@article{niedziela_depa_nelson_willits_peet_dickey_mingis_2018, title={Effects of Carbon Dioxide and Photosynthetic Photon Flux on Mineral Content in Chrysanthemum Allowing for Growth as a Covariate}, volume={53}, ISSN={["2327-9834"]}, DOI={10.21273/hortsci12425-17}, abstractNote={The effect of CO2 concentration (330 and 675 μL·L−1) and photosynthetic photon flux (PPF) (mean daily peaks of 550–1400 μmol·m−2·s−1) on total mineral contents in shoots was studied in chrysanthemum [Dendranthema ×grandiflorum (Ramat) Kitam ‘Fiesta’] during three times of the year. Growth (as measured by shoot dry weight) and shoot mineral contents (weight of nutrient per shoot) of hydroponically grown plants were analyzed after 5 weeks. There was a positive synergistic interaction of CO2 concentration and PPF on growth with the greatest growth at high PPF (1400 μmol·m−2·s−1) with high CO2 (675 μL·L−1). When growth was not used as a covariate in the statistical model, both CO2 concentration and PPF significantly affected the content of all eight nutrients. However, after growth was included as a covariate in the model, nutrients were classified into three categories based on whether CO2 concentration and PPF level were needed in addition to growth to predict shoot nutrient content. Neither CO2 concentration nor PPF level was needed for Mg, Fe, and Mn contents, whereas PPF level was needed for N, P, K, and Ca contents, and both CO2 concentration and PPF level were required for B content.}, number={1}, journal={HORTSCIENCE}, author={Niedziela, Carl E., Jr. and Depa, Mary A. and Nelson, Paul V. and Willits, Daniel H. and Peet, Mary M. and Dickey, David A. and Mingis, Nancy C.}, year={2018}, month={Jan}, pages={73–77} }
 @article{love_shah_grimes_willits_2014, title={Transpired solar collector duct for tempering air in North Carolina turkey brooder barn and swine nursery}, volume={102}, ISSN={0038-092X}, url={http://dx.doi.org/10.1016/J.SOLENER.2013.11.028}, DOI={10.1016/j.solener.2013.11.028}, abstractNote={Abstract Transpired solar collector (TSC) ducts were installed at a swine nursery and a turkey brooder farm in eastern North Carolina (NC), USA. Each farm had a Test (TSC duct-equipped) and an identical, adjacent Control treatment. Five swine herds and six turkey brooder flocks were monitored over two heating seasons (2010–2012). Propane uses were reduced by 55 and 27 L/m 2 -yr, respectively, in the swine and turkey barns; reductions were highly variable among herds or flocks and the modest reductions were due to warm weather and use of attic ventilation. Over a 14-d period, both the swine and turkey TSC units increased ambient temperature in the barns by ∼6 °C with a maximum increase of 22.5 °C in the turkey TSC. In the swine and turkey houses, calculated energy additions by the TSC were 433 and 81 MJ/yr-m 2 of collector surface area, or 16 and 3 L/m 2 , respectively, of propane saved. Calculated propane savings were much lower than measured values. Short-term efficiencies were higher in the swine TSC (>61%) vs. the turkey TSC (39–50%) probably due to the lower face velocity of the turkey TSC which increased collector heat losses. While barn CO 2 , RH, and temperature values were unaffected by the TSC, it was unclear why animal performance in the Test treatment was better. Simple payback periods for the TSC ducts at both farms were favorable (}, journal={Solar Energy}, publisher={Elsevier BV}, author={Love, Chris D. and Shah, Sanjay B. and Grimes, Jesse L. and Willits, Daniel W.}, year={2014}, month={Apr}, pages={308–317} }
 @article{yao_shah_willits_westerman_li_marshall_2011, title={Ammonia emissions from broiler cake stockpiled in a naturally ventilated shed}, volume={54}, DOI={10.13031/2013.39830}, abstractNote={Due to concerns about the negative environmental impacts of ammonia (NH3), the EPA may soon regulate NH3 emissions from livestock operations, including waste piles. This would require knowledge of NH3 emission rates, but there are very few field-scale studies on emission measurement from broiler waste stockpiles. This is the first study in which short-term NH3 fluxes from broiler cake stockpiled in a shed were measured, taking into account both forced and natural convection. Acid scrubbers were used to measure NH3 concentrations, while the integrated horizontal flux (IHF) method and Fick's law of diffusion were used to determine NH3 emissions due to forced and natural convection, respectively. Average daily air temperature and wind speed 0.75 m above the stockpile were 24.9°C and 0.65 m s-1 in summer and 8.5°C and 1.02 m s-1 in winter. Natural convection accounted for <0.01% of total emission, but not isolating gas concentrations during forced convection conditions generally led to overestimation of emission. In summer (7 d), NH3-N emission factors were 17 g m-2 d-1 (stockpile surface area), 30 g m-3 d-1 (stockpile volume), 1.8 g kg-1 N d-1 (initial cake N content), and 11 g AU-1 d-1 (where AU = 500 kg live weight marketed). During the first 7 d of the winter study, the emission factors were 27 g m-2 d-1, 43 g m-3 d-1, 2.1 g kg-1 N d-1, and 18 g AU-1 d-1, respectively. For the 15 d study, the emission factors changed very little. Higher emissions in winter were due to higher wind speeds, broiler cake total Kjeldahl N (TKN), and pH. While air temperature also affected emissions, stockpile temperatures (not measured) due to microbial activity were probably more important. Care should be taken in extrapolating this study's results to other stockpiles due to differences in stockpile dimensions, chemical properties, and environmental conditions.}, number={5}, journal={Transactions of the ASABE}, author={Yao, H. and Shah, Sanjay and Willits, D. H. and Westerman, P. W. and Li, L. W. and Marshall, T. K.}, year={2011}, pages={1893–1904} }
