)下小麦幼苗植株生长量、根系形态、有机碳分泌速率和硝酸还原酶(NR)活性对大气CO2浓度升高的响应。结果显示,大气CO2浓度倍增均增加了小麦幼苗各生长阶段根冠生物量以及根系长度、面积、有机碳分泌速率和叶片NR活性。随供氮水平的提高,各生长阶段幼苗根冠生物量、根长和面积以及叶片NR活性呈上升趋势,而有机碳分泌速率呈下降趋势;根冠比变化不同阶段表现不一致,一叶一心期呈下降趋势,二叶一心期和三叶一心期分别以15.0和10.0 mmol.L-1氮水平较高。研究表明,大气CO2浓度升高可促进小麦幼苗根系生长和有机碳分泌速率,提高其氮素同化能力;增加介质供氮有利于高CO2浓度条件下小麦幼苗根冠生长和氮素同化,提高根冠比,减少根系有机碳过度分泌引起的碳损耗。

外源硝酸还原酶(NR)抑制剂对油菜植株内NR活性的影响及其与硝酸盐含量的关系

为进一步揭示硝酸还原酶(nitrate reductase,NR)活性的调控机制及其与植株体内硝酸盐含量的关系。本试验在正常供氮(15 mmol L^(–1)NO_3~–)和缺氮(7.5 mmol L^(–1)NO_3~–)条件下,以氮高效(H1:742和H2:Xiangyou 15)和氮低效(L1:814和L2:H8)油菜基因型为研究材料,通过NR活性的专性抑制剂处理,研究NR活性和硝酸盐含量的基因型和氮水平差异。结果表明,NR专性抑制剂处理可以显著降低叶片NR活性,正常供氮和缺氮条件下分别降低53.0%和57.6%,但对叶片硝酸盐的含量没有显著影响。正常供氮条件下的NR活性和硝酸盐含量比缺氮条件下分别高46.9%和16.4%。氮高效油菜基因型的硝酸盐含量显著低于氮低效基因型。H2的NR活性(NRA_(act))显著高于氮低效基因型的本质原因是其主效基因(nia2)的相对表达量高于氮低效基因型。本研究充分表明NR活性和硝酸盐含量存在明显的基因型和氮水平差异,一定程度的NR活性变化对植株体内硝酸盐的含量并没有显著的影响。

氮胁迫对甜菜幼苗生理以及相关NRTs基因表达的影响

为了深入研究缺氮环境下甜菜(Beta vulgaris L.)的氮利用调控机制,并为利用分子育种以及基因工程途径提高植物的氮利用率奠定基础,本研究以甜菜幼苗‘780016B/12优’为试材,通过对其施加低氮和缺氮逆境胁迫,利用表型观察、叶绿素含量的测定以及相关基因和酶活性的应答变化分析,来研究甜菜植株在生理以及分子方面的应答机制。研究结果表明,甜菜叶片由于缺氮而表现出局部变黄,并且SPAD值显示,叶绿素含量随逆境时间呈下降趋势。qPCR表明,BvNRT2.1和BvNRT3.2基因均受到低氮和缺氮胁迫的诱导,且它们在根部的表达量要高于叶中,BvNRT2.1基因对逆境的应答更为显著。同时,随着胁迫时间的增长,甜菜体内的硝酸还原酶活性逐渐下降,但叶片中该酶的活性始终要高于根中。因此可以得出结论,低氮或缺氮逆境对甜菜幼苗的光合作用、硝酸还原酶活性造成了较为严重的影响,从而导致其生长在一定程度上受到抑制。可以推断,为了适应氮胁迫环境,甜菜自身可能通过上调硝酸盐转运蛋白基因的表达等途径来直接或间接的补偿由于环境氮缺乏或低氮造成的营养缺失,以抵御逆境伤害。

NR硫化返原动力学及主要抗硫化返原助剂

对硫化返原的动力学、抗硫化返原助剂的作用机理、不同抗硫化返原助剂在不同的配合体系中的用量及对硫化胶性能的影响进行评述。对于抗硫化返原助剂 ,在半有效硫化体系中Si6 9抗返原性最好 ,在传统硫化体系中HVA 2最好。

Timing and splitting of nitrogen fertilizer supply to increase crop yield and efficiency of nitrogen utilization in a wheat–peanut relay intercropping system in China

