George A. Duncan

Non–Water–Stressed Baseline as a Tool for Dynamic Control of a Misting System for Propagation of Poinsettias

A technique is presented for dynamically adjusting misting intervals during propagation of vegetative cuttings. A crop setpoint temperature for activation of misting was defined by a non-water-stressed baseline concept, using infrared thermometry to acquire canopy temperature for plant feedback. The critical crop setpoint temperature was calculated from instantaneous values of air temperature, incident radiation, and air vapor pressure deficit (VPD air ). Misting was activated when the actual crop temperature exceeded the critical crop setpoint temperature. The dynamic control was shown to have the potential to reduce the amount of applied water from 9 to 12 times during low levels of VPD air (0.8 to 1.1 kPa) and under dark conditions when compared to a conventional on/off misting interval of 5 S each 5 min. In addition, misting intervals were reduced three-fold, from 30 to 11 min, when incident radiation increased from 0 to 100 W m -2 and VPD air was maintained in the range from 2.3 to 2.6 kPa. Further increases in radiation levels from 200 to 300 W m -2 did not appreciably change the misting frequency. The dynamic misting control provides a large potential for increasing the period between misting events under dark conditions and with low to moderate levels of incident radiation. It automatically increases misting frequency as VPD air and/or radiation increase.

Development and Evaluation of a Cable-hoist System for Housing Burley Tobacco

A unique cable-hoist system has been developed that can reduce the labor by up to 45% for placing stalk-harvested tobacco in a barn for curing and later removing it for stripping. Workers are not required to climb and work in the barn, thus improving safety. Most of the physical drudgery is eliminated, thus offering desirable benefits to tobacco producers. Safety of operation has been a prime consideration in the development and evaluation of the method. A crew size of one or two workers can accomplish the same housing and bulking tasks of three to five workers by conventional methods. Labor savings do not compensate for the amortized cost of converting a conventional barn. However, new barn construction and installation of the system show a potential break-even situation for a 2 ha (5 acre) size in five to seven years.

DEVELOPMENT AND TESTING OF A LOW-COST CONDENSATION DETECTION SYSTEM

A condensation sensing and control system was designed to detect condensation using a commercially available leaf wetness sensor (LWS). The leaf wetness sensor was a variable resistance grid-type that responded to moisture on the surface. A circuit was developed to compare the LWS voltage output to a user specified reference voltage, and operate a relay for possible switching of a humidity control device (for example a fan and/or heater). The condensation detection system operation was validated in an environmental chamber in the laboratory using a heat exchanger and water bath. Condensate was immediately detected when the plate was cooled below the dew point temperature of the chamber. When the water temperature increased above the dew point temperature, there was a delay as the moisture evaporated from the plate. Soil and other foreign material were added to the leaf wetness sensor with little effect on system performance. The soil acted to further delay the sensor from drying and predicted slightly longer condensation and recovery periods. The condensation detection system was tested in a transplant growing greenhouse and a grain bin, with operation verified by simultaneously measuring the relative humidity and dry bulb temperature. There were frequent periods of condensation in the greenhouse and the system accurately predicted them. Condensation did not occur in the grain bin, as was verified using the relative humidity and dry bulb temperature. The condensation detection system can provide a low-cost, rugged method for determining periods of condensation without the need for routine maintenance and calibration.

A REDUCED–COST MECHANIZED SYSTEM FOR HANDLING AND CURING MECHANICALLY–HARVESTED BURLEY TOBACCO

An experimental system was tested in which mechanically harvested burley tobacco plants placed onto steel slotted receivers were retrieved from a field, transported to a field curing structure, and placed onto the structure for air curing by a single worker. The system consisted of a tractor–towed, trailer mechanism that engaged and hoisted loads of approximately 360 burley plants of approximately 1 Mg mass. Ten slotted steel rails, 3.05 m long, holding 36 notched plants were placed onto parallel wooden beams suspended at a height of 2.13 m by wooden posts set in the ground. Burley tobacco was cured in this configuration covered by polyethylene. Time–and–motion experiments showed that the system could retrieve tobacco from the field and place it onto a curing structure adjacent to the field at the rate of 0.1 to 0.18 ha/h. Replicated experiments also showed that the system operated with negligible leaf loss due to handling. Finally, experimental results showed that leaf grade index decreased with time that filled tobacco rails were left lying on the ground after being harvested and prior to being retrieved. This study further indicated that the estimated cost of the proposed harvesting system compares favorably with systems that require several manual laborers.

