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Title: Runoff and soil erosion plot-scale studies under natural rainfall: A meta-analysis of the Brazilian experience

item ANACHE, JAMIL - Universidade De Sao Paulo
item OLIVEIRA, PAULO - Federal University Of Mato Grosso
item Flanagan, Dennis
item Nearing, Mark
item WENDLAND, EDSON - Universidade De Sao Paulo

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2017
Publication Date: 1/9/2017
Citation: Anache, J.A., Oliveira, P.T., Flanagan, D.C., Nearing, M.A., Wendland, E. 2017. Runoff and soil erosion plot-scale studies under natural rainfall: A meta-analysis of the Brazilian experience. Catena. 152:29-39.

Interpretive Summary: Soil erosion is a serious problem throughout the world, and experiments to measure soil loss and the effects of various land management practices are critical in understanding and predicting the processes. Data on soil erosion rates from plots taken in the field under natural rainfall conditions, with typical or representative soil and crop management, are the backbone of information needed to develop models to help guide conservation management decisions. For example, in the United States beginning in the 1930s, and reaching a maximum number in the 1950s and 60s, such field plots were established across the eastern United States at many locations, thus representing a diversity of climate, soils, and cropping systems. The data from the field sites formed the basis of the Universal Soil Loss Equation (USLE), which has been used for implementing not only conservation practices, but also national conservation programs, such as the Conservation Reserve Program, that involves the spending of billions of taxpayer dollars. These are very important data for erosion science and cannot be obtained in any way other than through long-term experimental field plots. In other countries of the world, such as Brazil, field plot erosion data are not as plentiful. This study was designed to evaluate the situation and collate data from such erosion plots that have been established in Brazil during the past 40 years. Results of the study indicate that there is still a great need in Brazil for such data, and it points out geographic areas and cropping systems that are under-represented and should be addressed in order to better understand the situation for soil erosion in this agriculturally important country.

Technical Abstract: Research to measure soil erosion rates in the United States from natural rainfall runoff plots began in the early 1900’s. In Brazil, the first experimental study at the plot-scale was conducted in the 1940’s; however, the monitoring process and the creation of new experimental field plots have not continued through the years in either country, and are relatively rare in other parts of the world. To better understand runoff and soil erosion rates in Brazil, we review the plot-scale studies that have been conducted across the country. We also evaluated trends, challenges, and perspectives of plot-scale studies in Brazil. Runoff and soil loss records under natural rainfall were compiled from peer-reviewed journals, books, M.Sc. theses, and Ph.D. dissertations, and we organized a database containing the following information: geographic coordinates, region, rainfall, runoff, soil erosion, length of record (years), land cover, tillage system, slope length, and slope gradient. We found mean values of observed annual soil loss ranging from 0.1 t ha y-1 (grassland and pasture in southern region) to as great as 64.4 t ha y-1 (fallow plots in central-western region). Our findings indicated that the southern and southeastern regions of Brazil have the greatest number of runoff and soil loss monitoring sites and length of records (plot-years), corresponding to 68% and 89% of the totals, respectively. In addition, the number of plot-years of data collected has decreased 86% in the last 15 years. However, the number of published documents has increased around 70% in the same period. Around 50% of the experimental studies have 2 years or less of monitored data. In order to reduce the variability of the observed data, develop models, and support decisions, it is important to increase the monitoring period of the experimental sites. Moreover, efforts should continue to allow field observations in all regions of Brazil where data is scarce, in particular paying special attention to the central-western region, where cropland is the main land-use, and along the largest Brazilian agricultural expansion frontier (northern region).