Prickly pear cacti (Opuntia spp.) are widely used for cattle forage and fodder as well as human food, but their nutrient responses have received little attention. Therefore, soil levels of 13 elements were compared with growth over a 3-yr period for Opuntia engelmannii Salm-Dyck and 0. rastrera Weber at 11 sites in Coahuila, Mexico. Also, various levels of N and P were applied to 0. engelmannii growing for 1.5 yr at Kingsville, TX. The tenfold differences in growth at the Mexican sites were not correlated with soil element level, except for N (r=0.44; P<0.05) and B (r=0.64; P<0.01); 84% of the site-to-site variation in productivity could be accounted for by these two elements. Fertilizer studies in Texas showed that dryweight gain could be increased 73% by 160 kg N ha-• and 48% by 80 kg P ha-• compared to controls without Nor P applications (P< 0.01 in both cases), and that some N X P interaction occurred. Cladodes from the control plots in Texas had 21.1 g N kg-• and 1.97 g P kg-•, which was at least twofold higher than for the Mexican sites, and 23 mg B kg-•, which was over fivefold higher than the average for the Mexican sites. Thus, N, P, and possibly B fertilization can increase the growth of these cacti, which can achieve a relatively high dry weight productivity of about 15 Mg ha-• yr-• in semiarid areas without irrigation.----~------------Additional index words: Boron, Nitrogen, Opuntia engelmannii Salm-Dyck, Opuntia rastrera Weber, Phosphorus, Platyopuntia. (address for reprint requests); postdoctoral fellow and associate research scientist, respectively, Caesar Kleberg Wildlife Research Inst., Texas A&I Univ., Kingsville, TX 78363; head and research associate, respectively,

Within the mining industry, a safe and economical mine ventilation system is an essential component of all underground mines. In recent years, research scientists and engineers have explored operations research methods to assist in the design and safe operation of primary mine ventilation systems. The main objective of these studies is to develop algorithms to identify the primary mine ventilation systems that minimize the fan power costs, including their working performance. The principal task is to identify the number, location, and duty of fans and regulators for installation within a defined ventilation network to distribute the required fresh airflow at minimum cost. The successful implementation of these methods may produce a computational design tool to aid mine planning and ventilation engineers. This paper presents a review of the results of a series of recent research studies that have explored the use of mathematical methods to determine the optimum design of primary mine ventilation systems relative to fan power costs.

Totten Mine has been operating a ventilation control system (VCS) with remote activation capabilities under a manual mode since 2014. The system consists of on/off and variable frequency drive fans, variable opening louvers and doors to regulate the airflow across levels, ramps and headings. Parameters that are monitored within the VCS include air volume, relative humidity, dry bulb temperature and carbon monoxide. All of the VCS components installed and commissioned in 2014 were operational during the mine production ramp-up from 2015 to 2016. The managed ventilation system demonstrated its ability to accommodate the airflow requirements of the mine in an effective and efficient manner during this time. However, changes to the mining plan generated an increase in required air volumes. It was determined these could be accomplished by further enhancements of the ventilation control system. As a result, during 2016 the automation and ventilation departments reviewed the alternatives available in the market and selected the NRG1-ECO software provided by Bestech to achieve a tag and tracking-based level of automated ventilation control. The implementation of the software started at the end of 2016 with a single level and was then expanded to additional levels. This paper presents the state of the current VCS at Totten Mine in terms of the levels that have been commissioned, the control strategies in use and the energy reduction achieved in the range of 50 to 60%. These are compared to the baseline established before the implementation. Challenges encountered during commissioning, maintenance and the plan for future implementation and software versions are also discussed.