Optimizing Water Use for Three Old World Bluestems in the Texas High Plains
Agriculture in the Texas High Plains is challenged by rapid depletion of ground water. Warm-season grasses offer opportunities for grazing but information is needed on comparative water use efficiencies. Three old world bluestems (Bothriochloa spp.) are irrigated with 0, 33, 66, and 100% replacement of potential evapotranspiration (PET) to determine water use efficiency, yield, and quality. Thus far, ‘WW-B.Dahl’ and ‘caucasian’ were more water use efficient than ‘Spar’. Highest yields resulted from 100% replacement of PET but forage nutritive value is higher with 33% PET. Guides for optimizing economic returns, water use, quality, and quantity of forage will be developed.
The overall objective is to determine forage growth and nutrient yield per unit of added water (water use efficiency) for three warm-season perennial grasses in the Southern High Plains.
Specific objectives include:
1. To determine the influence of irrigation to replace 0%, 33%, 66%, and 100% of Potential Evapotranspiration (PET) on dry matter yield, water use efficiency, nutritive value, mineral composition, seed yield and viability, plant morphology including percentage live/dead, and leaf-stem ratio of Dahl, Spar, and Caucasian old world bluestems.
2. To calculate the economic return to inputs of water from these three forages when harvested for hay and seed production.
We have completed the second year of research and the first full year of data collection and analysis. We observed general differences in the response of the investigated old world bluestem species to differing water input in terms of water use efficiency (WUE), forage nutritive value, and plant morphology. Data was partially published in a progress report that was presented at our yearly field day in summer of 2002. Additionally, preparation of the dissertation was started during the first year of SARE support. Remaining analyses are still to be done on economical returns per unit water input when these grasses are harvested for hay and seed production. Thus far, we obtained seed yields from the first and second year of our research. Field research for the final year of this investigation will be completed during 2003. Manuscripts will be drafted during 2003 to prepare and submit publications in scientific journals. The data completed thus far will be presented at the 2003 annual meeting of the Crop Science Society of America and at other appropriate scientific and producer meetings.
Results from the first year of investigation (2001) suggested that Caucasian bluestem (Bothriochloa caucasica) is more efficient in converting water into biomass (20.63 kg of dry matter per ha and mm of water) than Dahl (B. bladhii; 19.35 kg ha-1 mm-1) and Spar bluestem (B. ischaemum; 14.53 kg ha-1 mm-1). Data from 2002 indicated that Dahl bluestem had a higher water use efficiency (WUE, 20.44 kg ha-1 mm-1) than Caucasian bluestem with 18.21 kg ha-1 mm-1. As was observed in 2001, Spar bluestem was lowest in WUE with 16.26 kg ha-1 mm-1.
Highest dry matter (DM) production in 2001 was observed in Caucasian bluestem under full irrigation (100% potential evapotranspiration) with 13,023 kg ha-1, followed by Dahl bluestem with 11,322 kg ha-1 and Spar bluestem with 7,900 kg ha-1. Similar to the pattern observed in the fully irrigated plots, Spar bluestem showed lowest dryland yields with 1,513 kg ha-1 compared with Dahl bluestem (2,393 kg ha-1 DM) and caucasian (3,184 kg ha-1 DM ). In 2002, Dahl bluestem showed a higher biomass yield under fully irrigated conditions with 21,537 kg ha-1 followed by Caucasian bluestem with 21,111 kg ha-1 and Spar bluestem with 18,466 kg ha-1. As was observed in 2001, Caucasian bluestem had higher yields under dryland conditions than the other investigated species. Evidence was also found that Caucasian bluestem is capable of generating higher biomass under 33% PET than the other two species.
Averaged over all water treatments, percentage crude protein was higher in Dahl than in other bluestems investigated. Dry matter digestibility was higher in Dahl subjected to 33% PET than at the other irrigation treatments tested. Irrigating these grasses with 33% PET appeared to result in higher forage quality as indicated by percentage CP and total non-structural carbohydrates compared with the other water treatments but the third year of research is needed to clarify these relationships. Dahl maintained a higher leaf:stem ratio under both dry land conditions and at 33% replacement of PET than either of the other bluestem species which may account for the higher forage nutritive value observed in Dahl. Conversely, NDF was lower in B. Dahl than in the other bluestems. As was observed in the first year of investigation, the amount of TNC measured during the growing season of 2002 was highest under a 33% PET replacement treatment in all species.
Impacts and Contributions/Outcomes
This research was presented during a field day in June 2002 to over 125 producers from the region. The number of participants at these field days increased steadily over the last years and we conclude that producers from the region understand the urgency of developing sustainable farming systems for the regions. An ever recurring concern at these meetings was the amount of optimum water inputs, forage nutritive value, and projected profitability of the proposed grass species that are already used in the area. We believe that with disseminating detailed information on water consumption and the relation to forage nutritive value of old world bluestems, we can enhance the knowledge base of farmers from the surrounding area such that they can make rational choices to conserve water resources. Spar old world bluestem was widely planted on the Conservation Reserve Program (CRP) acres in this region and is, thus, the species that area producers are familiar with. Our data clearly indicates that either Dahl or caucasian provide more biomass and nutrients than Spar under any moisture regime but particularly under limited or no irrigation.