Fixed Ammonium Content and Maximum Capacity of Ammonium Fixation in Major Types of Tillage Soils in Hunan Province,China

In order to understand the status of fixed ammonium, fixed ammonium content, maximum capacity of ammonium fixation, and their influencing factors in major types of tillage soils of Hunan Province, China, were studied with sampling on fields, and laboratory incubation and determination. The main results are summarized as follows： （1） Content of fixed ammonium in the tested soils varies greatly with soil use pattern and the nature of parent material. For the paddy soils, it ranges from 135.4 ± 57.4 to 412.8±32,4 mg kg^-1, with 304.7±96.7 mg kg^-1 in average; while it ranges from 59.4 to 435.7 mg kg^-1, with 230.1 ± 89.2 mg kg^-1 in average for the upland soils. The soils developed from limnic material and slate had higher fixed ammonium content than the soils developed from granite. The percentage of fixed ammonium to total N in the upland soils is always higher than that in the paddy soils. It ranges from 6.1 ±3.6% to 16.6±4.6%, with 14.0% ±5.1% in average for the paddy soils and it amounted to 5.8±2.0% to 40.1 ± 17.8%, with 23.5 ± 14.2% in average for upland soils. （2） The maximum capacity of ammonium fixation has the same trend with the fixed ammonium content in the tested soils. For all the tested soils, the percentage of recently fixed ammonium to maximum capacity of ammonium fixation is always bellow 20% and it may be due to the fact that the soils have high fertility and high saturation of ammonium-fixing site. （3） The clay content and clay composition in the tested soils are the two important factors influencing their fixed ammonium content and maximum capacity of ammonium fixation. The results showed that hydrous mica is the main 2：1 type clay mineral in 〈 0.02 mm clay of the paddy soils, and its content in 0.02-0.002 mm clay is much higher than that in 〈 0.002 mm clay of the soils. The statistical analysis showed that both the fixed ammonium content and the maximum capacity of ammonium fixation of the paddy soils were positively correlated with the total 2：1 type clay mineral content and hydrous mica content in 〈 0.02 mm clay and 0,02-0.002 mm clay at the significant level of P0.01 or P0.05, respectively, but not correlated with the total 2：1 type clay mineral content and hydrous mica content in 〈0.002 mm clay significantly, It demonstrated that the ammonium-fixing matrix of the tested soils mainly exists in the 0.02-0.002 mm clay. The above-mentioned results showed that fixed ammonium is a major form of N in the tillage soils in Hunan Province, China. It would play an important role in N nutrition of crops, especially for upland crops, and deserve to be further researched.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Novel Investigation on Ammonium Thiosulphate (ATS) as an Inhibitor of Soil Urease and Nitrification

Among the numerous products so far promoted as effective urease and/or nitrification inhibitors, it is possible to detect a renewed interest in environmentally friendly tools, such as ammonium thiosulphate (ATS, (NH4)2S2O3) which is currently used as fertilizer for N and S nutrition. Among contradictory results accounted in the current literature, there is reported that ammonium thiosulphate (ATS) exerts inhibitory activity at large but unlikely agronomic rates of 2500 - 5000 mg·kg-1 soil. We carried out a novel experiment aimed to: a) verify the inhibitory action of ATS, even when applied in soil at low rates (25 and 100 mg·kg-1 soil as S-ATS), towards urease activity and nitrification in urea treated and not treated soils;b) investigate on the influence of ATS on the soil microbial biomass as it is generally assumed that soil microorganisms are the main agents of urea hydrolysis. For these purposes we selected an arable sandy soil and a grassland sandy-loam soil which are treated with urea or/and ATS. Results obtained from this novel investigation showed that a) ATS significantly decreased urease activity in both soil types and that the exerted inhibitory effect was moderate and short-term;b) ATS retarded the hydrolysis of urea and lowered nitrate production in the urea treated soils;c) the available fraction of iron and manganese in the used soils might be involved in the mechanism of inhibition;d) ATS did not affect the size of soil microbial biomass pool;e) the efficiency of ATS as urease and nitrification inhibitor was more evident in the sandy soil. Because of its properties, ATS may be applicable on many crops without being harmful on the soil microbial pool.

