Soil cultures containing the ground roots of corn or sorghum were compared with respect to their ability to cause nitrate nitrogen to disappear in soil. The roots were employed in equal quantities by weight and by soluble-organic-matter content. Sorghum roots were found to cause a more rapid disappearance of supplied nitrates than did corn roots. An organism, designated as "guttation," which is known to assimilate both nitrate nitrogen and carbohydrates, increased in numbers, as revealed by plate counts, less rapidly in soil cultures containing the roots of corn than in those containing the roots of sorghum. It is assumed that other organisms which oxidize organic substances will react toward these residues as did "guttation." The evolution of carbon dioxide from cultural flasks was more rapid from soil containing sorghum roots than from soil containing corn roots. This was interpreted as indicating that the organic matter of sorghum roots is more easily oxidized than is that of corn roots. The results of the investigation suggest that the injurious after-effects of sorghum may be associated with the comparative ease with which its roots are oxidized in soil. This process, which is accompanied with an increase in the number of soil organisms and an increase in the assimilation of nitrate nitrogen, would tend to deplete the soil of available nitrogen. The extent to which these processes are operative in soil when young plants are in need of nitrogen may determine the amount of injury which the sorghum crop exerts on those crops which follow.

1. Nitrate of soda applications of 100, 200, and 400 pounds per acre to replicated plats at Davis gave significantly increased yields of barley following White Durra. The average yields were 810, 1,125, and 1,495 pounds per acre, respectively,, over 1,225 pounds, the average yield of the unfertilized check plats. 2. Significant increases in yield were secured with 200- and 400-pound applications of sulfate of ammonia to barley and wheat from replicated plats in the Imperial Valley following Hegari. All 400-pound applications and some 200-pound applications more than doubled the yields of barley. In general, higher yields were secured by applying the fertilizer 35 and 67 days after planting than at planting time. 3. In triplicate pot experiments where different weights of sorghum roots, corn roots, and sucrose were added to the soil, barley decreased in yield with an increase in sorghum roots and sucrose added; nitrates in uncropped pots were progressively depressed by increased additions of sorghum roots and sucrose; and fenugreek, a legume naturally inoculated at Davis, made normal growth. A close relationship is indicated between the depression of nitrates by sorghum roots and that by an equivalent amount of sucrose. Likewise, a relationship between barley yields and nitrates thus depressed is indicated. 4. In replicated field trials barley was depressed in yield progressively by following millet, corn, broom corn, and sweet sorghum below the yield following fallow, while fenugreek made normal growth on all of the plats previously in crop, in fact yielding higher than those following fallow. 5. The theory of sorghum injury as due to a heavy draft on available essential elements cannot satisfactorily explain observations under 3 above, while the toxin theory cannot explain 1, 2, and 4. The theory of competition between micro-organisms and the crop plants for nitrogen and possibly other essential elements very satisfactorily explains all of these observations. 6. The chance of profit from the use of some rates of application of nitrogenous fertilizers where small grains normally follow sorghums seems hopeful on the basis of increased yields secured, present prices, and increased costs of production involved. Where small grains do not normally follow sorghums because of poor yield, this initial loss must be less than the profit shown for the fertilizer applications themselves to make the sequence of sorghums and fertilized small grains profitable. 7. The practically normal growth of alfalfa and fenugreek following sorghums suggests that planting a legume may be the best way to dodge "the injurious after-effects of sorghum."

Eleven crops commonly found in southern states were grown in quartz cultures with different phosphorus treatments in order to determine their ability to use rock phosphate as a source of phosphorus for plant growth. Analyses were made on the plant tissue for calcium and phosphorus to see if they had relation to the feeding power of plants for rock phosphate. The results may be summarized as follows: Cotton, cowpeas, sorghum, seredella, beggarweed, lespedeza, bur clover, rice, and velvet beans made very little growth when phosphorus was supplied as rock phosphate. Vetch made about one-third and sweet clover about three-fourths as much growth from rock phosphate as with superphosphate (acid phosphate). There was no definite relation between the calcium-phosphorus ratio in the plants and their ability to feed upon rock phosphate. Other factors than the calcium content of the plants seem to play an important part in determining the ability of plants to use rock phosphate as a source of phosphorus.