SENSING SOIL CONDITION - INFRARED DIAGNOSTICS FOR AGRICULTURE AND THE ENVIRONMENT

Assessment of soil condition requires expensive and time-consuming measurements in the laboratory and the field. Many repetitions of the measurements are required to deal with high soil variability. As a result, scientists have been unable to measure and monitor soil condition (soil quality/health) and soil degradation over large areas.

Our Approach Test of Spectral Library Approach

THE PROJECT

Sensing Soil Condition is a technological approach for rapid assessment and large area surveillance of soil conditions for plant growth and ecosystem functioning (e.g. hydrological regulation, erosion

regulation, soil biodiversity). The technology is based on rapid screening of soil condition using infrared spectroscopy (IR). Soil properties and soil condition indices are predicted from infrared signatures of soils compiled into spectral libraries. Spectral libraries constructed from soils sampled from georeferenced locations may then used in conjunction with remote sensing imagery to map out soil quality and soil constraints over entire river basins.

Conventional assessments of soil capacity to perform specific production, engineering or environmental functions rely on local calibration of observations on soil functional attributes to measured soil properties. However, soil analyses are expensive and dense sampling is required to adequately characterize spatial variability of an area, making broad-scale quantitative evaluation difficult. Infrared reflectance spectroscopy, especially near infrared spectroscopy (NIR), is now routinely used for rapid non-destructive characterization of a wide range of materials in industry. Although soil scientists have investigated reflectance spectroscopy for several decades, the technology has not been widely taken up and routinely applied in soil studies.

World Food Prize winner Dr. Pedro Sanchez predicts that within a decade most developing countries will be using the technique for soil and plant analysis.

Our research focuses primarily on application of infrared spectroscopy in risk-based approaches to soil evaluation-approaches that explicitly consider uncertainty in prediction and interpretation of soil properties. We are applying these approaches to the development of soil evaluation and monitoring schemes at national and project scales, and in a pan-tropical research programme on the impWorld Agroforestry Centre of land use and land management on soil degradation.

In addition, we are developing an integrated approach to the application of infrared spectroscopy to diagnosis of soil, crop and livestock health in tropical developing countries. This involves use of infrared spectroscopy for a wide range of agricultural and agroforestry inputs and products, including: soils, sediments, crop tissues, manures, composts, organic wastes, seeds, feeds and fodders, livestock faecal samples, wood and charcoal, and tree-derived oils.

Some of our newest research is investigating use of infrared spectroscopy in the fields of genomics, metabolomics and metabolic fingerprinting. Here, IR is used to study changes in plant biochemical composition in response to plant genetic variation and environmental constraints.

WHY SOIL IS IMPORTANT

Soil fertility decline is not just a problem of nutrient deficiency. It is also a problem of physical and biological degradation of soils, of inappropriate crop varieties and cropping systems, and of pests and diseases. It relates to links between poverty and land degradation, often-perverse national and global incentive policies, and institutional failures.

The degradation of soil fertility is linked to other human and environmental problems. Malnutrition is a good example. It is a major factor in over 54% of deaths of children under 5 worldwide (Pelletier et al. 1995) and in Sub-Saharan Africa (SSA) the percentage is higher than the global average.

Soil provides essential ecosystem services. Measuring impaired water infiltration on a forest soil following many years of continuous cropping with low nutrient inputs. Photo credits: KD Shepherd

Most of these deaths are not due to famine but to malnutrition, which, being linked to infectious diseases, is widely recognized as an underlying cause of mortality (Caulfield et al. 2004; Villamor et al. 2005). Projections suggest that malnutrition will worsen in SSA over the next decade, with the incidence of underweight children increasing by 9% (Caulfield et al. 2004). Thus, the failure of African agriculture to make use of newly available germplasm, which supports higher productivity and greater nutritional quality, is tragic. Soil degradation lies at the heart of this failure, as there is little incentive for farmers to invest in new germplasm once soils are degraded.