Ammonium Oxidizing Bacteria Activity and Nitrification Rate in Oil Contaminated Wetland Soil under Remediation with Nutrient Supplements and Leguminous Plants

Previous investigation on the impact of crude oil on the growth of tropical legumes and its effect on nitrogen dynamics in wetland ultisol showed that oil contamination reduced N uptake by plants but increased N accumulation in soil microbial biomass. Moreover, the presence of hydrocarbons widened the C/N ratio in soil and led to more available N being immobilized by soil microorganisms. The present study was carried out to evaluate the activity of ammonium oxidizing bacteria (AOB) and their nitrification potential rate (NPR) in wetland soil under a remediation course. Mineralization studies showed that ammonium-N levels decreased while nitrate-N increased progressively in the uncontaminated soil (control) cultivated with leguminous plants (cover crops) during the 12 weeks remediation period. However, the remediated soils were affected in different ways. The experimented soil cultivated with Centrosema pubescens had higher mineral nitrogen (NH4-N, NO3-N, NO2-N, Total N and P) than soil cultivated with Calopogonium mucunoides and Pueraria phaseoloides. AOB counts recorded were in the ranged, 2.25 × 102 - 2.66 × 105, 2.31 × 102 - 2.11 × 104 and 4.25 × 102 - 2.98 × 104 respectively. The highest NPR was found in uncontaminated soil (11.68 - 60.92 nmol N/g dry weight soil (DWS)) followed by soil treated with poultry manure (9.65 - 24.86 nmol N/g DWS/h), NPK (7.88 - 39.45 nmol N/g DWS/h) and in the oil-contaminated soil (0.11 - 1.87 nmol N/g DWS/h). The relations between NH4-N concentration and NPR in soil cultivated with Centrosema (r = 0.852), Calopogonium (r = 0.745) and Pueraria (r = 0.722) were positively significant at 95% confidence limit. Similarly the relations between AOB density and NPR for Centrosema (r = 0.654;P = 0.05), Calopogonium (r = 0.588;P = 0.05) and Pueraria (r = 0.518;P = 0.05) were significant. The findings imply that nitrification potential of crude oil- contaminated soil differs significantly with the nutrient amendment/treatment technique adopted for remediation. Our research has shown that treatment of uncontaminated soil with cover crops increased AOB and nitrification rate. More so, contaminated soil treated with poultry manure and NPK-fertilizer, cultivated with covers crops resulted in remarkable reduction in hydrocarbons content and increased population of nitrifiers and nitrification potential rates of wetland soil over time. However, contaminated soil treated with poultry manure and cultivated with Centrosema pubescens is more effective in bioremediation of crude oil-contaminated soil.

Adsorption-desorption behavior of acetochlor to soils in the presence of some environmental substances

The behavior of herbicide acetochlor adsorption desorption to soil in the presence of humic acid (HA), anionic surfactant sodium dodecylbenzene sulfonate (SDBS), cationic surfactant hexadecyltrimethyl ammonium bromide (HDAB) and NH 4NO 3 as a chemical fertilizer was studied. Observed acetochlor adsorption isotherm were well described using Freundlich isotherm equation, from which the desorption isotherm equation has been deduced. The deduced equation can more directly describe acetochlor desorption process. The results showed that the enhance of acetochlor adsorption capacity by solid HA was greater than by soluble HA. The presence of NH 4NO 3 can slightly enhance acetochlor adsorption to soil by comparison with that measured in NH 4NO 3 free solution. In soil water system, surfactant acetochlor interaction is very complex, and the surfactant adsorptions as well as acetochlor adsorption need to be considered. When acetochlor soil suspensions contained lower concentration SDBS or HDAB (40 mg/L), K f for acetochlor adsorption was decreased in comparison to that measured in SDBS or HDAB free solution. When acetochlor soil suspensions contained higher concentration SDBS or HDAB (corresponding 1400 mg/L or 200 mg/L), K f for acetochlor adsorption was increased in comparison to that measured in SDBS or HDAB free solution.

