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1.
Root research needs to optimize sampling schemes to address different scales and dimensions of variability within a framework of feasible effort and, in some cases, acceptable soil perturbation. Both large and small sample volumes are utilized in root research, and this study is designed to help field researchers in optimizing root sampling. We evaluate the performance of three contrasting sampling strategies—large monoliths (LM, 25 dm?3), small monoliths (SM, 3?×?1 dm?3), and root auger (RA, 5?×?196.3 cm?3). We compare root biomass estimates obtained in a shifting cultivation agroecosystem in eastern Amazonia. We sampled a slash-and-burn field at 1/2 and 1 1/2 years of cultivation, and a paired 3-year-old spontaneous secondary forest regrowth down to 1 m soil depth, and we distinguish roots by diameter class and taxonomic origin (palm vs. non-palm roots). LMs are the only reliable quantification method for coarse roots. Both SM and RA methods are inadequate due to high variability and the frequent failure to detect the presence of coarse roots in the sampled soil. The SM method is acceptable for mid-sized (2–5 mm) roots, and both methods are adequate for fine root (<2 mm) quantification. Labor costs of LM, SM and RA methods are similar since reduced sampling effort in small sample volumes is compensated by increased costs in sample handling. The small sample volumes of SM or RA may be preferable in situations focusing on fine root dynamics, with the necessity to avoid major perturbations, or in repeated sampling schemes. Both SM and RA samplings gave a strong and systematic overestimation of root biomass in all fractions compared to the LM values, with differences being less pronounced for SM. We establish comparability between the three sampling schemes with transformation equations which are remarkably similar between shifting cultivation and secondary forest, between roots of the babassu palm and those of other origin and down the 1-m soil profile. Thus, future field studies in similar environments can utilize SM or RA fine root sampling and subsequently transform data to LM estimates. We recommend the SM rather than the RA method because of the lower data variability and the lower degree of root mass overestimation.  相似文献   

2.
Clustered binary data occur frequently in many application areas. When analyzing data of this form, ignoring key features, such as the intracluster correlation, may lead to inaccurate inference, e.g., inflated Type I error rates. For clustered binary data, Gerard and Schucany (Comput Stat Data Anal 51:4622–4632, 2007) proposed an exact test for examining whether the marginal probability of a response differs from 0.5, which is the null hypothesis considered in the classic sign test. This new test maintains the specified Type I error rate and has more power, when compared to both the classic sign and permutation tests. The test statistic proposed by these authors equally weights the observed data from each cluster, regardless of whether the clusters are of equal size. To further improve the performance of the Gerard and Schucany test, a weighted test statistic is proposed and two weighting schemes are investigated. Seeking to further improve the performance of the proposed test, empirical Bayes estimates of the cluster-level success probabilities are utilized. These adaptations lead to 5 new tests, each of which are shown through simulation studies to be superior to the Gerard and Schucany (Comput Stat Data Anal 51:4622–4632, 2007) test. The proposed tests are further illustrated using data from a chemical repellency trial.  相似文献   

3.
Emissions of gases from the soil are known to vary spatially in a complex way. In this paper we show how such data can be analysed with the wavelet transform. We analysed data on rates of N2O emission from soil cores collected at 4‐m intervals on a 1024‐m transect across arable land at Silsoe in England. We used a thresholding procedure to represent intermittent variation in N2O emission from the soil as a sparse wavelet process, i.e. one in which most of the wavelet coefficients are not significantly different from zero. This analysis made clear that the rate of N2O emission varied more intermittently on this transect than did soil pH, for which many more of the wavelet coefficients had to be retained. This account of intermittent variation motivated us to consider a class of random functions, which we call wavelet random functions, for the simulation of spatially intermittent variation. A wavelet random function (WRF) is an inverse wavelet transform of a set of random wavelet coefficients with specified variance at each scale. We generated intermittent variation at a particular scale in the WRF by specifying a binormal process for the wavelet coefficients at this scale. We showed by simulation that adaptive sampling schemes are more efficient than ordinary stratified random sampling to estimate the mean of a spatial variable that is intermittent at a particular scale. This is because the sampling can be concentrated in the more variable regions. When we simulated values that emulate the intermittency of our data on N2O we found that the gains in efficiency from simple adaptive sampling schemes were small. This was because the emission of N2O is intermittent over several disparate scales. More sophisticated adaptive sampling is needed for these conditions, and it should embody knowledge of the relevant soil processes.  相似文献   

