作物轮作对土壤中烟草青枯菌数量及发病的影响

为查明春烟换茬后青枯菌在土壤中的消长规律, 采用接种耐药性青枯菌的盆土种植烟草, 烟草枯死后种植不同轮作作物的方法, 研究不同作物对土壤中青枯菌数量及其越冬状况的影响。设茄子、大豆、花生、甘薯、大蒜、玉米、晚稻和双季稻8 个轮作物处理, 后作生长期间定期取样, 用含利福平的选择性培养基检测样品中的青枯菌数量。结果表明, 栽后第4 周起秋茄子和秋大豆根中皆测出青枯菌, 秋茄子根达10⁶ cfu·g^-1;晚稻和秋花生根只第2 周和第8 周测出带菌。秋茄子、秋大豆、秋花生和晚甘薯生长期间土壤皆测出青枯菌,数量先降后升至10⁴~10⁶ cfu·g^-1; 晚稻和秋玉米土壤中青枯菌数量持续下降; 大蒜处理先测出带菌后未测到。冬季对水稻残桩青枯菌数量监测显示, 稻桩根和土壤中青枯菌数量先后出现峰值, 分别达1.00×10⁵ cfu·g^-1 和5.17×10⁴ cfu·g^-1; 发现病菌能在稻根变黑腐烂时增殖。翌年春季从茄子、大豆、花生和甘薯茬口土壤中测出遗留青枯菌数量皆达10⁴ cfu·g^-1, 玉米为10³ cfu·g^-1。烟草移栽后青枯病调查表明, 不同处理发病迟早取决于茬口土壤中菌源数量, 两者相关系数r 为0.908 9。不同茬口土壤发病轻重有显著差异, 茄子茬土发病最重,病情指数100, 大豆和大蒜茬土发病略重于花生、甘薯和玉米茬土; 晚稻茬土发病最轻, 病情指数16.7, 与茄子茬土相比发病期推迟20 d, 病情指数下降83.3%; 双季稻茬土未见发病, 证明烟稻轮作对青枯病有较好的控制效果。     

中国养蜂业现代化发展的路径探析

养蜂业是我国传统农业, 也是现代农业的重要组成部分。蜜蜂为农作物提供授粉支持并附加产出蜂产品, 其在现代农业中的地位逐渐受到重视。养蜂业的稳定发展对促进农民增收、提高农作物产量和维护生态平衡作出了突出贡献。但我国蜂业生产及科技水平与发达国家相比仍有一定差距。本文从蜜蜂授粉对农作物生产和蜜蜂在农业生态环境监测和保护中的作用方面分析了养蜂业与现代农业发展的关系, 同时分析总结我国目前蜂业存在的问题, 包括重产品、轻授粉, 重原料和半成品生产、轻深加工开发, 重转地饲养、轻定地饲养, 重单一饲养、轻立体种养, 科技方面重实际应用、轻基础研究。在此基础上提出了我国养蜂业发展的措施, 如建立规模化昆虫授粉产业, 建立蜂业循环经济发展模式, 确立定地辅以转地养蜂方式, 进行蜂产品的深度开发和加强蜂业理论的研究等。     

模糊综合评判在杂种优势预测研究中的应用

本文根据匀浆互补和同工酶分析,用模糊综合评判法预测了30个水稻杂种的杂种优势,结果表明,模糊综合评判法能够利用更多的试验信息,提高预测结果的准确性,准确率达83.33％。此外,模糊综合评判法在玉米、小麦杂种的杂种优势预测中,也取得了满意的结果,证明模糊综合评判能有效地预测植物杂种优势。     

化肥与有机肥及两者配施长期定位试验

本文研究了长期施肥对作物产量、肥料效应和土壤肥力的变化。结果表明：土壤的地力贡献具有持久性的特点，肥料对产量的贡献率为４２．７％。不同施肥组合产量总趋势是：ＭＮＰＫ、ＮＰＫ＞ＭＮＰ、ＮＰ＞ＭＮ、Ｍ＞Ｎ＞ＣＫ。说明有机肥与氮磷钾化肥配施产量最高，氮磷钾化肥配施也能获得高产稳产，提高土壤肥力。在等氮量条件下，有机肥的增产作用主要是携入磷钾养分所致。氮肥单施肥料效应逐年下降，与磷钾肥配合施用时磷钾肥效应则呈上升趋势。化肥与有机肥配施，随着配合的完全程度增加，肥料效应也依次上升。氮肥利用率化肥大于有机肥，钾肥则相反，磷肥两者基本相同。从养分投入、产出平衡及土壤肥力变化，可为施肥结构调整提供科学依据。     

Just small potatoes (and ulluco)? The use of seed-size variation in “native commercialized” agriculture and agrobiodiversity conservation among Peruvian farmers

Farmers of the Peruvian Andesmake use of seed-size variation as a source offlexibility in the production of ``nativecommercial' farmer varieties of Andeanpotatoes and ulluco. In a case study of easternCuzco, the use of varied sizes of seed tubers isfound to underpin versatile farm strategiessuited to partial commercialization (combinedwith on-farm consumption and the next season'sseed). Use of seed-size variation also providesadaptation to diverse soil-moistureenvironments. The importance and widespread useof seed-size variation among farmers isdemonstrated in the emphasis and consistency oflinguistic expressions about this trait. Smalland small-medium seed is typically sown in thecommunity's ``Hill' unit of sub-humid,upper-elevation agriculture. Seed tubers ofmedium-size and larger are needed fordrought-stressed locales in lower-elevationlandscape units. Farm-level preferences for theseed-size of tubers also suggest potentialrelations to resource endowments of farmhouseholds and gender-related management,although these tendencies were notstatistically significant in the study. Anintra-varietal, landscape-environmentalperspective on seed-size management, whichincludes an emphasis on within-fieldversatility, helps to strengthen the researchsupport of local seed production in policiesand programs aiming for in situagrobiodiversity conservation, marketingcapacity, and food security.     