Effects of temperature and surfactants on naphthalene and phenanthrene sorption by soil

Adsorption experiments were carried out to investigate the sorption behaviors of naphthalene and phenanthrene in six different soils and to determine the effects of temperature, linear alkylbenzene sulfonate （LAS） and cetylrimethyl ammonium bromide （CTAB） on sorption. The results show that for a given sorbent phenanthrene exhibited greater nonlinear and stronger sorption than naphthalene. There was a strong negative correlation for the Koc values with organic carbon content （foc）. The increase of temperature was not favorable to sorption. Sorption decreased along with the increasing aqueous LAS concentration from 0 to 1000 mg/L. At low CTAB concentration （〈 100 mg/L）, the adsorption increased as CTAB hemimicelles formed on the soil surface. At high concentration, CTAB decreased the adsorption by occupying active hydrophobic adsorption sites and solubilization of naphthalene and phenanthrene.

Root Function in Nutrient Uptake and Soil Water Effect on NO3^- -N and NH4^+ -N Migration

Root function in uptake of nutrients and the effect of soil water on the transfer and distribution of NO3^--N in arable soil were studied using summer maize （Zea mays L. var. Shandan 9） as a testing crop. Results showed that root growth and water supply had a significant effect on NO3^--N transfer and made NO3^--N distributed evenly from bulk soil to rhizosphere soil. Under a natural condition with irrigation, the difference of NO3^--N concentration at different distance points from a maize plant was smaller, while obvious difference of NO3^--N concentration was observed under conditions of limited root growth space without irrigation. Whether root growth space was restricted or not, the content of soil NO3^--N decreased gradually from 10 to 0 cm from the plant, being opposite to the root absorbing area in soils. When root-grown space was limited, changes of NO3^--N concentration at different distances from a plant were similar to that of water content in tendency. Results showed that NO3^--N could be transferred as solute to plant root systems with water uptake by plants. However, the transfer and distribution of NH4^--N were not influenced by root growth and soil water supply, being different to NO3^--N.

长期紫云英配施减量化肥对土壤铵态氮吸附解吸特征的影响

为明确长期紫云英配施减量化肥对土壤铵态氮吸附解吸特征的影响,以13年长期定位试验为平台,设不施肥(CK)、单施化肥(CF)、22500 kg/hm^(2)紫云英+80%化肥(G+0.8CF)、22500 kg/hm^(2)紫云英+60%化肥(G+0.6CF)、22500 kg/hm^(2)紫云英+40%化肥(G+0.4CF)共5个处理,研究了不同施肥处理对土壤铵态氮吸附解吸特征的影响,并分析了土壤吸附解吸特征参数与土壤理化性质的关系。结果显示,Langmuir等温吸附方程能较好地拟合土壤铵态氮的吸附特征(R^(2)为0.9969~0.9979,P<0.01)。与CK相比,紫云英配施减量化肥处理土壤铵态氮的最大吸附量、最大缓冲容量分别降低了4.85%~13.46%、4.55%~7.36%;土壤铵态氮的平均解吸量和解吸率为G+0.8CF>G+0.6CF>G+0.4CF>CF>CK。与CK相比,紫云英配施减量化肥处理土壤全氮和速效氮含量分别增加了19.42%~46.60%、15.24%~25.88%。相关性分析结果显示,解吸率与土壤全氮、土壤速效氮呈显著正相关,与土壤pH呈显著负相关;冗余分析结果显示,pH和速效氮是造成土壤铵态氮吸附解吸特征参数差异的主要因素,分别解释了全部变异的56.7%和39.1%(P<0.05)。综上所述,长期紫云英配施减量化肥降低土壤对铵态氮的吸附,增加土壤对铵态氮的解吸,减少了土壤对氮的固持,提高氮的有效性。综合考虑土壤铵态氮的吸附解吸特性及土壤养分含量,以减量20%~40%化肥配施22500kg/hm^(2)紫云英处理效果较好。

