Soil photolysis in a moisture- and temperature-controlled environment. 2. Insecticides

The photolytic degradations of imidacloprid, carbofuran, diazinon, chlorpyrifos, pyridaben, propoxur, and esfenvalerate were independently compared in both moist (75% field moisture capacity at 0.33 bar) and air-dry microbially viable soils at 5 microg/g. All compounds were applied to sandy soil except for propoxur, which was applied to sandy loam soil. Diazinon was applied to both sandy soil and sandy loam soil. The samples were exposed for up to 360 h, depending on the half-life of the compound. Moisture and temperature were maintained through the use of a specially designed soil photolysis apparatus. Corresponding dark control studies were performed concurrently. With the exception of esfenvalerate, the other compounds exhibited significantly shorter half-lives in moist soils, attributed to the increased hydrolysis and microbial activity of the moist soil. The esfenvalerate metabolism was not first order due to limited mobility in the soil because of its very low water solubility. The overall half-life for esfenvalerate was 740 h, as the percent remaining did not drop below 60%. The imidacloprid half-life in irradiated moist soil was 1.8 times shorter than in air-dry soils. However, on dry soil the photodegradation showed poor first-order kinetics after 24 h of exposure. The metabolism of carbofuran and diazinon was highly dependent on soil moisture. Carbofuran exhibited 2.2 times longer half-lives when less moisture was available in the soil. Diazinon in moist sandy soil degraded rapidly, but slowed significantly in irradiated and dark control air-dry sandy soil. Diazinon photolysis on sandy loam soil was not first order, as it attained a constant concentration of 54.9%, attributed to decreased mobility in this soil. Chlorpyrifos photolysis was 30% shorter on moist sand than on air-dry sand. Pyridaben photolyzed rapidly throughout the first 72 h of irradiation but maintained 48% through 168 h. Propoxur metabolism in moist sandy loam soil was not first order and did not degrade below 50% after 360 h of exposure, but the overall half-life was still nearly half of that on irradiated air-dry soil. Three of the compounds showed differences in metabolism patterns during exposure on moist or air-dry soil. Typically, the moist soils produced a more linear decline than that seen in the dry soils, corresponding to the susceptibility of the particular chemical to hydrolysis and/or biodegradation. Four of the eight experiments had shorter half-lives in dark control moist soils than in irradiated dry soils.     

Influence of two insecticides, chlorpyrifos and quinalphos, on arginine ammonification and mineralizable nitrogen in two tropical soil types

Effects of seed treatments with chlorpyrifos [5 g of active ingredient (ai) kg(-1) of seed] and quinalphos (6.25 g of ai kg(-1) of seed) and standing crop treatments with chlorpyrifos (800 g of ai ha(-1)) and quinalphos (1000 g of ai ha(-1)) on arginine deamination and mineralizable nitrogen were monitored, in the sandy loam and loamy sand soils of two tropical semiarid fields, for three consecutive crop seasons. The arginine ammonification activity of rhizospheric microbes was inhibited after seed treatment with chlorpyrifos and quinalphos and their principal metabolites, 3,5,6-trichloro-2-pyridinol (TCP) and 3,5,6-trichloro-2-methoxypyridine (TMP) and 2-hydroxyquinoxaline and quinoxaline-2-thiol, respectively. Quinalphos produced transient inhibitions, whereas chlorpyrifos and its metabolites (TCP and TMP) exerted a greater inhibition in both loamy sand and sandy loam soils. Arginine ammonification by nonrhizospheric microbes was stimulated by standing crop treatments with both pesticides. In the loamy sand soil, the parent compounds stimulated rhizospheric N-mineralization, whereas the metabolites were inhibitory. However, nonrhizospheric N-mineralization was inhibited by both chlorpyrifos and quinalphos and stimulated by their metabolites. A higher magnitude of inhibition of arginine deamination in the loamy sand than in the sandy loam soil could be due to greater bioavailability of the pesticides in the former, resulting from lesser sorption of the pesticides due to alkalinity of the soil and its low content of clay and organic carbon. Although both pesticides affected mineralizable nitrogen, seed treatment with quinalphos and standing crop treatment with quinalphos and chlorpyrifos produced the most significant effects. The recommended doses of the pesticides not only efficiently controlled whitegrubs, which increased pod yields, but also left no residues in harvested kernels. They also caused no long-term inhibition of ammonification, which could have been of significant concern during the short crop period in semiarid areas where nitrogen determines plant productivity.     

