Glyphosate applied preharvest induces shikimic acid accumulation in hard red spring wheat (Triticum aestivum)

Glyphosate is a nonselective herbicide used as a harvest aid in a variety of crops. Glyphosate is absorbed into the foliage and translocated to metabolically active regions in the plant where it interferes with the shikimic acid pathway. Experiments were conducted to determine the accumulation and distribution of shikimic acid in wheat treated with glyphosate at soft and hard dough stages of kernel development and to determine the fate of shikimic acid during milling and bread making. Elevated levels of shikimic acid were detected throughout the wheat plant. Shikimic acid concentrations peaked 3-7 days after treatment and then declined until harvest. Shikimic acid content was 3-fold greater in flour and 2-fold greater in the bread derived from treated wheat than nontreated wheat. Similarly, elevated levels of shikimic acid were found in the crumbs and crust of bread made with flour from glyphosate treated wheat. Glyphosate applied preharvest resulted in shikimic acid accumulation in hard red spring wheat and subsequent end-use products.     

Aminomethylphosphonic acid, a metabolite of glyphosate, causes injury in glyphosate-treated, glyphosate-resistant soybean

Glyphosate-resistant (GR) soybean [Glycine max (L.) Merr.] was developed by stable integration of a foreign gene that codes insensitive enzyme 5-enolpyruvylshikimate-3-phosphate synthase, an enzyme in the shikimate pathway, the target pathway of glyphosate. Application of glyphosate to GR soybean results in injury under certain conditions. It was hypothesized that if GR soybean is completely resistant to the glyphosate, injury could be caused by a metabolite of glyphosate, aminomethylphosphonic acid (AMPA), a known phytotoxin. Glyphosate and AMPA effects on one- to two-trifoliolate leaf stage (16-18-days old) GR and non-GR soybean were examined in the greenhouse. In GR soybean, a single application of glyphosate-isopropylammonium (1.12-13.44 kg/ha) with 0.5% Tween 20 did not significantly reduce the chlorophyll content of the second trifoliolate leaf at 7 days after treatment (DAT) or the shoot dry weight at 14 DAT compared with Tween 20 alone. A single application of AMPA (0.12-8.0 kg/ha) with 0.5% Tween 20 reduced the chlorophyll content of the second trifoliolate leaf by 0-52% at 4 DAT and reduced shoot fresh weight by 0-42% at 14 DAT in both GR and non-GR soybeans compared with Tween 20 alone. AMPA at 0.12 and 0.50 kg/ha produced injury in GR and non-GR soybean, respectively, similar to that caused by glyphosate-isopropylammonium at 13.44 kg/ha in GR soybean. AMPA levels found in AMPA-treated soybean of both types and in glyphosate-treated GR soybean correlated similarly with phytotoxicity. These results suggest that soybean injury to GR soybean from glyphosate is due to AMPA formed from glyphosate degradation.     

Tolerance and accumulation of shikimic acid in response to glyphosate applications in glyphosate-resistant and nonglyphosate-resistant cotton (Gossypium hirsutum L.).

Measurement of shikimic acid accumulation in response to glyphosate inhibition of 5-enolpyruvylshikimate-3-phosphate synthase is a rapid and accurate assay to quantify glyphosate-induced damage in sensitive plants. Two methods of assaying shikimic acid, a spectrophotometric and a high-performance liquid chromatography (HPLC) method, were compared for their accuracy of recovering known amounts of shikimic acid spiked into plant samples. The HPLC method recovered essentially 100% of shikimic acid as compared with only 73% using the spectrophotometric method. Relative sensitivity to glyphosate was measured in glyphosate-resistant (GR) and non-GR cotton leaves, fruiting branches, and squares (floral buds) by assaying shikimic acid. Accumulation of shikimic acid was not observed in any tissue, either GR or non-GR, at rates of 5 mM glyphosate or less applied to leaves. All tissues of non-GR plants accumulated shikimic acid in response to glyphosate treatment; however, only fruiting branches and squares of GR plants accumulated a slight amount of shikimic acid. In non-GR cotton, fruiting branches and squares accumulated 18 and 11 times, respectively, more shikimic acid per micromolar of translocated glyphosate than leaf tissue, suggesting increased sensitivity to glyphosate of reproductive tissue over vegetative tissue. GR cotton leaves treated with 80 mM of glyphosate accumulated 57 times less shikimic acid per micromolar of translocated glyphosate than non-GR cotton but only 12.4- and 4-fold less in fruiting branches and squares, respectively. The increased sensitivity of reproductive structures to glyphosate inhibition may be due to a higher demand for shikimate pathway products and may provide an explanation for reports of fruit abortion from glyphosate-treated GR cotton.     

