Biological efficiency in agriculture / C.R.W. Spedding, J.M. Walsingham, and A.M. Hoxey. Spedding, C. R. W. Walsingham, J. M. Hoxey, A. M. Agricultural productivity. Biological productivity. Agriculture. Biology, Economic. S494.5.P75 S63 631.5 19 SPB Includes bibliographies and index. New York : Academic Press, c1981. c1981. 1981 Text x, 383 p. : eng