PT - JOURNAL ARTICLE AU - D. L. Karlen TI - Conservation tillage research needs DP - 1990 May 01 TA - Journal of Soil and Water Conservation PG - 365--369 VI - 45 IP - 3 4099 - http://www.jswconline.org/content/45/3/365.short 4100 - http://www.jswconline.org/content/45/3/365.full