A study was made of the experimental error of 2,492 yields of sorghum on duplicate pot cultures in the greenhouse. The total number of yields were equally divided in number between two successive crops of sorghum which followed Austrian winter peas on the same soil in pot cultures. A summary of the average yields and of the average deviation and of the standard deviation of the yields by class groups is given. On the basis of the same size of yields the experimental error between duplicate yields was larger on the second crop than it was on the first. For the first crop of sorghum the average deviation of the duplicate yields from their averages was 6.34% of the average yields and for the second crop 7.25% of the average yield. For the first crop of sorghum the standard deviation of duplicate yields from their averages was 8.55% of the average yield and for the second crop 9.84% of the average yield. On those pot cultures producing a yield of over 35 grams of dry matter per pot, the average deviation of duplicate yields of the first crop was 4.17% of the average yield and of the second crop 5.11% of the average yield. The corresponding standard deviation of these yields for the first crop was 5.22% of the average yield and, for the second crop, 6.56% of the average yield.

The results may be briefly summarized as follows: 1. Maximum plant response to phosphate fertilization on highly colloidal acid and calcareous soils was not obtained until the applications of the phosphates were requvalent to 1,800 and 2,000 pounds of superphosphate per 2 million pounds of soil, respectively. 2. The efficiency of the various phosphates used, as measured by plant response, decreased rapidly with the time of contact with the soil. 3. In the acid soil, di-calcium phosphate was slightly more available than mono-calcium phosphate. The relative efficiencies for mono-calcium, tri-calcium, mono-ammonium, ferric phosphates. and superphosphate were 100, 57, 110, 25, and 117, respectively. 4. Calcium carbonate greatly decreased the availability of readily soluble phosphates and the crop yield when applied immediately before planting to the acid clay soil, whereas after equilibrium was established and CaCO3 was no longer present in the soil the availability of the phosphates increased as shown by the yield of sorghum. Calcium carbonate decreased the availability of tri-calcium phosphate as measured by plant growth. 5. In general, the more soluble the phosphate used the more rapid was the rate of fixation. On the other hand, relatively insoluble phosphates were fixed slowly but were inefficient in supplying available phosphorus to the plants.

1. The experimental procedure included complete utilization of the nitrogen in the single salt solutions by the sorghum and maize seedlings used. Simultaneous comparisons were made between parallel solution cultures. Typical comparisons included NH4Cl vs. HCl, NaNO3 vs. NaHCO3, etc. Titrable acidity of the solutions before and after absorption and the pH values of the dried and ground plants after absorption were determined. 2. Parallel cultures of (NH4)2SO4 vs. H2SO4 and of NH4Cl vs. HCl gave residual titrable acidity in each case after the disappearance of the NH4 ions from the cultural solutions. The residual liquids from the ammonium salts showed a greater amount of acidity than did those where the acid was supplied chemically. The pH determinations of the ground material showed that the acids absorbed or physiologically formed within tbe plants were still in evidence. Parallel cultures of NaNO3 vs. NaHCO3 and KNO3 vs. KHCO3 gave residual titrable alkalinity in each case after the disappearance of NO3 ions from the cultural solutions. The residual liquids from the nitrate salts gave smaller amounts of alkalinity in each comparison. The alkalinity absorbed or physiologically formed in each case was clearly shown as still present by the pH determinations of the ground plants. 4. Parallel cultures in solutions of HNO3, NH4NO3, NH4HCO3, and H2O after absorption of all NH4 and NO3 ions gave small amounts of titrable alkalinity in each case. These titration values were practically equal to each other, although the original solutions of HNO3 had marked titrable acidity and those of NH4HCO, marked titrable alkalinity. The pH values determined on the plants from the nitrogen compounds furnished in this group were practically equal to those on the plants grown in water. This showed that the acidity and alkalinity absorbed by plants in this group had largely disappeared in the transformations following absorption. These findings are in accord with theories previously proposed. 5. The plants must use energy in forming proteins from NH4 and NO3 compounds. The amounts of energy required to secure OH ions to go with the NH4 ions and of H ions to go with NO3 ions seem to bear a qualitative relationship to the rates of NH4 and NO3 ion absorption from solutions of different pH values.