THE EFFECT OF CHEMICAL, PHYSICAL, PHYSIOLOGICAL, AND ENVIRONMENTAL FACTORS ON DRYING AND RESPIRATION RATES IN ALFALFA (MEDICAGO SATIVA L.)

SEIF-ELDIN ATTALLA SEIF, Purdue University

Abstract

Experiments were conducted to measure the effects of various chemical, physical, physiological, and environmental factors on drying and respiration rates in alfalfa. The objective was to identify treatments and conditions that maximize drying rate and minimize respiration during drying of alfalfa hay. Samples of field and greenhouse-grown alfalfa leaves and stems were treated and then placed in drying chambers at different relative humidities. Moisture fractions and respiration rates were monitored for up to 60 hours post-treatment. Triton X-100 and triton X-100 plus TBPA caused alfalfa leaves and stems drying at 0% RH to dry more rapidly than deionized water or anthium dioxide. These two chemical treatments also reduced respiration rates by 6 hours post-treatment, but the rates increased again after 12 hours post-treatment. TBPA plus triton X-100 was very effective in reducing respiration rates between 6 and 12 hours post-treatment. These same results were obtained when the treatments were made immediately after harvest or 18 hours prior to harvest. Hot petroleum ether was effective in reducing respiration rates, but both hot and cold petroleum ether vapor treatments tended to decrease the drying rate. Microwave treatment can remove substantial amounts of plant moisture and result in lower total drying time. These treatments reduce or stop the respiratory process in alfalfa leaves and stems. The treatments we imposed had a range of effects from relatively little reduction in drying time or respiration rate to halving the drying time and stopping the respiration completely. Maceration caused great increases in drying rate of alfalfa leaves and stems, slow freezing was more effective in reducing respiration rates of this material than fast freezing. Alfalfa cut at 8:00 a.m. dried somewhat faster and had much lower average respiration rates than material cut at 4:00 p.m. Late bud alfalfa leaves and stems had lower initial moisture fractions, reached lower moisture fractions more rapidly during the drying process, and seemed to equilibrate at lower moisture fractions at the end of the drying process than pre-bud material. Upper alfalfa stems dried somewhat faster than lower stems, and lower stems and leaves had higher respiration rates than upper stems and leaves. Samples at 40% moisture that had dried rapidly had higher respiration rates than samples that had dried more slowly. These results can be explained by the fact that the longer it takes the material to dry to 40% moisture the more substrate has been consumed by the respiratory process. The O(,10) of respiration between 10 and 35 C was higher in material that had dried at 50% relative humidity than that that had dried at 0% RH. The difference between respiration rate in the light and dark was greater in stems than leaves because of more light penetration in stem samples than leaf samples. In general, respiration rates of cut alfalfa peaked between 40 and 55 C, then declined at higher temperatures. Generally, respiration rates of wilted plants were higher than those of turgid plants. The gaseous composition of the atmosphere caused considerable difference in the respiration rates. Respiration rates were inversely proportional to the CO(,2) concentration in the air.

Degree

Ph.D.

Subject Area

Agronomy

COinS