Graduate Student: Ishwary P Acharya, Dairy Science Department, South Dakota State University
Faculty advisor: Dr. David P Casper, Dairy Science Department, South Dakota State University
A field plot study was laid out using a randomized complete block design (RCBD) with three replicates to evaluate two organic corn hybrids [MC 5300 (OC) and brown midrib (BMR) organic grazing corn (Masters Choice Mastergraze, MG)] with two organic soybeans [Viking 2265 (OS) and Vining (VS)] at four seeding ratios (R1 = 65:35; R2 = 55:45; R3 = 45:55, and R4 = 35:65 of corn and soybean respectively) in terms of forage yield, nutrient yields and quality. Forage was hand harvested at 101 d (MG corn with both soybeans) and 116 d (OC corn with both soybeans) after planting during the 2015 growing season, chopped, inoculated, packed into buckets, weighed, and ensiled for 90 d. Buckets were then re-weighed, opened, and forage samples collected and analyzed for nutrient composition. No interaction of corn × soybean × seeding ratio was detected for biomass yield and nutrient yields. The main effect of corn for dry matter yield (DMY) was greater (P < 0.05) for OC compared to MG (27.73 and 19.90 T/ha for OC and MG, respectively), while main effect of soybean for DMY was similar (P > 0.05, 23.77 and 23.86 T/ha for OS and VS, respectively). Main effect of seeding rate on DMY was higher (P < 0.05) for R1 and R2 compared to R3 and R4 (25.38, 24.48, 21.81 and 23.59 T/ha for R1, R2, R3 and R4, respectively). Yields of digestible dry matter (DDM; 19.55 and 13.67 T/ha) and CP (2.40 and 2.12 T/ha) were greater (P < 0.05) for OC compared to MG corn, similar (P > 0.05) for both soybean ( DDM; 16.65 and 16.57 T/ha and CP; 2.33 and 2.19T/ha for OS and VS respectively) and higher (P < 0.05) DDM for R1 and R2 compared to R3 and R4 (17.70, 17.08,15.13 and 16.54 T/ha for R1, R2, R3, and R4, respectively). Yield of starch (7.78 and 2.45 T/ha for OC and MG) and 30 h NDF digestibility (NDFD30; 44.47 and 52.49 % for OC and MG) for main effect of corn were different (P < 0.05), while similar (P > 0.05) for main effect of soybean (starch yield; 5.25 and 4.98 T/ha; NDFD30; 48.58 and 48.38% for OS and VS, respectively). The combination of OC corn either with OS or VS soybean at the ratio of R1 or R2 resulted in the greatest yield of DM, DDM and Starch. The production of forge blends through mixed cropping of corn and soybeans holds great potential for increasing the forage and nutrient yields to meet the nutrient requirements of lactating dairy cows.