Effects of long‐term applications of various nitrogen sources on chemical soil properties and composition of bromegrass hay

Effects of 15 annual applications (from 1979 to 1993) of ammonium nitrate (AN), urea, ammonium sulfate (AS), and calcium nitrate (CN) applied at 168 and 336 kg N ha^‐1 to bromegrass (Bromus inermis Leyss.) on soil acidification, and concentration of aluminum (Al), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) in soil and in hay were investigated in a field experiment on a thin Black Chemozemic (Typic Boroll) soil in Alberta, Canada. Soil was acidified and the concentration of extractable Al, Fe, and Mn was increased by nitrogen (N) application, but the magnitude varied with N source. Soil acidification was greatest with AS, followed by AN and urea, with no effect of CN. At 336 kg N ha^‐1 rate, soil was acidified to a depth of 10, 15 and 30 cm with urea, AN AS, respectively. Soil acidification was also greater at 336 kg than 168 kg N ha^‐1. The CaCl₂‐extractable Al and Fe in the 0–15 cm layer increased with N application, which closely followed the decrease in soil pH from various N sources. Extractable Al and Fe concentration in the 15–30 cm layer increased in response to reduction in soil pH by AS only, and there was no change in the extractable Al and Fe below the 30‐cm depth by any form of N. The DTPA‐extractable Mn in soil generally changed in response to N application. There was no effect of N source on the DTPA‐extractable Zn and Cu in soil. When soil pH had been lowered from N application, the concentration of Al in hay decreased while Zn concentration increased. The Mn concentration in forage increased markedly in response to reduced soil pH from application of AN, urea and AS. There was no effect of N fertilization on the Cu and Fe concentration in hay. In conclusion, the magnitude of soil acidification, changes in the Al, Fe, and Mn concentrations in soil and changes in the Al, Zn, and Mn concentrations in bromegrass hay varied with N source. The results suggest the need for periodic monitoring of soil pH and consideration of liming costs in the economics of various N fertilizers.     

Soil chemical properties after long‐term n fertilization of bromegrass: Nitrogen rate

Abstract

Nitrogen (N) fertilizers increase yield and quality of grass forage, and may also alter soil chemical properties. A field experiment was conducted in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate to bromegrass on concentration and downward mobility of soluble NO₃‐N, extractable NH₄‐N, P, Ca, Mg, and K, and total C and N in a Thin Black Chernozemic loam soil. The fertilizer was applied annually in early spring for 16 years at 0 to 336 kg N/ha. There was little accumulation of NO₃‐N in the soil at N rates of 112 kg/ha or less. However, at rates higher than 112 kg N/ha there was accumulation of NO₃‐N in the 15–30 and 30–60 cm layers, but very little in the 90–120 cm depth. The NH₄‐N accumulated in the 0–5 cm layer when the fertilizer was applied at rates between 168 to 280 kg N/ha and in the 5–10 cm layer at N rates exceeding 280 kg/ha. There was a decline in extractable P in soil with N application up to 84 kg N/ha rate, while it increased with high N rates. The increasing amounts of applied N resulted in a decline in extractable soil Ca, Mg and K, and this decrease was more pronounced in the 0–5,5–10,10–15, and 15–30 cm layers for K, 0–5 and 5–10 cm layers for Ca, and 0–5, 5–10, and 10–15 cm layers for Mg. There was a build‐up of total C and N in the surface soil with increasing rate of applied N.     