A study to determine effects of simulated acidic rain on yield of field-grown soybeans (Glycine max. cv. Hodgson)

A field study was conducted in 1985 and 1986, using a fully automated rain exclusion canopy system, to investigate the impact of simulated acidic rain (SAR) on yield of soybean (Glycine max cv. Hodgson). Treatment effects were determined for various yield components: seed yield (kg ha^?1), pod number per plant, seed number per pod, seed weight (g 100 seeds^?1). Plant height (cm) was also measured. Results of the 1985 fields study showed that increased acid content of SAR had a slight stimulatory effect on soybean seed yield. However, the 1986 study results did not show significant treatment effects on seed yield (kg ha^?1) or other components of yield. For each of five SAR treatments, soybean yield (kg ha^?1) obtained in 1985 was significantly greater than the 1986 yield. The yield results can be attributed to differences in seed weight caused by environmental conditions specific to the two growing seasons.     

水、肥和芸苔素内酯对油茶叶片养分、种仁出油率和开花量的影响

油茶（Camellia oleifera Abel）是世界四大木本油料树种之一,本试验选择油茶优良无性系长林166品系为研究对象,采用五因素五水平,二次正交旋转试验设计,1/2实施,共36个处理,研究水、 氮、 磷、 钾和芸苔素内酯（brassinolides,简称 BRs）及其耦合作用对油茶叶片氮、 磷、 钾含量、 开花数量及种仁出油率的影响,以期为油茶速生丰产栽培提供科学依据。结果表明: 1）在5个试验因子中,对油茶叶片氮、 磷、 钾含量、 开花数量及种仁出油率的影响,均以喷施BRs的处理最大,灌水量次之,而施肥量的影响最小; 2）各处理对油茶叶片含氮量和开花数量的影响可较好地运用二次多项式方程进行曲线拟合,且试验重复性较好,各处理对油茶叶片钾、 磷含量及种仁出油率的影响,运用二次多项式方程拟合较差,但由于试验重复性较好,故在实际应用中仍具有一定的借鉴价值; 3）5个因素单独作用时,油茶叶片含氮量和含钾量均随其用量的增加呈先降低后升高的变化趋势,叶片含磷量则随用量的增加呈先增加后降低的变化趋势,但对种仁出油率和开花数量的影响没有表现出明显的规律性。     

Effect of temperature on below-ground N-dynamics in a weedy model ecosystem at ambient and elevated atmospheric CO2 levels

Model multispecies terrestrial communities composed of four trophic levels (plants, herbivores, parasitoids, decomposers) were established in the Ecotron controlled environment facility. Two experimental runs enabled us to investigate the effects of enhanced temperature on below-ground microbial processes (N-mineralisation, urease, arginine deaminase, protease activity and potential denitrification) in both ambient and elevated (ambient +200 ppm) CO₂ atmospheres.The enzyme activities involved in nitrogen cycling showed weak responses to elevated temperature in both experimental runs. In the Ambient CO₂ Run, protease and arginine deaminase values tended to be lower in elevated temperature; on the other hand, N-mineralisation, urease and denitrification enzyme activity (DEA) were higher. In the Elevated CO₂ Run, all microbial variables showed higher activities at elevated temperature, although only the results for DEA and arginine deaminase were statistically significant. The interaction between higher temperature and elevated CO₂ weakly affected root growth and tissue C:N ratio, limiting feedbacks into the microbial community.Besides temperature and CO₂, substrate availability, water stress and successional development regulated the response of the soil microbes. The supply of organic carbon and nitrogen in the soil allowed plant growth and maintenance of the microbial population. Nitrogen competition between vegetation and microbes restricted net microbial growth. The increase of dissolved organic carbon (DOC) at higher CO₂ and temperature levels significantly favoured DEA. The high water regime in the soil also favoured DEA and inhibited oxidation of organic compounds, as indicated by low levels of enzyme activity. Additionally, water stress decreased rooting density in the soil; this resulted in negative feedback into microbial processes. We conclude that water stress and soil nitrogen deficiency caused an early levelling-off of both microbial population growth and activity rates during the early part of the model ecosystem's development.     