4.
In order to establish analysis-based quality guidelines for composts, it is necessary to have information about the variability of these traits as dependent on sampling methods. Composts exhibit significant spatial, site and time-related variability. In a preliminary survey of commercial and home users of compost in New York State, respondents indicated strong interest in test quality of purchased composts. However, little work has been done examining the consistency of reported values in composts sampled and shipped to laboratories. We evaluated within-farm and between-sampler variability of test traits at 7 farm compost sites. In one study we compared farmer and extension agents as separate samplers of the same compost piles. In the next study we examined repeated sampling by same sampler visiting the site a second time. Finally, we compared depth-based sampling variability at 3 selected farm compost sites. Analysis of variance was employed to distinguish effects of samplers, sampling timing and farms. The data showed very small differences in test values due to samplers for all parameters except weed seed and fecal coliforms. Geometric mean transformation eliminated fecal counts as a source of significant variability. Repeated sampling after two weeks of matured compost indicated no appreciable differences between points of time except for weed seeds. The sampling-depth study revealed significant variation of several selected test parameters attributed to pile stratification, and the variables most affected were moisture, potassium and weed seeds. Weed seed testing may not be useful for a quality parameter unless methodological variance is better understood. Overall, biological parameters varied less than chemical traits. The study underscores that prior to establishing numerical quality guidelines the preferred compost pile sampling protocol should be very carefully described.  相似文献   

5.
We evaluated the effect of three different sampling schemes used to organize spatially explicit biological information had on the spatial placement of conservation reserves in Utah, USA. The three sampling schemes consisted of a hexagon representation developed by the EPA/EMAP program (statistical basis), watershed boundaries (ecological), and the current county boundaries of Utah (socio-political). Four decision criteria were used to estimate effects, including amount of area, length of edge, lowest number of contiguous reserves, and greatest number of terrestrial vertebrate species covered. A fifth evaluation criterion was the effect each sampling scheme had on the ability of the modeled conservation reserves to cover the six major ecoregions found in Utah. Of the three sampling schemes, county boundaries covered the greatest number of species, but also created the longest length of edge and greatest number of reserves. Watersheds maximized species coverage using the least amount of area. Hexagons and watersheds provide the least amount of edge and fewest number of reserves. Although there were differences in area, edge and number of reserves among the sampling schemes, all three schemes covered all the major ecoregions in Utah and their inclusive biodiversity.  相似文献   

6.
The coexistence of genetically modified (GM) and non-GM crops is an important economic and political issue in the European Union. We examined the GM content in non-GM maize crops in Spain in 2005. Both the standing crop and the harvest were tested, and the %GM DNA was quantified by real-time polymerase chain reaction. We compared the level of GM as a function of distance from known GM source fields in a 1.2 km2 landscape. The distribution of GM was compared to predictions from previous studies, and good agreement was found. Control and monitoring of adventitious GM presence in non-GM crops can only be achieved by fit-for-purpose sampling and testing schemes. We used a GM dispersal function to simulate non-GM crops in the studied zone and tested the accuracy of five different sampling schemes. Random sampling was found to be the most accurate and least susceptible to bias by GM spatial structure or gradients. Simulations showed that to achieve greater than 95% confidence in a GM labeling decision of a harvest (when treated as a single marketed lot), 34 samples would be needed when the harvest was outside 50% of the GM threshold value. The number of samples required increased rapidly as the harvest approached the GM threshold, implying that accurate labeling when the harvest is within +/-17% of the threshold may not be possible with high confidence.  相似文献   

7.
Abstract

About 40% of soils used for agriculture in southwestern Australia (SWA) were acutely copper (Cu) deficient when first cleared, and Cu fertilizer needed to be applied to grow the first wheat (Triticum aestivum L.) crop, the major crop in the region. Tissue testing rather than soil testing is used in SWA to indicate when fertilizer Cu needs to be reapplied to wheat crops. In a glasshouse study using six Cu‐deficient soils from SWA, we compared four Cu soil test procedures as possible alternatives to tissue testing to predict Cu deficiency for wheat. Different critical values were obtained for different soils for all four soil test procedures, indicating separate soil test calibrations would be required for the four procedures for different soils in SWA. By contrast, critical tissue test values in plant parts (young leaves and rest of shoots) were unaffected by soil type. Developing soil Cu test calibrations would be time consuming and costly, and tissue testing has resulted in most deficiency being corrected by fertilizer applications, so there are few Cu‐deficient soils in SWA available to develop the soil test calibrations. Therefore, tissue testing using young leaves is likely to remain the most reliable method for diagnosing Cu deficiency for wheat in SWA and determining when reapplication of fertilizer Cu to soil is required.  相似文献   