夏播玉米根系分布与含氮量对氮肥类型与施氮量的响应

连续两年施用不同氮肥和用量,考察了夏玉米（郑单958）根系在不同土层的分布与含氮量,分析其与产量、地上部氮素累积量的相关性。结果表明:1）施氮抑制夏玉米生育前期根系生长与下扎,抑制作用表现为:复合肥＞包膜尿素＞尿素;施氮使吐丝期0—25与50—80 cm土层根量增大,25—50 cm土层根量减少;总根量表现出:尿素＞复合肥＞包膜尿素,且差异显著。2）施氮显著提高夏玉米9叶展开期0—25 cm土层与吐丝期25—80 cm土层根系含氮量;氮肥类型影响根系含氮量,且差异显著。3）吐丝期25—80 cm土层根系含氮量与产量呈显著正相关（P＜0.05),与地上部氮素累积量呈极显著正相关（P＜0.01﹚;在25—50 cm,根系鲜重密度、体积密度和干重密度与产量及氮素累积量表现为负相关,在其他土层表现为正相关。其中,0—80 cm土层根系干重密度与产量呈显著正相关（P＜0.05),0—25 cm土层根系鲜重密度与产量、0—80 cm土层根系鲜重密度与氮素累积量呈明显正相关（P＜0.1）。可见,玉米根系分布与含氮量明显受到氮肥类型与施氮量的影响,施氮主要通过提高表土层根系鲜重、根系总鲜重与总干重及中下层根系含氮量实现夏玉米增产增效目的。     

腐植酸氮肥对玉米产量、氮肥利用及氮肥损失的影响

【目的】 通过研究新型腐植酸氮肥对玉米产量、氮肥吸收利用和分配及氮肥在土壤中分布以及损失的影响,为促进新型肥料的应用,减少环境污染,提高作物产量提供理论依据。 【方法】 采用固定装置,应用同位素示踪技术进行田间试验。试验共设 4 个处理:CK1 (不施氮肥)、CK2 (普通尿素 N 225 kg/hm2)、HA1 (脲基活化腐植酸氮肥 N 225 kg/hm2)、HA2 (常规掺混腐植酸氮肥 N 225 kg/hm2)。采集玉米播种前、施肥前和收获后 0—20 cm、20—40 cm、40—60 cm 土壤样品,采用静态箱体内置硼酸吸收池法测定氨挥发,氧化亚氮通过静态箱体收集、真空瓶贮存后气相色谱仪测定。玉米成熟后采集地上部植株样品,将营养器官与籽粒分离,计产并测定产量构成指标。 【结果】 籽粒中氮素 34.6%～36.2% 来自肥料,营养器官中氮素 14.6%～17.4% 来自肥料。CK2、HA1 和 HA2 处理的氮肥利用率分别为 25.1%、30.9%、28.5%,氮肥损失率分别为 38.1%、19.8%、27.2%。与 CK2 相比:1) 施用 HA1 能提高玉米产量;2) HA1 和 HA2 处理的氮素吸收总量分别增加 25.8 和 16.3 kg/hm2,氮肥利用率分别提高 5.8 个百分点和 3.4 个百分点,氮肥损失率分别减少 18.3 个百分点和 10.9 个百分点;3) HA1 和 HA2 处理 0—60 cm 土壤氮素残留率分别增加 12.5 个百分点和 7.5 个百分点;4) 施用腐植酸氮肥明显提高 0—20、20—40 cm 土壤铵态氮和硝态氮含量。 【结论】 腐植酸氮肥能显著提高玉米产量和氮肥利用率,促进玉米对土壤氮素的吸收利用,显著增加 0—20 cm 土壤氮素残留量和 0—40 cm 土壤无机态氮含量,减缓氮素向深层土壤迁移,从而减少淋溶损失。腐植酸氮肥能改善氮素在土壤中的分布,满足作物根系需肥特性;腐植酸氮肥能显著降低氧化亚氮产生量和其它途径的氮素损失,从而减少氮素损失量。其中,脲基活化腐植酸氮肥作用效果更加明显。      

洱海流域减氮施肥条件下水稻产量和土壤剖面氮磷变化特征

[目的]研究实现水稻稳产和土壤氮磷淋失低风险的肥料管理措施,以减少农田养分进入流域水域的风险,并提高农业生产的效益.[方法]田间试验在云南大理国家农田生态系统野外观测研究站进行,种植制度为水稻–大蒜–水稻–蚕豆轮作,试验连续进行了两年.设置8个水稻施肥处理:不施肥(CK);常规施肥(CF);减施20％常规肥(T1);等...     