 @article{li_willits_browdy_timmons_losordo_2009, title={Thermal modeling of greenhouse aquaculture raceway systems}, volume={41}, ISSN={["1873-5614"]}, DOI={10.1016/j.aquaeng.2009.04.002}, abstractNote={A mechanistic model was developed to describe the thermal behavior of an indoor raceway system with an inflated double polyethylene cover. The model describes the heat balances of the two covers, the inside air, the water in the raceway and the soil beneath the raceway. On-site measurements were made with an experimental system at the Waddell Mariculture Center in South Carolina. The collected data were used to calibrate the model. Comparison of the predictions with observations showed that the average absolute errors of air temperature and water temperature were 1.4 and 0.5 °C, respectively and was 8% for the relative humidity. The accuracies are regarded as sufficient for the model to be useful for more general application. Model simulations were used to investigate the effects of the greenhouse on the air and water temperatures, to examine the heat fluxes and to calculate the heat consumption and costs at four different climatic locations. The results suggest that under the mild weather conditions in January near Charleston, SC where the daily mean temperature is 7.6 °C and solar radiation is 121 W m−2, the inside air temperature increases by 5.6 °C and water temperature increases by 9.7 °C on average for the system with the 0.85 m deep raceway covering 70% of the greenhouse floor. An examination of the heat fluxes suggests that thermal radiation is a major mechanism of heat loss for the greenhouse covers and the water surface. Convection from the water surface is also a significant mechanism for latent and sensible heat loss from the raceway. Reducing these heat flows will help conserve and utilize energy. The yearly heating requirements to keep the water temperature at 28 °C for the experimental system were estimated to be 870, 520, 274 and 221 kWh per square meter of raceway for Syracuse, NY, Roanoke, VA, Charleston, SC and Baton Rouge, LA, respectively. The model was deemed to be a useful tool for exploring the performance of greenhouse raceway systems under different scenarios, such as different cover materials, sizes and climates.}, number={1}, journal={AQUACULTURAL ENGINEERING}, author={Li, Shuhai and Willits, Daniel H. and Browdy, Craig L. and Timmons, Michael B. and Losordo, Thomas M.}, year={2009}, month={Jul}, pages={1–13} }
 @article{li_willits_2008, title={An experimental evaluation of thermal stratification in a fan-ventilated greenhouse}, volume={51}, DOI={10.13031/2013.25237}, abstractNote={Experiments were performed to investigate air velocity and vertical air temperature distributions in a fan-ventilated greenhouse. The effects of ventilation rate and canopy size on the allocation of airflow between canopy and non-canopy areas were examined. The data suggested that the ratio of the air velocity within the canopy to the mean velocity of the entire greenhouse cross-section depended on not only the area ratio of canopy to greenhouse cross-section, but also ventilation rate. The ratio of canopy air velocity to greenhouse average velocity decreased if ventilation rate increased. The effects of outside solar radiation, ventilation rate, evaporative cooling pads, and presence of a canopy on the vertical air temperature variations were also investigated. The vertical air temperature variation increased approximately linearly with solar radiation. Use of an evaporative pad increased the temperature variation. Increasing ventilation rate resulted in reduced air temperature variation. The presence of a canopy modified the vertical temperature distribution and reduced temperature variations as well.}, number={4}, journal={Transactions of the ASABE}, author={Li, S. and Willits, D. H.}, year={2008}, pages={1443–1448} }
 @article{li_willits_2008, title={Comparing low-pressure and high-pressure fogging systems in naturally ventilated greenhouses}, volume={101}, ISSN={["1537-5129"]}, DOI={10.1016/j.biosystemseng.2008.06.004}, abstractNote={The cooling performance of a low-pressure (405 kPa working pressure) and a high-pressure fogging system (6.89 MPa) was evaluated. Experiments were conducted in two empty, naturally ventilated greenhouses under summer conditions for a period of about two months. One greenhouse was used as the treatment greenhouse (fogged house) and another was used as the control house (un-fogged house). Cooling efficiency was defined by the ratio of the temperature difference between the un-fogged and fogged greenhouses to the difference between the temperature in un-fogged house and the wet-bulb temperature in the fogged greenhouse. Evaporation efficiency was defined as the ratio of fog evaporation rate to spray rate. Cooling efficiency and evaporation efficiency were compared for the low-pressure and high-pressure systems after accounting for differences in weather conditions under which the two systems were operated. It is suggested that on average evaporation efficiency for the high-pressure system was at least 64% greater than the low-pressure system; cooling efficiency for the high-pressure system was at least 28% greater than for the low-pressure system.}, number={1}, journal={BIOSYSTEMS ENGINEERING}, author={Li, S. and Willits, D. H.}, year={2008}, month={Sep}, pages={69–77} }
 @article{li_willits_2008, title={Modeling thermal stratification in fan-ventilated greenhouses}, volume={51}, DOI={10.13031/2013.25307}, abstractNote={A two-dimensional thermal model was developed to investigate the thermal stratification in fan-ventilated greenhouses. Model inputs include outside weather (air temperature, humidity, and solar radiation), geometric parameters of crop rows and leaf area index, greenhouse ground and roof temperatures, ventilation rate, and operation of evaporative cooling pads. Comparing predictions with observed data indicated that the air temperature and relative humidity were modeled at acceptable accuracies, with air temperature underpredicted by 1.3°C and relative humidity overpredicted by 9%, on average for a planted greenhouse. For an unplanted greenhouse, the air temperature was predicted with an absolute error of 0.7°C, while for relative humidity the absolute error was 3%. Vertical temperature variation, defined as maximum temperature minus minimum temperature at approximately the central location of greenhouse, was predicted with an absolute error of 0.1°C and a relative absolute error of 10% for the planted greenhouse, while for an unplanted greenhouse it was 0.6°C for the absolute error and 12% for the relative absolute error. Simulations with the model suggest