Seeding Rate Effects on Forage Mass and Vegetation Dynamics of Cool-Season Grass Sod Interseeded with Sorghum-Sudangrass

Interseeding annual warm-season grasses into perennial cool-season grasses has the potential to increase summer forage mass and nutritive value. Knowledge of how seeding rate affects annual warm-season grass establishment, forage mass, and vegetation dynamics remains limited. From 2016–2017, we conducted a field experiment evaluating the effects of seeding rates on sorghum-sudangrass (Sorghum bicolor × S. bicolor var. sudanense) density and forage mass and on the frequency of occurrence of plant species in cool-season grass sod in Lincoln, NE. The experiment had a completely randomized design consisting of six replicates of four seeding rates [0, 14, 28, and 35 kg pure live seed (PLS) ha−1] in sod mowed at a 2.5-cm height and one unseeded, non-mowed control treatment. Sorghum-sudangrass establishment increased with seeding rate from an average of 20 to 45 plants m−2 as the seeding rate increased from 14 to 35 kg PLS ha−1. Forage mass depended on a seeding rate × harvest interaction, showing positive linear and cubic responses to seeding rate in consecutive harvests at 45 and 90 d after interseeding. To increase forage mass in perennial cool-season grass sod, producers should interseed sorghum-sudangrass with at least 28 kg PLS ha−1. One-time seedings into cool-season, perennial grass sod have no residual effects on subsequent forage mass and vegetation dynamics.

Yield, Nutrient Composition, and Horse Condition in Integrated Crabgrass and Cool-Season Grass Rotational Grazing Pasture Systems

Integration of warm-season grasses into traditional cool-season pastures can increase summer forage for grazing cattle. The aim of this study was to determine impacts of this practice on yield and nutrient composition of equine rotational pasture systems as well as horse body condition. Two 1.5 ha rotational systems (6-0.25 ha sections/system) were evaluated: a control system (CON) [all sections mixed cool-season grass (CSG-CON)] and an integrated system (IRS) [3 CSG sections (CSG-IRS) and 3 Quick-N-Big crabgrass [Digitaria sanguinalis (L.) Scop.] (CRB-IRS)]. Three horses per system grazed in 3 periods: EARLY (mid-May to mid-Jul), SLUMP (mid-Jul to mid-Sep), and LATE (mid-Sep to mid-Nov). Herbage mass (HM) was measured prior to each rotation and samples were collected (0800-1000 h) for nutrient analysis. Grazing days were tracked to calculate carrying capacity (CC). Horse condition measures were assessed monthly. Over the full grazing season, 9125 kg of forage was available for grazing in IRS vs. 6335 kg in CON. The CC was 390 horse d for IRS, while only 276 horse d for CON. Total HM/section did not differ during EARLY when CRB was not available (CSG-IRS: 2537 ± 605; CSG-CON: 3783 ± 856 kg/ha), but CC was greater in CSG-IRS (220 ± 37 horse d/ha) than CSG-CON (92 ± 26 horse d/ha; P = 0.03). In SLUMP, both HM and CC were greater in CRB-IRS (HM: 4758 ± 698 kg/ha; CC: 196 ± 31 horse d/ha) than CSG-IRS (HM: 1086 ± 698 kg/ha; CC: 32 ± 31 horse d/ha) or CON (HM: 970 ± 493 kg/ha; CC: 46 ± 22 horse d/ha; P < 0.02). While HM did not differ by section type in LATE (1284 ± 158 kg/ha), CC was greater in CSG-CON (84 ± 9 horse d/ha) vs CRB-IRS (32 ± 13 horse d/ha; P = 0.03) and CSG-IRS (40 ± 13 horse d/ha; P = 0.06). During SLUMP, water-soluble carbohydrates (WSC) were lower in CRB-IRS (4.46 ± 0.80%) than CSG-CON (7.92 ± 0.90%; P < 0.04), but not CSG-IRS (5.93 ± 1.04%); however, non-structural carbohydrates (NSC) did not differ (7.05 ± 0.62%). There were no differences in WSC (6.46 ± 0.54%) or NSC (7.65 ± 0.54%) by section type in LATE. Horses in IRS maintained a body condition score (BCS) of 5.78 ± 0.48, but BCS did not differ by system (CON: 6.11 ± 0.48). Thus, integrated grazing increased summer pasture yield and provided adequate nutrition to maintain horse condition, but further research is needed to improve late-season production. Integrated grazing may not, however, provide an advantage in limiting dietary NSC, as NSC remained low for all pasture sections.

