Kosmowski Frédéric, Stevenson James, Campbell Jeff, Ambel Alemayehu, Haile Tsegay Asmelash
CGIAR Standing Panel on Impact Assessment, Food and Agriculture Organization of the United Nations, Rome, Italy.
Spatial Solutions Inc, Bend, OR, USA.
Environ Manage. 2017 Oct;60(4):705-716. doi: 10.1007/s00267-017-0898-0. Epub 2017 Jun 8.
Maintaining permanent coverage of the soil using crop residues is an important and commonly recommended practice in conservation agriculture. Measuring this practice is an essential step in improving knowledge about the adoption and impact of conservation agriculture. Different data collection methods can be implemented to capture the field level crop residue coverage for a given plot, each with its own implication on survey budget, implementation speed and respondent and interviewer burden. In this paper, six alternative methods of crop residue coverage measurement are tested among the same sample of rural households in Ethiopia. The relative accuracy of these methods are compared against a benchmark, the line-transect method. The alternative methods compared against the benchmark include: (i) interviewee (respondent) estimation; (ii) enumerator estimation visiting the field; (iii) interviewee with visual-aid without visiting the field; (iv) enumerator with visual-aid visiting the field; (v) field picture collected with a drone and analyzed with image-processing methods and (vi) satellite picture of the field analyzed with remote sensing methods. Results of the methodological experiment show that survey-based methods tend to underestimate field residue cover. When quantitative data on cover are needed, the best estimates are provided by visual-aid protocols. For categorical analysis (i.e., >30% cover or not), visual-aid protocols and remote sensing methods perform equally well. Among survey-based methods, the strongest correlates of measurement errors are total farm size, field size, distance, and slope. Results deliver a ranking of measurement options that can inform survey practitioners and researchers.
利用作物残茬保持土壤的永久覆盖是保护性农业中一项重要且普遍推荐的做法。衡量这种做法是提高对保护性农业采用情况及其影响的认识的关键一步。可以采用不同的数据收集方法来获取给定地块的田间作物残茬覆盖率，每种方法对调查预算、实施速度以及受访者和访谈者的负担都有不同影响。本文在埃塞俄比亚的同一农村家庭样本中测试了六种测量作物残茬覆盖率的替代方法。将这些方法的相对准确性与一种基准方法——样线法进行了比较。与基准方法相比的替代方法包括：（i）受访者估计；（ii）实地访问的调查员估计；（iii）未实地访问的有视觉辅助工具的受访者估计；（iv）实地访问的有视觉辅助工具的调查员估计；（v）用无人机收集并通过图像处理方法分析的田间图片；以及（vi）用遥感方法分析的田间卫星图片。方法学实验结果表明，基于调查的方法往往会低估田间残茬覆盖率。当需要覆盖率的定量数据时，视觉辅助方法能提供最佳估计。对于分类分析（即覆盖率是否大于30%），视觉辅助方法和遥感方法表现同样出色。在基于调查的方法中，测量误差的最强相关因素是农场总面积、地块面积、距离和坡度。研究结果给出了一个测量选项的排名，可为调查从业者和研究人员提供参考。
