CHANGES IN YIELD COMPONENTS OF A RYEGRASS SWARD, IN RESPONSE TO CUTTING FRECUENCY

Abstract

The effect of three cutting frequencies on yield components of a perennial ryegrass (Lolium perenne L.) sward was studied throughout the year, from June 1998 to July 1999, under field conditions at Montecillo, Texcoco, México. We compared irrigated swards of the cv. ‘American Tetraploid’ submitted to three defoliation frequencies (2, 4 and 6 weeks) through the four seasons of the year, under a randomized complete blocks design with four replicates in plots of 16 m² . The sward height cut was 5 cm. An analysis of varianza was carried out to compare cutting frequencies in each season and another to compare seasons within each frequency, regarding the variables: green leaf biomass production, tiller size, tiller population density, tiller appearance rate, tiller loss rate and leaf appearance rate. Among frequencies, the highest leaf biomass (4990 kg DM ha^-1 yr^-1) occurred with cuts every 4 weeks (P ≤ 0.05), because this treatment allowed to obtain the highest net tiller formation rate (tiller appearance rate – tiller loss rate) as a result of combining a high tiller density (21 428 tillers/ha) with medium size tillers (45 mg/tiller). In the annual average, as the cutting frequency increased from 6 to 2 weeks the tiller weight decreased, whereas the tiller appearance rate increased. The tiller appearance rate also varied among seasons since during summer and winter the rate was twice than in Autumn and Spring. Neither the cutting frequency averaged over seasons or the season averaged over frequencies did significantly affect the tiller loss rate. The highest leaf formation rate occurred in Summer in the three cut frequencies, whereas among frequencies there were not differences in the average of the four seasons.