Cumulative effects of a 17‐year chemical fertilization on the soil quality of cropping system in the Loess Hilly Region,China

Soil‐quality assessment provides a tool for evaluating the sustainability of alternative soil‐management practices. Understanding the effects of the long‐term use of chemical fertilizers on soil quality is essential for sustaining soil productivity. The cumulative effect of a 17‐y‐old chemical‐fertilizer application on integrated soil quality was investigated in the surface (0–15 cm) and subsurface (15–30 cm) soils of a soy–broomcorn–millet cropping system with an experiment design of two factors with three levels for each factor. The treatments were N0P0, N0P1, N0P2, N1P0, N1P1 (local farmer' fertilization strategy), N1P2, N2P0, N2P1, N2P2, and a control NF. The objectives were to describe and quantify the effect of continuous applications of chemical fertilizer through soil‐quality index (SQI) and attempt to offer an efficient and appropriate nutrient‐supply strategy for the local region. Following 17 y of chemical fertilization, the SQI increased markedly in the studied soil layers, and soil chemical indicators changed more significantly than physical properties. The soil‐quality indicators in the surface soil layer were more variable and sensitive to fertilizer application than the subsurface layer. The indicators that sensitively responded to long‐term fertilization could be classified into three types: soil‐fertility indicators (soil organic matter [SOM], total P, and available N), soil‐texture indicators (clay, silt), and soil‐structure indicators (bulk density, mean weight diameter [MWD]). The simplified indicators (SOM, sand, available N, bulk density, and total P in the surface soil and SOM, MWD, and silt content in the subsurface soil) preferably reflected the status of the integrated soil quality as influenced by continuous fertilization. Among the fertilized treatments, the combined‐fertilizer treatments maintained a higher SQI than the single‐fertilizer treatments in the surface and subsurface soils. The N1P2 treatment maintained the highest SQI in both soil layers, followed by N1P1 treatment. However, for the slope cropland, given the relative costs, soil resource, and environmental protection, the traditional treatment of N1P1 may be the optimal fertilizer treatment in the local region.     

Long‐term effects of manure and fertilization on soil organic matter and quality parameters of a calcareous soil in NW China

Long‐term applications of inorganic fertilizers and farmyard manure influence organic matter as well as other soil‐quality parameters, but the magnitude of change depends on soil‐climatic conditions. Effects of 22 annual applications (1982–2003) of N, P, and K inorganic fertilizers and farmyard manure (M) on total organic carbon (TOC) and nitrogen (TON), light‐fraction organic C (LFOC) and N (LFON), microbial‐biomass C (MB‐C) and N (MB‐N), total and extractable P, total and exchangeable K, and pH in 0–20 cm soil, nitrate‐N (NO ‐N) in 0–210 cm soil, and N, P, and K balance sheets were determined using a field experiment established in 1982 on a calcareous desert soil (Orthic Anthrosol) at Zhangye, Gansu, China. A rotation of irrigated wheat (Triticum aestivum L.)‐wheat‐corn (Zea mays L.) was used to compare the control, N, NP, NPK, M, MN, MNP, and MNPK treatments. Annual additions of inorganic fertilizers for 22 y increased mass of LFON, MB‐N, total P, extractable P, and exchangeable K in topsoil. This effect was generally enhanced with manure application. Application of manure also increased mass of TOC and MB‐C in soil, and tended to increase LFOC, TON, and MB‐N. There was no noticeable effect of fertilizer and manure application on soil pH. There was a close relationship between some soil‐quality parameters and the amount of C or N in straw that was returned to the soil. The N fertilizer alone resulted in accumulation of large amounts of NO ‐N at the 0–210 cm soil depth, accounting for 6% of the total applied N, but had the lowest recovery of applied N in the crop (34%). Manure alone resulted in higher NO ‐N in the soil profile compared with the control, and the MN treatment had the highest amount of NO ‐N in the soil profile. Application of N in combination with P and/or K fertilizers in both manured and unmanured treatments usually reduced NO ‐N accumulation in the soil profile compared with N alone and increased the N recovery in the crop as much as 66%. The N that was unaccounted for, as a percentage of applied N, was highest in the N‐alone treatment (60%) and lowest in the NPK treatment (30%). In the manure + chemical fertilizer treatments, the unaccounted N ranged from 35% to 43%. Long‐term P fertilization resulted in accumulation of extractable P in the surface soil. Compared to the control, the amount of P in soil‐plant system was surplus in plots that received P as fertilizer and/or manure, and the unaccounted P as percentage of applied P ranged from 64% to 80%. In the no‐manure plots, the unaccounted P decreased from 72% in NP to 64% in NPK treatment from increased P uptake due to balanced fertilization. Compared to the control, the amount of K in soil‐plant system was deficit in NPK treatment, i.e., the recovery of K in soil + plant was more than the amount of applied K. In manure treatments, the recovery of applied K in crop increased from 26% in M to 61% in MNPK treatment, but the unaccounted K decreased from 72% in M to 37% in MNPK treatment. The findings indicated that integrated application of N, P, and K fertilizers and manure is an important strategy to maintain or increase soil organic C and N, improve soil fertility, maintain nutrients balance, and minimize damage to the environment, while also improving crop yield.     