干旱及复水条件下草甘膦对抗草甘膦大豆幼苗渗透调节物质和莽草酸含量的影响

为探明干旱胁迫及复水条件下不同剂量草甘膦对抗草甘膦大豆(RR1)幼苗叶片渗透调节物质、莽草酸(shikimic acid, SA)含量及根系活力的影响,采用盆栽试验,在大豆的第3复叶期进行水分胁迫5d和除草剂草甘膦处理,研究RR1幼苗叶片可溶性蛋白(soluble protein, SP)、可溶性糖(soluble sugar, SS)、游离脯氨酸(free praline, FP)、莽草酸(shikimic acid, SA)含量和根系活力(RA)的变化。结果表明,干旱胁迫前期RR1叶片的SP含量随草甘膦剂量的增加呈先升高后降低趋势,0.46kg/hm2叶片SP的含量最高,胁迫后期SP含量随草甘膦剂量的增加而降低;SS、FP和SA含量随草甘膦剂量的增加和胁迫时间的延长而增加,RA随草甘膦剂量的增加和胁迫时间的延长而降低。复水12d后,不同剂量草甘膦处理的各指标均有所恢复。干旱条件下,经草甘膦处理的RR1叶片的SP含量和RA低于草甘膦在正常水分条件下的处理,而SS、FP和SA含量相反。相关性分析表明,FP和SA含量与草甘膦剂量的相关关系最明显;而SS和SA含量与干旱胁迫时间的相关关系最明显。说明正常水分条件下,草甘膦对RR1幼苗造成的伤害经过一段时间后有所缓解;干旱胁迫加剧了草甘膦对RR1幼苗叶片渗透调节物质、莽草酸含量和根系活力的影响。抗草甘膦大豆主要通过积累FP、SS和SA对草甘膦和干旱胁迫做出响应。     

Simulated glyphosate drift influences nitrate assimilation and nitrogen fixation in non-glyphosate-resistant soybean

Nontarget injury from glyphosate drift is a concern among growers using non-glyphosate-resistant (non-GR) cultivars. The effects of glyphosate drift on nitrate assimilation and nitrogen fixation potential, nodule mass, and yield of non-GR soybean were assessed in a field trial at Stoneville, MS. A non-GR soybean cultivar 'Delta Pine 4748S' was treated with glyphosate at 12.5% of use rate of 0.84 kg of active ingredient/ha at 3 (V2), 6 (V7), and 8 (R2, full bloom) weeks after planting (WAP) soybean to simulate glyphosate drift. Untreated soybean was used as a control. Soybeans were sampled weekly for 2 weeks after each glyphosate treatment to assess nitrate assimilation and N2 fixation potential. Nitrate assimilation was assessed using in vivo nitrate reductase assay in leaves, stems, roots, and nodules. Nitrogen fixation potential was assessed by measuring nitrogenase activity using the acetylene reduction assay (ARA). Nitrogen content of leaves, shoots, and seed and soybean yield were also determined. In the first sampling date (4 WAP), glyphosate drift caused a significant decrease in NRA in leaves (60%), stems (77%), and nodules (50%), with no decrease in roots. At later growth stages, NRA in leaves was more sensitive to glyphosate drift than stems and roots. Nitrogenase activity was reduced 36-58% by glyphosate treatment at 3 or 6 WAP. However, glyphosate treatment at 8 WAP had no effect on nitrogenase activity. Nitrogen content was affected by glyphosate application only in shoots after the first application. No yield, seed nitrogen, protein, or oil concentration differences were detected. These results suggest that nitrate assimilation and nitrogen fixation potential were significantly reduced by glyphosate drift, with the greatest sensitivity early in vegetative growth. Soybean has the ability to recover from the physiological stress caused by glyphosate drift.     

