Potato water content impact on soil moisture measurement by neutron meter

A field study was conducted to examine the effect of the water content of potato tubers on the neutron count ratios of a neutron probe in an irrigated potato field. At the 20 cm depth, where tubers are concentrated, the neutron count ratios within the potato row (CW) were significantly higher than the neutron count ratios between the rows (CB). In contrast, the measured soil water contents within the rows (SW) at this depth, tended to be less than those measured between the rows (SB). At 45 cm depth, results were similar in a dry but not a wet year. The SW values, in contrast, were less than SB. Neither (CW-CB) or (SW-SB) were significant at 75 cm depth and values of (CW-CB) and (SW-SB) were similar. This study provides qualitative information regarding the influence of a potato tuber water content on neutron measurements, resulting in an overestimations of soil moisture in a potato field. Further studies should be conducted to develop relationships for corrections.Contribution no 3879215Contribution no 3879215     

An electrical recording soil moisture tensiometer

Summary An automatically recording soil moisture tensiometer was produced by substituting the usual mercury manometer by an electrical pressure transducer. Like other tensiometers and unlike the neutron probe, this instrument samples relatively small volumes of soil. In tests, individual recording tensiometers gave results repeatable to ± 0.002 bar even in moist soils and responded twice as quickly as standard tensiometers. As a result it has been possible to describe and automatically record events in a forest soil profile following a period of precipitation clearly identifying differences at 2 and 7 cm below ground level.     

Factors affecting the occurrence of gangrene (Phoma exigua) in potatoes

The presence in soil from Scotland and England of Phoma exigua f. sp. exigua and P. exigua f.sp. foveata, which cause gangrene, is confirmed by isolation, and it is established that infection of tubers occurs before lifting, and after lifting from soil adhering to tubers. The distribution of the disease is related to soil moisture, gangrene being most prevalent in tubers from the north-eastern counties of Scotland where the moisture content of arable soils remains high throughout the growing season. The incidence of the disease may be affected by the haulm, either as a source of infection—though not an important source—or by its effect on the maturity of the tubers. The incidence of gangrene is less where haulm destruction is rapid. The incidence of gangrene in a crop is not related to its incidence in the seed tubers planted and, unless infection is severe, the effect on yield is not serious. Symptoms of skin necrosis were associated with tubers from acid soils, infected with P. exigua f.sp. foveata and stored at low temperature.     

Non-destructive measurement of wheat roots in large undisturbed and repacked clay soil cores

Summary Non-destructive observations of root growth and distribution can be obtained from counting root intercepts with observation tubers inserted in the root zone. This paper describes the technique of inserting clear acrylic tubes horizontally into large undisturbed and repacked soil cores. Counts of roots intersecting scribed lines on the sides of the tubes were made with a fibrescope. Comparison was made between observation root tubes of different diameter (25 and 38.5 mm).The r² values for the relationships between root intercept counts and destructively determined values of root length density (RLD) ranged from 0.78 to 0.96. The larger diameter tubes had higher r² values. Theoretical calibration of the technique does not appear to be possible since analysis indicated that fewer roots intersected the scribed lines on the observation tube than would have been expected from a non-disturbed, randomly distributed root system. It is not known if this discrepancy is due to non-randomness or to an artifact associated with the insertion of the observation tube. Roots were not more prolific at the edge of the soil cores. Comparison of values of root length per unit soil surface area, rates of downward root growth and water uptake rates were within the ranges previously reported for wheat roots of field crops grown on clay soils. Observed root growth and distribution was found to be sensitive to four soil and water treatments imposed. It is concluded that the technique will allow quantitative analysis of root growth and distribution in undisturbed soil cores.     

Adaption and survival strategies inCyperus rotundus L.—a perennial weed of pantropical distribution

The survival strategies ofCyperus rotundus L. have been studied in relation to osmotic potential, desiccation rate, bound water and dry matter content. Critical moisture level of the perennating organ, the tubers, is 43% and minimum soil moisture is about 0.4%, for its survival.     

