Utility of Plant Growth-Promoting Rhizobacteria for Sustainable Production of Bermudagrass Forage.

A two-year study was conducted in bermudagrass hay fields in central Alabama to estimate the potential of plant growth-promoting rhizobacteria (PGPR) as a tool for sustainable agriculture in forage management. This study compared the effects of two treatments of PGPR, applied with and without lowered rates of nitrogen, to a full rate of nitrogen fertilizer in a hay production system. The PGPR treatments included a single-strain treatment of Paenibacillus riograndensis (DH44), and a blend including two Bacillus pumilus strains (AP7 and AP18) and a strain of Bacillus sphaericus (AP282). Data collection included estimates of forage biomass, forage quality, insect populations, soil mesofauna populations, and soil microbial respiration. Applications of PGPR with a half rate of fertilizer yielded similar forage biomass and quality results as that of a full rate of nitrogen. All PGPR treatments increased soil microbial respiration over time. Additionally, treatments containing Paenibacillus riograndensis positively influenced soil mesofauna populations. The results of this study indicated promising potential for PGPR applied with lowered nitrogen rates to reduce chemical inputs while maintaining yield and quality of forage.

Building comprehensive glucosinolate profiles for brassica varieties.

Brassica plants play an important role in common agricultural practices, such as livestock feed or biofumigation, due to the bioactivity of the natural degradation products of glucosinolate metabolites. Therefore, the ability to survey comprehensive glucosinolate profiles for individual brassicas is essential for informing proper species selection for the intended application. Current methods for glucosinolate identification and quantification involve complex or unconventional procedures, and proper reference materials are not readily available. Therefore, researchers with limited resources that require glucosinolate profiles are at an extreme disadvantage. In this work, a simple and accurate HPLC-MS method was developed and validated to build preliminary glucosinolate profiles for three agriculturally relevant forage brassica varieties [turnip (B. rapa L.), canola (B. napus L.), and rapeseed (B. napus L.)]. The average glucosinolate content across three herbage collection dates for canola, rapeseed and turnip were 2.9 ± 0.9 mg g-1, 6.4 ± 1.3 mg g-1, and 14 ± 3.4 mg g-1, respectively. GLS concentrations are reported in milligrams of glucosinolate, calculated as sinigrin equivalents, per gram of dry plant material. This semi-quantitative approach for reporting total GLS content in brassicas is accurate within 15%. Several minor individual glucosinolates were identified that have not been previously reported in canola, rapeseed and turnip species, including glucotropaeolin and 4-hydroxyglucobrassicin (canola), glucoraphanin and glucoberteroin (rapeseed), and glucosinalbin and glucobarbarin (turnip). This non-targeted screen of several forage brassica varieties demonstrates the inherent variation in both the individual glucosinolate content and the total glucosinolate profile among brassicas, and highlights the importance of such glucosinolate characterization in agricultural practices. Additionally, the method developed in this study can be used as a tool for researchers with limited resources to build accurate glucosinolate profiles of brassica plants.

Ruminal fermentation and enteric methane production of legumes containing condensed tannins fed in continuous culture.

A continuous-culture fermentor study was conducted to assess nutrient digestibilities, volatile fatty acid (VFA) concentrations, microbial protein synthesis, bacterial nitrogen (N) efficiency, and enteric methane (CH4) production of four 50:50 grass-legume diets, randomly assigned in a 4 × 4 Latin square design. Four legumes with different concentrations of condensed tannins (CT) were tested: alfalfa [ALF; Medicago sativa L., non-CT legume]; birdsfoot trefoil [BFT; Lotus corniculatus L., low-CT legume]; crown vetch [CV; Securigera varia (L.) Lassen, moderate-CT legume]; and sericea lespedeza [SL; Lespedeza cuneata (Dum. Cours.) G. Don, high-CT legume]. Orchardgrass (Dactylis glomerata L.) was the common forage used in all diets. Four fermentors were evaluated over four 10-d periods by feeding 82 g of dry matter (DM)/d in 4 equal feedings. Methane output was recorded every 10 min. Effluent samples were collected during the last 3 d of the experiment, composited by fermentor and period, and analyzed for pH and VFA, as well as DM, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber for determination of apparent and true nutrient digestibilities. Microbial protein synthesis and bacterial efficiency were estimated by analysis of N flows and purines. The CT concentrations were 3, 21, 38 and 76 g/kg of DM for ALF, BFT, CV, and SL diets, respectively. The SL diet had decreased fiber digestibilities and total VFA concentrations compared with the other diets. This resulted in the least total CH4 production in the SL diet. Bacterial N efficiency per kilogram of organic matter truly digested was lower in the SL diet than in the BFT and CV diets. The lowest CH4 production per unit of digestible nutrients was also found in the SL diet. Further work should be conducted to find optimal diets (by testing other legumes, rations, and sources of CT) for reducing CH4 emissions without negatively affecting ruminal digestion to maintain or improve productivity.

Evaluation of a single-flow continuous culture fermenter system for determination of ruminal fermentation and enteric methane production.

A 4-unit, single-flow continuous culture fermenter system was developed to assess in vitro nutrient digestibility, volatile fatty acid (VFA) concentration and daily enteric methane (CH4 ) production of ruminant diets. The objective was to develop a closed-vessel system that maintained protozoal populations and provided accurate predictions of total CH4 production. A diet of 50% orchardgrass (Dactylis glomerata L.) and 50% alfalfa (Medicago sativa L.) was fed during 4, 10-day periods (7-day adaptation and 3-day collection). Fermenters were fed 82 g of dry matter (DM)/day in four equal feedings. pH and temperature were taken every 2 min, and CH4 concentration was measured every 10 min. Samples for DM and protozoal counts were taken daily, and daily effluent samples were collected for determination of DM, VFA and NH3 -N concentrations. There was no effect (p > 0.17) of adaptation versus collection days on vessel and effluent DM, temperature or pH. Initial protozoal counts decreased (p < 0.01), but recovered to initial counts by the collection period. Total VFA, acetate, propionate and isobutyrate concentrations did not differ (p ≥ 0.13) among periods or days of the collection period. There was no difference (p ≥ 0.37) among days or periods in total daily CH4 production and CH4 production per g of OM, NDF, digestible OM or digestible NDF fed. Data collected throughout 4 experimental periods demonstrated that the system was able to reach a steady state in fermentation well within the 7-day adaptation period and even typically variable data (i.e., CH4 production) were stable within and across periods. While further research is needed to determine the relationship between this system and in vivo data, this continuous culture fermenter system provides a valid comparison of in vitro ruminal fermentation and enteric CH4 production of ruminant diets that can then be further validated with in vivo studies.