Acid and Base Forming Fertilizers and Their Influence on the Reaction of Some Florida Soils

A consideration of fertilizer materials furnishing the three' major plant foods reveals the fact that sources of phosphoric acid and potash have remained almost constant while the sources of nitrogen have undergone decided changes. Superphosphate has been, and probably will continue to be, our main source of phosphoric acid in most fertilizer mixtures. In the year 1900, 79.8 per cent. of the total available phosphoric acid was attributed to superphosphate. At the present time superphosphate accounts for 86.6 per cent. of this plant food. This slight increase is due to a gradual decrease in the use of organic sources. High grade potash salts such as the muriate and sulphate have furnshed between 71.3 per cent. in 1900, and 61.7 per cent. in 1931, of our available potash. Nitrogen carriers have undergone noticeable changes. MEHRING and PETERSON (1) have made a study of fertilizer materials and fertilizer mixtures produced and marketed in the United States from 1880 to the present time. A portion of their findings in regard to nitrogen materials is plotted in Figure 1. From this chart one can see that organic ammoniates decreased from 88.3 per cent. of the total nitrogen consumed for fertilizer purposes in 1880 to 18.3 per cent. in 1932. The decrease is one of increasing magnitude. Nitrates during this same period while rising to various peaks and dropping from time to time, show a gradual trend upward until 1920, after which a fairly sharp decline in usage is shown. This ir-