乙二胺四乙酸-乙酸铵盐交换法测定阳离子交换量方法优化

针对乙二胺四乙酸(EDTA)-乙酸铵交换法测定土壤阳离子交换量耗时长的问题,对方法的搅拌方式、搅拌时间、蒸馏时间进行优化。优化后分析条件为:用磁力搅拌器代替人工橡皮头玻璃棒搅拌,确定搅拌时间为90 s,确定蒸馏时间为6 min。选择4个不同地区不同阳离子交换量的土壤标准物质用优化前、后的方法分别进行7次测定,其检测结果相对标准偏差为1.53%~5.32%;28个实际样品进行成对二样本均值分析,优化前、优化后测定的土壤阳离子交换量结果无显著性差异;对优化前、后28个土壤样品阳离子交换量测定结果进行相关性分析,线性相关显著,相关系数r=0.998。结果表明,EDTA-乙酸铵交换法优化前、后均具有较好的精密度和准确度,结果无显著性差异,EDTA乙酸铵交换法优化后的方法检测时间(1人测定8个样品)由280 min缩短到130 min,提高了检测效率,适合批量石灰性土壤阳离子代换量的测定。

生物炭包膜尿素的制备及其固氮潜力的研究

为了探究生物炭包膜尿素的缓释性能及对土壤固氮的影响,以300、500和700℃下制备的杨木生物炭为包膜材料制备了3种生物炭包膜尿素,采用间歇土柱淋溶试验对氮素的释放特征进行分析。结果表明,杨木生物炭对铵态氮和硝态氮具有较好的吸附性能,低温下制备的生物炭对铵态氮吸附效果更好;与尿素相比,施用生物炭包膜尿素土壤的总氮淋溶量减少了9.73%~14.67%,铵态氮淋溶量减少了25.28%~30.36%,硝态氮淋溶量减少了10.34%~18.38%;在同等施氮水平下,生物炭包膜尿素相较于尿素可以显著增加土壤铵态氮和硝态氮的含量。其中,土壤中铵态氮含量增加了66.4%~200.1%,土壤硝态氮的含量增加了477.9%~537.6%。因此,生物炭用作肥料的包膜材料具有广阔的应用前景。

聚磷酸铵磷肥对玉米苗期磷素吸收利用和潮土无机磷组分含量的影响

聚磷酸铵磷肥具有缓释性,在石灰性土壤中能够长效供磷,但是释放缓慢易导致作物苗期供磷不足进而影响最终产量,探讨玉米苗期聚磷酸铵磷肥合理施用量及其对潮土无机磷组分含量的影响,为合理施用聚磷酸铵磷肥提供科学依据。采用盆栽试验,设置6个聚磷酸铵磷肥水平,P_(2)O_(5)0、30、60、90、120和150 mg/kg(分别用P0、P30、P60、P90、P120、P150表示),测定玉米的生物学指标和玉米磷素吸收利用状况,同时测定土壤有效磷和无机磷组分含量。结果表明,相较于P0水平,聚磷酸铵磷肥能显著提高玉米的株高、茎粗、地上部和根系干重,株高、茎粗和地上部干重均表现出0~90 mg/kg增幅大、90~150 mg/kg增幅小的趋势,P150水平的株高、茎粗、茎和叶生物量比P0水平分别提高了71.0%、68.8%、334.5%和201.6%。P90水平的玉米茎、根磷含量和磷肥利用效率均为最低值,但磷肥利用效率与P120和P150水平无显著性差异;非根际土壤有效磷含量随施磷量的增加呈极显著的线性关系,每1 mg/kg聚磷酸铵施用量相当于增加了0.0894 mg/kg的非根际土壤有效磷,施磷70 d后根际和非根际土壤有效磷含量依然在13.23 mg/kg以上;土壤无机磷总量随聚磷酸铵磷肥施用量的增加呈上升趋势,相较于P0水平,Ca_(2)-P、Al-P含量出现了显著性变化,O-P含量与比例各施磷水平间无显著性差异,P150水平Ca_(10)-P含量显著高于P90及其以下各处理,相较于P0水平,其Ca_(10)-P累积量增加了101.70 mg/kg。基于本研究结果,聚磷酸铵磷肥可以在根际和非根际石灰性潮土上维持较高的土壤有效磷含量,P_(2)O_(5)60 mg/kg水平以下玉米生物量累积不足,P_(2)O_(5)120 mg/kg水平以上增加了土壤Ca_(10)-P的含量与比例,P_(2)O_(5)90 mg/kg是潮土上玉米苗期较为适宜的聚磷酸铵磷肥用量。