Rapid and Sensitive Analytical Method for Simultaneous Determination of Imidacloprid and Thiamethoxam Residues in Soils of Sugarcane Ecosystem by Reversed-Phase HPLC

A rapid, simple, sensitive and cost-effective analytical method has been standardised to determine the residues of imidacloprid and thiamethoxam in soil. This method does not require any cleanup with costly sorbents. The recoveries of imidacloprid and thiamethoxam obtained in this no-cleanup method were on par with the protocol involving primary?Csecondary amine-based cleanup. This method requires less volume of solvent (20?mL of acetonitrile/sample) and is suitable for high throughput analyses involving large number of samples. The limit of quantification of the method was 0.01???g/g. Dissipation kinetics of imidacloprid and thiamethoxam in the soils of sugarcane ecosystem was studied by adopting this rapid method. The half-life of imidacloprid and thiamethoxam was 9.07 and 6.22?days when applied at 70 and 100?g a.i./ha, respectively. The dissipation of both the neonicotinoids followed first-order kinetics with good fit.     

黄土高原旱地麦田26年免耕覆盖对土壤肥力及原核微生物群落多样性的影响

为明确黄土高原旱作麦田长期保护性耕作对土壤肥力和土壤原核微生物的效应,以位于山西省临汾市实施保护性耕作26年的小麦田为试验基地,采用Illumina Hiseq 2500高通量测序等手段,开展了不同耕作措施[免耕覆盖（NTS）、深松免耕覆盖（SNTS）和传统耕作（TT1）]对土壤理化性质和土壤原核微生物多样性的影响分析。研究结果表明：1）NTS和SNTS处理比TT1处理显著提高了土壤全氮、碱解氮、速效磷及速效钾的含量,降低了土壤pH,提高了土壤贮水能力和水分含量,降低了0~10 cm土层的土壤容重,但提高了10~20 cm土层的土壤容重;同时,SNTS处理显著增加了土壤的有机质含量。2）Illumina Hiseq高通量16S rRNA基因V4区测序结果表明：NTS和SNTS处理比TT1处理显著降低了绿弯菌门的相对丰度;NTS比SNTS处理显著降低了土壤中疣微菌门和绿弯菌门的相对丰度;NTS处理显著增加了土壤原核微生物群落的多样性,但未显著改变原核微生物群落的丰度;SNTS对原核微生物群落的多样性和丰富度均未有显著改变;NTS处理的显著性差异物种（Biomarker）高于其他2个处理;其他原核微生物门的相对丰度,在3个处理间尚未有明显差异。3）聚类分析可见：NTS和SNTS处理与TT1处理的微生物群落结构差异较大;NTS处理与SNTS处理间的微生物群落结构差异较小。4）CCA分析可知：土壤pH、有机质、速效氮、速效磷、速效钾含量对土壤原核微生物群落遗传多样性的变化起着重要作用;与TT1处理相比,NTS和SNTS处理在一定程度上改变了土壤原核微生物群落结构,但仍存在结构的相似性。综上所述,长期进行NTS和SNTS处理对黄土高原旱地麦田土壤微生物多样性、丰富度以及土壤肥力因子等的正效作用明显。     