8.
An extensive knowledge of how sampling density affects soil organic C (SOC) estimation at regional scale is imperative to reduce uncertainty to a meaningful confidence level and aid in the development of sampling schemes that are both rational and economical. Using kriging prediction, this paper examined the effect of sampling density on regional SOC‐concentration estimations in cultivated topsoils at six scales in a 990 km2 area of Yucheng County, a typical region in the N China Plain. Except the original data set (n = 394), five other sampling densities were recalculated using grids of 8 km × 8 km (n = 28), 8 km × 4 km (n = 44), 4 km × 4 km (n = 82), 4 km × 2 km (n = 142), and 2 km × 2 km (n = 257), respectively. Experimental SOC semivariances and kriging interpolations at six sampling density scales were calculated and modeled to estimate regional SOC variability. Accuracy of the effects of the five sampling densities on regional SOC estimations was assessed using the indices of mean error (ME) and root mean square error (RMSE) with 100 independent validation samples. By comparison with the kriged grid map derived from the 394 samples data set, the relative error (RE,%) was spatially calculated to highlight the spatial variability of prediction errors at five sampling‐density scales due to the intrinsic limitations of ME and RMSE in accuracy assessment. The results indicated that sampling density significantly affected the estimation of regional SOC concentration. Particularly when the sampling density was < 4 km × 4 km, the large spatial variation of SOC was concealed. Semivariance analysis indicated that different sampling density had significant effect on reasonable detection of the dominant factors which influenced SOC spatial variation. Greater sampling density could more exactly reveal regional SOC variation caused by human management. The prediction accuracy for regional SOC estimation increased with the increasing of sampling density. The critical areas with larger RE values should be intensified in the future sampling scheme, and the areas of lower RE values should be decreased relatively. A specific sampling scheme should be considered in accordance with the demand to the estimation accuracy of regional SOC stock at a certain confidence level. Our results will facilitate a better understanding of the effect of sampling density on regional SOC estimation for future sampling schemes by providing meaningful confidence levels.  相似文献   

9.
Abstract

Tissue diagnostic norms for Valencia orange (Citrus sinensis L. Osbeck) were developed by searching for, detecting, and sampling the most productive individuals of this crop, using a survey approach. The study involved trees of different ages, grafted on different rootstocks in several plantations, located in the most important orange producing areas (four states) of Venezuela. Data for 214 leaf samples, corresponding to the top 20% of the trees sampled, were used to develop the norms. Norms developed were compared for validation against previously published sufficiency range values and other published orange Diagnosis and Recommendation Integrated System (DRIS) norms. The close general agreement among the published values and the norms developed here, suggests that this approach could become an economic, relatively fast and reliable method for developing tissue diagnostic norms.  相似文献   

10.
Abstract

Soil test values from three laboratories using the Mehlich‐3 extradant on Coastal Plain soils with a wide range in soil test levels were compared. Soil samples were collected over a four year period from four Southeastern/Mid‐Atlantic states (SC, NC, VA and DL). The results among labs were highly correlated (r > 0.9) for all elements analyzed (P, K, Ca, Mg, Mn, Zn, and Cu). Regression equations were developed to predict the soil test values among laboratories for each element. Comparisons of extractable levels for the elements shown above among the three laboratories are given.  相似文献   

11.
精确农业田间土壤空间变异与采样方式研究   总被引：35，自引：8，他引：35       下载免费PDF全文
以英国Hillsborough农业研究所附近的一块7.9 hm2的牧草地为研究区，采用地统计的半方差分析和克立格方法研究其空间变异性和空间插值。同时对研究田块的样点根据不同间距、不同形状进行删选，对不同布局状况下的结果进行统计比较，以获取满足一定精度下的最少采样个数和采样形状。研究结果表明，单纯利用样方统计，土壤有效钾需要65个采样点，大致为原始采样点的一半。而在考虑空间采样形状和空间插值效果，再采用最小显著性差异（LSD）进行比较，该田块土壤有效钾采样最好使用规则三角网布点（样点数为62个）。  相似文献   

12.
Spatial sampling density influences the reliability and feasibility of environmental studies. Optimizing spatial sampling schemes is important, particularly when multiple observations must be repeated over extended periods.

