00366nam a2200109Ia 4500008004100000082001700041245007100058260004900129490003600178650002700214700001500241220204s9999    xx            000 0 und d  a631/635bBLA 0aAgronomy in a changing world and research needs for the seventies.  aAmericabAmerican Society for Agronomyc1971  aASA Special publication; no. 19  aAgricultural economics  aBLACK, C A