that increasing ventilation rate reduced the vertical temperature gradient. Increased ventilation reduced air temperature more at the top than the bottom of the greenhouse. Greater air temperature variation was produced when using evaporative pad cooling than not. Air temperature was reduced more at the bottom than at the top with evaporative pad cooling. The presence of a canopy altered the vertical air temperature distribution and reduced the temperature variation. A sample simulation showed that on a typical summer day at Raleigh, North Carolina, the presence of a canopy row with a height of 1.75 m occupying 69% of the ground area reduced the air temperature variation from 11.5°C to 1.8°C in a fan-ventilated greenhouse operating with a ventilation rate of 0.087 m3 m-2 s-1 and using evaporative pad cooling. The peak air temperature generally occurred at the top of canopy or somewhat below the canopy top. This finding may have some significance in establishing the location of temperature control sensors in future control systems.}, number={5}, journal={Transactions of the ASABE}, author={Li, S. and Willits, D. H.}, year={2008}, pages={1735–1746} }
 @article{ponce_peet_harlow_cheng_willits_2004, title={Assessment of swine waste bioremediation using greenhouse tomatoes}, ISBN={["90-6605-627-4"]}, ISSN={["0567-7572"]}, DOI={10.17660/actahortic.2004.633.51}, abstractNote={ISHS XXVI International Horticultural Congress: Protected Cultivation 2002: In Search of Structures, Systems and Plant Materials for Sustainable Greenhouse Production ASSESSMENT OF SWINE WASTE BIOREMEDIATION USING GREENHOUSE TOMATOES}, number={633}, journal={PROTECTED CULTIVATION 2002: IN SEARCH OF STRUCTURES, SYSTEMS AND PLANT MATERIALS FOR SUSTAINABLE GREENHOUSE PRODUCTION}, author={Ponce, KH and Peet, MM and Harlow, CD and Cheng, J and Willits, DH}, year={2004}, pages={415–423} }
 @article{willits_gurjer_2004, title={Heat pumps for the heating and night-cooling of greenhouse crops: A simulation study}, volume={47}, DOI={10.13031/2013.16038}, abstractNote={The use of air-to-air heat pumps in greenhouses was investigated using a computer simulation model and weather 
data for Raleigh and Wilmington, North Carolina. A greenhouse model taken from the literature, along with the heat pump subroutines 
developed in this study, were used for the simulations. Heat pumps were investigated for heating only and heating plus 
night cooling, using both standard and time-of-use electrical rates for two North Carolina utilities. Three capacities of heat 
pump were examined: 76.6, 38.3, and 19.2 W m-2 floor area. The results suggest that heat pumps installed at a capacity of 19.2 W 
m-2 may be economically viable for the locations studied, yielding pre-tax returns on investment of 20.4% and 16.3% for 
heating-only in Raleigh and Wilmington, respectively, using LP gas costs of $0.185 per liter ($0.70 per gal). When LP gas costs 
of $0.264 per liter ($1.00 per gal) were used, these values increased to 36.8% and 32.8%, respectively. Using the heat pumps 
for night cooling increased return on investment to as much as 49.7% due to increased yields; however, a market for the increased 
production must exist for this to be realized. Time-of-use rates were an advantage when the heat pumps were used for heating 
only, but when night cooling was employed there was no consistent effect. Heat pumps used for heating only yielded larger 
returns on investment in Raleigh than in Wilmington because the cooler climate in Raleigh allowed for greater heat pump 
utilization. When night cooling was added, the returns were higher in Wilmington than in Raleigh for tomato but slightly lower 
for chrysanthemum. The difference is attributed to the greater heat sensitivity of tomato compared to chrysanthemum.}, number={2}, journal={Transactions of the ASAE}, author={Willits, D. H. and Gurjer, Y. R.}, year={2004}, pages={575–584} }
 @inproceedings{cheng_peet_willits_2004, title={Swine wastewater treatment and reclamation}, volume={1}, booktitle={Progress on bioproducts processing and food safety, selected papers from the 1st International Conference of CIGR section VI on bioproducts processing and food safety, Beijing, China, 11-14 October 2004}, author={Cheng, J. J. and Peet, M. M. and Willits, D. H.}, year={2004} }
 @misc{cheng_shearin_peet_willits_2004, title={Utilization of treated swine wastewater for greenhouse tomato production}, volume={50}, ISSN={["0273-1223"]}, DOI={10.2166/wst.2004.0093}, abstractNote={An integrated system has been developed to recycle waste organics and treated wastewater from a swine farm to make value-added products and to protect the environment from potential contamination. The farm is a farrow-to-wean swine operation with approximately 4,000 sows. A high-strength wastewater (chemical oxygen demand, 18,000 mg/l; total Khejdal nitrogen, 1,600 mg/l; total phosphorus, 360 mg/l) is produced from the swine operation. An ambient-temperature anaerobic digester has been used to treat the swine wastewater and to produce biogas (from an average 475 m3/day in winter to 950 m3/day in summer). The biogas is combusted in an engine to produce electricity (around 900 kW-hr/day). The digester effluent that is rich in nutrients (N, P, and minerals) is then utilized for fertigation for greenhouse tomato production. A trickling nitrification biofilter has been developed to convert ammonium in the effluent into nitrate. The nitrified anaerobic effluent is used as both fertilizer and irrigation water for approximately 14,400 tomato plants in greenhouses. Experimental data indicate that the tomato greenhouses have used approximately 12 m3 of the effluent and 3.84 kg nitrogen per day. At the same time, the greenhouses have a daily yield of 520 kg (37 g/plant) of marketable fruit.}, number={2}, journal={WATER SCIENCE AND TECHNOLOGY}, author={Cheng, J and Shearin, TE and Peet, MM and Willits, DH}, year={2004}, pages={77–82} }
 @inproceedings{cheng_peet_willits_2003, title={Ambient temperature anaerobic digester and greenhouse for swine waste treatment and bioresource recovery at Barham farm}, ISBN={0966977025}, booktitle={Proceedings : North Carolina Animal Waste Management Workshop : Oct. 16-17, 2003, Sheraton Imperial Hotel, Research Triangle Park, North Carolina}, author={Cheng, J. and Peet, M. M. and Willits, D. H.}, year={2003} }