Pesticides and nitrogen fixation in a paddy soil

The influence of six pesticides, applied singly or in combination, on ¹⁵N₂ incorporation and C₂H₂ reduction in a submerged paddy soil was studied under laboratory conditions. While the application of diazinon had no marked effect, benomyl, carbofuran, parathion, nitrofen and γ-HCH, at concentrations close to recommended field application rates (5μg ^?1) significantly stimulated N₂ fixation. Synergistic stimulatory effects of the pesticides on N₂ fixation were evident particularly in combinations of carbofuran with benomyl, nitrofen and γ-HCH. On the contrary, diazinon slightly retarded the stimulatory effect of benomyl and carbofuran. Results indicated that the differential effects of pesticides on N₂ fixation could be attributed partly to fluctuations in the population of certain groups of N₂ fixers in submerged soil.     

不同减量氮肥配施紫云英对田面水氮磷流失及水稻生长的影响

为指导水稻田合理施肥,防治稻田面源污染,试验开展了不同氮肥减施比例对紫云英—水稻轮作体系下稻田田面水氮磷流失的影响研究。2020年在浙江建德开展田间小区试验,设置冬闲(CK)和冬种紫云英(CT)2个处理,并在冬种紫云英基础上设置4个减氮比例,分别为0(CT0),10%(CT1),20%(CT2),30%(CT3),共5个处理,每个处理重复3次。在水稻移栽施肥后开始稻田田面水样品采集(包括施肥2周内的连续采样以及2周后相隔7,14,28天的间隔采样),测定田面水氮磷浓度;于水稻成熟后采集土壤和植物样品,测定土壤理化性状以及水稻生长性状和产量。各处理田面水总氮、可溶性氮、铵态氮以及总磷、可溶性磷均在施肥后第1天达到峰值,总氮在基肥后4天内降幅明显,为最大值的4.2%~9.1%,可溶性磷在施基肥5天内降至最大值的4.7%~13.7%。采样期内,CK处理田面水总氮、可溶性氮、总磷和可溶性磷的平均浓度分别为48.87,36.82,0.82,0.64 mg/L,CT0、CT1、CT2、CT3的总氮平均浓度分别为CK的93.9%,78.1%,79.7%,69.7%;可溶性氮平均浓度分别为CK的95.1%,84.1%,85.7%,73.2%;总磷平均浓度分别为CK的90.9%,76.9%,96.2%,81.3%;可溶性磷平均浓度分别为CK的79.4%,73.8%,87.3%,68.7%。与CK相比,CT2、CT3显著提高土壤有效磷含量,增加幅度分别为61.7%和37.0%。比较冬闲处理,翻压紫云英使水稻株高增高0.7%~3.5%,有效穗数增加7.0%~15.2%,水稻增产0.4%~4.9%。与冬闲处理相比,冬种紫云英配合不同比例氮肥减施均能降低稻田田面水氮磷流失风险,其中以30%氮肥减量效果最好;紫云英配合减氮施肥措施能够提升土壤有效磷、全氮含量和水稻产量,其中均以紫云英配合20%减氮施肥效果最好。综合稻田田面水氮磷流失风险、土壤肥力以及水稻产量,紫云英配合20%减氮施肥是较为适合该地区的种植方式。     

Fate and Transport of Nursery-Box-Applied Tricyclazole and Imidacloprid in Paddy Fields

The fate and transport of tricyclazole and imidacloprid in paddy plots after nursery-box application was monitored. Water and surface soil samples were collected over a period of 35 days. Rates of dissipation from paddy waters and soils were also measured. Dissipation of the two pesticides from paddy water can be described by first-order kinetics. In the soil, only the dissipation of imidacloprid fitted to the simple first-order kinetics, whereas tricyclazole concentrations fluctuated until the end of the monitoring period. Mean half-life (DT₅₀) values for tricyclazole were 11.8 and 305 days, respectively, in paddy water and surface soil. The corresponding values of imidacloprid were 2.0 and 12.5 days, respectively, in water and in surface soil. Less than 0.9% of tricyclazole and 0.1% of imidacloprid were lost through runoff during the monitoring period even under 6.3 cm of rainfall. The pesticide formulation seemed to affect the environmental fate of these pesticides when these results were compared to those of other studies.     

