STUDIES ON THE SCREENING OF LOW K——TOLERANT RICE SPECIES (VARIETIES) AND THEIR K——ABSORBING CHARACTERISTICS

Rice varieties were scored in five grades through the determination of their symptom responsibility to K-deficient rice plants sensitivity to K fertilizer application and suitability to low K environments under greenhouse or field conditions to identify their resistance to low K environments. Of the 439 rice varieties identified, 34 possessed strong tolerance for low K environments. Some of them were provided for K-deficient plot trails (the average available K : 65 ppm). Under the condition of no or little K fertilizer application, these varieties increased the grain yield by 10-15% more than the conventional rice varieties.The results of soil and solution cultivation showed that in low K environments tolerant varieties took up 29% K than sensitive varieties; the K amount transferred to grains was increased about 10%) and K efficiency was increased 7 %. The low critical K concentrations absorpted by tolerant varieties was lower then sensitive varieties,so it increased their efficiemcy ustillization of soils slow available K, possfsion of this characteris-tics was closely related to the quality and quantity of their root developemnt. Especially, the low K-tolerant varieties showed the excellent characteristics of strong vitality of root systems and normal growth of plants without early declining in the late growth period.