AGRICULTURAL HANDBOOK 395, U.S. DEPT. OF AGRICULTURE 



Treatments for frozen or thnwinp; around and 

 tliat covered with snow or ice are of possible 

 agricultural interest. 



Mechanical snow removal was quite effective 

 in removing radioactivity from areas where a 

 fallout simulant had been spread on top of loose 

 snow. Under good operating conditions, a blade 

 snow plow or motor grader left less than 5 per- 

 cent of tlie radioactivity, and a carryall scraper, 

 bulldozer, or rotarj' snowblower left less than 

 15 percent. More effoi't was required to reach the 

 same level of decontamination with warm, sticky 

 loose snow than with cold snow using either a 

 road grader or rotary snow blower. 



Ice or frozen gi'ound surface was effectively 

 decontaminated by sweeping. Hand sweeping left 

 less than 5 percent of the radioactivity on ice. 

 Mechanical sweeping left less than 15 pei'cent on 

 a frozen ground surface. It made little difference 

 whether the temperature was just below freezing 

 or subzero. 



Thawing ground was scraped with a carryall 

 scraper, bulldozer, or motor grader, which left 

 less than 10 percent of the radioactivity after 

 one or two passes of the equipment. With addi- 

 tional passes it was possible to leave less than 

 one percent of the radioactivity on the ground. 

 About the same effort was required to scrape 

 either a thawing soil or a warm soil. 



No-tilla{3;e Management 



When radionuclides are left on the soil sur- 

 face In' not cultivating during the planting and 

 growth of crops, uptake by many crops is less 

 than would be obtained with normal cultivation. 

 For example, irrigated barley grown on a silt 

 loam soil in central Washington (4) took up 

 half as much radiostrontium when it was left 

 on the surface as when it was thoroughly mixed 

 through 4 inches of soil by cultivation (4). Simi- 

 lar trends were shown for wheat, barley, po- 

 tatoes, and sugar beets grown in field experiments 

 on several widely varying soil types in England 

 (24) . However, shallow-rooted crops such as rye- 

 grass and kale took up twice as much radio- 

 strontium when it was left on the surface as 

 when it was plowed 4 inches deep. 



The relative uptake of radiostrontium from 

 no tillage, compared with normal cultivation, has 



varied widely in our trials at the Agricultural 

 Research Center (unpublislied data). In the no- 

 tillage treatment, a fescue meadow was killed 

 with herbicide, and the crops were seeded 21/^ 

 or 5 inches deep with a sod planter. On two soil 

 types and with three crops grown in 1968, the 

 relative uptakes were roughly as follows (nor- 

 mal cultivation = 1.0) : 



Soil type 

 Elkton silt loam 

 Sassafras sandy loam 2 



Wheat Corn Bush Beans 

 1.5 ='1.5(1) 3 



0.2 



'0.6(0.3) 



Although poor weed control was obtained and 

 crop growth was generally unsatisfactory, it ap- 

 pears that no-tillage management reduced radio- 

 strontium uptake only on the sandy loam with 

 corn and beans. These crops tend to be deeper 

 rooted than wheat. The sandy loam is better 

 aerated and thus encourages deeper rooting than 

 the silt loam. This factor and the minimum dis- 

 turbance of the soil surface during planting are 

 probably most important for reducing the up- 

 take of radionuclides from the soil surface. 



Deep Placement of Contaminated Soil 



Field plot experiments have usually shown re- 

 ductions in the uptake of radiostrontium when 

 it was placed deeper in the soil than it would 

 be with normal cultivation. Deep placement has 

 been accomplished in several experiments by ex- 

 cavating and refilling field plots. Placement of 

 strontium-89 in a layer 15 inches deep in a silt 

 loam soil at Beltsville, Md. did not reduce uptake 

 by soybeans compared with rotary tillage into 

 the top 6 inches of soil {17). 



In other experiments, placement treatments 

 were combined factorially with lime, irrigation, 

 and potassium fertilizer treatments to test for 

 effects on root distribution that might increase 

 the benefit from deep placement. No such effects 

 were found. With various soil types and climatic 

 conditions in several states, the lowest strontium- 

 90 content of corn, soybean, oats, or wheat grain 

 with deep placement was about 40 percent of that 

 with normal plowing {8). The reduction in up- 



' Rflative uptake values in parentheses are from plant- 

 ing 5 inches deep. Otherwise, uptake was the same from 

 both depths of planting. 



