?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Ley%2C+G+J&rft.aufirst=G+J&rft.aulast=Ley&rft.issn=0167-1987&rft.pages=367-381&rft.atitle=Spatial+variability+in+penetration+resistance+of+a+hardsetting+tropical+alfisol&rft.volume=29&rft.issue=4&rft.title=Soil+%26+Tillage+Research&rft.date=1994&rft.genre=article