Economic Comparison of Alternative Burley Tobacco Harvesting Practices by Computer

ABSTRACT THE computer model CATCH (Computer Analysis of Tobacco Cutting and Housing) was developed to pro-vide the individual tobacco producer with management information concerning alternative methods of harvest-ing burley tobacco. CATCH utilizes specific producer in-puts to analyze 24 alternative burley production systems and presents up to four economic rankings containing costs, equipment and labor for each system. The economic rankings aid the producer in decision making with regard to his own operation.

Determination of Strategy for Harvesting Burley Tobacco

ABSTRACT THE decision-making process associated with the scheduling of burley tobacco harvesting operations was formulated as a multi-stage decision process, and solved using a procedure called dynamic programming. The solution of a stochastic dynamic programming model provides a set of optimal decision rules, that is, a strategy. When certain user-specified parameters are provided, the decision model provides information concerning the optimal date to start harvesting, the optimal number of hours to harvest on each day, the optimal date to introduce hired labor, and the optimal number of workers which should be hired. The solution of the dynamic programming model makes it possible to compute a timeliness cost which is defined as the amount of the expected total return which is lost because of delaying harvest initiation be-yond the optimal starting day. Thus, a decision-maker can consult tabulated strategy solutions in any situation during the harvesting season and make decisions with the aid of timeliness cost information.

A field curing structure and mechanized housing system for burley tobacco

Two deterrents to expanded production of burley tobacco are a lack of barns located conveniently to the tobacco fields and a lack of hired labor for harvesting and housing. The objective was to meet these needs by developing a mechanized housing system and a one-tier field curing structure that would accommodate the mechanized housing system and provide an economical alternative to the conventional curing barn. The mechanical housing system for the field curing structure requires only 39% of the labor required to load, transport, and house burley tobacco in the conventional barn. The mechanical housing system for the field curing structure requires two workers compared to three or four for conventional barns. Using Net Present Value as a means of comparing capital investment decisions showed the field curing structure with mechanized housing system to be a better investment than the conventional and tiered field curing structure systems for land areas of and above 0.7 ha (1.6 acre) and 6 ha (15 acre), respectively.

Elliptical Combing Motion for Harvesting Bell Peppers

A new concept for mechanically harvesting bell peppers, intended specifically for multiple-pass harvesting, utilized spaced horizontal fingers combing vertically upward through plant foliage in an elliptical path alternating from both sides of the row. An apparatus based on this concept was designed and built, and harvest tests were conducted to determine the effect of two main machine operating parameters, vertical picking speed and disk angle. Harvesting performance was evaluated in terms of harvest efficiency, fruit damage, and plant damage as it related to multiple-pass harvesting. Fruit removal, both harvestable size and immature, increased significantly as vertical picking speed increased. Branch breakage also tended to increase as vertical picking speed increased, partially accounting for the increased fruit removal. Fruit damage increased significantly as the disk angle increased. Overall, the average harvest efficiency for the tests was 81% and the average fruit damage was 5.9%.

Curing Primed Burley Tobacco Leaves with Natural Air

ABSTRACT BURLEY tobacco leaves were cured with unheated forced air in both spiked racks and in boxes designed to simulate big box curing. Airtlow rates of 5.61 and 7.48 m3/h/kg (1.5 and 2 cfm/lb) yielded the best rack-cured tobacco. The box-cured tobacco was of very poor quality. All of the experimentally cured tobacco was significantly lower in equivalent market price than stalk-cut barn-cured control.

Simulation of Burley Tobacco Harvesting-Housing Systems

ABSTRACT A computer model has been developed using systems analysis techniques to simulate the labor and equip-ment aspects of harvesting burley tobacco. By varying the parameters of the model the user can determine a harvesting and housing strategy based on labor and equipment availability.