长期不同培肥措施下玉米产量稳定性及棕壤氮素累积分布特征

  【目的】  研究长期不同培肥措施下玉米产量的稳定性、可持续性和土壤矿质氮累积分布、微生物量氮含量特征,为制定合理的施肥措施和保证东北棕壤地区农业的可持续绿色发展提供理论依据。  【方法】  棕壤肥料长期定位试验始于1979年。选取其中的12个处理:不施肥对照(CK)、单施氮肥(N)、氮磷肥配施(NP)、氮磷钾肥配施(NPK)、低量有机肥(M1)及其与化肥配施(M1N、M1NP和M1NPK)、高量有机肥(M2)及其与化肥配施(M2N、M2NP和M2NPK),分析长期施肥下玉米产量的变化,并于2018年在玉米收获期采集植株和土壤样品,阐明玉米地上部吸氮量变化,0—100 cm土层土壤矿质氮分布、累积及微生物量氮含量的差异。  【结果】  长期不同施肥下玉米产量呈波动变化,且在1979—1998年内玉米产量变化趋势较平稳,1999—2018年内变幅较大。M1NPK、M2NPK处理玉米平均产量最高,在试验前20年较NPK处理分别提高了10.3%、11.7%,后20年分别提高了17.1%、19.4%。随着试验年限增加,玉米产量的稳定性和可持续性增加,有机肥配施化肥各处理高于单施化肥处理,在试验前20年和后20年玉米产量的可持续性指数(SYI)介于0.43～0.58和0.50～0.67,低量有机肥配施处理高于高量有机肥配施处理。配施有机肥各处理肥料贡献率高于单施化肥处理,且试验后20年M1NPK处理肥料贡献率最高,达54%。施肥40年后(2018年)玉米地上部吸氮量以M1NPK处理最高(302 kg/hm2),与M2NPK处理差异不显著。配施低量有机肥玉米收获期80—100 cm土层土壤矿质氮含量较低,M1NPK处理 0—100 cm土层土壤矿质氮贮量为127 kg/hm2,显著低于M1N和M1NP处理。而高量有机肥配施各处理0—100 cm土层土壤矿质氮贮量较化肥试区和低量有机肥试区分别增加了324.5%和172.9%,增加了氮素损失风险。此外,长期配施有机肥处理0—40 cm土层土壤微生物量氮含量增加,但低量和高量有机肥试区各处理间差异不显著。  【结论】  长期不同培肥措施会影响玉米产量的稳定性和可持续性,改变土壤氮素分布和累积,进而影响玉米氮素吸收。低量有机肥(13.5 t/hm2)配施氮磷钾化肥可促进玉米生长和氮素吸收,降低0—100 cm土层土壤矿质氮贮量,降低氮素损失风险,增加微生物量氮含量,较高的微生物量氮又可作为有机氮库来增加土壤供氮并固持易损失的矿质氮和肥料氮,以保证玉米的高产稳产和环境友好。     

