Sách tham khảo

1895, Pennsylvania

1963

1964

1965

1965, Bartholomew, W. V.

1966, Bartelli, L.J.

1967, Whitney, Robert S

1967, Hamilton, Harry

1957, Luthin, James N

1964

1964

1965, Black, C. A.

1965

1967, Dinauer, Richard C.

1967, Drew, J. V.

1968, Harrison, C.M

1961, Coffman, Franklin A.

1964, Army, T.J.

1965, Black, C.A.

1965, Stelly Matthias

1966, American Society of Agronomy

1967

1967

1968, Kilmer, V. J.