 @article{willits_2003, title={Cooling fan-ventilated greenhouses: A modelling study}, volume={84}, ISSN={["1537-5110"]}, DOI={10.1016/S1537-5110(02)00270-2}, abstractNote={A model for fan-ventilated greenhouse cooling is presented in which the primary heat transfer surfaces (cover/structure, canopy and floor) are represented as three parallel planes. Validation of the model was accomplished using data collected over 14 days. Agreement was good, with canopy temperatures over-predicted by only 0·1%, air temperatures in the canopy under-predicted by 0·5%, humidity of the canopy air under-predicted by 1·6% and transpiration rates under-predicted by 1·4%. Simulation runs suggest that when evaporative pad cooling is not used, little advantage is derived from increasing airflow rates beyond about 0·05 m3 m−2 s−1. When evaporative pad cooling is used, however, both air and canopy temperatures decline with increasing airflow rates up to 0·13 m3 m−2 s−1, the highest level considered. Increasing canopy size is predicted to be more influential in reducing air temperatures when evaporative pad cooling is used than when it is not, but its effect on canopy temperature is expected to be approximately the same whether or not evaporative pad cooling is used. With no evaporative pad cooling, the evapotranspiration coefficient (i.e., the ratio of energy used for transpiration to incoming solar energy) is predicted to range from 1·75 for an outside temperature of 36·8°C and an outside humidity ratios of 3·3 g kg−1 to 0·8 for an outside humidity ratio of 29·9 g kg−1 at the same temperature. With evaporative pad cooling, the coefficient is predicted to range from 0·6 to 0·8 at the same outside temperature and the same range of outside humidity ratios.}, number={3}, journal={BIOSYSTEMS ENGINEERING}, author={Willits, DH}, year={2003}, month={Mar}, pages={315–329} }
 @article{willits_2003, title={The  effect of cloth temperature on the cooling efficiency of shade cloths in greenhouses}, volume={46}, DOI={10.13031/2013.13959}, abstractNote={Tests were conducted to examine the role of cloth temperature in the cooling efficiency of shade cloths applied 
to greenhouses. In the first test, shade cloths (with two thermocouples attached to each) were placed over a pair of small 
wooden frames, supported by a single layer of clear polyethylene attached to each frame. Water was intermittently applied 
to one of the shade cloths every other day. A 60% shade, black cloth was used for the first half of testing and a 40% shade, 
white cloth was used for the second half. A mathematical model was developed to describe the energy balance on the shade 
cloths. A second set of tests placed 50% shade, black plastic shade cloths (with six thermocouples attached to each) over two 
6.7 . 12.2 m, double–polyethylene covered, Quonset–style greenhouses. Water was intermittently applied to one of the 
greenhouses on an alternate basis every other day. The greenhouses were kept empty so that energy gain could be determined 
by air temperature rise alone. Output from the thermal model was compared to data observed during the shade frame tests. 
Model output agreed well with the observed shade cloth and floor temperatures, except that floor temperatures under the wet 
white cloth were significantly overpredicted. The model and data showed a clear correlation between shade cloth temperature 
and floor temperature. For the greenhouse tests, the data showed that energy gain was directly correlated with shade cloth 
temperature, and that shade cloth temperature was directly correlated with the frequency of water application. Neither set 
of tests showed radiation screening by the water film to be a major factor influencing cooling.}, number={4}, journal={Transactions of the ASAE}, author={Willits, D. H.}, year={2003}, pages={1215–1221} }
 @inproceedings{shearin_cheng_peet_willits_2003, title={Utilization of nutrients in anaerobically-pretreated swine wastewater for greenhouse tomato production}, ISBN={1892769328}, DOI={10.13031/2013.15240}, abstractNote={Swine waste treatment in North Carolina typically consists of an anaerobic lagoon and sprayfieldupon which crops are grown to utilize the nutrients. Currently, swine lagoon effluent must beapplied at agronomic rates to satisfy the crops nitrogen (N) needs. The majority of landapplication occurs in the summer months, when the weather is typically hot and dry. Agreenhouse tomato production system has been tested for more efficient utilization of nutrients inanaerobically-pretreated swine wastewater. Two 2,600-m2 greenhouses were constructed on a4,000-sow farm located in Johnston County, North Carolina. The swine wastewater was firsttreated in an Ambient Temperature Anaerobic Digester (ATAnD) and the effluent stored in astorage pond. Before being applied to 14,000 tomato plants in the greenhouses, the effluent wastreated in a nitrification biofilter to convert the ammonium (NH4+) into nitrate (NO3-) becausetomato plants prefer the latter as the nitrogen nutrient for their growth. Preliminary data indicatedthat the tomato greenhouses have used approximately 12 m3 of the effluent per day. Based on anaverage inorganic N (NH4+ plus NO3-) concentration of 123 mg/l in the biofilter effluent, thegreenhouses have utilized approximately 1.48 kg N/day. At the same time, the greenhousesproduced a daily yield of 711 kg of marketable fruit, sold at a gross price of $2.20/kg. Thepreliminary findings have shown that the utilization of nutrients in swine wastewater forgreenhouse tomato production is a viable alternative to the traditional system. In addition to thehigh daily N utilization rate, the fruit yields are comparable to conventional greenhouseproduction. Also, the utilization of the treated wastewater during the winter months decreases thepossibility of lagoon overflows and/or spills.}, booktitle={Animal, Agricultural and Food Processing Wastes IX : proceedings of the Ninth International Symposium, 12-15 October, 2003, Raleigh, North Carolina}, author={Shearin, T. E. and Cheng, Jay and Peet, M. M. and Willits, D. H.}, year={2003} }
