EVALUATION OF YIELD AND NUTRITIVE VALUE OF PHOTOPERIOD-SENSITIVE SORGHUM AND SORGHUM-SUDANGRASS 1, 2 / Background

Transcription

1 EVALUATION OF YIELD AND NUTRITIVE VALUE OF PHOTOPERIOD-SENSITIVE SORGHUM AND SORGHUM-SUDANGRASS, 2 / / This project is partially supported by a Midwest Forage Association Research Grant. 2/ This work is partially supported by the USDA National Institute of Food and Agriculture, Hatch project / Research Assistant, Assistant Scientist/Extension Specialist, and Post-doc Research Associate, Dept. of Dairy Science, 675 Observatory Dr., University of Wisconsin, Madison, / Research Agronomist/Leader, USDA Dairy Forage Research Center IEIDM, 265 Yellowstone Dr, Marshfield, WI Elizabeth Remick 3/, Matt Akins 3/, Huawei Su 3/, Wayne Coblentz 4/ Background Growing moderate quality forages that meet the nutrient requirements of dairy heifers is not a common practice; however, this forage management option would have a positive impact on the dairy industry. Heifers gain excess bodyweight when they consume diets high in energy; this is especially true post-puberty, and may negatively impact first lactation production. Replacement dairy heifers are typically fed high forage diets comprised of corn, alfalfa, or grass silages. Corn silage is high energy (70-75% TDN, DM basis) and exceeds the requirements for lb heifers (62% TDN). Sorghum and sorghum-sudangrass have a moderate nutritive quality (higher fiber, lower starch) and provide an alternative to reduce excess weight gain. New types of sorghum (photoperiod sensitive) are being marketed as forage or biofuel crops. Photoperiod sensitive (PS) varieties stay vegetative until total daylight reaches 2 hours and 20 minutes (mid-september), allowing the plant to accumulate greater forage mass. The delayed maturation can cause harvesting challenges because the plant has not dried to a recommended level for silage harvest (60-70% moisture). Photoperiod sensitive sorghums have been evaluated in Iowa (Salas-Fernandez, 200) with average yields of 2 tons DM/ha compared to 6 tons DM/ha for conventional forage sorghums. The objective of this study was to evaluate the yield of PS forage sorghum and sorghumsudangrass compared to non-ps sorghum, sorghum-sudangrass and corn silage planted at 2 dates and harvested using single or multi-cut strategies. We chose to conduct the study at the Hancock and Marshfield Agricultural Research Stations due to differences in soil characteristics (silt loam soil at Marshfield and sandy soil at Hancock). Methods Forages evaluated included PS forage sorghum, PS sorghum-sudangrass, forage sorghum, BMR forage sorghum, sorghum-sudangrass, BMR sorghum-sudangrass, and PS BMR sudangrass hybrid. Variety information is in Table. Two factors were evaluated in a factorial treatment design (planting date and harvest strategy). The two plantings were ) early June or 2) mid-june. Harvest methods were either ) single harvest in fall once corn was ½ milkline, sorghum was soft-dough, or forage was killed by frost or 2) multiple harvests with one in early August and another in October after a killing frost. Plots were planted in a split-split plot design with the planting date as the whole plot, harvest methods as the sub-plot, and variety as the sub-sub plot. Harvest method treatments were arranged within each planting date to avoid shading of multiple harvest plots. Four replications were performed for each treatment combination.