The effects of soil moisture at the time potato tubers are forming on the incidence of common scab (Streptomyces scabies)

Two complementary field experiments at Rothamsted in 1965, with the potato variety Majestic, related the incidence of common scab (Streptomyces scabies) to rainfall, soil moisture and time of tuber formation. In plots where the soil was maintained at field capacity (less than 10 cm. Hg moisture tension) by watering, tubers had little or no scab; infection increased in amount on plots allowed to dry to 30 cm., 50 cm. or more Hg moisture tension during late June. The time tubers formed was varied by planting sprouted (chitted) and non-sprouted seed tubers, and tuber development and scab incidence were observed on sample plants lifted at frequent intervals from unwatered plots. Scab lesions were first seen on 12 July when the distribution of lesions on the surface of tubers was affected by size of tuber both within and between the different seed-tuber treatments. These differences were correlated with estimates of tuber size on 28 June, the beginning of the first dry period. Tubers 1.0 cm. or more in diameter on 28 June had few or no lesions at the stolon attachment (heel) end of tubers on 12 July, whereas tubers smaller than this on 28 June had many lesions in this region on 12 July. The larger the tuber was on 28 June, the greater was the area free from scab lesions on 12 July.     

宇宙射线中子法在农田土壤水分监测中的适用性

近年来,宇宙射线中子法(CRNS法)逐渐被应用到农田生态条件下的土壤水分监测领域,但其在田间应用时的空间代表性和测定精度还需进一步研究。本研究在华北平原冬小麦农田开展宇宙射线中子法应用效果的评价研究,采用超快速中子适应性(URANOS)模型计算CRNS法的空间权重,对CRNS法获得的土壤含水量与实测土壤含水量进行对比,以准确估算监测空间内的蓄水量。结果表明: 通过URANOS直接模拟得到的权重分布更符合理论值,测定半径在127~139 m。CRNS法估算的土壤含水量与实测土壤含水量的决定系数达到0.64,均方根误差达到0.05 cm³·cm^-3。CRNS法所得土壤含水量对探测区域内总体水分的变化响应灵敏,测定准确度有季节性变化规律。宇宙射线中子法是一种可用于冬小麦农田的连续、可靠的区域总体水分监测方法。     

宇宙射线快中子法在华北平原典型农田土壤水分测量中的应用

宇宙射线快中子法是一种新兴的能够实现区域土壤水分观测的方法.以中国科学院山东禹城综合试验站的宇宙射线连续观测数据和无线网络土壤水分观测数据为基础,研究了该方法在华北平原典型农田生态系统的适用性,重点探讨了采用标定法获得的土壤完全干燥条件下中子数(N₀)的稳定性和降雨灌溉对土壤水分估算的影响.结果表明: N₀的变化受下垫面变化影响,变化周期与试验区冬小麦和夏玉米的种植和收割期较一致.宇宙射线法估算的土壤水分对降雨和灌溉有明显响应,但在灌溉或降雨发生时会高估土壤水分.在华北农田生态系统条件下,宇宙射线法能有效地估算区域土壤水分,估算结果与浅层土壤水分观测值(10 cm深度)最为接近.     

Tuber surface microorganisms influence the susceptibility of potato tubers to late blight

Potato tubers (cvs Cara and Bintje) were grown in compost in a glasshouse and immature tubers harvested 57, 68 and 78 days after planting. Two moisture levels were imposed after the first harvest by disconnecting the water supply to one of the treatments and allowing the soil in that treatment to dry naturally. Tubers from wetter compost (59.4% moisture holding capacity) were more resistant to Phytophthora infestans than those from drier compost (14.7% moisture holding capacity) 78 days after planting. The potential causes of this difference were investigated. Aqueous extracts of wet compost did not inhibit the growth of P. infestans. The susceptibility of the internal tuber tissue, from which the periderm had been removed, was different to whole tuber susceptibility. The internal tissue of tubers from wet compost was more susceptible (cv. Cara), or as susceptible (cv. Bintje) as that of tubers from dry compost 78 days after planting. Fungi were isolated from the surface of whole tubers and there were no differences between the populations of potentially antagonistic fungal genera on tubers from wet and dry compost. As the experiment progressed, the number of bacteria per gram fresh weight on tubers grown in wet compost increased, whereas that on tubers from drier compost decreased (cv. Bintje) or remained similar (cv. Cara). There were significantly (P= 0.008) more bacteria on the surface of tubers from wet compost 78 days after planting. When P. infestans was co-cultured in Petri dishes with randomly selected tuber surface bacteria, some isolates (≤ 16.7%) inhibited the growth of the fungus. The percentage of the total bacterial population that was antagonistic to P. infestans was not significantly affected by soil moisture level (P= 0.368). The greater numbers of bacteria, of which a proportion are antagonistic to P. infestans, on the surface of tubers grown in wet compost may account for the greater resistance to tuber blight in that instance.     