 @inproceedings{cheng_shearin_peet_willits_2003, title={Utilization of treated swine wastewater for greenhouse tomato production}, volume={4}, ISBN={1843394839}, booktitle={Wastewater reclamation and reuse IV : selected proceedings of the 4th International Symposium on Wastewater Reclamation and Reuse, held at Mexico City, 12-14 November 2003}, author={Cheng, J. and Shearin, T. E. and Peet, M. M. and Willits, D. H.}, year={2003} }
 @inproceedings{harlow_peet_ponce_cheng_willits_casteel_2003, title={Utilizing a greenhouse tomato crop to recover bio-resources from swine waste}, booktitle={Proceedings of the ASHS centennial conference (Providence, Rhode Island)}, author={Harlow, C. and Peet, M. M. and Ponce, A. K. and Cheng, J. and Willits, D. H. and Casteel, M.}, year={2003} }
 @inproceedings{willits_marbis_cheng_peet_shearin_2003, title={Waste heat utilization in a greenhouse used for the removal of nutrients from a swine waste stream}, volume={034043}, booktitle={ASAE annual International Meeting 2003, Las Vegas : The Riviera Hotel, July 27-30, 2003}, author={Willits, D. H. and Marbis, J. M. and Cheng, J. and Peet, M. M. and Shearin, T.}, year={2003} }
 @inproceedings{ponce_peet_cheng_harlow_willits_2002, title={Preliminary assessment of swine waste bioremediation using greenhouse tomatoes}, booktitle={XXVIth International Horticultural Congress & Exhibition (IHC 2002) : horticulture : art & science for life : Metro Toronto Convention Centre, August 11-17, 2002}, author={Ponce, K. H. and Peet, M. M. and Cheng, J. and Harlow, C. and Willits, D. H.}, year={2002} }
 @inproceedings{peet_ponce_willits_cheng_2001, title={Bioremediation of swine waste using greenhouse tomatoes: a systems approach}, booktitle={98th Conference of the American Society for Horticultural Science}, author={Peet, M. M. and Ponce, K. and Willits, D. H. and Cheng, J.}, year={2001} }
 @inproceedings{cheng_peet_willits_pace_2001, title={Integrated farming for sustainable agriculture.}, booktitle={Proceedings of the International Conference for Agricultural Science and Technology (Beijing, China)}, author={Cheng, J. and Peet, M. M. and Willits, D. H. and Pace, J.}, year={2001} }
 @article{willits_peet_2001, title={Measurement of chlorophyll fluorescence as a heat stress indicator in tomato: Laboratory and greenhouse comparisons}, volume={126}, ISSN={["2327-9788"]}, DOI={10.21273/jashs.126.2.188}, abstractNote={Chlorophyll fluorescence was measured under both laboratory and greenhouse conditions in an effort to develop a quick, reliable, and inexpensive laboratory procedure capable of predicting heat stress experienced by tomato (Lycopersicon esculentum Mill.) under greenhouse conditions. The laboratory tests consisted of measurements of the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) performed on leaf discs taken from whole tomato leaves and placed on a temperature controlled plate. Comparisons were made with greenhouse measurements of the same parameter conducted on intact leaves of whole plants exposed to different temperature treatments imposed by manipulation of the aerial environment of the greenhouse. Dark adaption periods ranging from 15 min to all day in the greenhouse and temperature exposure periods ranging from 5 min to 60 min in the laboratory were compared to find the best correlation between the two tests. Best agreement was obtained with 60 min treatment times in the laboratory and 60 min dark adaption periods in the greenhouse. Fv/Fm decreased quadratically with increasing leaf temperature in a similar fashion in both tests, suggesting that the laboratory approach can adequately predict plant response to greenhouse heat stress.}, number={2}, journal={JOURNAL OF THE AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE}, author={Willits, DH and Peet, MM}, year={2001}, month={Mar}, pages={188–194} }
 @article{willits_2001, title={The effect of cloth characteristics on the cooling performance of external shade cloths for greenhouses}, volume={79}, ISSN={["0021-8634"]}, DOI={10.1006/jaer.2001.0702}, abstractNote={Four shade cloths were examined for their ability to reduce temperatures in a greenhouse: (1) a black flat-weave cloth rated by the manufacturer at 30% shade, (2) a black flat-weave cloth rated at 55% shade, (3) a black knitted cloth rated at 50% shade and (4) a white knitted cloth rated at 40% shade. The cloths were examined both dry and wet. The dry, 40% shade, white knitted cloth reduced the rate of energy gain, air temperature rise and electrical energy consumption by more than the dry black cloths. Leaf temperatures were lower under the heavier black cloths (but not the 30% shade) than under the white. When dry the heavier black cloths performed better than the 30% shade black cloth in all respects, except air temperature rise where there was no difference. When wet, both the 55 and 50% shade, black cloths performed better in all respects than either the 40% shade, white or the 30% shade, black. The knitted 50% shade, black cloth performed marginally better than the flat-weave 55% shade, black cloth in several categories, despite a lower shade rating. This was attributed to differences between the two fabrics in the dependence of shade factor on incidence angle.}, number={3}, journal={JOURNAL OF AGRICULTURAL ENGINEERING RESEARCH}, author={Willits, DH}, year={2001}, month={Jul}, pages={331–340} }
 @inproceedings{cheng_pace_peet_willits_shearin_2001, title={Using a greenhouse tomato crop to recover the nutrients from swine wastewater}, ISBN={0966977017}, booktitle={Proceedings of the International Symposium Addressing Animal Production and Environmental Issues}, author={Cheng, J. and Pace, J. and Peet, M. M. and Willits, D. H. and Shearin, T.}, year={2001} }
 @article{willits_2000, title={Constraints and limitations in greenhouse cooling: Challenges for the next decade}, ISBN={["90-6605-952-4"]}, ISSN={["0567-7572"]}, DOI={10.17660/actahortic.2000.534.5}, number={534}, journal={PROCEEDINGS OF THE INTERNATIONAL CONFERENCE AND BRITISH-ISRAELI WORKSHOP ON GREENHOUSE TECHNIQUES TOWARDS THE 3RD MILLENNIUM}, author={Willits, DH}, year={2000}, pages={57–66} }
 @article{willits_peet_2000, title={Intermittent application of water to an externally mounted, greenhouse shade cloth to modify cooling performance}, volume={43}, DOI={10.13031/2013.3018}, abstractNote={The cooling performance of an externally mounted, flat-woven, black-polypropylene shade cloth 
