Using Simple Quantitative and Qualitative Field Tests to Diagnose Soil Limitations.

Smallholder farmers in poor countries may have severely limited resources with respect to the fertility of their soils and the cash available to themselves and to their agricultural advisors. Therefore, problem solving in the field may have to rely on the most inexpensive and simple kinds of equipment and materials. Many observations can be made with no equipment at all. Growing crops (and weeds) can indicate soil limitations, so training on how to recognize shoot and root symptoms of various chemical, physical and biological stresses is invaluable in the smallholder farm setting. Certain quantitative and semi-quantitative tests can be performed with materials commonly available in any Third World town. Other tests may be performed with new inexpensive yet accurate handheld field instruments. One of the most useful instruments available is the miniaturized pH meter. With an initial cost of under $40 and a lifetime measured in years, cost per analysis is just a few cents but the information obtained about soil and irrigation water can be priceless. Many models will also measured electrical conductivity, yielding additional information about the level of soil fertility or salinity. Other tests such as extractable P using a miniature colorimeter, aggregate stability using mini-sieves in a parts box, active carbon using a permanganate oxidation method and soil strength using a pocket penetrometer or even a wire flag can provide additional information to diagnose problems. Perhaps the most challenging aspect is to then "connect the dots" and do so in the context of the local landscape and community. Finally, diagnosis of the problem should be accompanied by suggested actions or solutions to alleviate the problem, and by suggestions for simple farmer testing of the validity of both the diagnosis and the solutions. Small scale farmer testing is essential before encouraging the adaptation of new technology on a wider scale by the farmer or the community.