不同肥料/改良剂对冷泥田水稻生长、养分吸收及土壤性质的影响

【目的】西南地区冷泥田的水稻生长不良可归因于多种障碍因子,包括土壤物理、化学和生物因子。本文针对冷泥田影响水稻生长的土壤化学障碍因子,研究了不同肥料或改良剂对冷泥田水稻生长、养分吸收和土壤性质的影响,旨在为这类土壤的培肥、改良利用和水稻高产提供科学依据和实用技术。【方法】试验地点选在四川省东南地区冷泥田集中的泸县,试验历时2年。试验设无肥对照(CK)、全量化肥(NPK)、NPK+泥炭(NPK+Pe)、NPK+商品有机肥(NPK+COF)、NPK+鸡粪(NPK+CM)、NPK+硅肥(NPK+Si)、NPK+石灰(NPK+L)、NPK+硅钙肥(NPK+Si Ca),NPK+锌肥(NPK+Zn)9个处理。在水稻收获前采集代表性植株样,调查水稻农艺性状,分析水稻对氮、磷和钾的吸收量;水稻收获后采集土壤样品,测定不同处理的土壤p H、全氮、有效磷、速效钾、有机质、还原性物质总量、活性还原物质以及亚铁和亚锰含量。【结果】结果表明,在所有处理中,NPK+L和NPK+Si Ca处理可改善水稻的产量构成因子,稻谷产量比NPK处理显著提高15.40%和10.64%;而其他处理的增产效果则均不显著。NPK+L和NPK+Si Ca处理的土壤p H明显高于其他处理,土壤还原性物质总量和活性还原物质(含Fe2+和Mn2+)含量显著降低;NPK+L和NPK+Si Ca处理可增加土壤养分的有效性,促进水稻对氮、磷、钾养分的吸收,改善土壤的化学性质。同时,土壤分析结果表明,该试验土壤的有效钙和有效硅均缺乏,而NPK+L和NPK+Si Ca处理增加了土壤的有效钙和有效硅,对提高水稻产量有重要贡献。有机肥对土壤相关性质的影响与石灰和硅钙肥相反,特别是鸡粪。施用锌肥对水稻有一定的增产效果,但差异不显著。水稻收获后土壤中氮、磷、钾养分残留量与施肥量和水稻吸收携出量密切相关。【结论】对长期淹水地势低洼的酸性冷泥田来说,石灰和硅钙肥是比较理想的土壤改良剂,能同时起到改善土壤性质和提高作物产量的效果;而有机肥,特别是未腐熟的有机肥或有机物料,则不宜在冷泥田中施用或大量施用。     

稻田冬种绿肥对水稻产量和土壤肥力的影响

为探讨冬季种植绿肥作物改良土壤的生态作用, 以冬闲连作为对照, 通过连续8年的定位试验研究了冬种绿肥(紫云英、油菜和黑麦草)收获后翻压还田对后作水稻产量及土壤肥力的影响。结果表明: 连续8年冬种绿肥期间, 冬种绿肥各处理的水稻平均产量均高于冬闲对照, 但不同处理增产效果有所不同, 其中紫云英 早稻 晚稻处理增产效果最明显, 为10.48%, 其次是油菜 早稻 晚稻处理(7.31%), 黑麦草 早稻 晚稻处理的增产效果较差, 仅为5.76%。紫云英 早稻 晚稻处理的土壤pH和碱解氮含量最高, 与其他处理相比, pH增加0.58%~1.37%, 碱解氮增加6.59%~35.35%。黑麦草 早稻 晚稻处理的土壤有机质、有效磷、速效钾含量和C/N在各处理中最高, 分别较其他处理高2.99%~4.98%、19.25%~31.05%、16.97%~22.15%和0.97%~6.61%。相关性分析结果表明, 水稻产量与每穗颖花数、结实率、千粒重及土壤碱解氮、有效磷极显著相关(P<0.01), 与每穗粒数、有机质、速效钾显著相关(P<0.05), 而与穗长、有效穗数及土壤pH和C/N相关不显著; 水稻产量各构成要素与土壤养分之间的关系极为密切。综合来看, 稻田冬种绿肥有利于增加水稻产量和改善土壤肥力。     