冀东野生大豆对草甘膦的耐性鉴定及耐性机制初步研究

为筛选耐草甘膦野生大豆种质并了解其耐性机制,本试验对采集于冀东地区的862份野生大豆进行了草甘膦的耐性鉴定。在草甘膦处理后,测定了高耐和敏感材料的莽草酸、丙二醛和叶绿素含量,过氧化物酶(POD)、过氧化氢酶(CAT)和超氧化物歧化酶(SOD)活性,以及草甘膦相关基因EPSPS表达量。结果显示,喷施草甘膦后,862份野生大豆材料中,药害等级在4级以上的材料占82.84%,3级占9.51%,2级占4.87%,1级占2.78%。筛选到高耐草甘膦的野生大豆材料Yong-33,其在1.125 kg a.i·hm^-2 草甘膦处理后植株存活率达到96.67%。经草甘膦处理后,与对照相比,高耐材料的叶绿素、丙二醛和莽草酸含量在检测的各时间点均无显著差异,敏感材料叶绿素含量显著降低,丙二醛和莽草酸含量显著升高;高耐材料POD、CAT和SOD活性以及EPSPS基因表达量均显著升高,而敏感材料酶活性及EPSPS基因表达量无显著差异。以上结果表明,野生大豆中存在高耐草甘膦的种质资源,在草甘膦处理后其植株内活性氧清除酶系活性升高,EPSPE基因上调表达,推测这是野生大豆对草甘膦耐性较好的原因。本研究筛选到的耐草甘膦野生大豆材料可为培育耐草甘膦栽培大豆新品种提供种质资源。     

New insights on glyphosate mode of action in nodular metabolism: Role of shikimate accumulation

The short-term effects of the herbicide glyphosate (1.25-10 mM) on the growth, nitrogen fixation, carbohydrate metabolism, and shikimate pathway were investigated in leaves and nodules of nodulated lupine plants. All glyphosate treatments decreased nitrogenase activity rapidly (24 h) after application, even at the lowest and sublethal dose used (1.25 mM). This early effect on nitrogenase could not be related to either damage to nitrogenase components (I and II) or limitation of carbohydrates supplied by the host plant. In fact, further exposure to increasing glyphosate concentrations (5 mM) and greater time after exposure (5 days) decreased nodule starch content and sucrose synthase (SS; EC 2.4.1.13) activity but increased sucrose content within the nodule. These effects were accompanied by a great inhibition of the activity of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31). There were remarkable and rapid effects on the increase of shikimic and protocatechuic (PCA) acids in nodules and leaves after herbicide application. On the basis of the role of shikimic acid and PCA in the regulation of PEPC, as potent competitive inhibitors, this additional effect provoked by glyphosate on 5-enolpyruvylshikimic-3-phosphate synthase enzyme (EPSPS; EC 2.5.1.19) inhibition would divert most PEP into the shikimate pathway, depriving energy substrates to bacteroids to maintain nitrogen fixation. These findings provide a new explanation for the effectiveness of glyphosate as a herbicide in other plant tissues, for the observed differences in tolerance among species or cultivars, and for the transitory effects on glyphosate-resistant transgenic crops under several environmental conditions.     

Empirical analysis and prediction of nitrate loading and crop yield for corn-soybean rotations

Nitrate nitrogen losses through subsurface drainage and crop yield are determined by multiple climatic and management variables. The combined and interactive effects of these variables, however, are poorly understood. Our objective is to predict crop yield, nitrate concentration, drainage volume, and nitrate loss in subsurface drainage from a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation as a function of rainfall amount, soybean yield for the year before the corn-soybean sequence being evaluated, N source, N rate, and timing of N application in northeastern Iowa, U.S.A. Ten years of data (1994-2003) from a long-term study near Nashua, Iowa were used to develop multivariate polynomial regression equations describing these variables. The regression equations described over 87, 85, 94, 76, and 95% of variation in soybean yield, corn yield, subsurface drainage, nitrate concentration, and nitrate loss in subsurface drainage, respectively. A two-year rotation under average soil, average climatic conditions, and 125 kg N/ha application was predicted to loose 29, 37, 36, and 30 kg N/ha in subsurface drainage for early-spring swine manure, fall-applied swine manure, early-spring UAN fertilizer, and late-spring split UAN fertilizer (urea ammonium nitrate), respectively. Predicted corn yields were 10.0 and 9.7 Mg/ha for the swine manure and UAN sources applied at 125 kg N/ha. Timing of application (i.e., fall or spring) did not significantly affect corn yield. These results confirm other research suggesting that manure application can result in less nitrate leaching than UAN (e.g., 29 vs. 36 kg N/ha), and that spring application reduces nitrate leaching compared to fall application (e.g., 29 vs. 37 kg N/ha). The regression equations improve our understanding of nitrate leaching; offer a simple method to quantify potential N losses from Midwestern corn-soybean rotations under the climate, soil, and management conditions of the Nashua field experiment; and are a step toward development of easy to use N management tools.     