An economic evaluation of site-specific herbicide application

The objective of this study was to determine if site-specific application of postemergence herbicide was economically viable with current technologies. This objective was accomplished by: developing an algorithm that determined the economic optimal postemergence herbicide rate; creating models to determine the impact that postemergence herbicide rate has on yield; and determining whether site-specific application of postemergence herbicide has greater net returns than those from a uniform application of postemergence herbicide. Weed species identification and population counts were done on a regular grid in five fields across Kansas. A decision algorithm was developed to determine the economic optimal rate of postemergence herbicide for each grid cell. The site-specific herbicide rate and four standard herbicide rates [0, 0.5, 0.75, and full (1×) label rate] were applied according to a split-plot design. Weed population observations made three weeks after application showed that the site-specific treatment controlled the weeds present in the fields. Production functions developed to determine whether postemergence herbicide rate had an impact on yield showed that it had a positive, yet statistically insignificant, effect on yield. The difference in estimated net returns between applications of site-specific rate and uniform full-label rate covered all of the costs associated with site-specific application of postemergence herbicide. The margin between the estimated net returns for site-specific and uniform application of the economic optimal rate covered only a portion of the costs associated with site-specific application of postemergence herbicide.     

Canopy-air temperature differential for potato under different irrigation regimes

Abstract

The main objective of this study was to determine canopy-air temperature differential, which can be used to quantify crop water stress index (CWSI) for potato. The crop was cultivated under furrow irrigation and subjected to three irrigation regimes in which irrigation was applied when 30, 50 and 70% of the available water holding capacity was consumed, and three irrigation levels (100, 50 and 0% replenishment of soil water depleted). The highest yield and water use was obtained under non-water-stressed treatments (100% replenishment of soil water depleted) for each irrigation regime. The lower (non-stressed) and upper (stressed) baselines were determined empirically from measurements of canopy temperatures, ambient air temperatures and vapour pressure deficit values and the CWSI was calculated with three irrigation levels for each irrigation regime. Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Average CWSI before irrigation values of 0.49 for irrigation when 30% of the available water holding capacity was consumed, 0.55 for irrigation when 50% of the available water holding capacity was consumed and 0.69 for irrigation when 70% of the available water holding capacity was consumed, produce maximum tuber yield. The yield was also directly correlated with seasonal CWSI values.     

Widespread Deficiencies of Sulfur,Boron, and Zinc in Indian Semi-Arid Tropical Soils: On-Farm Crop Responses

On-farm studies were conducted during 2002–2004 to determine fertility status, including sulfur (S) and micronutrients, and crop response to fertilization on farmers' fields in the semi-arid zone of India. Nine hundred-twenty four soil samples taken from farmers' fields, spread in the three districts of Andhra Pradesh (India), were analyzed for soil chemical fertility parameters. Results showed that samples were low in organic carbon (C), total nitrogen (N), and low to moderate in extractable phosphorus (P), but adequate in available potassium (K). Analyses of soil samples for extractable S and micronutrients was most revealing and showed that 73–95% of the farmers' fields were deficient in S, 70–100% in boron (B), and 62–94% in zinc (Zn). On-farm trials conducted during three seasons (2002–2004) showed significant yield responses of maize, castor, groundnut, and mung bean to the applications of S, B, and Zn. The yield responses were larger when S, Zn, and B were applied along with N and P. Applications of S, B and Zn also significantly increased the uptake of N, P, K, S, B, and Zn in the crop biomass. Results show widespread deficiencies of S, B, and Zn under dryland agricultural conditions; results also show that the nutrient deficiencies can be diagnosed by soil testing. It was concluded that the drylands in the semi-arid regions of India were not only thirsty (water shortage), but also hungry (nutrient deficiencies).     

Determination of actual evapotranspiration and crop coefficients of broad bean (Vicia Faba L.) grown under field conditions in the jordan valley,jordan: Bestimmung der aktuellen evapotranspiration und pflanzenbestandskoeffizienten von bohnen (Vicia Faba L.) unter feldbedingungen im jordantal,jordanien

This study was conducted to determine actual evapotranspiration and crop coefficients at different growth stages of broad bean (Vicia faba L.) grown in an open field in the Jordan Valley, Jordan using a precise and accurate approach. The study involved 30-min fluxes measurements of energy budget components over broad bean crop using a complete setup of an Eddy Correlation (EC) system. The measurements were conducted during the three main crop growth stages namely initial, development, and midseason growth stages following the Food and Agriculture Organization of the United Nations (FAO) crop coefficient model for green harvested broad bean crop. The average crop coefficients during the initial (K_{C ini}), development (K_{C dev}) and midseason (K_{C mid}) growth stages were 0.37, 0.8 and 1.05, respectively. The measured weighted average crop coefficient over the entire growing season K_{C GS} was 9.5% lower than the FAO corresponding value.

Results showed that there was a clear decrease of (bulk) surface resistance (r_s) as crop canopy developed. Daily average r_s values were 855, 337, and 166?s/m for initial, development, and midseason growth stages, respectively. Moreover, r_s was found to be highly correlated to crop height (h_c). A simple linear relation between r_s and h_c with R² of 0.91 was found. This relation will enable future direct determination of crop evapotranspiration (ET_C) using Penman-Monteith equation without the need to calculate both grass reference evapotranspiration (ET_O) and crop coefficient (K_C) values.