Synopsis Early growth of corn was progressively retarded by increasing amounts of mulch.

On corn plots in Iowa, South Carolina, Ohio and Minnesota which were treated with oat straw either plowed under or on the surface and with two levels of N, measurements were made of soil temperature at the 4‐inch depth, and these measurements were correlated with dry matter yields of corn early in the season. The data from Iowa, Minnesota and Ohio support a theory that early season corn growth is decreased by low temperatures caused by a mulch of crop residues. The data from South Carolina, where soil temperatures were considerably higher than in the three other states, showed that the mulch did not appreciably influence the growth rates. The data from all four of the states agreed in a general way with data of Lehenbauer who found that for a range of temperatures from about 50° to 86° F. there is an increase with temperature of seedling growth rate; whereas around 86° to 90° F. there is little influence; and from about 90° to 111° F. there is a decrease. From the soil temperature measurements taken at a 4‐inch depth it was shown how temperatures for other depths could be deduced from a theoretical expression based on heat flow theory. A detailed example of the use of the heat flow theory in studying the mulch problem in practical experimentation is presented.

Corn growth was measured in 23 locationyears in the eastern United States, where an average soil temperature reduction of 2.2°F. at the 4inch depth was obtained by a strawmulch treatment as compared to unmulched treat ments during the first 6 weeks following planting. For soil temperatures ranging from 60° to 83°F., the ratio of the dry matter produced on the mulched treatment to that produced on the unmulched treatment was linearly re lated to the 4inch soil temperature. The validity of this linear relation was supported by data from experiments in the greenhouse and laboratory where growth of corn was observed under carefully controlled temperatures. For field conditions, a corn growth vs. soil temperature relation was constructed from the above linear relation, and the estimated optimum soil temperature for corn growth (dry matter production) was 81.3°F.The effect of soil temperature on four different growth measurements (height, dry matter production, yield of N, and yield of K) of corn was different for each growth measurement in both the field and the greenhouse.

Synopsis Low nitrogen fertility and the presence of crop residue on the soil surface were coincident with low incidence of rot. Potassium fertilization contributed slightly to decreased disease incidence. All factors that decreased disease incidence were also closely correlated with retarded early growth. Yield was depressed by severe infestation. However, it was impossible to show differential effect of disease on yield as affected by treatment because of interactions of yield, treatment, and disease incidence.

An experiment to determine the moisture vs time curve, and hence the field capacity, was carried out at 6‐inch increments to a depth of 5 feet on 4 soils. Plots of soil were soaked with water and a soil moisture meter employing neutron scattering used to determine the moisture content of the soil profile at different times following water entry into the soil. The data were plotted as curves of soil moisture content on a volume basis vs time in hours following wetting. The general shape of the curves was about as expected for 2 silt loam soils and 1 sandy loam soil, but certain layers in these 3 soils deviated from the normal pattern. The deviations are explained on the basis of physical conditions of the soil existing some distance from the soil layer in question. A clay loam soil showed extreme variability, with little movement of appreciable quantities of water; a field capacity for it could not be defined. The neutron meter used was found to be an excellent device for this type of study; confounding of soil variation in sampling errors was, through its use, eliminated.