氮素营养对黄土高原旱地玉米产量、品质及水分利用效率的影响

20022003年在陇东旱塬的甘肃省农科院镇原旱农试验基地秋覆膜玉米地上进行了不同施氮量对旱地玉米产量、品质及水分利用效率影响试验。结果表明,不同年份氮肥用量对不同类型玉米品种产量均有极显著差异,但同一年份不同类型玉米品种或不同年份同一类型玉米品种产量无显著性差异。玉米产量随着施氮量的增加而提高,且每公斤氮肥增产量、水分利用效率(WUE)、光合速率(Pn)等均以中氮(N.180.kg/hm2)时最大。在中等氮肥水平以下,玉米子粒粗脂肪、粗蛋白和淀粉含量随施氮量的增加而提高,同时,歉水年份有利于容重、粗蛋白和淀粉的累积。     

第二复叶期喷施草甘膦对抗草甘膦大豆生理指标及产量构成的影响

采用随机区组的设计方法,在第二复叶期喷施不同剂量的农达41%水剂,研究了其对不同大豆品种叶片叶绿素含量指数、莽草酸含量、SOD活性等生理指标和产量构成的影响。结果表明:喷施农达41%水剂可以降低抗草甘膦大豆RR1、RR2和普通大豆晋大75、晋豆27叶片的叶绿素指数,而抗草甘膦大豆RR1和RR2的降低幅度远小于普通大豆晋大75和晋豆27。抗草甘膦大豆可以忍受较高剂量(7.38kg/hm2)的农达41%水剂,普通大豆晋大75和晋豆27在较低剂量(0.46kg/hm2)时体内莽草酸就大量积累。随着农达41%水剂剂量的增加,抗草甘膦大豆体内的SOD活性也提高,而普通大豆随着剂量的增加,体内SOD活性受到抑制。RR2和RR1分别以农达41%剂量为1.85kg/hm2和0.92kg/hm2时的各产量构成因素值最高,晋大75和晋豆27以0.46kg/hm2时最高。作物不同品种对草甘膦的敏感程度不同,对农达41%水剂的抗性抗草甘膦大豆大于普通大豆,RR2的抗性和RR1相差不大,晋大75(早熟)的抗性和晋豆27(晚熟)相差不大。在这3个生理指标中,叶片莽草酸含量和叶绿素含量指数的变化比SOD活性敏感。     

Nitrogen metabolism and seed composition as influenced by glyphosate application in glyphosate-resistant soybean

Previous research has demonstrated that glyphosate can affect nitrogen fixation or nitrogen assimilation in soybean. This 2-year field study investigated the effects of glyphosate application of 1.12 and 3.36 kg of ae ha(-1) on nitrogen metabolism and seed composition in glyphosate-resistant (GR) soybean. There was no effect of glyphosate application on nitrogen fixation as measured by acetylene reduction assay, soybean yield, or seed nitrogen content. However, there were significant effects of glyphosate application on nitrogen assimilation, as measured by in vivo nitrate reductase activity (NRA) in leaves, roots, and nodules, especially at high rate. Transiently lower leaf nitrogen or (15)N natural abundance in high glyphosate application soybean supports the inhibition of NRA. With the higher glyphosate application level protein was significantly higher (10.3%) in treated soybean compared to untreated soybean. Inversely, total oil and linolenic acid were lowest at the high glyphosate application rate, but oleic acid was greatest (22%) in treated soybean. These results suggest that nitrate assimilation in GR soybean was more affected than nitrogen fixation by glyphosate application and that glyphosate application may alter nitrogen and carbon metabolism.     

