Theme 2-2: Forage Production and Utilization--Poster Sessions

G. Jones, Oregon State University

Description

Persistence is an important factor in the economic management of perennial grass swards. Frequent harvest is occasionally attributed to poor stand persistence, but self-thinning theory indicates that infrequent harvest should cause swards to thin as tillers compete for light. This experiment aimed to demonstrate and qualify self-thinning in orchardgrass managed under differing harvest frequencies. Orchardgrass was planted in September 2018 and then clipped, fertilized and divided into experimental units in March 2019. Plots were randomly assigned one of four harvest frequency treatments (n = 5): No harvest, one harvest, two harvests, and four harvests. Irrigation water and fertilizer were applied to allow for vigorous growth. On 9 October 2019, all plots were harvested and whole tillers were destructively sampled, counted, dried, and weighed. Cumulative herbage mass from the no harvest treatment was less than that from one, two, and four harvest treatments (p < 0.001). Average tiller weight was greater in the no harvest and one harvest treatments as compared to the two and four harvest treatments (p < 0.001) while the no harvest and one harvest treatment had a lower average tiller density (p < 0.001) of 1094 and 1534 tillers m-2, respectively, than the two and four harvest treatments with an average of 2376 and 2546 tillers m-2, respectively. To evaluate tiller size/density compensation, log10 tiller weight and log10 tiller density were plotted and compared to an arbitrarily-placed line with slope -3/2. These results indicate that orchardgrass swards thin under infrequent harvest management and that relatively frequent harvest appears to be required to maintain sward tiller density.

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Effects of Harvest Frequency on Yield and Self-Thinning in Irrigated Orchardgrass (Dactylis glomerata L.) in Oregon, USA

Persistence is an important factor in the economic management of perennial grass swards. Frequent harvest is occasionally attributed to poor stand persistence, but self-thinning theory indicates that infrequent harvest should cause swards to thin as tillers compete for light. This experiment aimed to demonstrate and qualify self-thinning in orchardgrass managed under differing harvest frequencies. Orchardgrass was planted in September 2018 and then clipped, fertilized and divided into experimental units in March 2019. Plots were randomly assigned one of four harvest frequency treatments (n = 5): No harvest, one harvest, two harvests, and four harvests. Irrigation water and fertilizer were applied to allow for vigorous growth. On 9 October 2019, all plots were harvested and whole tillers were destructively sampled, counted, dried, and weighed. Cumulative herbage mass from the no harvest treatment was less than that from one, two, and four harvest treatments (p < 0.001). Average tiller weight was greater in the no harvest and one harvest treatments as compared to the two and four harvest treatments (p < 0.001) while the no harvest and one harvest treatment had a lower average tiller density (p < 0.001) of 1094 and 1534 tillers m-2, respectively, than the two and four harvest treatments with an average of 2376 and 2546 tillers m-2, respectively. To evaluate tiller size/density compensation, log10 tiller weight and log10 tiller density were plotted and compared to an arbitrarily-placed line with slope -3/2. These results indicate that orchardgrass swards thin under infrequent harvest management and that relatively frequent harvest appears to be required to maintain sward tiller density.