(manufacturer’s shade rating of 55%) was examined under both dry and wet conditions. Wetting was accomplished by 
intermittently sprinkling the cloth with water when outside solar levels were greater than 400 W m–2. Compared to an 
unshaded greenhouse, the dry shade cloth reduced the rate of energy gain by about 26%, less than one-half the amount 
suggested by the shade rating. At the same time, electrical energy consumption was also reduced by about 8% due to 
reduced operation of the cooling equipment in the shaded house. Under the wet cloth, the reduction in rate of energy gain 
improved to about 41%, of which 3.5% was attributable to the increased shading provided by the water film. Air 
temperature rise along the house was reduced by 18% under the dry cloth and 40% under the wet cloth. Leaf temperature 
rise was reduced by only about 9% under the dry cloth; however, the value is misleading because leaf temperatures were 
reduced nearly uniformly along the house whereas air temperatures were reduced primarily at the exhaust end. Under wet 
shade, leaf temperature rise was reduced nearly 43% and electrical energy consumption by 21%.}, number={5}, journal={Transactions of the ASAE}, author={Willits, D. H. and Peet, Mary}, year={2000}, pages={1247–1252} }
 @article{willits_bailey_2000, title={The effect of night temperature on chrysanthemum flowering: heat-tolerant versus heat-sensitive cultivars}, volume={83}, ISSN={["0304-4238"]}, DOI={10.1016/s0304-4238(99)00091-6}, abstractNote={The effect of night temperature on the flowering of heat-tolerant and heat-sensitive cultivars of potted chrysanthemum (Chrysanthemum xgrandiflorum) was examined in four experiments over a period of 4 years. Temperature reductions were imposed only while the plants were under black cloth using a combination of air-conditioning and under-cloth ventilation. The two heat-sensitive cultivars tested were ‘Yellow Mandalay’ and ‘Coral Charm’ and the two heat-tolerant cultivars were ‘Iridon’ and ‘Dark Bronze Charm’. Differences in time-to-flower (TTF) between heat tolerance classifications were less than anticipated. TTF was affected the most in ‘Iridon’, a heat-tolerant cultivar, decreasing by an average of 4.2 days/°C as mean diurnal temperatures (MT) decreased from about 26°C to about 23°C. TTF was affected the least in ‘Coral Charm’, a heat-sensitive cultivar, decreasing by an average of 2.8 days/°C over the same range. Inflorescence diameter, on the other hand, increased by as much as 9% in the two heat-sensitive cultivars but by only about 4% in the heat-tolerant cultivars. The results suggest that the heat-tolerant cultivars tested here may have been classified based on consistency of flower quality rather than TTF.}, number={3-4}, journal={SCIENTIA HORTICULTURAE}, author={Willits, DH and Bailey, DA}, year={2000}, month={Mar}, pages={325–330} }
 @article{willits_peet_1999, title={USING CHLOROPHYLL FLUORESCENCE TO MODEL LEAF PHOTOSYNTHESIS IN GREENHOUSE PEPPER AND TOMATO}, volume={12}, ISBN={["90-6605-812-9"]}, ISSN={0567-7572 2406-6168}, url={http://dx.doi.org/10.17660/actahortic.1999.507.36}, DOI={10.17660/actahortic.1999.507.36}, number={507}, journal={Acta Horticulturae}, publisher={International Society for Horticultural Science (ISHS)}, author={Willits, D.H. and Peet, M.M.}, year={1999}, month={Dec}, pages={311–317} }
 @article{jacobson_willits_1998, title={Developing relationships between environmental variables and stem elongation in chrysanthemum}, volume={41}, DOI={10.13031/2013.17221}, abstractNote={The main objective of this research was to model the relationships between the environmental variables and 
stem elongation in chrysanthemum with the end-goal of producing a model appropriate for use in the dynamic control of a 
greenhouse environment. The plants used were Dendranthema grandiflora cv. ‘Spice’. The model developed uses 
Richards’ growth equation (Richards, 1969) as its base. Adaptations were made to Richards’ growth equation to explicitly 
include the effects of day and night temperature, daily PPF (photosynthetic photon flux), end-of-day red to far-red ratio, 
and position of the internode on the stem on internode elongation. The model fit the observed final length data reasonably 
well (R2 = 0.89). Sensitivity analyses indicated that increasing day temperature had a positive effect on internode length 
while increasing night temperature had a negative effect, with night temperature having a considerably larger effect than 
the effect of day temperature. The analyses suggests that both high and low end-of-day red to far-red ratios will produce 
increased lengths and that increasing daily PPF will produce decreased lengths. The analyses also suggests that 
internodes which develop later on the plant will generally have larger lengths as reflected by the measured data.}, number={3}, journal={Transactions of the ASAE}, author={Jacobson, B. M. and Willits, D. H.}, year={1998}, pages={825–832} }
 @article{strojny_nelson_willits_1998, title={Pot soil air composition in conditions of high soil moisture and its influence on chrysanthemum growth}, volume={73}, ISSN={["0304-4238"]}, DOI={10.1016/S0304-4238(97)00156-8}, abstractNote={Chrysanthemums were grown in 15.2 cm standard pots in a heavy mix of clay loam soil+sphagnum peat moss (2:1). A fine texture mix was used to accentuate undesirable gas profiles in the soil. Soil air was analyzed at five depths in the soil profile. In one set of tests, water was applied to the top of the pot at a matrix potential in the center of the soil profile of −5 kPa. The average gas concentrations in soil air in the top and bottom fifths of soil were for O2—20.0 and 14.5%, for CO2—0.8 and 2.4%, and for C2H4—0 and 0.08 μl dm−3. Smooth concentration gradients of each gas occurred from top to bottom of the soil profile. The composition of soil air changed greatly during the drying cycle. At soil moisture tensions of −0.7, −2.5, and −5 kPa in the center of the soil profile, the gas concentrations in the lowest fifth of soil were for O2—9.6, 15.3, and 20.3%, and for CO2—4.5, 3.5, and 0.6%, respectively. Thus, soil