78 AXXl'AL REPORTS' OF DEPARTMENT OF AGRICULTURE, 1940 
soil INJURY FROM CALCIUM ARSENATE 
The investigations conducted in cooperation with the Mississippi 
Experiment Station on the effect of arsenic on productivity of some 
of the major soil types of the Cotton Belt were discontinued and the 
results published during the year. The yields of cotton in field plots 
on Houston clay loam. Memphis silt loam, Sarpy silty clay loam, and 
Sarpy line handy loam were unaffected even from an application of 
1,600 pounds of calcium arsenate per acre. On Rust on sandy loam a 
beneficial effect was obtained from light applications of 50 to 100 
pound- of calcium arsenate per acre although a detrimental effect was 
caused by heavier applications. The arsenical toxicity was reduced 
with time, and 4 years after the calcium arsenate was applied the plot 
that had been given the 400-pound dosage also gave an increase in yield 
over the untreated check while those given the 800- and 1, 000-pound 
treatments had lost much of their toxicity. The ability of the unaf- 
fected soils to render arsenic insoluble was probably due to their high 
pll and their high colloidal content. 
The effect of arsenic on the germination, seedlings, and production 
of cotton, corn, soybeans, hairy vetch. Austrian peas, and oats was 
studied on seven important soil types. Neither germination nor seed- 
lings were injured on any soil until 400 pounds or more of calcium 
arsenate per acre were applied. The extent of the seedling injury 
from heavier applications depended on the soil type and crop, and 
was greatest in the Cahaba, Norfolk, and Ruston sandy loam types 
that contained the smallest amounts of clay, iron, aluminum, calcium, 
and magnesium. Crop yields from oats, Austrian peas, and hairy 
vetch planted immediately after calcium arsenate was applied and 
1 year later showed that yields were affected by the application of 
400 or more pounds per acre, but that much of the toxicity was lost 
in 1 year's time. Oats were more sensitive to arsenic than the other 
crops, but all were injured more on the lighter soils than on the heavier 
Houston clay loam, Memphis silt loam. Sarpy fine sandy loam, and 
Orangeburg fine sandy loam. Since the yearly application of calcium 
arsenate for the control of cotton insects is rarely more than 30 pounds 
per acre and since much of it is lost every year, accumulations of 
arsenic will probably never be sufficient to injure the crops usually 
grown on the soils studied. 
LEAF APHIDS 
The increase in aphid populations following the use of calcium 
arsenate is a serious disadvantage to its use against cotton insects and 
is seemingly becoming more important. In field plots at Tallulah, 
La., an average additional increase of 00 pounds of seed cotton per 
acre was obtained by also controlling the aphids where calcium arsen- 
ate was used for the boll weevil. There was also a definite cot relat ion 
between aphid populations and the effectiveness of the insecticides 
used against the 1><>11 weevil and the leaf worm, the greatest number 
of aphids being found in the plots treated with the mosl effective in- 
secticides. Attention was given to means of overcoming the aphid 
damage by developing aphid-resistant variet ies of cotton, by decreasing 
t ln< »iiL r li tin- use 01 diluents the amount of arsenic used, and by adding 
aphicides to calcium arsenate. In the selections of cotton for aphid 
