Purdue University-Agricultural Experiment Station Agronomy Department
AY-9 (Rev.) April, 1951 (1M)
RESULTS OF PHOSPHATE COMPARISONS Bedford Silt Loam Bedford, Indiana 1916-1948
A comparison of rock and superphosphate was started in 1916 by applying P2O5 in the form of rock phosphate at four times the rate of	applied in superphosphate.
During the earlier years of the experiment 16 percent superphosphate and 30 percent rock were applied. In more recent years 20 percent superphosphate was compared with 33 percent finely ground rock phosphate. In all cases, the amounts of P205 applied per rotation were the same in both periods.	
In this comparison, a rotation of corn, wheat, and hay was used. In all cases, the com was cut and removed from the plots. The land was disced and seeded to wheat and timothy in the fall. A mixed seeding of legumes was made early in the spring. One cutting of hay was removed and the second growth plowed under the following spring for com. Manure was returned in amounts equal to the total weight of the produce removed except for the wheat grain. Limestone was applied at the beginning of the experiment at the rate of 4 tons per acre. In 1935, an additional two tons per acre were applied.
In 1948, the limed soils tested pH 6.4 to 6.7 while the unlimed plots were pH 5.0 to 5.3.
Before 1939, all phosphates were broadcasted for corn. Since then .25 of the superphosphate has been drilled in the row for corn and the other 3/4 has been applied at the time of seeding wheat. For three years after this change the superphosphate for wheat was applied broadcasted, but since the fall of 1942 the superphosphate going on wheat has been applied through the fertilizer attachment of the grain drill. The method of applying rock phosphate has been the same over the entire period.
Potash produced little or no response during the first years on similar soil adjacent to the land used for this experiment. In 1939, potash started to show profitable increases. Since then 60 pounds of K2O and 20 pounds of nitrogen per acre have been broadcasted as a top dressing to the wheat in early spring. In 1949 the rate was increased to 120 pounds of K20 and is now applied broadcast for corn rather than for wheat.	
Table 1 shows the results of the basic treatments in the way of increases in yields per acre over and above the untreated yields.	In order to	expose any change	in yield
trends, the period has been broken into three	parts. From	these results, it	will be
noticed that although lime alone was profitable it was not as valuable as manure. The return on the investment was best for the combination of lime and manure and should be considered a vital part of a maintenance program for soils of similar nature.
Table 2 shows the relative effectiveness of rock and superphosphate when applied with lime and manure at three different rates. The total value of all the crops is shown in the table. When this is divided by the total amount, in tons, of fertilizer applied, it will be noted that on this soil, phosphate is a very important material. Low application rates of superphosphate produced large increases and were worth $276.00 per ton.
This was 7 times its actual cost. In the last	column it may be noticed that	the return
was enough higher per pound of superphosphate	that in all	cases it was 3 or	more times
as effective as rock phosphates in producing gross dollar returns.
The effect of a single rate of phosphorus supplied in two different carriers, rock superphosphate, and the effects of each additional application of these same materials when the basic rate is doubled and trebled is shown in table 3.