Potential of interplanted soybean and grain sorghum as a forage Potential of interplanted soybean and grain sorghum as a forage for dairy cattle for dairy cattle

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Introduction
Localized groups of farmers in Kentucky, Indiana, Tennessee, Virginia, West Virginia, Georgia, South Carolina, Alabama, and Arkansas have been utilizing interseeded soybean-grain sorghum combinations as silage for dairy and beef cattle for many years.More recently, this practice has received much attention because of economic factors.
Selected varieties of soybeans and grain sorghum, under fa vorable management, will produce as much dry matter per acre as corll silage and cost less to produce.Further, soybean and grain sorghum (soy-sorghum) haylage is higher in protein and mineral content, thus reducing the amount of supplement needed to balance the ration relative to corn silage.Soy-sorghum haylage is of lesser quality than alfalfa but fits into a rotation schedule and has the potential of being an exceJlent emergency forage crop.
Seeding dates range from early May (soil temperature approximately 60 degrees F) to mid-July (dependent on soil moisture availability).Fertilization rate 1 H.utgers tJniversity, New Jersey.is dependent on soil test but generally includes 30 to 40 lbs of actual nitrogen, 60 to 90 lbs of P 2 0 S ' and 90 to 120 Ibs of K 2 0 per acre applied preplant.An additional 30 lbs of K 2 0 is used if the soy-sorgnum follows small grain silage.
Harvest dates range from 65 days postseeding (total vegetative stage) to 125 days postseeding (mature).The wide range in potential harvest dates adds flexibility to a soy-sorghum forage system.
The purpose of this study was to ascertain 1) the dry matter and nutritive contribution of vegetative and seed parts of the soybean and grain sorghum to the total composition of the mass, 2) the change in nutrient composition of vegetative and seed parts at various stages of maturity, and 3) the potential nutritive value of soy-sorghum as a forage for ruminants.

Procedures
Lee 74 soybeans and Dekalb C42A grain sorghum were mixed in the ratio of 120 lbs of soybeans to 20 lbs. of grain sorghum then seeded in 7-inch rows with a conventional John Deere grain drill calibrated to deliver 120 lbs of soybean and 20 lbs of grain sorghum seed per acre.Fertilization program included 36 lbs. of actual N, 90 lbs of P 205 and 120 lbs. of K 2 0 per acre.Fertilizer was applied pre-plant and disked into tfle top 4 inches of soil.
Plots were replicated 5 times and samples taken from each plot at days 64, 88, 102, 123, and 130 postseeding.Sample sites were selected at random by tossing a large plastic ring of known area into the plots at either two or four locations, dependent on sampling date.A11 mater ial within the ring was collected and sorted into soybean vegetative (leaves and stems), soybean pod (pod and seed), grain sorghum vegetative (leaves and stems), and grain sorghum seed head (seed head severed from stalk one inch below bottom seed).Plant parts were air dried to 90% dry matter by spreading in a large room maintained at 85 degrees Fahrenheit and equipped with a forced-air ventilation system.Each air-dried plant part was weighed and analyzed for nutr ients, and the values from plots were averaged for statistical analyses.Chemical analyses were done by K-C Agriculture Laboratory Services, Nevada, Missouri, except for neutral detergent fiber (NDF) and sodium dl10ride insoluble nitrogen (Na-I-N), which were determined at Rutgers University, New Jersey.
Total dry matter yield per acre and percent contribution from individual plant parts were determined by relating the amount harvested within the ring to the area represented in the ring and expanding to a per acre basis.Values obtained with this method were determined to be reasonable estimates by direct comparison to weights obtained from whole plot harvest.

Results and Discussion
Total dry matter yield per acre and the contribution of vegetative and seed parts to the total dry matter over time is shown in Table 1.Maximum dry matter

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(OM) yield occurred at day 123 postseeding and just prior to a heavy frost (day 125).Soy pod and grain sorghum head contributions to total O,\J\ increased rapidly between day 88 and day 102.This followed a rapid increase in grain sorghum heads from 0% at day 64 to 14% at day 88.
Total digestible nutrients (TON) reil1abed relatively constant 'Jver time (Table 2) in the vegetative plant parts and the soy pod but increased from 62% at day 88 to 77% at day 123 in the grain sorghum head.TON from all sources maximized at clay 123.Acid detergent fiber insoluble protein (ADF-I-P) remained relatively constant in seed parts but increased in the vegetative parts of both soybean and grain sorghum through day 123 (Table 5).These results suggest that soy-sorghum may be harvested as silage either in the vegetative stage or during various stages of soy pod and grain .iorghumhead, formation with little change in total nutrient composition.However, maximum dry matter yield per acre is obtained when the grain sorghum is near the soft dough stage.Decreased TDN and protein percentage in vegetative parts with advancing maturity were offset by an increase in TDN and protein percentage of the seed parts.Subsequent animal acceptance of soy-sorghum silage was apparently not affected by stage of maturity.
Further studies involving animal performance and digestibility at the various soy-sorghum maturity stages is needed to ascertain the best time to harvest the crop.

Table 1 .
Contribution of soybean and grain sorghum plant parts to dry

Table 5 .
ADF IP, % of total protein