Effect of drought stress on morpho-physiological characteristics, nutritive value, and water-use efficiency of sorghum [Sorghum bicolor (L.) Moench] varieties under various irrigation systems

Efeito do estresse hídrico sobre características morfofisiológicas, valor nutritivo e eficiência no uso da água de variedades de sorgo [Sorghum bicolor (L.) Moench] sob diferentes sistemas de irrigação

Abstract

Addressing water scarcity and the need for high-quality forage in arid regions necessitates the development of efficient irrigation techniques. This study assesses the impact of various irrigation methods on the performance and irrigation water-use efficiency (IWUE) of sorghum cultivars under water-deficit conditions in a semi-arid region of Iran during the 2019 and 2020 cropping seasons. Three irrigation methods—variable alternate furrow irrigation (AFI), fixed alternate furrow irrigation (FFI), and conventional furrow irrigation (CFI)—were evaluated alongside three levels of drought stress (severe stress: I₅₀, moderate stress: I₇₅, and full irrigation: I₁₀₀) and two sorghum cultivars. The results indicated that increasing drought stress, as well as the transition from CFI to AFI and FFI, led to reductions in metabolizable energy yield (MEY), plant height, cellulose, hemicellulose, and lignin. Conversely, there were increases in leaf-to-stem ratio, digestible organic matter, metabolizable energy content, crude protein content, and IWUE for metabolizable energy production (IWUE_ME). The highest MEY (211.68 GJ ha^-1) was recorded under CFI×I₁₀₀, albeit at the expense of maximum water consumption (7261 m³ ha^-1). Meanwhile, the AFI×I₅₀ and FFI×I₅₀ treatments exhibited the highest IWUE_ME (44.46 MJ m^-3) and metabolizable energy content (8.736 MJ kg^-1), respectively, while conserving over 60% of water. Hybrid Speedfeed outperformed in forage yield and IWUE_ME, while cultivar Pegah excelled in forage quality. Transitioning from CFI to AFI or FFI resulted in decreased forage yield but improved forage quality and IWUE_ME. Principal component analysis revealed that leaf-to-stem ratio and plant height serve as effective indicators for assessing the nutritive value and forage yield of sorghum, respectively. Considering the overall results, cultivating the hybrid Speedfeed under AFI×I₇₅ conditions is recommended for optimal water utilization, achieving satisfactory forage yield and quality, and enhancing IWUE.

Keywords:
cell wall; deficit irrigation; metabolizable energy; partial root-zone drying; protein