Defoliation and water deficit: their influence on pasture growth and water use of white clover

With the objective of understanding the physiological basis of defoliation and water use relationships of white clover (Trifolium repens L.) pastures during water deficits, an experiment in controlled conditions was carried out. Outdoors nine liters pots were filled whith a loam-clay soil with a water content at field capacity (FC), of 35% (w/w), at a bulk density of 1.1 g/cm(3). Pre-germinated and inoculated clover seeds were transplanted, and the number of plants was adjusted to permit the development of full plant cover. The level of P in the soil did not limit plant establishment or growth. The factors studied were: defoliation frequencies (cut every 20 days and cut every 40 days), and soil water levels (watering to mantain soil water content at 80% of FC and watering delayed until soil water content fell to 40-50% of FC). There were two white clover cultivars: the medium leaved Zapican and the large leaved ladino type Regal. Treatments were set out in a factorial arrangement in a randomized blocks design with three replicates and data were analysed using ANOVA, correlation estimates and regression models. The results indicated a positive correlation between the amount of water lost by evapotranspiration (ET), and forage yield or root weight. Managements and cultivars which promoted less production of aerial biomass and less root growth thus resulted in better water conservation.