Productivity and light use efficiency of perennial ryegrass with contrasting water and nitrogen supplies

Light use efficiency (LUE) is one of the most useful parameters for estimating crop productivity. LUE relates dry matter (DM) productivity to solar radiation received on the canopy in a region. The aim of this research was to determine LUE and productivity of ryegrass (Lolium perenne L.) cv. Liprenta under different water and nitrogen (N) levels. Two separate experiments, one in 1994 (Experiment 1) and other in 1995 (Experiment 11), were carried out at the Institute of Plant Production, University Bonn, Germany. Two water (low versus high) and two N (low versus high) levels were supplied to plants during the growth seasons. All observations were plotted against a thermal scale. Plant DM was significantly higher (P < 0.05) under both sufficient water and N supply but treatment interaction was found significant for DM production during the crop re-growth. Maximum DM was reached in about 700 growing degree days (GDDs). Sufficient water with higher N supply out yielded the other treatments for DM, tiller number per plant and leaf number per plant throughout sampling. Differences were more pronounced in the field (Experiment 11) than in the pot trial (Experiment 1). Higher DM production of the high water supply treatment was not only due to more tillers and leaves but also due to longer and wider blades that enlarged the leaf area as well as mass of the individual plant leaves. Insufficient water supply to ryegrass was found more critical than insufficient N supply. The adverse effect of insufficient water and N supply to plants decreased both the individual leaf area as well as the whole canopy leaf area index (LAI). The canopy light interception rose sharply with increasing LAI, reached the maximum at canopy closure and remained at plateau with further LAI development during the crop growth. Canopy extinction coefficient k was empirically determined as 0.86 for light interception efficiency of the ryegrass. LUE, calculated as the slope of the regression of total DM (roots + shoot) and accumulated PAR intercepted, was observed as 2.01 (N1W1), 2.82 (N2W1), 3.34 (N2W2) and 4.24 (N2W2) g DM MJ(-1) PAR for Experiment I and 1.22 (N1W1), 2.01 (N2W1), 3.18 (N1W2) and 3.24 (N2W2) g DM MJ(-1) PAR for Experiment II. The average LUE under sufficient water was almost double than that of the insufficient water treatment both under pot and field conditions. However, the effect of N treatments was far lower in intercepting light than the effect of water treatments both in pot and field conditions on ryegrass vegetative growth. (C) 2004 Elsevier B.V. All rights reserved.