2Schnitzer M and Poapst P A. Effects of a soil humic compound on root initiation [J].Nature, 1967, 213:598-599.
3Poapst P A and Schnitzer M. Fulvic acid and adventitious root forrelation [J], Soil Biol Biochem, 1971,3:215-219.
4Linehan D J. Some effects of a fulvic acid component of soil organic matter on the growth of cultivated excised tomato roots [ J]. Soil Biol Biochem, 1976,8:511-517.