A dynamic model for determining the optimum cutting schedule of Italian ryegrass

Authors

• Veli Pohjonen Department of Plant Husbandry, University of Helsinki

DOI: https://doi.org/10.23986/afsci.71842

Abstract

A quantitative approach to the determination of the optimum cutting schedule of Italian ryegrass (Lolium multiflorum Lam.) was presented. Optimization was based on a dynamic growth model which included the concepts crop growth rate, development rate and proper growth rate. The proper growth rate measured the growth potential associated with the stages of development in the sward. The crop growth rate of Italian ryegrass was studied at the Arctic Circle Experiment Station during 1973 and 1974. The proper growth rate was determined from primary observations as the derivative of an ordinary logistic curve which passes through origin. The maximum theoretical daily growth of Italian ryegrass was calculated as approx. 300 kg • ha-1• day-1. The optimum cutting schedules using gradient method were sought for Italian ryegrass sward. First, the maximum total dry-matter yield was looked for. Then the maximization was extended to the case, when the yield was weighted with the digestibility of the dry-matter. The maximum yield was obtained when the sward was cut three times, and when the cuttings were concentrated into the latter half of the growing season. The yield of the optimum cutting schedule was not sensitive to small changes in the cutting dates. In the conditions of Finnish Lapland the optimum cutting schedule of Italian ryegrass was: first cut at the end of July, second cut at the end of August and the third cut at the end of September.