不同覆盖施肥措施对黄土旱塬冬小麦土壤水分的影响

于2007年9月—2008年7月在位于黄土高原渭北旱塬的王东沟试验区进行冬小麦不同覆盖施肥措施（包括不施肥、农民习惯施肥、推荐施肥、推荐施肥+有机肥、推荐施肥+垄上覆膜、推荐施肥+垄上覆膜+沟内覆草、推荐施肥+全区覆草7个处理）田间试验,并采用水分中子仪定期观测土壤含水量,研究黄土高原旱塬区不同栽培措施下土壤水分的变化特征.结果表明：在干旱季节（春季）,推荐施肥+垄上覆膜+沟内覆草措施有利于贮存更多的土壤水分,其土壤储水量约比最低值（推荐施肥+有机肥）高48.2 mm,并可将土壤水分保持到冬小麦需水的关键期,而且推荐施肥+垄上覆膜措施仅次于推荐施肥+垄上覆膜+沟内覆草,表明这两种措施能够在田间蓄积较多天然降水,有利于黄土高原旱区雨养农业的发展.     

The control of common scab of potatoes by irrigation

Irrigation applied early during tuberization significantly decreased scab on tubers of Majestic, King Edward and Record, but not on Pentland Crown, a resistant cultivar, where tubers had little scab even from the driest soil. There was little benefit from keeping soils wetter than 0.6 in (15.24 mm) soil moisture deficit (S.M.D.) for more than 3 weeks after tuber initiation, and irrigation to 0.8 in (20.32 mm) S.M.D. gave economic control. Irrigating only after the ‘marble stage’ increased yield but the tubers were scabbed. Irrigation did not alter the rate eyes (nodes) separated from the apical bud but speeded the swelling of tubers.     

Experimental determination and modelling of the soil water extraction capacities of crops of maize,sunflower, soya bean,sorghum and wheat