土膜耕作法的土壤与作物效应研究

【目的】探索土膜耕作法对农田土壤水分、温度和养分变化的影响,揭示土膜对作物根系生长及产量效应,明确土膜的农业生产价值,为其应用提供理论依据与技术。【方法】在宁夏引黄灌区通过喷施1.0%浓度羧甲基纤维素铵(carboxymethyl cellulose ammonium,CMC-NH4)水溶液促使土膜产生。设CMC-NH4用量0(CK)、50.0(T1)、100.0(T2)、200.0(T3)和300.0 kg·hm^(-2)(T4)5个处理,开展春小麦-夏玉米复种下的土壤水分、温度、养分、微生物、作物根系及产量效应研究。【结果】喷施CMC-NH4的各处理春小麦和夏玉米田土壤日均含水量提高3.3%—7.0%(P<0.05,下同)和1.9%—6.1%,日平均温度提高7.9%—12.6%和5.6%—11.7%,土壤积温增加88.98—141.94℃和60.25—136.65℃;0—30 cm土层根长提高37.5%—17.1%和11.2%—1.7%,根表面积提高15.3%—4.5%和12.5%—9.2%,土层根系干重增加17.0%—41.5%和30.9%—36.7%;提高春小麦籽粒产量7.3%—18.8%和夏玉米地上部干重33.6%—49.0%,提高土壤氮磷钾含量和促进土壤微生物多样性增加。【结论】喷施CMC-NH4形成的土膜具有农田覆盖功能,能够改善土壤水热环境,促进作物养分吸收利用、根系生长、提高产量;土膜耕作法为构造“表实上虚下实”良好耕层结构提供了技术方法,对作物产能提升、农田土壤改良及农业高质量发展有支撑作用。宁夏引黄灌区CMC-NH4推荐喷施量为100.0 kg·hm^(-2)。

强降水对不同肥期麦田氨挥发损失的影响

在极端降水事件频发的背景下,为明确强降水对麦田不同肥期氨挥发损失的影响,本研究利用田间模拟降水试验,研究了强降水对麦田氨挥发损失和耕层土壤铵态氮含量及硝化潜势的影响,并结合微域试验分析了氨挥发损失与土壤含水量的关系。田间试验设置施氮处理(CF)与不施氮(CK)对照,以CF处理施肥时间为基准,分别在基肥、越冬肥和穗肥施肥后第7天模拟强降水(90 mm),监测农田氮素径流和渗漏损失,并进行连续10 d的氨挥发排放监测。结果表明,施肥显著提高中上层(0~10 cm)土壤的铵态氮含量,增加了降水驱动的生育前期(基肥期,越冬肥期)氮径流和渗漏损失,而穗肥期损失量相当。施肥和降水对基肥期氨挥发排放强度(AVI)无显著影响,但对追肥期(越冬肥期,穗肥期)的AVI影响显著。降水-施肥处理(CF-R)的追肥期AVI(越冬肥期35.02 mg·m^(-2)·d^(-1);穗肥期12.84 mg·m^(-2)·d^(-1))显著高于其他处理(越冬肥期15.46~17.29 mg·m^(-2)·d^(-1);穗肥期7.95~11.23 mg·m^(-2)·d^(-1))。此外,越冬肥期氨挥发损失对平均AVI的差异贡献高于穗肥期和基肥期。相关分析表明,表层(0~5 cm)土壤铵态氮含量与氨挥发损失强度呈显著线性关系(P<0.05)。但值得注意的是,非降水条件下CF和CK处理的追肥期AVI均无显著差异,且培养系统的NH_(3)挥发损失量随土壤持水量的增加而降低。而土壤硝化潜势分析表明,施肥对不同土层土壤的硝化潜势均无显著影响,但降水显著降低了中上层土壤的硝化潜势。研究表明,降水对施肥处理的氨挥发驱动效应是施肥后表层土壤氮素含量升高和降水后硝化潜势降低的叠加作用结果。除驱动麦田氮素径流和渗漏损失,强降水对追肥期氨挥发损失的激发效应应予重视,特别是在越冬肥期。

