Use of Multispectral Ikonos Imagery for Discriminating between Conventional and Conservation Agricultural Tillage Practices

There is a global concern about the increase in atmospheric concentrations of greenhouse gases. One method being discussed to encourage greenhouse gas mitigation efforts is based on a trading system whereby carbon emitters can buy effective mitigation efforts from farmers implementing conservation tillage practices. These practices sequester carbon from the atmosphere, and such a trading system would require a low-cost and accurate method of verification. Remote sensing technology can offer such a verification technique. This paper is focused on the use of standard image processing procedures applied to a multispectral Ikonos image, to determine whether it is possible to validate that farmers have complied with agreements to implement conservation tillage practices. A principal component analysis (PCA) was performed in order to isolate image variance in cropped fields. Analyses of variance (ANOVA) statistical procedures were used to evaluate the capability of each Ikonos band and each principal component to discriminate between conventional and conservation tillage practices. A logistic regression model was implemented on the principal component most effective in discriminating between conventional and conservation tillage, in order to produce a map of the probability of conventional tillage. The Ikonos imagery, in combination with ground-reference information, proved to be a useful tool for verification of conservation tillage practices. Introduction The long-term conversion of grass and forest lands to crop and grazing land has resulted not only in historic losses of soil carbon worldwide but has also added additional carbon dioxide to the atmosphere. Atmospheric concentrations of CO2 can be lowered by reducing emissions or by sequestering it from the atmosphere and storing it as soil carbon. A potentially important way of increasing soil carbon is through the restoration of degraded soils and the widespread adoption of soil conservation practices, including the use of conservation tillage (Falloom et al., 1998; Uri et al., 1999; Schlesinger, 2000). Conventional tillage practices aerate the soil and increase microbial activity responsible for oxidizing plant residue. In contrast, conservation tillage practices limit microbial oxygen supply, and reduce microbial activity, which lowers soil carbon consumption. If continued on an annual basis, these practices allow the amount of soil carbon, in the form of plant residue, to increase over time. Thus, conservation tillage practices result in sequestration of carbon dioxide in the soil as organic carbon. Residue also acts as a mechanical barrier to the effects of wind and rain, which reduces soil erosion and improves plant germination (Uri et al., 1999). Plant residue also modifies soil temperature by intercepting solar radiation and insulating the soil, thus reducing thermal variation (Evans and Young, 1970). Changes in soil temperature produced by plant residue may directly influence plant growth, but also may enhance the rate of mineralization, and therefore nutrient availability (Knapp and Seastedt, 1986). Also, plant residue reduces maximum soil temperatures and creates a barrier to water vapor diffusion (Holland and Coleman, 1987), thereby reducing evaporation from the soil and increasing water availability in the root zone. One way that could efficiently and economically encourage greenhouse gas mitigation efforts is to provide a trading system whereby carbon emitters can buy effective mitigation credits from others who can either avoid emissions or sequester carbon from the atmosphere, such as farmers implementing conservation tillage practices. As an example, CQuest Ltd. of West Des Moines, Iowa, specializes in documenting greenhouse gas mitigation efforts by agricultural producers and landowners and adding services that turn these efforts into tradable Carbon Emission Reduction Credits (CERC). CERCs are standardized greenhouse gas mitigation products measured in terms of the natural warming effect of one metric ton of carbon dioxide (CO2) in the atmosphere. CERCs are defined by describing various management practices or resource uses that avoid or sequester greenhouse gases and the measurement protocol for quantifying the amount of CO2 equivalent removed from the atmosphere versus what would have been emitted. CERCs are, by themselves, pure information products. As such, their basic value depends upon the integrity of the system that produces them and the accuracy of the data that creates them. Such a trading system requires a low-cost and accurate technique for guaranteeing compliance. Verification of such a trading system would require low-cost methods to implement, and remote sensing technology offers a means of keeping costs low. Several remote sensing techniques for distinguishing residue type and amount using the middle infrared portion of the spectrum have been documented in the literature (e.g., Mcnairn and Protz, 1993; van Deventer et al., 1997; Nagler et al., 2000). However, the only operational PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING May 2003 537 Center for Advanced Land Management Information Technologies (CALMIT), Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln, 113 Nebraska Hall, Lincoln NE 68588 ([email protected]).