The goal of this study was to develop a sampling density reduction method for a network of 57 soil water content (SWC) measurement locations in an 8-ha microwatershed, given observations taken at five different dates. We sought a subset of 10 points that would best predict (via spatial interpolation) the SWC at the remaining locations.

Three observation dates (calibration set) were used to develop the method, and the remaining two (validation set) were used to test it. Calibration date semivariograms were coalesced into one scaled semivariogram, used with ordinary kriging to predict SWC outside the chosen subset. We defined four different scenarios by combining two simulated annealing algorithms, Sacks and Schiller (S&S) and Spatial Simulated Annealing (SSA), and two fitness functions, one based on scaled kriging variance (SKV), and the other based on actual mean squared prediction error (scaled mean squared error, SMSE).

We searched for an optimal subset in each calibration scenario; each was then used to predict SWC throughout the microwatershed on the validation dates. The results were compared with those of regular grids and randomly generated patterns. Temporal stability was tested by analyzing deviations between individual and field average observations and using Spearman's rank correlation.

The S&S and SSA algorithms performed similarly well, although SSA converged better. The SKV-based scenarios had lower SKV in the calibration and validation sets than the SMSE-based scenarios, the regular grids, and the random patterns. However, the SMSE-based scenarios produced an optimal subset having minimal SMSE over both data sets vs. the other methods. This subset produced mostly low relative errors: for January 25, 1993, 50% of the predicted points fell within ±5%, 82% within ±10%, and 6.5% fell outside 15%; for December 23, 1993, 35% were within ±5%, 72% within ±10%, and 23% fell beyond 15%. However, kriging assumptions were violated on December 23.

The SMSE-based scenarios predicted validation set SWC better than the SKV scenarios because they included microwatershed locations that did not obey the stationarity assumptions of kriging but were temporally stable and captured the full range of SWC variation. Modifying the proposed method to perform kriging with a physically based trend model will further improve its predictive accuracy.  相似文献   


13.
城镇圩区排涝泵站群日常运行方案优化   总被引：3，自引：1，他引：2  
为降低城镇圩区排涝泵站群日常运行能耗,提出排涝站群总能耗最小的多方案试验选优、圩外河道水位控制去劣的优化运行调度方法。将圩区泵站群分组作为试验因素、每组泵站的开机方案为试验水平,以泵站群总能耗为试验结果开展正交试验,对试验结果应用正交分析得到泵站群若干种优化运行方案序列,选择总能耗最小且满足圩外河道的水位控制要求的方案为最优运行调度方案。以上海市城区某区域为实例,应用优化方法编制了2种潮水过程、4种降水条件下的优化调度预案;在不能利用潮水自排的最不利水文工况下,应用优化调度方案与现行调度方案相比,总电功耗最大可节省12%。通过开展优化调度方案与现行方案的节能效益比较,验证了现行方案的合理性并对现行方案提出了优化建议。一方面可为城镇圩区水行政主管部门优化日常调水预案提供参考,另一方面也为丰富和完善排泵站群优化调度方法的理论研究作了有益尝试。  相似文献   

14.
Abstract

A glasshouse experiment was conducted with young grafted kiwifruit plants to evaluate a rapid sap nitrate test using Merck nitrate test strips, and to establish critical values for maximum vine growth. Total N leaf concentration for these plants was also related to vine growth. Sap nitrate nitrogen was significantly related to growth of the plant expressed as unit leaf rate (ULR) over four and six week periods from the time of sampling. Total N, on the other hand, was only significantly related to the total cane length at the time of sampling but not to the ULR. Using Cate‐Nelson graphical method, the critical sap NO3‐N value for maximum growth was established at 500–600 ppm. The critical value for total N was established at around 3.2%.  相似文献   

15.
Survey and monitoring rangelands projects is one the important plans in rangelands management. For this purpose, the survey and monitoring methods could be time-consuming and costly. Sampling strategies of plant patches are effective in sampling procedures that cause minimizing sampling variance and time. In this study, for decreasing sampling time and cost, increasing speed, plant patches parameters (including length, width, height, area, and distance between the patches) were compared. Three transects with 50 m length at three aspect slopes were located randomly systematic at the selected site with different grazing intensities. Soil samples for nitrate (NO3?), total nitrogen (TN), ammonium (NH4+), phosphorus (P), sodium absorption ration (SAR), soil acidity or soil reaction (pH), sodium (Na), electrical conductivity (EC), organic carbon (OC), and potassium (K) content were taken in these transects. The data were subjected to analysis of variance (ANOVA), and the average of the measured parameters in the transects was compared by Duncan Multiple Range test using SPSS16 software. The soil characteristics compared between the regions were analyzed with Discriminant Function Analysis using STATISTICA10 software. Results showed that the transect slope aspect and soil characteristics had an effect on measured parameters. It was suggested to withdraw the located transect at one of the North or South and West or East Slope aspects for increasing sampling efficiency. It was also suggested that to avoid time consumtion, sampling can be recorded on plant patches’ width instead of area. It is also suggested that it would be better to record the length of the plant patches instead of their area in the non-grazed zones and record the length and the width of the plant patches in the moderate- and the high-grazed zones.  相似文献   

