Geostatistical modeling of the spatial variability and risk areas of southern root-knot nematodes in relation to soil properties.
ABSTRACT Identifying the spatial variability and risk areas for southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] (RKN) is key for site-specific management (SSM) of cotton (Gossypium hirsutum L.) fields. The objectives of this study were to: (i) determine the soil properties that influence RKN occurrence at different scales; and (ii) delineate risk areas of RKN by indicator kriging. The study site was a cotton field located in the southeastern coastal plain region of the USA. Nested semivariograms indicated that RKN samples, collected from a 50×50 m grid, exhibited a local and regional scale of variation describing small and large clusters of RKN population density. Factorial kriging decomposed RKN and soil properties variability into different spatial components. Scale dependent correlations between RKN data showed that the areas with high RKN population remained stable though the growing season. RKN data were strongly correlated with slope (SL) at local scale and with apparent soil electrical conductivity deep (EC(a-d)) at both local and regional scales, which illustrate the potential of these soil physical properties as surrogate data for RKN population. The correlation between RKN data and soil chemical properties was soil texture mediated. Indicator kriging (IK) maps developed using either RKN, the relation between RKN and soil electrical conductivity or a combination of both, depicted the probability for RKN population to exceed the threshold of 100 second stage juveniles/100 cm(3) of soil. Incorporating EC(a-d) as soft data improved predictions favoring the reduction of the number of RKN observations required to map areas at risk for high RKN population.
Article: Yield-loss Models for Tobacco Infected with Meloidogyne incognita as Affected by Soil Moisture.[show abstract] [hide abstract]
ABSTRACT: Yield-loss models were developed for tobacco infected with Meloidogyne incognita grown in microplots under various irrigation regimes. The rate of relative yield loss per initial nematode density (Pi), where relative yield is a proportion of the value of the harvested leaves in uninfected plants with the same irrigation treatment, was greater under conditions of water stress or with high irrigation than at an intermediate level of soil moisture. The maximum rate of plant growth per degree-day (base 10 C) was reduced as nematode Pi increased when plots contained adequate water. When plants were under water stress, increasing Pi did not luther reduce the maximum rate of plant growth (water stress was the limiting factor). Cumulative soil matric potential values were calculated to describe the relationship between available water in the soil (matric potential) due to the irrigation treatments and subsequent plant growth.Journal of nematology 11/1991; 23(4):365-71. · 0.52 Impact Factor
Article: Potential for Site-specific Management of Meloidogyne incognita in Cotton Using Soil Textural Zones.[show abstract] [hide abstract]
ABSTRACT: The effect of various edaphic factors on Meloidogyne incognita population densities and cotton yield were evaluated from 2001 to 2003 in a commercial cotton field in southeastern Arkansas. The 6.07-ha field was subdivided into 512 plots (30.5 m x 3.9 m), and each plot was sampled for M. incognita prior to fumigation (Ppre), at planting (Pi), at peak bloom (Pm) and at harvest (Pf) each year. Soil texture (percent sand fraction) and the pre-plant soil fertility levels each year were determined from each plot. To ensure that a range of nematode population densities was available for study, 1,3-dichloropropene was applied in strips (3.9-m wide) at rates of 14.1, 29.2 and 42.2 liter/ha (128 plots each) each year 2 wk prior to planting. Data were evaluated using both stepwise and multiple regression analyses to determine relationships among edaphic factors, nematode population densities and yield. Although Pi and the percent sand fraction of the soil were the most important factors in explaining the variation in cotton yield, regression models only accounted for <26% of the variation in yield. When the same data were evaluated on a more homogeneous large-scale platform based on similar geographic locations, soil types and nematicide treatments, regression models that included both Pi and sand content explained 65%, 86% and 83% of the variability in yield for 2001, 2002 and 2003, respectively. Prediction profiles of the combined effects also demonstrated that damage potential for M. incognita on cotton in this study varied by soil texture.Journal of nematology 03/2007; 39(1):1-8. · 0.52 Impact Factor
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ABSTRACT: The spatial and temporal dynamics of Meloidogyne incognita, relative to soybean shoot and root growth in field microplots, were determined at 11 sampling dates during a growing season. The population dynamics of M. incognita on soybean were dependent on initial population (Pi), soil moisture, and root spatial distribution. Final egg and juvenile population densities were greatest in plots with higher Pi. The population densities of juveniles and eggs were highest from mid- to late-season and were associated with increased soil moisture. Root spatial distributions and M. incognita numbers were closely related. Numbers of juveniles and eggs decreased with soil depth and distance from the center of the row. Greater numbers of juveniles and eggs were found in the upper 30 cm in the row center, and in the upper 15 cm at 10 and 20 cm from the center of the row. There were no consistent differences in root weights between nematode-infected and uninfected plants at any depth or distance from the center of the row. The optimum time for determining the relationship between Pi and soybean shoot growth was from late mid-season (September) to final harvest (14 November). The relationship between Pi and seed yield for the final harvest was best described by a quadratic model: yield (g) = 71.4 + 1.1(log[Pi + 1]) - 2.3(log[Pi + 1])(2), (R(2) = 0.99, P = 0.03).Journal of nematology 01/1994; 25(4 Suppl):738-45. · 0.52 Impact Factor