酸中性土壤交换性盐基总量检测方法的影响因素

目前,酸中性土壤交换性盐基总量的检测方法主要为乙酸铵交换-中和滴定法,其特点为步骤繁杂、操作难度大,也是全国“三普”内业指标实验中的技术难点之一。通过采用多类土壤标准物质为研究对象,探讨样品质量、交换试剂、检测方式对盐基总量的影响,并对土壤交换性盐基总量与交换性盐基各离子之间的相关性进行分析。结果表明,高含量盐基样品ASA-7a在添加与不添加EDTA的乙酸铵溶液交换下,电感耦合等离子体发射光谱(ICP-OES)测定的加和盐基总量值分别为(34.71±0.10)、(33.26±0.18) cmol/kg,中和滴定检测后一交换液的值则偏高,达到(38.80±0.62) cmol/kg,并且不同交换试剂间和检测方式间均有一定差异性(P<0.05),但样品质量的多少对盐基总量的结果无显著影响(P>0.05)。对于选取土壤样品,尽管ICP-OES测定加和盐基总量的相对误差RE与相对标准偏差RSD分别小于7%、1.2%,其精密度与准确度均优于中和滴定法,两种检测方式结果仍然在标准参考值范围内。但是,对于更多类型和批量样品土壤交换性盐基总量的测定与数据的比对统计分析,建议遵照统一的规程并保持方法的一致性,避免因方法的不同而增大结果的差异性。

液相色谱串联质谱法检测草铵膦、草甘膦及其代谢物在水和土壤中的残留

利用超高效液相色谱-串联质谱仪(UHPLC-MS/MS),结合固相萃取净化建立了在水和土壤中同时快速测定草甘膦、草铵膦及其6种代谢物的多残留分析方法。前处理采用Oasis MCX和Oasis MAX固相萃取柱提取,2%甲酸甲醇-水(体积比为1∶1)洗脱,旋干后0.1%氨水定容,UHPLC-MS/MS检测。方法的线性范围为0.02~0.5 mg/L;在水中添加水平为0.0001 mg/L和0.001 mg/L时,草甘膦、草铵膦及其代谢物的回收率为72.8%~94.2%,RSD为2.3%~16.1%;土壤中添加水平为0.001 mg/kg和0.01 mg/kg时,草甘膦、草铵膦及其代谢物的回收率为70.6%~88.5%,RSD为3.6%~12.8%。本方法准确、灵敏、全面,适用于草甘膦、草铵膦及其代谢物在水土环境中的残留检测及监测。