2 Seeding rates were as follows: corn at 32,000 seeds/acre, forage sorghum at 00,000 seed/acre (~7 lb/acre), sorghum-sudangrass at 20 lb/acre, and sudangrass at 5 lb/acre. Soil was tilled prior to planting. Corn was planted using a 4-row planter at 30 inch rows. All other forages were established using a 5 foot no-till drill at 5 inch rows. Plot length was 5 feet. Plots were harvested at approximately a 4-inch cutting height. The multiple harvest treatments were first harvested on August 7, 205 at Hancock and August 3, 205 at Marshfield. The second harvest of multiple harvest treatment and the harvest of single harvest treatment occurred in late September to early-october depending on corn kernel milk-line and development of seeds in sorghum. The varieties that did not develop a seed-head were harvested following a killing frost in mid-october. Harvested forage was weighed, chopped using a wood chipper, and analyzed for dry matter (DM) content by drying at 55 C. Forage DM yield (tons per acre) was calculated as wet forage yield x DM content, adjusted for total area harvested (length x width; ex. 2.5 ft x 5 ft). Dried forage samples were ground to pass a mm screen using a cutter mill. Samples were analyzed for ash, crude protein (CP), neutral detergent fiber (NDF), neutral detergent insoluble crude protein (NDICP), in vitro NDF digestibility (NDFD), and in vitro true digestibility (IVTD). Total digestible nutrients (TDN) was calculated according to the NRC Dairy (200). Data were statistically analyzed using Proc MIXED of SAS. Each site was analyzed separately. Multiple harvest yields were combined to give a total season yield. Nutrient compositions of the forage from multiple harvests were averaged over the 2 harvests. Corn harvested in August did not have regrowth so the multiple harvest yields and nutrient composition is only from the first harvest. Results Forage Yield Generally, growing conditions were seasonally normal with a stretch of dry, warm weather in mid-august which helped to accelerate sorghum growth. Lodging was not an issue for most varieties except for BMR forage sorghum (~50-75% lodging) due to lower lignin content, and a heavy grain head. The PS varieties did not show signs of reproductive development, while all other sorghum varieties had reproductive development with formation of a seed-head. Forage yields were greater at Hancock compared to Marshfield for all forages and management factors except corn silage. The soil conditions allowed for faster emergence and growth at Hancock. A later planting date had a negative impact on yield at Hancock but less or little impact on yield at Marshfield (Table 2). At Hancock, yields decreased across most forage types at Hancock when planted 2 weeks later with reductions of 2.3 tons dry matter for corn silage and 0 to 2.5 tons dry matter for sorghum varieties. The BMR sorghum-sudangrass, PS sorghum-sudangrass, and PS BMR sorghum-suduangrass did not have reduced yields when planted later and using a single cut system. At Marshfield, the early June planting date was followed by heavy rains that caused soil crusting and delayed germination. The recommended planting depth of sorghum is 0.5 to inch in poorly drained soils, such as those at Marshfield. Actual planting depth of the sorghums was.5 inches, which when coupled with wet conditions, delayed and reduced germination and yield. This resulted in no significant difference in yields between the early and late planting date. The planting depth had less impact at Hancock due to the sandy soils in that location. Harvest method had an effect on forage yields (Table 2) with single harvest yields being 2 3 times greater than the multiple harvest yields at both sites. The first harvest was delayed until early August which may have limited subsequent forage regrowth during the ideal growing period in August. The single harvest yields of some varieties were similar to or better than corn silage at Hancock. Producers could partially substitute these varieties for corn silage without

3 sacrificing tonnage and have a crop that better meets heifer requirements. A single harvest system would work well in a direct-cut silage making system. The varieties that were reproductive (conventional forage sorghum and sorghum-sudangrass) were at recommended dry matter content (30-35%) for silage at Hancock due to lower soil moisture. At Marshfield, the sorghums were between 22-3% dry matter which would requirement additional drying after a frost. The sorghums did require a seed maturity of hard dough to have the whole plant dry matter in the recommend range. Dry down would likely not occur until after a killing frost for the photoperiod-sensitive varieties since these stay vegetative the entire growing season. Future work is needed to evaluate the drying time after a killing frost and the potential toxins (nitrates and prussic acid) that can accumulate when sorghums are frosted. A multiple cut system would result in less mature stems and likely dry more quickly for making hay or haylage that could potentially be used for animals with higher nutrient needs such as lactating cows or young heifers. The varieties responded differently when using different harvest systems. At Hancock, the conventional sorghum-sudangrass had the highest single cut yield of all the varieties, but had a similar multiple harvest yield to the PS sorghum-sudangrass. Both conventional and PS sorghum-sudangrass had the highest multiple harvest yields compared to the other varieties tested. The BMR sorghum varieties had lower yields than the other sorghums with a single harvest system, similar multiple harvest yields to PS forage sorghum and conventional forage sorghum, but lower multiple harvest yields than conventional sorghum-sudangrass and PS sorghum-sudangrass. At Marshfield, corn silage and PS sorghum-sudangrass had the highest single cut harvest yields. However, when harvested twice, conventional and PS sorghumsudangrass had similar yields to corn silage under a multiple harvest system and greater yields than the other sorghum varieties. The PS sorghum-sudangrass and PS BMR sudangrass both had consistent single cut yields across both planting dates and sites. The PS sorghum-sudangrass yields range from 7.9 to 9.6 tons dry matter per acre while PS BMR sudangrass yields ranged from 5.2 to 6. tons dry matter per acre across both sites. The conventional sorghum-sudangrass had the highest single cut yields at Hancock but yields were 45% lower at Marshfield. Nutrient Content Harvesting strategy and variety interacted with each other to affect all nutrients tested for Hancock (Table 3) and Marshfield (Table 4). At both sites, the single harvest strategy decreased NDF levels especially for varieties that were reproductive (corn silage, non-ps forage sorghums, and the conventional sorghum-sudangrass) due to the accumulation of starch in the corn kernels or seed-head which diluted NDF. The decreased NDF in the PS sorghum varieties and BMR sorghum-sudangrass could be due to increases in sugars accumulating in the stalk due to cool temperatures in the fall, however this is speculative and needs further analysis. It was anticipated that these forages would have higher NDF content with increased growth. Crude protein was also lower when using a single harvest at both sites. At Hancock, the protein levels were numerically lower than at Marshfield possibly due to differences in soil properties and available N. Brown mid-rib varieties had higher protein levels using a multiple harvest compared to a single harvest system at the Hancock station. Protein levels for all forages at Hancock would not be sufficient to meet dairy heifer needs if feed as the sole forage and would need to be fed with a higher quality forage or with a protein supplement. However, at Marshfield the protein content of the multiple harvest sorghums (except conventional sorghum-sudangrass) would meet the needs of pregnant dairy heifers.