The estimation of soil water reserves is essential for irrigation management. The usual way of calculating these reserves, held between the soil moisture content at field capacity and the classical limit of –1.5 MPa considered as the lower limit of available water, over the rooting depth of the crop, does not correspond with the real behaviour of crops as regards their ability to extract soil water and should be only considered as the apparent available water (AAW). Measurements of moisture profiles made using a neutron probe soil moisture meter from 1970 until 1991 on unirrigated crops at the INRA Agronomy Station at Toulouse-Auzeville, France, on a deep silty clay soil with a high water holding capacity have enabled us to define the water extraction capacities of maize ( Zea mays L.), sunflower (Helianthus annuus L.), sorghum (Sorghum bicolor L. Moench), soya bean (Glycine max L. Merr.), and winter wheat (Triticum aestivum L.). The results show, not only that all the crops can extract soil water from beyond –1.5 MPa in the surface layers to varying degrees and depths, depending on the crop, but also that deeper down, AAW is not fully used, as the moisture profile gradually returns to field capacity. Of the five crops studied, maize extracts the most water from the top 0.5 m, removing 150% of AAW. This amount falls rapidly lower down, reaching nil at 1.6 m. Conversely sunflower extracts less near the surface, but uses all AAW up to 1.2 m, and still extracts 85% of AAW at 1.6 m. Sorghum is somewhat comparable to sunflower, but with a lower use over the entire profile. Soya bean exhibits strong extraction to 1.0 m, and then much less at depth. As to wheat, its extraction capability is quite high near the surface, and then falls steadily with depth where it is still 30% of AAW at 1.6 m. Soil moisture measurements realised on a bare soil during several successive years were used to fix the maximum soil evaporation and to suggest the contribution of crops in soil water depletion from uppermost layers.The water extraction capacities have been modelled and introduced into the model EPICphase, a modified version of the model EPIC, adapted for irrigation management. Four parameters have been introduced to simulate: (1) the rooting pattern of the crop (parameter ), (2) the degree of involvement of deep layers (parameter p), (3) the fraction of AAW beyond which crop transpiration is affected (parameter t) and (4) the intensity of extraction beyond the limit of –1.5 MPa as a function of soil depth (parameter d). Calibrated on the basis of the driest year since 1970 for each crop, the model was then validated under unirrigated conditions, and then tested on irrigated maize plots. Under unirrigated conditions, the simulations correctly reproduced the water extraction by the five crops, both in an extremely dry year and in a wet year. The observed differences between simulations and observations were found mostly at about 0.1 m depth, and were due to lack of precision of moisture measurements with the neutron probe. From 0.2 to 0.6 m the simulations have a tendency to overestimate the extraction. These differences are explained by water fluxes which are especially high in these layers because of the processes of evaporation from the soil and plant transpiration, which are difficult to simulate with precision. Below 0.6 m, a more stable zone where water movements are of minor importance, the simulations are very precise. For irrigated maize, the results show a very good fit between simulation and measurement, indicating that these water extraction capacity figures could be used for irrigation management provided that the rules for exploitation of the water reserves are well established.     

Spatial Patterns of Entomopathogenic Nematodes in Microcosms: Implications for Laboratory Experiments

Laboratory microcosms were used to: i) measure the effects of soil moisture on survival of Steinernema riobravis and ii) investigate the suitability of using microcosms to study motility and survival of these nematodes. Nematodes recovered from soil contained in petri dishes declined by more than 95% during 7 days, whereas nematodes recovered from the inner surfaces of dishes increased 35-fold. After 7 days in dishes, >20 times as many nematodes were recovered from dish surfaces than from soil. Nematodes exhibited a negative geotropism; greater numbers of nematodes were recovered from the lid surfaces than from the surfaces of dishes. Survivorship of nematodes in soil in plastic centrifuge tubes was somewhat greater than in petri dishes, and fewer nematodes ascended above the soil line in tubes than dishes. Downward migration of nematodes was inversely related to soil column diameter, possibly due to relatively unimpeded movement along container surfaces. An assay was developed by which nematodes were rinsed from the inner surfaces of centrifuge tubes into the soil. The resulting slurry was then processed on Baermann trays to recover motile nematodes. Nematode survival in soil in centrifuge tubes was higher at soil moistures between 2-4% than at lower (0.5-1.0%) and higher (4.0-12.0%) moisture levels. Survival of S. riobravis may be enhanced by quiescence induced by moisture deficits.     

不同龄阶梭梭根区土壤水分时空变化特征

土壤水是荒漠植被发育最主要的制约因子。不仅影响植物的生长和发育,还限制着植被的种类、数量和分布。梭梭作为北方荒漠区重要的固沙植物,研究梭梭林地土壤水分动态对其植被生存或恢复以及群落稳定性维持具有重要意义。鉴于少有学者研究过不同龄阶梭梭根区的土壤含水率差异,于2014年2月至2014年11月,采用中子仪法和烘干法对0—400 cm沙层土壤含水率进行了原位观测,分析了不同龄阶梭梭根区土壤水分的时空变化规律。结果表明:(1)梭梭根区土壤水分时间变化可分为4个阶段:2月下旬—3月下旬是土壤水分快速补给期,4月上旬—5月下旬是土壤水分均衡期,6月上旬—10月下旬是土壤水分耗损期,11月上旬—次年2月中旬是土壤水分稳定期;(2)梭梭根区0—50 cm土层,受降雨、融雪水入渗补给和蒸发的影响较大,土壤水分变异系数较大且随深度增加迅速减小,50 cm以下土层变异系数较小且随深度变化微小;(3)不同龄阶梭梭根区剖面平均土壤含水率全年与春、夏、秋季均表现为:枯树成熟梭梭中龄梭梭裸地;(4)随距梭梭树干距离的增大(0—5 m范围内),土壤含水率整体呈减小趋势;降雨前后,梭梭根区浅层(0—10 cm)土壤含水率增量大于裸地土壤含水率增量。     