红壤区旱作花生地剖面氮素迁移转化模拟研究

为探究红壤区花生种植地氮素的垂向迁移影响因素及其损失特征,本研究利用HYDRUS-1D模型构建适用于红壤地区的水氮耦合模型。该模型结合实地监测数据和室内淋溶实验结果,对模型参数进行率定和验证,并利用校验过的模型模拟研究区不同环境条件下土壤剖面氮素的动态迁移与转化过程。结果表明:HYDRUS-1D模型模拟值与实测值之间吻合度较高,模型可用于模拟花生地不同深度土壤水氮运移过程。土壤铵态氮和硝态氮在降雨施肥后迅速升高,随后下降。施肥量变化主要影响0~40 cm土层内氮素浓度变化,而改变降雨量影响0~80 cm土层内氮素的迁移转化。此外,氮素浓度随土层深度的增加而减小。模拟结果显示,施氮量为225.0 kg·hm^(-2)时,雨季发生总降雨量大于173 mm且降雨强度大于11 mm·d^(-1)降雨事件时,或旱季发生强降雨事件,即总降雨量大于135 mm且降雨强度大于135 mm·d^(-1)时,80 cm土层硝态氮浓度至少上升到1 mg·L^(-1)。受红壤质地黏重的影响,深层土壤氮素对降雨响应具有一定的滞后效应。随着施肥量的增加,作物根系对氮素的吸收通量增大,但氮素吸收量与氮肥施用量的比例却有所下降;降雨量对根系吸收氮素的影响相对较小。在花生生长季,土壤中的主要氮损失形式为硝态氮的淋失。模拟分析表明,降雨和施肥均会影响硝态氮的淋失量,其中降雨量的增加显著提高了硝态氮的浸出量,硝态氮累积淋失量变化范围在5.23~42.97 kg·hm^(-2)之间,证明了花生地对红壤区地下水硝酸盐潜在污染不可忽视。

河套灌区垄膜沟灌不同灌水量对土壤水氮迁移转化的影响

在引黄配额减少情况下,节水优先、减少污染和稳定粮食产量势必成为河套灌区未来的发展方向。垄膜沟灌方式具有提高水肥利用效率的功能,但其节水保肥增产机理尚不明确。因此,通过在河套灌区进行5个灌水量的垄膜沟灌春玉米田田间试验(T1,200 mm;T2,275 mm;T3,350 mm;T4,425 mm,T5,500mm),探讨不同灌水量下的土壤水分、土壤硝态氮及土壤铵态氮迁移转化特征。结果表明:土壤耗水量从T1处理的326.8 mm随灌溉定额的增加线性增加到T5处理的487.1mm;T2与T3处理下收获时硝态氮贮量高于播种前,保肥能力强;T3处理的春玉米籽粒氮含量显著高于其他处理;T3处理与T4和T5处理的春玉米产量无显著差异;T3处理与T1和T2处理的春玉米氮素利用效率无显著差异;春玉米水分利用效率则随灌溉定额的增加呈先增加后减少趋势。综上,垄膜沟灌下350mm灌溉定额可有效提升春玉米的水氮利用效率,并在节水保肥增产的基础上提升春玉米籽粒品质。

缓控释肥配施脲铵运筹对水稻产量、氮素利用效率和土壤养分的影响

通过田间试验,以传统配方肥+尿素一基两追施肥模式(CG)为对照,研究了以脲甲醛类缓控释肥(NC)和木质素类缓控释肥(MC)为基肥、脲铵为分蘖或穗分化追肥的缓控释肥+脲铵一基一追施肥模式对水稻产量、氮吸收累积、氮素利用效率以及土壤养分的影响。结果表明:缓控释肥+脲铵一基一蘖施肥模式水稻产量与CG处理相比无明显差异,但脲甲醛类缓控释肥+脲铵(NC-S)和木质素类缓控释肥+脲铵一基一穗(MC-S)处理分别比CG处理明显增产3.96%和6.01%,主要原因为NC-S和MC-S处理每穗粒数分别比CG处理明显增加16.7%和17.6%;与CG处理相比,脲甲醛类缓控释肥+脲铵(NC-F)和木质素类缓控释肥+脲铵一基一蘖(MC-F)处理成熟期地上部氮累积分别比CG处理增加2.50%和5.89%,NC-S和MC-S处理分别比CG处理明显增加10.0%和11.6%;NC-S和MC-S处理氮素利用效率(NUE)分别比CG处理高3.96%和6.01%。缓控释肥+脲铵一基一追施肥模式增加了水稻氮吸收效率(NupE)和表观氮肥回收效率(ANR),其中MC-S处理的NupE明显比CG处理高11.6%,NC-S和MC-S处理的ANR分别比CG处理明显高25.4%和29.3%。缓控释肥+脲铵一基一追施肥模式土壤碱解氮含量明显比CG处理增加6.58%~10.7%,其中,一基一穗施肥模式增加比例更大;另外,土壤有机质含量比CG处理增加1.11%~7.56%。由此可见,缓控释肥+脲铵一基一穗施肥模式更有利于提高水稻产量和氮素利用效率,增加土壤肥力。

