Barley growth, physiology, and forage quality as influenced by defoliation and water stress
Information on how limited water supply might affect the physiological changes that take place after defoliation of barley (Hordeum vulgare L.) after defoliation and their effects on forage-quality characteristics is needed. The objectives of this study were to investigate defoliation and water deficit stress effects on regrowth, physiology and forage quality characteristics of four barley cultivars known to differ in response to grazing. Two studies were conducted in the greenhouse, and in the field; one on defoliation intensity at two maturity stages and the other on defoliation during water stress;In the first study, defoliation generally decreased grain yield and its components and dry matter (DM) in plant parts, delayed anthesis, and shortened the grain filling period. In the greenhouse, defoliation reduced DM of 'Acsad 176', 'Barlis 628', 'Asni' and 'Tamallalt' by 30, 40, 18 and 30%, respectively, relative to plants that were not defoliated. In the field, however, severe defoliation resulted in increased final DM yield of Tamallalt and Asni (7 and 13%, respectively) compared to plants not defoliated. Severe defoliation increased crude proteins (CP) concentration of Asni and Tamallalt at tillering, increased cell-soluble concentration of all cultivars at anthesis except Tamallalt. In the second study, defoliation reduced tiller number, plant height, and water-use efficiency (WUE), but did not affect water potential (WP), solute potential (SP) or turgor pressure (TP). Water stress reduced plant height, leaf area, carbon exchange rate (CER) by more than 50%, WP, SP, total DM by more than 11%, and grain yields by more than 45% for all cultivars. It increased WUE and delayed anthesis of all cultivars. The highest rate of decrease of grain yield per unit DM was for Tamallalt (1.4 g/kgDM) and the lowest was for Acsad 176 (0.6 g/kgDM). Straw of the six-row barleys contained an 11% greater CP concentration than that of the two-row cultivars. Defoliation improved the forage quality at early growth stages over nondefoliated plants. Water stress maintained 55% CP, 2% IVDDM, and 6% cell-soluble concentrations greater in straw of stressed plants than in nonstressed plants. IVDDM and CP in straw were positively correlated with the leaf-to-stem ratio, forage yield, and turgor pressure, but negatively related to grain yield. Forage yield, turgor pressure and grain yield were negatively related with cell wall components of straw;It was concluded that cultivars like Acsad 176, which have high tillering capacity, well developed roots, higher CER, adjust osmotically, and a high yield potential, compared to other cultivars, are suitable for dual-use under a range of environmental conditions. Moreover, defoliation effects on forage quality were inconsistent depending on growth stages and cultivars, water stress improved quality by maintaining higher CP and cell-solubles concentrations and remarkably higher digestibility, and high grain yielding barley cultivars had high forage quality.