Tài liệu tham khảo

1895, Pennsylvania

1963

1964

1965, Stelly Matthias

1965

1966, Bartelli, L.J.

1967, Whitney, Robert S

1967, Drew, J. V.

1957, Luthin, James N

1964

1964, Army, T.J.

1965, Bartholomew, W. V.

1965, Black, C.A.

1967

1967, Hamilton, Harry

1968, Kilmer, V. J.

1961, Coffman, Franklin A.

1964

1965

1965, Black, C. A.

1966, American Society of Agronomy

1967

1967, Dinauer, Richard C.

1968, Harrison, C.M