COPING WITH SOIL AND CLIMATIC HAZARDS DURING CROP ESTABLISHMENT IN THE SEMIARID TROPICS

Climatic induced hazards (e.g. water deficit, high soil temperature an d high soil strength) that adversely affect seedling emergence and est ablishment of annual crops on red earth soils (Kandsols) at Katherine in the Daly basin of the Northern Territory are reviewed and results o f some recent simulation studies and experiments are presented. Simula tion studies, using 100 years of historical weather data, have shown t hat maize and sorghum density at Katherine is rarely reduced by water deficit during crop establishment. However, the median number of days between 1 December and 20 January during which seedlings may be expose d to damagingly high soil temperature (> 55 degrees C between 2 and 7 days after sowing) was 5.5, out of an estimated 21 days suitable for s owing. While the exposure of a crop to inclement conditions during est ablishment may have immediate and dramatic effects on the mortality of pre-emergent and post-emergent seedlings, there may also be longer-te rm and less evident adverse effects on crop growth and development. Th e responses of developing seedlings to inclement conditions following sowing are described and management options leg adjusting planting dat es, changing crop species, changing seedbed configurations, using surf ace mulch) for the amelioration of the seedbed environment are discuss ed. Of the possible management options for ameliorating adverse seedbe d conditions during crop establishment in the semi-arid tropics (SAT), it appears that the best practice is to maintain. soil surface cover (mulch) in close proximity to the emerging seedlings. The presence of surface mulch extends the window of opportunity for establishing crops by slowing soil drying, delaying the onset of high soil temperatures and high soil impedance, and by improving the availability of water to the young seedlings at this critical stage.