Growth, mineral composition and digestibility of maize, sorghum and barnyard millets at different temperatures

Abstract

Barnyard millets (Echinochloa utilis and E. frumentacea), maize (Zea mays) and a sorghum hybrid (Sorghum bicolor x S. sudanense) were grown as spaced plants at temperature regimens from 15/10 to 33/28�C (dayhight). Leaf and stem dry weight, leaf area and leaf number were recorded every 2 weeks and the dry matter analysed for nitrogen, sulfur, sodium and in vitro digestibility. Tolerance to low temperatures was in the order maize > E. utilis >sorghum >E. frumentacea. At mean temperatures above 25�C, relative growth rates were similar for all species. Differences in leaf area, for which individual leaf size was mainly responsible, accounted for most of the dry weight responses to temperature, although net assimilation rate responses were also apparent. The dry weight response to temperature became negligible after adjusting for differences in stage of development. Dry matter digestibility decreased with temperature; it also decreased with time because of deteriorating stems, except in sorghum. Maize leaves were of low digestibility, similar to stems. The nitrogen : sulfur ratio of all species remained steady with age; in sorghum at low temperature it exceeded the 15: 1 maximum considered desirable for animals. Sodium was highest in E. utilis stems and increased with temperature, in contrast to sorghum. Maize had a marginal nitrogen: sulfur ratio and unacceptably low sodium concentration. It was concluded that more attention should be given to E. utilis as a forage for cool climates.