The hydrocyanic acid content of various parts of the sorghum plant was determined in material grown in Texas, New Mexico, Colorado, and Virginia in 1936 and 1937. The HCN content of sorghum leaves was 3 to 25 times that of the corresponding stalks of plants that had reached the boot stage. Heads and leaf sheaths were low in HCN. Upper (younger) leaves contained more HCN than lower (older) leaves. The proximal half of the leaf was higher in HCN than the distal (older) half. The HCN content of leaf blades was six times that of the midribs. The HCN content of stalk internodes decreased progressively downward, the lower (older) internodes containing only small quantities. Axillary (side) branches were much higher in HCN than the older main stalks and in most cases tillers (suckers) were higher in HCN than the older main stalks of the same plants.

Studies of the effect of several crops and certain soil treatments on the degree of aggregation of soils in the field and in the greenhouse are presented. The organic carbon contents of various size groups of soil aggregates obtained from a single soil sample were determined. Samples taken from the soil under growing corn and kafir in field and greenhouse showed as good aggregation under the sorghum crop as under corn. When oats succeeded these two crops in the field, however, soil samples removed from the oats stubble revealed a greater degree of dispersion where oats followed sorghum than where corn was the preceding crop. Sweet clover left the soil better aggregated after 1 year's growth than soybeans, while alfalfa and sweet clover gave similar results. Soil fallowed for 2 years in the field was less aggregated than soil fallowed for 1 year. Limed soil supporting sweet clover and red clover in a greenhouse experiment was more highly aggregated than similar soil unlimed but supporting these crops. Unlimed and unleached fallow soil in the greenhouse was as well aggregated as limed fallow soil. It is suggested that perhaps the combined action of lime and a legume crop, or possibly other crops, produces an aggregating force which lime alone may not exert. The grasses failed to produce the aggregation of the soil expected of them, but their failure in this experiment may have been due to the shortness of the growth period. The more aggregated portions of the soil contained significantly more organic carbon than the less aggregated portions. Ultimate particle size in the various size groups of aggregates was quite similar. Hence it is believed these results lend weight to the assignment of an important role to organic matter in the aggregation of the mineral particles of soils.

In the grasshopper outbreak of 1936 outstanding instances of differential injury among corn varieties, top crosses, and hybrids were noted. In one series of 52 hybrids, defoliation ranged from 40% to 59.8% as averages of five randomized replications. Extreme contrasts between grasshopper injury of corn and of sorghums were noted. In some cases corn in one field was eaten to the ground while sorghum in an adjacent field was practically uninjured. Although all sorghums show considerable resistance, the sorgos and kafirs were injured less than milo and milo derivatives. As a rule, the varieties and inbred lines of corn showing the greatest resistance originated in areas where grasshoppers are a natural element of the environment. It is suggested that natural selection operating in the development of adapted varieties of corn has tended to intensify resistance to grasshoppers and to other natural insect pests of the region.

Dwarf varieties of sorghum adapted to combine harvesting must have sturdy stalks and peduncles to prevent the heads from breaking over. Many selections, particularly from milo-kafir crosses, have shown high tendency for the production of weak peduncles. The term "weak neck" has been designated to describe this condition. The cause of the malady has not yet been determined. The affected tissues become disintegrated and so weakened that the heads break over. The break occurs most frequently at the base of the peduncle. The sorgos and strains of Blackhull kafir show high resistance to "weak neck," while the milo and milo derivatives having milo characteristics often show high susceptibility. "Weak neck" is not yet of wide occurrence on farms because the varieties grown are for the most part resistant to the disease. The distribution of varieties susceptible to "weak neck," however, will increase the prevalence of the disease. Late planting on a well-prepared seedbed tends to reduce the prevalence of "weak neck" in susceptible varieties. More complete control may be expected from plant breeding methods.

The purpose of this investigation was to determine the factors involved in cyanide poisoning of livestock by Sudan grass in order that a program of crop management might be formulated which would eliminate this danger. In the course Of this investigation, a rapid chemical method for determining the cyanide content of Sudan grass and sorghum was developed. This method has proved invaluable in elucidating the factors involved and in determining whether or not Sudan grass is safe to pasture. The results obtained are summarized as follows: It is the short, dark green Sudan grass which is high in cyanide and which is dangerous to pasture. Second growth, after pasturing or removal of a hay crop, when short and clark green is especially dangerous. Sudan grass which is 2 feet or more in height, whether first or second growth, is low in cyanide and is relatively safe to pasture. Sudan grass, short or tall, which is of a pale or yellowish green color is low in cyanide and is relatively safe to pasture. Both from the standpoint of danger from poisoning and possibility of obtaining the most pasture, Sudan grass should usually not be pastured until it has reached a height of 18 inches and better, 2 or 3 feet. This is best accomplished by having two or more fields so that the cattle may be rotated from one field to another. A high level of available nitrogen and a low level of available phosphorus in the soil tend to increase the poison content, while a low level of available nitrogen and a high level of available phosphorus have the opposite effect. A high cyanide content may still occur in short plants, however, especially in the second growth, even though the level of available phosphorus is high. A high level of available phosphorus along with other favorable growth factors makes it possible for the plant to attain quickly a height of 2 to 3 feet, at which stage it is relatively free of poison. Drought probably operates as a factor, largely by keeping the plants small when they are always much higher in cyanide than when larger. Drought keeps the plants small by withholding water and probably lessening the availability of phosphates to plants much more than that of nitrogen. Fall or early spring plowing followed by cultivation should be practiced on fields to be sown to Sudan grass so as to conserve moisture and prevent the ill effects of drought. When Sudan grass is dried and made into hay without undue exposure and then well stored, the cyanide content does not change greatly. Since it is usually not cut for hay until it reaches a height of 3 feet or more, there is little if any danger of cyanide poisoning from Sudan grass hay. However, if short Sudan grass, high in cyanide, is made into hay, it will be dangerous as a feed. Cattle when turned into Sudan grass of high poison content usually stop eating after about 15 minutes due to the action of the poison. If the animals are not too hungry and are in a high state of vigor, they may stop eating before they take a fatal dose. Cattle vary in the amount of cyanide that it takes to be fatal. If they are in a low state of vigor and very hungry, they are more apt to eat a fatal dose than when the opposite is the case. When there is doubt as to possible danger, samples should be collected and tested for poison. The whole field should be examined carefully. If spots of small Sudan grass are found, samples from each of these should be taken for analysis.