00350nam a2200109Ia 450000500170000000800410001702000150005805000190007310000190009224500850011126000440019620251229192335.0251229s9999    xx            000 0 und d  a0471934178  aS 540  .O53P43  aTripp, Robert. 0aPlanned Change in Farming Systemsb  Progress in on Farm Research.cRobert Tripp  aChichesterb  John Wiley and Sonsc1991