ECOLOGICALLY-BASED SOIL AND CROP MANAGEMENT SYSTEMS FOR SUSTAINABLE AGRICULTURE
Location: North Central Agricultural Research Laboratory
Title: Soil Structure Examined
Submitted to: Trade Journal Publication
Publication Type: Trade Journal
Publication Acceptance Date: December 6, 2007
Publication Date: January 5, 2008
Citation: Schumacher, T.E., Riedell, W.E. 2008. Soil Structure Examined. The Leading Edge 7(1):398-405:
Interpretive Summary: Dirt, which is a non-technical term for the solid part of soil, is considered by many to be something that needs to be cleaned up and discarded. When we speak of dirt we usually are not thinking that it is the loss of soil structure (in this case, the removal of the soil pore space between the soil solids) that turned a valuable substance (soil) into an annoyance. With this article, we hope to provide information on soil structure and its importance in the value and utility of soil. This article defines soil structure, and answers, among others, the following questions: how does soil structure come about, what role do biological organisms have in creating soil structure, how does human activity affect soil structure, what effect does soil structure have on crop productivity, and what management practices are useful for creating and maintaining soil structure? This information will be useful to producers and farmers who seek to understand how to maintain or improve the structure of the soils they farm.
Soil structure is the product of the inter-play of all the observed and unobserved forces acting on and within the soil. The most critical component of soil structure for crop productivity is the structure of pore space. Biological organisms play a major role in the development of pore structure and stabilization/maintenance of pore space. Physical and chemical forces also play a significant role in the localized development of fracture lines within the soil that correspond to lines of weakness and cracks within the soil. Soil structure is a result of the continual flow and transformation of energy (mechanical and chemical) within the soil system. The agents of energy transformation are primarily biological organisms, but also include physical phenomenon such as wetting-drying and freeze-thaw cycles. Biological organisms cycle and recycle energy from the sun through food webs. Roots and plant debris are the primary source of energy captured from photosynthesis. This material is utilized by a myriad of organisms that feed off of each other creating mechanical and chemical forces that create tensions between soil particles. These tensions can cause soil particles to move forming pores with various shapes, sizes, and connectivity. Humans have a profound affect on soil structure both directly and indirectly. A loss of soil structure can have catastrophic consequences. Since soil structure is heavily dependent on biological activity within the soil and is related at least in part to the complexity of soil food webs, anything that humans do to consciously or unconsciously manipulate the biological community in the soil will affect pore structure within the soil. Pore size distribution, pore connectivity, as well as total amount of pore space are determined to a large extent by soil structure and determine the below-ground environment. Water storage, water drainage, air availability, ease of root growth are examples of components of below ground environment determined by pore structure. Consider a building that does not have proper air circulation, plumbing, or proper room size for its function (eg. an office building with only closets for rooms) and you have a good idea of how soil structure can affect the productivity and viability of plants and crops.