Crop Rotation,Monoculture and Soil Ecology1

Crop rotation and monocultural systems are discussed in relation to disease management and control. The ecological basis of both systems is examined. In crop rotation the leading principle is that in the absence of host-plants parasite populations invariably decline below threshold levels, mostly within a few years. Knowledge of the behaviour of parasite populations in the soil is becoming vast, especially in the case of plant parasitic nematodes. Analysis of soil samples for nematodes and fungi often helps the farmer to plan rotation schemes. From the ecological point of view, crop rotation is interpreted as a system of interrupted monocultures. Monocultural practices cannot be applied so universally as crop rotation, but in a number of cases monoculture is feasible, e.g. with cereals. In the equilibrium situation between host-plant (e.g. cereals), parasite (Gaeumannomyces graminis [Sacc.] v. Arx & Olivier) and the antagonists of the parasite, growth of the crop is satisfactory. These cases illustrate the role of antagonists, and it is proposed to investigate more systematically monocultures in relation to antagonisms. This may lead to more opportunities for biological control of soil-borne diseases.     

Effects of Crop Rotation and Irrigation on Verticillium dahliae Microsclerotia in Soil and Wilt in Cauliflower

ABSTRACT Experiments were conducted in field plots to evaluate the effects of broccoli residue on population dynamics of Verticillium dahliae in soil and on Verticillium wilt development on cauliflower under furrow and subsurface-drip irrigation and three irrigation regimes in 1994 and 1995. Treatments were a factorial combination of three main plots (broccoli crop grown, harvested, and residue incorporated in V.dahliae-infested plots; no broccoli crop or residue in infested plots; and fumigated control plots), two subplots (furrow and subsurface-drip irrigation), and three sub-subplots (deficit, moderate, and excessive irrigation regimes) arranged in a split-split-plot design with three replications. Soil samples collected at various times were assayed for V. dahliae propagules using the modified Anderson sampler technique. Incidence and severity of Verticillium wilt on cauliflower were assessed at 7- to 10-day intervals beginning a month after cauliflower transplanting and continuing until harvest. Number of propagules in all broccoli plots declined significantly (P < 0.05) after residue incorporation and continued to decline throughout the cauliflower season. The overall reduction in the number of propagules after two broccoli crops was approximately 94%, in contrast to the fivefold increase in the number of propagules in infested main plots without broccoli after two cauliflower crops. Disease incidence and severity were both reduced approximately 50% (P < 0.05) in broccoli treatments compared with no broccoli treatments. Differences between furrow and subsurface-drip irrigation were not significant, but incidence and severity were significantly (P < 0.05) lower in the deficit irrigation regime compared with the other two regimes. Abundance of microsclerotia of V. dahliae on cauliflower roots about 8 weeks after cauliflower harvest was significantly (P < 0.05) lower in treatments with broccoli compared with treatments without broccoli. Rotating broccoli with cauliflower and incorporating broccoli residues into the soils is a novel means of managing Verticillium wilt on cauliflower and perhaps on other susceptible crops. This practice would be successful regardless of the irrigation methods or regimes followed on the susceptible crops.     

Long-Term Crop Rotation Effects on Organic Carbon,Nitrogen, and Phosphorus in Haplustoll Soil Fractions

Soil organic matter (SOM) or carbon (SOC) consists of a number of fractions (which can be separated by granulometric wet sieving) having different properties among them. Information on fraction nutrient distribution and long-term crop rotations is lacking for semiarid environments. The objective of this research was to study the agronomic effects on soil OC, N, and P fractions. The humified OC was the largest and least variable fraction of the SOC. Soil under continuous mixed pasture had higher OC contents than under annually tilled treatments. Similarly, soil total nitrogen under the cropped treatments decreased from 1.7 g N kg-¹ in noncultivated soils (reference plots) to 1.0, 0.7 an 0.7 g N kg-¹ under mixed pasture, pasture-crop, and wheat-crop respectively, in the fine soil fraction. The reference plots also showed significantly lower levels of organic phosphorus (P o ) in comparison to the other treatment (from 67.1 w g P o g-¹ to greater than 100 w g P o g-¹ in the fine fraction of the treatments and years). The noncultivated soil showed larger values of P o and inorganic P in the large-size granulometric fraction (0.1-2 mm) than in the soil fine fraction (0-01 mm). However, the rotation treatments had greater concentrations of P in the fine fraction. The P o from the coarse fraction appears to be the most labile and sensitive fraction to tillage and environmental conditions, and may be closely related to P availability.     

