Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)


The difficulty in determining the stage of the curing process at any given time was largely overcome in these studies by the perfection of a weighing device which enabled the operator to determine the moisture content of the hay as it was being cured in the field.

The presence of living cells in the stems and leaves of field-cured hay plants was shown.

The evidence and theories on heating of hay indicate that heating is due largely to chemical oxidation processes. These processes may be helped along by the respiration of the living cells in the plant up to 40-45 °C. and by the work of microorganisms from air temperatures to 70° C. in producing unstable, unsaturated compounds. It is believed that beyond this point the heating is due entirely to chemical processes.

Alfalfa hay was found to cure more rapidly in the swath than in the windrow and more rapidly in the windrow than when cocked.

Hay that was one-fourth, one-half or three-fourths cured in the swath prior to windrowing cured more rapidly than the hay windrowed at once, and the longer the hay was allowed to remain in the swath, the less time was required for curing.

Cocking hay, either at once or after partial swath Or windrow-curing, delayed the curing process. Green hay in large cocks heated and lost its color. Good quality hay was made by cocking after partial swath or windrow-curing.

Turning average sized windrows with the rake in good curing weather was found to be slightly detrimental as no appreciable time was gained and the quality of the hay was slightly lowered. Turning large windrows or windrows wet by rain caused them to cure more rapidly and gave a better quality of hay.

Tedding hay was not found to be advantageous in any way in these experiments and was detrimental to the quality of the hay. The tedder may be valuable in curing extremely heavy swaths of hay.

Complete swath-curing resulted in the greatest loss of leaves; three-fourth and one-half swath-curing were next in amount of leaves lost. Windrowing at once and one-fourth swath-curing followed by windrowing resulted in the least loss of leaves. The leaf-loss in swath-curing hay was increased by the use of the tedder. The turning of the windrow with the rake caused an additional leaf-loss in windrow-cured hay.

DurIng these experiments hay was placed in the mow with as low as 20 percent and as high as 58.7 percent of moisture. The degree of heating was not found to be directly proportional to the moisture content of the hay. Hay with below 30 percent of moisture ordinarily may be considered safe from heating to a destructive or dangerous degree. Hay with less than 27 percent of moisture may be expected to retain its green color.

The hay generally heats immediately on being mowed, then cools; this is followed by a second heating period in which the highest temperature is usually reached in 8 to 10 days after mowing, after which the hay cools gradually.

The amount of carbon dioxide present in the mow, is a fair indication of the degree of heating of the hay . . The accumulation of carbon dioxide in the presence of moist, hot material results in a transformation of the chlorophyll, accompanied by a change in color from green to brown.

The green color of hay was usually destroyed when the heating exceeded 50°C. Clean, brown hay is formed at temperatures above 55°C. and below 70 °C. In general, moldy, grayish-brown hay results when hay heats to between 40 and 50°C. during the storage period.

Clean, brown hay is formed by heating quickly to 55° C., while if the heating is prolonged at 50° C. or less and later heats to above 55°C., the hay is "dusty."

The value of salting hay in the mow was tested eight times, with a distinctly beneficial effect once, slightly beneficial once and apparently no benefit in six trials.

When hay baled from the field with 23 percent of moisture was carefully stored, there was no detrimental heating.



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