Extraradical development and contribution to plant performance of an arbuscular mycorrhizal symbiosis exposed to complete or partial rootzone drying

Sweet potato plants were grown with or without Glomus intraradices in split-root pots with adjacent root compartments containing a soil with a low availability of phosphate. One fungal tube, from which root growth was excluded, was inserted into each root compartment. During 4 weeks before harvest, the soil moisture level in either both or only one of the two root-compartments of each pot was decreased. Controls remained well watered. Low soil moisture generally had a negative effect on the amount of extraradical mycelium of G. intraradices extracted from the fungal tubes. Sporulation in the fungal tubes was much higher compared with the soil in the root compartment, but remained unaffected by the soil moisture regime. Concentrations of P in extraradical mycelium were much lower than usually found in plants and fungi, while P concentrations in associated mycorrhizal host plant tissues were in an optimum range. This suggests efficient transfer of P from the extraradical mycelium to the host plant. Despite the negative effect of a low soil moisture regime on extraradical G. intraradices development, the symbiosis indeed contributed significantly to P uptake of plants exposed to partial rootzone drying. The possibility that extraradical arbuscular mycorrhizal fungal development was limited by P availability under dry soil conditions is discussed.     

Growth of crop roots in relation to soil moisture extraction

Growth of the roots of sugar beet, potato and barley in the field was observed through glass panels and related to changes in soil moisture measured by a neutron probe during 1969–71. The depth of observed root growth was generally related to, but 10–15 cm deeper than, the maximum depth of soil-moisture extraction. On average of three years, sugar beet, potato and barley used water from the top 23, 33 and 45 cm soil respectively by the beginning of June, and from the top 70, 68 and > 100 cm soil by the end of June. Maximum soil drying in each horizon gave an in situ measure of available water capacity, and showed that sugar beet and barley eventually extracted similar amounts of water from each horizon, but potatoes extracted less, especially from below 60 cm. Between 30 and 100 cm deep, the in situ available water capacity (per 10 cm soil) progressively decreased from 16 to 10, 15 to 5 and 16 to 8 mm under sugar beet, potato and barley respectively. The calculated soil-moisture deficit (potential evapotranspiration minus rainfall) and measured soil moisture deficit were not related early in the growing period before the crops established much leaf cover.     

太子参微块根发育的解剖学与组织化学定位

采用植物组织培养、解剖学及组织化学定位方法研究太子参试管微块根发育的形态结构与营养物质积累特征的结果表明：太子参微块根由组培苗膨大的腋芽基部长出的不定根发育而成,经历了初生结构与次生结构发育,其膨大加粗是由于不定根的次生生长。维管形成层向内形成大量的次生木质部构成微块根的主要部分。淀粉粒是太子参微块根的主要营养存储方式。随着微块根的次生生长,淀粉粒先在次生木质部薄壁细胞中形成,随后在次生韧皮薄壁细胞中也大量积累。膨大的微块根可以合成太子参皂苷,成熟微块根中次生韧皮部的皂苷含量略高于次生木质部。离体太子参微块根的生长发育和营养物质的积累与块根中的相同。     

