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Influence of N and P on the Yield and Chemical Composition of Quackgrass Growing on an Organic Soil¹

Infestation of pure grass swards by quackgrass (Agropyron repens L.) has been a problem in grask production on organic soils in northern Minnesota. To determine if these problem areas could be utilized and managed effectively for forage production of quackgrass, trials were established in 1974 to determine the influence of N and P fertilization. In 1975, N and P fertilizer treatments were reapplied to the same plots.

In this 2 year study, the effects of 9 N and 5 P treatments were studied on an existing stand of quackgrass on an organic soil in northern Minnesota. Nitrogen at 168 kg/ha significantly increased dry-matter yields by 62% in the first year, and 66% in the second, with a maximum yield of 6.96 metric tons/ha. Splitting of N applications influenced seasonal forage production, but had no effect on total yield. The percent crude protein ranged from 15.8 to 27.9, and was significantly increased by the application of N. Phosphorus at 50 kg/ha increased dry matter yields by 37% in the first year, and 52% in the second, with a maximum yield of 7.30 metric tons/ha. The application of P fertilizer significantly increased the P concentration of the plant tissue with optimum yields being obtained with tissue P concentrations ranging from 0.24 to 0.41%.

Key Words: Infestation • Agropyron repens L., • Crude protein • Forage production

² Assistant professor, South Dakota State Univ., formerly instructor at Univ. of Minn., St. Paul, MN, and assistant professor and professor, Dep. of Soil Sci., Univ. of Minn., St. Paul, MN.

Received for publication September 13, 1978.