长期定位施肥对潮土磷素形态和有效性的影响

研究长期定位施肥对潮土各形态磷含量变化及磷有效性的影响,为潮土合理施用磷肥提供理论依据.长期定位施肥试验开始于1990年,设CK(不施肥)、N2(单施尿素)、N2P(不施钾肥)、N2K(不施磷肥)、N1PK(低量氮肥和磷钾肥)、N2PK(平衡施肥)、N3PK(中高量施肥)、N4PK(高量氮肥和磷钾肥)、N2PKM(化肥...     

施用方式和氮肥种类对砂姜黑土氮素迁移的影响

采用田间微区试验,在砂姜黑土中研究了施肥方式(上层12 cm土混施、土下12 cm点施、土下12 cm条施)和氮肥种类(尿素、磷酸氢二铵)对氮素垂直运移和水平迁移动态的影响。不同施用方式试验结果表明,在处理的90 d内,砂姜黑土中土壤NH_4~+-N和NO_3~–-N含量均呈现土下12 cm点施土下12 cm条施上层12 cm土混施的趋势。尿素在土下12 cm点施条件下,土壤NH_4~+-N主要集中在垂直方向6~18 cm土层和水平距离0~7 cm范围内;而NO_3~–-N的分布核心区土层超过21 cm,水平距离大于15 cm;NH_4~+-N和NO_3~–-N核心区浓度均随处理时间延长而明显下降。土下12 cm点施90 d后,尿素和磷酸铵的氮素养分在砂姜黑土中的横向移动距离为5~7 cm,垂直方向上养分主要集中在6~18 cm的土层范围;点施90 d时,磷酸铵处理在土下18 cm和水平距离12 cm处无机态氮(NH_4~+-N和NO_3~–-N)含量分别为148.9和77.4 mg/kg,其含量远大于尿素处理(96.3和53.2 mg/kg),而在施肥点两种氮肥处理土壤无机态氮含量差异更大,说明磷酸铵较尿素具有更高的保肥性。研究表明:点施延缓了NH_4~+-N向NO_3~–-N转化速率,提高了肥际养分供应浓度。结合作物生长和需肥特性,预示通过优化施肥位置和氮肥种类,采用一次施肥可以实现90 d持续供应高浓度养分以满足旱地作物生长发育的养分需求。     

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.     

RELATIVE RESPONSE OF FORAGE AND SEED YIELD OF ALFALFA TO SULFUR,PHOSPHORUS, AND POTASSIUM FERTILIZATION

A field experiment was conducted from 2000 to 2007 on three-year old alfalfa stand near Star City in northeastern Saskatchewan to determine the influence of balanced application of sulfur (S), phosphorus (P), or potassium (K) fertilizers on forage dry matter yield (DMY) and seed yield, protein concentration (PC) in forage, concentration and uptake of total nitrogen (N), P, K, S, and boron (B) in forage and seed, and residual soil extractable P, exchangeable K and sulfate-S. Appropriate application of S, P, or K fertilizer nutrients was required to obtain optimum yield, PC, and nutrient concentration and uptake, especially when alfalfa was grown for hay production. Yield response to fertilization was much more frequent and much higher when alfalfa was managed as hay compared to when managed for seed production. The results suggest the importance of proper fertilization in increasing longevity of alfalfa stands. Under both hay and seed plots, there was only a small increase in residual sulfate-S from S fertilization, but significant accumulation of extractable P mainly in the 0–15 soil layer from P application. There was relatively higher concentration of exchangeable K in soil in the seed plots than in hay plots. In hay plots, concentrations of residual exchangeable K in soil were negatively related to DMY, especially in 2007. The findings suggest that when a soil is testing low (or deficient) in a nutrient and alfalfa growth is reduced, then alfalfa producers should consider applying fertilizers to supply adequate amounts of nutrients that are lacking in the soil, especially for optimum forage production. However, it is still difficult to predict accurately if a profitable alfalfa seed yield response to fertilization would occur, particularly when soils are testing marginal in some nutrient levels and yields are negatively affected by abnormal weather conditions (drought soil moisture conditions reducing plant growth, wet, cloudy and cool weather conditions decreasing pollination activity and late summer and/or early autumn frost damage to seed formation) that often occur in the growing season in this region.     