Spatial Relationships of Soil Texture and Crop Rotation to Aspergillus flavus Community Structure in South Texas

ABSTRACT Aspergillus flavus, the causal agent of aflatoxin contamination of cottonseed, is a natural inhabitant of soils. A. flavus can be divided into the S and L strains, of which the S-strain isolates, on average, produce greater quantities of aflatoxins than the L-strain isolates. Aflatoxin contamination can be severe in several crops in South Texas. The structure of A. flavus communities residing in soils of South Texas was determined from 326 soil samples collected from 152 fields located from the Rio Grande Valley in the south to Fort Bend County in the north from 2001 through 2003. Analysis of variance indicated significant differences in the incidence of A. flavus isolates belonging to the S strain (percent S) among regions. The Coastal Bend (30.7%) and Upper Coast (25.5%) regions had significantly higher percent S incidence than the Rio Grande Valley (4.8%). No significant differences in percent S among years were detected. The CFU per gram of soil were not significantly different among regions. Strain S incidence was positively correlated with clay content and negatively correlated with sand content. Fields cropped to cotton the previous year had a higher S-strain incidence, whereas fields cropped to corn had greater total quantities of A. flavus propagules. Maps of S-strain patterns show that the S strain constitutes >30% of the overall A. flavus community in the area extending from the central Coastal Bend region to the central Upper Coast region. The west Rio Grande Valley had the lowest S-strain incidence (<10%). Geographic variation in S-strain incidence may influence the distribution of aflatoxin contamination in South Texas.     

Crop Rotation and Integrated Control of Animal Pests1

That crop rotation may be a valuable means of reducing pest populations has been shown in field-grown rape. On an isolated area of about 800 ha, preliminary observations showed the beneficial effects in containing Dasyneura brassicae Winn. populations by substituting spring rape by winter rape. It appeared to be more difficult to control Meligethes aeneus F. and Ceuthorrhynchus assimilis Payk. through crop rotation but, with an improved trapping system and surveying of populations, the prospects are encouraging. Possibilities of combining crop rotation with integrated control are also examined.     

茴香轮作调控土壤细菌群落缓解三七连作障碍的效应及机制

三七是我国特有的中药材,但连作障碍严重制约了其产业发展,轮作是生产上最常用且有效的缓解措施.本研究在三七收获后的土壤上轮作茴香,通过测定轮作土壤水浸液对三七存苗的影响来评价轮作对三七连作障碍的缓解效果,并从轮作对土壤细菌群落的影响方面深入阐释轮作缓解连作障碍的机制.结果表明,茴香轮作后的土壤水浸液可以显著提高三七的存苗...     

莠去津在土壤及作物中残留量测定

本文建立了一种土壤和作物中痕量莠去津的高效液相色谱分析方法,比较了超声波提取与振荡提取的回收率,研究了弗罗里硅土净化效果。以甲醇：水（８０／２０,Ｖ／Ｖ）为流动相,检测波长２３５ｎｍ,在ＯＤＳ柱上实现了莠去津与杂质的良好分离。方法简单,分析速度快,测定费用低,检测限为２４ｎｇ／ｇ,回收率为９５％～９７％。     

2019年湖北省农作物主要病虫害发生趋势

2019年3月13日-15日,湖北省植保总站组织区域测报站和相关专家对2019年全省农作物病虫害发生趋势进行了会商,根据各地监测的病虫基数,结合主要病虫发生规律、农作物种植结构、品种布局及气象等因素综合分析,预计2019年我省农作物主要病虫害总体呈偏重发生态势。“两夏”作物方面:小麦赤霉病、小麦条锈病、油菜菌核病、马铃薯晚疫病偏重发生,局部大发生。     

2007年全国农作物重大病虫害发生趋势

根据农业部组织有关专家综合分析和会商,预计2007年小麦条锈病、小麦蚜虫、稻飞虱、稻纵卷叶螟、水稻螟虫、玉米螟仍将严重或偏重发生,小麦赤霉病、稻瘟病、稻曲病呈严重流行态势,小麦吸浆虫、水稻条纹叶枯病、粘虫、棉铃虫在部分地区呈加重发生趋势,蝗虫、草地螟仍将中等发生,     

稻田轮作对水稻病、虫、草害的影响

目前南方大部分稻田采用连作耕作制度,并且滥用农药现象严重,这对农田生态环境造成极其不利的影响。为探讨稻田轮作对减轻稻田病、虫、草害的生态作用,本试验以长期水稻连作为对照,根据14年田间定位试验,详细研究了稻田轮作对水稻病、虫、草害的影响。结果表明,稻田轮作在一定程度上能减轻稻田水稻的病虫草害。稻田轮作处理的早稻纹枯病发病率平均比连作处理低10%,病情指数低0.4%;晚稻纹枯病的病株率平均比连作处理低17.7%,病情指数低13.3%。轮作处理的早晚稻稻曲病的病株率和病情指数也都低于连作处理。轮作处理所受虫害比连作处理要轻,轮作稻纵卷叶螟造成的白叶率和二化螟造成的白叶率明显低于连作。轮作处理的杂草生长情况比连作处理弱。     

2007年湖北省农作物病虫害发生趋势预测

根据2007年3月6~7日全省农作物病虫鼠害发生趋势会商会上各地提供的病虫基数,结合全年气候趋势和我省重大病虫年度间消长规律、农作物种植结构及品种布局等情况综合分析,预计2007年我省农作物病虫害发生的总趋势为:迁飞性害虫、气候性病害、粮食作物常发病虫害呈中等偏重至大发     

