Plant culture and other studies with some guanidine compounds

Greenhouse pot-culture studies to determine the nutrient value of di-guanidine phosphate, tri-guanidine phosphate, di-guanidine sulfate, and dicyanodiamide, which have been suggested as possibly possessing fertilizer value, have been made. Pot-culture experiments were conducted with millet (German), oats, and wheat. The guanidine salts were employed in the greenhouse studies in different quantities, namely, 40, 80, 120, and 160 pounds per acre in 2-8-8, 4-8-8, 6-8-8, and 8-8-8 nutrient mixtures. Compared with the control (no-nitrogen mixture, 0-8-8), the nitrogen of the guanidine compounds proved to be fairly effective at the 40- and 80-pound rates, but lowered the yields of all indicator crop plants when stepped up to 120 and 160 pounds of nitrogen per acre. These findings indicate that any attempt to use the guanidine salts as nitrogen sources would have to be made cautiously and limited to probably not more than 80 pounds of nitrogen per acre. In comparing the millet, oats, and wheat yields obtained with the guanidine salts with those from the urea and the ammonium sulfate-sodium nitrate-dried blood mixtures, the guanidine compounds generally were less effective throughout than the standard nitrogen sources. The guanidine salts gave greater increases in yields of millet on close-to-neutral soils than on distinctly acid soil. With respect to dicyanodiamide, nothing favorable can be ascribed to it as a source of nitrogen on the basis of findings in these tests. Throughout the plant tests in the greenhouse it made a poor showing, with indications of a toxic action toward the indicator plants as evidenced by a bleached-out or chlorotic appearance. It is also conceivable that bacterial action might have been inhibited so that the nitrogen of the dicyanodiamide was not rendered available in time to be of any nutrient use to the plants grown. The latter hypothesis is supported by both the ammonification and nitrification studies, which tend to show that the guanidine compounds and dicyanodiamide were not easily broken down. Of the different compounds the di-guanidine phosphate was the least resistant to change.