Effects of Slow‐Release Fertilizers on Tomato Growth and Nitrogen Leaching

Tomatoes (Lycopersicon esculentum Mill.) were grown in 9.46‐L plastic pots in a glasshouse for evaluation of their growth and nitrogen (N) losses through leaching. Plants were fertilized with either ammonium nitrate (AN) or one of three slow‐release N fertilizers. The slow‐release N fertilizers were Georgia Pacific liquid 30‐0‐0 (L30), Georgia Pacific granular 42‐0‐0 (N42), and Georgia Pacific granular 24‐0‐0 (N24). Each fertilizer was applied at 112 low N rate (L) and 224 high N rate (H) kg N ha^?1. The pots were filled with either a sandy soil from Florida or a loam soil from Georgia. Increasing the N rate did not influence shoot biomass at 19 days after transplanting (DAT) and increased biomass production at 77 DAT. Shoot biomass differed significantly among fertilizer treatments. The accumulation of N in shoots was significantly influenced by fertilizer source, rate, and soil type. The plants grown in the loam soil accumulated significantly more N than those grown in the sandy soil with the same treatment. In the loam soil, the highest and lowest N accumulations occurred in the N42‐H and N24‐L treatments, respectively; and in the sandy soil the corresponding treatments were AN‐H and N24‐L. The amount of N leached varied with the different fertilizers, soils, and time. The net leaching of N ranged from ?0.4% to 6.3% of the fertilizer N applied for the loam soil and 6.5% to 32.9% for the sand soil. The net amount of N leached from the loam soil at both high and low application rates declined in the following order: AN > N24 > N42 > L30; the corresponding order for the sandy soil was AN‐H > N42‐H > L30‐H > N24‐H. L30 had the least leaching potential, and ammonium nitrate had the most. Slow‐release fertilizers had significantly less leaching N than did ammonia nitrate.     

优化施氮对设施番茄土壤硝态氮残留及土壤氮平衡的影响

[目的]设施蔬菜生产中普遍存在氮肥施用过量、有机无机肥配合不合理以及灌水频繁等问题,我们通过田间试验研究了优化施氮模式对番茄产量、土壤硝态氮残留和氮平衡的影响,为蔬菜生产优质高效和减量优化施肥提供科学依据.[方法]试验在山东惠民蔬菜大棚内进行,灌水量为农户平均灌水量(482.5 mm)的80％(390 mm),供试蔬菜...     

不同氮磷钾肥对土壤pH和镉有效性的影响

采用土壤培养方法研究了不同氮、磷、钾肥对土壤pH和镉有效性的影响。结果表明,在培养60 d时,所有氮肥处理均降低了土壤pH,增加了Cd的提取量;但高量尿素和氯化铵处理土壤pH降低最多,提取的Cd也最多;硫酸铵提取的Cd较对照增加最小。所有磷肥处理均引起土壤pH小幅降低,但对土壤Cd提取量的影响以普钙稍大。3种钾肥处理均降低了土壤pH,其中氯化钾在0 d时提取的Cd在所有钾肥处理中为最高,其提取能力15 d后逐渐消失,试验结束时所有钾肥处理对Cd提取量均低于对照。本研究进一步表明,在土壤Cd含量处于污染临界值附近或已受Cd污染的土壤上,应避免施用高量的酸性肥料如尿素、氯化铵、普钙,以及其他酸性物料。在常用磷、钾肥中,磷酸二铵和硫酸钾在Cd污染土壤上施用更为适合。     