中药废渣对干旱区弃耕盐碱地土壤理化性质及微生物数量和酶活性的影响

在宁夏干旱区弃耕盐碱地施用苦豆子草渣、苦豆子籽渣和甘草渣3种中药废渣,对表层土壤理化性质、微生物数量和土壤酶活性的变化进行了研究,探讨3种中药废渣改良弃耕盐碱地的效应。结果表明:施用3种中药废渣后,土壤容重、pH值、全盐均低于CK(未施药渣),其中pH值、全盐含量显著降低;土壤水分含量均显著高于CK;土壤养分含量全面提高,其中土壤有机质、全磷、速效氮、速效磷、速效钾得到显著提高,不同处理间速效氮、速效磷、速效钾差异显著(p0.05),其中苦豆子籽渣提供速效氮、速效钾的能力显著高于甘草渣和苦豆子草渣,而甘草渣提供速效磷的能力显著高于苦豆子草渣和籽渣;施用废渣后的表层土壤细菌、真菌和放线菌数量均显著高于CK;苦豆子草渣、苦豆子籽渣和甘草渣对土壤碱性磷酸酶的活性有显著性的促进作用,苦豆子籽渣对土壤过氧化氢酶的活性有显著性的促进作用;土壤有机质、速效氮、速效磷、速效钾与土壤微生物的数量和土壤酶相互促进作用明显,有密切的相关关系。     

Dry Matter,Nitrogen, Phosphorous,and Potassium Partitioning,Accumulation, and Use Efficiency in Transgenic Cotton-Based Cropping Systems

A better understanding of the fate of nutrients in transgenic cotton (Gossypium hirsutum L.) fields will improve nutrient efficiencies, will optimize crop growth and development, and may help to enhance soil quality. A study was made to evaluate and quantify the effect of cropping system [sole cotton and groundnut (Arachis hypogaea) intercropping with transgenic cotton] and nitrogen (N) management [control (0N), 100% recommended dose of nitrogen (RDN) through urea, substitution of 25% RDN through farmyard manure (FYM), and substitution of 50% RDN through FYM] on dry matter (DM) and nutrient partitioning and accumulation by transgenic cotton and groundnut at New Delhi during 2006–2007. Soil and plant samples were collected and analyzed at 60, 90, and 120 days after sowing and at harvest. Results revealed that intercropping of groundnut with cotton did not significantly affect DM and nutrient partitioning in cotton, but residual soil fertility in terms of potassium permanganate (KMnO₄) N showed an improvement in contrast to Olsen's P and ammonium acetate (NH₄OAc)–exchangeable K over sole cotton. At harvest, of total DM assimilated, leaves constituted 10–20%, stem 50%, and reproductive parts of cotton accounted for the rest. For each kilogram of seed cotton produced, the crop assimilated 61 g of N, of which 23 g was partitioned to harvested seed cotton. Substitution of 25% RDN through FYM, being on par with 100% RDN through urea, recorded greater DM, nutrient uptake in different parts of cotton, agronomic N-use efficiency (9.5 kg seed cotton kg N^?1), and apparent N recovery (83.3%) over 50% RDN substitution through FYM and control. The control, being on par with 50% RDN substitution through FYM, recorded significantly greater DM and nutrient uptake by intercropped groundnut over other treatments. Apparent N and potassium (K) balance at the end of study was negative in all treatments; however, the actual change in KMnO₄ N was positive in all the treatments except control. Our study suggests that intercropping of groundnut with transgenic cotton and substitution of 25% dose of N through FYM is sustainable in tropical countries.     

