Manure use on cropland has raised concern about nutrient contamination of surface and ground waters. Warm-season perennial grasses may be useful in filter strips to trap manure nutrients and as biomass feedstock for nutrient removal. We explored the use of 'Alamo' switchgrass (Panicum virgatum L.) in a biomass production-filter strip system treated with dairy manure. We measured changes in extractable P in the soil, NO3 -N in soil water, and changes in total reactive P and chemical oxygen demand (COD) of runoff water before and after a switchgrass filter strip. Five rates of dairy manure (target rates of 0, 50, 100, 150, and 200 kg N ha(-1) from solid manure in 1995; 0, 75, 150, 300, and 600 kg N ha(-1) from lagoon effluent in 1996 and 1997) were surface-applied to field plots of switchgrass (5.2 by 16.4 m) with a 5.2- by 16.4-m switchgrass filter strip below the manured area. Yield of switchgrass from the manured area increased linearly with increasing manure rate in each year. Soil water samples collected at 46 or 91 cm below the soil surface on 30 dates indicated < 3 mg L(-1) of NO3-N in all plots. Concentrations of total reactive P in surface runoff water were reduced an average of 47% for the 150 kg N rate and 76% for the 600 kg N rate in 1996 and 1997 after passing through the strip. Manure could effectively substitute for inorganic fertilizer in switchgrass biomass production with dual use of the switchgrass as a vegetative filter strip.
In 1994, the Crop Science Society of America (CSSA) appointed an ad hoc committee to study various developmental indexes for crops. As part of this committee's activity, our objective was to compare three developmental indexes for use with switchgrass (Panicum virgatum L.) and two indexes for use with bermudagrass [Cynodon dactylon (L.) Pers]. Two cultivars of switchgrass (Alamo and Cave‐in‐Rook at Stephenville, TX, and Kanlow and Cave‐in‐Rock at Ames, IA) were scored once or twice weekly during primary growth according to the Nebraska index, the Texas Agricultural Experiment Station (TAES) index, and the BBCH (European) uniform decimal code. Two hybrids of bermudagrass (Midland and Tifton‐44 at Fayetteville, AR, and Coastal and Tifton‐44 at Stephenville) were scored once or twice weekly during a spring and summer growth cycle according to the BBCH system and an index developed for bermudagrass (West index). The main difference among scales was that the Nebraska and TAES scales were developed for perennial grasses, whereas the BBCH index is a generic scale with some stage descriptors not applicable to perennial grasses. The indexes share several common stage descriptors, but with different decimal codes. For bermudagrass, the main limitation with the BBCH system was that it applied to grass crops having a well‐defined main stem and sideshoots (tillers) and a relatively uniform maturation of the shoots. The BBCH Principal Growth Stages 2 and 3 were difficult to reconcile with the West system, which does not define tillering, whereas subsequent principal stages are reconcilable with minor modifications. We conclude that the BBCH index would require substantial modification to adapt the system for perennial forage grasses.
Cardiac MR thermometry shows promise for real-time guidance of radiofrequency ablation of cardiac arrhythmias. This technique uses ECG triggering, which can be unreliable in this situation. A prospective cardiac triggering method was developed for MR thermometry using the active tracking (AT) signal measured from catheter microcoils. In the proposed AT-based cardiac triggering (AT-trig) sequence, AT modules were repeatedly acquired to measure the catheter motion until a cardiac trigger was identified to start cardiac MR thermometry using single-shot echo-planar imaging. The AT signal was bandpass filtered to extract the motion induced by the beating heart, and cardiac triggers were defined as the extremum (peak or valley) of the filtered AT signal. AT-trig was evaluated in a beating heart phantom and in vivo in the left ventricle of a swine during temperature stability experiments (6 locations) and during one ablation. Stability was defined as the standard deviation over time. In the phantom, AT-trig enabled triggering of MR thermometry and resulted in higher temperature stability than an untriggered sequence. In all in vivo experiments, AT-trig intervals matched ECG-derived RR intervals. Mis-triggers were observed in 1/12 AT-trig stability experiments. Comparable stability of MR thermometry was achieved using peak AT-trig (1.0 ± 0.4°C), valley AT-trig (1.1 ± 0.5°C), and ECG triggering (0.9 ± 0.4°C). These experiments show that continuously acquired AT signal for prospective cardiac triggering is feasible. MR thermometry with AT-trig leads to comparable temperature stability as with conventional ECG triggering. AT-trig could serve as an alternative cardiac triggering strategy in situations where ECG triggering is not effective.
Continuous AT was used for cardiac synchronization of MR-thermometry with on-line signal filtering, calibration, and triggering. Experiments in a porcine animal model, where AT-trig was compared to ECG triggering, showed that AT-trig could potentially serve as alternative cardiac triggering strategy in situations where ECG triggering is not effective.
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