稳定性氮肥减施对春玉米氮素吸收及土壤无机氮供应的影响

  【目的】  稳定性氮肥减量施用在玉米上表现出良好的稳产和增产效果,但缺乏针对不同土壤和气候条件下春玉米生产的推荐施用量。为此,我们在辽中、辽南地区春玉米上开展了稳定性氮肥一次性施用最佳用量试验。  【方法】  2017年在辽宁省沈阳市和海城市两地开展田间试验。供试稳定性氮肥中同时添加了脲酶抑制剂和硝化抑制剂。两个试验区均设置了不施氮处理 (CK)、普通尿素常规施氮量 (CK1) 和普通尿素减氮10%对照 (CK2)。沈阳试验区设置稳定性氮肥比其CK1 (244 kg/hm2) 分别减氮10%、15%、20% 3个处理 (S1、S2、S3),海城试验区设置比其CK1 (217 kg/hm2) 分别减氮10%、15% 2个处理 (S1、S2)。采集玉米生长季内各生育时期的土壤样品和植株样品,测定土壤无机氮含量和植株不同部位养分含量,每个小区单独采收,记录产量。  【结果】  与CK1相比,稳定性氮肥能显著提高玉米产量 (P < 0.05),且以减氮15%的S2处理肥效稳定,沈阳试验较CK1增产、增收幅度分别为7.5%、1795元/hm2,较CK2增产、增收幅度分别为11.1%、2808元/hm2;而海城试验产量与CK1没有显著区别,收入减少184元/hm2,与CK2相比,增产19.5%,增收2685元/hm2。与CK1相比,稳定性氮肥处理氮素表观利用率、氮肥农学效率和氮肥偏生产力依次提高10.4%～12.4%、3.4%～6.2%和6.5%～10.8%;与CK2相比,分别提高10.2%～12.2%、3.3%～6.1%和3.3%～7.6%。与普通尿素相比,施用稳定性氮肥显著提高了玉米生育中后期植株氮素吸收强度,稳定性氮肥各处理氮素总积累量表现为S2 > S1 > S3 > CK1 > CK2。土壤无机氮含量主要在0—20、20—40 cm土层表现出较大差异,总体上稳定性氮肥处理 (S1、S2、S3) 耕层土壤无机氮含量在玉米生育前期 (苗期、拔节期) 低于普通尿素处理 (CK1、CK2),在玉米生育中后期 (大喇叭口期至成熟期) 0—40 cm土层无机氮含量显著高于普通尿素处理,但总体上无机氮含量在0—40 cm土层中变化幅度较普通尿素处理平缓。  【结论】  稳定性氮肥减施可以维持或提高土壤无机氮含量。在沈阳试验点,稳定性尿素施氮量减少15％时,玉米的产量和经济效益、氮素累积总量和氮素表观利用率、氮肥农学效率和氮肥偏生产力等都最高;而在海城试验点,由于普通尿素投入量相对较低,最佳稳定性尿素推荐量为减氮10%。     

施肥对日光温室黄瓜和土壤硝酸盐含量的影响

通过田间试验研究了不同施肥对日光温室黄瓜NO2--N和NO3--N含量和土壤NO3--N以及黄瓜产量的影响。结果表明,在黄土高原黄绵土上,施N400kg.hm2和P2O5250kg.hm2,黄瓜生长期间,NO3--N含量变化与黄瓜的生长发育阶段关系密切,黄瓜结瓜前020和2040cm土层NO3--N含量较高,随黄瓜生长速度加快和结瓜盛期的到来,土壤NO3--N含量降低;黄瓜收获后,NO3--N含量又有增加。不同施肥种类比较,施用化肥40160cm土层NO3--N的累积和淋洗量最大,施用沼肥其累积和淋洗量小于施用化肥,而施用有机肥(牛粪)NO3--N的累积和淋洗量小于施用沼肥。采用叶面喷施尿素和有机钾肥,可以减少化肥和有机肥用量,从而降低土壤剖面0200cmNO3--N的累积。使用沼肥、叶面肥的黄瓜产量都明显高于不施肥和NP化肥处理。     