Residual effects of nitrogen sources,sulfur and boron levels on mungbean (Vigna radiata) in a sunflower (Helianthus annuus)–mungbean system

Field experiments were conducted during spring–rainy (kharif) seasons of 2005 and 2006 on a sunflower–mungbean cropping system at the research farm of the Division of Agronomy, Indian Agricultural Research Institute (IARI), New Delhi, India. The objectives of this study were to investigate the residual effect of nitrogen sources, sulfur and boron levels applied to sunflower on productivity, nutrient concentrations and their uptake by the succeeding mungbean crop in a sunflower–mungbean cropping system. The experiment with 19 treatments was laid out in factorial randomized block design for both sunflower and mungbean. The residual effects of nutrients applied to sunflower were significant on the succeeding mungbean crop in terms of biometric parameters, yield attributing characters, seed yield and soil nutrient status. The highest mungbean seed yield (961.2 kg ha^?1) was produced with 50 kg ha^?1 sulfur application to the preceding sunflower crop, which was significantly (p < 0.05) higher than with 0 and 25 kg sulfur ha^?1. The concentrations and uptake of nitrogen, sulfur and boron were also greater in the succeeding mungbean crop due to the residual effects of nutrients applied to the preceding sunflower crop. The soil nutrient status before and after mungbean indicated that the available nitrogen and sulfur were higher due to application to the preceding crop, while available boron after mungbean was even higher than after sunflower due to its slow release and static nature in the soil.     

Effect of tillage practices on wheat performance in a semi-arid environment

Sodosol soils are at risk of degradation under existing fallow management practices involving tillage. Topsoil erosion exposes horizons with reduced infiltration and low concentrations of plant nutrients. Conservation management systems are needed on these soils to avoid a reversion to low intensity grazing. This paper reports on a 4 year study (1986–1989) of the effects of tillage practices on profile soil water and crop yield in a Sodosol (Typic Natrustalf) in central Queensland, Australia. The tillage treatments were: zero till fallow (weed control by herbicides), reduced till fallow (chisel plough/scarifier or herbicides) and conventional till fallow (chisel plough/scarifier) in two linked experiments. In the first experiment, wheat was grown in three contour bays (approximately 1 ha), and in the second, wheat was grown in replicated plots (30 m × 6 m) to allow statistical comparisons.

Zero till provided consistent advantages in grain yield in all 4 years compared with conventional till. Zero till also outyielded reduced till as well as conventional till in the plot experiment. The average yield increase of 0.5 t ha⁻¹ in zero till compared with convention till was associated with greater water use and increased water use efficiency. Tillage practice caused only marginal differences in the available water content in the root zone (0–100 cm) at sowing; zero and reduced till contained, on average, an additional 4 and 8 mm, respectively, compared with conventional till. The tillage treatments had no effect on plant available water capacity. Some of the soil water that accumulated during the fallow drained beyond the root zone in all treatments and was not available to the following wheat crop. At the conclusion of the experiment, soil water accumulation in the 100–180 cm soil layer was 86 mm in zero till, 39 mm in reduced till and 40 mm in conventional till.

Results indicate that zero till can be a more productive wheat farming practice than conventional mechanical tillage. The increase in water storage below the root zone of the wheat crop shows that there may be benefit in using a deeper-rooting crop or pasture species in rotation with wheat, particularly after zero till fallows.     

干湿交替程度对土壤速效养分的影响

降雨和灌溉引起的干湿交替显著影响土壤速效养分的转化和迁移.为了探究干湿交替程度对土壤速效养分的影响,采用室内模拟干湿交替试验,设置轻度(DW1,复水至60％WHC)、中度(DW2,复水至45％WHC)、重度(DW3,复水至30％WHC)3种干湿交替程度,并以恒湿处理(CM,恒定60％WHC)为对照,探究试验前后土壤pH...     