作物和土壤中乙酰甲胺磷及其代谢物甲胺磷消解研究

为评价乙酰甲胺磷在作物上使用的安全性,采用气相色谱法研究了不同气候条件(亚热带和暖温带)下的4种作物(甘蓝、萝卜、水稻、柑桔)和8个土壤样品(4种作物各自在两个试验地点的土壤)中乙酰甲胺磷及其代谢物甲胺磷的消解情况。结果表明:乙酰甲胺磷在作物和土壤中均可代谢产生甲胺磷,作物中的2 h甲胺磷代谢产率主要由作物种类决定。作物中乙酰甲胺磷的消解半衰期为3.1~13.5 d,甲胺磷为2.7~12.8 d;土壤中乙酰甲胺磷的半衰期为1.4~6.4 d,甲胺磷为4.5~10.7 d。土壤pH值对乙酰甲胺磷的消解影响显著,其在碱性土壤中消解较快。具有较高净辐射的气候条件会促进乙酰甲胺磷及甲胺磷在作物中的消解,因此种植在暖温带气候条件下的作物上使用乙酰甲胺磷较种植在亚热带气候条件下的具有更高的甲胺磷残留风险。乙酰甲胺磷施用在叶菜类蔬菜上可能会有较高的甲胺磷残留风险,建议叶菜类蔬菜应谨慎使用乙酰甲胺磷。     

湖北省2019年下半年农作物病虫害发生趋势

根据各地监测的病虫基数,结合主要病虫发生规律、农作物种植结构、品种布局及气象等因素,经过会商,预计2019年我省下半年农作物主要病虫害总体呈中等至偏重发生趋势。水稻:主害代"两迁"害虫、三代二化螟和纹枯病等病虫害偏重发生,局部稻区有大发生的风险,感病品种上的稻瘟病、稻曲病大流行风险较高。玉米:夏玉米上的草地贪夜蛾、三代玉米螟和感病品种上的大斑病偏重发生。棉花:菜棉混栽区棉盲蜻、枯萎病、黄萎病和棉叶蛾偏重发生。     

Eyespot in Winter Wheat: Effects of Crop Rotation and Tillage,and the Prediction of Incidence1

Eyespot in winter wheat is an important disease in the Netherlands. Symptoms can be found in almost every wheat crop. Italian ryegrass was shown to be a host crop and is able to maintain a high level of inoculum in the soil. In rotations with winter wheat every other year, ploughing compared with cultivating the soil in autumn resulted in a lower incidence of eyespot and a higher yield in the following wheat crop. A system of predicting the incidence at the beginning of May in order to indicate the necessity of chemical control is outlined.     

2008年湖北省下半年农作物病虫害发生趋势预报

6月17~18日,湖北省植保总站组织16个市、州及区域监测站就下半年全省农作物病虫发生趋势进行了会商,根据当前病虫发生基数,结合历史资料、耕作制度、品种布局、作物长势和气象条件等因素综合分析,预计下半年我省农作物病虫害总体呈偏重发生趋势,其中主害代稻飞虱、稻纵卷叶螟、     

宁夏平原灌淤土土壤养分与作物产量的空间变异性

在宁夏吴忠市利通区国家农业科技示范园区,以100 m间距采集耕层土样157个,利用ASI联合浸提法测定土壤养分,同时调查相应地点的作物产量。利用澳大利亚精准农业中心(ACPA)开发的Vesper软件,对所得数据进行空间变异性分析。结果表明:①主要养分含量和作物产量均存在半方差结构,变异系数在22.85%～70.22%之间,在宏观上属于中等程度变异;②使用块段克里格法能较好地反映各变量的空间变异,利用三维表面图可直观表示之,例如氨态N含量由南向北呈条带状降低,需要重点施N肥补充;③各养分之间具有一定的相关性,但水稻产量与养分呈现出弱相关性,表明作物的养分需求可能主要由施肥供给,必须重视合理施肥,同时注意培肥地力。     

盐碱土微生物功能群季节动态与土壤理化因子的关系

选取河西走廊东端永登县6种盐碱土壤类型,对各样地微生物功能群的季节动态与土壤理化因子之间的关系进行分析.结果表明:①盐碱环境中土壤细菌＞放线菌＞真菌,细菌和放线菌数量在夏季出现峰值,真菌数量在秋季和冬季出现峰值;不同微生物功能群基本上只有一个峰值且峰值出现的季节不同,与碳循环相关的纤维素分解菌功能群的峰值出现在冬季,与...     

Low Temperature–Short Duration Steaming of Soil Kills Soil-Borne Pathogens, Nematode Pests and Weeds

Agricultural soil samples containing survival structures of the fungal crop pathogens Verticillium dahliae, Sclerotinia sclerotiorum, Sclerotium cepivorum, Pythium ultimum, potato cyst nematodes Globodera rostochiensis and G. pallida and weeds Chenopodium album and Agropyron repens [Elymus repens] were treated in the laboratory with aerated steam at temperatures ranging from 40 to 80°C in a specially constructed apparatus. Steaming at 50 or 60°C for 3min, followed by an 8-min resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, diseases and nematodes. When steamed at 45°C, there was a small but significant reduction in the survival of V. dahliae microsclerotia but no reduction in survival of S. cepivorum.