Agronomically optimizing the timing and rates of nitrogen(N) fertilizer application can increase crop yield and decrease N loss to the environment. Wheat(Triticum aestivum L.)–peanut(Arachis hypogaea L.) relay intercropping systems are a mainstay of economic and food security in China. We performed a field experiment to investigate the effects of N fertilizer on N recovery efficiency, crop yield, and N loss rate in wheat–peanut relay intercropping systems in the Huang-Huai-Hai Plain, China during 2015–2017. The N was applied on the day before sowing, the jointing stage(G30) or the booting stage(G40) of winter wheat, and the anthesis stage(R1) of peanut in the following percentage splits: 50-50-0-0(N1), 35-35-0-30(N2), and 35-0-35-30(N3), using 300 kg N ha-1, with 0 kg N ha-1(N0) as control. ^(15)N-labeled(20.14 atom %) urea was used to trace the fate of N in microplots. The yields of wheat and peanut increased by 12.4% and 15.4% under the N2 and N3 treatments, relative to those under the N1 treatment. The ^(15)N recovery efficiencies( ^(15)NRE) were 64.9% and 58.1% for treatments N2 and N3, significantly greater than that for the N1 treatment(45.3%). The potential N loss rates for the treatments N2 and N3 were23.7% and 7.0%, significantly lower than that for treatment N1(30.1%). Withholding N supply until the booting stage(N3) did not reduce the wheat grain yield; however, it increased the N content derived from ^(15)N-labeled urea in peanuts, promoted the distribution of ^(15)N to pods, and ultimately increased pod yields in comparison with those obtained by topdressing N at jointing stage(N2). In comparison with N2, the N uptake and N recovery efficiency(NRE) of N3 was increased by 12.0% and 24.1%,respectively, while the apparent N loss decreased by 16.7%. In conclusion, applying N fertilizer with three splits and delaying topdressing fertilization until G40 of winter wheat increased total grain yields and NRE and reduced N loss. This practice could be an environment-friendly N management strategy for wheat–peanut relay intercropping systems in China.

2种紫花苜蓿氮代谢及其关键酶(NR、GS)活性差异研究

为探究不同紫花苜蓿氮代谢差异及氮代谢差异的生理机制,采用盆栽砂培法,通过对2个具有典型特征的紫花苜蓿品种(LW6010和陇东苜蓿)在2个氮素水平及3个生育时期下其氮代谢产物及氮代谢酶活性差异进行研究,探讨氮代谢产物与氮代谢酶活性的相互关系。结果表明:LW6010和陇东苜蓿在N210水平下其干物质重、氮含量、氮积累量及硝酸还原酶(NR)、谷氨酰胺合成酶(GS)活性均高于N21。在2个氮水平下,LW6010的干物质重、NR和GS活性均显著大于陇东苜蓿,而LW6010的氮含量显著低于陇东苜蓿。其中,LW6010的NR活性比陇东苜蓿在N210和N21下分别高24%和15%(苗期)、31%和40%(现蕾期)、20%和11%(盛花期);GS活性分别高30%和29%(苗期)、33%和20%(现蕾期)、7%和14%(盛花期)。在苗期和盛花期时,LW6010的氮积累量显著大于陇东苜蓿,而在现蕾期差异不显著。LW6010的氮积累量在N210下各生育期分别比陇东苜蓿高25%,3%和16%,而在N21下LW6010的氮积累量在苗期和盛花期下比陇东苜蓿高45%和12%。同时,紫花苜蓿干物质重、氮积累量、NR活性与GS活性呈极显著正相关关系。综上分析,紫花苜蓿的不同品种在不同氮素水平下其氮代谢能力不同,不同紫花苜蓿品种间氮代谢具有差异;LW6010较陇东苜蓿具有较好的氮代谢能力;NR和GS活性可为不同紫花苜蓿氮代谢差异评价提供参考。

Composition and recovery method for electrolytic manganese residue

According to the statistic analysis,the reserve of manganese in electrolytic manganese residue deposit is over 780 kt. The average contents of available manganese and ammonium reach 3.90% and 1.68% (mass fraction),respectively. Large amount of manganese compounds and ammonium sulfate are detruded without any treatment or recovery. The compositions of the main elements in electrolytic manganese residue were analyzed comprehensively based on the extensive research data. According to the new development of electrolytic manganese residue comprehensively used in recent years,a water washing residue-twice precipitation process was also proposed. The experimental results indicate that manganese dioxide silicon dioxide and calcium sulfate are presented as amorphous state in the manganese residues. The recovery rates of manganese and nitrogen reach up to 99.5% and 94.5 %,respectively. The recovery process can be easily implemented,environment-friendly and fitting for industrial production.

Effects of recovery time after fire and fire severity on stand structure and soil of larch forest in the Kanas National Nature Reserve, Northwest China

Forest recovery may be influenced by several factors, of which fire is the most critical.However, moderate-and long-term effects of fire on forest recovery are less researched in Northwest China.Thus, the effects of different forest recovery time after fire(1917(served as the control), 1974, 1983 and 1995) and fire severities(low, moderate and high) on larch(Larix sibirica Ledeb.) forest were investigated in the Kanas National Nature Reserve(KNNR), Northwest China in 2017.This paper analyzed post-fire changes in stand density, total basal area(TBA), litter mass, soil organic carbon(SOC) and soil nutrients(total nitrogen, total phosphorus and total potassium) with one-way analyses of variance.Results indicate that litter mass, TBA, SOC and soil nutrients increased with increasing recovery time after fire and decreasing fire severity, while the stand density showed an opposite response.The effects of fire disturbance on SOC and soil nutrients decreased with increasing soil depth.Moreover, we found that the time of more than 43 a is needed to recover the litter mass, TBA, SOC and soil nutrients to the pre-fire level.In conclusion, high-severity fire caused the greatest variations in stand structure and soil of larch forest, and low-severity fire was more advantageous for post-fire forest stand structure and soil recovery in the KNNR.Therefore, low-severity fire can be an efficient management mean through reducing the accumulation of forest floor fuel of post-fire forests in the KNNR, Northwest China.