Effect of Daylength on the Nitrogen Status of Timothy (Phleum pratense L.)

Abstract

In two experiments timothy plants (Phleum pratense L., cultivars ‘Bodin’ and ‘Grindstad’, well established and vernalized in the first experiment and 7 weeks old in the second) were given daylength treatments with 12 h of photosynthetically active radiation (PAR) and day-lengthening light of low irradiance for from 2 to 13 weeks. Significant daylength effects on dry-matter, total nitrogen, nitrate and soluble protein content in the leaves of plants were demonstrated after only two weeks of treatment. The nitrogen and protein content decreased with increasing daylength, irrespective of the developmental stage of the plants. The dry-matter content increased with daylength when long days had induced generative development and decreased when all treatments at the same harvest were vegetative. The total nitrogen and protein per plant did not decrease from short to long days. The lower nitrogen and protein content in long days can therefore be regarded as a dilution caused by the increased dry-matter production found in these treatments. The observed effects of daylength on the ratio of assimilated nitrogen to assimilated carbon might be direct or indirect, since long days induce both enhanced dry-matter production and generative development in Bodin and Grindstad.     

Measurement of available soil phosphorus under conventional and no‐till management

Abstract

The objective of the investigation was to compare the predominant forms of P in fields of an acid Matapeake soil under no‐till and conventional‐till management. The fields, which differed in extent of contact between soil and fertilizer P, also differ in forms of P. Fertilizer P remained in the uppermost layer of no‐till fields and was, therefore, not in as close proximity to the plant (corn) roots as P was in conventional‐till fields. Nevertheless, fertilizer P in the no‐till fields underwent only limited conversion to forms less available to plants and thus, in part, may have accounted for similar plant uptake rates of P in no‐till and conventional‐till fields.

One method used to analyze P in the Matapeake soil was the double‐acid‐extraction method. This method is used by several state soil‐testing laboratories of the eastern and southeastern United States, where acid soils like Matapeake are common. The double‐acid‐extraction method underestimated the soil P available for plant uptake.     

改良剂对旱地红壤微生物量碳、氮及可溶性有机碳、氮的影响

基于室内模拟培养试验,研究改良剂(生物质炭、过氧化钙)对旱地红壤微生物量碳、氮及可溶性有机碳、氮的影响。试验设置4个处理,即CK、Ca(过氧化钙,1.72g/kg)、C(生物质炭,21.46g/kg)、C+Ca。结果表明:各处理土壤微生物量碳、氮以及可溶性有机碳具有相同的变化趋势,即前期(3d内)都增加较快,在第3天达到最大值,随试验进行有所下降,配施效果优于单施。各处理可溶性有机氮在21d内缓慢增加;第21天时,C+Ca、Ca、C相比CK分别显著增加了62.1%,55.5%,40.9%;35d以后,配施(C+Ca)与单施过氧化钙(Ca)的效果显著优于单施生物质炭(C)和对照(CK)。120d培养期内,配施(C+Ca)处理能够明显提高微生物量碳、氮以及可溶性有机碳、氮的平均含量;微生物量碳的平均含量大小顺序为C+CaCCKCa,微生物量氮的平均含量C+Ca处理显著高于其他处理;可溶性有机碳的平均含量大小顺序为C+CaCaCCK,可溶性有机氮的平均含量C+Ca、Ca处理显著高于CK、C处理。微生物量碳、氮以及可溶性有机碳之间互为极显著正相关(P0.01),而微生物量碳与可溶性有机氮之间呈极显著负相关。因此,生物质炭和过氧化钙能有效提高旱地红壤微生物量碳、氮及可溶性有机碳、氮,且生物质炭与过氧化钙配合施用更有助于土壤改良。