Effects of irrigation and plant density on yield, composition and in vitro digestibility of a new forage sorghum variety, Tal, at two maturity stages

Most of the commercial varieties of forage sorghum belong to the tall types. Use of low types is limited, mainly due to their lower forage productivity. Recently a new low variety of forage sorghum, Tal, was developed in Israel. This study examined effects of irrigation level (IL) and plant density (PD) on Tal productivity and quality, as measured by field performance, chemical composition and in vitro digestibility. The optimal harvest stage for getting the best combination of yield amount and forage quality was explored. Irrigation included levels of 20, 100 and 180 mm, and PD consisted of 200,000, 260,000 and 330,000 plants/ha. Harvests were carried out at maturity stages of early heading (EH) and soft dough (SD). Tal resistance to lodging was high. High irrigation increased plant height and dry matter (DM) yield in both harvests, and enhanced the content of neutral detergent fiber (NDF) and lignin, at EH. In most cases, additional irrigation decreased DM content, DM ratio of leaves/stems, and in vitro DM digestibility (IVDMD). Plant density did not affect significantly plant height or DM yield at either harvest, but did affect DM digestibility at EH. Maturation from EH to SD increased considerably DM content under all irrigation levels, and DM yield only under high irrigation. Maturation increased DM allocation to the panicles and enhanced their DM digestibility. Tal has the potential to become a successful forage crop, which under sufficient irrigation attains the best digestible DM and NDF yields at SD.