PSXIII-2 Effect of varying proportions of cereal rye and turnip on ruminal fermentation and methane output through in vitro batch culture

Ruminant animal performance has been variable in studies grazing annual cool-season grass and brassica monocultures and mixtures. There is little understanding of the fermentation mechanisms causing variation. The aim of this study was to determine apparent dry matter (DM) digestibility, methane, and volatile fatty acid (VFA) concentration from different proportions of cereal rye (Secale cereal; R) and turnip (Brassica rapa L.; T) (0R:100T, 40R:60T, 60R:40T, and 100R:0T) via in vitro batch fermentation. Freeze-dried forage samples from an integrated crop-livestock study was assembled into the four treatments with a 50:50 leaf to root ratio for turnip. Measurements were made following a 48 hr fermentation with 2:1 buffer and ruminal fluid inoculum. Data were analyzed using Mixed Procedure of SAS with batch (replicate) and treatment (main effect) in the model; differences were declared at P ≤ 0.05, with tendencies declared at > 0.05 but < 0.10. Rumen apparent DM digestibility (26.8%; overall mean) was not different among treatments. Methane production was less (P < 0.01) with inclusion of turnip ranging from 774 nmol/ml for 0R:100T to 1416 nmol/ml for 100R:0T. Total VFA production, acetate to propionate ratio, acetate, and valerate were not affected by forage treatments (117 mM, 1.45, 39.84 mol/100 mol, and 7.86 mol/100 mol, respectively; overall mean). Propionate, isobutyrate, and isovalerate concentrations were greater and butyrate concentration less with greater (P < 0.01) proportions of rye in the mixture. No effect of R:T ratio on digestibility or total VFA production along with the observed differences in individual VFA concentration do not explain variable response in grazing animals. Additionally, methane production results indicate that grazing turnips could potentially reduce methane production and thus reduce ruminant livestock’s contribution to greenhouse gas emissions.

PSI-3 Effects of Mowing on Forage Availability and Quality During the Summer

The objective was to determine how mowing date affected forage availability and quality. Cool season grass plots were randomly assigned to 4 treatments (n=2): mowed on day 1 (M1), mowed on day 15 (M15), mowed on day 29 (M29), and not mowed (NM). During the 56-day experiment, forage heights were measured using a rising plate meter to determine forage availability and samples were clipped for proximate analysis. The MIXED procedure of SAS was used to analyze data. On day 14, CP in M1 was 37.5% greater (P = 0.05) than the composite of M15, M29, and NM. However, the composite of M15, M29, and NM had greater (P = 0.02) forage availability than M1 on day 14. On day 28, M15 had greater (P = 0.02) ADF than M1, while the composite of M29 and NM was intermediate and not different than other treatments. There was also a treatment effect (P < 0.01) on forage availability on day 28; the composite of M29 and NM was greatest followed by M1 and M15, respectively. On day 42, the NDF of M29 was greater (P = 0.01) than M1, M15, and NM. Decreased CP was observed (P = 0.05) for NM compared with M1, M15, and M29 on day 42. Forage availability was different (P < 0.01) for all treatments on day 42 with NM being the greatest followed by M1, M15, M29, respectively. On day 56, NM tended (P = 0.08) to have the greatest DM, but there was no difference (P ≥ 0.31) in NDF, ADF, and CP. Forage availability was different (P < 0.01) for all treatments on day 56 with NM being the greatest followed by M1, M15, M29, respectively. In conclusion, mowing reduced forage availability as expected, but it also increased CP on day 14 and 42.

Natural variation of physiological traits, molecular markers, and chlorophyll catabolic genes associated with heat tolerance in perennial ryegrass accessions

Background Identification of genetic diversity in heat tolerance and associated traits is of great importance for improving heat tolerance in cool-season grass species. The objectives of this study were to determine genetic variations in heat tolerance associated with phenotypic and physiological traits and to identify molecular markers associated with heat tolerance in a diverse collection of perennial ryegrass (Lolium perenne L.). Results Plants of 98 accessions were subjected to heat stress (35/30 °C, day/night) or optimal growth temperature (25/20 °C) for 24 d in growth chambers. Overall heat tolerance of those accessions was ranked by principal component analysis (PCA) based on eight phenotypic and physiological traits. Among these traits, electrolyte leakage (EL), chlorophyll content (Chl), relative water content (RWC) had high correlation coefficients (− 0.858, 0.769, and 0.764, respectively) with the PCA ranking of heat tolerance. We also found expression levels of four Chl catabolic genes (CCGs), including LpNYC1, LpNOL, LpSGR, and LpPPH, were significant higher in heat sensitive ryegrass accessions then heat tolerant ones under heat stress. Furthermore, 66 pairs of simple sequence repeat (SSR) markers were used to perform association analysis based on the PCA result. The population structure of ryegrass can be grouped into three clusters, and accessions in cluster C were relatively more heat tolerant than those in cluster A and B. SSR markers significantly associated with above-mentioned traits were identified (R2 > 0.05, p < 0.01)., including two pairs of markers located on chromosome 4 in association with Chl content and another four pairs of markers in association with EL. Conclusion The result not only identified useful physiological parameters, including EL, Chl content, and RWC, and their associated SSR markers for heat-tolerance breeding of perennial ryegrass, but also highlighted the involvement of Chl catabolism in ryegrass heat tolerance. Such knowledge is of significance for heat-tolerance breeding and heat tolerance mechanisms in perennial ryegrass as well as in other cool-season grass species.