16.
We explore two methods that correct for differential sampling effort when estimating the true number of species in a region based on samples such as those typically recorded in museum or conservation databases. The two methods are: (1) a phenomenological model that relies on a saturating sampling curve; and (2) a model based on a lognormal distribution of species abundances. We test these methods using a database for the butterflies of Oregon and find that the distribution of high-diversity areas, using the estimated, or “asymptotic”, diversities, is strikingly different from the geographic pattern one would deduce if the raw data were used, without correcting for differential sampling effort. Further, we show that differences in accuracy exist between the two estimation procedures, and that these differences are aggravated at small sample sizes; we argue that estimates based on the lognormal distribution should be preferred because they can offer substantial improvement over analyses based solely on the raw data, generally without risking overestimation. Lastly, using both the database and estimated values of butterfly diversity, we show that the distribution of endangered and numerically rare butterflies rarely coincides with “hotspots” or centers of biodiversity. Thus, protecting regions of Oregon rich in overall butterfly diversity will not normally protect the bulk of rare or endangered butterfly species.  相似文献   

17.
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18.
Data from monitoring projects often include sampling or analytical changes that preclude trend analysis on the entire period of record. A modification of the nonparametric Kendall's test for monotonic trends, which accounts for such changes in the period of record, is described here. This approach blocks the data so that only data collected or analyzed under similar circumstances are compared. Alternatively, when appropriate data exist, data collected using the old method may be calibrated to values expected from the new method. Traditional trend tests may then be applied to resulting data sets. Results from simulations assessing both the power of the blocked test and the standard test performed on calibrated data are presented. The power of the blocked test exceeded the power of the calibration approach only when the calibration error was extremely large. Both the blocking and calibration approaches were applied to and compared for chemical data from Vermont lakes.  相似文献   

19.
基于图像处理的冬小麦氮素监测模型   总被引：6，自引：1，他引：5  
为探索基于数字图像处理技术的冬小麦氮素无损诊断图像评价指标及构建方法,设计拍摄2012-2014年度不同种植方案下冬小麦冠层图像,基于归一化的H分量K均值聚类分割算法提取基础颜色特征值,与同期叶片氮含量(leaf nitrogen content,LNC)进行线性拟合,调优并确定三原色分量最佳拟合系数,提出RGB空间下的颜色组合标准化指数(normalized color mix index,NCMI)。对比深绿色指数(dark green color index,DGCI)、红光标准化值(normalized redness intensity,NRI)和绿光与红光比值G/R发现,3个采样期NCMI与LNC的决定系数R~2均高于3个对比指标,分别为0.77、0.79、0.94,均方根误差(root mean square error,RMSE)相较同期最低的指标,分别降低了0.18%、0.37%和1.67%;生选6号和扬麦18号NCMI与LNC的相关性,在一定冠层覆盖度下均优于其他3个指标;D2密度(3×106株/hm~2)N1(纯氮150 kg/hm~2)处理下NCMI效果明显优于其他3个指标,R~2和RMSE较NRI分别改善了7.69%和4.11%,该研究可为一定冠层覆盖度下的冬小麦氮素营养诊断图像评价指标提供参考。  相似文献   

20.
Abstract

Leaf samples were collected from 24 pecan trees on three dates 1 month apart in June, July, and August. Soil samples were collected in June from each site at three depths: 0–6, 6–12, and 12–18 inches. Correlations between leaf analyses and soil test values were significant for Zn, Ca, Mg, and P. Values were not correlated for K. There was a high negative correlation for leaf Mn and soil pH. Means of leaf analysis values for the three sampling dates were not statistically different for any element. The data indicate that soil sampling should be a satisfactory means of determining fertility needs of pecan orchards, except for N.  相似文献   

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