Visual soil evaluation - Spade vs. profile methods and the information conveyed for soil management

摘要

Visual soil evaluation (VSE) techniques, established in soil management and quality assessment are categorised into spade and profile methods. Both approaches have merits and limitations. For example, VESS, a widely used spade method, requires basic equipment and is quick, thereby enabling wide spatial deployment, but only gives a general indication of soil structural quality to 25 cm depth, potentially missing important features below the cultivation zone in arable soils. SubVESS, the profile equivalent of VESS, gives detailed information to approximate to 1 m at specific points but is time consuming, relatively expensive and cannot be deployed over wide areas. Despite giving more detailed information, full (to approximate to 1 m) profile methods may not always be desirable. Our aim was to compare possible management recommendations derived from soil structure, obtained by VESS, SubVESS and a new procedure that bridged both approaches, called the Double Spade method (DS). In-field and headland zones at 10 arable sites in Ireland under conventional tillage were surveyed using the methods, assessing to approximate to 25 (VESS), 40 (DS) and 80 (SubVESS) cm depth respectively. Results showed significant difference between field zones, indicating structural damage at headlands, occasionally to 80 cm depth. From the soils surveyed, VESS was not always sufficient for determining soil quality related management requirements. DS indicated that damage occurred below 20 cm depth. SubVESS gave additional information to the other VSE techniques regarding the extent of damage, in some cases only evident below 40 cm depth. Quantitative measurements showed significant difference only to 20 cm depth. It was concluded that the extra information obtained using DS was worth the time spent collecting the data. It is suggested that SubVESS may be appropriate to further investigate suspected issues as indicated by DS, but not for routine survey over large areas.