灌水对水肥一体化制种玉米产量和水分利用效率的影响

研发和推广应用高效节水技术是提升扬黄灌区制种玉米产量、支撑制种玉米产业增效和持续发展的重要途径。为了给建立制种玉米水肥一体化技术模式下的科学高效灌溉制度提供科学依据。在甘肃扬黄灌区滴灌水肥一体化条件下,研究了不同灌溉定额和灌水次数下制种玉米的产量表现和水分利用效果。结果表明,灌溉定额从2 250 m3/hm2增加到3 000 m3/hm2时,制种玉米增产幅度达33.84%,但灌溉定额高于3 000 m3/hm2并继续增大时增产效果不明显,生育期耗水量增加,水分利用效率降低明显。灌水次数从10次增加至20次时,制种玉米产量及水分利用效率均呈降低趋势,灌水次数多于15次并继续增加时,制种玉米减产显著。灌水次数和灌溉定额之间不存在互作效应。在灌溉定额偏低条件下,增加灌水次数会造成制种玉米严重减产。当生育期灌溉定额为3 000 m3/hm2、灌水次数为10次时,折合产量较高,为7 386.9 kg/hm2,较其余处理增产-2.77%～93.58%;水分利用效率最高,为17.83 kg/(mm·hm2),较其余处理提高5.32%～78.30%;种植纯收益较高,为29 683.6元/hm2,较其余处理增加-511.8～20 675.4元/hm2;产投比最高,为3.03,较其余处理增加0.07～1.38。可见,灌水10次、灌溉定额为3 000 m3/hm2时灌溉水利用效果相对优化。     

不同氮肥用量及其生育期分配比例对四川丘陵区带状种植小麦氮素利用的影响

【目的】带状种植是四川小麦的典型种植方式,主要分布在丘陵旱地,与玉米构成小麦/玉米复合种植系统。本文通过两年大田试验研究了不同氮肥用量和生育期分配比例对四川丘陵旱地带状种植小麦氮素吸收累积、 分配与转运的影响,以及氮素利用效率和土壤氮残留问题,筛选适合于该地区带状种植小麦的适宜氮肥用量和分配比例,为生产应用提供理论和技术依据。【方法】试验在四川省仁寿县进行,试验材料为四川主推品种川麦42,带状种植(即2 m为一带,种5行小麦,行距20 cm,小麦幅宽80 cm,预留行1.2 m),2BSF-4-5A型谷物播种机播种,密度150104 plant/hm2。试验采用二因素裂区设计,施氮量为主区,设N 90(N1)、 135(N2)、 180(N3)、 225(N4) kg/hm2 4个水平;生育期分配比例为裂区,设基肥一次性施入(R1)、 底肥:苗肥=7:3(R2)、 底肥:拔节肥=7:3(R3)和底肥:苗肥:拔节肥:孕穗肥=5:1:2:2(R4)4个水平,并以不施肥(CK)为对照。【结果】 1)施用氮肥后收获期地上部植株总吸氮量显著提高,开花期植株各营养器官氮素积累量、 成熟期叶和茎鞘中氮素残留量以及转运氮的贡献率均随施氮量的增加而增加,而花后氮素同化量及其对籽粒氮的贡献率随施氮量增加呈先增后降的趋势,在施氮量为N 135 kg/hm2时达最大。底肥:拔节肥=7:3的施氮方式有利于提高花后氮素同化量及其对籽粒氮贡献率,而底肥:苗肥:拔节肥:孕穗肥=5:1:2:2的施氮方式有效地促进了花前贮存氮素向籽粒转移,同时也增加了成熟期氮素在营养器官中的残留,降低了氮素在籽粒中的分配比例;2)氮利用效率和植株氮生产力均随施氮量的增加而降低,土壤中残留的全氮、 NO-3-N及NH+4-N含量则随施氮量的增加而增加;在施氮量较高(N 180～225 kg/hm2)的条件下,底肥一次施极大地增加了土壤中氮的残留,且随施氮量增加,拔节期一次性追肥土壤中氮残留也增加,氮肥分次追施和加大分配比例能够有效降低土壤中的氮素残留; 3)在四川丘陵旱地套作条件下,施氮量和籽粒产量的关系可用二次曲线方程来拟合,平均每生产100 kg籽粒需N 3.6 kg;施氮量为180 kg/hm2、 分配比例为底肥:拔节肥=7:3时籽粒产量最高,可达4800 kg/hm2(第二年4706 kg/hm2),较CK增产27.6%(第二年增产25.6%)。【结论】综合考虑小麦籽粒产量、 氮吸收利用特性以及土壤中残留氮量,在保证获得较高小麦产量(4650 kg/hm2以上)的前提下,应适当减少氮肥用量,采取氮肥后移及分次施用的方式。本试验条件下带状种植小麦推荐的氮肥用量为N 135～180 kg/hm2,分配比例为底肥:拔节肥=7:3。     

