Rice seedlings were hydroponically grown using coconut coir as culture medium for manual transplanting in the tropics. When the rice seedlings were grown on coir saturated culture solution with a nutrient concentration 5-, 10-, 15- and 20-fold that of a standard culture solution for rice, the values of the shoot and root dry weight were higher of the 10-fold concentration than at the other concentrations of the solution at 20 days after sowing (DAS). The dry weight volumes of the plant parts of the seedlings grown on coir saturated with the 10-fold concentration (CH) solution were similar to or even higher than those of the seedlings grown in soil medium (SM) at 11 DAS. The dry weight increases in CH, however, became less appreciable than that in SM thereafter, and the dry weight values of the shoots and roots in CH were lower than those in SM after 19 DAS. The CH seedlings had more primary roots but fewer branch roots, resulting in a lower value of the total root length than that SM for the seedlings at 19 DAS. Moreover, the contents of chlorophyll and proteins in the leaf blades of the CH seedlings were lower than those of the SM seedlings during this period. Growth analysis indicated that the lower crop growth rate of the CH seedlings from 23 to 27 DAS was ascribed to the lower value of the leaf dry weight and lower net assimilation rate than those of the SM seedlings. Measurement of the photosynthetic rate supported the results of growth analysis. These results suggest that although rice seedlings can be hydroponically grown on coir media, their characteristics are inferior to those of the seedlings grown in soil.
Characteristics of sago palm suckers collected from mother palms at different growth stages and grown in different soil types were investigated for vegetative growth, nutrient contents in the pith including starch and total sugar, and subsequent growth during the nursery period. Significant differences in the vegetative growth parameters between the suckers collected from palms grown in mineral and deep peat soils, irrespective of the mother palm stages, were observed. The suckers collected from palms grown in mineral soil showed a better vegetative growth performance in terms of leaf emergence and elongation of sucker length than those collected from palms grown in deep peat soil. Nitrogen content in the pith tissues of the suckers from the mineral soil (average; 6.6-7.3 mg g-1) was significantly higher than that of the suckers from the deep peat soil (average; 2.4-2.9 mg g-1). On the other hand, due to the application of wood ash for the palm clumps grown in the deep peat soil, the pith potassium content in the suckers from the deep peat soil (4.6-15.0 mg g-1) was significantly higher than that of the suckers from the mineral soil (2.1-8.2 mg g-1). Nevertheless, no significant differences in the starch content were observed (41.3-70.9 %). The soil type significantly affected almost all the growth parameters of the suckers in the subsequent establishment in the nursery, except for the number of newly emerged leaves and root dry matter percentage. However, no significant difference was found in the sucker survival rate between the materials collected from mother palms at both stages and grown in the mineral (78 %) and deep peat soils (77 %).
A field emergence (FE) experiment was carried out in a farm practicing oasis agriculture under arid conditions in Djibouti, using 3 seed lots (‘Koshu 1’, ‘Koshu 2’ and ‘Shiro’) of maize. The objectives of the experiment were to evaluate to what extent treatments including stone mulching (SM) or pre-soaking (PS) and both treatments (SM+PS) affected FE and early seedling growth (ESG), and to determine the effects of vigour differences between the 3 seed lots on FE and ESG. Although the SM or/and PS treatments increased the speed of FE and ESG significantly, they did not affect the FE percentage at 9 days after sowing (DAS). Results of the germination test indicated that the 3 seed lots displayed the same level of germination capacity. However, although the vigour tests used in the present study might include variables influencing the results, it was considered that there were differences in seed vigour between the 3 seed lots, i.e. vigour of ‘Shiro’ was lower than that of ‘Koshu 1’ and ‘Koshu 2’. The percentage of FE of maize at 9 DAS in the high vigour lots (‘Koshu 1’ and ‘Koshu 2’) was significantly higher than that in the low vigour lot (‘Shiro’) in all the treatments. In the seed lots with high vigour, the speed of FE increased with the SM, PS and SM+PS treatments to a higher extent than in the seed lot with low vigour. These results suggested that the use of seed lots with high vigour may decrease the number of vacant hills and contribute to the increase of the productivity of maize in oasis farms.