Harvesting regimens were tested to determine the influence of residue height and stage of plant growth at harvest on crabgrass forage yields. In general, the more advanced the green plant growth stage and the taller the residue (up to 6 inches), the higher the forage yield. Forage quality was inferior when seed heads were mature.

Crabgrass (Digitaria ciliaris, D. sanguinalis, and other species) is a forage plant. It is a naturalized volunteer plant throughout the semiarid to humid mild and temperate zones of the world, including every state except possibly Alaska. It is the most useful forage alternative from Nebraska to the east and south coasts. It has some practical use to the north of this area as well. The forage responds very well to moisture and can be grown where irrigation is a choice.

The forage production and quality of crabgrass was recognized several decades ago, but there was no specific management information available. We began to research, evaluate, and demonstrate such management, and this is a brief report of one of those studies.

The experiment had a six-treatment, three-replicate randomized block design. The blocks were set in a circular pattern to facilitate irrigation with one Rainbird rotating sprinkler head. The harvesting-regimen treatments were as follows:

treatment 1: harvested to a 1-inch residue at 4 to 6 inches of growth to simulate continuous grazing
treatment 2: harvested to a 3-inch residue at 8 to 10 inches of growth
treatment 3: harvested to a 3-inch residue during the preboot to few head stage
treatment 4: harvested to a 3-inch residue during early green head stage
treatment 5: harvested to a 3-inch residue at seed maturity
treatment 6: harvested to a 6-inch residue at seed maturity

All treatments were managed to simulate approaches to rotational grazing. All treatments were harvested to a 1-inch residue at the end of the year to provide the same residue heights for all treatments at harvest termination. Since crabgrass is an annual, the short final residue is appropriate.

The initial plots were established with 10 pounds of pure live seed per acre from a good type of naturalized crabgrass (D. ciliaris) on an excellent fresh seedbed. This high seeding rate was used to assure rapid development and relatively dense initial stands. Second-season stands were from volunteer seed produced during the first season.

The soil on the study area was a Wilson silt loam of moderate depth.

Plants were fertilized at 67-46-60 pounds of actual N-P₂O₅-K₂O per acre early in the season. The first fertilization was done soon after stand emergence. A second application of 67-0-0 pounds of actual nitrogen per acre was applied after the first harvests in each treatment. A total of 134-46-60 pounds of N-P₂O₅-K₂O per acre was applied each of the two years of the study. Plants were irrigated as needed to keep the forage green and growing, but not fully irrigated.

The data show, in general, that crabgrass forage yields increase as harvest is delayed and recovery period increases, allowing plants to age (tables 1 through 6).¹ The data also show that as residue height increases, so does total season yield, if the last harvest's residue is uniform and the minimum height. There are differences in production uniformity (tables 1 through 3). Two extreme examples are treatment 1 (short residue) compared with treatment 6 (seldom harvested; tall residue).

Some of these data were converted to estimated beef yield per acre and other information via conversion factors (table 7). These simulated controlled rotational grazing figures illustrate the influence of different harvesting regimens (rotational grazing) on potential beef yield and cost, the "real ranch" reason for the research.

1. Dr. Bill Ward, Statistician, Oklahoma State University, assisted with statistical analysis.