100 



MISCELLANEOUS PUBLICATION NO. 1065, U.S. DEPARTMENT OF AGRICULTURE 



mands that any changes in handling procedures 

 be made at the lowest cost possible. 



Use of Reclaimed Sewage and Industrial Effluent 



Effluent from industry and domestic sewage is 

 now a costly waste disposal problem. Possibilities 

 exist in many regions of the United States for 

 utilizing these waste waters for agricultural pur- 

 poses. Criteria need to be established for agricul- 

 tural use of such waters in irrigation. In addition 

 to the nature and content of organic constituents, 

 water use for various crops on different soils will 

 be affected by such water quality aspects as total 

 dissolved solids, suspended solids, acidity, and 

 content of metallic elements. Since demands for 

 irrigation water are seasonable, storage or other 

 uses of such waters may need to be developed. 



Evidence indicates that the best way to reclaim 

 sewage or industrial effluent is to permit it to per- 

 colate downward through soil. Overirrigation 

 should be explored as a means of purifying water 

 and recharging aquifers. 



Crop Residues 



A major use of crop residues is as a part of 

 stubble-mulch farming to protect fallow lands 

 against the erosive forces of wind and water. Un- 

 der some conditions such mulches appear to de- 

 press crop yields. Also, the mulch may harbor 

 diseases and insects and form sources of reinfec- 

 tion. Additional information is needed so that the 

 soil-protecting aspects of mulch may be realized 

 without undue losses from the adverse effects. 



The process of microbial decomposition of crop 

 residue is accompanied by great changes in the 

 microbial populations in the soil. There is ample 

 evidence that plant pathogens are sometimes sup- 

 pressed or eliminated during this surge of micro- 

 bial activity (79). If the basis for this biological 

 control (79) of disease organisms was known so 

 that the residue could be treated or amended to 

 augment this response, it would be one of the most 

 important breakthroughs in soil microbiology. 

 Much research effort is being placed on this prob- 

 lem throughout the world, but so far with little 

 success. Since it is known, however, that the dis- 

 ease-controlling effect can be modified by simply 

 changing the C/N ratio of the residues, there is 

 definite hope that accumulating knowledge will 

 lead to useful biological control practices. 



It is also known that certain decomposing crop 

 residues have a toxic effect on subsequent crops, 

 particularly in the seedling stage. Detailed knowl- 

 edge on the chemistry and biological effects of 

 residue decomposition may reveal many unsus- 

 pected harmful or beneficial effects on crop growth. 

 Eventually, it may be possible to manage the de- 

 composition of crop residue, not only to reduce 

 harmful effects, but even to stimulate crop re- 

 sponse. 



Another possible side effect of improved man- 

 agement of crop residues is the detoxification of 

 pesticide residues in soil. Many pesticide materials 

 are adsorbed or complexed by the organic matter 

 in soil and the enhancement of microbial activity 

 should be advantageous in favoring decomposition 

 of those pesticides that are susceptible to microbial 

 degradation. 



The straw from grass seed harvesting is pres- 

 ently burned in the field along with remaining 

 stubble, The emitted smoke and hydrocarbons 

 often create a serious air pollution problem in the 

 immediate locality. Other ways of handling this 

 residue need to be found — ways that will also pro- 

 vide disease and insect control. 



In some grain production areas, and in many 

 areas in some years, straw production is too great 

 for efficient use of equipment under stubble-mulch 

 farming. Progress in breeding varieties of cereals 

 with short straw without sacrificing yields needs 

 to be expedited. 



In rangeland renewal operations, the prevail- 

 ing brush is frequently bulldozed, chained, or 

 otherwise mechanically removed. Evidence indi- 

 cates that the brush residue may be distributed 

 over areas newly seeded to grass, thereby reducing 

 moisture losses and aiding emerging grass seed- 

 lings. This possibility needs to be vigorously ex- 

 ploited as a means of utilizing brush residue in 

 meeting the urgent demands for grassland restora- 

 tion. 



Forest Slash 



The millions of tons of forest slash produced 

 each year provide a serious fire hazard, a serious 

 air pollution problem when burned, and a source 

 of insect and disease infestation when not burned. 

 Thus, there is an urgent need to develop new tech- 

 nology for slash disposal. Mechanical means in- 

 volving chipping, crushing, or mastication are far 



