Gene A Giacomelli

PMID: 11540180;Abstract:

Acquisition and analysis of sensory information are foremost for the control and continued operation of any complex system. The sensors and their attributes must be selected by understanding the biological and physical parameters which, first, can describe, and second, when linked to control systems, can modulate, the plant growth system. These parameters are not all understood, or known, and practical sensors may not even exist for their measurement. A systematic analysis of the general plant system would: focus without prejudice on all the descriptive parameters, as well as, their interrelationships within the biophysical system; highlight the significance of each parameter; expose the areas of weakness and strength of current knowledge; expand the knowledge base; provide the platform for the development of operational models for real-time monitoring and control requirements; and support the longer term tactical and strategic planning needs. Components of such a procedure of systematic analysis which is in development for intensive plant production systems within controlled environments will be discussed. © 1994.

Abstract:

Greenhouse crop production in semi-arid climates is desirable because high solar radiation levels are consistent year round. The use of evaporative cooling will further increase yields and crop consistency. However, these regions typically receive less than 500 mm of rain annually, making water use management a critical concern. This study evaluated water use for irrigation (WU I) and pad-and-fan (WU PF) evaporative cooling systems in a single-span, polyethylene-covered greenhouse in Tucson, Arizona, from March to October 2006. A single-use, non-recirculating irrigation system delivered water to hydroponically grown tomatoes. The pad-and-fan system was computer controlled to maintain day/night air temperatures of 24°C/18°C. The total eight-month WU I and WU PF were 780 and 1450 L m ^-2, respectively. WU I increased steadily from 4.3 L m ^-2 d ^-1 during crop establishment to 7.2 L m ^-2 d ^-1 when the plants were mature. WU PF increased from 1.1 L m ^-2 d ^-1 during early spring to a peak of 11 L m ^-2 d ^-1 during the hottest, driest outside conditions. The water use efficiency (WUE, kg yield per m ³ water use) of the irrigation and pad-and-fan cooling systems was 30 and 16 kg m ^-3, respectively. When WUE was calculated by combining WU I and WU PF, the total greenhouse WUE was 11 kg m ^-3. Theoretically, using a 100% recirculating irrigation system could have produced a greenhouse WUE of 13 kg m ^-3. This study demonstrates that although greenhouses achieve high annual yields with low irrigation rates, using an evaporative cooling system reduces greenhouse WUE to field WUE levels. To minimize greenhouse water use while maintaining high crop yields, this study recommends further examination of the use of recirculating irrigation systems, variable-speed fans to improve climate control, alternative cooling systems, and drought-tolerant crops. © 2011 American Society of Agricultural and Biological Engineers.

Abstract:

The rate of change of top projected leaf area (TPLA) of lettuce (Lactuca sativa L.) seedlings was determined with machine vision technology. Differences of TPLA between control and treatment plants were detectable with this technique within 48 hours from the onset of an imposed nutrient stress. The nutrient stress treatments were 0%, 50%, 150% of the control (100%). There were no differences for the 50% and 150% treatments compared to the control plants, even after a 6-day observation period. However, the 0% treatment caused different TPLA expansion within 48 hours and required a recovery period of 3 or 4 days after being returned to normal EC levels before again attaining prestressed growth rates.

Abstract:

Water management is an essential task for all crop production. However, it is difficult to determine short term plant water needs, as the plant does not exhibit readily detectable indicators of stress until well beyond optimum water conditions. The plant utilizes water in several critical ways, such as, to maintain turgidity, for nutrient uptake, and in photosynthesis, all of which vary in proportion to the environmental conditions. The traditional procedure for supplying plant water needs is to provide a storage of water within the root zone which becomes an immediately available source. Soil or soilless mixes for potted plants have moisture contents which can range from field capacity after watering, to high soil water tensions associated with the onset of wilting conditions of the plant. Alternatively, the root zone volume and storage capacity has for some crops been significantly reduced, requiring a more "on-demand" water feeding schedule. Hydroponic crop production systems, for example, ebb and flood, where there is little or no buffer within the root zone for water, require automated watering schemes which are extremely dependable, reasonably accurate, and uniform in distribution for production of quality crops. In theory, the plant transpires water and thus requires replenishment at rates which are dependent on the plant microclimate (leaf temperature, solar radiation, air humidity, wind speed), as well as, the plant age, morphology, health, and the ease at which the water is available within the root zone. Water requirement can be determined in either of two ways: (1) correlated to plant and its environment with physical or mathematical models, or (2) measured directly with an electronic transducer, such as with stem "sap flow" device. Each has been applied to selected plants species with reasonable success, but generally maintaining some margin of safety, through a water storage buffer within the root zone. The most practical application of each procedure has been in minimizing over-watering and minimizing plant stress while utilizing traditional irrigation techniques. The "speaking plant" approach can provide new opportunities for application of water and nutrients, and ultimately for control of plant growth, but such procedures require that one must "listen" to the speaking plant. Tjie challenge is to focus on the development of sensors to interpret the plant indicators, and then to respond to them within a control system. Machine vision which utilizes the spectral features (by reflectance), or morphological features (physical shape or dynamic growth response) of the plant is one relatively new option for determining the real-time plant condition. Real-time sensors that directly monitor the plant and its water requirements, which are non-intrusive, non-invasive, reliably calibrated, and integrated within a microclimate control system will be necessary for the ultimate success of such systems. In this paper, the plant water requirements, the delivery systems and the potential of automated monitoring of plant water status within integrated crop production systems will be discussed.

Abstract:

The ability to cool greenhouse air is essential in growing many warm weather greenhouse crops. Present methods, such as fan-and-pad cooling are lacking in both the amount of cooling at high humidity and the uniformity of distribution of cooled air within the greenhouse. One method, a wetted overhead energy-saving blanket, was devised and tested. The blanket (open weave, 55% shading) acted as an evaporative cooling surface when wetted by mist nozzles placed in the greenhouse attic above the blanket. Results have shown good uniformity as well as temperature reduction of up to 8 degree C.