Manganese in RR Cotton as Affected by Glyphosate

There is evidence that glyphosate application in soybean tolerant to herbicides could interfere in the manganese (Mn) nutrition of the crop, but there is no information on this effect in cotton plants. This study aimed at assessing manganese accumulation and distribution in cotton as affected by glyphosate application. The experiment was conducted in nutrient solution with four Mn concentrations and two cotton cultivars: conventional NuOpal and NuOpal tolerant to glyphosate (RR). Glyphosate was applied or not to the tolerant cultivar. The inclusion of the glyphosate resistance gene in cotton and herbicide, application increased shikimic acid (ShA) concentration in the plants. Glyphosate application decreased cotton leaf area and the dry matter production of the plant structures. The adverse effects of glyphosate were not overcome with higher Mn rates in the solution.     

Evaluating and predicting agricultural management effects under tile drainage using modified APSIM

An accurate and management sensitive simulation model for tile-drained Midwestern soils is needed to optimize the use of agricultural management practices (e.g., winter cover crops) to reduce nitrate leaching without adversely affecting corn yield. Our objectives were to enhance the Agricultural Production Systems Simulator (APSIM) for tile drainage, test the modified model for several management scenarios, and then predict nitrate leaching with and without winter wheat cover crop. Twelve years of data (1990-2001) from northeast Iowa were used for model testing. Management scenarios included continuous corn and corn-soybean rotations with single or split N applications. For 38 of 44 observations, yearly drain flow was simulated within 50 mm of observed for low drainage (< 100 mm) or within 30% of observed for high drain flow. Corn yield was simulated within 1500 kg/ha for 12 of 24 observations. For 30 of 45 observations yearly nitrate-N loss in tile drains was simulated within 10 kg N/ha for low nitrate-N loss (< 20 kg N/ha) or within 30% of observed for high nitrate-N loss. Several of the poor yield and nitrate-N loss predictions appear related to poor N-uptake simulations. The model accurately predicted greater corn yield under split application (140-190 kg N/ha) compared to single 110 kg N/ha application and higher drainage and nitrate-N loss under continuous corn compared to corn/soybean rotations. A winter wheat cover crop was predicted to reduce nitrate-N loss 38% (341 vs. 537 kg N/ha with and without cover) under 41-years of corn-soybean rotations and 150 kg N/ha applied to corn. These results suggest that the modified APSIM model is a promising tool to help estimate the relative effect of alternative management practices under fluctuating high water tables.     

Effect of harvest method and feed value on the economic optimum nitrogen rate for corn

Abstract

Consideration of the harvest method and protein content of corn grain and forage may be important variables for estimating Economic Optimum Nitrogen (N) (EON) rates for corn. Corn grain yield, forage yield, grain protein and forage protein data from twenty five N response experiments conducted in Pennsylvania were analyzed to determine the effect of harvest method and a price adjustment based on grain and forage protein content on the EON rate. The value of the protein in this study was assumed to be that of substituting soybean meal in the ration for growing beef cattle or dairy cattle. There was no difference in the EON for corn harvested for grain compared to corn harvested for forage when the protein content was not considered. When price adjustments were made for the protein content of the grain and forage, the EON rates increased 10 kg/ha for grain and 22 kg/ha for forage. With the protein price adjustments, the EON was 14 kg/ha higher for forage than grain. These results support the recommendation for higher N rates for corn harvested for forage, where the protein value of the forage is considered, compared to corn harvested for grain. In situations where the amino acid composition of the grain is important, such as for poultry or swine, or where urea or anhydrous ammonia can be substituted in the ration for protein, it is unlikely that a higher EON level would result when protein content or quality is considered.     

不同种植模式对土壤矿质氮累积量的影响—以北京通州区为例

运用对通州区调查资料和试验结果,分析了不同典型种植模式对0—2 m土壤矿质氮累积量的影响。结果表明,不同种植模式对0—2 m土壤矿质氮提取利用能力顺序为:向日葵—向日葵﹥冬小麦—夏玉米（玉米秸秆还田）﹥冬小麦—夏玉米（玉米秸秆不还田）﹥冬小麦—大豆﹥玉米—玉米。在大田作物生产中,应进行合理的作物轮作、增加地面覆盖度、轮作中加入有固氮能力的豆科作物、注重与根系发达或深根作物进行轮作,能有效地提取利用土壤深层NO3--N,并能有效减少氮肥向土壤下层的淋洗。蔬菜生产田0—2 m土壤含有较高的NO3--N和NH4+-N,累积量达1935.03 kg/hm2和201.8 kg/hm2,因此,应通过减少氮肥投入量,优化轮作种植模式以提高作物对深层土壤NO3--N的回收利用。     