atmospheric conditions for plant growth were poorest immediately after watering and continuously improved up to the time of watering. When pots of chrysanthemum were watered by capillary action from mats, the average concentration of gases in soil air in the lowest fifth of soil were 5.8% O2, 3.6% CO2, and 0.38 μl dm−3 C2H4. This gas profile was less desirable for growth than the profile found in top-watered pots. Unlike the situation in top-watered pots, the gas concentrations in mat-watered pots were stable. Roots in top-watered pots were restricted to the upper two thirds of the soil ball, and were distributed evenly in the inner part of the soil and at the periphery. Roots of mat-watered plants developed further down the vertical periphery of the pot than roots of top-watered plants, but they did not grow inside the ball. Chrysanthemum plants were grown through a hole in the side wall of each of five 3.9 cm tall by 15.2 cm diameter plastic rings stacked vertically and separated by stainless steel screens that allowed for passage of water but not roots. Water was applied to the top of these cylinder stacks. The largest plants developed in the top ring with progressively smaller plants at lower depths. Plants in the lower two rings developed interveinal chlorosis and did not reach commercial size.}, number={2-3}, journal={SCIENTIA HORTICULTURAE}, author={Strojny, Z and Nelson, PV and Willits, DH}, year={1998}, month={Mar}, pages={125–136} }
 @article{willits_peet_1998, title={The effect of night temperature on greenhouse grown tomato yields in warm climates}, volume={92}, ISSN={["0168-1923"]}, DOI={10.1016/S0168-1923(98)00089-6}, abstractNote={Data from six seasons of night cooling experiments conducted at north Carolina State University were analyzed to determine the effect of night temperature on the yield of tomato. Each season contained at least one treatment where night temperatures in one greenhouse were kept below 20°C, using air conditioning, and one treatment where night temperatures in a separate greenhouse were essentially the same as those outside. Two seasons included additional treatments where night cooling took place only from 01:00 hours until dawn. Regression analysis indicated a strong dependence of yield on the night temperature during fruitset when the warm treatment temperature exceeded 21°C. Total fruit numbers were as much as 39% higher, and total weights as much as 53% higher, than that observed in the warmer treatment. The effect on fruit quality was even greater, with No. 1 number and No. 1 weight increases as high as 85% and 106%, respectively, as the warm treatment approached 24°C. Regression also suggested the possibility of secondary effects: (1) night temperature reductions over the whole season (as opposed to only during fruit set) and higher night time relative humidities in the warm treatment during fruitset were independently predicted to decrease the quality advantage in the cool treatment(s); (2) higher levels of irradiance were predicted to increase the weight advantage in the cool treatment(s).}, number={3}, journal={AGRICULTURAL AND FOREST METEOROLOGY}, author={Willits, DH and Peet, MM}, year={1998}, month={Oct}, pages={191–202} }
 @article{peet_willits_gardner_1997, title={Response of ovule development and post-pollen production processes in male-sterile tomatoes to chronic, sub-acute high temperature stress}, volume={48}, ISSN={["0022-0957"]}, DOI={10.1093/jxb/48.1.101}, abstractNote={In order to determine the effects of high temperature on ovule development and reproductive processes subsequent to pollen production, nine day/night temperature combinations were imposed over a 9 month period as four separate experiments, each with three treatments, including one common treatment. In order to eliminate known effects of high temperatures on pollen production and stylar position, high temperature treatments were applied only to male-sterile tomatoes (Lycopersicon esculentum Mill.). Pollen was obtained from male-fertile plants given optimal growth conditions. This allowed comparison of mean daily temperatures from 25-29 °C; day/night temperature differentials (DIFs) of 2, 6, and 10 °C; day temperatures of 28, 30 and 32 °C at night temperatures of 22, 24, and 26 C; and night temperatures of 22, 24 and 26 °C at day temperatures of 28, 30 and 32 °C. Average weight per fruit and flower number did not demonstrate a consistent pattern of response to high temperature. Other reproductive characteristics (% fruitset, total number and weight of fruit per plant, and seediness index) decreased as mean daily temperature rose from 25 °C to 26 °C and from 28 °C to 29 °C. The primary parameter affecting these variables was mean daily temperature, with day temperature having a secondary role. Thus, in determining reproductive responses of tomato to temperatures within this range, day temperature, night temperature and DIFs do not need to be considered independently of their effect on mean daily temperature. If this relationship holds true in other species, and for pre-pollen production processes as well, modelling the effects of projected climate change should be simplified.}, number={306}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Peet, MM and Willits, DH and Gardner, R}, year={1997}, month={Jan}, pages={101–111} }
 @article{willits_peet_1994, title={Misting external shade cloths. Part I: Relief from the heat?}, volume={39}, number={2}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H. and Peet, M. M.}, year={1994}, pages={1} }
 @article{willits_1994, title={Misting external shade cloths. Part II: Does it matter what kind of cloth?}, volume={39}, number={6}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H.}, year={1994}, pages={1} }
 @article{willits_bailey_1994, title={Night cooling as a means of improving warm weather chrysanthemum production: The effect of night temperature on growth and flower development in mums}, number={944072}, journal={Paper (American Society of Agricultural Engineers)}, publisher={American Society of Agricultural Engineers (ASAE)}, author={Willits, D. H. and Bailey, D. A.}, year={1994}, pages={12} }
 @article{willits_1993, title={Greenhouse cooling}, volume={38}, number={2}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H.}, year={1993}, pages={15} }
