A Vess Assessment of Tillage and Stover Harvest Effects in Iowa, U.S.a.

Soil quality/health reflects physical, chemical, and biological properties, processes, and interactions occurring in response to management practices such as tillage and crop residue harvest. Increased global interest in harvesting crop residues for bioenergy, animal feed, or other bio-products has resulted in questions regarding effects on soil structure. Few studies have assessed the combined effects of stover harvest and tillage practice on soil structural quality.  The purpose of this study was to determine if the semi-quantitative approach – the Visual Evaluation of Soil Structure (VESS) would effectively evaluate the soil structural quality for different levels of stover harvest. VESS integrates soil properties related to size, strength and porosity of aggregates, roots and soil color into a single number – the Sq (structural quality) scores. Sq ranges from 1 (good structural quality) to 5 (poor structural quality). We evaluated non-harvest, moderate and high stover harvest levels for no-tillage (NT) and chisel plow (CP) following seven years of continuous corn. Undisturbed 10 x 20 x 25 cm soil blocks were taken using a spade in April 2015. Were measured the thickness and Sq score of layers with distinct soil structural qualities and computed an overall Sq (weighted average). A significant interaction was found between corn stover harvest versus tillage system for the overall Sq score. There were no significant Sq differences between NT and CP since an average of 50% of the corn stover is kept on the soil surface. Under complete corn stover harvest Sq CP > Sq NT. For NT, stover harvest significantly increased in Sq while for CP only the high level of stover harvest had an adverse effect on Sq. The VESS approach was sensitive for detecting effects of corn stover harvest and tillage practice on soil structural quality and should be further evaluated as an integrative soil quality/health indicator.