施氮量对白萝卜硝酸盐含量和土壤硝态氮淋溶的影响

在保护地栽培条件下,通过6个施氮水平的田间小区试验,结合土层原位渗滤装置,研究了施用氮肥对白萝卜（Raphanus sativus L.）产量和硝酸盐含量及土壤硝态氮淋溶的影响。结果表明,施氮处理白萝卜产量比不施氮处理仅增加6.04%～10.92%,当尿素氮施用量大于N 100 kg/hm2时,增产幅度开始下降。不同施氮处理白萝卜产量没有显著差异,说明在土壤基础肥力较高的情况下,增施氮肥不能明显提高白萝卜的产量;单施有机肥白萝卜体内硝酸盐含量为 196.86 mg/kg,比不施氮处理降低 5.08%。在此基础上加施尿素后,硝酸盐含量随氮肥施用量的增加显著升高（p0.05）;0—100cm土壤剖面硝态氮累积量随氮肥施用量的增加而增加,且与氮肥施用量显著正相关（r=0.993, r0.01=0.917）;白萝卜生长期间收集到的土壤淋溶液中硝态氮浓度较高,平均为32.88 mg/L,硝态氮的淋失量为 4.42～6.14 kg/hm2,不同施氮量处理之间没有显著差异。     

Early-season nutrient competition between weeds and soybean

Abstract

Soybean [Glycine max (L.) Merr.] yield losses may be attributable to early-season nutrient competition with weeds; however, research investigating macro- and micronutrient accumulation of weeds in soybean is scarce. Field experiments were conducted across eight site-years in Illinois, USA to determine which soybean nutrients are most susceptible to weed competition. Weeds were controlled by applying glyphosate at 10-, 20-, 30-, or 45-cm weed heights during which accumulation of 11 nutrients were measured in soybean and broadleaf and grass weeds. For both weed groups, K and Fe were the macro- and micronutrient, respectively, with the greatest rate of accumulation. Variations in nutrient uptake between broadleaf and grass weeds were largely explained by differences in weed density, except for Ca and B, which were greater in broadleaf weeds regardless of density. Canonical discriminant analysis (CDA) identified soybean accumulation of N, P, K, Fe, and Cu as the nutrients most affected by weed competition, with P, K, and Fe uptake being particularly susceptible during droughty conditions. The weed height causing a 10% reduction in uptake was 11, 12, 12, 7, and 10?cm for N, P, K, Fe, and Cu, respectively. Soybean grain yield, seed weight, pods plant^?1, and seed oil content were identified through CDA as the yield parameters most affected by weed competition. Results indicate weeds should be removed before reaching 18?cm (V2 to V3 soybean) to avoid a 5% loss in grain yield. Early-season weed control preserves yield potential and may improve efficiency of nutrient management programs in soybean.     

施肥对小麦/玉米带田养分吸收及土壤硝态氮累积的影响

小麦与玉米间作是西北干旱灌区常见的高产栽培模式,为了给小麦/玉米带田高效施肥提供科学依据,通过在干旱灌区进行的小麦/玉米带田田间试验,研究了不同施肥模式对小麦/玉米带田产量、养分吸收及土壤硝态氮累积的影响。结果表明,以有机肥与化肥配施、养分均衡供给与合理运筹为核心的优化施肥模式(施有机肥22.5 t/hm2、N 300 kg/hm2、P2O5 120 kg/hm2、K2O 120 kg/hm2,有机肥、全部磷钾肥及20%的氮肥做底肥,80%的氮肥在小麦三叶期追施10%、小麦挑旗期追施20%、玉米喇叭口期追施30%、玉米灌浆中期追施20%)促进了间作体系作物植株对氮、磷、钾等养分的吸收,相对于增量施肥模式,优化施肥模式的氮肥偏生产力和氮肥农学效率分别提高了38.8%和36.9%,氮肥利用效率增加了14百分点,0～120 cm土层土壤硝态氮累积量减少43.9%～58.0%,小麦产量达5 358 kg/hm2,玉米产量达12 453 kg/hm2。