Physiological Changes and Nutritional Value of Forage Clitoria Grown in Arid Agro-Ecosystem as Influenced by Plant Density and Water Deficit

Abstract

Forage crop productivity has lately reduced in countries located in arid and semi-arid regions worldwide due to intensive consumption and the successive years of drought. This problem is exacerbated by the progress of water scarcity. Thus, the current study is aimed at improving the forage productivity and quality of clitoria as a leguminous fodder crop to be involved in crop rotations under low water supply conditions. As an attempt for facing the drought issue, a two-year (SI and SII) field experiment was conducted to evaluate the influence of irrigation pattern (IP) and plant density (PD) on clitoria morpho-physiological attributes, nutritive value, productivity, and irrigation water-use efficiency (IWUE) in two growth cycles (GCI and GCII). Based on the soil water depletion method, three irrigation patterns of 100% (IP0%, full irrigation), 80% (IP20%), and 60% (IP40%) were applied. The tested plant densities were 33 (PD33), 22 (PD22), and 17 (PD17) plants m−2. Findings revealed that IP0% × PD22 was the efficient treatment for enhancing the physio-biochemical attributes. However, in SI IP0% × PD22 statistically at par (p≥0.05) with IP0% × PD33, IP20% × PD22, and IP20% × PD17 (for chlorophyll content in GCI); IP0% × PD17 and IP20% × PD22 (for leaf relative water content in GCII); and IP0% × PD33, IP20% × PD33, and IP20% × PD22 (for cell membrane stability index in GCII). Along the two seasons, IP40% × PD33 was the potent practice for producing the highest leaf: stem ratio in both GCI (2.07 and 1.78) and GCII (1.18 and 0.96). Under IP40%, PD33 treatment recorded the greatest protein content in both GCI (24.1–27.0%) and GCII (21.7–19.5%) of SI and SII equaling PD22 in GCII (21.2–18.9%) of both seasons and PD17 in both GCI (24.0%) and GCII (21.5%) of SI and GCII (19.3%) of SII. The best aggregate protein yield for SI and SII was obtained under IP20% × PD33 interaction (1.36 and 1.40 t ha−1) without significant difference (p≥0.05) with IP0% × PD33 or IP40% × PD33 interactions. The greatest aggregate dry forage yield was observed in SI under IP0% or IP20% combined with PD33 (7.77 and 7.52 t ha−1) which did not differ significantly (p≥0.05). It could be concluded that irrigation by 80% water of full irrigation was found to be an efficient water-saving tactic coupled with adjusting the plant density of 33 plants m−2, which improved clitoria forage quantitative and qualitative properties, in addition to enhancing IWUE. Since leaf relative water content and cell membrane stability index decreased and proline increased in plant tissues under deficit water, clitoria is plant considered a moderately drought tolerant. Thus, clitoria is a promising plant could be successfully grown under arid agro-ecosystems.