温度和湿度对我国内蒙古羊草草原土壤净氮矿化的影响

土壤氮素的矿化是反映土壤供氮能力的重要因素之一 ,也是目前国内外研究的热点。通过测定内蒙古典型羊草草原自由放牧地土壤净氮矿化量和净氮矿化速率 ,揭示影响草地生态系统土壤氮循环过程的有关机理 ,为草地生态系统建模提供理论依据。在实验室条件下 ,运用恒温恒湿培养箱控制土壤的温度与湿度 ,测定羊草草原长期自由放牧地土壤氮素矿化量的积累。将不同水分含量的土柱分别放在温度为 - 10℃、0℃、5℃、15℃、2 5℃和 35℃的恒温恒湿培养箱中培养 ,培养 1、2、3、5周后取出 ,分析培养前后的 NH 4- N和 NO- 3- N含量 ,以确定土壤净氮矿化 (NH 4- N NO- 3- N)的累积和不同时间段内的矿化速率。结果表明 :不同处理温度和水分之间的差异均达到显著水平 (p<0 .0 0 0 1)。温度和水分之间具有显著的交互作用 (p<0 .0 0 0 1)。随着培养时间的延长 ,矿化氮累积量增加 ,但是矿化速率下降     

Seasonal Migration of Meloidogyne chitwoodi and its Role in Potato Production

Seasonal vertical migration of Meloidogyne chitwoodi through soil and its impact on potato production in Washington and Oregon was studied. Nematode eggs and second-stage juveniles (J2) were placed at various depths (0-180 cm) in tubes filled with soil and buried vertically or in holes dug in potato fields. Tubes were removed at intervals over a 12-month period and soil was bioassayed on tomato roots. Upward migration began in the spring after water had percolated through the tubes. Nematodes were detected in the top 5 cm of tubes within 1-2 months of burial, depending on depth of placement. Potatoes were grown in field plots for 4 or 5 months before the tubers were evaluated for infection. One hundred eggs and J2 per gram soil placed at 60 and 90 cm caused significant tuber damage at the Washington and Oregon sites, respectively. At the Washington site, inoculum placed at 90, 120, and 150 cm caused potato root infection without serious impact on tuber quality, but inoculum diluted 2-8 times and placed at 90 cm did not cause root or tuber infection. Nematode migration was dependent on soil texture; 9 days after placement at the bottoms of tubes, J2 had moved up 55 cm in sandy loam soil (Oregon) but only 15 cm in silt loam (Washington). Thus, the importance of M. chitwoodi which occur deep in a soil profile may depend on soil texture, population density, and length of the growing season.     

Detection of the nec1 virulence gene and its correlation with pathogenicity in Streptomyces species on potato tubers and in soil using conventional and real-time PCR

AIMS: To evaluate the virulence gene nec1 as a reliable marker for the detection of pathogenic Streptomyces species on potato tubers and in soil samples using conventional and real-time quantitative PCR assays. Methods AND RESULTS: Two pairs of conventional primers (outer and nested) and one set of primers/probe for use in real-time PCR were designed to detect the necrogenic protein encoding nec1 gene of Streptomyces scabiei strain ATCC 49173(T). The conventional PCR primers were also incorporated into a multiplex PCR assay to simultaneously detect the nec1 gene in conjunction with the potato pathogens Helminthosporium solani and Colletotrichum coccodes. The specificity of each PCR assay was confirmed by testing 32 pathogenic and nonpathogenic reference strains of Streptomyces representing 12 different species and 74 uncharacterized streptomycete strains isolated from diseased tubers. A clear correlation between pathogenicity and the detection of nec1 by PCR was demonstrated. The sensitivity and specificity of both the conventional and real-time PCR assays allowed the detection of nec1 on potato tubers in the absence of visible symptoms of common scab, and in seeded soil down to a level equivalent to three S. scabiei spores per gram soil. CONCLUSIONS: Reliable and quantitative PCR techniques were developed in this study for the specific detection of the virulence gene nec1 of pathogenic Streptomyces species on potato tubers and in soil samples, and the data demonstrated a clear correlation between pathogenicity in Streptomyces species and the presence of the nec1 gene. SIGNIFICANCE AND IMPACT OF THE STUDY: Together with the DNA extraction protocols, these diagnostic methods will allow a rapid and accurate assessment of tuber and soil contamination by pathogenic Streptomyces species.