4 In vitro digestibility was highest for the BMR varieties harvested using both methods at Hancock but not at Marshfield. This may be due to the better growing conditions at Hancock, causing faster growth and maturity. The digestibility of the corn was not different when harvested in the fall compared to early August likely due to accumulation of highly digestible starch in the corn grain offsetting the less digestible fiber. The PS and conventional sorghumsudangrass varieties had the lowest digestibility at both sites under a single harvest system. Few differences in digestibility were found using a multiple harvest system in Marshfield due to low forage yields and immature forages. A planting date by harvest strategy interaction was observed at Hancock with forages planted later and harvested multiple times having increased digestibility compared to a single-cut system; however no difference was found between harvest methods for the early planting date (Table 5). Fiber digestibility was highest for the BMR varieties at Hancock when harvested twice with minimal differences at Marshfield. Fiber digestibility was generally high using multiple harvests ranging from 62% up to about 75%. Harvesting in fall with increased maturity caused lower fiber digestibility at both sites especially for sorghum varieties with higher yields including PS forage sorghum, PS sorghum-sudangrass and conventional sorghum-sudangrass at Hancock and PS sorghum-sudangrass and conventional sorghum-sudangrass at Marshfield. The same result was found for total digestible nutrients (TDN) with the higher yielding sorghums having lower energy values. Corn had the highest energy level using a single cut system at Hancock but was similar to other sorghum varieties at Marshfield except PS sorghum-sudangrass, conventional forage sorghum, and conventional sorghum-sudangrass which were lower. Overall, the energy levels of single cut sorghum forages would better meet the needs of dairy heifers compared to corn silage. Conclusions In conclusion, some sorghum varieties are able to produce similar forage yields to corn in central Wisconsin. These varieties may be useful to provide significant quantity of moderate quality forage for heifers or other livestock with moderate nutritive needs. For high tonnage, it is recommended to use a single cut system. Moisture level at harvest can be challenging as sorghums often are frost-killed before drying to an adequate moisture for ensiling. Harvest should be delayed - 2 weeks after a killing frost to dissipate prussic acid and allow for drying. Photoperiod sensitive varieties did not lodge after a killing frost which may allow for additional drying time. Varieties that reached the hard-dough stage were in the moisture range for silage harvest so a producer could select a short to medium maturity (85-00 days) variety if concerned about dry-down time after frost. The non-ps forage sorghums had company estimates of 85 days for BMR forage sorghum and 00 days for conventional forage sorghum to reach soft-dough. Growers can incorporate sorghums in the crop rotation as part of a double-cropping system after harvesting of a cereal grain forage (triticale, rye, wheat) in May or early June. This would allow an additional time to apply manure and a high-yielding crop. Both the cereal grain forage and sorghum forage would work well as dairy heifer feeds. Another option is as an emergency crop planted after a low yielding winter injured first-crop alfalfa or frost-killed corn. Forage nutritive value of the sorghums would meet the needs of pregnant dairy heifers (58-62% TDN) or if the energy level is lower these could be used to help dilute the excess energy of corn silage that many producers desire to use. Protein supplementation or feeding with high protein forages is needed to meet protein requirements of 2-4% protein for pregnant heifers and 4-6% protein for heifers less than one year old. Harvesting at a less mature stage increases protein and energy value but lowers yield. These less mature forages could be used in lactating cow rations to replace part of corn silage and possibly alfalfa or grass silage.

