Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 1997
Publication Date: N/A
Interpretive Summary: Soils must be kept in good condition for continued good crop production. Soil organic matter content is a measure of soil condition (quality). Soil organic matter affects soil dry and water-stable aggregate size distributions, which affect soil quality. In this study, relationships among dry aggregate, water-stable aggregate, and organic matter content variables of Pullman clay loam (a Torrertic Paleustoll) were found by usin regression procedures. Samples were from the 0- to 3-cm depth of 18 dryland field sites ranging from areas cropped to winter wheat and grain sorghum for over 20 yr to grasslands converted to cropland in 1994. Of 110 relationships analyzed, 78 were significant. The 0.84- to 2.0-mm dry aggregates often were related to other dry aggregate and water-stable aggregate variables and to organic matter content variables. Included was a positive relationship with bulk soil organic matter content. The 0.84- to 2.0-mm dry aggregates resist erosion by wind. Their close relationship with some water-stable aggregate variables suggests they also affect water infiltration. If water freely infiltrates a soil, erosion by water decreases and soil water storage increases. Reduced- or no-tillage practices keep crop residues on the soil surface. As a result, surface soil organic matter contents remain constant or improve. This, in turn, results in more dry aggregates in this size range. Reduced-and no-tillage practices, therefore, help keep Pullman clay loam and similar soils in a good condition for continued crop production.
Technical Abstract: Good-quality soil is important for crop production sustainability of agricultural lands. An indicator of soil quality is soil organic matter content (OMC), which affects soil dry aggregate (DA) and water-stable aggregate (WSA) size distribution. These, in turn, affect soil quality. This study established relationships among various DA, WSA, and OMC variables of a Torrertic Paleustoll (Pullman clay loam) using simple and multiple regression procedures. Samples were obtained from the 0- to 3-cm depth of 18 differently-managed dryland treatment areas or fields to determine DA and WSA size distributions and OMCs of bulk soil. Water- stability and OMC of aggregates obtained by dry sieving were determined also. Areas sampled ranged from plots or fields cropped to winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] for over 20 yr to grasslands converted to cropland in 1994. Of the 110 relationships analyzed, 78 were significant. Variables involving the 0.84 to 2.0-mm DAs often were significantly related to various other DA and WSA variables and to OMC variables, including a positive relationship with bulk soil OMC. The DAs in this size range resist erosion by wind. Because of their significant relationship with WSAs, they are important also for maintaining water infiltration, thereby reducing the potential for erosion by water and increasing the potential for greater soil water storage. Practices such as reduced- or no-tillage retain crop residues on the soil surface and thereby maintain or enhance surface soil OMCs, which enhances the development of DAs in this size range. By inference, these practices, therefore, are important also for maintaining production sustainability of Torrertic Paleustolls such as Pullman clay loam and similar soils.