Soil Water Deficit Effect on Yield, Leaf Area, and Net Assimilation Rate of Three Forage Grasses: Crested Wheatgrass, Smooth Bromegrass, and Altai Wildrye¹

Abstract

Annual forage yield in the northern Great Plains depends primarily on quantity and temporal distribution of precipitation. This study was conducted to examine the effect of water deficit on yield, leaf area, and net assimilation rate (NAR) of three forage grasses under field conditions. The grasses, smooth bromegrass (Bromus inermis Leyss.) (Br), Altai wildrye [Leymus angustus (Trin.) Pilger] (AWr), and crested wheatgrass [Agropyron cristatum (L.) Beauv. spp. pectinatum (Bieb.) Tzvel.] (CWg), were chosen because of their contrasting morphologies. The grasses were grown on deep black soil (Melfort silty clay, Typic Cryoboroll) under two moisture regimes: DRY plots were covered by rain‐out shelters starting at the end of May, and IRR plots were watered when soil water potential averaged −0.07 MPa. Crested wheatgrass expanded leaf area more rapidly in spring than Br and AWr, and responded to increasing soil water deficits by sharply reducing its leaf area through senescence of older leaves. Altai wildrye developed its leaf area slowly, probably because more dry matter was required to produce a unit of leaf area. It responded to soil water deficit by reducing rate of leaf expansion. Smooth bromegrass developed its leaf area rapidly although somewhat later than CWg. The effect of soil water deficit on leaf expansion was less in Br than AWr, and its effect on reduction of leaf area through leaf senescence was less in Br than CWg. In late May, AWr yielded less than CWg but more than Br. At the end of June, yield of CWg was greater than both Br and AWr in 1983, and greater than AWr but similar to Br in 1984. Altai wildrye recovered most rapidly after clipping among the species in both years but yielded more regrowth only in 1984. No interaction was found between moisture regime and species for either leaf area or yield on any of the sampling dates, probably because soil water deficits developed gradually under the conditions of this experiment, thus minimizing the effects of the different growth patterns. Soil water deficit affected leaf area proportionately more than NAR in AWr and CWg but not in Br. The findings suggest that the relative effect of drought on these two yield components depends on species and environment.

Water use efficiency of marandu palisadegrass as affected by nitrogen and sulphur rates

“…In this experiment, water was provided by a self-irrigating system, which maintained the soil moisture at 70% of water retention capacity throughout the experiment, not being, therefore, a limiting factor for nutrients absorption. Bittman and Simpson (1987) observed that under low water availability in the soil, the grass leaf area is reduced because the balance between the productions of assimilates and the demand for the development of the reproductive organs is affected.…”

“…Soil moisture was maintained by a subsurface selfirrigated system prepared as described in Bonfim- Silva, Monteiro and Silva (2007), which allowed the continuous water replacement according to evapotranspiration, of the soil-plant system, ensuring the soil water retention capacity. This irrigation system was composed of pottery capsule (5 cm diameter and 7 cm height), inserted into the soil and a water reservoir (Mariotte tube) connected by flexible silicone microtubes to keep the reservoir capacity of 1.8 L with constant water level.…”

“…Because of the interdependence of biochemical pathways of nitrogen and sulphur in protein synthesis, sulphur can interfere with the response of forage grasses to nitrogen fertilization and these nutrients combination can affect their yield (BONFIM-SILVA; SILVA, 2007;DE BONA;MONTEIRO, 2008).…”

Agronomic characteristics and nutritive value of 11 grasses grown with irrigation on a saline soil in southwestern Saskatchewan

“…The poor persistence of crested wheatgrass is more difficult to explain. Crested wheatgrass is well know for longevity (Looman and Heinrichs 1973) and its ability to respond favourably to irrigation (Bittman and Simpson 1987) but has been described as less tolerant of salinity than tall wheatgrass (Barnes et al 1995) and Dewey (1960) considered it to have only low to moderate tolerance. It seems likely that the soils used in this experiment may have exceeded the salinity tolerance of crested wheatgrass.…”

“…Crested wheatgrass is widely considered suitable only for early-season grazing because its quality and palatability decline rapidly with senescence and it is considered inferior to most other grasses, including Altai wild ryegrass and intermediate wheatgrass for later season grazing (Barnes et al 1995). Crested wheatgrass has such a well-established reputation for drought tolerance and its ability to produce a large amount of high-quality forage during spring that its ability to respond to irrigation (Bittman and Simpson 1987) is frequently overlooked. Although the persistence of crested wheatgrass was poor in this experiment, probably due to salinity, the good PDMD at heading and seed set suggest that late-season vegetative re-growth may have occurred following irrigation and otherwise above normal rainfall.…”