5 Table. Corn hybrid and sorghum variety information Treatment Hybrid/Variety Company Corn LNG9595 Legend Seeds Forage sorghum AF830 Alta Seeds Sorghum-sudangrass AS520 Alta Seeds PS forage sorghum 4-Ever Green Walter Moss Seeds PS sorghum-sudangrass Mega Green Walter Moss Seeds BMR forage sorghum 2 BMR 34 Croplan BMR sorghum-sudangrass Greentreat 73 Croplan PS BMR sorghum-sudangrass Greentreat Rocket Croplan PS = photoperiod sensitive 2 BMR = brown mid-rib

6 Table 2. Forage yields (tons DM/hectare) for sorghums and corn silage planted at 2 dates and using a single or multiple cut harvest strategy at Hancock and Marshfield Agricultural Research Stations Hancock Marshfield Planting: Early June Mid-June Early June Mid-June Forage Harvest: Single Multi Single Multi Single Multi Single Multi Corn Silage PS forage sorghum PS sorghum-sudan Forage sorghum Sorghum-sudan BMR forage sorghum BMR sorghum-sudan PS BMR sudangrass Treatment Factors Planting Date P = 0.0; SEM = 0.7 P = 0.84 ; SEM = 0.54 Harvest Method ; SEM = 0.7 P <0.00; SEM = 0.45 Planting x Harvest P = 0.66 ; SEM = 0.24 P = 0.77 ; SEM = 0.62 Variety P = <0.00; SEM = 0.30 P = <0.00 ; SEM = 0.55 Variety x Planting P = 0.58; SEM = 0.42 P = 0.90 ; SEM = 0.74 Variety x Harvest ; SEM = 0.42 P = 0.09; SEM = 0.68 Variety x Planting x Harvest P = 0.48; SEM = 0.59 P = 0.89; SEM = 0.98 Corn was harvested once due to no regrowth; 2 PS = Photoperiod sensitive; 3 BMR = Brown mid-rib;

7 Table 3. Forage nutrient values (DM basis) of sorghums and corn silage sampled using a single or multiple cut harvest strategy at Hancock Agricultural Research Station Forage Variety NDF CP IVTD IVNDFD TDN Harvest: Single Multi Single Multi Single Multi Single Multi Single Multi Corn Silage PS forage sorghum PS sorghum-sudan Forage sorghum Sorghum-sudan BMR forage sorghum BMR sorghum-sudan PS BMR sudangrass Treatment Factors Variety Harvest Variety x Harvest SEM = 0.9 SEM = 0.66 SEM =.29 SEM = 0.3 SEM = 0.23 SEM = 0.45 SEM = 0.59 SEM = 0.30 SEM = 0.97 Corn was harvested once due to no regrowth; 2 PS = Photoperiod sensitive; 3 BMR = Brown mid-rib SEM = 0.9 SEM = 0.75 SEM =.37 SEM = 0.6 SEM = 0.32 SEM =.09

8 Table 4. Forage nutrient values (DM basis) for sorghums and corn silage sampled using a single or multiple cut harvest strategy at Marshfield Agricultural Research Station Forage NDF CP IVTD IVNDFD TDN Harvest: Single Multi Single Multi Single Multi Single Multi Single Multi Corn Silage PS forage sorghum PS sorghum-sudan Forage sorghum Sorghum-sudan BMR forage sorghum BMR sorghum-sudan PS BMR sudangrass Treatment Factors Variety Harvest Variety x Harvest P = 0.0 SEM =.05 SEM = 0.66 P = SEM =.77 P = 0.00 SEM = 0.54 SEM = 0.40 P = SEM = 0.78 SEM = 0.82 SEM = 0.58 P = 0.06 SEM =.22 SEM =.04 SEM = 0.83 SEM =.72 SEM = 0.72 SEM = 0.53 P = 0.05 SEM =.0 Corn was harvested once due to no regrowth; 2 PS = Photoperiod sensitive; 3 BMR = Brown mid-rib

9 Table 5. Forage nutrient values (DM basis) of sorghums and corn silage planted at two dates and sampled using a single or multiple cut harvest strategy at Hancock and Marshfield Agricultural Research Stations. NDF CP IVTD IVNDFD TDN Location: Single Multi Single Multi Single Multi Single Multi 3 Single Multi Hancock Early June Mid- June Planting x Harvest (P =) SEM Marshfield Early June Mid- June Planting x Harvest (P =) SEM Corn was harvested once due to no regrowth

10 Tons DM/acre Early June Single Mid-June Single Early June Multi Mid-June Multi Figure. Forage yields at Hancock of corn and sorghum varieties planted at 2 dates and harvested using a single or multiple cut system. PS = Photoperiod sensitive variety, BMR = Brown mid-rib variety Early June Single Mid-June Single Early June Multi Mid-June Multi Figure 2. Forage yields at Marshfield of corn and sorghum varieties planted at 2 dates and harvested using a single or multiple cut system. PS = Photoperiod sensitive variety, BMR = Brown mid-rib variety

11 Photo. Comparison of forage growth of multi-cut (left) and single (right) harvest plots in late- September Photo 2. Lodging of BMR sorghum with large grain head