长期不同施肥处理对棕壤氮储量的影响

为揭示施肥对棕壤氮素状况的影响,利用29年长期肥料定位试验,研究了不同施肥处理条件下土壤全氮在0―60 cm土层的分布特征,并在此基础上计算0―60cm土层氮库的储量变化。结果表明,不同施肥处理土壤全氮含量、C/N比值均随土层深度增加而降低,其影响主要表现在表层;而对0―60cm 土层全氮储量有显著性影响（P0.05）。长期不同施肥处理后土壤全氮及其储量变化趋势是:高量有机肥区＞低量有机肥区＞化肥区＞无肥区＞试验前（1979年）,特别是高量有机肥和化肥配合施用效果最显著;单施化肥处理土壤全氮含量和储量虽有缓慢提高,但差异不显著。说明土壤氮素含量的提高与施肥措施密切相关,有机肥和化肥配合施用能提高土壤全氮含量和储量,是维持土壤肥力的最优施肥方式。     

Ammonia volatilization from Vertisols

Farmers want to minimize losses of nitrogen (N) by volatilization of ammonia when adding fertilizers and improve fertilizer recovery of N by plants. We aimed to quantify the losses of N through NH₃ volatilization as affected by soil moisture content, type of fertilizer, and placement method in Vertisols in Kenya, and conducted three experiments for the purpose under controlled conditions in the laboratory. We found that NH₃-N losses were greatest at 80% water holding capacity, which we ascribed to the ready availability of water to dissolve the fertilizer at that water content. The soil's cation exchange capacity (CEC) did not influence volatilization, whereas the soil's pH indicated the potential of the soil to volatilize ammonia. Ammonia losses from the fertilizers were in the order urea > ammonium sulphate > ammonium nitrate applied. Incorporating fertilizer within the 0–5 cm soil layer more than halved NH₃ volatilization but did not prevent it completely. These results indicate that soil pH, rather than CEC, is the main inherent characteristic influencing ammonia volatilization from Vertisols. Ammonium-based fertilizers should be incorporated within the 0–5 cm soil layer, or preferably somewhat deeper, to avoid losses via NH₃ volatilization, particularly in alkaline soils. Nitrate fertilizers are preferable to urea where the risks of NH₃ volatilization are large, provided due consideration is given to denitrification risks.     

Potassium‐fertilizer management in winter oilseed‐rape production in China

Optimal potassium (K) fertilization is beneficial for oilseed‐rape (Brassica napus L.) yield and quality. However, the discrepancy between the high K demand of winter oilseed rape and low soil fertility and insufficient potassium input has limited the sustainable development of oilseed‐rape production. A series of on‐farm experiments in the key winter oilseed‐rape domains of China was conducted from 2004 to 2010 to evaluate K‐fertilizer management for winter oilseed rape. Currently, the average NH₄OAc‐extractable K content in the 0–20 cm soil layer is 89.1 mg kg^–1 indicative of “slight deficiency”. In addition, farmers in China usually fail to use sufficient K fertilizer in oilseed‐rape production, the average mineral‐potassium‐fertilizer input in 2010 being only 35 kg K ha^–1, far lower than the recommended rate of potassium for winter oilseed rape. Adequate potassium fertilization significantly raises seed yield. The average yield‐increase rate for the major production regions due to K‐fertilizer application was 18.5%, and the average K fertilizer–use efficiency 36.1%. Based on the negative correlation between yield response to potassium fertilization and available soil K content, a soil‐K‐test index was established for winter oilseed rape with a threshold value for NH₄OAc‐extractable soil K of 135 mg kg^–1. When available soil K‐content is below this threshold value, more K fertilizer should be applied to achieve high seed yield and to increase soil fertility. The major challenge for K‐fertilizer management in winter oilseed‐rape production in China will be to guide farmers in the different regions in making reasonable use of K fertilizer through soil K‐testing technology in order to maintain both seed yield and soil fertility.