Crop tolerance to suboptimal land conditions : proceedings of a symposium - Plucknett, D. L.; Baker, D. E.; Fleming, A. L.; Engelstad, O. P.; Jung, Gerald A.; Stelly, Matthias; Kral, David M.; Nauseef, Judith H. (American Society of Agronomy ; Crop Science Society of America ; Soil Science Society of America, 1978)