Effect of daylength and temperature on introduced legumes and grasses for the tropics and subtropics of coastal Australia. 2. N-concentration, estimated digestibility and leafiness

Abstract

Twelve legumes and eight grasses were grown from seed in controlled environment rooms at 14 hours daylength and daylnight temperatures of 32¦/24¦C. After 35 days the plants were cut and the following regimes were imposed-I : 14 hours, 32¦/24¦C ; 2 : 14 hours, 26¦/15¦C ; 3 : 11 hours, 26¦/15¦C; 4: 11 hours, 20¦/6¦C. Regimes 1 and 4 represent approximate summer and winter conditions in coastal Queensland, excluding frosts. A complete nutrient application, except nitrogen, was made to the legumes. Three regrowth harvests were obtained at 28 day intervals. There were few differences between primary growth and regrowth in N-concentration and estimated dry matter digestibility (DMD) of whole plant tops. The N-concentration and DMD of regrowth of all grasses increased as the conditions became less tropical. The legumes had a varied response, but there was little regime effect on N and DMD in Trifolium repens and T. semipilosum. Many of the tropical legumes made little or no regrowth in regime 4, but differences in N and DMD were small and inconsistent between other regimes. The legumes showed a general trend towards increased leafiness as conditions became less tropical, but in the grasses there was no consistent response, although nearly all had a higher percentage leaves in regime 4 than in 1. N concentration of the leaves of all legumes and of most grasses was higher than that of stems, but DMD of stems was higher than that of leaves in T. repens, T. semipilosum and Pennisetum clandestinum. N concentration of legume leaves was little affected by regime, but that of grasses was much higher in regime 4 than in the others. Stems of legumes showed a varied response in N and DMD, as did DMD of grass stems, but the latter generally tended to increase in N with decreasing temperature and daylength. N-concentration and DMD of the grasses had a negative linear correlation with DM yield, and most grasses a positive linear correlation between DMD and N-concentration. Of the legumes only M. sativa and Pueraria phaseoloides had a negative linear relation between DMD and DM yield and M. sativa a positive linear relation between DMD and N.