 @article{willits_peet_1993, title={The effect of evaporative cooling on the efficiency of external greenhouse shade cloths}, number={93-4042}, journal={Paper (American Society of Agricultural Engineers)}, author={Willits, D. H. and Peet, M. M.}, year={1993}, pages={13} }
 @article{willits_nelson_peet_depa_kuehny_1992, title={Modeling Nutrient Uptake in Chrysanthemum as a Function of Growth Rate}, volume={117}, ISSN={0003-1062 2327-9788}, url={http://dx.doi.org/10.21273/jashs.117.5.769}, DOI={10.21273/jashs.117.5.769}, abstractNote={The results of six experiments conducted over 3 years were analyzed to develop a relationship between nutrient uptake rate and growth rate in hydroponically grown Dendranthema ×grandiflorum (Ramat.) Kitamura, cv. Fiesta. Plants subjected to two levels of CO, and three levels of irradiance in four greenhouses were periodically analyzed for growth and the internal concentration of 11 mineral elements. The resulting data were used to determine relative accumulation rate and relative growth rate, which were included in linear regression analyses to determine the dependence of uptake on growth. The regression equations were significant, with a slight trend toward nonlinearity in some elements. This nonlinearity seems to be related to the aging of the plant and suggests a process in the plant capable of controlling uptake rate, perhaps as a result of changes in the rate of formation of different types of tissues.}, number={5}, journal={Journal of the American Society for Horticultural Science}, publisher={American Society for Horticultural Science}, author={Willits, D.H. and Nelson, P.V. and Peet, M.M. and Depa, M.A. and Kuehny, J.S.}, year={1992}, month={Sep}, pages={769–774} }
 @article{willits_peet_1992, title={Nighttime cooling using heat pumps in warm-weather greenhouse tomato production}, number={92-4005}, journal={Paper (American Society of Agricultural Engineers)}, author={Willits, D. H. and Peet, M. M.}, year={1992}, pages={11} }
 @article{willits_ahmad_peet_1991, title={A model for greenhouse cooling}, number={91-4041}, journal={Paper (American Society of Agricultural Engineers)}, author={Willits, D. H. and Ahmad, I. and Peet, M. M.}, year={1991}, pages={24} }
 @article{willits_1991, title={Greenhouse engineering research at NCSU}, volume={36}, number={4}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H.}, year={1991} }
 @article{willits_1991, title={Greenhouse shading}, volume={36}, number={6}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H.}, year={1991}, pages={8} }
 @article{willits_peet_depa_kuehny_nelson_1990, title={Modulation of nutrient uptake in chrysanthemum by irradiance, CO2, season and developmental stage}, number={20}, journal={Monograph (British Society for Plant Growth Regulation)}, author={Willits, D. and Peet, M. and Depa, M. and Kuehny, J. and Nelson, P.}, year={1990}, pages={59} }
 @article{willits_peet_1989, title={Predicting yield responses to different greenhouse CO2 enrichment schemes: cucumbers and tomatoes}, volume={44}, ISSN={0168-1923}, url={http://dx.doi.org/10.1016/0168-1923(89)90022-1}, DOI={10.1016/0168-1923(89)90022-1}, abstractNote={Data from six years of carbon dioxide (CO2) enrichment studies at North Carolina State University were analyzed in an attempt to develop predictive relationships for plant responses to different enrichment schemes and CO2 levels (600–5000 μl l−1). Cucumbers (Cucumis sativus L.) and tomatoes (Lycopersicon esculentum Mill.) were enriched using: (i) closed-loop cooling to extend enrichment periods beyond that generally practicable and (ii) elevated CO2 levels to compensate for short enrichment times normally encountered in conventional enrichment. Yields of nine cultivars of cucumber and seven of tomato, from both ground bed and bag culture, were regressed against solar energy, number of enrichment hours, fractional enrichment time, CO2 set point concentration (i.e., target concentration), and actual daily CO2 concentration. Absolute yields for cucumber were found to be strongly related to the solar energy received and, to a lesser degree, the number of enrichment hours. CO2 concentration, either set point or actual, was significant only when included in quadratic form. The relationship developed suggests that the optimum concentration is inversely related to the length of the enrichment period and that the product of the number of enrichment hours and the set point concentration should equal 14 400 μl h l−1. Absolute yields for tomato were also highly dependent upon solar energy, and to a lesser degree, either actual CO2 concentration, number of enrichment hours, or fractional enrichment time. Weight gain advantages for cucumber were found to be a linear function of fractional enrichment time (enrichment time divided by solar daylength), reaching a maximum value of 54% when continuously enriched during daylight hours. Weight gain advantages for tomato were found to be a non-linear function of fractional enrichment time with values of fractional enrichment time less than 0.5 producing little or no gain.}, number={3-4}, journal={Agricultural and Forest Meteorology}, publisher={Elsevier BV}, author={Willits, D.H. and Peet, M.M.}, year={1989}, month={Jan}, pages={275–293} }
 @article{willits_karnoski_mcclure_1980, title={A microprocessor-based control system for greenhouse research: Part I. Hardware}, volume={23}, DOI={10.13031/2013.34648}, abstractNote={ABSTRACT A microprocessor-based control system for greenhouse energy research has been developed, tested, and is now operational. Advantages of the system over standard control systems include increased precision, increased flexibility of control algorithms, and the power to collect and process data. This paper describes the hardware phase of the development and reports the results of the performance testing.}, number={3}, journal={Transactions of the ASAE}, author={Willits, D. H. and Karnoski, T. K. and McClure, W. F.}, year={1980}, pages={688} }
 @article{willits_1975, title={Heating greenhouses with solar energy}, volume={19}, number={5}, journal={North Carolina Flower Growers' Bulletin}, author={Willits, D. H.}, year={1975}, pages={1} }