Summer forages under irrigation. 1. Growth and development

Abstract

Summer forages, including Sorghum bicolor hybrids, S, sudanense, S. bicolor x S. sudanense hybrids, perennial sorghum, maize and Pennisetum and Echinochloa millets were grown on an alkaline clay soil at Trangie, New South Wales. They were fertilized and flood irrigated to allow the expression of potential growth characteristics. Fractional dry matter accumulation was measured during primary growth and subsequent regrowths. The accumulation pattern in primary growth was described by quadratic regressions of logarithmically transformed data. The highest dry matter yield of 31-33 t/ha was obtained in a single cut from late flowering sweet sorghum hybrids. Under a multiple cutting regime, however, these were inferior to sudangrass and sorghumxsudangrass hybrids, which produced up to 14 and 16 t/ha, respectively. The latter group maintained tiller numbers in regrowth in contrast to the poor tillering and slow regrowth of sweet sorghum hybrids. Regrowth of maize was negligible following tiller decapitation. Piper Sudangrass and Indian barnyard millet were the only species to yield as much under multiple cutting as from a single cut. The latter was exceptional among the millets in that most millets tillered poorly after the second cut. The millets produced less than half the cumulative regrowth yield of sorghum hybrids. Removal of the apical meristem appeared to jeopardize their regrowth. Consequently, if maximum dry matter production is the sole aim of forage production, millets do not compete with sorghum hybrids in a warm temperate climate.