不同硝态氮、铵态氮素配比对植烟土壤和烤烟生长及产质量的影响

为探究不同硝态氮、铵态氮素配比对贵州安顺地区植烟土壤和烤烟生长及产质量的影响,寻找适宜于当地烟叶优质生产的最佳配比,设置了5个处理(CK;T_(1):100%硝态氮肥;T_(2):70%硝态氮+30%铵态氮;T_(3):50%硝态氮+50%铵态氮;T_(4):30%硝态氮+70%铵态氮;T_(5):100%铵态氮),分析了不同处理下的烤烟生育期、农艺性状、经济性状、病害发生情况以及烤后烟叶化学成分及根际土壤理化性状和酶活性,以期为该地区优化烟草施肥、改善植烟土壤、提高烟叶产质量提供一定的理论依据。结果表明:T_(2)处理大田生育期为112 d,现蕾期较T_(3)处理提前了6 d,T_(2)、T_(4)、T_(5)处理有效叶数显著高于T_(3)处理;T_(2)处理发病率最低,SPAD值显著高于T_(1)、T_(3)、T_(4)和T_(5)处理,发病率与土壤速效钾含量呈极显著负相关;T_(2)和T_(3)处理烤后烟叶的经济性状表现较好,T_(2)处理增加了中上等烟比例;T_(3)、T_(4)处理烤烟的钾含量显著高于T_(1)、T_(2)、T_(5)处理,且符合优质烟标准,T_(2)处理的烟碱含量显著高于T_(1)、T_(4)和T_(5)处理,氯含量显著低于其他处理,化学成分协调性综合评分最高;T_(2)处理显著增加了成熟期根际土壤pH值及酸性磷酸酶、脲酶、蔗糖酶活力。因此,综合考虑烟株的生长情况、发病率、烤后烟叶的化学成分以及植烟土壤肥力状况,在安顺地区硝铵氮素配比为7∶3施用效果更优,更有利于云烟87的生长。

离子吸附型稀土矿区硫酸铵原位浸矿与淋洗过程的室内模拟

离子吸附型稀土尾矿中残留的大量硫酸铵浸矿剂随雨水淋滤进入周边环境,可造成矿区及周边土壤和水体严重污染。本研究通过实地采集稀土矿区土壤,开展室内一维土柱实验分别模拟浸矿过程和淋洗过程,并建立Hydrus-1D模型,评价该模型对稀土矿浸矿和淋洗过程的模拟性能。Hydrus-1D模型的弥散度的率定值为0.5 cm,浸矿与淋洗过程的K d的率定值分别为0.07 cm^(3)/g和1.2 cm^(3)/g;在浸矿过程模拟中,4个观测孔模型的R^(2)为0.95~0.99,E_(RMS)为1.3~6.8 mmol/L;淋洗过程的R^(2)为0.93~0.98,E_(RMS)为0.2~1.6 mmol/L;Hydrus-1D能够较好模拟浸矿和淋洗过程中NH_(4)^(+)的迁移行为。示踪实验中Cl^(-)穿透耗时为30~90 min;浸矿实验中,4个观测孔达到吸附饱和耗时为60~150 min;淋洗实验中,4个观测孔的NH_(4)^(+)浓度低于检测限的耗时为360~540 min;土壤吸附作用对浸矿与淋洗过程中NH+4运移过程的影响显著。