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The objective of the study was to examine lowland (Alamo and Kanlow) and upland (Blackwell and Caddo) cultivars of switchgrass (Panicum virgatum L.) for differences in response to water deficit and nitrogen fertilizer. Cultivars were grown in pots with fritted clay at two water levels: well watered and deficit conditions (-0.1 and -1.0 MPa) and two nitrogen levels (10 and 100 kg ha(-1)). Nitrogen determined growth potential of the cultivars more than water availability. The lowland cultivars produced greater biomass yields than upland cultivars. However, upland cultivars showed a smaller response to drought stress. Under water stress conditions all cultivars exhibited a higher leaf percentage of total dry matter (DM), with the upland cultivars having the highest leaf percentage of total DM. Nitrogen proved to have more of an effect on single-leaf photosynthesis rates than water. Alamo demonstrated the greatest biomass production among all cultivars. The differences found between the two lowland cultivars suggest that Alamo would be better suited for forage and biomass production in central Texas, being a higher producer under drought and non-drought conditions than Kanlow as well as upland cultivars.

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-Rock 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.

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.