Field Guide of Discovery-based Exercises for - Aseanipm ...

Exercise No. 3.05 53
THE ‘FEEL METHOD’: CLASSIFYING SOIL TEXTURES
AND STRUCTURES FOR ORGANIC VEGETABLE
PRODUCTION
BaCKGroUND aND raTIoNalE
The common field method of classifying a soil is by its
feel 54 . Much can be judged about texture and class of a soil
merely by rubbing it between thumb and fingers than by any
other superficial means. Usually, it is helpful to wet sample
in order to estimate plasticity more accurately. The way a
wet soil ‘slick out’ (e.g., develops a continuous ribbon when
pressed between thumbs and fingers) gives a good idea of the
68
Field Guide of Discovery-based Exercises for Organic Vegetable Production
when is this exercise most
appropriate?
ɶ In FFS, TOT and VST
sessions, as component
of ‘Integrated Nutrient
Management’ topic; and
ɶ When farmers want to
learn from others some
soil texture and structure
management practices
for organic vegetable
production.
amount of clay present. The slicker a wet soil, the higher its clay content. Sand particles are gritty;
silt has a floury or talcum powder-feel when dry and is only slightly plastic and sticky when wet.
Silt and clay generally impart persistent cloddiness. However, soil textures are not subject to easy
modification in farmers’ field. For most field crop production areas, soil texture is not changed by
cultural management. We turn to a physical property of the soil that is subject to some change – the
soil structure.
Nevertheless, for some garden and organic vegetable crops with high economic value, large quantities
of sand may be added to a fine-textured soil to improve its tillage properties. In greenhouses, mixtures
of different soils and organic materials are commonly used and a textural class of mixtures may be
varied. Thus, one factor to consider in raising healthy and vigorous organic vegetable crops is to
understand soil texture and structure. Soils that are coarse or stony have low water holding capacity
and organic matter content, while crumbly and friable soils are richer in organic matter, easier to
work on, and more suited for growing organic vegetables. On the other hand, fine-textured soils,
especially those without a stable granular structure, allow relatively slow gas and water movement
despite the usually large volume of total pore space. Aeration, especially in subsoil, frequently is
inadequate for satisfactory root development and desirable microbial activity. Therefore, the size
of individual pore spaces rather than their combined volume is an important consideration. The
loosening and granulating of fine-textured soils promotes aeration not so much by increasing total
pores space as by raising the proportion of macro-spaces.
53 Adapted from Callo, Jr., D.P., L.B. Teofilo, and H.A. Tauli (eds). 2002. Field Guide of Discovery-based Exercises for Vegetable IPM, Volume II.
SEAMEO Regional Center for Graduate Study and Research in Agriculture (SEARCA), Los Baños, Laguna, Philippines. pp68-71.
54 Brady, N.C. 1985. The nature and properties of soils. 9 th Edition. Macmillan Publishing Co., 866 3 rd Ave., New York, New York, U.S.A. pp36-71.